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Texacephale langstoni, a new genus of pachycephalosaurid (Dinosauria: Ornithischia) from the Upper Campanian Aguja Formation, southern Texas, USA

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Recent work in the Campanian Aguja Formation of Big Bend, Texas, has resulted in the recovery of two frontoparietal domes from a new genus of pachycephalosaur. Texacephale langstoni gen. et sp. nov. is diagnosed by a tall, arched nasal boss, flange-like processes articulating the dome with the peripheral elements, and a low pedicel separating the cerebral fossa from the skull roof. The skull dome is composed largely of the fused frontals and parietals, with limited participation of the peripheral elements, and the supratemporal fenestrae remain open. Phylogenetic analysis indicates that Texacephale langstoni is a basal member of the Pachycephalosauria. The discovery of Texacephale supports previous suggestions that the dinosaur fauna of Texas was distinct from that of contemporary assemblages to the north. The phylogenetic analysis presented here indicates that the Asian pachycephalosaurs form a monophyletic group, deeply nested within the Pachycephalosauridae, and that the basal members of the group are all North American. This finding indicates that pachycephalosaurids originated in North America, rather than Asia, as previously believed. The high diversity of North American pachycephalosaurs and the late appearance of pachycephalosaurs in Asia are consistent with this hypothesis. The biology of Texacephale and other Pachycephalosauridae are also discussed. The morphology of the dome in Texacephale and other pachycephalosaurs supports the hypothesis that pachycephalosaurids engaged in intraspecific combat, while the occurrence of Texacephale and other pachycephalosaurs in nearshore deposits argues that the pachycephalosaurs were not restricted to inland habitats.
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... • A series of papers by Julia Sankey, one of Judith Schiebout's students, beginning with her dissertation (Sankey, 1998); some publications of particular interest for dinosaurs with Sankey as lead author or coauthor include Sankey (2001), Sankey et al. (2005), the description of BIBE dinosaur eggshell fragments in Welsh and Sankey (2008), and the description of the pachycephalosaurid Texacephale langstoni in Longrich et al. (2010); ...
... It is a complex unit with several members and a variety of facies, from nearshore marine to deltaic to fluvial and marsh (Wick and Corrick, 2015). Accounting for superseded terminology, both biological and geological, the Aguja Formation of BIBE has yielded the following dinosaur taxa: a gracile tyrannosaurid (Lehman and Wick, 2012); ornithomimids (Longrich et al., 2010); a caenagnathid (Longrich et al., 2010); small theropods of the poorly understood Paronychodon and Richardoestesia lineages, including Richardoestesia isosceles (Standhardt, 1986;Sankey, 2001;Sankey et al., 2005); the dromaeosaurid Saurornitholestes (Sankey, 2001;Sankey et al., 2005); an undescribed small theropod (Fortner, 2015); a nodosaurid (Longrich et al., 2010); a possible ankylosaurid (Standhardt, 1986); the pachycephalosaurid Texacephale langstoni (Longrich et al., 2010;"Troodon" teeth of Sankey, 1998 and other publications were redescribed as pachycephalosaurid in Sankey, 2001); two chasmosaurine ceratopsid species, Agujaceratops mariscalensis and the more recent A. mavericus (Lehman et al., 2017); a hypsilophodont-grade ornithopod (Davies, 1983); and at least two hadrosaurids, Kritosaurus cf. K. navajovius (Davies, 1983) and the lambeosaurine Angulomastacator daviesi (Wagner and Lehman, 2009). ...
... It is a complex unit with several members and a variety of facies, from nearshore marine to deltaic to fluvial and marsh (Wick and Corrick, 2015). Accounting for superseded terminology, both biological and geological, the Aguja Formation of BIBE has yielded the following dinosaur taxa: a gracile tyrannosaurid (Lehman and Wick, 2012); ornithomimids (Longrich et al., 2010); a caenagnathid (Longrich et al., 2010); small theropods of the poorly understood Paronychodon and Richardoestesia lineages, including Richardoestesia isosceles (Standhardt, 1986;Sankey, 2001;Sankey et al., 2005); the dromaeosaurid Saurornitholestes (Sankey, 2001;Sankey et al., 2005); an undescribed small theropod (Fortner, 2015); a nodosaurid (Longrich et al., 2010); a possible ankylosaurid (Standhardt, 1986); the pachycephalosaurid Texacephale langstoni (Longrich et al., 2010;"Troodon" teeth of Sankey, 1998 and other publications were redescribed as pachycephalosaurid in Sankey, 2001); two chasmosaurine ceratopsid species, Agujaceratops mariscalensis and the more recent A. mavericus (Lehman et al., 2017); a hypsilophodont-grade ornithopod (Davies, 1983); and at least two hadrosaurids, Kritosaurus cf. K. navajovius (Davies, 1983) and the lambeosaurine Angulomastacator daviesi (Wagner and Lehman, 2009). ...
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Dinosaurs have captured the interest and imagination of the general public, particularly children, around the world. Paleontological resource inventories within units of the National Park Service have revealed that body and trace fossils of non-avian dinosaurs have been documented in at least 21 National Park Service areas. In addition there are two historically associated occurrences, one equivocal occurrence, two NPS areas with dinosaur tracks in building stone, and one case where fossils have been found immediately outside of a monument's boundaries. To date, body fossils of non-avian dinosaurs are documented at 14 NPS areas, may also be present at another, and are historically associated with two other parks. Dinosaur trace fossils have been documented at 17 NPS areas and are visible in building stone at two parks. Most records of NPS dinosaur fossils come from park units on the Colorado Plateau, where body fossils have been found in Upper Jurassic and Lower Cretaceous rocks at many locations, and trace fossils are widely distributed in Upper Triassic and Jurassic rocks. Two NPS units are particularly noted for their dinosaur fossils: Dinosaur National Monument (Upper Triassic through Lower Cretaceous) and Big Bend National Park (Upper Cretaceous). To date, fourteen dinosaur species have been named from fossils discovered in NPS areas, the most famous probably being the sauropod Apatosaurus louisae. Increasing interest in the paleontology of the parks over the past few decades has brought many of these body and trace fossils to light. Future paleontological field inventories and research will likely yield new dinosaur finds from NPS areas.
... Of particular interest is the newly named taxon Texacephale langstoni, recently described by Longrich et al. (2010). The holotype specimen (LSUMNS 20010), a weathered frontoparietal dome, bears close similarity to NMMNH P-30067. ...
... The "vertical flanges" identified by Longrich et al. (2010) as an autapomorphy of Texacephale langstoni are simply the irregular, inter- locking sutural surfaces of the frontoparietal dome with the peripheral skull elements. These so-called "flanges" have no pattern, are seen on every pachycephalosaurid where these surfaces are exposed, and have no taxonomic utility. ...
... Aside from the defining characters used by Longrich et al. (2010), we note additional characters that are either misinterpreted or misrepresented. They use a hybrid nomenclature for peripheral skull elements, contrary to that used by , Sullivan (2003), and Schott et al. (2009). ...
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Two partial pachycephalosaurid skulls, from the upper Fruitland and lower Kirtland formations (Upper Cretaceous), are recognized as belonging to a new species of Stegoceras Lambe, S. novomexicanum, n. sp. Stegoceras novomexicanum differs from the only other recognized species of Stegoceras (sensu Sullivan, 2003) in possessing: a reduced and sub-rectangular posteromedial extension of the parietal; parallel squamosal sutural surface contacts of the posteromedial extension of the parietal; enlarged and medially positioned supratemporal fenestrae; and a small (adult) size. Fusion of the frontal and parietal in one specimen, coupled with a smooth dorsal surface of the frontoparietal dome, is consistent with an adult ontogenetic stage. Gross histology reveals four histomorphs, the fourth (outer-most layer) indicates arrested growth, further attesting to its mature state. Stegoceras novomexicanum is known from, and restricted to, the upper Fruitland Formation (Fossil Forest Member) and lower Kirtland Formation (Hunter Wash Member); the collective vertebrates from these contiguous strata make up the Hunter Wash local fauna. Contrary to previous reports, the Prenocephale (= Sphaerotholus)-like pachycephalosaurids are not known from the early Kirtlandian, but are restricted to the Willow Wash local fauna of the upper Kirtland Formation (De-na-zin Member). Stegoceras novomexicanum is temporally younger (Kirtlandian) than the well-known S. validum from the Judithian of Alberta, Canada. A reassessment of the newly named taxon Texacephale langstoni demonstrates that it is not based on diagnostic material and, therefore, is a nomen dubium.
... Pachycephalosaurian dinosaurs (Ornithischia: Marginocephalia) are a group of generally small, bipedal herbivores that formed a significant part of the ornithischian-dominated Late Cretaceous dinosaur faunas of North American and Asia. Pachycephalosaur phylogeny is currently poorly resolved, and recent phylogenetic analyses conflict on most aspects of pachycephalosaurian relationships and taxonomy (Sereno, 1999(Sereno, , 2000Sullivan, 2000Sullivan, , 2003Sullivan, , 2006Williamson and Carr, 2002;Maryańska et al., 2004;Ryan and Evans, 2005;Schott et al., 2009;Longrich et al., 2010). The morphology of the parietosquamosal bar and its associated ornamentation is critical in the differentiation and diagnoses of taxa, and in the construction of hypotheses of in-group relationships in all published phylogenetic analyses. ...
... Discussions of pachycephalosaur cranial ontogeny based on reasonably large samples from restricted geological units postulate extreme transformations from flat-headed juvenile to * Corresponding author highly domed adults in Stegoceras validum (Goodwin et al., 1998;Williamson and Carr, 2002;Sullivan, 2003;Ryan and Evans, 2005), and Pachycephalosaurus wyomingensis (Horner and Goodwin, 2009). These studies suggest the possibility that flat-headed specimens attributed to the Asian taxa Goyocephale lattimorei, Homalocephale calathocercos, and Wannanosaurus yansiensis may represent either juvenile stages of domed taxa, or perhaps exhibit pedomorphosis in dome development (Sullivan, 2005(Sullivan, , 2007Butler and Sullivan, 2009;Bakker et al., 2006;Longrich et al., 2010). Recent work by Butler and Zhao (2009) confirms that Wannanosaurus yansiensis is likely represented only by specimens that pertain to juvenile individuals, and therefore questioned its ubiquitously inferred basal phylogenetic position within Pachycephalosauria, a contention that has been supported by a recent cladistic study by Longrich et al. (2010). ...
... These studies suggest the possibility that flat-headed specimens attributed to the Asian taxa Goyocephale lattimorei, Homalocephale calathocercos, and Wannanosaurus yansiensis may represent either juvenile stages of domed taxa, or perhaps exhibit pedomorphosis in dome development (Sullivan, 2005(Sullivan, , 2007Butler and Sullivan, 2009;Bakker et al., 2006;Longrich et al., 2010). Recent work by Butler and Zhao (2009) confirms that Wannanosaurus yansiensis is likely represented only by specimens that pertain to juvenile individuals, and therefore questioned its ubiquitously inferred basal phylogenetic position within Pachycephalosauria, a contention that has been supported by a recent cladistic study by Longrich et al. (2010). This underscores the need for more detailed comparative work on other Asian flat-headed forms. ...
Article
The cranial roof ornamentation and the degree of neurocentral closure in the holotype of the pachycephalosaurian dinosaur Homalocephale calathocercos is described in detail for the first time in order to assess its ontogenetic status and taxonomic validity. The parietosquamosal ornamentation consists of five primary nodes along the posterior margin of the skull roof on each side of the midline. The medial-most node is prominently enlarged relative to the others in the series and is bisected by the parietal-squamosal suture. Beneath the primary node row, a second enlarged node occurs immediately medial to lateroventral corner node on each side of the parietosquamosal bar. The degree of suture closure in the vertebral column suggests that the holotype specimen of H. calathocercos is immature, rather than adult. The presence of cranial doming at maturity is therefore unknown in H. calathocercos, and hypotheses that it represents a primitive flat-headed stage in pachycephalosaur evolution or is pedomorphic in the development of its skull roof cannot be supported or refuted at this time. Despite the probable immaturity of the holotype, H. calathocercos has a unique pattern of parietosquamosal ornamentation that is distinct from all other pachycephalosaurs, including Prenocephale prenes from the same host formation. Morphological differences in the cranial ornamentation, jaws, and dentition between the similarly sized holotype skulls of H. calathocercos and P. prenes provide weak support for recent suggestions that H. calathocercos is conspecific with the latter taxon. This study tentatively reaffirms the presence of two pachycephalosaur species in the Nemegt Formation
... These dinosaurs are easily characterised by the fusion and doming of the frontals and parietals (Maryańska et al. 2004;Sullivan 2006). Dome morphology is taxonomically informative (although ontogenetically variable), and their high preservation potential (Evans et al. 2013) make isolated domes a focus in pachycephalosaurid research (Sullivan 2003;Goodwin & Horner 2004;Sullivan 2006;Schott et al. 2009;Lehman 2010;Longrich et al. 2010;Schott et al. 2011;Evans et al. 2013;Mallon & Evans 2014;Schott & Evans 2016;Evans et al. 2018). ...
... Galton (1971) argued that because the dome is comprised of dense compact bone (revised as porous compact bone (Goodwin et al. 1998) rather than porous trabecular bone, and the density of the dome increased through ontogeny (Goodwin & Horner 2004;Schott et al. 2011;Schott & Evans 2016)), the dome would not have been strictly used as a display feature, but was adapted to resisting the forces of intraspecific combat. Longrich et al. (2010) converged on a similar argument, elaborating on the unlikelihood of natural selection favouring such a physiologically expensive structure for the sole purpose of species recognition. Furthermore, Finite Element Analyses have demonstrated that the dome would have been capable of dispersing hypothetical combat-induced forces before reaching the brain cavity (Snively & Cox 2008;Snively & Theodor 2011). ...
... The study of palaeopathology is a common method of inferring the behaviours, life histories, and biotic interactions of extinct animals (Bermúdes de Castro 1988;Skinner et al. 1995;Cabral et al. 2011;Hone & Tanke 2015;García et al. 2016;Kierdorf et al. 2016;Pardo-Pérez et al. 2018;Pruden et al. 2018;Xing et al. 2018;Siviero et al. 2020). Pathological pachycephalosaurid domes have occasionally been reported, but these reports are generally anecdotal, speculative, or are considered indistinguishable from weathered domes (Maryańska 1990;Sullivan 2003;Lehman 2010;Longrich et al. 2010;Schott & Evans 2016). More recently, lesions in some frontoparietal domes have been identified as evidence of osteomyelitis (bone infections) secondary to trauma (Peterson & Vittore 2012;. ...
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Recent studies have identified numerous pathologies in the cranial domes of pachycephalosaurid dinosaurs. These studies utilized CT images of domes to identify secondary woven bone and sclerosis associated with the pathologies. These features were critical for diagnosing post-traumatic osteomyelitis, which supported the head-butting behaviour hypothesis. However, conventional CT image resolution may not be sufficient to identify secondary woven bone or sclerotic bone in fossil specimens. UALVP 8504 (cf. Foraminacephale brevis), a dome possessing putative bone lesions, was thin-sectioned and micro-CT scanned. Thin sections revealed the lesions are lytic, without any secondary woven bone or sclerosis, falsifying the diagnosis of osteomyelitis. The morphology and histology of the lesions of UALVP 8504 are not diagnostic and resemble both post-traumatic and non-traumatic lesions. However, UALVP 8504 possesses shifted vascular canals (repositioning via remodeling, which maintains anatomical position throughout ontogeny) that are decoupled from growth (), and drifting osteons (secondary osteons where resorption occurs longitudinally and transversely). These demonstrate that the dome has sustained external mechanical loading, likely resulting from an impact or multiple impacts, consistent with the head-butting hypothesis. These impacts may have damaged overlying soft tissues and formed the lesions along the surface. Therefore, we suspect that the pathologies in UALVP 8504 are post-traumatic.
... Mya; Eberth et al., 2013;Mallon et al., 2015;Fowler, 2017). Specimens now assigned to Foraminacephale brevis (Lambe, 1918) had also been suggested to be members of Sphaerotholus (Longrich et al. 2010), but new material and a recent revision of this taxon by Schott & Evans (2016) indicated that F. brevis is not closely related to S. goodwini and was, therefore, referred to its own genus. past two decades. ...
... They recognized this specimen as the holotype of a second species of Sphaerotholus, S. buchholtzae, while concurrently considering the holotype of S. edmontonensis as non-diagnostic to the genus and species levels. Subsequent studies suggested that S. edmontonensis is a valid species of either the genus Prenocephale (Sullivan, 2006) or Sphaerotholus (Longrich et al. 2010;Mallon et al., 2015) or it was tentatively referred to S. buchholtzae (e.g. Evans et al., 2013;Williamson & Brusatte, 2016). ...
... In the strict consensus tree of the parsimony analysis, Pachycephalosauridae consists of a Stegoceras clade that is comprised of a large polytomy of Hanssuesia sternbergi (Brown & Schlaikjer, 1943), Bakker et al., 2006, Stygimoloch spinifer Galton & Sues, 1983 and Pachycephalosaurus wyomingensis are united within the previously recognized Pachycephalosaurini (Sullivan, 2006;Longrich et al., 2010) by the presence of a long rostrum (Character 26) and by large nodes projecting laterally from the jugal (Character 47). Importantly, the three species of Sphaerotholus are recovered in an unresolved Sphaerotholus clade. ...
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The ontogeny and taxonomy of the dome-headed pachycephalosaurs are topics of continued debate. Pachycephalosaurid diversity in the Maastrichtian of North America is particularly controversial, and the validity and composition within the genus Sphaerotholus remains unresolved. While the type species, S. goodwini, is generally considered valid, debate has centred around the validity and taxonomy of S. buchholtzae and S. edmontonensis. Here we employ morphometrics, histology and phylogenetic analysis to resolve these issues. An ontogenetic assessment of S. buchholtzae (N > 20) confirms previously observed ontogenetic morphologies: inflation of the frontoparietal dome, obliteration of tesserate surface texture, blunting of the peripheral nodes and decreasing void space within the dome. While linear bivariate analysis finds S. edmontonensis nested within S. buchholtzae, three-dimensional geometric morphometrics supports S. edmontonensis and S. buchholtzae as distinct species. Phylogenetic analysis recovers a Sphaerotholus lineage with S. goodwini as sister-taxon to a clade formed by S. edmontonensis and S. buchholtzae. The stratigraphic, phylogenetic, morphometric and ontogenetic data support the validity of both S. edmontonensis and S. buchholtzae, and their placement within the genus Sphaerotholus. The morphological similarities of S. edmontonensis to immature S. buchholtzae, and the slightly older geological age of S. edmontonensis, suggest that S. edmontonensis and S. buchholtzae may be part of an anagenetic lineage.
... The second hypothesis suggests the dome’s structure served a mechanical function, specifically, that the thickened dome was used in intraspecific agonistic bouts [8]–[11], with pachycephalosaurids butting flanks or heads. The hypothesis that the dome functioned as a weapon is supported by a number of lines of evidence. ...
... It is also difficult to explain in any other context. Meanwhile, the absence of pathology in flat-headed pachycephalosaurids- which presumably represent juveniles or females [11] is consistent with the hypothesis that these injuries are the result of intraspecific combat; agonistic bouts among extant bovids occur relatively more frequently among mature males [14]. Interestingly, the frequency of injury appears to be comparable in different species, despite the fact that they vary in dome architecture and size, and existed at different times. ...
... More recently, pathologies have been identified in pachycephalosaurid domes [11], [15]. Pathologies are of interest because injuries tend to occur in parts of the anatomy that are used frequently and/or subject to unusually high strains; insofar as pathologies reflect the wear-and-tear experienced by an animal, they can provide a record of the behavior of the living organism [15]–[18]. ...
Article
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Pachycephalosaurids are small, herbivorous dinosaurs with domed skulls formed by massive thickening of the cranial roof. The function of the dome has been a focus of debate: the dome has variously been interpreted as the product of sexual selection, as an adaptation for species recognition, or as a weapon employed in intraspecific combat, where it was used in butting matches as in extant ungulates. This last hypothesis is supported by the recent identification of cranial pathologies in pachycephalosaurids, which appear to represent infections resulting from trauma. However, the frequency and distribution of pathologies have not been studied in a systematic fashion. Here, we show that pachycephalosaurids are characterized by a remarkably high incidence of cranial injury, where 22% of specimens have lesions on the dome. Frequency of injury shows no significant difference between different genera, but flat-headed morphs (here interpreted as juveniles or females) lack lesions. Mapping of injuries onto a digitial pachycephalosaurid skull shows that although lesions are distributed across the dome, they cluster near the apex, which is consistent with the hypothesis that the dome functioned for intraspecific butting matches.
... Ryan & Evans (2005) recognized 'St.' brevis as a distinct species, but chose to follow a more conservative taxonomy and thus did not recognize the generic assignment of Sullivan (2003). Sullivan (2006) continued to support the generic placement of 'P.' brevis in Prenocephale, whereas most recently Longrich et al. (2010) suggested the possibility that 'P.' brevis may be congeneric with Sphaerotholus based on their phylogenetic results. Etymology: Combination of for amina (Latin: foramina) and cephale (Greek: head), referring to the numerous foramina that cover the dorsal surface of the skull of this taxon. ...
... Recent phylogenetic analyses conflict as to the affinities of F. brevis. Williamson & Carr (2002) found F. brevis to be outside Pachycephalosaurinae, and to form part of a clade that includes St. validum, whereas other studies (Sullivan, 2003;Longrich et al., 2010) have found F. brevis to be a pachycephalosaurine closely related to Prenocephale or Figure 23. Bivariate logarithmic plots with reduced major axis regression lines showing the correlation between the first three principal components (PC 1-3) and size (width of the frontoparietal, W:f/p). ...
... Measurements are log (mm). (Horner & Goodwin, 2009;Goodwin & Evans, 2016; but see Longrich et al., 2010). We also analysed the character matrix with these three species removed. ...
Article
Studies of large-scale diversity changes and patterns of evolution can be adversely affected by a lack of understanding of alpha-taxonomy and systematics, and pachycephalosaur dinosaurs have significantly contributed to this problem. This is primarily a result of the relatively incomplete nature of the pachycephalosaur fossil record and the lack of understanding of specific and ontogenetic variation within the group. The taxon previously known as ‘Prenocephale’ brevis has been particularly problematic and has been placed in several different genera in addition to being synonymized with the species Stegoceras validum multiple times. Here we evaluate the validity of this taxon based on old and new material and using multiple, independent lines of evidence. We identify and describe the first peripheral skull elements, as well as the first juvenile and adult specimens, assignable to this taxon. These provide information on key parts of the morphology that have previously been lacking. Comparative anatomy, bivariate and multivariate morphometrics, osteohistology, and systematic analyses were used to test the hypothesis that this material is representative of a distinct taxon and to evaluate the differences between the other pachycephalosaur species of the closely related Belly River Group assemblage. No support was found for the assignment of ‘P.’ brevis to Stegoceras or Prenocephale, and thus we have erected a new genus, Foraminacephale gen. nov., to contain this species. Our data support the conclusion that the Foraminacephale brevis material represents an ontogenetic growth series of a single species distinct from St. validum. Evaluation of the two other members of the Belly River Group assemblage (Hanssuesia sternbergi and Colepiocephale lambei) was hindered by the small number of known specimens, but our results suggest that specimens currently referred to H. sternbergi may represent at least two species. We find that both ontogeny and osteohistology can vary greatly amongst even closely related species. It is therefore critical that multiple, independent lines of evidence be used to establish the ontogenetic trajectories of species prior to delineation, and that results of these analyses are used to produce robust and phylogenetically informative characters for use in phylogenetic analyses.
... Sullivan (2003Sullivan ( , 2006 formally referred the two species of Sphaerotholus to the Mongolian genus Prenocephale, and this assignment was followed by Schott et al. (2009) and Watabe et al. (2011). The name Sphaerotholus, however, was retained by Marya nska et al. (2004), Longrich et al. (2010), and Evans et al. (2013), and we follow this taxonomy. Likewise, some workers synonymize S. edmontonensis with S. buchholtzae (Williamson and Carr, 2002), but we provisionally follow Sullivan (2003Sullivan ( , 2006, Schott et al. (2009), Longrich et al. (2010, and Watabe et al. (2011) in accepting the validity of the species epithet edmontonensis. ...
... The name Sphaerotholus, however, was retained by Marya nska et al. (2004), Longrich et al. (2010), and Evans et al. (2013), and we follow this taxonomy. Likewise, some workers synonymize S. edmontonensis with S. buchholtzae (Williamson and Carr, 2002), but we provisionally follow Sullivan (2003Sullivan ( , 2006, Schott et al. (2009), Longrich et al. (2010, and Watabe et al. (2011) in accepting the validity of the species epithet edmontonensis. All recent authors regard Stegoceras as a relatively basal pachycephalosaurid and Sphaerotholus as part of a diverse clade of more derived pachycephalosaurine taxa including Prenocephale (Sereno, 2000;Williamson and Carr, 2002;Sullivan, 2003Sullivan, , 2006Marya nska et al., 2004;Schott et al. 2009;Longrich et al., 2010;Watabe et al., 2011). ...
... Likewise, some workers synonymize S. edmontonensis with S. buchholtzae (Williamson and Carr, 2002), but we provisionally follow Sullivan (2003Sullivan ( , 2006, Schott et al. (2009), Longrich et al. (2010, and Watabe et al. (2011) in accepting the validity of the species epithet edmontonensis. All recent authors regard Stegoceras as a relatively basal pachycephalosaurid and Sphaerotholus as part of a diverse clade of more derived pachycephalosaurine taxa including Prenocephale (Sereno, 2000;Williamson and Carr, 2002;Sullivan, 2003Sullivan, , 2006Marya nska et al., 2004;Schott et al. 2009;Longrich et al., 2010;Watabe et al., 2011). ...
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The nasal region plays a key role in sensory, thermal, and respiratory physiology, but exploring its evolution is hampered by a lack of preservation of soft-tissue structures in extinct vertebrates. As a test case, we investi-gated members of the "bony-headed" ornithischian dinosaur clade Pachyce-phalosauridae (particularly Stegoceras validum) because of their small body size (which mitigated allometric concerns) and their tendency to preserve nasal soft tissues within their hypermineralized skulls. Hypermineralization directly preserved portions of the olfactory turbinates along with an internal nasal ridge that we regard as potentially an osteological correlate for respi-ratory conchae. Fossil specimens were CT-scanned, and nasal cavities were segmented and restored. Soft-tissue reconstruction of the nasal capsule was functionally tested in a virtual environment using computational fluid dynamics by running air through multiple models differing in nasal soft-tissue conformation: a bony-bounded model (i.e., skull without soft tissue) Abbreviations used: acPM 5 anastomotic canal in premaxilla; aEth 5 ethmoid artery; air 5 airway; anas 5 anastomosis between pal-atine, lateral nasal, and dorsal alveolar vessels; aSO 1 LN 5 anastomo-sis between supraorbital and lateral nasal vessels; aSph 5 sphenopalatine artery; at 5 potential accessory turbinate; bch 5 bony choana (fenestra exochoanalis); bLN 5 branches of lateral nasal vessels; bMN 5 branches of medial nasal vessels; cap 5 cartilaginous nasal cap-sule; caud co 5 caudal concha; cDA 5 dorsal alveolar canal; ch 5 choana (fenestra endochoanalis); cLN 5 canal for lateral nasal vessels; cMN 5 canal for medial nasal vessels; co 5 concha; cPM 5 canal in pre-maxilla; cSO 1 LN 5 canal for anastomosis between supraorbital and lateral nasal vessels; cSO 5 canal for supraorbital vessels; DA 5 dorsal alveolar vessels; f 5 frontal; fSO 5 suborbital fenestra; gLN 5 groove for lateral nasal vessels; j 5 jugal; lac 5 lacrimal; Lc 5 lacrimal canal; LN 5 lateral nasal vessels; max 5 maxilla; mid co 5 middle concha; MN 5 medial nasal vessels; mu 5 mucosa; nar 5 naris; nas 5 nasal; nc 5 nasal capsule; ng 5 nasal gland; npd 5 ductus nasopharyngeus; ns 5 nasal septum; ob 5 olfactory bulb; OfC 5 olfactory conchal vessels; olf e 5 olfactory epithelium; om 5 olfactory meatus; ot 5 olfactory turbi-nate; p 5 parietal; PA 5 palatine vessels; pl 5 palatine; pm 5 premax-illa; po 5 postorbital; post 5 postvestibular ridge; preco 5 preconcha; preco rec 5 preconchal recess; prf 5 prefrontal; ps 5 parasphenoid ros-trum; pt 5 pterygoid; q 5 quadrate; qj 5 quadratojugal; RC 5
... A similar problem concerns the identities of the Asian flatheaded pachycephalosaurs Goyocephale lattimorei and Homalocephale calathocercos, as the known specimens may represent juvenile stages of domed taxa (Longrich et al., 2010;Evans et al., 2011) or adults that possibly exhibit pedomorphosis in dome development (Bakker et al., 2006;Sullivan, 2007). Homalocephale is found in the Nemegt Formation of Mongolia, in strata that have also yielded the highly-domed Prenocephale prenes, and it has been suggested that it may be a subadult or sexual dimorph of that taxon (Butler and Sullivan, 2009;Longrich et al., 2010). ...
... A similar problem concerns the identities of the Asian flatheaded pachycephalosaurs Goyocephale lattimorei and Homalocephale calathocercos, as the known specimens may represent juvenile stages of domed taxa (Longrich et al., 2010;Evans et al., 2011) or adults that possibly exhibit pedomorphosis in dome development (Bakker et al., 2006;Sullivan, 2007). Homalocephale is found in the Nemegt Formation of Mongolia, in strata that have also yielded the highly-domed Prenocephale prenes, and it has been suggested that it may be a subadult or sexual dimorph of that taxon (Butler and Sullivan, 2009;Longrich et al., 2010). Evans et al. (2011) considered that question and concluded that although Homalocephale likely was based on an immature specimen, it is taxonomically distinct from Prenocephale based on its large size and unique pattern of parietosquamosal ornamentation, features that appear not to change significantly through ontogeny in Stegoceras validum Schott et al., 2011;Schott and Evans, 2012). ...
... Southern late Campanian faunas have not yet yielded anywhere as many specimens as the northern units, but growing discoveries hint at a considerable diversity of pachycephalosaurs. At least one taxon is known from the Aguja Formation of west Texas, (Lehman, 2010;Longrich et al., 2010). A new pachycephalosaur taxon, Texacephale langstoni was named based on a frontoparietal from the Aguja Formation (Longrich et al., 2010), although Jasinski and Sullivan (2011) concluded that it is a nomen dubium, a decision that we agree with and is followed here. ...
Article
Pachycephalosaurs, a group of ornithischian dinosaurs with distinctive cranial ornamentation and skull domes, underwent dramatic changes in cranial morphology during ontogeny. This has caused debate about whether some specimens belong to juveniles or adults, which impacts studies of pachycephalosaur phylogeny and evolution. One such debate concerns a small skull roof specimen from the Campanian (Upper Cretaceous) of New Mexico, NMMNH P-33898, which was originally described as an indeterminate juvenile but later regarded as a mature adult and erected as the holotype of a new small-bodied species, Stegoceras novomexicanum. We restudied NMMNH P-33898 using computed tomography scanning, morphometric and phylogenetic analyses, and comparisons to growth series of other pachycephalosaurs (Stegoceras validum, Pachycephalosaurus wyomingensis). We conclude that two purported paratype specimens of Stegoceras novomexicanum cannot be referred to the same taxon as the holotype, that the holotype and controversial paratypes all belong to immature specimens and not aberrant small-bodied adults, but that current evidence cannot clearly determine whether NMMNH P-33898 is a juvenile belonging to its own diagnostic species (S. novomexicanum) or is a juvenile of Stegoceras validum, Sphaerotholus goodwini, or another known taxon. We review the pachycephalosaur record of New Mexico and demonstrate that pachycephalosaurs were important components of dinosaur faunas in the southern part of Western North America during the ∼15 million years before the end-Cretaceous extinction, just as they were in roughly contemporaneous northern localities.
... Among theropods, North America's tyrannosaurids (Brusatte, Benson, & Norell, 2011), alvarezsaurs (Longrich & Currie, 2009a), caenagnathids (Longrich, Barnes, Clark, & Millar, 2013), microraptorines (Longrich & Currie, 2009b) and ornithomimids (Xu et al., 2011) all have relatives in Asia. Among ornithischians, saurolophine (Godefroit, Bolotsky, & Lauters, 2012) and hadrosaurine (Prieto-M arquez, Chiappe, & Joshi, 2012) duckbills, ceratopsids (Xu, Wang, Zhao, & Li, 2010b), leptoceratopsids (Ryan, Evans, Currie, Brown, & Brinkman, 2012), pachycephalosaurids (Longrich, Sankey, & Tanke, 2010) and ankylosaurids (Sullivan, 1999) show the same. These patterns show that a high-latitude land corridor joined North America and Asia in the Late Cretaceous (Russell, 1993), with extensive dispersal between the two continents. ...
... Leptoceratopsids and other basal neoceratopsians have short, deep jaws that would be well-suited to shearing tough, fibrous vegetation (Longrich, 2010), and Leptoceratopsidae in particular are characterized by teeth with a unique combination of crushing and shearing facets (Ostrom, 1966) and very short, deep, 'nutcracker' jaws (Brown, 1914;Chinnery, 2004;Chinnery & Horner, 2007;Kurzanov, 1992;Ryan et al., 2012) with the dentigerous process of the maxilla being correspondingly short and deep (Chinnery, 2004;Chinnery & Horner, 2007). As the strength of a structure in bending or shearing increases with depth (Gordon, 1978), this jaw structure suggests adaptation to produce high bite forces and process highly resistant food items. ...
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Tyrannosaurs and hadrosaurs from the Late Cretaceous of eastern North America (Appalachia) are distinct from those found in western North America (Laramidia), suggesting that eastern North America was isolated during the Late Cretaceous. However, the Late Cretaceous fauna of Appalachia remains poorly known. Here, a partial maxilla from the Campanian Tar Heel Formation (Black Creek Group) of North Carolina is shown to represent the first ceratopsian from the Late Cretaceous of eastern North America. The specimen has short alveolar slots, a ventrally projected toothrow, a long dentigerous process overlapped by the ectopterygoid, and a toothrow that curves laterally, a combination of characters unique to the Leptoceratopsidae. The maxilla has a uniquely long, slender and downcurved posterior dentigerous process, suggesting a specialized feeding strategy. The presence of a highly specialized ceratopsian in eastern North America supports the hypothesis that Appalachia underwent an extended period of isolation during the Late Cretaceous, leading the evolution of a distinct dinosaur fauna dominated by basal tyrannosauroids, basal hadrosaurs, ornithimimosaurs, nodosaurs, and leptoceratopsids. Appalachian vertebrate communities are most similar to those of Laramidia. However some taxa-including leptoceratopsids-are also shared with western Europe, raising the possibility of a Late Cretaceous dispersal route connecting Appalachia and Europe.
... Pachycephalosaurid dinosaurs are a group of bizarre ornithischian dinosaurs, distinguished by their unusual dome heads. They have been known for more than 100 years, but only recently has there been intense interest in the taxonomy, phylogenetic systematics, biostratigraphy and paleobiogeography of this unusual group of dinosaurs (Sereno, 2000;Sullivan, 2000Sullivan, , 2003Sullivan, , 2006Ryan and Evans, 2005;Butler and Qi, 2009;Butler and Sullivan, 2009;Lehman, 2010;Longrich et al., 2010). Known mostly from North America and Asia (Sullivan, 2006;Butler and Sullivan, 2009;Lehman, 2010), pachycephalosaurids are typically represented in the fossil record by their ossified skull, especially the bones of the frontals and parietal that are often fused and commonly form a distinctive dome. ...
... A critical re-evaluation of the characters used in previous analyses of pachycephalosaurid phylogeny by Sereno (2000), Sullivan (2003) and Schott et al. (2009) is necessary in light of recent papers by Butler and Sullivan (2009) and Goodwin and Horner (2009). We do not accept the characters utilized by Longrich et al. (2010) and regard Texacephale langstoni as a nomen dubium (Jasinski and Sullivan, 2011). We used Yinlong (Xu et al., 2006) and rescored Stenopelix, based on Butler and Sullivan's (2009) paper; together they served as our out group. ...
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A nearly complete pachycephalosaurid frontoparietal dome, from the Baynshire Formation at Amtgai, southern Gobi Desert, Mongolia, is identified as a new taxon. Amtocephale gobiensis n. gen., n. sp. differs from all other pachycephalosaurids in a combination of features that include: deep supratemporal fossae; broad (craniocaudally) prefrontal sutural surfaces with the nasal; prefrontal and anterior supraorbital sutural surfaces lying in a single plane; short parietal (parietal length to the frontoparietal length is 2.44); the medial posterior extension the parietal sharply downturned and wide relative to the maximum width of the frontoparietal; and lacking supratemporal fenestrae. Amtocephale gobiensis may be the oldest known pachycephalosaurid as it comes from rocks that are no younger than late Santonian. While it may be the oldest known pachycephalosaurid, phylogenetic analysis Amtocephale gobiensis suggests relationship to the more derived pachycephalosaurids.
... The hypothesized ontogenetic series of Pachycephalosaurus proposed by Horner and Goodwin (2009) is not universally accepted, and it remains possible that putatively extreme ontogenetic and individual variation is an artifact of poor taxonomy (Bakker et al., 2006;Longrich et al., 2010). However, little is known about ontogeny and variation in other pachycephalosaur taxa. ...
... The morphology and ornamentation of the squamosal is important in pachycephalosaur species diagnoses and forms the basis of numerous characters in phylogenetic analyses, many of which include critical synapomorphies in resultant tree topologies (Williamson and Car, 2002;Sullivan, 2003;Schott et al., 2009;Longrich et al., 2010;Evans et al., 2011). These characters include, but are not limited to, the number of nodes in the posterior node row (e.g., Sullivan, 2003, chars. ...
Article
The pachycephalosaurian squamosal is one of the most diagnostic bones in this enigmatic group of dinosaurs, but little is known about variation in its morphology. Despite this, features of squamosal morphology are often used in diagnoses and phylogenetic studies. The recently proposed hypothesis of an ontogenetic transition from Dracorex to Pachycephalosaurus implies a large amount of ontogenetic variation in squamosal ornamentation that has not been well documented due to the small number of squamosals for these taxa. Stegoceras validum provides an important model for examining variation in squamosal morphology due to the large number of squamosals available. Here we examine the morphology of 14 S. validum squamosals both qualitatively and quantitatively. We find that although both node number and shape vary considerably, there is no clear ontogenetic pattern, which suggests a high degree of individual variation. The ornamental pattern, however, is maintained throughout the sample. Increase in node size is isometric for the enlarged medial node and normal posterior nodes, but negatively allometric for the vertex node. The squamosal bar is taller laterally than medially in nearly all specimens and increases in height with positive allometry at the same rate medially and laterally. We found no correlation between the width of the supratemporal fenestra on the squamosal and the size of the squamosal itself. Rather, this feature appears to exhibit a large degree of individual variation. Overall, these findings have implications for previous hypotheses of ontogenetic growth and function of the ornamentation, as well as the construction of phylogenetic characters.
... This fluctuating asymmetry-i.e. random deviation from perfect bilateral symmetry-is commonly seen in other chasmosaurs such as Mojoceratops 5 and also in pachycephalosaurs 55 and is typical of structures under strong sexual selection 55 . ...
... This fluctuating asymmetry-i.e. random deviation from perfect bilateral symmetry-is commonly seen in other chasmosaurs such as Mojoceratops 5 and also in pachycephalosaurs 55 and is typical of structures under strong sexual selection 55 . ...
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The horned dinosaur Chasmosaurus from the late Campanian Dinosaur Park Formation of Alberta, is known from numerous skulls and skeletons, but over a century after its description, the taxonomy of the genus is controversial. Two species, Chasmosaurus belli and C. russelli, are currently recognized, with a third species, C. irvinensis, recently placed in a new genus, Vagaceratops. Here, the Yale Chasmosaurus skull is described, and implications for Chasmosaurus systematics are explored. The Yale skull is intermediate between typical C. belli and C. irvinensis. C. belli-like features include large, triangular lateral epiparietals, large parietal fenestrae, and an emarginate parietal. Yet the skull also exhibits derived features of C. irvinensis, including a posteriorly inclined narial strut, brow horns replaced by rugose bosses, reduced parietal emargination, five pairs of epiparietals, and epiparietals that fuse at their bases and hook forward over the frill. Specimen-level phylogenetic analysis provides a hypothesis of relationships upon which to base the taxonomy of Chasmosaurus. C. belli is paraphyletic with respect to C. irvinensis, and the Peabody skull is closer to C. irvinensis than to other C. belli. The holotype of C. russelli clusters with C. belli, making C. russelli a junior synonym of C. belli. Accordingly, Chasmosaurus can be divided into three species: C. belli, C. irvinensis, and C. priscus sp. nov, including specimens previously referred to C. russelli. The systematics of Chasmosaurus show how specimen level phylogeny can provide an evolutionary framework upon which to establish taxonomies. However, the resulting phylogenies may lead to paraphyletic species and genera.
... wyomingensis) rather than two distinct taxa (Horner & Goodwin, 2009). Nevertheless, the name Pachycephalosaurini may still be considered useful as recent studies indicate close relationships between P. wyomingensis and Alaskacephale gangloffi (Longrich, Sankey & Tanke, 2010;Evans et al., 2013;Williamson & Brusatte, 2016;Schott & Evans, 2017;Woodruff et al., 2021). Owing to the unsettled phylogenetic ties between the latest Cretaceous pachycephalosaurs, we prefer to establish a maximum-clade definition for ...
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Ornithischians form a large clade of globally distributed Mesozoic dinosaurs, and represent one of their three major radiations. Throughout their evolutionary history, exceeding 134 million years, ornithischians evolved considerable morphological disparity, expressed especially through the cranial and osteodermal features of their most distinguishable representatives. The nearly two-century-long research history on ornithischians has resulted in the recognition of numerous diverse lineages, many of which have been named. Following the formative publications establishing the theoretical foundation of phylogenetic nomenclature throughout the 1980s and 1990s, many of the proposed names of ornithischian clades were provided with phylogenetic definitions. Some of these definitions have proven useful and have not been changed, beyond the way they were formulated, since their introduction. Some names, however, have multiple definitions, making their application ambiguous. Recent implementation of the International Code of Phylogenetic Nomenclature (ICPN, or PhyloCode) offers the opportunity to explore the utility of previously proposed definitions of established taxon names. Since the Articles of the ICPN are not to be applied retroactively, all phylogenetic definitions published prior to its implementation remain informal (and ineffective) in the light of the Code. Here, we revise the nomenclature of ornithischian dinosaur clades; we revisit 76 preexisting ornithischian clade names, review their recent and historical use, and formally establish their phylogenetic definitions. Additionally, we introduce five new clade names: two for robustly supported clades of later-diverging hadrosaurids and ceratopsians, one uniting heterodontosaurids and genasaurs, and two for clades of nodosaurids. Our study marks a key step towards a formal phylogenetic nomenclature of ornithischian dinosaurs.
... Four frontoparietal domes from the San Carlos and Aguja Formations (Campanian) of Texas are referable to the Pachycephalosauridae and suggest an affinity with Stegoceras and Gravitholus (Lehman, 2010). Recently, the genus and species Texacephale langstoni was erected for a frontoparietal dome (Longrich et al., 2010), but the validity of this taxon has been questioned (Jasinski and Sullivan, 2011). Regardless, CPC 538 demonstrates the presence of pachycephalosaurids in northern Mexico, although it cannot be assigned to any genus until more diagnostic material is found. ...
... During the 1960s, more ceratopsian remains were collected in the Olmos Formation near Palau, northern Coahuila, and were tentatively referred to Chasmosaurus [3]. In 1984, a multinational team from the Royal Ontario Museum collected includes theropods, hadrosaurids, chasmosaurine ceratopsids and pachycephalosaurids [24,25] is found. The site is located about 23.3 km south of Big Bend, and outcrops of the Aguja Formation are roughly continuous across the Rio Grande. ...
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While centrosaurines and ceratopsids in general are abundant in the Late Campanian of northern Laramidia, they are much less commonly found in southern Laramidia. This has supported hypotheses of dinosaur provinciality and endemism in the Late Cretaceous with the delineation of at least two separate faunal zones, north and south Laramidia. There have been 12 genera of centrosaurines recognized from northern Laramidia while two genera, Diabloceratops and Nasutoceratops, have been named from southern Laramidia. We present an osteological description and taphonomic outline for a new centrosaurine ceratopsid from the Aguja Formation of northern Coahuila, Mexico that is not currently diagnosable to the generic level, but likely represents a new taxon. Further, we have included three-dimensional surface scans of all material attributed to this animal. Considering the large number of centrosaurines from northern Laramidia, it is likely that cladistic analyses are biased towards this faunal zone. New findings of southern centrosaurines are needed to correct this bias. This discovery expands the range of centrosaurines south to Coahuila, Mexico and adds new information to better characterize the morphology and taxonomy of centrosaurines from southern Laramidia and their evolution in comparison to their northern counterparts.
... Second, Late Cretaceous ecosystems had high levels of endemism. Campanian ceratopsids had relatively restricted ranges, with different species occurring in different regions (Lehman 2001;Longrich et al. 2010;Sampson et al. 2010;Longrich 2011). During the Late Campanian, Chasmosaurus and Mojoceratops were restricted to the North, Kosmoceratops and Utahceratops were found in Utah, Pentaceratops and Titanoceratops occurred in New Mexico, and Agujaceratops occurred in Texas. ...
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North America hosted a diverse assemblage of horned dinosaurs from the late Campanian until the end of the Cretaceous, but comparatively little is known about earlier horned dinosaurs. This paper reports on previously undescribed ceratopsian remains from the middle Campanian beds of the Judith River Formation of Montana, which represent the oldest known chasmosaurine. The Judith River chasmosaur shows a combination of characters not seen in any previously described ceratopsid. The parietal has a broad median bar, a rounded caudal margin, and highly reduced epiparietals. Episquamosals are enlarged anteriorly but decrease in size posteriorly, and imbricate as in centrosaurines. The postorbital horns are moderately elongate, inclined anterolaterally, and have an unusual teardrop-shaped cross section. The unique combination of characters seen in the Judith River chasmosaurine precludes referral to any previously known genus, and it is therefore described as a new genus and species, Judiceratops tigris. The addition of Judiceratops to the dinosaurian fauna of North America underscores the diversity of horned dinosaurs in the Late Cretaceous, which results from a combination of high diversity within faunas, a high degree of endemism, and rapid faunal turnover. © 2013 Peabody Museum of Natural History, Yale University. All rights reserved.
... Discussions of dinosaur biogeography have emphasized the highly endemic nature of North American faunas during the Campanian (Lehman, 1987(Lehman, , 1997(Lehman, , 2001Wagner and Lehman, 2009;Longrich et al., 2010;Sampson et al., 2010;Longrich, 2011;Gates et al., 2012;Longrich et al., 2013;Sampson et al., 2013). Some studies have gone further, proposing the existence of discrete northern and southern faunal provinces with limited faunal overlap (Lehman, 1997;Sampson et al., 2010;Gates et al., 2012;Sampson et al., 2013) and endemic radiations , implying isolation of the regions. ...
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The upper Campanian of the American Southwest has produced dinosaurs that are unknown from the northern Great Plains and vice versa. This has led to the idea that North America's Campanian dinosaur fauna was characterized by high levels of endemism and distinct faunal provinces. Here, two horned dinosaurs known from the Southwest, Pentaceratops and Kosmoceratops, are described from southern Canada. Pentaceratops aquilonius sp. nov. is represented by two frill fragments from the uppermost Dinosaur Park Formation near Manyberries, southeast Alberta. Features shared with Pentaceratops include large, triangular epiparietals, an M-shaped parietal posterior bar, and an epiparietal P1 that curls up and twists laterally. The Manyberries specimens differ from Pentaceratops sternbergii and Utahceratops gettyi in that the posterior bar is broader, emargination is weakly developed, and P1 is directed dorsally, rather than anteriorly. Phylogenetic analysis places P. aquilonius as sister to a clade comprising P. sternbergii and Utahceratops. Kosmoceratops is documented by a partial skull from Dinosaur Provincial Park. Previously referred to Chasmosaurus, the skull exhibits derived features inconsistent with this referral, including a reduced septal flange, a caudally inclined narial strut, a triangular narial process, a reduced frontal fontanelle, a weakly hooked rostral, and a narrow, caudally inclined internal naris. Phylogenetic analysis recovers the animal as sister to Kosmoceratops richardsoni, but differences in the shape of the naris and nasal horn suggest that it likely represents a distinct species. The presence of Pentaceratops and Kosmoceratops in Canada argues against the idea of distinct northern and southern faunal provinces, but the fact that they differ from their southern relatives confirms that endemism was high in the Campanian. The ability of dinosaur lineages to disperse long distances across North America suggests that dinosaur distribution was not constrained by geographic barriers, climate, or flora. Instead, dinosaur endemism may result from competitive exclusion of immigrants by established populations adapted to local environmental conditions.
... Williamson and Carr (2002) referred these same specimens to Sphaerotholus sp., which is represented by numerous specimens from the Hell Creek Formation. The referral to Sphaerotholus is consistent with several recent phylogenies (Longrich et al. 2010;Evans, et al. 2013), and we therefore follow that taxonomy here. Although these specimens may represent a species distinct from S. buchholtzae (S. edmontonense) we refer them to Sphaerotholus sp. until better material is available for study. ...
Article
A high-resolution biostratigraphic analysis of 287 dinosaurian macrofossils and 138 bonebeds in the Edmonton Group (Upper Cretaceous) of southern Alberta provides evidence for at least three dinosaurian assemblage zones in the Horseshoe Canyon Formation (HCFm). From bottom to top the zones comprise unique assemblages of ornithischians and are named as follows: (1) Edmontosaurus regalis – Pachyrhinosaurus canadensis (lower zone); (2) Hypacrosaurus altispinus – Saurolophus osborni (middle zone); and (3) Eotriceratops xerinsularis (upper zone). Whereas the lower and middle zones are well defined and based on abundant specimens, the validity of the uppermost zone (E. xerinsularis) is tentative because it is based on a single specimen and the absence of dinosaur taxa from lower in section. The transition from the lower to the middle zone coincides with the replacement of a warm-and-wet saturated deltaic setting by a cooler, coastal-plain landscape, characterized by seasonal rainfall and better-drained substrates. Whereas changes in rainfall and substrate drainage appear to have influenced the faunal change, changes in mean annual temperature and proximity to shoreline appear to have had little influence on faunal change. We speculate that the faunal change between the middle and upper zones also resulted from a change in climate, with ornithischian dinosaurs responding to the re-establishment of wetter-and-warmer climates and poorly-drained substrates. Compared with the shorter duration and climatically-consistent dinosaurian assemblage zones in the older Dinosaur Park Formation of southern Alberta, HCFm assemblage zones record long-term morphological stasis in dinosaurs. Furthermore, the coincidence of faunal and paleoenvironmental changes in the HCFm suggest climate-change-driven dinosaur migrations into and out of the region.
... During their long evolutionary history they gave rise to multiple highly recognizable clades including ceratopsids (e.g. C. M. Brown & Henderson 2015;Evans & Ryan 2015), pachycephalosaurs (e.g. Longrich et al. 2010;Evans et al. 2013) and hadrosaurids (e.g. Prieto-M arquez 2010). ...
Article
During their long evolutionary history, neornithischian dinosaurs diverged into several clades with distinctive adaptations. However, the early evolution within Neornithischia and the resolution of the phylogenetic relationships of taxa situated near the base of the clade remain problematic. This is especially true for those taxa traditionally placed at the base of Ornithopoda, either as ‘hypsilophodontids’ or at the base of the diverse clade Iguanodontia. Recent studies are improving our understanding of the anatomy and relationships of these taxa, with discoveries of several new non-ankylopollexian ornithopods from South America and Europe providing key insights into early ornithopod evolution and palaeobiogeography. Here, we describe a new basal ornithopod, Burianosaurus augustai gen. et sp. nov., based on a well-preserved femur from the upper Cenomanian strata (Korycany Beds of the Peruc-Korycany Formation) of the Czech Republic. The new taxon is diagnosed by a unique suite of characters and represents the only occurrence of a Cenomanian non-avian dinosaur in Central Europe north of the Alpine Tethyan areas. Histological examination of the type specimen reveals the presence of a loosely packed Haversian system which suggests relatively mature bone from a possible young adult. Phylogenetic analyses of two different data sets, selected to test the placement of B. augustai in various parts of the neornithischian tree, reconstruct B. augustai as a basal ornithopod, firmly nested outside Ankylopollexia. These results also support a diverse Elasmaria as a basal clade within Ornithopoda and reconstruct Hypsilophodon outside Ornithopoda as the sister taxon to Cerapoda. However, the relationships of ‘hypsilophodontids’ within Neornithischia remain contentious. http://zoobank.org/urn:lsid:zoobank.org:pub:D28A9FB8-A253-4032-8710-4F51668A1E4F
... Dinosaur bones in the Upper Cretaceous Xiaoyan Formation of the southern Anhui Province are rare, but include Wannanosaurus yansiensis a pachycephalosaur (Hou, 1977) and skeletal remains referred to sauropod indet (Yu, 1998). Wannanosaurus was less than one meter in length, and has been considered a flat skull-type pachycephalosaur (Butler and Zhao, 2009), but may also represent a juvenile of the domed skull-type (Longrich et al., 2010). Cervical vertebrae and partial limb girdles of sauropods have been collected from the Xiaoyan Formation. ...
... Pachycephalosaur remains from the southern region of the Western Interior Basin, which preserves the Late Cretaceous terrestrial biotas of southern Laramidia, are rare and remain poorly understood (Lucas, Heckert, and Sullivan, 2000;Williamson and Carr, 2002;Sullivan, 2003Sullivan, , 2006Lehman, 2010;Longrich, Sankey, and Tanke, 2010). Recent fi eldwork focused on vertebrate macrofossils in the Upper Cretaceous Wahweap and Kaiparowits formations of southern Utah have greatly increased our knowledge of these stratigraphic units and have resulted in the recovery of the fi rst nondental pachycephalosaurian remains from these formations (Kirkland, 2001;Kirkland and DeBlieux, 2005;Sampson, Gates, et al., 2010;Sampson et al., this volume, Chapter 28). ...
Chapter
Recent fieldwork in the Upper Cretaceous (Cam-panian) Wahweap and Kaiparowits formations of southern Utah have resulted in the recovery of the fi rst cranial remains of pachycephalosaurian dinosaurs from these units. Pachy-cephalosaurs from the Wahweap Formation are represented by isolated teeth and a single, incomplete frontoparietal dome, whereas the Kaiparowits Formation has yielded isolated teeth plus six fragmentary cranial specimens. The available material is incomplete and the sample remains small, but it suggests the possible presence of at least two new taxa, one in each of the two formations. These specimens significantly expand our knowledge and understanding of pachy-cephalosaurian dinosaur diversity from southern Laramidia.
... Although some structures, such as ceratopsian frill epoccipitals, have been suggested to show fluctuating asymmetry (Longrich, 2010;Longrich et al., 2010) previously claimed to function as honest signalling of mate quality (Møller & Höglund, 1991;Møller, 1992;Grammer & Thornhill, 1994;Ditchkoff et al., 2001), the connection between fluctuating asymmetry and sexual selection has been doubted due to difficulty in replicating results (Balmford et al., 1993). ...
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Despite reports of sexual dimorphism in extinct taxa, such claims in non-avian dinosaurs have been rare over the last decade and have often been criticized. Since dimorphism is widespread in sexually reproducing organisms today, under-reporting in the literature might suggest either methodological shortcomings or that this diverse group exhibited highly unusual reproductive biology. Univariate significance testing, especially for bimodality, is ineffective and prone to false negatives. Species recognition and mutual sexual selection hypotheses, therefore, may not be required to explain supposed absence of sexual dimorphism across the grade (a type II error). Instead, multiple lines of evidence support sexual selection and variation of structures consistent with secondary sexual characteristics, strongly suggesting sexual dimorphism in non-avian dinosaurs. We propose a framework for studying sexual dimorphism in fossils, focusing on likely secondary sexual traits and testing against all alternate hypotheses for variation in them using multiple lines of evidence. We use effect size statistics appropriate for low sample sizes, rather than significance testing, to analyse potential divergence of growth curves in traits and constrain estimates for dimorphism magnitude. In many cases, estimates of sexual variation can be reasonably accurate, and further developments in methods to improve sex assignments and account for intrasexual variation (e.g. mixture modelling) will improve accuracy. It is better to compare estimates for the magnitude of and support for dimorphism between datasets than to dichotomously reject or fail to reject monomorphism in a single species, enabling the study of sexual selection across phylogenies and time. We defend our approach with simulated and empirical data, including dinosaur data, showing that even simple approaches can yield fairly accurate estimates of sexual variation in many cases, allowing for comparison of species with high and low support for sexual variation.
... The matrix consisted of 24 in-group taxa coded for 103 characters, with Thescelosaurus neglectus selected as the outgroup. Characters and codings for the matrix were primarily taken from Longrich et al. (2010), the most complete analysis to date, with the addition of 4 new cranial and 9 new addendicular characters, as well as codings for Acrotholus (Evans et al., 2013); Amtocephale (Watabe et al., 2011); Stegoceras novomexicanum (Jasinski & Sullivan, 2011); and the Sandy Site Pachycephalosaurine, with codings taken from their respective descriptions and a combination of published photographs (Horner & Goodwin, 2009) and personal observations for the Sandy Site specimen. ...
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Since the 1900s, dinosaur fossils have been discovered from Jurassic to Cretaceous age strata, from all across the prairie provinces of Canada and the Western United States, yet little material is known from the outer provinces and territories. In British Columbia, fossils have long been uncovered from the prevalent mid-Cambrian Burgess Shale, but few deposits date from the Mesozoic, and few of these are dinosaurian. The purpose of this paper is to review the history of dinosaurian body fossils in British Columbia. The following dinosaur groups are represented: ankylosaurians, hadrosaurids, pachycephalosaurids, ornithomimosaurians, dromaeosaurids and tyrannosaurids.
... Although some structures, such as ceratopsian frill epoccipitals, have been suggested to show fluctuating asymmetry (Longrich, 2010;Longrich et al., 2010) previously claimed to function as honest signalling of mate quality (Møller & Höglund, 1991;Møller, 1992;Grammer & Thornhill, 1994;Ditchkoff et al., 2001), the connection between fluctuating asymmetry and sexual selection has been doubted due to difficulty in replicating results (Balmford et al., 1993). ...
Article
Despite reports of sexual dimorphism in extinct taxa, such claims in non-avian dinosaurs have been rare over the last decade and have often been criticized. Since dimorphism is widespread in sexually reproducing organisms today, under-reporting in the literature might suggest either methodological shortcomings or that this diverse group exhibited highly unusual reproductive biology. Univariate significance testing, especially for bimodality, is ineffective and prone to false negatives. Species recognition and mutual sexual selection hypotheses, therefore, may not be required to explain supposed absence of sexual dimorphism across the grade (a type II error). Instead, multiple lines of evidence support sexual selection and variation of structures consistent with secondary sexual characteristics, strongly suggesting sexual dimorphism in non-avian dinosaurs. We propose a framework for studying sexual dimorphism in fossils, focusing on likely secondary sexual traits and testing against all alternate hypotheses for variation in them using multiple lines of evidence. We use effect size statistics appropriate for low sample sizes, rather than significance testing, to analyse potential divergence of growth curves in traits and constrain estimates for dimorphism magnitude. In many cases, estimates of sexual variation can be reasonably accurate, and further developments in methods to improve sex assignments and account for intrasexual variation (e.g. mixture modelling) will improve accuracy. It is better to compare estimates for the magnitude of and support for dimorphism between datasets than to dichotomously reject or fail to reject monomorphism in a single species, enabling the study of sexual selection across phylogenies and time. We defend our approach with simulated and empirical data, including dinosaur data, showing that even simple approaches can yield fairly accurate estimates of sexual variation in many cases, allowing for comparison of species with high and low support for sexual variation.
... The matrix consisted of 24 in-group taxa coded for 103 characters, with Thescelosaurus neglectus selected as the outgroup. Characters and codings for the matrix were primarily taken from Longrich et al. (2010), the most complete analysis to date, with the addition of 4 new cranial and 9 new addendicular characters, as well as codings for Acrotholus (Evans et al., 2013); Amtocephale (Watabe et al., 2011); Stegoceras novomexicanum (Jasinski & Sullivan, 2011); and the Sandy Site Pachycephalosaurine, with codings taken from their respective descriptions and a combination of published photographs (Horner & Goodwin, 2009) and personal observations for the Sandy Site specimen. ...
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Since the 1900s, dinosaur fossils have been discovered from Jurassic to Cretaceous age strata, from all across the prairie provinces of Canada and the Western United States, yet little material is known from the outer provinces and territories. In British Columbia, fossils have long been uncovered from the prevalent mid-Cambrian Burgess Shale, but few deposits date from the Mesozoic, and few of these are dinosaurian. The purpose of this paper is to review the history of dinosaurian body fossils in British Columbia. The following dinosaur groups are represented: ankylosaurians, hadrosaurids, pachycephalosaurids, ornithomimosaurians, dromaeosaurids and tyrannosaurids.
... Sternberg 1940Sternberg , 1949Sternberg , 1951Russell 1987;Ryan and Russell 2001;Brown et al. 2015). Despite this long history of palaeontological work in the Scollard Formation, published records of pachycephalosaurid ornithischians from this unit have consisted only of several isolated teeth (Russell 1987;Ryan and Russell 2001;Sullivan 2003), with unconfirmed reports of cranial fragments (Longrich et al. 2010;Eberth et al. 2013). Described and figured material is limited to two reports of teeth collected from vertebrate microsites (Russell 1987;Baszio 1997). ...
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Maastrichtian terrestrial deposits throughout Laramidia (western North America) have yielded a wealth of ancient dinosaur diversity. Yet, despite intense collecting in some areas, latitudinal sampling unevenness still limits biogeographic studies, making new records of dinosaur occurrences significant. Here, we describe the first non-dental pachycephalosaurid cranial material from the late Maastrichtian Scollard Formation of central Alberta, Canada, which allows more precise taxonomic identification of pachycephalosaurids from the northern part of the Western Interior Basin during this time interval. A domed parietal, although weathered, retains several features that allow it to be referred to the tribe Pachycephalosaurini within the subfamily Pachycephalosaurinae, and likely to the genus Pachycephalosaurus. This specimen provides further support for the suggestion that late Maastrichtian dinosaur communities were generally cosmopolitan with no discrete faunal provinces in Laramidia, and underscores the importance of collecting fragmentary, but identifiable remains that often go unreported.
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The traditional view of North American pachycephalosaurids holds that their domes are typically worn, as though they had undergone extensive fluvial transport, and that these animals therefore inhabited upland environments (e.g. piedmont/intermontane settings) relative to where their remains are typically found. Using a statistically robust sample of domes from Alberta, Canada, we subject these hypotheses to various forms of quantitative testing and show that: (1) domes typically exhibit minimal rounding; (2) dome roundness does not positively correlate with distance from the presumed intermontane origin; and (3) pachycephalosaurid remains are not relatively more abundant in intermontane than in alluvial or coastal plain palaeoenvironments. These findings contradict the traditional view of North American pachycephalosaurid dome taphonomy and support the argument that pachycephalosaurids frequented alluvial and coastal lowlands.
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Ornithischia, a diverse clade of herbivorous dinosaurs, has numerous members with structures hypothesized to function in combat. These include the horned ceratopsids, dome-headed pachycephalosaurs, spike-thumbed iguanodonts, tail-clubbed ankylosaurs and spiked stegosaurs, among others. Three main lines of evidence support such inferences: (1) analogy with modern animals; (2) biomechanical analysis and simulation; and (3) paleopathology. The most solid inferences utilize multiple pieces of evidence, although this is hampered by a limited understanding of combat in modern animals.
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ABSTRACT The late Campanian?aged (= Judithian) squamates from the Terlingua Local Fauna of the Aguja Formation, southern Texas, includes four scincomorphans: a new taxon (Catactegenys solaster, gen. et sp. nov.), referable to Xantusiidae, that has massive teeth and tooth crown morphology similar to that of contogeniid lizards; an indeterminate scincomorphan (Apsgnathus triptodon, gen et sp. nov.) with robust teeth; and two unnamed scincomorphan morphotypes. Anguimorphans in the fauna include Odaxosaurus piger, cf. Parasaniwa wyomingensis, and a likely xenosaur. Ophidian jaw fragments confirm the presence of a snake in the fauna. The Aguja squamate assemblage is one of the most southerly of a series of paracontemporaneous squamate faunas extending from central Alberta to northern Mexico. Comparison of these faunas reveals that, although two taxa are endemic to the Aguja Formation, others show some latitudinal trends. Odaxosaurus and Parasaniwa are present in all well-sampled faunas from Alberta to Texas. http://www.tandfonline.com/eprint//full
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Several fragmentary frontoparietal domes from the San Carlos and Aguja Formations (Campanian) of Brewster and Presidio Counties, Texas, are referable to Pachycephalosauridae (Dinosauria: Ornithischia) and represent a southern extension of the known range of these dinosaurs in North America. Although the specimens are insufficient for confident generic identification, the size, relative dome height and width, continuity of frontal and parietal portions of the dome, and obliteration of sutures between these bones suggest affinity with pachycephalosaurids as Stegoceras and Gravitholus. More than one taxon is probably represented in the collection. Sections taken from one of the domes reveal histological tissue zonation comparable to that found in other pachycephalosaurids and growth lines indicating that at least 5 years were required to attain adult size. The bone tissue is well suited for strengthening the dome to resist compressional loading, and is compatible with the hypothesis that these animals engaged in head-butting behavior.
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Taphonomic biases dictate how organisms are represented in the fossil record, but their effect on studies of vertebrate diversity dynamics is poorly studied. In contrast to the high diversity and abundance of small-bodied animals in extant ecosystems, small-bodied dinosaurs are less common than their large-bodied counterparts, but it is unclear whether this reflects unique properties of dinosaurian ecosystems or relates to taphonomic biases. A new, fully domed pachycephalosaurid dinosaur, Acrotholus audeti, from the Santonian of Alberta predates incompletely domed taxa, and provides important new information on pachycephalosaur evolution and the completeness of the ornithischian fossil record. Here we provide the first empirical evidence that the diversity of small-bodied ornithischian dinosaurs is strongly underestimated based on ghost lineages and the high proportion of robust and diagnostic frontoparietal domes compared with other pachycephalosaur fossils. This suggests preservational biases have a confounding role in attempts to decipher vertebrate palaeoecology and diversity dynamics through the Mesozoic.
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New end-stage juvenile specimens of Pachycephalosaurus from the Upper Cretaceous Hell Creek Formation, Montana, confirm the earliest expression of squamosal nodes, parietal ornamentation, and jugal morphology in the smallest and presumably youngest individuals yet known. High-resolution computed tomography of the slightly thickened, undomed parietal reveals a dense cortex, a highly cancellous interior of irregularly shaped erosion cavities, and bony trabeculae indicative of primary, fast growing bone. The parietal, with its highly ornamented septum morphology and patent sutures, is nearly identical to the holotype of ‘Dracorex hogwartsia,’ and combined with these new internal histological details, supports the alternative interpretation that ‘D. hogwartsia’ is a juvenile Pachycephalosaurus wyomingensis. The squamosal nodes grow into an array of horns and secondary nodes exemplified by the pachycephalosaurin ‘Stygimoloch spinifer’ considered in this study to be a subadult P. wyomingensis. Unlike the squamosal ornamentation, the hypertrophied midline row of parietal nodes is transient as the frontoparietal dome expands later in ontogeny. We propose the term ‘ontogimorph’ as a substitute for ‘semaphoront’ to describe these taxon-specific morphological variants that grow allometrically and express extreme cranial morphology along a postnatal growth continuum ontogenetically. These juvenile-, sub-adult-, and adult-specific features in the skull of Pachycephalosaurus may have allowed the visual identification of ontogimorphs and signal their changing sociobiological status. Citation for this article: Goodwin, M. B., and D. C. Evans. 2016. The early expression of squamosal horns and parietal ornamentation confirmed by new end-stage juvenile Pachycephalosaurus fossils from the Upper Cretaceous Hell Creek Formation, Montana. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1078343.
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Caenagnathid theropods are a relatively common part of the theropod fauna in the Late Cretaceous of Asia and North America, but have not previously been described from the southernmost United States. Here, we describe caenagnathid fossils from the late Campanian Aguja Formation of West Texas, and revise the systematics of caenagnathids from the Campanian of North America. Caenagnathids from the late Campanian of Canada represent three species in three genera: Caenagnathus collinsi, Chirostenotes pergracilis and Leptorhynchos elegans gen. nov. Leptorhynchos is diagnosed by its small size, its short, deep mandible, and the upturned tip of the beak. A single caenagnathid is known from the late Campanian of Utah, Hagryphus giganteus. Two caenagnathid species occur in the Aguja Formation, ?Chirostenotes sp. and Leptorhynchos gaddisi sp. nov. L. gaddisi differs from L. elegans in that the tip of the beak is narrower and less upturned. Phylogenetic analysis recovers Caenagnathidae and Oviraptoridae as monophyletic sister taxa. Within Caenagnathidae, the North American species seem to form a monophyletic assemblage, the Caenagnathinae, within which Chirostenotes and Caenagnathus form a clade to the exclusion of Leptorhynchos. The discovery of Chirostenotes gaddisi provides more evidence for the existence of a distinct dinosaurian fauna in southern North America during the Campanian. Furthermore, the Aguja fossils show that caenagnathids were widespread and highly diverse in the Late Cretaceous of North America. This diversity was maintained in two ways. First, variation in body size and beak shape suggests that diversity within formations is maintained by niche partitioning, in a way analogous to Darwin's finches. Second, diversity is maintained by high degree of endemism, with different species of caenagnathids occurring in different habitats. © 2013 Peabody Museum of Natural History, Yale University. All rights reserved.
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The attachments of jaw muscles are typically implicated in the evolution and shape of the dorsotemporal fenestra on the skull roof of amniotes. However, the dorsotemporal fenestrae of many archosaurian reptiles possess smooth excavations rostral and dorsal to the dorsotemporal fossa which closely neighbors the dorsotemporal fenestra and jaw muscle attachments. Previous research has typically identified this region, here termed the frontoparietal fossa, to also have been attachment surfaces for jaw‐closing muscles. However, numerous observations of extant and extinct archosaurs described here suggest that other tissues are instead responsible for the size and shape of the frontoparietal fossa. This study reviewed the anatomical evidence that support soft‐tissue hypotheses of the frontoparietal fossa and its phylogenetic distribution among sauropsids. Soft‐tissue hypotheses (i.e., muscle, pneumatic sinus, vascular tissues) were analyzed using anatomical, imaging and in vivo thermography techniques within a phylogenetic framework using extant and extinct taxa to determine the inferential power underlying the reconstruction of the soft tissues in the skull roofs of dinosaurs, pseudosuchians and other reptiles. Relevant anatomical features argue for rejection of the default hypothesis—that the fossa was muscular—due to a complete lack of osteological correlates reflective of muscle attachment. The most‐supported inference of soft tissues is that the frontoparietal fossa contained a large vascular structure and adipose tissue. Despite the large sizes and diverse morphologies of these fossae found among dinosaur taxa, these data suggest that non‐avian dinosaurs had the anatomical foundation to support physiologically‐significant vascular devices and/or vascular integumentary structures on their skull roofs. This article is protected by copyright. All rights reserved.
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Small herbivorous dinosaurs of the clades Pachycephalosauridae and Thescelosauridae occur in multiple Cretaceous formations in North America, their coexistence likely made possible by differences in feeding style. Fossils of these taxa are generally rare, but isolated pachycephalosaurid and thescelosaurid teeth are common at microfossil sites, and easily confused with one another in field and museum settings. Using qualitative features and a set of 12 measurements, the dentitions of the pachycephalosaurid Stegoceras validum and the thescelosaurid Thescelosaurus neglectus were compared, based on teeth preserved in identified skeletons. S. validum and T. neglectus possess heterodont dentitions, and their teeth differ in size, denticulation, crown symmetry, root and crown cross-sectional shapes, apical geometry, crown ornamentation, and wear facet patterns. Principal components analysis of the measurements shows that T. neglectus premaxillary, maxillary, and dentary crowns are readily morphologically distinguishable from one another, whereas all S. validum crowns cluster close to each other and to dentary crowns of T. neglectus. Linear discriminant analysis shows little overlap between S. validum and T. neglectus. The results indicate strong heterodonty in T. neglectus, whereas S. validum teeth are more uniform. Dental differences between the two species may imply that they differed in feeding function. The teeth of T. neglectus, combined with the narrow rostrum, suggest a selective feeding strategy. By contrast, S. validum has a wide rostrum and may have engaged in indiscriminate bulk-feeding behavior. This analysis of dental differences between S. validum and T. neglectus should facilitate identification of isolated pachycephalosaurid and thescelosaurid teeth from microfossil sites.
Article
The first recorded pachycephalosaurid dinosaur from outside of North America, “Troodon” bexelli, was described from the Upper Cretaceous of Nei Mongol (Inner Mongolia) Autonomous Region, China, in 1953 based on a partial parietal dome. The holotype, and only, specimen has not been redescribed or figured since the original description and is currently considered lost. As a result, researchers have generally considered this taxon a nomen dubium. Here, we identify and describe two high-fidelity plaster casts of the holotype and assign them as plastotypes for this taxon. Examining these replicas allows for an updated comparative description and complete systematic revision of this enigmatic taxon and its inclusion within a phylogenetic analysis for the first time. The material is distinct from all other pachycephalosaur material and can be diagnosed by a single autapomorphy (a wide and deeply embayed posterior parietal margin) and a unique combination of characters, including lack of primary nodes on the parietal and a highly arched, fully roofed temporal chamber. A new genus, Sinocephale gen. nov. is established to receive this species as Sinocephale bexelli. Sinocephale bexelli is phylogenetically removed from Stegoceras (formerly “Troodon”), to which it was previously affiliated, and recovered as a pachycephalosaurine pachycephalosaurid.
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Late Cretaceous deposits of the North American Western Interior represent the best, if not only, opportunity to construct a high-resolution chronostratigraphic framework within which to conduct continental-scale geological and paleontological analyses. This is due to the serendipitous combination of large areas of outcrop, interfingering marine units with biostratigraphically informative fossils, and a consistent scattering of radiometric dates due to synorogenic volcanic activity. Accurate correlation is essential for testing a large number of current geological and paleobiological hypotheses; however, despite the large amount of data available, many published correlations suffer from inaccuracies or are simply based on outdated information. Here I present a comprehensive high-resolution stratigraphic chart for terrestrial Late Cretaceous units of North America, combining published chronostratigraphic, lithostratigraphic, and biostratigraphic data. For the first time, nearly two hundred ⁴⁰ Ar / ³⁹ Ar radiometric dates are recalibrated to both current standard and decay constant pairings, correcting errors in previous recalibrations. Revisions to the stratigraphic placement of most units are slight, but important changes are made to the proposed correlations of the Aguja and Javelina Formations, Texas, and miscalculations in recently published analyses are corrected which in particular affects the relative age positions of the Belly River Group, Alberta; Judith River Group, Montana, Kaiparowits Formation, Utah, and Fruitland and Kirtland Formations, New Mexico. This work represents the most extensive and accurate interbasinal correlation currently available for the North American Western Interior and should replace all previously published similar works and diagrams. The stratigraphic ranges of selected dinosaur clades are plotted on the chronostratigraphic framework, typically forming stacks of short-duration species which do not overlap stratigraphically with preceding or succeeding forms. This is the expected pattern which is produced by an anagenetic mode of evolution, suggesting that true branching (speciation) events were rare and may have geographic significance. Purported north-south provinciality of dinosaurs is shown to be mostly an artifact of stratigraphic miscorrelation. Rapid stepwise acquisition of display characters in many dinosaur clades, in particular chasmosaurine ceratopsids, suggests that they may represent the highest resolution biostratigraphic markers to be used where radiometric dates are not available.
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Interbasinal stratigraphic correlation provides the foundation for all consequent continental-scale geological and paleontological analyses. Correlation requires synthesis of lithostratigraphic, biostratigraphic and geochronologic data, and must be periodically updated to accord with advances in dating techniques, changing standards for radiometric dates, new stratigraphic concepts, hypotheses, fossil specimens, and field data. Outdated or incorrect correlation exposes geological and paleontological analyses to potential error. The current work presents a high-resolution stratigraphic chart for terrestrial Late Cretaceous units of North America, combining published chronostratigraphic, lithostratigraphic, and biostratigraphic data. ⁴⁰ Ar / ³⁹ Ar radiometric dates are newly recalibrated to both current standard and decay constant pairings. Revisions to the stratigraphic placement of most units are slight, but important changes are made to the proposed correlations of the Aguja and Javelina Formations, Texas, and recalibration corrections in particular affect the relative age positions of the Belly River Group, Alberta; Judith River Formation, Montana; Kaiparowits Formation, Utah; and Fruitland and Kirtland formations, New Mexico. The stratigraphic ranges of selected clades of dinosaur species are plotted on the chronostratigraphic framework, with some clades comprising short-duration species that do not overlap stratigraphically with preceding or succeeding forms. This is the expected pattern that is produced by an anagenetic mode of evolution, suggesting that true branching (speciation) events were rare and may have geographic significance. The recent hypothesis of intracontinental latitudinal provinciality of dinosaurs is shown to be affected by previous stratigraphic miscorrelation. Rapid stepwise acquisition of display characters in many dinosaur clades, in particular chasmosaurine ceratopsids, suggests that they may be useful for high resolution biostratigraphy.
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Full-text available
Interbasinal stratigraphic correlation provides the foundation for all consequent continental-scale geological and paleontological analyses. Correlation requires synthesis of lithostratigraphic, biostratigraphic and geochronologic data, and must be periodically updated to accord with advances in dating techniques, changing standards for radiometric dates, new stratigraphic concepts, hypotheses, fossil specimens, and field data. Outdated or incorrect correlation exposes geological and paleontological analyses to potential error. The current work presents a high-resolution stratigraphic chart for terrestrial Late Cretaceous units of North America, combining published chronostratigraphic, lithostratigraphic, and biostratigraphic data. ⁴⁰ Ar / ³⁹ Ar radiometric dates are newly recalibrated to both current standard and decay constant pairings. Revisions to the stratigraphic placement of most units are slight, but important changes are made to the proposed correlations of the Aguja and Javelina Formations, Texas, and recalibration corrections in particular affect the relative age positions of the Belly River Group, Alberta; Judith River Formation, Montana; Kaiparowits Formation, Utah; and Fruitland and Kirtland formations, New Mexico. The stratigraphic ranges of selected clades of dinosaur species are plotted on the chronostratigraphic framework, with some clades comprising short-duration species that do not overlap stratigraphically with preceding or succeeding forms. This is the expected pattern that is produced by an anagenetic mode of evolution, suggesting that true branching (speciation) events were rare and may have geographic significance. The recent hypothesis of intracontinental latitudinal provinciality of dinosaurs is shown to be affected by previous stratigraphic miscorrelation. Rapid stepwise acquisition of display characters in many dinosaur clades, in particular chasmosaurine ceratopsids, suggests that they may be useful for high resolution biostratigraphy.
Article
Principal coordinates analysis (PCoA) is a statistical ordination technique commonly applied to morphology-based cladistic matrices to study macroevolutionary patterns, morphospace occupation, and disparity. However, PCoA-based morphospaces are dissociated from the original data; therefore, whether such morphospaces accurately reflect body-plan disparity or extrinsic factors, such as body size, remains uncertain. We collated nine character–taxon matrices of dinosaurs together with body-mass estimates for all taxa and tested for relationships between body size and both the principal axis of variation (i.e., PCo1) and the entire set of PCo scores. The possible effects of body size on macroevolutionary hypotheses derived from ordinated matrices were tested by reevaluating evidence for the accelerated accumulation of avian-type traits indicated by a strong directional shift in PCo1 scores in hypothetical ancestors of modern birds. Body mass significantly accounted for, on average, approximately 50% and 16% of the phylogenetically corrected variance in PCo1 and all PCo scores, respectively. Along the avian stem lineage, approximately 30% of the morphological variation is attributed to the reconstructed body masses of each ancestor. When the effects of body size are adjusted, the period of accelerated trait accumulation is replaced by a more gradual, additive process. Our results indicate that even at low proportions of variance, body size can noticeably affect macroevolutionary hypotheses generated from ordinated morphospaces. Future studies should thoroughly explore the nature of their character data in association with PCoA-based morphospaces and use a residual/covariate approach to account for potential correlations with body size.
Article
We analyzed samples for paleomagnetism, ⁴⁰Ar/³⁹Ar detrital sanidine ages, and mammalian fauna to produce a precise chronostratigraphic framework for the Upper Cretaceous to Lower Paleocene Dawson Creek section of Big Bend National Park, west Texas. Prior to this work, the absolute ages and durations of the Upper Cretaceous Aguja and Javelina Formations and Paleocene Black Peaks Formation were relatively poorly constrained. The documented polarity zones can be correlated to C32n-C31n, C29r, and C27r of the geomagnetic polarity time scale, with three hiatuses spanning more than 1.5 m.y. each. Rock magnetic analyses indicate that the dominant magnetic carrier in the Aguja and Black Peaks Formations is titanomagnetite, while the Javelina Formation has varying magnetic carriers, including hematite, magnetite, and maghemite. An overprint interval surrounding the Cretaceous-Paleogene boundary suggests the primary magnetic carrier, titanohematite, was likely reset by burial and/or overlying basaltic flows. These are the first independent age constraints for the Cretaceous-Paleocene strata at the Dawson Creek section that determine the age and duration of deposition of each formation in the section, as well as the age and duration of multiple unconformities through the succession. As a result, these age constraints can be used to reassess biostratigraphic and isotopic correlations between the Big Bend area and other Cretaceous-Paleogene basins across North America. Based on this new data set, we reassign the age of the mammalian fauna found in the Black Peaks Formation from the Puercan to the Torrejonian North American Land Mammal age. Our age constraints show that the dinosaur fauna in the Javelina Formation in the Dawson Creek area is latest Maastrichtian and restricted to chron C29r. Thus, the Javelina dinosaur fauna is correlative to the Hell Creek Formation dinosaur fauna from the Northern Great Plains, indicating differences between the faunas are not due to differences in age, and providing support for the hypothesis of provinciality and endemism in dinosaur communities in the late Maastrichtian. Further, the age constraints indicate that the previously documented mid-Maastrichtian and late Maastrichtian greenhouse events were rapid ( < 200 k.y.) and correlate closely with climate events documented in the marine record.
Article
Compared to earlier representatives of the family, pachycephalosaurids are less well known from upper Maastrichtian deposits around the world. Here, we report on a nearly complete left postorbital attributable to the pachycephalosaurid Sphaerotholus cf. Sphaerotholus buchholtzae from the upper Maastrichtian Frenchman Formation of Saskatchewan. This marks a probable northern range extension for the species into Canada, and the first occurrence of a pachycephalosaurid from this formation. We further demonstrate the taxonomic distinction between Stegoceras edmontonense and S. buchholtzae, which has been debated, based on postorbital sutural proportions. The northerly occurrence of Sphaerotholus cf. S. buchholtzae is consistent with the hypothesis of low beta diversity during the late Maastrichtian of North America, and its high stratigraphic incidence documents the persistence of non-pachycephalosaurin pachycephalosaurines in a critical interval for understanding the end-Cretaceous mass extinction event.
Article
To date, only three pachycephalosaur specimens have been reported from the Nemegt Formation, two of which are holotypes (Homalocephale calathocercos and Prenocephale prenes) and all of which were collected from the classic Nemegt locality. Here, we describe several new cranial specimens from this formation, but which originate from Bügiin Tsav, Guriliin Tsav, and Tsagaan Khushuu localities. The specimens consist of an incomplete frontoparietal dome that is slightly smaller than the holotype of P. prenes, and two specimens that are larger than the holotype –a second incomplete frontoparietal and a complete squamosal with ornamentation. All specimens are referable to P. prenes or cf. Prenocephale. Cranial histology is investigated in an Asian pachycephalosaur for the first time on the basis of these new specimens. The specimens increase the ontogenetic representation for Prenocephale, and show that the squamosal ornamentation pattern is consistent across the known size range. These specimens expand the geographic range of pachycephalosaurs in the Nemegt Formation, and provide new ontogenetic data for P. prenes that reinforces the taxonomic distinction between it and Homalocephale.
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'Species' are often treated as existing only at a single specific time slice. In fact, they are timely limited entities with a beginning, a time of persistence and an end, the consequences of which are discussed here. Here we try to understand how reliably we can precisely reconstruct the events that took place close to a species split. Therefore, we discuss different scenarios of a hypothetical population undergoing split and/or character evolution. Subsequently, we compare how a Hennigian ideal reconstruction would look like in comparison to a possible actual reconstruction. We also evaluate the character evolution at such splits. Last, we compare how the different reconstructions resolve appearance of new species and new characters through time. We summarize the major consequences of these observations on certain problems, notably the sister species vs. ancestor problem, "chronospecies", fossil species, character evolution, and mapping on stratigraphic charts. We strongly argue for basing scientific investigations on proper philosophical backgrounds (epistemology), but epistemology still needs to be practically applicable. With this contribution, we aim at providing additional philosophical bases for certain aspects of evolutionary reconstructions, while still keeping the approaches practically applicable.
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In light of a recent paper, we review, and reassess, the validity of the pachycephalosaurid dinosaur Stegoceras novomexicanum (Dinosauria: Ornithischia: Pachycephalosauridae). Specimens that are referred to Stegoceras novomexicanum are all late Campanian (early Kirtlandian) in age and are not only from a restricted stratigraphic horizon at the Fruitland/Kirtland transition, but also from a small geographic area of the San Juan Basin, New Mexico. While some of the characters initially used in diagnosing this taxon may be representative of an earlier (sub-adult) ontogenetic stage, such as the reduction of the size of the posteromedial extension of the parietal and the size of the supratemporal fenestrae, several other characters confirm its validity. These include the shape of the posteromedial extension of the parietal, the relative position of the supratemporal fenestrae, the shape and degree of inflation of the nasal boss, morphology of the prefrontal-frontal suture, curvature of the frontal-parietal suture, and its relative overall size and gracile form relative to the type (lectotype) of Stegoceras validum from the Judithian of Alberta, Canada. Although the holotype of Stegoceras novomexicanum may represent a sub-adult individual, it also possesses some diagnostic features that are indicative of an adult. This combination of features may indicate heterochrony for Stegoceras novomexicanum within the Pachycephalosauridae. Recently recovered small-bodied, high-domed pachycephalosaurid specimens from the Fruitland-Kirtland transition further support our interpretation that this taxon represents a distinct, small-bodied adult pachycephalosaurid in New Mexico. The previously described paratypes, and newly collected specimens, are conservatively assigned to cf. Stegoceras novomexicanum, as all this material comes from a very restricted stratigraphic interval and geographic area.
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The extraordinary paleontological record from Big Bend National Park (BIBE), Texas chronicles nearly 120 million years of largely uninterrupted deposition through Late Cretaceous, Paleogene and Neogene time. Therefore, the park records one of the most complete and continuous fossil records of its kind in North America, if not the world. Paleontologists have collected and studied fossils from BIBE for over a century and nearly 1400 fossil species have been reported thus far. The BIBE paleontological record includes type specimens representing 44 scientifically valid species (five plants, nine invertebrates, and 30 vertebrates). Numerous other reported specimens are very likely new to science but have yet to be formally named. The present catalog presents the currently known assemblage of fossil plant, invertebrate, and vertebrate species from BIBE within a single, comprehensive record with significant references for each. This work is designed and written to be a research and resource management tool for scientists and non-scientists alike.
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The morphological disparity of species within major clades shows a variety of trajectory patterns through evolutionary time. However, there is a significant tendency for groups to reach their maximum disparity relatively early in their histories, even while their species richness or diversity is comparatively low. This pattern of early high-disparity suggests that there are internal constraints (e.g. developmental pleiotropy) or external restrictions (e.g. ecological competition) upon the variety of morphologies that can subsequently evolve. It has also been demonstrated that the rate of evolution of new character states decreases in most clades through time (character saturation), as does the rate of origination of novel bodyplans and higher taxa. Here, we tested whether there was a simple relationship between the level or rate of character state exhaustion and the shape of a clade’s disparity profile: specifically, its centre of gravity (CG). In a sample of 93 extinct major clades, most showed some degree of exhaustion, but all continued to evolve new states up until their extinction. Projection of states/steps curves suggested that clades realized an average of 60%of their inferred maximumnumbers of states. Despite aweak but significant correlation between overall levels of homoplasy and the CG of clade disparity profiles, there were no significant relationships between any of our indices of exhaustion curve shape and the clade disparity CG. Clades showing early high-disparity were no more likely to have early character saturation than those with maximum disparity late in their evolution. © 2015 The Author(s) Published by the Royal Society. All rights reserved.
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The sudden appearance of Asian dinosaur clades within Lower Cretaceous strata of western North America has long been recognised as a biotic dispersion event related to initial establishment of a Beringian land bridge. To date, uncertainty exists regarding the timing of the Early Cretaceous Laurasian interchange event (EKLInE) and the pattern of associated biotic dispersal. Here, we report a tyrannosauroid premaxillary tooth (FMNH PR 2750) from the Cloverly Formation, Wyoming, USA, that pushes back the earliest Cretaceous record of the clade in North America. Although fragmentary, the tooth is consistent with mounting evidence for a pre-108 Ma initiation of EKLInE and earliest Albian emplacement of Beringia. Previous authors have considered the Aptian/Albian of western North America a depauperate dinosaur fauna, characterised by regional extinction and diversity decline. Documentation of Albian tyrannosauroids in the region indicates a more dynamic ecosystem than previously appreciated and marks an early start to faunal mixing between immigrant and endemic dinosaur clades. Finally, we find that the enamel microstructure of FMNH PR 2750 conforms to the morphotype of tyrannosaurids, yet exhibits poor columnar differentiation. This morphology bolsters prior interpretations on the phylogenetic utility of enamel microstructure and suggests a trend of increasing enamel complexity within Tyrannosauroidea.
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Stegoceras (sensu lato) has been the recipient of a number of species. Most have been placed into synonymy with S. validum, some have been transferred to other genera (i.e., Gravitholus, Ornatotholus), whereas others have been interpreted as being sexual dimorphs. A parsimonious phylogenetic analysis using 49 characters, which include 9 new cranial characters based on pachycephalosaur frontoparietal domes, now permits a revision of the genus Stegoceras. This analysis concludes that Stegoceras validum (sensu stricto) is a primitive, incipiently-domed pachycephalosaur that is characterized by a well-developed squamosal shelf and open supratemporal fossae. It is the sister taxon to the fully-domed Pachycephalosaurinae. The taxon Ornatotholus browni has a parietal and displays features identical to S. validum and is therefore a subjective junior synonym. Specimens consisting of flat, paired frontals are immature individuals of S. validum. The holotype of “Stegoceras” lambei, and all morphotypes of this species, are unique in the construction of the posterior squamosal region and are placed in a new genus, Colepiocephale. Colepiocephale lambei is known solely from the Foremost Formation and is the oldest diagnostic pachycephalosaur from North America. An incomplete, and indeterminate, skull from the upper part of the Milk River Formation (upper Santonian) has the distinction of being the oldest known North American pachycephalosaur. “S.” sternbergi lacks a posterior squamosal shelf and has squamosals directed laterally and is placed in a new genus, Hanssuesia, as H. sternbergi. Although the taxon Gravitholus albertae displays some characters (i.e., retention of the posterior squamosals separated by a distinct median parietal) and is similar to H. sternbergi in some respects, the holotype is too incomplete for any definitive diagnosis and thus it is considered a nomen dubium. Sphaerotholus is a subjective junior of Prenocephale and the species Sphaerotholus buchholtzae is a subjective junior synonym of Prenocephale edmontonensis. The taxa Prenocephale brevis, P. edmontonensis, and P. goodwini, form a monophyletic clade with monotypic Asian taxa Prenocephale prenes and Tylocephale gilmorei as an unresolved sister group. They are united by the possession of a distinct row of nodes on the squamosal and parietale. Tylocephale, if valid, is interpreted as the sister taxon to the Prenocephale clade. Stenotholus kohleri is formally recognized as a junior synonym of Stygimoloch spinifer. Based on the presence of hypertrophied nodes Stygimoloch spinifier and Pachycephalosaurus wyomingensis are united in the clade Pachycephalosaurini new taxon. Small-to-medium size Late Cretaceous pachycephalosaurs were rather diverse, especially during the late Campanian (ludithian), and many species coexisted during Campanian and Maastrictian times. Ancestry and directionality of dispersal (in part) of the North American and Asian taxa remains uncertain and certainly antedates Campanian time.
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The recent discovery of a nearly complete ceratopsid skull in the Aguja Formation of southwest Texas supports previous conclusions that the Aguja ceratopsid represents a distinct species, Chasmosaurus mariscalensis. The diagnostic features of C. mariscalensis include an extensive anteromedian projection of the nasal between the premaxillae, erect supraorbital horns, and laterally rounded squamosal. Nine cranial features that vary among Chasmosaurus species, Pentaceratops sternbergii, and other chasmosaurines are analyzed. Chasmosaurus mariscalensis appears to be most closely related to northern species of Chasmosaurus (C. belli, C. russelli), which also exhibit a transversely flattened nasal horn and modifications of the anterior margin of the external naris. The genus Chasmosaurus, in turn, appears to be most closely related to the other southern chasmosaurine, Pentaceratops sternbergii. The biogeographic history inferred from these relationships suggests that the biogeographic exchange between northern and southern chasmosaurines cannot be explained by a single dispersal event to the south.
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The Terlingua local fauna is a rich assemblage of predominantly terrestrial micro vertebrates from the Upper Cretaceous Aguja Formation of Trans-Pecos Texas. Marine invertebrates (which include elements of both Cretaceous Western Interior and Gulf Coast zoogeographic provinces) from conformably underlying strata suggest that the fauna is of late Campanian age, probably correlative with Judithian assemblages of the Western Interior. A Judithian “age” for the fauna is further supported by its mammal and theropod assemblages, and by the faunas of overlying deposits. The previously reported diversity of the Aguja Formation, which we summarize, is significantly enriched by this new fauna. The fauna also fills a major gap in the biogeography of Campanian terrestrial vertebrates.Notable occurrences in the Terlingua local fauna include the therian mammal Gallolestes, previously known only from Baja California, and a hitherto unrecorded type of primitive ‘tribothere.’ At least 4 marsupial and 6 multituberculate taxa are present, several of which represent new taxa. Squamates comprise at least 10 taxa, including xenosaurs, necrosaurs, glyptosaurines, scincids, teiids, and a snake, several of which represent new taxa. In addition, the fauna includes at least 7 dinosaurs, 1 pterosaur, 2 crocodylomorphs, 3 turtles, 3 lissamphibians, 3 actinopterygians, and 8 chondrichthyans. Wood, amber, leaves, seeds, pollen, molluscs, and dinoflagellates are also preserved. The fauna is not strictly comparable to others from the Western Interior. It includes taxa that are either endemic or otherwise known only from relatively low latitudes, indicating an appreciable degree of latitudinal differentiation among Campanian terrestrial faunas bordering the Western Interior seaway.
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Butler, R.J. and Sullivan, R.M. 2009. The phylogenetic position of the ornithischian dinosaur Stenopelix valdensis from the Lower Cretaceous of Germany and the early fossil record of Pachycephalosauria. Acta Palaeontologica Polonica 54 (1): 21-34. The holotype of Stenopelix valdensis is the most completely known dinosaur specimen from the "Wealden" (Lower Cre− taceous) of northwestern Germany, but its phylogenetic position has remained highly controversial. Most recent authors have suggested affinities with the ornithischian clade Marginocephalia, and most commonly to the marginocephalian subclade Pachycephalosauria. A pachycephalosaurian identity would make Stenopelix the only confirmed pre−Late Cre− taceous member of this clade, breaking up an extensive ghost lineage which extends to the inferred origin of Pachy− cephalosauria in the Middle-Late Jurassic. Based upon re−examination of the holotype we here review the characters that have previously been used to assign Stenopelix to either Pachycephalosauria or Ceratopsia. All of these characters are problematic, being based upon inaccurate anatomical interpretations, or having more widespread distributions within Ornithischia than previously realised. We conclude that although the overall anatomy of Stenopelix is consistent with marginocephalian affinities, there is insufficient evidence to support referral to either Pachycephalosauria or Ceratopsia; we consider Stenopelix ?Marginocephalia. A brief review indicates that there is no compelling fossil evidence for pachycephalosaurs prior to the Late Cretaceous. Key wor ds: Dinosauria, Ornithischia, Pachycephalosauria, Marginocephalia, Stenopelix, Cretaceous, Germany.
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Several biologically significant domes of pachycephalosaurid dinosaurs are described and figured. One unusual specimen from the Oldman Formation (Upper Cretaceous) of Alberta is placed into a new genus and another specimen from the same formation is assigned to a new species of Stegoceras. Domes referable to Stegoceras sp. (Judith River and Hell Creek Formations) are the first conclusive evidence of the presence of this genus in the United States. A large dome from the Oldman Formation of Alberta is referred to Pachycephalosaurus; this specimen is the oldest described to date and is the first record of this genus in Canada.Endocranial casts of Yaverlandia bitholus and Stegoceras validus are described along with a discussion of endocranial trends in pachycephalosaurids. The separation between the cerebrum and cerebellum found in Yaverlandia, and typical of ornithopods in general, is lacking in Stegoceras and Pachycephalosaurus. The loss of this separation may be the result of head butting.The family Pachycephalosauridae possesses sufficient ornithopod characters to justify their retention in that suborder. It does, however, represent an aberrant side branch of ornithopod evolution, which can best be visualized taxonomically by placing this family into a separate infraorder within the Ornithopoda.
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Pachycephalosaurian specimens from the Upper Cretaceous (upper Campanian) Kirtland Formation of northwestern New Mexico include a partial skull that preserves much of the basicranium. It represents a new genus and species, Sphaerotholus goodwini. A new species, S. buchholtzae, from the upper Maastrichtian Hell Creek Formation of Montana is referred to this genus. Additional New Mexico pachycephalosaurians include a partial dentary with associated skull material that is tentatively referred to S. goodwini and a partial frontoparietal that is referred to Pachycephalosauridae incertae sedis. On the basis of a hypothetical growth series of Stegoceras, we excluded characters based on dome development and suture closure from a cladistic analysis of pachycephalosaurian relationships. Ornatotholus browni, the only putative “flat-headed” pachycephalosaurian from North America, is considered a nomen dubium and may represent a juvenile Stegoceras. Gravitholus albertae is an adult Stegoceras sp.; Stegoceras edmontonense is a nomen dubium and is referred to cf. Sphaerotholus sp. Based on the results of a quantitative cladistic analysis, Stegoceras (including Stegoceras breve, S. lambei, S. sternbergi, and UCMP 130051) is the sister taxon to all other domed pachycephalosaurians. Derived pachycephalosaurids consist of two principal clades: a lineage that includes Stygimoloch, Pachycephalosaurus, and Sphaerotholus and a lineage represented by the Asian taxa, Tylocephale and Prenocephale. With biogeographic occurrences mapped onto the phylogeny, a single dispersal event from Asia into North America, followed by dispersal of Prenocephale and Tylocephale into Asia prior to the late Campanian is indicated (ACCTRAN) or two independent dispersals into North America prior to the late Campanian is indicated (DELTRAN). Pachycephalosaurian phylogeny does not support Asian-North American contiguity throughout the Campanian and Maastrichtian.
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Stegoceras (sensu lato) has been the recipient of a number of species. Most have been placed into synonymy with S. validum, some have been transferred to other genera (i.e., Gravitholus, Ornatotholus), whereas others have been interpreted as being sexual dimorphs. A parsimonious phylogenetic analysis using 49 characters, which include 9 new cranial characters based on pachycephalosaur frontoparietal domes, now permits a revision of the genus Stegoceras. This analysis concludes that Stegoceras validum (sensu stricto) is a primitive, incipiently-domed pachycephalosaur that is characterized by a well-developed squamosal shelf and open supratemporal fossae. It is the sister taxon to the fully-domed Pachycephalosaurinae. The taxon Ornatotholus browni has a parietal and displays features identical to S. validum and is therefore a subjective junior synonym. Specimens consisting of flat, paired frontals are immature individuals of S. validum. The holotype of “Stegoceras” lambei, and all morphotypes of this species, are unique in the construction of the posterior squamosal region and are placed in a new genus, Colepiocephale. Colepiocephale lambei is known solely from the Foremost Formation and is the oldest diagnostic pachycephalosaur from North America. An incomplete, and indeterminate, skull from the upper part of the Milk River Formation (upper Santonian) has the distinction of being the oldest known North American pachycephalosaur. “S.” sternbergi lacks a posterior squamosal shelf and has squamosals directed laterally and is placed in a new genus, Hanssuesia, as H. sternbergi. Although the taxon Gravitholus albertae displays some characters (i.e., retention of the posterior squamosals separated by a distinct median parietal) and is similar to H. sternbergi in some respects, the holotype is too incomplete for any definitive diagnosis and thus it is considered a nomen dubium. Sphaerotholus is a subjective junior of Prenocephale and the species Sphaerotholus buchholtzae is a subjective junior synonym of Prenocephale edmontonensis. The taxa Prenocephale brevis, P. edmontonensis, and P. goodwini, form a monophyletic clade with monotypic Asian taxa Prenocephale prenes and Tylocephale gilmorei as an unresolved sister group. They are united by the possession of a distinct row of nodes on the squamosal and parietals. Tylocephale, if valid, is interpreted as the sister taxon to the Prenocephale clade. Stenotholus kohleri is formally recognized as a junior synonym of Stygimoloch spinifer. Based on the presence of hypertrophied nodes Stygimoloch spinifier and Pachycephalosaurus wyomingensis are united in the clade Pachycephalosaurini new taxon. Small-to-medium size Late Cretaceous pachycephalosaurs were rather diverse, especially during the late Campanian (Judithian), and many species coexisted during Campanian and Maastrictian times. Ancestry and directionality of dispersal (in part) of the North American and Asian taxa remains uncertain and certainly antedates Campanian time.
Article
Pachycephalosaurian specimens from the Upper Cretaceous (upper Campanian) Kirtland Formation of northwestern New Mexico include a partial skull that preserves much of the basicranium. It represents a new genus and species, Sphaerotholus goodwini. A new species, S. buchholtzae, from the upper Maastrichtian Hell Creek Formation of Montana is referred to this genus. Additional New Mexico pachycephalosaurians include a partial dentary with associated skull material that is tentatively referred to S. goodwini and a partial frontoparietal that is referred to Pachycephalosauridae incertae sedis. On the basis of a hypothetical growth series of Stegoceras, we excluded characters based on dome development and suture closure from a cladistic analysis of pachycephalosaurian relationships. Ornatotholus browni, the only putative “flat-headed” pachycephalosaurian from North America, is considered a nomen dubium and may represent a juvenile Stegoceras. Gravitholus albertae is an adult Stegoceras sp.; Stegoceras edmontonense is a nomen dubium and is referred to cf. Sphaerotholus sp. Based on the results of a quantitative cladistic analysis, Stegoceras (including Stegoceras breve, S. lambei, S. stembergi, and UCMP 130051) is the sister taxon to all other domed pachycephalosaurians. Derived pachycephalosaurids consist of two principal clades: a lineage that includes Stygimoloch, Pachycephalosaurus, and Sphaerotholus and a lineage represented by the Asian taxa, Tylocephale and Prenocephale. With biogeographic occurrences mapped onto the phytogeny, a single dispersal event from Asia into North America, followed by dispersal of Prenocephale and Tylocephale into Asia prior to the late Campanian is indicated (ACCTRAN) or two independent dispersals into North America prior to the late Campanian is indicated (DELTRAN). Pachycephalosaurian phylogeny does not support Asian-North American contiguity throughout the Campanian and Maastrichtian.
Article
One of the southernmost North American late Campanian microvertebrate assemblages was collected from the upper Aguja Formation, Big Bend National Park, Texas. The dinosaurs provide additional evidence that distinct southern and northern terrestrial vertebrate provinces occurred contemporaneously during this time due to latitudinal differences in temperature and rainfall. Southern areas, such as west Texas, were warm dry, with non-seasonal climates, and with open-canopy woodlands; they appear to be less fossil-rich and less diverse than northern areas. Nine dinosaurs are present, based on isolated teeth: pachycephalosaurid; hadrosaurid; ceratopsian; tyrannosaurid; Saurornitholestes cf. langstoni (Sues, 1978); Richardoestesia cf. gilmorei (Currie et al., 1990); a new species of Richardoestesia , which is named here; and a undetermined theropod unlike any previously described. Previous reports of Troodon sp. from the Talley Mt. and Terlingua microsites are mistaken; they are a pachycephalosaurid. Many of the dinosaur teeth are small, and are probably from juveniles or younger individuals, evidence that dinosaurs nested in the area. Paleoecologically, the upper Aguja was probably more similar to the lower and more inland faunas of the Scollard Formation (~66 Ma) of Alberta than to contemporaneous northern faunas: both had drier, open environments and lower dinosaur abundance. This connection between climate and dinosaur abundance suggests that climatic factors were important in the Late Cretaceous dinosaur extinctions.
Chapter
Pachycephalosauria is a group of bipedal ornithischians with thickened bones of the skull roof. The group is widely distributed throughout the Northern Hemisphere, mostly in western North America and central Asia, but also in Europe. This chapter examines the anatomy, phylogeny, and paleobiology of pachycephalosaurians. Pachycephalosaurians are often called dome-headed or thick-headed dinosaurs. They were bipedal herbivores with unspecialized teeth and their necks were thick and short. Pachycephalosaurians also have weakly curved dorsal ribs, broad pelvis, widely spaced femora, and unusually long ribs on the proximal caudal vertebrae, which indicate that they had a bulky trunk and a heavy tail.
Chapter
The disappearance of nonavian dinosaurs is only a small part of a greater class of extinctions known as “mass extinctions.” Mass extinctions are global events characterized by unusually high rates of extinction. The five episodes of mass extinctions in Earth history are the Permo-Triassic extinction, the Late Ordovician extinction, the Late Devonian extinction, the Triassic-Jurassic extinction, and the Cretaceous-Tertiary (K/T) extinction. This chapter focuses on patterns of geologic and biotic changes that occurred during the Cretaceous-Tertiary (K/T) extinction. It also highlights the similarities and differences in interpretations of geologic and fossil records. It concludes with two scenarios explaining the differing views about dinosaur extinction.
Book
— We studied sequence variation in 16S rDNA in 204 individuals from 37 populations of the land snail Candidula unifasciata (Poiret 1801) across the core species range in France, Switzerland, and Germany. Phylogeographic, nested clade, and coalescence analyses were used to elucidate the species evolutionary history. The study revealed the presence of two major evolutionary lineages that evolved in separate refuges in southeast France as result of previous fragmentation during the Pleistocene. Applying a recent extension of the nested clade analysis (Templeton 2001), we inferred that range expansions along river valleys in independent corridors to the north led eventually to a secondary contact zone of the major clades around the Geneva Basin. There is evidence supporting the idea that the formation of the secondary contact zone and the colonization of Germany might be postglacial events. The phylogeographic history inferred for C. unifasciata differs from general biogeographic patterns of postglacial colonization previously identified for other taxa, and it might represent a common model for species with restricted dispersal.
Article
A new skull of Stygimoloch spinifer (MPM 8111) from the Upper Cretaceous Hell Creek Formation of North Dakota is the most complete specimen discovered to date. It allows much of the skull and braincase of this unusual pachycephalosaurid to be described for the first time and confirms a suite of diagnostic characters for the species. The skull is long with a vaulted, transversely narrow frontoparietal dome and a robust squamosal forming a prominent posterior shelf. The shelf is ornamented by three to four large, low-angle horns and multiple clusters of smaller bony nodes. The orientation of the squamosal is preserved along an unambiguous contact with the frontoparietal suture, allowing definitive determination of the orientation of the squamosal horns. These cranial features indicate a different mode of agonistic behavior than previously suggested for Stegoceras and Pachycephalosaurus. The high, narrow dome of S. spinifer is not suited for head-butting, and the orientation of its squamosal horns and ornamental nodes strongly suggest display functions. Several additional specimens are described and referred to S. spinifer.
Article
Chasmosaurus mariscalensis is a new species of ceratopsian dinosaur (Ornithischia; Ceratopsia) from the upper part of the Aguja Formation (late Campanian, Judithian) in Big Bend National Park, Brewster County, Texas. This species is distinguished from other species of Chasmosaurus by its relatively short and broad squamosal bearing six very large epoccipitals, maxilla without pronounced lateral shelf, premaxilla without posterodorsal extension, and very long supraorbital horncores in adults. A bone bed accumulation comprising disarticulated remains of 10–15 juvenile, subadult, and fully adult individuals forms the hypodigm of C. mariscalensis, and allows the first full description of the postcranial skeleton for the genus. Males and females are separated on the basis of brow horncore orientation. This is the most advanced species of Chasmosaurus and is morphologically intermediate with Pentaceratops in several characters.
Article
The concept of a sudden extinction of the dinosaurs, consequent upon the impact of some extraterrestrial object, is so dramatic that it has taken hold upon the imaginations of many scientists, as well as of the general public. The evidence for an impact, at approximately the level of the Cretaceous-Tertiary boundary, is impressive. Whether it was the cause for the iridium concentrations, so widely distributed at that level, remains disputable. The wave of extinctions, so often attributed to the impact, is equally disputable. It is now evident that no clear line can be drawn between the smaller theropod dinosaurs and the birds. In that sense, the dinosaurs are not extinct. The dating of the extinction of the larger saurischians and of the ornithischians, based as it is upon evidence from only one small corner of the globe, is equally disputable. Whenever it happened, that extinction appears to have been the product of natural causes - a slow decline, occasioned by environmental changes, and not an extraterrestrially induced catastrophe. Whether the impact had any effect at all upon the dinosaurs is questionable; if so, it appears to have been not worldwide, but confined to a limited region of the Americas.
Article
Three classifications of the Dinosauria have been proposed, which differ from each other in the principles on which their authors proposed to make the divisions. First in time is Professor Cope’s classification (‘Philadelphia, Acad. Nat. Sci. Proc.,’ November 13th, 1866, and December 31st, 1867; ‘Amer. Phil. Soc. Trans.,’ vol. 14, Part I). He relied upon the characters of the tarsus and the ilium; and on their varied condition divided Dinosaurs into three orders named Orthopoda, Goniopoda, and Symphopoda. In the Orthopoda , the generic types associated are Scelidosaurus, Hylæosaurus, Iguanodon, and Hadrosaurus. And in this group the relations of the tibia and fibula are compared to those of modern Lizards, the proximal tarsals being distinct from each other and from the tibia. The ilium has a narrowed anterior prolongation.
Article
Sediments of the Upper Cretaceous (Campanian) Oldman Formation at Dinosaur Provincial Park, Alberta, have yielded an exceedingly rich fauna of dinosaurs. These fluviatile sediments show characteristics of both meandering and braided channels. Fossil molluscs, plants, and diverse salamanders indicate that Oldman sediments were deposited in fresh water, and the very sparse agglutinated Foraminifera recovered fail to controvert this conclusion. Annual growth rings in wood and vertebrate of Champsosaurus demonstrate that the climate was seasonal, and current botanic interpretations suggest that the climate was an equable, warm temperate one. Dinosaurian remains represent all stages of disarticulation from complete skeletons to isolated bones. They are common in channel sediments and rare in overbank deposits, suggesting that the animals preserved died in the water of channels. The persistence of the characteristics sedimentary association of fossils over a 200 ft. stratigraphic interval demonstrates that regular, not catastrophic events determined the preservation of individuals. Stages of progressive decomposition of dinosaurs are inferred from the condition of fossils collected from the Park. Disarticulated small bones occur at interfaces between mudstone and sandstone in which the sandstone lies above the mudstone, and also in intraformational conglomerates. Ceratopsians are identified as dwellers of the swampy lowlands along with hadrosaurs. Hadrosaurs, ceratopsians, and possibly even carnosaurs spent significant portions of their daily lives in water. These dinosaurs did not breed in “uplands”, but possibly in dry areas lateral to the streams.
Article
Fluctuating asymmetry is an epigenetic measure of the ability of individuals to undergo identical development of a usually bilaterally symmetrical character on both sides of the body. Horns of beetles and spurs of birds are elaborate structures usually restricted to or enlarged in individuals of the limited sex and frequently used in intrasexual combat. Individuals with large horns usually win fights against individuals with small horns which suggests that horn size may reliably signal male fighting ability. A comparative study of the patterns of fluctuating asymmetry in horns of beetles and spurs of birds showed that the degree of asymmetry in these secondary sex traits was considerably larger than in elytra and wing length, which are apparently not subjected to sexual selection. There was a negative relationship between the degree of asymmetry and size of the secondary sex trait while the relationship for elytra and wing length was flat or U-shaped. This demonstrates that horn and spur size may reliably reflect male quality as determined by the degree of fluctuating asymmetry.
Article
Extravagant secondary sexual characters, i.e. sexual ornaments, are exaggerated, often bilaterally symmetrical traits of great intricacy of design. The full expression of such traits is likely to be very costly and close to the limits of production. Any kind of environmental stress is therefore more likely to affect the expression of ornaments than that of any other morphological trait not subjected to strong directional selection. One measure of the ability of individuals to produce extravagant sexual traits is their degree of fluctuating asymmetry. This occurs when symmetry is the normal state and there is no tendency for the trait on one side of the body to have larger character values than that on the other. The degree of fluctuating asymmetry has been shown to reflect the ability of individuals to cope with a wide array of environmental stress (review in Parsons (1990)). We predicted that sexual ornaments should show a larger degree of fluctuating asymmetry than other morphological traits or than homologous traits in non-ornamented species. If ornaments honestly indicate the quality of individuals, high quality individuals should develop little asymmetry and large traits. Thus, we predicted a general negative relation between the degree of asymmetry and the size of ornaments. This should not be the case for other traits or for homologous traits in conspecific females or in either sex of monomorphic species. We tested these predictions on elaborate feather ornaments in birds, as these have been shown to be used as cues during female choice. We made pairwise comparisons between males and females of ornamented species and between males of ornamented and of non-ornamented, confamilial species. Sexual ornaments showed both a larger absolute and relative degree of fluctuating asymmetry than did wing length or did traits homologous to the feather ornament in females and in males of non-ornamented species. The degree of fluctuating asymmetry for tail ornaments generally showed a negative relation with the size of the ornament, whereas that was not the case for wing length or for traits homologous to the feather ornament in females and in males of non-ornamented species. The large degree of fluctuating asymmetry in ornaments and the negative relation between ornament size and degree of asymmetry suggest that fluctuating asymmetry in ornaments reliably reflects male phenotypic quality.
Article
The new genus and species Stenotholus kohleri from the Late Cretaceous Hell Creek Formation of McCone County, Montana is a pachycephalosaurid omithischian. The species possesses a vertically high and transversely narrow dome, elimination of the parietosquamosal shelf, closure of the supratemporal fenestra in the subadult, a highly sculptured frontal, and a sagittally shortened occipital region. The possibility that this skull represents a previously described pachycephalosaurid is rejected on the basis of the unique suite of traits presented.
Article
The concept of a sudden extinction of the dinosaurs, consequent upon the impact of some extraterrestrial object, is so dramatic that it has taken hold upon the imaginations of many scientists, as well as of the general public. The evidence for an impact, at approximately the level of the Cretaceous–Tertiary boundary, is impressive. Whether it was the cause for the iridium concentrations, so widely distributed at that level, remains disputable. The wave of extinctions, so often attributed to the impact, is equally disputable. It is now evident that no clear line can be drawn between the smaller theropod dinosaurs and the birds. In that sense, the dinosaurs are not extinct. The dating of the extinction of the larger saurischians and of the ornithischians, based as it is upon evidence from only one small corner of the globe, is equally disputable. Whenever it happened, that extinction appears to have been the product of natural causes — a slow decline, occasioned by environmental changes, and not an extraterrestrially induced catastrophe. Whether the impact had any effect at all upon the dinosaurs is questionable; if so, it appears to have been not worldwide, but confined to a limited region of the Americas.