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Anatomy and relationships of a new hypsilophodontid dinosaur from the Lower Cretaceous of North America
... Orodromines, as defined by Brown et al. (2013), share characteristics that include a sacropubal articulation, a sharp scapular spine, and a D-shaped cross-section of the fibula. Excluding Oryctodromeus, other orodromine taxa include Zephyrosaurus schaffi from the Aptian-Albian Cloverly Formation of Montana (Sues, 1980), Orodromeus makelai from the Campanian Two Medicine Formation of Montana (Horner & Weishampel, 1988;Scheetz, 1999), Albertadromeus syntarsus from the Campanian Belly River Group of Alberta (Brown et al., 2013), Koreanosaurus boseongensis from the Santonian to Campanian Seonso Conglomerate of South Korea (Huh et al., 2010), and an unnamed 'Kaiparowits orodromine' from the Campanian Kaiparowits Formation of southern Utah (Boyd, 2015;Gates et al., 2013). ...
... Comparisons with Orodromeus, Zephyrosaurus, and the unnamed Kaiparowits Formation orodromine were based on direct specimen comparisons and published osteological descriptions (Scheetz, 1999;Sues, 1980;Varricchio et al. 2007). Comparisons to other genera were conducted through the literature. ...
... A complete skull for Oryctodromeus is unknown. As best as can be determined from available elements, the overall shape of the skull ( Fig. 2A) is similar to other orodromines, such as Orodromeus (Scheetz, 1999) and Zephyrosaurus (Sues, 1980). The skull is triangular in lateral view and the orbit is proportionately large. ...
The vertebrate assemblages of the Albian to Cenomanian Wayan Formation of southeastern Idaho and southwestern Montana’s coeval Vaughn Member of the Blackleaf Formation are dominated by the small, burrowing orodromine dinosaur Oryctodromeus cubicularis. Here, we describe in detail the osteology of Oryctodromeus based on new specimens from Idaho and Montana that add substantially to the preliminary description of the types from Montana, and provide a suite of additional diagnostic characters for the taxon: ilium with elongate preacetabular process; elongate cervical vertebra centra with an anteroposterior length 1.6 times the dorsoventral height; elongate dorsal vertebra centra with an anteroposterior length 1.4 times the dorsoventral height; more than 55 elongate caudal vertebrae enveloped in hypaxial and epaxial ossified tendons; and a femoral head on an elongate neck—similar to that of Koreanosaurus—projecting from the greater trochanter at about 35°. The tail, comprising two-thirds of the animal’s roughly 3 meters length, and associated tendon sheaths in the axial column indicate greater flexibility than previously supposed for ossified tendons or, alternatively, suggest that the Oryctodromeus burrows had separate, or multiple entrances and exits. The elongated and angled femoral head likely facilitated digging via a braced splayed-leg posture. Our phylogenetic analysis incorporates new characteristics and supports the monophyly of Orodrominae, a clade of neornithischian dinosaurs from the middle to Late Cretaceous of Asia and western North America that utilized burrowing.
... After reaching its widest point at the level of the cerebral hemispheres (6.42 mm wide), the crista cranii flexes medially, possibly delimiting the posterior portion of the cerebellum (Hopson, 1979). The orbital rim formed by the frontals is pierced by small foramina, but its surface is not as rugose as in Heterodontosaurus (Norman et al., 2011) and ornithopods, such as Zephyrosaurus (Sues, 1980). The ventral surfaces of the frontals roofing the intracranial space form well-marked osteological correlates of the forebrain, with raised margins, although these are less marked than previously thought (Pol et al., 2011). ...
... observ.), Hypsilophodon (Galton, 1974), possibly Zephyrosaurus (Sues, 1980), some hadrosaurid species (e.g., Horner et al., 2004), and Yinlong (Han et al., 2015). Contrastingly, the frontal-parietal contact forms a straight, finely interdigitating suture in Lesothosaurus (Porro et al., 2015). ...
... The maxilla-jugal articulation continues along the lateromedially thin ventral margin of this process, a beveled articular region with its dorsal boundary marked by a step-like unevenness at both sides of the process. The ventral margin of this jugal process fits into a narrow and long sulcus in the posterodorsal region of the maxilla, covering most of the lateral side of this process, as in Zephyrosaurus (Sues, 1980). In medial view, the medial depression of the jugal and the posterior widening of the narrow sulcus of the maxilla form a depressed articulation face with raised margins for the ectopterygoid, a depression limited posteriorly and laterally by , and posterodorsal (R) views. ...
Heterodontosauridae is a clade that appears early in the ornithischian fossil record, and includes small-bodied, highly specialized species characterized by an unusual heterodont dentition. Although known from relatively few taxa, the early representation of the clade and unsolved phylogenetic relationships within heterodontosaurids and among early ornithischians implies that novel information has a marked effect on broader phylogenetic hypotheses and our understanding of early diversification patterns within Ornithischia. This paper describes the cranial osteology of the heterodontosaurid Manidens condorensis based on computed micro-tomographic scans of MPEF-PV 3211 and MPEF-PV 3809. This enabled more detailed descriptions of previously recognized bones, corrections to the literature, and the identification of undescribed elements. We present a new skull reconstruction and propose an emended diagnosis in light of novel anatomical information. Areas of jaw muscle attachment were identified and compared with Heterodontosaurus and Lesothosaurus, and mandibular function among heterodontosaurids is discussed. Our results indicate that diverse skull morphologies and functions existed among Early Jurassic ornithischians, with Manidens being intermediate between the plesiomorphic cranial shape and function associated with a generalist diet in ornithischians such as Tianyulong and Lesothosaurus, and the more derived cranial construction specialized for herbivory identified in heterodontosaurids from South Africa such as Heterodontosaurus.
... The resulting feature forms a "ledge" on the distolingual surface. This feature, which some authors have described as a lingually curved distal carina, is observed in Orodromeus makelai (Scheetz, 1999), Zephyrosaurus (Sues, 1980;Galton, 1999), and the Upper Jurassic ornithischian Nanosaurus agilis (Scheetz, 1999 In Thescelosaurus neglectus (NCSM 15728), worn maxillary crowns appear asymmetrical in buccal view, and lack the broad appearance typical of the maxillary teeth of basal ornithischians (Norman et al., 2004b). The average CH of worn maxillary teeth is only 2.9 mm, considerably less than in unworn maxillary teeth, whereas the average CBL of unworn maxillary teeth is similar to that of worn teeth at 4.9 mm. ...
... The denticles are longer in T. neglectus than they are in S. validum. Large ridgeassociated denticles are also present in other thescelosaurids, and are an important feature for identifying isolated teeth from microsites (Parks, 1926;Sues, 1980 Statistically significant differences between the two species were identified using twosample Mann-Whitney U tests, and the PC plot captured clear separation between the dentition of the two species ( Fig. 7 and 9). Based on raw data, both worn and unworn crowns of Other thescelosaurid maxillary teeth have not been extensively investigated to determine to what degree they resemble their counterparts in T. neglectus, but prominent ridge-associated denticles do seem to be present in at least some other thescelosaurids (Parks, 1926;Sues, 1980;Scheetz, 1999; Barrett ...
... Large ridgeassociated denticles are also present in other thescelosaurids, and are an important feature for identifying isolated teeth from microsites (Parks, 1926;Sues, 1980 Statistically significant differences between the two species were identified using twosample Mann-Whitney U tests, and the PC plot captured clear separation between the dentition of the two species ( Fig. 7 and 9). Based on raw data, both worn and unworn crowns of Other thescelosaurid maxillary teeth have not been extensively investigated to determine to what degree they resemble their counterparts in T. neglectus, but prominent ridge-associated denticles do seem to be present in at least some other thescelosaurids (Parks, 1926;Sues, 1980;Scheetz, 1999; Barrett ...
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.
... The anteriormost points of the nasals opposite the external nares from the ascending 5) is best considered a taphonomic artifact because confluent external nares (i.e., with loss of a complete internarial bar) are unknown among dinosaurs except for some diplodocoid and titanosaur sauropods (Upchurch, 1995;Wilson et al., 2016). In Haya, the surface of the premaxilla is smooth, in contrast to the rugose anterior premaxillary surfaces of Lesothosaurus, Jeholosaurus, Changchunsaurus, Oryctodromeus, Zephyrosaurus, Thescelosaurus, and Hypsilophodon (Galton, 1974a;Sues, 1980;Sereno, 1991;Varricchio et al., 2007; Barrett and Han, 2009;Jin et al., 2010;Boyd, 2014). Such rugose surfaces have been interpreted as evidence of a ramphotheca (Galton, 1974a), but the extent and attachment of a ramphotheca in Haya, if present, is unclear. ...
... The surface of the jugal in all examined Haya specimens is smooth, with no trace of the jugal rugosities seen in some Jeholosaurus and Changchunsaurus specimens (Barrett and Han, 2009;Jin et al., 2010). It further lacks the jugal bosses present in Heterodontosaurus, Manidens, Zephyrosaurus, and Orodromeus (Sues, 1980;Scheetz, 1999;Norman et al., 2011;Pol et al., 2011). ...
... 9). Orodromeus and Zephyrosaurus possess similar protuberances (Sues, 1980;Scheetz, 1999). As revealed by the intact posterior supraorbitals of IGM 100/2019 and IGM 100/3178 (figs. ...
Haya griva is an early-diverging neornithischian (“hypsilophodontid”) dinosaur known from several well-preserved skulls and articulated postcranial skeletons, in addition to dozens of partial or isolated finds from the Upper Cretaceous Khugenetslavkant and Zos Canyon localities (Javkhlant Formation and equivalent beds) in the Gobi Desert of Mongolia. Collectively, nearly the entire skeletal anatomy of Haya is known, including partial growth series of skulls and femora. Detailed description and comparisons with other ornithischians, including novel anatomical information about the palate and braincase gleaned through high-resolution x-ray microcomputed tomography, reveals a wealth of osteological data for understanding the growth and relationships of this key taxon. Though the Haya specimens span a wide size range, bone histology reveals that all are likely perinatal to subadult individuals, with specimens of intermediate age the most common, and skel- etally mature specimens absent. Phylogenetic analyses place Haya as one of the few Asian members of Thescelosauridae, an important noncerapodan neornithischian group of the Late Cretaceous.
... Extensive fusion of the premaxillae has been reported in Changchunsaurus (Jin et al., 2010), Oryctodromeus and Zephyrosaurus, and interpreted as an adaptation to burrowing behavior (Varricchio, Martin & Katsura, 2007). The rostral surface of the paired premaxillae is rugose (Fig. 5A), as also observed in Hypsilophodon (Galton, 1974), Zephyrosaurus (Sues, 1980), Jeholosaurus (Barrett & Han, 2009) and Changchunsaurus (Jin et al., 2010), and likely served for the attachment of a rhamphotheca. The rugosities slightly overhang the rostroventral corner of the external naris. ...
... Parietal -The parietal is wide and robust, and its dorsal surface is regularly convex without any trace of a sagittal crest (Figs. 3 and 4), unlike in Jeholosaurus (Barrett & Han, 2009), Haya (Makovicky et al., 2011), Hypsilophodon (Galton, 1974) and Zephyrosaurus (Sues, 1980). Rostrally, the parietals form a rounded process that wedges between the caudal margins of the frontals; in Jeholosaurus, on the contrary, the parietals are notched at the midline to receive a short triangular process from the caudal margin of the frontals (Barrett & Han, 2009). ...
... Archaeoceratops: IVPP V11114) and Yinlong (Xu et al., 2006). In Haya (Makovicky et al., 2011), Zephyrosaurus (Sues, 1980) and Orodromeus (Scheetz, 1999), a rugose crest, which could have served as an area of attachment for the postpalpebral, projects from the orbital rim near the juncture of the ventral and medial rami, (Makovicky et al., 2011). ...
A new basal ornithopod dinosaur, based on two nearly complete articulated skeletons, is reported from the Lujiatun Beds (Yixian Fm, Lower Cretaceous) of western Liaoning Province (China). Some of the diagnostic features of Changmiania liaoningensis nov. gen., nov. sp. are tentatively interpreted as adaptations to a fossorial behavior, including: fused premaxillae; nasal laterally expanded, overhanging the maxilla; shortened neck formed by only six cervical vertebrae; neural spines of the sacral vertebrae completely fused together, forming a craniocaudally-elongated continuous bar; fused scapulocoracoid with prominent scapular spine; and paired ilia symmetrically inclined dorsomedially, partially covering the sacrum in dorsal view. A phylogenetic analysis places Changmiania liaoningensis as the most basal ornithopod dinosaur described so far. It is tentatively hypothesized that both Changmiania liaoningensis specimens were suddenly entrapped in a collapsed underground burrow while they were resting, which would explain their perfect lifelike postures and the complete absence of weathering and scavenging traces. However, further behavioural inference remains problematic, because those specimens lack extensive sedimentological and taphonomic data, as it is also the case for most specimens collected in the Lujiatun Beds so far.
... 5A and 6), as also occurs in Hypsilophodon (e.g. NHM R2477: Galton 1974) and Zephyrosaurus (Sues 1980). This area probably served for the attachment of a rhamphotheca. ...
... In most respects, the premaxilla of Jeholosaurus is similar to that of non-iguanodontian ornithopods and non-cerapodan neornithischians, including Agilisaurus (ZDM T6011: Peng 1992; Barrett et al. 2005), Bugenasaura (Galton 1999), Hypsilophodon (NHM R197: Galton 1974), Orodromeus (Scheetz 1999) and Zephyrosaurus (Sues 1980). It differs substantially from the premaxillae of non-ceratopsid ceratopsians, which possess relatively smaller external narial openings and an articular surface for the rostral bone (You & Dodson 2004). ...
... Six premaxillary teeth are also known in the early ornithischian Lesothosaurus (NHM RUB17: Sereno 1991) and the ankylosaurs Silvisaurus and Cedarpelta (Eaton 1960;Carpenter et al. 2001). However, all cerapodans have fewer teeth: five are present in Bugenasaura (Galton 1999), Changchunsaurus (Zan et al. 2005), Hypsilophodon (NHM R2477: Galton 1974), Orodromeus (Scheetz 1999) and Zephyrosaurus (Sues 1980) -the same number is also present in Agilisaurus (ZDM T6011: Peng 1992; Barrett et al. 2005); Archaeoceratops (IVPP V11114: Dong & Azuma 1997), Liaoceratops (IVPP V12738: Xu et al. 2002) and Yinlong ) each possess three teeth; two teeth are present in Chaoyangsaurus (IGCAGS V371: Zhao et al. 1999); and premaxillary teeth are absent in Psittacosaurus (e.g. You & Dodson 2004). ...
A detailed description of the skull and mandible of the Chinese cerapodan ornithischian dinosaur Jeholosaurus shangyuanensis (Lower Cretaceous, Yixian Formation) is presented for the first time and this information is used to reassess its phylogenetic position. Jeholosaurus can be distinguished from all other cerapodans on the basis of one autapomorphy (a row of small foramina on the nasal) and a character combination that is unique among ornithischians. Previously undescribed specimens add considerably to our knowledge of Jeholosaurus, providing new insights into its anatomy and ontogeny. Revised character scores increase the resolution of phylogenetic hypotheses and provide additional support for placement of Jeholosaurus within Ornithopoda.
... The process is more prominent on the larger specimen SMU 70635. This process is also present in Haya griva [15], Orodromeus makelai [16], and Zephyrosaurus schaffi [17]; however, it is more pronounced in these taxa than in Convolosaurus marri. Dorsal to the antorbital fossa the maxilla ascends as a thin sheet, curving posteriorly to contact the lacrimal, forming the anterior margin of the antorbital fenestra. ...
... The frontals are anteroposteriorly longer than they are wide and form the majority of the dorsal margin of the orbits as seen in basal ornithopods Hypsilophodon foxii [18] and Parksosaurus warreni [20]. The frontals are arched over the orbit and the orbital margins are rugose as is noted in Haya griva [15] and Zephyrosaurus schaffi [17]. The anterolateral surfaces of SMU 72834 (Fig 9), SMU 70456, and SMU 74087 contain a deep notch where the frontal articulates with the prefrontal. ...
... The orbital margin is smooth unlike the orbital margin formed by the frontals. The anterodorsal corner of the postorbital articulates to the frontal and parietal forming a triple junction consisting of pronounced interlocking projections as in Hypsilophodon foxii [18], Zephyrosaurus schaffi [17], and Orodromeus makelai [16]. The postorbital splits into two distinct processes directed ventrally and posteriorly that occur in the same plane. ...
Material from a minimum of twenty-nine individuals of a new ornithopod, represented by nearly every skeletal element, was recovered from the Proctor Lake locality in the Twin Mountains Formation (Aptian) of north-central Texas. This material includes various ontogenetic stages, providing insight into the growth patterns of this species. The new ornithopod, Convolosaurus marri gen. et sp. nov., is recovered outside of Iguanodontia, but forms a clade with Iguanodontia exclusive of Hypsilophodon foxii. The presence and morphology of four premaxillary teeth along with a combination of both basal and derived characters distinguish this taxon from all other ornithopods. Basal characters present in C. marri including the presence of premaxillary teeth, the shape of the dentary teeth, and position of the pterygoid wing on the quadrate, whereas the presence of opisthocoelous cervical vertebrae, large proximal caudal neural spines, and curved maxillary tooth roots suggest C. marri is more derived than 80% of the basal neornithischians included in this analysis.
... In ventral view, the olfactory tract is narrower than that of Orodromeus (MOR 623) and, although hourglass-shaped, exhibits a less distinct lateral swelling for the olfactory bulbs than does the frontal of O. makelai (Fig. 9). Dorsally, the location and extent of emargination of the postorbital suture is similar to that of Orodromeus ( Sues, 1980). The frontal is convexly bowed dorsally in lateral view. ...
... Dentary Teeth-Within the dentary of TMP 1997.128.0002, the sixth and eighth alveoli preserve partially erupted teeth that reveal the apical crown and the crown base, respectively ( Fig. 11A-C, composite tooth in 9D). The teeth have a smooth lingual surface lacking the secondary ridges that are exhibited by Thescelosaurus (CMN 8537), Parksosaurus (ROM 804), and Zephyrosaurus (MCZ 4392; Sues, 1980), and exhibits the central vertical thickening typical of Orodromeus (MCZ 3729 and AMNH 8537; Galton, 1995). They are triangular in lingual view and laterally compressed, with a rounded apical ridge, and multiple rounded denticles on the anterior and posterior carinae (Fig. 11D). ...
... The number of denticles is unknown, but would likely have been between six and eight on both carinae (based on the size of the denticles). This is similar to that reported for Orodromeus (Horner and Weishampel, 1988), but fewer than for Zephyrosaurus (MCZ 4392;Sues, 1980) or Thescelosaurus (SDSM 7210 and CMN 8537; Galton, 1999). ...
... 5A and 6), as also occurs in Hypsilophodon (e.g. NHM R2477: Galton 1974) and Zephyrosaurus (Sues 1980). This area probably served for the attachment of a rhamphotheca. ...
... In most respects, the premaxilla of Jeholosaurus is similar to that of non-iguanodontian ornithopods and non-cerapodan neornithischians, including Agilisaurus (ZDM T6011: Peng 1992; Barrett et al. 2005), Bugenasaura (Galton 1999), Hypsilophodon (NHM R197: Galton 1974), Orodromeus (Scheetz 1999) and Zephyrosaurus (Sues 1980). It differs substantially from the premaxillae of non-ceratopsid ceratopsians, which possess relatively smaller external narial openings and an articular surface for the rostral bone (You & Dodson 2004). ...
... Six premaxillary teeth are also known in the early ornithischian Lesothosaurus (NHM RUB17: Sereno 1991) and the ankylosaurs Silvisaurus and Cedarpelta (Eaton 1960;Carpenter et al. 2001). However, all cerapodans have fewer teeth: five are present in Bugenasaura (Galton 1999), Changchunsaurus (Zan et al. 2005), Hypsilophodon (NHM R2477: Galton 1974), Orodromeus (Scheetz 1999) and Zephyrosaurus (Sues 1980) -the same number is also present in Agilisaurus (ZDM T6011: Peng 1992; Barrett et al. 2005); Archaeoceratops (IVPP V11114: Dong & Azuma 1997), Liaoceratops (IVPP V12738: Xu et al. 2002) and Yinlong ) each possess three teeth; two teeth are present in Chaoyangsaurus (IGCAGS V371: Zhao et al. 1999); and premaxillary teeth are absent in Psittacosaurus (e.g. You & Dodson 2004). ...
A detailed description of the skull and mandible of the Chinese cerapodan ornithischian dinosaur Jeholosaurus shangyuanensis (Lower Cretaceous, Yixian Formation) is presented for the first time and this information is used to reassess its phylogenetic position. Jeholosaurus can be distinguished from all other cerapodans on the basis of one autapomorphy (a row of small foramina on the nasal) and a character combination that is unique among ornithischians. Previously undescribed specimens add considerably to our knowledge of Jeholosaurus, providing new insights into its anatomy and ontogeny. Revised character scores increase the resolution of phylogenetic hypotheses and provide additional support for placement of Jeholosaurus within Ornithopoda.
... 5, referred teeth); for Othnielia from Upper Jurassic of western USA, GALTON (1983GALTON ( , 1989; for Parksosaurus from Upper Cretaceous of Alberta, Canada, GALTON (1973b, in prep. b); for Yandusaurus from Middle Jurassic of China, HE & CAl (1984); and for Zephyrosaurus (Figs. 3I-L) from Lower Cretaceous of western USA, SUES (1980) and GALTON (1989, in prep. a). ...
... Immediately above this is a small step against which the posterior end of the lacrimal fitted. Medially (Fig. 5G), on the constricted region, there is a prominent subhorizontal and tapering sheet of bone with a maximum transverse width of 6 mrn, the maxillary process of SUES (1980), which is proportionally shorter and represented only by the broken base in Zephyrosaurus. The maxilla fitted against the rugose sutural areas anterior to this sheet and ventrally on the anterior half; the ectopterygoid Ectopterygoid (Figs. 5H,51). ...
... Therefore, the character "premaxillary diverticulum" is a synapomorphy of the Hypsilophodontidae (including Thescelosaurus) (node 1, Fig. 8D) rather than to the Hypsilophodontidae (excluding Thescelosaurus) (node 2, Fig. 8D) as used by SERENO (1986) and BENTON (1990 (WEISHAMPEL, 1984: 23; visible in cast MCZ 4198 of SAM KI332), so this presumably represents the plesiomorphic condition for the Ornithischia. The derived condition with the peg-and-socket type joint has been described only for Hypsilophodon (Fig. IOE, GALTON, 1974b) and Zephyrosaurus (SUES, 1980). There is no information concerning this joint in other hypsilophodontids. ...
The cranial anatomy is described for the basal hypsilophodontid dinosaur Thescelosaurus neglectus GILMORE (1913), the only valid species. Two characters that have been used to separate the other hypsilophodontids from Thescelosaurus, the midorbital width of the frontals and the steepness of the braincase, probably had a more complicated evolutionary history within the Ornithischia than previously thought. Autapomorphic characters of Thescelosaurus include: frontals wide at midorbital level, supraoccipital almost excluded from dorsal margin of foramen magnum, surangular with prominent lateral process; low angle to ventral margin of braincase, buccal surface of maxillary teeth (lingual on dentary teeth) have two converging crescentic patterns formed by numerous secondary ridges; femur longer than tibia.
... scans throughout their length. The presence of at least partial fusion of the premaxillae is reported in Changchunsaurus, Oryctodromeus, and Zephyrosaurus (Sues, 1980;Varricchio, Martin & Katsura, 2007;Jin et al., 2010). The anterior end of the premaxilla is broadly rounded in lateral view (Fig. 5A). ...
... The anterodorsal shelf ends just anterior to the contact with the nasals, and the posterolateral corners of the shelf formed prominent projections (damaged on left side), giving the anterodorsal shelf a 'V-shaped' outline in dorsal view (Fig. 5B). The dorsal surface of the shelf and the anterior tip of the premaxillae are rugose and covered with foramina ( Fig. 5B), as seen in the basal ornithischian Lesothosaurus (Sereno, 1991) and the neornithischians Changchunsaurus, Hypsilophodon, Jeholosaurus, Oryctodromeus, and Zephyrosaurus (Galton, 1974a;Sues, 1980;Varricchio, Martin & Katsura, 2007;Barrett & Han, 2009;Jin et al., 2010). This rugose region likely supported a rhamphotheca (Sereno, 1991). ...
... In the lateral surface of the premaxilla, ventral to the rugose anterodorsal shelf, a premaxillary foramen (sensu Sereno, 1991) and a rostral premaxillary foramen (sensu Sereno, 1991) are present, with the former situated directly posterior to the latter ( Fig. 5A: pmf and apmf, respectively). Premaxillary foramina also are present in the basal ornithischian Lesothosaurus (Sereno, 1991), the neornithischians Changchunsaurus, Haya, Hypsilophodon, Jeholosaurus, Oryctodromeus, and Zephyrosaurus (Galton, 1974a;Sues, 1980;Varricchio, Martin & Katsura, 2007;Barrett & Han, 2009;Jin et al., 2010;Makovicky et al., 2011), and the basal iguanodontian Zalmoxes (Weishampel et al., 2003). The surface of the premaxilla ventral to the anterodorsal shelf and anterior to the nares is dorsoventrally concave, though a distinct subnarial fossa is not present. ...
Though the dinosaur Thescelosaurus neglectus was first described in 1913 and is known from the relatively fossiliferous Lance and Hell Creek formations in the Western Interior Basin of North America, the cranial anatomy of this species remains poorly understood. The only cranial material confidently referred to this species are three fragmentary bones preserved with the paratype, hindering attempts to understand the systematic relationships of this taxon within Neornithischia. Here the cranial anatomy of T. neglectus is fully described for the first time based on two specimens that include well-preserved cranial material (NCSM 15728 and TLAM.BA.2014.027.0001). Visual inspection of exposed cranial elements of these specimens is supplemented by detailed CT data from NCSM 15728 that enabled the examination of otherwise unexposed surfaces, facilitating a complete description of the cranial anatomy of this species. The skull of T. neglectus displays a unique combination of plesiomorphic and apomorphic traits. The premaxillary and ‘cheek’ tooth morphologies are relatively derived, though less so than the condition seen in basal iguanodontians, suggesting that the high tooth count present in the premaxillae, maxillae, and dentaries may be related to the extreme elongation of the skull of this species rather than a retention of the plesiomorphic condition. The morphology of the braincase most closely resembles the iguanodontians Dryosaurus and Dysalotosaurus, especially with regard to the morphology of the prootic. One autapomorphic feature is recognized for the first time, along with several additional cranial features that differentiate this species from the closely related and contemporaneous Thescelosaurus assiniboiensis. Published phylogenetic hypotheses of neornithischian dinosaur relationships often differ in the placement of the North American taxon Parksosaurus, with some recovering a close relationship with Thescelosaurus and others with the South American taxon Gasparinisaura, but never both at the same time. The new morphological observations presented herein, combined with re-examination of the holotype of Parksosaurus, suggest that Parksosaurus shares a closer relationship with Thescelosaurus than with Gasparinisaura, and that many of the features previously cited to support a relationship with the latter taxon are either also present in Thescelosaurus, are artifacts of preservation, or are the result of incomplete preparation and inaccurate interpretation of specimens. Additionally, the overall morphology of the skull and lower jaws of both Thescelosaurus and Parksosaurus also closely resemble the Asian taxa Changchunsaurus and Haya, though the interrelationships of these taxa have yet to be tested in a phylogenetic analysis that includes these new morphological data for T. neglectus.
... It is relatively short and broad, with a maximum length to width ratio of approximately 2.1. This is similar to the condition in Hexinlusaurus (2.2: ZDM T6001; He and Cai, 1984), Lesothosaurus (2.2: NHM R8501, NHM RU B23; Sereno, 1991), Liaoceratops (2.2: Xu et al., 2002), Orodromeus (2.2: Scheetz, 1999), Psittacosaurus (1.8: Sereno et al., 1988), and Thescelosaurus (1.9: Galton, 1997), but differs from the more elongate frontals seen in Agilisaurus Sues, 1980). The caudal margin is straight and represents the widest part of the element. ...
... Palpebral-The left palpebral is exposed in both dorsal and ventral views (Fig. 4A, B, G, H). It is an almost flat triangular bone that is very similar to the corresponding element in Zephyrosaurus (Sues, 1980) and Psittacosaurus (e.g., , but differs from the more cylindrical palpebrals seen in other basal ornithischians and basal ornithopods, including Bugenasaura (SDSM 7210: Galton, 1999), Hexinlusaurus (ZDM T6001; He and Cai, 1984), Hypsilophodon (e.g., NHM R194, NHM R197; Galton, 1974), Jeholosaurus (IVPP V15716), Orodromeus (Scheetz, 1999), and Thescelosaurus (Galton, 1997). The dorsal surface of the palpebral is weakly convex in Albalophosaurus and bears a rugose, sculptured texture. ...
... The dorsal surface of the palpebral is weakly convex in Albalophosaurus and bears a rugose, sculptured texture. These features are also present in Zephyrosaurus (Sues, 1980). In ventral view, a strong ridge close to the rostral border of the element defines a distinct articular facet for attachment of the palpebral to the prefrontal: the remainder of the ventral surface is gently concave. ...
A new ornithischian dinosaur, Albalophosaurus yamaguchiorum gen. et sp. nov., is described on the basis of a partial skull and lower jaw recovered from the Lower Cretaceous Kuwajima Formation (Tetori Group) of central Japan. The specimen exhibits a unique suite of characters in the dentition, maxilla, and dentary. A phylogenetic analysis recovers Albalophosaurus as a basal member of Ceratopsia: however, this placement is weakly supported and no unambiguous ceratopsian synapomorphies can be identified in the material. This new taxon should, therefore, be regarded as Cerapoda incertae sedis until further material is discovered. Nevertheless, Albalophosaurus offers additional information on the diversity of east Asian dinosaur faunas during the Early Cretaceous and represents only the third valid dinosaur taxon to be described from Japan.
... 42-46 ). To date, no digital endocasts have been generated for any putative thescelosaurids, whereas physical endocasts are either incomplete and provide limited information 47,48 or are known 48 from a probable juvenile 27 (the holotype of T. assiniboiensis 27 ). The latter is problematic, as ornithischian endocasts are known to vary considerably through ontogeny 49 . ...
... Thescelosaurus is reconstructed primarily from NCSM 15728 but with additional anatomical data and maximum estimated length from 31 . Character coding follows22,39,[45][46][47][48]73,74,89,97,121,122 and discussion in the main text. Oro = Orodrominae. ...
Ornithischian dinosaurs exhibited a diversity of ecologies, locomotory modes, and social structures, making them an ideal clade in which to study the evolution of neuroanatomy and behaviour. Here, we present a 3D digital reconstruction of the endocranial spaces of the latest Cretaceous neornithischian Thescelosaurus neglectus, in order to interpret the neuroanatomy and paleobiology of one of the last surviving non-avian dinosaurs. Results demonstrate that the brain of Thescelosaurus was relatively small compared to most other neornithischians, instead suggesting cognitive capabilities within the range of extant reptiles. Other traits include a narrow hearing range, with limited ability to distinguish high frequencies, paired with unusually well-developed olfactory lobes and anterior semicircular canals, indicating acute olfaction and vestibular sensitivity. This character combination, in conjunction with features of the postcranial anatomy, is consistent with specializations for burrowing behaviours in the clade, as evidenced by trace and skeletal fossil evidence in earlier-diverging thescelosaurids, although whether they reflect ecological adaptations or phylogenetic inheritance in T. neglectus itself is unclear. Nonetheless, our results provide the first evidence of neurological specializations to burrowing identified within Ornithischia, and non-avian dinosaurs more generally, expanding the range of ecological adaptations recognized within this major clade.
... A smaller foramen is located anteriorly on the premaxillary body. Other taxa such as Hypsilophodon and Zephyrosaurus (Galton 1974a;Sues 1980) show three small anteroventral foramina. ...
... The presence of lingual ridges on the dentary crowns occurs in 'Atlascopcosaurus', Gasparinisaura, Anabisetia and Qantassaurus (Rich & Rich 1989;Coria & Salgado 1996a;Coria & Calvo 2002;Agnol ın et al. 2010;Boyd 2016) and was considered by Boyd (2016) as a synapomorphic feature uniting these four taxa in an unnamed Gondwanan clade. In basal taxa such as Kangnasaurus, Zephyrosaurus and Othnielosaurus (Galton 1977;Sues 1980;Cooper 1985), the lingual ridges are poorly developed, whereas in Hypsilophodon and derived iguanodontians they are absent (Galton 1974a). ...
Talenkauen santacrucensis represents one of the most complete South American ornithopods yet discovered. This dinosaur comes from the Mata Amarilla Formation (Turonian) of Santa Cruz Province, Argentina. The aim of this contribution is to present a detailed description of Talenkauen santacrucensis. Features of the cervical series of Talenkauen, which are shared with other elasmarians, indicate that these dinosaurs have a proportionally longer neck than other ornithopods. These traits were convergently acquired by several saurischian clades. Additionally, some features, including an ornamented labial surface of the mandibular teeth and a sigmoidal greater trochanter of femur, are traits shared by most elasmarians, and may prove to be synapomorphies of this clade. A phylogenetic analysis recovers most Cretaceous Gondwanan ornithopods in the clade Elasmaria. This analysis indicates that Elasmaria was distributed more widely geographically and temporally than previously thought.
... Bifurcation of the neurovascular tract in the maxilla forming two anterior exits is also unique. For example, in Tenontosaurus tilletti (see Thomas, 2015) and Zephyrosaurus schaffi Sues, 1980(Sues, 1980, a single maxillary foramen is reported within the anteroventral fossa. However, there is the possibility that dual foramina in other ornithischians have been previously overlooked. ...
... Bifurcation of the neurovascular tract in the maxilla forming two anterior exits is also unique. For example, in Tenontosaurus tilletti (see Thomas, 2015) and Zephyrosaurus schaffi Sues, 1980(Sues, 1980, a single maxillary foramen is reported within the anteroventral fossa. However, there is the possibility that dual foramina in other ornithischians have been previously overlooked. ...
The Flat Rocks locality in the Wonthaggi Formation (Strzelecki Group) of the Gippsland Basin, southeastern Australia, hosts fossils of a late Barremian vertebrate fauna that inhabited the ancient rift between Australia and Antarctica. Known from its dentary, Qantassaurus intrepidus Rich and Vickers-Rich, 1999 has been the only dinosaur named from this locality. However, the plethora of vertebrate fossils collected from Flat Rocks suggests that further dinosaurs await discovery. From this locality, we name a new small-bodied ornithopod, Galleonosaurus dorisae n. gen. n. sp. from craniodental remains. Five ornithopodan genera are now named from Victoria. Galleonosaurus dorisae n. gen. n. sp. is known from five maxillae, from which the first description of jaw growth in an Australian dinosaur is provided. The holotype of Galleonosaurus dorisae n. gen. n. sp. is the most complete dinosaur maxilla known from Victoria. Micro-CT imagery of the holotype reveals the complex internal anatomy of the neurovascular tract and antorbital fossa. We confirm that Q. intrepidus is uniquely characterized by a deep foreshortened dentary. Two dentaries originally referred to Q. intrepidus are reassigned to Q. ? intrepidus and a further maxilla is referred to cf. Atlascopcosaurus loadsi Rich and Rich, 1989. A further ornithopod dentary morphotype is identified, more elongate than those of Q. intrepidus and Q. ? intrepidus and with three more tooth positions. This dentary might pertain to Galleonosaurus dorisae n. gen. n. sp. Phylogenetic analysis recovered Cretaceous Victorian and Argentinian nonstyracosternan ornithopods within the exclusively Gondwanan clade Elasmaria. However, the large-bodied taxon Muttaburrasaurus langdoni Bartholomai and Molnar, 1981 is hypothesised as a basal iguanodontian with closer affinities to dryomorphans than to rhabdodontids.
UUID: http://zoobank.org/4af87bb4-b687-42f3-9622-aa806a6b4116
... The primary ridge is more strongly expressed than the secondary ridges and extends basally onto the root; however, in no case are any of the ridges as prominent as would be expected on maxillary or dentary teeth. The presence of distinct primary and secondary ridges in LRF 660 differs from the premaxillary teeth of Hypsilophodon foxii (Galton, 1974) and Thescelosaurus neglectus (Boyd, 2014), which have finer, more numerous apicobasal ridges, and also from Changchunsaurus parvus, Jeholosaurus shangyuanensis, and Zephyrosaurus schaffi, which have smooth crowns (Sues, 1980;Barrett & Han, 2009;Jin et al., 2010). No premaxillary teeth of any other Australian ornithopod are known, although two edentulous premaxillae (NMV P208539, NMV P212800; Herne, 2014) from the Wonthaggi Formation (Victoria) (= 'undifferentiated Strzelecki Group' of Toslini, McLoughlin & Drinnan, 1999) preserve alveoli that suggest teeth considerably smaller than LRF 660. ...
... The jugal is a triradiate element with an elongated anterior process, a shorter postorbital process, and an even more abbreviated posterior process although it is possible that the latter is incompletely preserved (see below). The lateral surface of the jugal is dorsoventrally convex as in most ornithopods, and lacks ornamentation (present in Thescelosaurus; Boyd et al., 2009) or a boss (present in Zephyrosaurus schaffi and Orodromeus makelai; Sues, 1980;Scheetz, 1999). The postorbital and anterior processes form an arc delimiting the posteroventral and ventral margins of the orbit, respectively. ...
During the Early Cretaceous, dinosaur communities of the Australian-Antarctic rift system (Eumeralla and Wonthaggi formations) cropping out in Victoria were apparently dominated by a diverse small-bodied 'basal ornithopod' fauna. Further north, in Queensland (Winton and Mackunda formations), poorly-represented small-bodied ornithopods coexisted with large-bodied iguanodontians. Our understanding of the ornithopod diversity from the region between the Australian-Antarctic rift and Queensland, represented by Lightning Ridge in central-northern New South Wales (Griman Creek Formation), has been superficial. Here, we re-investigate the ornithopod diversity at Lightning Ridge based on new craniodental remains. Our findings indicate a diverse ornithopod fauna consisting of two-to-three small-bodied non-iguanodontian ornithopods (including Weewarrasaurus pobeni gen. et sp. nov.), at least one indeterminate iguanodontian, and a possible ankylopollexian. These results support those of previous studies that favour a general abundance of small-bodied basal ornithopods in Early to mid-Cretaceous high-latitude localities of southeastern Australia. Although these localities are not necessarily time-equivalent, increasing evidence indicates that Lightning Ridge formed a 'meeting point' between the basal ornithopod-dominated localities in Victoria and the sauropod-iguanodontian faunas in Queensland to the north. Subjects Paleontology, Taxonomy
... The systematic relationships of Y. tiantaiensis have never been assessed in a phylogenetic analysis. Zephyrosaurus schaffi Sues, 1980. Zephyrosaurus schaffi, a North American taxon from the Early Cretaceous Cloverly Formation, is based upon an incomplete skull and extremely fragmentary postcranial skeleton. ...
... The close relationship between the South American members of Elasmaria and the North American taxa Thescelosaurus and Parksosaurus warreni may also answer some questions regarding the known stratigraphic distribution of parksosaurid taxa in North America during the Cretaceous. During most of the Cretaceous, orodromine taxa were the dominant basal neornithischian taxa present in North American faunas (Sues, 1980;Scheetz, 1999;Weishampel et al., 2004;Varricchio, Martin & Katsura, 2007;Krumenacker, 2010;Brown et al., 2013;Gates et al., 2013). At the end of the Campanian, all orodromine taxa disappear from the North American fossil record. ...
The systematic relationships of taxa traditionally referred to as ‘basal ornithopods’ or ‘hypsilophodontids’ remain poorly resolved since it was discovered that these taxa are not a monophyletic group, but rather a paraphyletic set of neornithischian taxa. Thus, even as the known diversity of these taxa has dramatically increased over the past two decades, our knowledge of their placement relative to each other and the major ornithischian subclades remained incomplete. This study employs the largest phylogenetic dataset yet compiled to assess basal ornithischian relationships (255 characters for 65 species level terminal taxa). The resulting strict consensus tree is the most well-resolved, stratigraphically consistent hypothesis of basal ornithischian relationships yet hypothesized. The only non-iguanodontian ornithopod (=basal ornithopod) recovered in this analysis is
Hypsilophodon foxii
. The majority of former ‘hypsilophodontid’ taxa are recovered within a single clade (Parksosauridae) that is situated as the sister-taxon to Cerapoda. The Parksosauridae is divided between two subclades, the Orodrominae and the Thescelosaurinae. This study does not recover a clade consisting of the Asian taxa
Changchunsaurus
,
Haya
, and
Jeholosaurus
(=Jeholosauridae). Rather, the former two taxa are recovered as basal members of Thescelosaurinae, while the latter taxon is recovered in a clade with
Yueosaurus
near the base of Neornithischia.The endemic South American clade Elasmaria is recovered within the Thescelosaurinae as the sister taxon to
Thescelosaurus
. This study supports the origination of Dinosauria and the early diversification of Ornithischia within Gondwana. Neornithischia first arose in Africa by the Early Jurassic before dispersing to Asia before the late Middle Jurassic, where much of the diversification among non-cerapodan neornithischians occurred. Under the simplest scenario the Parksosauridae originated in North America, with at least two later dispersals to Asia and one to South America. However, when ghost lineages are considered, an alternate dispersal hypothesis has thescelosaurines dispersing from Asia into South America (via North America) during the Early Cretaceous, then back into North America in the latest Cretaceous. The latter hypothesis may explain the dominance of orodromine taxa prior to the Maastrichtian in North America and the sudden appearance and wide distribution of thescelosaurines in North America beginning in the early Maastrichtian. While the diversity of parksosaurids has greatly increased over the last fifteen years, a ghost lineage of over 40 myr is present between the base of Parksosauridae and Cerapoda, indicating that much of the early history and diversity of this clade is yet to be discovered. This new phylogenetic hypothesis provides a comprehensive framework for testing further hypotheses regarding evolutionary patterns and processes within Ornithischia.
... sosaurus (GALTON 1973; western Canada, cranium poorly preserved) and Thescelosaurus (GALTON 1974 b, 110RRIS 1976; western Canada and U.S.A., braincase incomplete). In some cases descriptions of the cranial foramina are included (JANENSCH 1955, GALTON 1974 a, 1983, SUES 1980). However, endocranial casts are described only for Camptosaurus (11ARSH 1894, 1896; just dorsal view) and the hypsilophodontid Leaellynasaura (RICH & RICH 1989; Lower Cretaceous, Australia, dorsal view of part of cerebrum). ...
... Cranial kinesis has been discussed for Hypsilophodon (GALTON 1974 a; SUES 1980; NORMAN 1984b; WEISHAMPEL 1984), Zephyrosaurus (SUES 1980) and Dryosaurus (GALTON 1983). GALTON (1974 a) suggested that a slight hinging movement occurred at the fronto-parietal joint (mesokinetic joint) in Hypsilophodon with the mesokinetic axis on the line across the frontals joining the two laterally developed spikes (Text-figs. 2 E, F). ...
... Strong rugosities are present on the thin orbital margin of the frontal of the basal ornithopod Zephyrosaurus (Sues 1980) and the orbital margins of the frontal are thickened and rugose in O. makelai (Scheetz 1999, fig. 7C). ...
... The postorbitals of Zephyrosaurus and O. makelai have striated orbital margins that Scheetz (1999) suggested was for attachment of the eyelid or a posterior extension of the palpebral in the latter taxon (Scheetz 1999, characters 18, 20). The postorbitals of both taxa also bear inflated central portions that project anteriorly into the orbit (Sues 1980;Scheetz 1999). ...
... For example, the premaxilla in Thescelosaurus neglectus shows an anterodorsal shelf and the anteroventral tip bears rugosities and foramina(Boyd 2014). Similar structures, most likely supporting rhamphotheca during the animal's life (Sereno 1991), were reported in a number of ornithischian dinosaurs, including Changchunsaurus parvus, Changmiania liaoningensis, Convolosaurus marri, Hypsilophodon foxii, Jeholosaurus shangyuanensis, Lesothosaurus diagnosticus, Oryctodromeus cubicularis, Thescelosaurus neglectus, and Zephyrosaurus schaffi(Galton 1974, Sues 1980, Sereno 1991, Varricchio et al. 2007, Barrett and Han 2009, Jin et al. 2010, Boyd 2014, Andrzejewski et al. 2019, Yang et al. 2020). Similarly, in the majority of these taxa, a shallow fossa is present laterally, with the premaxillary foramen and anterior premaxillary foramen present just adjacent to the border of the rugose area. ...
At the climax of their evolutionary history in the latest Cretaceous, ceratopsian dinosaurs were among the most dominant components of North American and Asian land ecosystems. In other continental landmasses, however, ceratopsians were extraordinarily rare and the affinities of their proposed representatives often turned out to be inconclusive. Arguably the most significant evidence of Ceratopsia from outside North America and Asia is represented by Ajkaceratops kozmai from the Santonian (Upper Cretaceous) of Hungary. We provide a detailed osteological description of Ajkaceratops and highlight its bizarre anatomy. Ajkaceratops has been ‘traditionally’ interpreted to represent a Bagaceratops-like coronosaur, and its occurrence on the European islands was hypothesized to probably result from an early Late Cretaceous dispersal event from Asia. However, while the snout of Ajkaceratops may resemble that of some ceratopsians, closer inspection of the preserved elements indicates that these similarities are largely superficial. While it cannot be ruled out that Ajkaceratops represents a highly peculiar member of the clade, its placement is far from certain. Still, the discovery of Ajkaceratops exemplifies the importance and uniqueness of European dinosaur faunas.
... b the complicated relationships of what was formerly referred to as the "hypsilophodonts" (i.e., Boyd et al. 2009, Brown et al. 2013, Boyd 2015. During mid-Cretaceous time there are several well documented members of Orodrominae documented from western North America: Zephyrosaurus (Sues 1980) from the Aptian Cloverly Formation and Oryctodromeus (Varricchio et al. 2007, Krumenacker 2017 from the Cenomanian Wayan and Blackleaf formations (Fig. 1). However, the fossil record of Thescelosaurinae in North America is absent until the Maastrichtian (Boyd et al. 2009, Eberth et al. 2013. ...
In 2008, and subsequent collecting trips, the remains of a partial basal neornithischian were recovered from the Cenomanian Willow Tank Formation of southern Nevada. Bones identified include the proximal femora, a series of vertebrae missing neural arches, several pedal phalanges, fragments of ossified tendons, and some as yet unidentified elements. Size and shape of the femora are consistent with other known basal neornithischians of both orodromine- and thescelosaurine-grade. The round femoral head exhibits a convex anterior side but a concave posterior surface. The neck beneath the head projects proximodorsally at an obtuse angle (~100°) from the femoral shaft. The greater trochanter sits slightly posterior to and offset from the neck of the femoral head. Anterior and lateral to the greater trochanter is a pointed lesser trochanter. The three-sided lesser trochanter bows slightly posterior toward the greater trochanter. A
prominent and deep notch separates the lesser from the greater trochanter and is characteristic of thescelosaurine-grade ornithischians. This deep intertrochanteric notch is absent in the femora of orodromines. A raised but taphonomically truncated base on the posterior femoral diaphysis likely represents the remnants of a pendant fourth trochanter. The vertebrae of the Nevada basal neornithischian are similar to both thescelosaurine- and orodromine-grade morphology. The laterally biconcave vertebrae are asymmetrical in having a boss on the posteroventral end of the centrum. The centra are nearly twice as long as they are tall with the oval articular surfaces, taller than they are wide. Due to the very fragmentary nature of this specimen, parsimonious phylogenetic analysis yields statistically insignificant results. Nevertheless, a few taxonomically important characters, particularly those of the femur, support the hypothesis that this is a
thescelosaurine, and a new genus and species, herein referred to as Nevadadromeus schmitti gen. et sp. nov. This would represent the earliest occurrence of thescelosaurines in the fossil record of North America as all other thescelosaurines from the continent date to the Maastrichtian. The geographic position of the Willow Tank Formation depocenter, very proximal to the Sevier highlands of the time, likely experienced some biogeographic insularity from other areas represented by contemporaneous units of western North America, e.g., Mussentuchit Member of the Cedar Mountain Formation of Utah, the Wayan Formation of Idaho, and the Blackleaf Formation of Montana.
... Although alveolus count appears to be a good indicator of ontogenetic state in ornithopods (Hübner and Rauhut, 2010), a variation of alveolus count by one is probably insignificant. This is especially so since such variability is sometimes evident in the two sides of a single ornithopod individual: as an example, the holotype of Zephyrosaurus schaffi (MCZ 4392) has 14 alveoli in its left maxilla and 15 in its right maxilla (Sues, 1980). Furthermore, as the anteriormost portion of the toothrow of NMV P253862 is missing, it is possible that one or more additional alveoli were present anterior to the anteriormost preserved. ...
Ornithopod dinosaurs are relatively common in the Cretaceous of Australia, particularly in the state of Victoria, which has yielded five taxa to date: two from the upper Strzelecki Group (upper Barremian–lower Aptian), and three from the Eumeralla Formation (upper Aptian–upper Albian). Whereas four of these are based solely on cranial material, Diluvicursor pickeringi is represented by a partial postcranium and is the only ornithopod specimen heretofore reported from the Eric the Red West (ETRW) site. Herein, we describe nine ornithopod dentulous elements from the Eumeralla Formation: seven from ETRW, and two from nearby sites. The four ETRW maxillae are divided into three morphotypes that are morphologically compatible with Leaellynasaura amicagraphica, Atlascopcosaurus loadsi, and cf. Galleonosaurus dorisae, respectively. Although this implies that Diluvicursor might not represent a distinct taxon, this is circumstantial. The new Leaellynasaura maxillae are evidently adult exemplars, contrasting with the juvenile holotype, whereas the sole Atlascopcosaurus maxilla is more complete than all previously referred specimens; consequently, revised diagnoses of both taxa are presented. Finally, the presence in the Eumeralla Formation of cf. Galleonosaurus—otherwise known only from the upper Strzelecki Group—implies that this taxon persisted from the Barremian to the Albian, and potentially indicates remarkable environmental stability in southeast Australia during the late Early Cretaceous.
... Also assigned to this genus at the time of its description was another, more complete left maxilla with teeth from Point Lewis (NMV P157390; Fig. 20I), together with numerous upper and lower jaws and teeth of varying levels of completeness from Dinosaur Cove ). Subsequently, Sues & Norman (1990) likened Atlascopcosaurus to Zephyrosaurus schaffi Sues 1980, whereas Galton (1999 identified differences between Bugenasaura infernalis Galton 1995 (=Thescelosaurus Gilmore 1913) and Atlascopcosaurus. Later it was noted that teeth and dentulous elements morphologically congruent with the Atlascopcosaurus type and referred specimens were most abundant among the ornithopod material from the Early Cretaceous of Victoria . ...
Although Cretaceous fossils (coal excluded) from Victoria, Australia, were first reported in the 1850s, it was not until the 1950s that detailed studies
of these fossils were undertaken. Numerous fossil localities have been identified in Victoria since the 1960s, including the Koonwarra Fossil
Bed (Strzelecki Group) near Leongatha, the Dinosaur Cove and Eric the Red West sites (Otway Group) at Cape Otway, and the Flat Rocks site
(Strzelecki Group) near Cape Paterson. Systematic exploration over the past five decades has resulted in the collection of thousands of fossils representing
various plants, invertebrates and vertebrates. Some of the best-preserved and most diverse Hauterivian–Barremian floral assemblages in
Australia derive from outcrops of the lower Strzelecki Group in the Gippsland Basin. The slightly younger Koonwarra Fossil Bed (Aptian) is a
Konservat-Lagerstätte that also preserves abundant plants, including one of the oldest known flowers. In addition, insects, crustaceans (including
the only syncaridans known from Australia between the Triassic and the present), arachnids (including Australia’s only known opilione), the stratigraphically
youngest xiphosurans from Australia, bryozoans, unionoid molluscs and a rich assemblage of actinopterygian fish are known from the
Koonwarra Fossil Bed. The oldest known—and only Mesozoic—fossil feathers from the Australian continent constitute the only evidence for tetrapods
at Koonwarra. By contrast, the Barremian–Aptian-aged deposits at the Flat Rocks site, and the Aptian–Albian-aged strata at the Dinosaur
Cove and Eric the Red West sites, are all dominated by tetrapod fossils, with actinopterygians and dipnoans relatively rare. Small ornithopod
(=basal neornithischian) dinosaurs are numerically common, known from four partial skeletons and a multitude of isolated bones. Aquatic meiolaniform
turtles constitute another prominent faunal element, represented by numerous isolated bones and articulated carapaces and plastrons. More
than 50 specimens—mostly lower jaws—evince a high diversity of mammals, including monotremes, a multituberculate and several enigmatic
ausktribosphenids. Relatively minor components of these fossil assemblages are diverse theropods (including birds), rare ankylosaurs and ceratopsians,
pterosaurs, non-marine plesiosaurs and a lepidosaur. In the older strata of the upper Strzelecki Group, temnospondyl amphibians—the youngest
known worldwide—are a conspicuous component of the fauna, whereas crocodylomorphs appear to be present only in up-sequence deposits of
the Otway Group. Invertebrates are uncommon, although decapod crustaceans and unionoid bivalves have been described. Collectively, the Early
Cretaceous biota of Victoria provides insights into a unique Mesozoic high-latitude palaeoenvironment and elucidates both palaeoclimatic and
palaeobiogeographic changes throughout more than 25 million years of geological time.
... A wide variety of jaw mechanisms have been hypothesized for ornithopods. Propalinal motion of the hadrosaurid jaw was presented by Ostrom (1961) and transverse (mediolateral) chewing mechanisms have been hypothesized for more basal members of Ornithopoda, such as Hypsilophodon (Galton, 1974) and Zephyrosaurus (Sues, 1980), in accordance with the morphology of their dentition. For over two decades, however, the most accepted mechanism proposed for most ornithopods has been pleurokinesis (Norman, 1984;Weishampel, 1984;Norman and Weishampel, 1985;see Fig. 2.5), a highly sophisticated feeding style using a unique form of cranial kinesis involving many different cranial elements in motion with each other at various joints. ...
Jaw mechanics in ornithischian dinosaurs have been widely studied for well over a century. Most of these studies, however, use only one or few taxa within a given ornithischian clade as a model for feeding mechanics across the entire clade. In this study, mandibular mechanical advantages among 52 ornithischian genera spanning all subclades are calculated using 2D lever arm methods. These lever arm calculations estimate the effect of jaw shape and difference in adductor muscle line of action on relative bite forces along the jaw. Results show major instances of overlap between taxa in tooth positions at which there was highest mechanical advantage. A relatively low bite force is seen across the tooth row among thyreophorans (e.g., stegosaurs and ankylosaurs), with variation among taxa. A convergent transition occurs from a more evenly distributed bite force along the jaw in basal ornithopods and basal marginocephalians to a strong distal bite force in hadrosaurids and ceratopsids, respectively. Accordingly, adductor muscle vector angles show repeated trends from a mid-range caudodorsal orientation in basal ornithischians to a decrease in vector angles indicating more caudally oriented jaw movements in derived taxa (e.g., derived thyreophorans, basal ornithopods, lambeosaurines, pachycephalosaurs, and derived ceratopsids). Analyses of hypothetical jaw morphologies were also performed, indicating that both the coronoid process and lowered jaw joint increase moment arm length therefore increasing mechanical advantage of the jaw apparatus. Adaptive trends in craniomandibular anatomy show that ornithischians evolved more complex feeding apparatuses within different clades as well as morphological convergences between clades. This article is protected by copyright. All rights reserved.
... An incomplete skull plus four vertebrae (SDSM 7210) from South Dakota, USA (also Hell Creek Formation) were described as ?Thescelosaurus sp.. It was briefly discussed as the Hell Creek hypsilophodontid bySUES (1980) and listed as an unnamed hypsilophodontid by SUES &NORMAN (1990).GALTON (1989) described the braincase and endocranial cast from a partial skeleton (SMNH P. 1225.1) of Thescelosaurus neglectus from the Frenchman Formation (late Maastrichtian) of Saskatchewan, Canada. Recent cladistic analyses position Thescelosaurus near the base of the Hypsilophodontidae, either as the sister group to the Hypsilophodontidae(SERENO 1986) or as the sister taxon to the remaining genera of the family (WEISHAMPEL & HEINRICH 1992).The purpose of this paper is to consider the validity of the species of the basal hypsilophodontid Thescelosaurus and, in addition, to discuss the status of specimens referred to this genus from the Hell Creek and Judith River formations.Institutions abbreviations: AMNH -American Museum of Natural History, New York; LACM -Los Angeles County Museum, California; MCZ -Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts; N M C -National Museum of Natural Science, Ottawa, Ontario; R O M -Royal Ontario Museum, Toronto, Ontario; SDSM -South Dakota School of Mines and Technology, Rapid City, South Dakota; SMNM -Saskatchewan Museum of Natural History, Regina, Saskatchewan; UCMP -University of California Museum of Paleontology, Berkeley, California; USNM -United States National Museum, Smithsonian Institution, Washington DC. ...
... The Early Cretaceous Hypsiloichnus ichnites ( fig. 8 C) posses the grallatorid-like pedal digit group II-IV with elongate toes and the third digit as the longest one, which is associated (contrary to Grallator Hitchcock, 1985) with the large functional hallux and the small mesaxonic manus. According to Stanford et al. (2004), their trackmakers were related to basal ornithopods like Zephyrosaurus Sues, 1980 andHypsilophodus Huxley, 1869. In our opinion, the Hypsiloichnus morphotype resemble also the Late Triassic Atreipus Olsen & Baird, 1986 (fig . ...
... Ostrom and his predecessors were primarily interested in dinosaurs and collected other vertebrate fossils only incidentally. Expeditions in the early 1970s, headed by Farish A. Jenkins, Jr., of Harvard University, found the first mammals from the Cloverly Formation, including the gobiconodontid Gobiconodon ostromi (described by Jenkins and Schaff, 1988) and an as yet unnamed triconodontid similar to Astroconodon (Jenkins and Crompton, 1979), as well as the hitherto unreported hypsilophodontid dinosaur Zephyrosaurus (Sues, 1980). Field parties from the Oklahoma Museum of Natural History have collected in the Cloverly sporadically since 1989 (mainly 1995-2002), focusing on recovery of mammals and other microvertebrates. ...
We report a diverse assemblage of tribosphenidan mammals from several localities in the Cloverly Formation (Lower Cretaceous, Albian) of Montana and Wyoming. This unit is of historical significance for yielding well-known dinosaurs (e.g., Deinonychus antirrhopus, Tenontosaurus tilletti) and early mammals (e.g., Gobiconodon ostromi, Montanalestes keeblerorum). We provisionally identify 13 taxa (five of which are formally recognized), including Pappotherium pattersoni, a new species of the deltatheroidan Oklatheridium (O. wiblei, sp. nov.), a eutherian (Montanalestes, previously named), and two new basal tribosphenidans (Argaliatherium robustum, gen. et sp. nov., and Carinalestes murensis, gen. et sp. nov.). An unnamed taxon, represented by associated but almost edentulous dentaries, is interpreted to have had four incisors, a single-rooted canine, three premolars, and four molars, indicating that the metatherian tooth formula was established by the Albian. In addition, an indeterminate lower molar fragment preserving twinned talonid cusps and a buccal postcingulid provides the earliest evidence for Marsupialiformes. We also provide a more detailed description of the associated dentaries (holotype) of Montanalestes keeblerorum. The mammalian fauna from the Cloverly Formation shares several taxa with the roughly contemporaneous Trinity Group of Oklahoma and Texas, an observation that also applies to the dinosaur fauna, suggesting some degree of latitudinal homogeneity among described terrestrial vertebrates in this part of the North American Early Cretaceous.
... Paradoxically, although reasonably well-represented vertebrate faunas are known from both the Antlers (and its lateral equivalent in Texas, the Trinity Group) and the Cloverly Formations, the faunas are not entirely comparable. The assemblage from the Cloverly Formation is represented mainly by dinosaurs which, thanks to the works of Ostrom (1969a,b;1970a;1976a) and Sues (1980), are known in great detail. In contrast, only four dinosaur taxa (Acrocanthosaurus, Tenontosaurus, a possible brachiosaurid, and an indeterminate sauropod), and several undescribed small theropod tooth morphotypes, previously have been reported from the Antlers Formation of Oklahoma (Larkin, 1910;Stovall and Langston, 1950;Langston, 1974;Cifelli and others, 1997). ...
... The combination of these cranial and postcranial characteristics, in sum or in part, distinguish the Proctor Lake ornithopod from fabrosaurids, Zephrosaurns, Tenontosaurus, Dryosaurus, Laosaurus, Parksosaurus, Thescelosaurus and Camptosaurus (see Galton, 1974aGalton, , 1974bGalton, , 1975Galton and Jensen, 1975;Sues, 1980). ...
... The evolution of ornithopod jaw mechanisms has been subject to investigation for over a century, with in-depth analyses of craniomandibular structure, intracranial joint morphology, and dental microwear (Marsh, 1893;Nopcsa, 1900;Versluys, 1910Versluys, , 1912Versluys, , 1923Lambe, 1920;Kripp, 1933;Lull and Wright, 1942;Ostrom, 1961;Thulborn, 1971;Galton, 1974;Hopson, 1980;Sues, 1980;Weishampel, 1984;Norman, 1984;Norman and Weishampel, 1985;Rybczynski et al., 2008;Bell et al., 2009;Williams et al., 2009;Cuthbertson et al., 2012). Ornithopod skulls, mandibles, and dentition are of such unique morphology that there is no modern analog with which to compare them sufficiently. ...
28 A bs t r ac t The predentary is a single bone found in the lower jaw complex of all ornithischian dinosaurs. Located rostral to the paired dentary bones of the mandible, it occludes with the premaxilla (or apomorphically with the rostral bone in ceratopsians). Although it is universally accepted that the predentary was used in nipping vegetation, its absence in all other fossil and extant vertebrate herbivores (including sau-ropodomorphs) indicates that the functional significance of this element is not well understood. The overall morphology of the lower jaw elements, the articular surface between the predentary and dentary, other associations of the mandible with the cranium, and dental wear orientation of hadrosau-roids are described here with emphasis on function. Wid-ened expansions and bifurcated processes on the predentary as well as an absence of a firm, clasping junction with the dentary (or between the dentaries themselves) suggest mo-bility at this junction. A distinct medial curvature of the rostral portion of the dentary, medially recurved coronoid processes, and ball-and-socket articulation between the quad-rate and articular of the mandible suggest a rotating surface and range of movement at the predentary-dentary junction, which in turn allows medial rotation of both dentary bones independent of the predentary. These morphologies, and dental micro-and mesowear, suggest palinal jaw movement to initially shear vegetation and medial rotation of the den-taries against the maxillae, maneuvering vegetation into the oral cavity independently on both sides.
... None of these ridges is more strongly pronounced than the others, and there is no distinct primary ridge. This tooth morphology is similar to that seen in 'hypsilophodontid' ornithopods such as Zephyrosaurus (Sues, 1980), Parksosaurus (Galton, 1973b) and Bugenasaura (Galton, 1999). The labial surfaces of the maxillary teeth of Y. multidens have 2-3 weak, sub-parallel ridges extending from the crown apex to the base ( Fig. 2A). ...
... Deinonvchus. Ornitbomimus, Microvenator and a sauropod (Ostrom, 1969;Sues, 1980). Triconodont mammal: Cobiconodon (Jenkins and Schaff, 1988). ...
The terrestrial Mesozoic sediments, floras and faunas of Montana are reviewed and interpreted. Environmental diversity was low, and apparently depended upon the relative position of the interior seaways. With the exception of the areas bordering the seaways where the climates were temperate to subtropical, most of Montana was semi-arid to arid throughout the Mesozoic. The upland coastal plain regions became much drier as the seaways regressed. Faunal and floral diversity was much higher in the lowland regions than in the upland regions, probably because the water ways were much larger in the lowlands, and could support more life. INTRODUCTION The terrestrial Mesozoic sediments of Montana have yielded an
... A similar transverse ridge is also observed in hadrosaurids (Horner 1992;Evans 2006) and in basal euornithopods (Weishampel et al. 2003), in which the sphenethmoid suture extends onto the ridge. Such a ridge is absent in basal ornithopods (Sues 1980;Galton 1989Galton , 1997 and pachycephalosaurs (TM pers. obs.). ...
... Ostrom (1970) divided the upper Mesozoic rocks of the region into eight distinctive units, of which Units IV-VII represent four divisions of the Cloverly Formation (Jacobs and Winkler, 1998 use the older nomenclature of Moberly, 1960). The primary fossil-yielding divisions of the Cloverly Formation are Units V and VII, with some fossils also known from Unit VI (Ostrom, 1969(Ostrom, , 1970Sues, 1980;Jenkins and Schaff, 1988;Maxwell, 1993Maxwell, , 1996Maxwell and Ostrom, 1995;Maxwell et al., 1997;Cifelli et al., 1998;Gardner, 1999). The lizards reported herein were collected at three localities, one in unit V and two in unit VII. ...
... The majority of specimens represent small, immature individuals, suggesting high mortality rates for younger members of the species, frequenting of the area by this taxon during time intervals corresponding to certain early, ontogenetic growth stages, or some other unknown factor(s). Three small, hypsilophodontid ornithopods are also present in the fauna; of these, one is similar to Zephyrosaurus, otherwise known from the Cloverly Formation of Montana (Sues, 1980). The Mussentuchit local fauna includes a nodosaurid (based on teeth) similar to Pawpawsaurus, which was described from upper Albian rocks of Texas (Lee, 1996). ...
... In contrast, other Cloverly Formation dinosaur taxa are less well known and have not been a substantial source of data for studies of Cloverly Formation paleoecology or dinosaur paleoecology in general. For example, only single exemplars of the oviraptorosaur Microvenator celer and the ornithopod Zephyrosaurus schaffi have been described (Ostrom, 1970;Sues, 1980). Still other Cloverly Formation dinosaurs are only represented by remains that are indeterminate to the genus level, such as ornithomimids and large-bodied theropods (body mass > 1000 kg), which are limited to a handful of teeth and bones reported by Ostrom (1970). ...
A partial theropod skeleton from the Albian (ca. 105 ma) Cloverly Formation of Wyoming is shown to exhibit many features in common with members of Carcharodontosauria and is referred to Acrocanthosaurus atokensis on the basis of an autapomorphy and a unique combination of characters. The absence of neurocentral fusion in dorsal and caudal vertebrae and bone histology of the femur indicate that the specimen is a juvenile. The circumferences of lines of arrested growth were used to estimate mass over successive years of the animal's life. These mass estimates suggest that early in ontogeny, Acrocanthosaurus grew at rates on par with growth rates inferred in Allosaurus and most tyrannosaurid theropods, which are similar to rates expected for scaled-up precocial birds. Histological data from adult specimens suggest that Acrocanthosaurus reached adult body size in two to three decades. Gigantism in Acrocanthosaurus likely evolved via acceleration of growth rates relative to those of basal members of Allosauroidea, a transition also observed within tyrannosauroid theropods. Contrary to previous assessments, there is only evidence for one large-bodied theropod species in the Early Cretaceous of North America, though many fragmentary specimens are indeterminate to the genus level. Aptian–Albian and Maastrichtian-aged dinosaur communities were more similar to one another than to those of the intervening Campanian stage in that both seem to have featured a single, extremely large-bodied, fast growing, geographically widespread theropod dinosaur.
Thescelosaurines are a group of early diverging, ornithischian dinosaurs notable for their conservative bauplans and mosaic of primitive features. Although abundant within the latest Cretaceous ecosystems of North America, their record is poor to absent in earlier assemblages, leaving a large gap in our understanding of their evolution, origins, and ecological roles. Here we report a new small bodied thescelosaurine—Fona herzogae gen. et sp. nov.—from the Mussentuchit Member of the Cedar Mountain Formation, Utah, USA. Fona herzogae is represented by multiple individuals, representing one of the most comprehensive skeletal assemblages of a small bodied, early diverging ornithischian described from North America to date. Phylogenetic analysis recovers Fona as the earliest member of Thescelosaurinae, minimally containing Oryctodromeus, and all three species of Thescelosaurus, revealing the clade was well‐established in North America by as early as the Cenomanian, and distinct from, yet continental cohabitants with, their sister clade, Orodrominae. To date, orodromines and thescelosaurines have not been found together within a single North American ecosystem, suggesting different habitat preferences or competitive exclusion. Osteological observations reveal extensive intraspecific variation across cranial and postcranial elements, and a number of anatomical similarities with Oryctodromeus, suggesting a shared semi‐fossorial lifestyle.
The fossil record of Late Cretaceous non-hadrosaurid neornithischians from the Western Interior of North America is sparse. Parksosaurus warreni is an early Maastrichtian taxon currently known only from a skull and much of the associated postcranial skeleton and a referred isolated tooth from the Horseshoe Canyon Formation of Alberta, Canada. This article presents a detailed anatomical account of the holotype of this dinosaur following extensive additional preparation of the holotype and provides photographs of the postcranial elements for the first time. The premaxilla has a dorsoventrally deep posterolateral process, which overlaps the maxilla. The antorbital fenestra is small and teardrop-shaped. The lingual surfaces of dentary teeth bear nine or 10 vertically extending ridges that terminate in apical denticles. The suprascapula is mineralized or ossified. The dorsal margin of the ischium is posterodorsally concave at mid-length. The greater and lesser trochanters of the femur are not separated by a distinct cleft. The pendent fourth trochanter is placed on the proximal half of the femur. The more distal caudal vertebrae have greatly elongated prezygapophyses, which, together with a basket of ossified tendons ensheathing the caudal vertebrae, indicate that the tail may have functioned as a dynamic stabilizer during locomotion. The substantial new anatomical information from the holotype and only known skeleton of Parksosaurus warreni will allow more detailed comparisons to other closely related taxa and facilitate further discussions of unresolved aspects of the interrelationships of neornithischian dinosaurs.
Montana is renowned for its rich paleontological treasures, particularly those of vertebrate animals such as fishes, dinosaurs, and mammals. For example, the most speciose fish fauna in the world comes from Fergus County. The first dinosaur remains noted from the western hemisphere came from an area near the mouth of the Judith River in what would become Fergus County. The first Tyrannosaurus rex skeleton, and many more since, have come from Garfield and McCone Counties. The first dinosaur recognized to show the relationship between dinosaurs and birds came from Carbon County, and the first dinosaur eggs, embryos, and nests revealing dinosaur social behav- iors were found in Teton County. The first dinosaur confirmed to have denned in burrows was found in Beaverhead County.
Although Montana is not often thought of for mammal fossils, a great diversity of late Mesozoic and Cenozoic mammals also occurs within the State. Especially noteworthy are the mid to Late Cretaceous primitive mammals found within the great dino- saur-producing formations of eastern Montana, the early and late Paleocene mammals of the Fort Union Formation in central and eastern Montana, and the late Eocene/early Oligocene deposits in southwestern Montana. Additionally, middle Eocene and middle Miocene strata contain important mammal fossils, in some cases representing unique occurrences.
This chapter highlights Montana’s most significant vertebrate fossils, and the environments in which the animals lived and died. We have chosen to list representative Holotypes, and taxa that have been formally described in the literature, rather than listing all of the species reported in “faunal lists,” since these lists often contain very fragmentary remains, and only best guesses of their identities. The taxa listed here are what we consider to be the most representative, from which important and interesting hypotheses have been derived concerning the evolution, behavior, and paleoecology of vertebrate fossil taxa from Montana.
All Paleozoic vertebrates from Montana come from marine sediments, whereas the Mesozoic assemblages are derived from transgressive–regressive alternating marine and freshwater deposits, and the Cenozoic faunas are derived strictly from freshwater terrestrial environments.
This work attempts at providing a revised framework for ornithischian phylogeny, based on an exhaustive data compilation of already published analyses, a critical re-evaluation of osteological characters and an in-depth checking of characters scoring to fix mistakes that have accumulated in previous analyses; we have also included recently described basal ornithischians, marginocephalians and ornithopods. ‘Heterodontosaurids’ are recovered as a paraphyletic group of basal Marginocephalia that progressively lead to the dome-headed ‘true’ pachycephalosaurs. ‘Heterodontosaurids’ consequently fall within Pachycephalosauria sensu Sereno, 1998. The reconfiguration of basal cerapodan relationships pulls the origins of ornithopods to the earliest stages of the Jurassic. Based on the present analysis, we also discuss ornithopod relationships, with a particular focus on basal Iguanodontia. Tenontosaurus is found as the basalmost iguanodontian. The monophyly of Rhabdodontomorpha in a position more derived than Tenontosaurus is supported by the present analysis.
The Triassic reptile Euparkeria has been frequently given a pivotal position in interpretations of the evolution of archosaurs. Most recently, Welman (1995) has argued from braincase data that Euparkeria is more closely related to birds than are either theropod dinosaurs or crocodilians - a conclusion clearly at odds with the current orthodoxy. The braincase of a single specimen of Euparkeria is described in detail and compared with previous descriptions and with the braincases of other diapsids. Variations among the known specimens are documented. The homology of various braincase structures are reassessed in light of the study by Welman (1995). We argue that the braincase of Euparkeria has an undivided metotic fissure, an incompletely ossified medial wall of the otic capsule, a well-defined ‘semilunar depression’, and posteroventrally positioned foramina in the parabasisphenoid for the entrance of the cerebral branches of the internal carotid arteries. It lacks enclosure of the Eustachian system in bone, well-developed tympanic sinuses, or a well-defined recess for the lagena. A review of braincase morphology in extinct and extant diapsids suggests that braincase features of Euparkeria are largely plesiomorphic for Archosauria. The evolutionary relationships between Euparkeria and extant archosaurs (birds and crocodilians) are considered by reviewing braincase morphology in extant and extinct diapsids. No shared derived characters could be found that support the resolutions (crocodilians (Euparkeria+ birds)) or (birds (Euparkeria+ crocodilians)). Three derived characters shared by extant archosaurs support the resolution (Euparkeria (crocodilians + birds)), but only the presence of laterally positioned foramina in the parabasisphenoid for the entrance of the cerebral branches of the internal carotid arteries appears to represent strong evidence. The other two features are a degree of ossification (of the medial wall of the otic capsule) that exhibits some homoplasy among archosaurs, and an absence (of the ‘semilunar depression’), and therefore do not represent particularly robust hypotheses of homology. Our interpretation of the braincase of Euparkeria is fully congruent with the consensus among recent explicit phylogenetic analyses that this taxon is close to, but not a member of, the archosaur crown group. Birds and crocodilians share a number of other derived similarities (subdivided metotic fissure, elongated and tubular cochlear recess, enclosed Eustachian system, extensive tympanic sinuses, quadrate-prootic articulation) that are probably not homologous because of their absence in a number of non-avian dinosaurs and crocodilian-line crown-group archosaurs.
The first occurrence of an iguanodontian from the Lower Cretaceous Poison Strip Member of the Cedar Mountain Formation, Utah, is described and named. This new taxon is represented by a well-preserved ilium, femora, tibiae, and vertebrae, as well as other material. The fe-mora are typical for an ornithopod, but the ilium has a short, horizontal postacetabular process that is functionally an antitrochanter.
The vertebrate fauna from the Lower Cretaceous Patuxent Formation of Virginia is composed of a single partial fish impression from the James River at Dutch Gap and a diverse tetrapod ichnofauna from near Fredericksburg that includes trace fossils made by frogs, turtles, theropods, sauropods, ankylosaurs, and ornithopods. The footprints occur on overbank deposits preserved locally within a fluvial braided-stream sequence that formed near the western border of the Early Cretaceous Atlantic Coastal Plain.
New age related individual variation for Hypsilophodon foxii, a basal euornithopod with no confirmed record outside of the Isle of Wight (late Barremian), includes an extensor groove on the distal femur that is absent and then shallow. The sequence of fusion of the neurocentral sutures follows the archosaurian caudal forwards pattern but fusion in the sacrum occurs in different sized individuals. Detailed figures are given of the form and wear patterns of the teeth. The "Iguanodon/Hypsilophodon/Polacanthus" distal femur from Hastings (mid-Valanginian) is probably Euornithopoda indet. Large distal femora from the Isle of Wight (late Barremian) and Bedfordshire (Aptian), with an extensor groove of medium depth, are basal Iguanodontia indet. "Hypsilophodon" wielandi GALTON & JENSEN, 1978 (Barremian, Western USA) is basal Euornithopoda indet, not a dryosaurid ; it is not a junior synonym of probable dryosaurid "Camptosaurus" valdensis LYDEKKER, 1889a (late Barremian, Isle of Wight), and both taxa are nomina dubia. the record of the dryosaurid Valdosaurus, a femur of which was first described by OWEN (1842) as Iguanodon, is restricted to England (Sussex, middle Valanginian ; Isle of Wight, late Barremian). Based on differences in horizon and form of the femur, Elrhazosaurus n. gen. is erected for the dryosaurid Valdosaurus nigeriensis Galton & taquet, 1982 (Aptian, Niger). The holotype dentary of Iguanodon hoggii OWEN, 1874 from Dorset (middle Berriasian) is made the type species of the new non-camptosaurid genus Owenodon ; a femur referred to "Camptosaurus" hoggii from Dorset is Iguanodontoidea indet. A small dentary from the Isle of Wight (late Barremian) is not Valdosaurus but basal Iguanodontoidea indet. An incomplete hindlimb (with tibia showing a very large callus from a healed fracture) of "Camptosaurus" hoggii from Yorkshire (mid-Berriasian) is very similar to that of "Iguanodon" hollingtoniensis lydekker, 1889b, the femur of which is Camptosaurus-like except for the Iguanodon-like distal end. This species represents a new genus of basal Iguanodontoidea, but its diagnosis must await a review of all Sussex Wadhurst Clay (middle Valanginian) material. Dentary teeth of Owenodon sp. occur in the bauxite fssure fll (Berriasian-Valanginian) of Cornet, Romania. The bones more derived than those of Camptosaurus but not Styracosterna or Iguanodontea (which is represented by metacarpal II, ungual phalanges) are tentatively referred to Owenodon sp. These include a maxilla and teeth, cervical vertebra 6, fused medial carpals+metacarpal I, distal femora (and, tentatively, a frontal, a braincase, a dorso-sacral centrum, larger humerus). A smaller humerus is basal Euornithopoda indet, but most of the described bones are Euornithopoda indet. The possible stegosaurian pubis from the Isle of Wight (late Barremian) is basal Iguanodontoidea indet.
The incomplete skull of the hypsilophodontid dinosaur Bugenasaura infernalis GALTON, 1995 (Hell Creek Formation, late Maastrichtian, South Dakota, USA) is described. Bugenasaura is characterized by a very deeply recessed cheek tooth row and a truncated distal end to the long palpebral (probably for an accessory palpebral). Bugenasaura is included with Thescelosaurus (Upper Cretaceous, USA) in the Thescelosaurinae. A dentary tooth from the Upper Jurassic of England is referred to as cf. Bugenasaura.
Segnosaurus Perle, 1979, and Erlikosaurus Barsbold & Perle, 1980, are recently described dinosaurs of unusual form from the Late Cretaceous of Mongolia. Both taxa are medium-sized herbivores with small skulls, beaks, spatulate teeth, retroverted pubes, and broad four-digit hindfeet. Barsbold and Perle consider them to be theropods. However, the feet of segnosaurs are much less derived than are the bird-like feet of theropods. Further, the segnosaurs do not show any distinctive theropod-like characters that justify their assignment to this group. They appear, instead, to be derived prosauropods with a number of early ornithischian adaptations. Notable among these ornithischian-like adaptations are their beaked jaws with cheeks. A cladistic comparison of the segnosaurs with thecodonts and early dinosaurs of the Triassic suggests that, despite their late appearance, the segnosaurs are phylogenetic intermediates between herbivorous prosauropods and early ornithischians. As such the segnosaurs strengthen the hypothesis of dinosaur monophyly. Segnosaurs cannot be placed in the theropods, but traditional schemes of dinosaur classification do not recognize the possibility of dinosaur monophyly. Here the segnosaurs are considered to represent a clade between the prosauropods and ornithischians.
A detailed description is given of the osteology of the holotype of Sphenosuchus. The skull, particularly the braincase, is excellently preserved and shows a wealth of anatomical detail. Sphenosuchus was one of the largest of the early crocodylomorphs, with a skull length of 192 mm and an estimated total length of 1.4 m. The primary head of the quadrate meets the prootic and squamosal but not the opisthotic (or laterosphenoid); quadrate and pterygoid are not fused to the braincase and the basipterygoid articulation is free. The braincase and some other skull bones are pneumatized. The otic capsule is crocodilian but the subcapsular buttress (ossified subcapsular process) does not enclose the vagus nerve or the internal carotid artery. The scapula blade is triangular; the coracoid has a long posteroventral extension which is thought to have articulated firmly with a large interclavicle. Clavicles were absent. Metatarsal I is reduced; metatarsals II and IV are symmetrical about III, which is longest. A paired series of dorsal scutes was present. Sphenosuchus is considered to have been cursorial and carnivorous. Comparison is made between the pneumatic spaces in the Sphenosuchus skull and those of modern crocodiles and birds, and homologies are discussed. Representatives of the main cavities found in the crocodilian skull are present in the skull of Sphenosuchus, in some cases in a less clearly defined state. On the other hand, certain pneumatic spaces in the Sphenosuchus skull are not found in the modern crocodile but resemble cavities in the bird skull. The courses of the internal carotid and stapedial arteries are reconstructed; the latter is considered to have passed through the postquadrate foramen, temporal canal and anterior temporal foramen as it does in modern forms. The problem of the position of the stapedial artery in the crocodile is discussed. It is believed that enclosure of the artery took place as a result of the forward migration of the quadrate head, leading to the formation of a temporal canal. Detailed comparisons are made between the otic capsule of Sphenosuchus and those of modern crocodiles and birds, which it closely resembles. Changes in otic capsule structure in archosaurs to give the crocodilian or bird condition, starting from a primitive form like Euparkeria, are outlined. The skull is believed to have been kinetic, and the quadrate streptostylic, in the juvenile Sphenosuchus. The parts of the proximal end of the crocodilian quadrate are differentiated; in particular, the `true' head is distinguished from the anterodorsal process. Although very reduced in the modern crocodile, the `true' head is in the same morphological position as in Sphenosuchus; contact with the laterosphenoid has been brought about, not by further forward movement of the head, but by geniculation of the upper portion of the bone. The anterodorsal process is considered to have arisen as a result of the dorsal migration of an anterolateral projection somewhat similar to that of the thecodontian Stagonolepis. This change was also responsible for the elongation of the quadratojugal in crocodylomorphs. The validity of the order Crocodylomorpha is discussed. It is concluded that the most important steps in crocodylomorph evolution, particularly in the skull, had taken place in sphenosuchians, hence they should be included in the same taxon as protosuchians and more advanced crocodilians, rather than with thecodontians.
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