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Montanoceratops cerorhynchus (Dinosauria: Ceratopsia) and relationships among basal neoceratopsians

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Montanoceratops cerorhynchus has been described as the sister group of Ceratopsidae, even though analyses and diagnosis of this taxon have been tentative and incomplete. A second specimen of M. cerorhynchus includes new diagnostic elements, most notably a partial skull including the caudal half of the braincase, pectoral girdle and manus. Results of a cladistic analysis of eight basal neoceratopsians (Protoceratops, Leptoceratops, Bagaceratops, Microceratops, Breviceratops, Montanoceratops, Asiaceratops, and Udanoceratops) and four ceratopsids (Centrosaurus, Anchiceratops, Chasmosaurus, and Styracosaurus) confirm Montanoceratops as the sister group of Ceratopsidae. Microceratops and Asiaceratops are positioned at the base of Neoceratopsia. Protoceratops, Leptoceratops, and Udanoceratops constitute a monophyletic Protoceratopsidae. Paleogeographical interpretation of the cladogram suggests that Neoceratopsia originated in Asia, and that there were at least two migrations of ceratopsians from Asia to North America.

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... The cultriform process also moves dorsally as the basisphenoid deepens throughout ontogeny. The anterolateral projection of the basipterygoid processes observed here are present in all psittacosaurids (Sereno et al., 1988;You, Tanoue & Dodson, 2008;Dodson, You & Tanoue, 2010) and similar rostrally projecting processes are present in several basal neoceratopsians including Archaeoceratops (Dodson, You & Tanoue, 2010) and Protoceratops (Brown & Schlaikjer, 1940;Chinnery & Weishampel, 1998;Dodson, You & Tanoue, 2010). Conversely, posteroventrally projecting basipterygoid processes are found in the Leptoceratopsidae (Chinnery & Weishampel, 1998;Ott, 2007) and the Ceratopsidae (Hatcher, Osborn & Marsh, 1907;Dodson & Currie, 1990;Chinnery & Weishampel, 1998). ...
... The anterolateral projection of the basipterygoid processes observed here are present in all psittacosaurids (Sereno et al., 1988;You, Tanoue & Dodson, 2008;Dodson, You & Tanoue, 2010) and similar rostrally projecting processes are present in several basal neoceratopsians including Archaeoceratops (Dodson, You & Tanoue, 2010) and Protoceratops (Brown & Schlaikjer, 1940;Chinnery & Weishampel, 1998;Dodson, You & Tanoue, 2010). Conversely, posteroventrally projecting basipterygoid processes are found in the Leptoceratopsidae (Chinnery & Weishampel, 1998;Ott, 2007) and the Ceratopsidae (Hatcher, Osborn & Marsh, 1907;Dodson & Currie, 1990;Chinnery & Weishampel, 1998). Throughout growth, these basipterygoid processes become progressively more ventrally projecting. ...
... The anterolateral projection of the basipterygoid processes observed here are present in all psittacosaurids (Sereno et al., 1988;You, Tanoue & Dodson, 2008;Dodson, You & Tanoue, 2010) and similar rostrally projecting processes are present in several basal neoceratopsians including Archaeoceratops (Dodson, You & Tanoue, 2010) and Protoceratops (Brown & Schlaikjer, 1940;Chinnery & Weishampel, 1998;Dodson, You & Tanoue, 2010). Conversely, posteroventrally projecting basipterygoid processes are found in the Leptoceratopsidae (Chinnery & Weishampel, 1998;Ott, 2007) and the Ceratopsidae (Hatcher, Osborn & Marsh, 1907;Dodson & Currie, 1990;Chinnery & Weishampel, 1998). Throughout growth, these basipterygoid processes become progressively more ventrally projecting. ...
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Ontogenetic sequences are relatively rare among dinosaurs, with Ceratopsia being one of the better represented clades, and especially among geologically earlier forms, such as Psittacosaurus . Psittacosaurus is a small, bipedal basal ceratopsian abundant in the Lower Cretaceous deposits of Asia, whose cranial and endocranial morphology has been well studied, but only cursory details have been published on the bones surrounding the brain. Using reconstructions created from micro-computed tomography scans of well-preserved skulls from the Barremian–Aptian Yixian Formation, China, we document morphological changes in the braincase of Psittacosaurus lujiatunensis through three growth stages, hatchling, juvenile, and adult, thus providing the first detailed study of ceratopsian braincase morphology through ontogeny. Notable ontogenetic changes in the braincase of P. lujiatunensis include a dramatic relative reduction in size of the supraoccipital, an increase in the lateral expansion of the paroccipital processes and a decrease in the angle between the lateral semicircular canal and the palatal plane. These ontogenetic morphological changes in the braincase relate to expansion of the cranium and brain through growth, as well as reflecting the switch from quadrupedal juveniles to bipedal adults as documented in the changing orientation of the horizontal semicircular canal through ontogeny. Recognition of these patterns in a basal ceratopsian has implications for understanding key events in later ceratopsian evolution, such as the development of the parieto-squamosal frill in derived neoceratopsians.
... Interestingly, the Fig. 3M). Furthermore, Montanoceratops has a flared distal end of the scapula even in juvenile specimen (Chinnery & Weishampel, 1998; Fig. 3N). A scapular crest, extending from the caudal side of the supraglenoid ridge to the cranial part of the blade, forms a low ridge in adult Protoceratops andrewsi (e.g., AMNH 6418). ...
... The widening of the glenoid cavity varies among neoceratopsians (Fig. 4). It is very small in Psittacosaurus mongoliensis (e.g., AMNH 6535, 6534, NHMW 1998z0064/0001; (Chinnery & Weishampel, 1998; Fig. 4N). The glenoid expands more laterally in small subadult Protoceratops andrewsi (ZPAL MgD-II/3; MgD-II/35; Fig. 4B) and a lateral extension of the glenoid is similar to that in Xuanhuaceratops (Zhao et al., 2006;Fig. ...
... The caudoventral projection occurs in non-ceratopsid neoceratopsians. The caudal notch is shallow in Psittacosaurus mongoliensis (NHMW 1998z0064/0001), Xuanhuaceratops (Zhao et al., 2006), Graciliceratops (ZPAL MgD-I/156), and young Montanoceratops (Chinnery & Weishampel, 1998). By contrast, in Leptoceratops (AMNH 5205), Auroraceratops (Morschhauser, 2012) and Protoceratops (e.g., AMNH 6471), the caudal notch is deep and narrow (Fig. 4). ...
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Protoceratops andrewsi is a well-known ceratopsian dinosaur from the Djadokhta Formation (Upper Cretaceous, Mongolia). Since the 1920s, numerous skeletons of different ontogenetic stages from hatchlings to adults, including fully articulated specimens, have been discovered, but the postcranial anatomy of Protoceratops has not been studied in detail. A new, mostly articulated subadult individual provides an excellent opportunity for us to comprehensively describe the anatomy of the limb skeleton, to compare to other ceratopsian dinosaurs, and to study the ontogenetic and intraspecific variation in this species. New data provided by the specimen shed light on the lifestyle of P. andrewsi. The young subadult individuals present an array of morphological characters intermediate between the bipedal Psittacosaurus and fully quadrupedal adult P. andrewsi. We compare these observations with a broad range of non-ceratopsid Neoceratopsia (of various locomotor adaptations) and Psittacosauridae (obligate bipeds), which gives us insight into the evolution of the skeletal characters informative for the postural change in ceratopsian dinosaurs.
... The free cervical vertebrae of Auroraceratops are like those of other non-ceratopsid neoceratopsians. The free cervical centra of MOR 542, a specimen that is ambiguously referred to Montanoceratops (Chinnery and Weishampel, 1998;Makovicky, 2010), are craniocaudally shortened, unlike the centra seen in Auroraceratops, Protoceratops (Brown and Schlaikjer, 1940), the holotype of Montanoceratops (Makovicky, 2010), or Leptoceratops (Sternberg, 1951). The 1. Presacral vertebral column measurements of Auroraceratops rugosus, specimen ZMNH M8801. ...
... The neural spines of Psittacosaurus sibiricus are like those of Auroraceratops in that both taxa show increasing proximodistal length of the spine in successively caudal vertebrae (Averianov et al., 2006). The transverse processes of Protoceratops, MOR 542, and the Montanoceratops holotype show a similar pattern to those of Auroraceratops, with ventrally curved transverse processes on c4 and c5 and dorsally inclined transverse processes on c8 and c9 (Brown and Schlaikjer, 1940;1942;Chinnery and Weishampel, 1998;Makovicky, 2010). In contrast, none of the transverse processes of Leptoceratops curve ventrally (Sternberg, 1951). ...
... These likely connect venous drainage of the sacrum to that of the vertebral venous plexus, similar to the venous drainage seen in other amniotes (Zippel et al., 2003). The sacral centra may bear a strong ventral ridge, termed the ventral crest by Chinnery and Weishampel (1998). The distribution of the ventral crest exhibits polymorphism in Auroraceratops. ...
Article
The species Auroraceratops rugosus was originally described based upon a single skull. With the recovery of over 80 individuals, a complete description of the postcranial skeleton is presented. Auroraceratops is currently the most complete exemplar we have of ceratopsian postcranial anatomy between Psittacosaurus and Leptoceratops. Adult Auroraceratops had a length of approximately 125 cm and an approximate hip height of 44 cm. Osteological correlates of stance in the fore- and hind limb unequivocally indicate a bipedal gait. The phylogenetically corrected quadrupedal mass-estimation equation modified for mass estimation of bipedal terrestrial vertebrates estimates an average mass of Auroraceratops at 15.5 kg. It has the phylogenetically and temporally earliest documentation of the syncervical in Ceratopsia. The mid-caudal neural spines are elongate and erect, a feature previously only known in Leptoceratopsidae and Protoceratopsidae. Despite being longer than in most ceratopsians, the mid-caudal neural spines are not as tall as in some leptoceratopsids. Most of the phylogenetically relevant characters of the postcranial skeleton in Auroraceratops are a mosaic of features plesiomorphic to Neoceratopsia and features previously considered to be unique to later diverging clades, such as Leptoceratopsidae and Protoceratopsidae. Citation for this article: Morschhauser, E. M., H. You, D. Li, and P. Dodson. 2019. Postcranial morphology of the basal neoceratopsian (Ornithischia: Ceratopsia) Auroraceratops rugosus from the Early Cretaceous (Aptian–Albian) of northwestern Gansu Province, China; pp. 75–116 in Hailu You, Peter Dodson, and Eric Morschhauser (eds.), Auroraceratops rugosus (Ornithischia, Ceratopsia) from the Early Cretaceous of northwestern Gansu Province, China. Society of Vertebrate Paleontology Memoir 18. Journal of Vertebrate Paleontology 38(Supplement). DOI: 10.1080/02724634.2017.1524383.
... The exoccipitals of Auroraceratops have three openings for cranial nerves X, XI, and XII, which is a condition seen in many basal neoceratopsians, such as Liaoceratops, Cerasinops (Chinnery and Horner, 2007), Montanoceratops (Chinnery and Weishampel, 1998;Makovicky, 2001), Leptoceratops, Protoceratops (Brown and Schlaikjer, 1940), and Bagaceratops (Maryanska and Osm olska, 1975). Ceratopsids only have two openings for these nerves (Dodson and Currie, 1990). ...
... They are also different from the strongly downcurved paroccipital processes seen in other ornithischian clades (Gilmore, 1924;Galton, 1974). The exoccipitals of leptoceratopsids (Chinnery and Weishampel, 1998;Makovicky, 2001;Chinnery and Horner, 2007) and protoceratopsids (Brown and Schlaikjer, 1940;Maryanska and Osm olska, 1975) are much more elongate than those of Auroraceratops. Among the basal neoceratopsians closest to Auroraceratops, Liaoceratops and Archaeoceratops have similar paroccipital processes as Auroraceratops, whereas the processes of Yamaceratops are more elongate (Makovicky and Norell, 2006). ...
... Montanoceratops has a dentary with a straight ventral margin similar to Auroraceratops in some respects (Chinnery and Weishampel, 1998;Makovicky, 2010). However, unlike Auroraceratops, the tooth row of Montanoceratops is not parallel to the ventral margin of the dentary. ...
Article
The basal neoceratopsian dinosaur Auroraceratops rugosus was described based on a single skull from the Gongpoquan Basin in northwestern Gansu Province, China. The genus is now known from over 80 specimens, including many from the neighboring Yujingzi Basin. Auroraceratops is one of the best-known basal neoceratopsians. Auroraceratops can be diagnosed by the following autapomorphies: inflated premaxillary teeth; a fungiform expansion of the lacrimal; large tuber caudodorsally on the dentary near the contact with the surangular; and tubercle on the lateral face of the dentary at about the middle of the mandible. Auroraceratops also has a combination of plesiomorphic and derived characters. It possesses characters plesiomorphic to Neoceratopsia, such as broad nasals (seen in basal ceratopsians, such as Yinlong), the absence of a lateral ridge on the surangular, a relatively high number of premaxillary teeth (three), and rugosity on the dentary, jugal, surangular, and sometimes the postorbital, which is in detail similar to that seen in chaoyangsaurids. At the same time, Auroraceratops possesses derived characters not seen in Liaoceratops, the earliest diverging member of Neoceratopsia. These features include an epijugal and a surangular wall lateral to the mandibular glenoid fossa. The cranial anatomy of the early horned dinosaur Auroraceratops rugosus is described. Citation for this article: Morschhauser, E. M., D. Li, H. You, and P. Dodson. 2019. Cranial anatomy of the basal neoceratopsian Auroraceratops rugosus (Ornithischia: Ceratopsia) from the Yujingzi Basin, Gansu Province, China; pp. 36–68 in Hailu You, Peter Dodson, and Eric Morschhauser (eds.), Auroraceratops rugosus (Ornithischia, Ceratopsia) from the Early Cretaceous of northwestern Gansu Province, China. Society of Vertebrate Paleontology Memoir 18. Journal of Vertebrate Paleontology 38(Supplement). DOI: 10.1080/02724634.2017.1399136.
... This reduction of exoccipital cranial nerve foramina from three to two is often cited as a synapomorphy for Ceratopsidae (e.g. Dodson & Currie 1990; Chinnery & Weishampel 1998). Makovicky (2001: 252), refers to this synapomorphy as a 'reduction of number of hypoglossal [XII] exits from three to two' in spite of the fact that he himself interpreted in the same paper these openings in Montanoceratops as for X, XI and XII. ...
... References A B C Brown & Schlaikjer 1940 XII, or XII 2 † XI, or XII 1 † IX and X, or IX, X, and XI * Galton 1974 XII IX Maryańska & Osmólska 1974 XII X and XI IX Maryańska & Osmólska 1975; Dodson & Currie 1990 XII XI IX and X Forster 1996; Chinnery & Weishampel 1998;Makovicky 2001 XII XI X Interpretation accepted in this work XII 3 XII 1+2 X and XI † 'more reasonable explanation' (Brown & Schlaikjer 1940: 193). & Osmólska 1974), Protoceratops andrewsi (C, modified from Brown & Schlaikjer 1940) and Psittacosaurus sibiricus (D, PM . ...
... In Psittacosaurus the clavicle is a short, rod-like, structure lying along the anterior margin of the scapula and coracoid at their junction and not contacting the opposite clavicle medially. Such a clavicle is characteristic also for Protoceratops (Brown & Schlaikjer 1940), but not for Montanoceratops, where the clavicles are slim, flat, S-shaped bones contacting the end of the scapula and coracoid laterally and, by the medial end, each other (Chinnery & Weishampel 1998). In Leptoceratops gracilis Brown the clavicles also contact each other medially, but have a unique boot-like shape and contact only the coracoid (Sternberg 1951). ...
Article
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Psittacosaurus sibiricus from the Aptian–Albian Ilek Formation at Shestakovo, Kemerovo Province, West Siberia, is represented by two almost complete adult skeletons, several associated groups of bones and numerous isolated bones of individuals ranging from post-hatchling to fully grown animals. Psittacosaurus sibiricus differs from nine other species of the genus by a unique combination of 32 diagnostic characters, six of which are autapomorphies of the species: small infratemporal fenestra, anteroposteriorly short premaxilla, short medial process of postorbital, deep cleft for qaudratojugal on jugal, extending to the posterior side of jugal horn, angular with prominent tuber and 23 presacrals. Psittacosaurus sibiricus is the sister species of P. sinensis, with which it shares the prominent pyramidal laterally projecting jugal horn, but more derived than the latter in having more developed palpebral and postorbital horns. The three lateral foramina on the exoccipital/opisthotic are interpreted as exits for cranial nerves X+XI, XII1+2 and XII3, in contrast with previous interpretations. Cranial nerve IX exits the brain cavity through the metotic fissure. Most Psittacosaurus localities are confined to lacustrine deposits and this animal undoubtedly inhabited areas around the great lakes widely distributed in Central Asia during the Early Cretaceous. The age of the Psittacosaurus biochron is estimated as Hauterivian–Albian.
... (i. e., Ryan and Currie, 1998;Chinnery et al., 1998). One additional genus has recently been described, Prenoceratops pieganensis (Chinnery, 2004a), and the current description is of another new genus and species, Cerasinops hodgskissi, thus doubling the number of North American genera and species in this taxonomic group. ...
... Supraoccipital-The Cerasinops supraoccipital indicates a definite contribution of this element to the foramen magnum, also found in Protoceratops, Leptoceratops, Bagaceratops, and most likely Montanoceratops (contrary to Chinnery and Weishampel, 1998;Makovicky, 2001). Dorsal to the foramen magnum a single prominent midline ridge extends up to the parietal ( Fig. 2A). ...
... Teeth-Preserved teeth of Cerasinops are nearly all worn and in place in the mandibles and maxillae. Tooth morphology conforms to that seen in Leptoceratops and Prenoceratops, but Cerasinops does not have a primary ridge on the buccal side of the dentary teeth as described for Montanoceratops (Chinnery and Weishampel, 1998). The tooth wear pattern of Cerasinops is the same as that found in all known North American genera as well as Udanoceratops from Asia. ...
Article
Basal (cladistically) neoceratopsians are relatively small, gracile members of Ceratopsia (‘horned” dinosaurs), which also includes larger forms such as Triceratops and Centrosaurus. The Asian basal neoceratopsians share some very important traits not found in any North American group until now, including a fenestrated frill and premaxillary teeth. Likewise, the North American basal taxa have some traits not found in the Asian forms, the most important of which is a very specialized tooth wear pattern. Cerasinops hodgskissi, a new basal neoceratopsian from the Lower Two Medicine River Formation of Montana, exhibits all of the above characters along with others previously found on only one of the two continents. The new species is a sister group to Leptoceratopsidae in a cladistic analysis, and is a link between the taxa on the two continents. Cerasinops also exhibits extremely interesting anatomical and histological features that indicate the possibility of bipedality in this taxon, a locomotor pattern not found previously in basal neoceratopsians (it has been suggested in some, but with little evidence).
... As on the maxillary teeth, wear facets are steeply inclined or vertical (Sternberg 1951). At the base of this wear facet, there is a horizontal shelf, as is also seen in other North American basal neoceratopsians and some Asian forms, including Udanoceratops and Archaeoceratops (Sternberg 1951;Kurzanov 1992;Chinnery and Weishampel 1998;Chinnery 2004;Chinnery and Horner 2007;You et al. in press). It is difficult to confirm the distribution of enamel in the teeth of CMN 8889 since the entire specimen is stained black. ...
... Worn dentary teeth of North American basal neoceratopsians, as well as Udanoceratops and a new species of Archaeoceratops from Asia, exhibit horizontal shelves in addition to vertical or subvertical wear facets (Sternberg 1951;Kurzanov 1992;Chinnery and Weishampel 1998;Chinnery 2004;Chinnery and Horner 2007;You et al. in press), which suggests that shearing and crushing functions were combined in these taxa (Sternberg 1951;Ostrom 1966). However, the apex of the maxillary tooth bears no horizontal wear facet to occlude with the horizontal shelf of the dentary tooth. ...
... Although isolated teeth are considered of little taxonomic utility, dental characters, including the notch on cingulum of maxillary teeth in Leptoceratops (Fig. 10B), V-shaped indentations of the maxillary tooth crown in Bagaceratops rather than U-shaped depressions in other basal ceratopsians (Maryańska and Osmólska 1975), and a primary ridge on the labial side of dentary tooth crown in Montanoceratops (Chinnery and Weishampel 1998), can be utilized for identification. In addition, the various species of Psittacosaurus differ in the relative sizes of the primary ridges in maxillary and dentary tooth crowns (Sereno 1990). ...
Article
The dental structure of basal ceratopsians is described. Evolutionary trends in maxillary and dentary teeth of basal ceratopsians include decrease and possible loss of enamel on the occluding side of tooth crowns, increase in the angle of wear facet, development of a prominent primary ridge and deep indentations on mesial and distal sides of the primary ridge, and increase in tooth size in neoceratopsians. Premaxillary teeth in the basalmost ceratopsian Yinlong and basal neoceratopsian Archaeoceratops oshimai exhibit wear facets and denticles along the carina, which imply use for feeding. Maxillary and dentary teeth of basal ceratopsians were probably not as effective in feeding as those in ceratopsids because of the relatively less prominent primary ridges. Some dental characters can be used to identify taxon and tooth position of isolated basal ceratopsian teeth.
... Makovicky (2001) identified a braincase (AMNH 5244) of Montanoceratops from the Maastrichtian beds of the upper Horseshoe Canyon Formation of Alberta; however, the exact locality for the quarry of this specimen is unknown and it may have been collected from the Scollard Formation, which also has extensive exposure in the area. A review of Montanoceratops by Makovicky (2010), building on work by Chinnery and Weishampel (1998), highlighted important information about the skeleton of Montanoceratops including the fact that the nasal is unknown for the taxon. Miyashita et al. (2010) clarified that the provenance of TMP 82.11.1, a partial neoceratopsian skeleton referred to Montanoceratops, is derived from the Willow Creek Formation (Maastrichtian), rather than the Campanian Belly River Group of Alberta as suggested by Ryan and Currie (1998). ...
... Additionally, in Prenoceratops, the flange is separated from the ventral margin by a notch. Unescoceratops is similar to Leptoceratops, Montanoceratops, and Zhuchengceratops in having a dentary that is deeper anteriorly than it is posteriorly (Chinnery and Weishampel, 1998), but the presence of the chin gives its dentary a distinct hatchet-shape when viewed laterally. Unescoceratops shares with Cerasinops a distinctly recumbent coronoid process, but it can be differentiated from this taxon in having the contacts for the surangular and articular being positioned more posteriorly below the coronoid process. ...
... Finally, the separate codings used by Makovicky (2010) for the Montanoceratops specimens AMNH 5464, AMNH 5244, and MOR 542 were collapsed into one data line designated as Montanoceratops. Characters 72e83, 145, 146, Brown and Schlaikjer, 1940); Montanoceratops cerorhynchus (modified from Chinnery and Weishampel, 1998); Cerasinops hodgskissi MOR 300 (modified from Chinnery and Horner, 2007); Prenoceratops pieganensis (MNHCM, no number); Udanoceratops tschizhovi PIN 3907/11 (modified from Kurzanov, 1992); Leptoceratops gracilis (CMN 8889); Zhuchengceratops inexpectus (ZCDM V0015); Unescoceratops koppelhusae (TMP 95.12.6). Gryphoceratops morrisoni (ROM 56635). ...
... Together with the scapula and the coracoid, the furcula also participates in the formation of the canalis triosseus, which houses a strong tendon connecting the supracoracoideus muscles to the humerus; this system is responsible for lifting the wings during the flight recovery stroke 4,[6][7][8][9]12,13 . The homology of the furcula relative to the elements of the pectoral girdle in non-avian tetrapods is debated [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] . The ancestry of the avian furcula from the homonymous element widespread in non-avian theropods is well-supported [14][15][16][17][18][19][20] , indicating that this bone evolved well-before the origin of avian flight among bipedal ground-dwelling dinosaurs. ...
... It is usually assumed that dinosaurs retained the clavicles all along the avian stem and lost the interclavicle during their earliest evolution 18,[21][22][23][24] . Unfused clavicles are documented in both the ornithischian 29,30 and sauropodomorph 22,24 lineages, with at least the latter group occasionally retaining a rod-like interclavicle 22 . Regardless its homology, the origin of the furcula is thus firmly constrained close to the divergence of theropods from the other dinosaurs 18 . ...
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The furcula is a distinctive element of the pectoral skeleton in birds, which strengthens the shoulder region to withstand the rigor of flight. Although its origin among theropod dinosaurs is now well-supported, the homology of the furcula relative to the elements of the tetrapod pectoral girdle (i.e., interclavicle vs clavicles) remains controversial. Here, we report the identification of the furcula in the birdlike theropod Halszkaraptor escuilliei . The bone is unique among furculae in non-avian dinosaurs in bearing a visceral articular facet in the hypocleideal end firmly joined to and overlapped by the sternal plates, a topographical pattern that supports the primary homology of the furcula with the interclavicle. The transformation of the interclavicle into the furcula in early theropods is correlated to the loss of the clavicles, and reinforced the interconnection between the contralateral scapulocoracoids, while relaxing the bridge between the scapulocoracoids with the sternum. The function of the forelimbs in theropod ancestors shifted from being a component of the locomotory quadrupedal module to an independent module specialized to grasping. The later evolution of novel locomotory modules among maniraptoran theropods, involving the forelimbs, drove the re-acquisition of a tighter connection between the scapulocoracoids and the interclavicle with the sternal complex.
... However, excellent postcranial material is known for many taxa, making it possible to identify diagnostic features in RBCM P900 despite the absence of cranial material for this specimen. Leptoceratops, Montanoceratops, and Cerasinops are all known from multiple partial or complete skeletons (Chinnery & Weishampel, 1998;Chinnery & Horner, 2007;Ostrom, 1978;Brown & Schlaikjer, 1942;Sternberg, 1951;Brown, 1914), and Prenoceratops specimens described by Chinnery (2004) come from a single mixed bonebed from which multiple composite skeletons have been assembled. ...
... Campanian Laramidian taxa include Cerasinops from the lower Two Medicine Formation, Prenoceratops from the upper Two Medicine Formation of Montana and the Oldman Formation of Alberta, and Unescoceratops from the lower Dinosaur Park Formation (Chinnery, 2004;Chinnery & Horner, 2007;Ryan et al., 2012). Only two genera are known from the Maastrichtian of Laramidia: Montanoceratops from the St Mary River and Horseshoe Canyon formations (Brown & Schlaikjer, 1942;Chinnery & Weishampel, 1998;Makovicky, 2001), and Leptoceratops from the Scollard and Hell Creek formations (Sternberg, 1951;Ott, 2007) and the Pinyin Conglomerate (McKenna & Love, 1970). RBCM P900 was most likely collected from approximately 68.2-67.2 ...
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A partial dinosaur skeleton from the Sustut Basin of northern British Columbia, Canada, previously described as an indeterminate neornithischian, is here reinterpreted as a leptoceratopsid ceratopsian, Ferrisaurus sustutensis , gen. et. sp. nov. The skeleton includes parts of the pectoral girdles, left forelimb, left hindlimb, and right pes. It can be distinguished from other named leptoceratopsids based on the proportions of the ulna and pedal phalanges. This is the first unique dinosaur species reported from British Columbia, and can be placed within a reasonably resolved phylogenetic context, with Ferrisaurus recovered as more closely related to Leptoceratops than Montanoceratops . At 68.2–67.2 Ma in age, Ferrisaurus falls between, and slightly overlaps with, both Montanoceratops and Leptoceratops , and represents a western range extension for Laramidian leptoceratopsids.
... A small bone that is located at the lateralmost side of metacarpal IV may represent metacarpal V, although it may also be part of the proximal end of metacarpal IV (Fig. 8B). Five metacarpals are known in the neoceratopsians Auroraceratops, Protoceratops, Leptoceratops and Montanoceratops (Brown & Schlaikjer 1940;Chinnery & Weishampel 1998;Morschhauser 2012), as well as in basal ornithischians such as Heterodontosaurus (Santa Luca 1980), Lesothosaurus (Baron et al. 2017) and Hexinlusaurus (He & Cai 1984). However, only four metacarpals are preserved in the most complete specimens of Psittacosaurus (Sereno 1990). ...
... The phalangeal formula of Yinlong is 2-3-4-?-?. There are no preserved phalanges associated with metacarpal 4. The phalangeal formula is 2-3-4-1-0 in Psittacosaurus (Sereno 1990), 2-3-4-2-1 in Auroraceratops (Morschhauser 2012) and 2-3-4-3-1(or 2) in Protoceratops, Leptoceratops and Montanoceratops (Brown & Schlaikjer 1940;Chinnery & Weishampel 1998). The phalangeal count for the first three digits is stable in basal ornithischians (Sereno 2012), but it is increased in digits 4 and 5 in derived ceratopsians. ...
Article
Ceratopsia includes some of the best-known ornithischian dinosaurs. Many species are erected based on cranial elements alone, and the postcranial skeletons are either missing or undescribed in many taxa. Here we provide the first detailed postcranial description of Yinlong downsi based on the holotype and eight other well-preserved skeletons. Yinlong downsi from the early Late Jurassic Shishugou Formation of the Wucaiwan area, Xinjiang, China, represents one of the most basal ceratopsians. The detailed study of the postcranial skeleton reveals one feature unique to it among ceratopsians: a blade-like prepubic process of the pubis with an elongate notch near its ventral margin. The postcranial material of Yinlong shares some unique features with that of the ornithischian Stenopelix valdensis from the Early Cretaceous of Germany, and provides further evidence that the latter is a basal ceratopsian. A comprehensive phylogenetic analysis of basal ornithischians was built based on 72 taxa and 380 characters. Most of the characters are illustrated for the first time in order to clarify character states. The new ornithischian phylogeny confirms that Yinlong belongs to Chaoyangsauridae. Chaoyangsaurids and Psittacosaurus form a monophyletic group that is sister to all other ceratopsians. The new phylogeny also supports Stenopelix valdensis as a basal ceratopsian, and Mosaiceratops to be close to Coronosauria. Additionally, the new phylogeny agrees with other recent analyses that place heterodontosaurids as the most basal ornithischians rather than with marginocephalians. Furthermore, Isaberrysaura, which has been hypothesized to be a basal ornithopod, is recovered as one of the most basal stegosaurs for the first time. The former ‘hypsilophodontid’ taxa are recovered within Ornithopoda rather than outside Cerapoda, and Jeholosauridae is shown to be valid in this analysis.
... 8887 (Brown, 1914) housed at the PIN. Published data were analyzed as well (Brown, 1914;Schlaikjer, 1940, 1942;Sternberg, 1951;Chinnery and Weishampel, 1998;etc.). ...
... During the study of specimen PIN, no. 614-33, we considered the possibility of displaying the intraspecific variability characteristic of protoceratopsids (Brown and Schlaikjer, 1940;Rozhdestvenskii, 1965;Kurzanov, 1972;Maryanska and Osmólska, 1975; Bainoceratops efremovi , a New Protoceratopid Dinosaur (Protoceratopidae, Neoceratopsia) from the Bain-Dzak Locality (South Mongolia) TERESCHENKO, ALIFANOV Dodson, 1976), including age-related variations (Brown and Schlaikjer, 1940;Sternberg, 1951;Chinnery and Weishampel, 1998;Tereschenko, 2001) and sexual dimorphism, well-known for the axial skeleton of terrestrial tetrapods (Barbadillo and Sanz, 1983;Porkert and Grosseova, 1984;Tereschenko, 1991aTereschenko, , 1997Tereschenko, , 2001. Because the discussed specimen differs appreciably from Protoceratops andrewsi and other protoceratopids with known postcranial morphology, it is described as a new genus and species, Bainoceratops efremovi gen. ...
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A new horned dinosaur, Bainoceratops efremovi gen. et sp. nov., is described on the basis of vertebral series from the well-known Bain-Dzak locality (Mongolia). The new form is distinguished from Protoceratops andrewsi Granger et Gregory, 1923, which is typical of Djadokhta deposits, by vertebral morphology and shows close relationships to Udanoceratops tschizhovi Kurzanov, 1992 and Leptoceratops gracilis Brown, 1914 in the following characters. The cranial surfaces of the centra of the presacral vertebrae are concave, while the caudal surfaces are flat. The diapophyses of the ninth dorsal vertebra are round in cross section, and the interprezygapophyseal spaces in this and the next vertebra are narrow. The synapophyseal facets of the posteriormost dorsal vertebra are sculptured.
... The lack of strong eversion of the dorsal margin of the iliac blade distinguishes Ischioceratops from iguanodontians (Fig 6B1-6B5), Pachycephalosaurs ( Fig 6D1) and ceratopsids (Fig 6F1-6F4). However, Protoceratops (Fig 6E6), Montanoceratops (Fig 6E7, [42]) and Leptoceratops are more similar to Ischioceratops in that the iliac blade is only slightly everted in these taxa. ...
... Outlines are not to scale. A1, Heterodontosaurus tucki, outlined from[45]; A2, Othnielia rex, outlined from[46]; A3, Hypsilophodon foxii, outlined from[34]; A4, Hexinlusaurus multidens, based on ZDM 6001, outlined from[47]; A5 Agilisaurus louderbacki, based on ZDMT 6011, outlined from[47]; B1, Tenontosaurus tilleti, outlined from[48]; B2, Dryosaurus altus, outlined from[49]; B3, Camptosaurus dispar, outlined from[50]; B4, Iguanodon atherfieldensis, outlined from[50]; B5, Ouranosaurus nigeriensis, outlined from[50]; C1, Gryposaurus incurvimanus, outlined from[51]; C2, Parasaurolophus walkeri, based on FMNH P27393, outlined from[52]; C3, Corythosaurus casuarius, outlined from[53]; C4, Gilmoreosaurus mongoliensis based on AMNH 6551, outlined from[52]; C5, Edmontosaurus regalis ROM 5167, outlined from[54]; C6, Shantungosaurus giganteus, outlined from[62]; D1, Homocephale calathocercos, outlined from[21]; E1, Yinlong downsi, based on IVPP V18679; E2, Psittacosaurus neimongoliensis, based on IVPP 12-0888-2, outlined from[55]; E3, Archaeoceratops oshimai, based on IVPP V11114, outlined from[24]; E4, Auroraceratops rugosus, outlined from[29]; E5, Protoceratops andrewsi, outlined from[4]; E6, Leptoceratops gracillis, based on NMC 8889, outlined from[56]; E7, Montanoceratops cerorhynchus, based on AMNH 6466, outlined from[42]; E8, Ischioceratops zhuchengensis, right and left ilium and ischium, based on ZCDM V0016; F1, Centrosaurus apertus, outlined from[57]; F2, Chasmosaurus belli, outlined from,[58]; F3, Triceratops horridus, based on YPM 1821, outlined from[59]; F4, Styracosaurus albertensis, based on AMNH 5372, outlined from[60].doi:10.1371/journal.pone.0144148.g008Table 1. Measurements of the caudal vertebrae of the holotype specimen of Ischioceratops zhuchengensis (ZCDM V0016). ...
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The partial skeleton of a leptoceratopsid dinosaur, Ischioceratops zhuchengensis gen. et sp. nov., was excavated from the bone-beds of the Upper Cretaceous Wangshi Group of Zhucheng, Shandong Province, China. This fossil represents the second leptoceratopsid dinosaur specimen recovered from the Kugou locality, a highly productive site in Zhucheng. The ischium of the new taxon is morphologically unique among known Dinosauria, flaring gradually to form an obturator process in its middle portion and resembling the shaft of a recurve bow. An elliptical fenestra perforates the obturator process, and the distal end of the shaft forms an axehead-shaped expansion. The discovery of Ischioceratops increases the known taxonomic diversity and morphological disparity of the Leptoceratopsidae.
... The basipterygoid processes are relatively robust and short as in Liaoceratops and unlike the more elongate and slender processes of Protoceratops or the recurved ones that are diagnostic of leptoceratopsids (Chinnery and Weishampel, 1998;Makovicky, 2001). They project lateroventrally below the hypophysial fossa as in other neoceratopsians, but unlike psittacosaurids and other outgroups, in which they are directed rostrolaterally. ...
... This ridge overhangs the surface of the mandible and extends on to the dentary in Yamaceratops as in Archaeoceratops, Protoceratops, and Bagaceratops. A more reduced ridge is present on the surangular of a juvenile Montanoceratops specimen (Chinnery and Weishampel, 1998), but the surangular of the adult holotype is too poorly preserved to confirm its size and presence. Leptoceratops, Udanoceratops, Prenoceratops, and ceratopsids bear either a very faint, rounded ridge or have no ridge at all (Chinnery, 2004). ...
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A new basal neoceratopsian taxon from the eastern Gobi Desert is described. Yamaceratops dorngobiensis, tax. nov., is probably of late Early Cretaceous age, and occupies a phylogenetic position intermediate between Liaoceratops and Archaeoceratops. It is the most basal taxon to display a number of traditional neoceratopsian synapomorphies concentrated in the cheek region and mandible. These include presence of an epijugal, lateral displacement of the coronoid process, a lateral ridge on the surangular for insertion of the jaw adductors, and a lateral wall to the mandibular glenoid. Yamaceratops shares two synapomorphies (tubercles on the ventral edge of the angular and shape of the jugal) with Liaoceratops, indicating that the transient presence of derived characters may be prevalent in the early evolutionary history of Ceratopsia. Yamaceratops shares aspects of frill morphology with Liaoceratops and Leptoceratops that suggest a function unrelated to display for this anatomical structure in basal neoceratopsians, and hints at a more complex evolutionary history for ceratopsian frills. Considerations of patristic distances and mosaic evolution among basal neoceratopsian taxa indicate that a greater diversity of these animals remains undiscovered.
... A cast of a Leptoceratops gracilis skeleton (NMC 8887) stored at PIN was used for comparisons. Published data on Montanoceratops cerorhynchus (Brown and Schlaikjer, 1942;Chinnery and Weishampel, 1998) and L gracilis (Sternberg, 1951;Russel, 1970) were also used. ...
... The determination of age stages of protoceratopsids was performed by two methods based on morphologi cal changes and on the extent to which sexual dimor phism in the vertebral column and pelvic girdle devel oped. In the first case (Table 2), original data and previ ously published data on the age variation in protoceratopsid postcranial skeletons were used (Brown and Schlaikjer, 1940;Sternberg, 1951;Chinnery and Weishampel, 1998). The main difficulties encountered in distinguishing age stages were associated with the absence of data on the axial skeleton of juveniles. ...
... This condition is retained in the basal neoceratopsians Chaoyangsaurus and Liaoceratops. In all the other neoceratopsians, the enamel is absent on the lingual side of the maxillary teeth and on the labial side of the dentary teeth (CHINNERY & WEISHAMPEL, 1998;SERENO, 2000;MAKOVICKY, 2001;YOU & DODSON, 2003), as observed in the teeth referred to Craspedodon. The corollary of this condition is the development of a single well-defined triturating surface on the side of the crown that is not covered with enamel. ...
... In ceratopsids, teeth occlude at a more vertical angle, with an apical plane orientation more than 45° from the primary axis of the root (SERENO, 2000). In Leptoceratops and Montanoceratops, teeth also occlude at a vertical angle, but dentary teeth have a horizontal shelf on the labial side (CHINNERY & WEISHAMPEL, 1998;MAKOVICKY, 2001;YOU & DODSON, 2003). ...
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Craspedodon lonzeensis DOLLO, 1883 is based on three teeth discovered in the Lonzée Member (?Coniacian-Santonian, Upper Cretaceous) in the surroundings of the village of Lonzée (Namur Province, Belgium). Previous authors identified Craspedodon as an iguanodontian dinosaur. We rather propose that these fossils belong to a neoceratopsian dinosaur, because of the following characters: the enamelled side of the crown bears deep indentations and a prominent basal cingulum, the opposite side of the crown is very convex vertically and bulbous in mesial view, and secondary ridges start from the apical edge but end prior to the base of the crown. Within Neoceratopsia, it is suggested that Craspedodon has more affinities with Ceratopsoidea (sensu You & DODSON, 2003) than with Protoceratopsidae. It is the first time that ceratopsian dinosaurs are described in Europe. Neoceratopsians probably migrated from Asia into Europe during the Aptian-Albian, when intermittent land bridges were established across the Turgai Straits. This implies a relatively long ghost lineage for neoceratopsians in Europe, of more than nine million years, between their migration towards Europe and their proposed presence in the Lonzée Member.
... The proximal end of the left clavicle is marginally thicker than the rest of this element and gently tapers laterally. Among ornithischians, clavicles are mostly known in basal ceratopsians and neoceratopsians from the Cretaceous, for example, Psittacosaurus mongoliensis (Fairfield, 1924;Sereno, 1990), Psittacosaurus sibiricus (Averianov et al., 2006), Auroraceratops rugosus (Morschhauser et al., 2018a), Leptoceratops gracilis (Sternberg, 1951), Montanoceratops cerorhynchos (Chinnery and Weishampel, 1998), and Protoceratops andrewsi (Brown and Schlaikjer, 1940) but are also present in the basal thyreophoran Scelidosaurus harrisonii (Norman, 2020) as well as a new, undescribed taxon that is purported to be at the base of Ornithopoda (Spencer et al., 2020). The clavicles of H. tucki are similar to those of ceratopsians in contouring the anterior margin of the scapulocoracoid, with no apparent contact present between the clavicles along their length. ...
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Ornithischian dinosaurs were ecologically prominent herbivores of the Mesozoic Era that achieved a global distribution by the onset of the Cretaceous. The ornithischian body plan is aberrant relative to other ornithodiran clades, and crucial details of their early evolution remain obscure. We present a new, fully articulated skeleton of the early branching ornithischian Heterodontosaurus tucki . Phase-contrast enhanced synchrotron data of this new specimen reveal a suite of novel postcranial features unknown in any other ornithischian, with implications for the early evolution of the group. These features include a large, anteriorly projecting sternum; bizarre, paddle-shaped sternal ribs; and a full gastral basket – the first recovered in Ornithischia. These unusual anatomical traits provide key information on the evolution of the ornithischian body plan and suggest functional shifts in the ventilatory apparatus occurred close to the base of the clade. We complement these anatomical data with a quantitative analysis of ornithischian pelvic architecture, which allows us to make a specific, stepwise hypothesis for their ventilatory evolution.
... Neurocentral suture fusion data are rare among ornithischians. Several ceratopsians possess anterior-to-posterior patterns of neurocentral suture fusion ['Brachyceratops' (Gilmore, 1917); Montanoceratops (Chinnery & Weishampel, 1998)], but others contradict this [Chasmosaurus (Figs 12 & 14 in Currie et al., 2016); Ceratopsia sp. (Xu et al., 2006)]. ...
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Morphology forms the most fundamental level of data in vertebrate palaeontology because it is through interpretations of morphology that taxa are identified, creating the basis for broad evolutionary and palaeobiological hypotheses. Assessing maturity is one of the most basic aspects of morphological interpretation and provides the means to study the evolution of ontogenetic changes, population structure and palaeoecology, life‐history strategies, and heterochrony along evolutionary lineages that would otherwise be lost to time. Saurian reptiles (the least‐inclusive clade containing Lepidosauria and Archosauria) have remained an incredibly diverse, numerous, and disparate clade through their ~260‐million‐year history. Because of the great disparity in this group, assessing maturity of saurian reptiles is difficult, fraught with methodological and terminological ambiguity. We compiled a novel database of literature, assembling >900 individual instances of saurian maturity assessment, to examine critically how saurian maturity has been diagnosed. We review the often inexact and inconsistent terminology used in saurian maturity assessment (e.g. ‘juvenile’, ‘mature’) and provide routes for better clarity and cross‐study coherence. We describe the various methods that have been used to assess maturity in every major saurian group, integrating data from both extant and extinct taxa to give a full account of the current state of the field and providing method‐specific pitfalls, best practices, and fruitful directions for future research. We recommend that a new standard subsection, ‘Ontogenetic Assessment’, be added to the Systematic Palaeontology portions of descriptive studies to provide explicit ontogenetic diagnoses with clear criteria. Because the utility of different ontogenetic criteria is highly subclade dependent among saurians, even for widely used methods (e.g. neurocentral suture fusion), we recommend that phylogenetic context, preferably in the form of a phylogenetic bracket, be used to justify the use of a maturity assessment method. Different methods should be used in conjunction as independent lines of evidence when assessing maturity, instead of an ontogenetic diagnosis resting entirely on a single criterion, which is common in the literature. Critically, there is a need for data from extant taxa with well‐represented growth series to be integrated with the fossil record to ground maturity assessments of extinct taxa in well‐constrained, empirically tested methods.
... There are four main matrices that, with some modification, form the basis for our present understanding of basal neoceratopsian phylogeny. One was developed by Brenda Chinnery and first seen in Chinnery and Weishampel (1998). It has passed through two further iterations (Chinnery, 2004;Chinnery and Horner, 2007) (Fig. 4B). ...
Article
Basal neoceratopsians are a relatively diverse group of small- to medium-sized herbivorous dinosaurs from the Early to Late Cretaceous of Asia and North America. Although known for over a century, this group has only relatively recently received intense independent study, tied to the rapid increase in known diversity since 1997. Auroraceratops rugosus is one of these recently discovered species and is one of the best-known basal neoceratopsians, being represented by over 80 specimens, and is also the most completely represented neoceratopsian from the Early Cretaceous. A phylogenetic analysis focusing on non-ceratopsid ceratopsians examines the phylogenetic context of Auroraceratops. The analysis is based on a new matrix of 41 taxa and 257 characters. The results recover an Auroraceratops-Aquilops-ZPAL MgD-I/156 clade within basal Neoceratopsia that is sister to a clade composed of Asiaceratops, Yamaceratops, Mosaiceratops, and the larger clades Leptoceratopsidae and Coronosauria. This phylogeny recovers a monophyletic Coronosauria, Leptoceratopsidae, and Protoceratopsidae. Helioceratops is recovered as sister to the rest of Leptoceratopsidae, Ischioceratops is recovered nested within Leptoceratopsidae, and the enigmatic genus Mosaiceratops is recovered as a basal neoceratopsian, sister to Yamaceratops. Yinlong, and Hualianceratops are recovered in an expanded Chaoyangsauridae, and the genus Psittacosaurus is recovered as the earliest diverging lineage in Ceratopsia. Ajkaceratops, the only European ceratopsian, is robustly recovered as sister to the rest of Ceratopsoidea. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Morschhauser, E. M., H. You, D. Li, and P. Dodson. 2019. Phylogenetic history of Auroraceratops rugosus (Ceratopsia: Ornithischia) from the Lower Cretaceous of Gansu Province, China; pp. 117–147 in Hailu You, Peter Dodson, and Eric Morschhauser (eds.), Auroraceratops rugosus (Ornithischia, Ceratopsia) from the Early Cretaceous of northwestern Gansu Province, China. Society of Vertebrate Paleontology Memoir 18. Journal of Vertebrate Paleontology 38(Supplement). DOI: 10.1080/02724634.2017.1509866.
... The preserved caudal series of the basal thyreophoran Scutellosaurus show this sequential type as well (Rosenbaum & Padian 2000). Neoceratopsians seem to possess the opposite sequence, mainly due to their autapomorphic syncervical (Chinnery & Weishampel, 1998, Irmis 2007. ...
Ornithopoda is a diverse clade of ornithischian dinosaurs, which superficially shows a conservative postcranial bauplan. A closer look, however, reveals many morphological changes during their evolution which often reflect adaptations towards larger and heavier bodies, as well as towards more graviportal and, at least facultative, quadrupedal locomotion. To study the pattern and distribution of these changes, analysis of the ontogeny of a well-preserved taxon, which ideally represents an intermediate stage of both body size and phylogenetic position, is crucial. Dysalotosaurus, a basal iguanodontian ornithopod, is known from numerous well preserved skeletal elements of different ontogenetic stages and is here used as a model taxon. Although somatically mature individuals of Dysalotosaurus are not known, a combination of qualitative and quantitative methods reveals several aspects of its ontogeny, such as precocial breeding behavior, the posterior-to-anterior sequence of neurocentral suture closure, and the increasing robustness of many parts of the skeleton. Additionally, the ontogeny of Dysalotosaurus also demonstrates that morphological changes in the ornithopod postcranium were influenced by a mosaic of different heterochronic processes taking place even within single skeletal elements with changing relative intensity and developmental sequence.
... Dentary, posterior extent of tooth row: (0) -terminates anterior to the center of the coronoid process (1) -terminates even with the coronoid process (2) -terminates posterior to the coronoid process (Brown & Schlaikjer, 1940a;Chinnery and Weishampel 1998;modified from Makovicky and Norell, 2006:82;Sampson et al., 2010:118;Farke et al., 2011:73) ...
... Body size commonly is used as a proxy for ontogenetic status and morphological maturity (e.g. Colbert, 1990;Chinnery & Weishampel, 1998;Benton et al. 2000;Hunt, 2001;Currie, 2003;Bybee et al. 2006;Heckert et al. 2006;Buckley et al. 2010;Carpenter, 2010;Piechowski et al. 2014;Griffin & Nesbitt, 2016a). However, ontogenetic status, body size, and morphological maturity as determined by ontogenetic characters may all be somewhat disjunctive, with similarly sized individuals possessing differing levels of morphological maturity in early dinosaurs (Griffin & Nesbitt, 2016b), and perhaps even in all non-avian dinosaurs (Hone et al. 2016). ...
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Understanding ontogenetic patterns is important in vertebrate paleontology because the assessed skeletal maturity of an individual often has implications for paleobiogeography, species synonymy, paleobiology, and body size evolution of major clades. Further, for many groups the only means of confidently determining ontogenetic status of an organism is through the destructive process of histological sampling. Although the ontogenetic patterns of Late Jurassic and Cretaceous dinosaurs are better understood, knowledge of the ontogeny of the earliest dinosaurs is relatively poor because most species-level growth series known from these groups are small (usually, maximum of n ~ 5) and incomplete. To investigate the morphological changes that occur during ontogeny in early dinosaurs, I used ontogenetic sequence analysis (OSA) to reconstruct developmental sequences of morphological changes in the postcranial ontogeny of the early theropods Coelophysis bauri and Megapnosaurus rhodesiensis, both of which are known from large sample sizes (n = 174 and 182, respectively). I found a large amount of sequence polymorphism (i.e. intraspecific variation in developmental patterns) in both taxa, and especially in C. bauri, which possesses this variation in every element analyzed. Megapnosaurus rhodesiensis is similar, but it possesses no variation in the sequence of development of ontogenetic characters in the tibia and tarsus. Despite the large amount of variation in development, many characters occur consistently earlier or later in ontogeny and could therefore be important morphological features for assessing the relative maturity of other early theropods. Additionally, there is a phylogenetic signal to the order in which homologous characters appear in ontogeny, with homologous characters appearing earlier or later in developmental sequences of early theropods and the close relatives of dinosaurs, silesaurids. Many of these morphological features are important characters for the reconstruction of archosaurian phylogeny (e.g. trochanteric shelf). Because these features vary in presence or appearance with ontogeny, these characters should be used with caution when undertaking phylogenetic analyses in these groups, since a specimen may possess certain character states owing to ontogenetic stage, not evolutionary relationships.
... Contribution of the supraoccipital to the foramen magnum also occurs in the neoceratopsian Leptoceratops gracilis (Sternberg, 1951) and Bagaceratops rozhdestvenskyi (Maryanska and Osmólska, 1975). Chinnery and Weishampel (1998) confirm that the paired exoccipitals meet above the foramen magnum and exclude the supraoccipital from any contribution to the foramen magnum in a juvenile braincase of Montanaceratops cerorhynchus (MOR 542). Fusion of the supraoccipital with the exoccipitals obscures this arrangement in an isolated braincase of M. cerorhynchus (AMNH 5244) described by Makovicky (2001). ...
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The discovery of the smallest Triceratops skull (UCMP 154452) provides a new ontogenetic end member for the earliest stage of ceratopsid (Centrosaurinae plus Chasmosaurinae) cranial development. The lack of co-ossification among the parietal, squamosals, postorbitals, quadratojugal arch, and the braincase preserves sutural contacts and bone surfaces that later become obscured in adults. The ability to document the early development and morphology of the horns and frill in Triceratops allows a reevaluation of their functional roles. UCMP 154452 shows that the cranial ornamentation of the frill and the postorbital horns were not restricted to adults, but began at an early age in this species. This evidence supports the hypothesis that the function of ceratopsid horns and frills was potentially important for visual communication and species recognition because in this young form it could not have functioned in sexual display. Although some features of UCMP 154452 anticipate or mimic the adult character states, some braincase characters recapitulate the juvenile and adult stages of more basal neoceratopsians.
... Figures 3 and 4 summarize much of the work over the past decade (Gauthier, 1986;Holtz, 1994Holtz, , 2000Sues, 1997;Forster et al., 1998;Makovicky and Sues, 1998;Sereno, 1999Sereno, , 2001Currie and Carpenter, 2000;Chiappe, 2001), with particular attention to the theropods. Additional work discussing relationships within the terminal taxa shown in Figure 3 can be found in Sereno (1986Sereno ( , 1991b, Weishampel et al. (1990), Forster (1990Forster ( , 1997, Upchurch (1995), Currie and Padian (1997), Wilson and Sereno (1998), Chinnery and Weishampel (1998), Head (1998), andMakovicky (2001). ...
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The basic structure of archosaurian phylogeny is understood to include two primary crown-group lineages—one leading to living crocodiles and including a broad diversity of Triassic animals (e.g., phytosaurs, rauisuchians, aetosaurs), and another leading to dinosaurs (living and extinct). These lineages were established by the middle Triassic. A few extinct groups remain controversial, such as the pterosaurs, and debate persists over the phylogenetic relationships among extant bird lineages, which have proved difficult to resolve, and divergence timing estimates within Aves and Crocodylia remain the source of contention. A few analyses support a close relationship between archosaurs and turtles, or even a nesting of turtles within Archosauria. All sources of information used to resolve these issues have weaknesses, and these problems all involve highly derived lineages when they first appear in the fossil record.
... Next we reviewed the fossil record. Although paired, clavicle-like elements have been reported for various non-theropod dinosaurs (e. g., basal ceratopsians, prosauropods; Chinnery & Weishampel 1998;Yates & Vasconcelos 2005) and the pectoral apparatus of basal ornithodirans (the immediate ancestors of dinosaurs) remains poorly understood. Therefore, it remains uncertain if the furcula of theropods represents the fusion of clavicles or if the paired elements of non-theropods represent the non-fusion of the interclavicular primordia. ...
... In western North America, the oldest welldated and well-identified lambeosaurines have been discovered in Upper Campanian formations (WEISHAMPEL & HORNER, 1990); all belong to the advanced parasaurolophini or corythosaurini clades. It means that lambeosaur-ines migrated towards western North America before or at the beginning of the late Campanian, like many other dinosaur taxa: basal Neoceratopsia (CHINNERY and WEISHAMPEL, 1998), Ceratopsidae (NESSOV & KAZNYSH- KINA, 1989), Ankylosauridae (MARYANSKA, 1977), Tyrannosauridae (MADER & BRADLEY, 1989;BUFFETAUT et al, 1996), and Troodontidae (RUSSELL & DONG, 1993). During most of the Late Cretaceous, an interior seaway divided North America into a western Cordilleran region and an eastern shield region. ...
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Aralosaurus tuberiferus Rozhdestvensky, 1968 (Dinosauria: Hadrosauridae) is based on a fragmentary skull from the Beleutinskaya Svita (?Turonian, Late Cretaceous) from the Sakh-Sakh locality of central Kazakhstan. Redescription of the type material reveals that it is a valid taxon, characterised by a hollow nasal crest-like structure located far in front of the orbits and by a well-developed curved crest on the maxilla that borders laterally the caudal part of the premaxillary shelf Phylogenetic analysis, based on 36 cranial characters, indicates that A. tuberiferus is the most basal lambeosaurine hadrosaurid known to date; it is therefore not a gryposaur-like hadrosaurine as previously described. Lambeosaurines originated from Asia and then migrated to North America before or at the beginning of the late Campanian. They remained well diversified in eastern Asia until the late Maastrichtian.
... Description. Anteroposteriorly shorter than mediolaterally wide (Table 1), as in all non-ungual manual phalanges of Leptoceratops gracilis (Brown 1914;You & Dodson 2004) and Montanoceratops cerorhynchus (Chinnery & Weishampel 1998). D-shaped in proximal view (Fig. 2c), with the apex of the convex dorsal surface slightly medial to the mid-line. ...
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Mesozoic dinosaur fossils are exceptionally rare in Scandinavia. The Swedish record is typically depauperate, with the Kristianstad Basin of Skåne (Scania) yielding all of the known fossils from Swedish Cretaceous strata. Although highly fragmentary, these body remnants are important because they provide evidence of a relatively diverse fauna, including previously recognized hesperornithiform birds and leptoceratopsid ceratopsians, as well as indeterminate ornithopods that are confirmed here for the first time. In this paper, we describe three phalanges (from Åsen) and an incomplete right tibia (from Ugnsmunnarna) from the Kristianstad Basin. One of the phalanges appears to pertain to a leptoceratopsid ceratopsian, providing further evidence of these small ornithischians in the Cretaceous sediments of Sweden. The other two phalanges are interpreted as deriving from small ornithopods similar to Thescelosaurus and Parksosaurus. The tibia appears to represent the first evidence of a non-avian theropod dinosaur in the Cretaceous of Sweden, with a previous report of theropod remains based on fish teeth having been corrected by other authors. The remains described herein provide important additions to the enigmatic dinosaurian fauna that inhabited the Fennoscandian archipelago during the latest Cretaceous.
... These tapered processes are rostrocaudally compressed and bound the rostral margin of the carotid canal (the tubera form the caudal margins of the canal). The basipterygoid processes arise below the lateral processes and extend caudoventrally, as in some leptoceratopsids (Chinnery and Weishampel, 1998;Makovicky, 2001), but unlike other ceratopsians where they are ventrally or rostroventrally directed (Dodson et al., 2010). They extend well below the basal tubera and are subtriangular in cross-section. ...
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Yinlong downsi, from the Upper Jurassic Shishugou Formation, Xinjiang, northwestern China, is the oldest known ceratopsian dinosaur. Here we provide a detailed description of the skull and mandible based on the holotype, three partial skulls, and disarticulated materials from several other specimens. Yinlong can be diagnosed by six autapomorphies: a distinct fossa along the midline of the frontals; a slit-like carotid canal bordered by laminae; premaxillary teeth with a vertical wear facet and a basal shelf; a deep sulcus on the ventral surface of the quadratojugal; large oval nodules concentrated on the lateral surface of the jugal; and a squamosal with an expanded dorsal surface and a long, constricted quadrate process. A detailed comparison with other basal ceratopsians suggests that Yinlong downsi may belong within Chaoyangsauridae. Yinlong also shares many derived characters both with Psittacosaurus and neoceratopsians, suggesting that character evolution in early ceratopsians is complex. Additionally, a caniniform premaxillary tooth is present in one small specimen (IVPP V18636), which may suggest sexual dimorphism or individual variation.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Han, F.-L., C. A. Forster, J. M. Clark, and X. Xu. 2015. Cranial anatomy of Yinlong downsi (Ornithischia: Ceratopsia) from the Upper Jurassic Shishugou Formation of Xinjiang, China. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.1029579.
... Next we reviewed the fossil record. Although paired, clavicle-like elements have been reported for various non-theropod dinosaurs (e. g., basal ceratopsians, prosauropods; Chinnery & Weishampel 1998;Yates & Vasconcelos 2005) and the pectoral apparatus of basal ornithodirans (the immediate ancestors of dinosaurs) remains poorly understood. Therefore, it remains uncertain if the furcula of theropods represents the fusion of clavicles or if the paired elements of non-theropods represent the non-fusion of the interclavicular primordia. ...
... This contrasts with the remarkable diversity of Asian basal neoceratopsians during this time (You and Dodson 2004;Makovicky and Norell 2006). Recent discoveries (Ryan and Currie 1998;Chinnery 2004;Chinnery and Horner 2007) (Brown 1914;Sternberg 1951;Chinnery and Weishampel 1998;Ryan and Currie 1998;Makovicky 2001;Chinnery 2004;Chinnery and Horner 2007 Except for excellent skeletons of Leptoceratops (Brown 1914;Sternberg 1951) from the Scollard Formation and that of cf. Rogers (1997Rogers ( , 1998 (Horner and Currie 1994). ...
... Montanoceratops cerorhynchos is known from one specimen, a braincase, from the upper Tolman Member, with an estimated age of 69.0-69.5 Ma. Two specimens of Montanoceratops are known from the lower portions of the St. Mary River Formation in Montana(Brown and Schlaikjer 1942;Chinnery and Weishampel 1998), with an age that we estimate broadly at 69.5-71.0 Ma based on subsurface correla- ...
Article
A high-resolution biostratigraphic analysis of 287 dinosaurian macrofossils and 138 bonebeds in the Edmonton Group (Upper Cretaceous) of southern Alberta provides evidence for at least three dinosaurian assemblage zones in the Horseshoe Canyon Formation (HCFm). From bottom to top the zones comprise unique assemblages of ornithischians and are named as follows: (1) Edmontosaurus regalis – Pachyrhinosaurus canadensis (lower zone); (2) Hypacrosaurus altispinus – Saurolophus osborni (middle zone); and (3) Eotriceratops xerinsularis (upper zone). Whereas the lower and middle zones are well defined and based on abundant specimens, the validity of the uppermost zone (E. xerinsularis) is tentative because it is based on a single specimen and the absence of dinosaur taxa from lower in section. The transition from the lower to the middle zone coincides with the replacement of a warm-and-wet saturated deltaic setting by a cooler, coastal-plain landscape, characterized by seasonal rainfall and better-drained substrates. Whereas changes in rainfall and substrate drainage appear to have influenced the faunal change, changes in mean annual temperature and proximity to shoreline appear to have had little influence on faunal change. We speculate that the faunal change between the middle and upper zones also resulted from a change in climate, with ornithischian dinosaurs responding to the re-establishment of wetter-and-warmer climates and poorly-drained substrates. Compared with the shorter duration and climatically-consistent dinosaurian assemblage zones in the older Dinosaur Park Formation of southern Alberta, HCFm assemblage zones record long-term morphological stasis in dinosaurs. Furthermore, the coincidence of faunal and paleoenvironmental changes in the HCFm suggest climate-change-driven dinosaur migrations into and out of the region.
... It conformably overlies the Horsethief Fm (and to the west and south, the Two Medicine Fm) and is itself overlain by additional terrestrial deposits of the Willow Creek Fm, generally thought to be correlative with the upper parts of the Lance and Hell Creek formations (Russell, 1975) and lower part of the Fort Union Fm (Fig. 1). To date, the only vertebrate described from the St. Mary River Fm of Montana is the ceratopsian dinosaur Montanoceratops cerorhyncus (Brown and Schlaikjer, 1942) (see Weishampel and Horner, 1987; Chinnery and Weishampel, 1998 ), although a more diverse vertebrate fauna has been described from the St. Mary River Fm of Alberta (Langston, 1976), including the fragmentary dental remains of 11 mammalian taxa (Sloan and Russell, 1974; Fox and Naylor, 1986). Although mammalian teeth recovered from the St. Mary River Fm of Alberta did figure into Loris Russell's original conception of an Edmontonian terrestrial stage (Russell, 1964Russell, , 1975), it was the molluscan and non-mammalian vertebrate, mainly dinosaurian, faunas from what was then called the Edmonton Fm (now known as the Horseshoe Canyon Fm) as well as the St. Mary River Fm that were the original basis of the Edmontonian. ...
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River Formation (Fm) crops out in restricted parts of southwestern Alberta and northwestern Montana. Mammals are poorly known from the formation, but material collected from Alberta has played a role in recognizing an 'Edmontonian' Land Mammal Age between the better sampled Judithian (∼79–74 Ma) and Lancian (∼67–65 Ma) land mammal ages. New and well-preserved multituberculate and metatherian material collected from a single locality in the lower third of the St. Mary River Fm of Montana adds complexity to the interpretation of a discrete 'Edmontonian' Land Mammal Age. We report here three taxa of multituberculates (Paracimexomys propriscus, sp. nov., Nidimys occultus, gen. et sp. nov., and a primitive ptilodontoid of comparable size to the smallest species of Mesodma Jepsen, 1940, and Cimexomys Sloan and Van Valen, 1965) and two metatherian taxa (Leptalestes toevsi, sp. nov., and Turgidodon russelli). Paracimexomys propriscus and Turgidodon russelli are probably conspecific with Judithian forms that did not survive to the Lancian. Leptalestes toevsi and Nidimys occultus are taxa unique to the 'Edmontonian' but may represent lineages that separated from their closest relatives prior to the Judithian. Lack of Lancian-aspect mammals contrasts sharply with other 'Edmontonian' faunas, including an older fauna recovered from the Williams Fork Fm of Colorado, suggesting that the replacement of Judithian mammals by Lancian forms was a complex transition. We tentatively suggest that the Lancian fauna may have expanded into the northern part of the Western Interior in response to the appearance of new terrestrial habitats as sea level fell.
... It conformably overlies the Horsethief Fm (and to the west and south, the Two Medicine Fm) and is itself overlain by additional terrestrial deposits of the Willow Creek Fm, generally thought to be correlative with the upper parts of the Lance and Hell Creek formations (Russell, 1975) and lower part of the Fort Union Fm (Fig. 1). To date, the only vertebrate described from the St. Mary River Fm of Montana is the ceratopsian dinosaur Montanoceratops cerorhyncus (Brown and Schlaikjer, 1942) (see Weishampel and Horner, 1987; Chinnery and Weishampel, 1998 ), although a more diverse vertebrate fauna has been described from the St. Mary River Fm of Alberta (Langston, 1976), including the fragmentary dental remains of 11 mammalian taxa (Sloan and Russell, 1974; Fox and Naylor, 1986). Although mammalian teeth recovered from the St. Mary River Fm of Alberta did figure into Loris Russell's original conception of an Edmontonian terrestrial stage (Russell, 1964Russell, , 1975), it was the molluscan and non-mammalian vertebrate, mainly dinosaurian, faunas from what was then called the Edmonton Fm (now known as the Horseshoe Canyon Fm) as well as the St. Mary River Fm that were the original basis of the Edmontonian. ...
Article
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The St. Mary River Formation (Fm) crops out in restricted parts of southwestern Alberta and northwestern Montana. Mammals are poorly known from the formation, but material collected from Alberta has played a role in recognizing an ‘Edmontonian’ Land Mammal Age between the better sampled Judithian (∼79–74 Ma) and Lancian (∼67–65 Ma) land mammal ages. New and well-preserved multituberculate and metatherian material collected from a single locality in the lower third of the St. Mary River Fm of Montana adds complexity to the interpretation of a discrete ‘Edmontonian’ Land Mammal Age. We report here three taxa of multituberculates (Paracimexomys propriscus, sp. nov., Nidimys occultus, gen. et sp. nov., and a primitive ptilodontoid of comparable size to the smallest species of MesodmaJepsen, 1940, and CimexomysSloan and Van Valen, 1965) and two metatherian taxa (Leptalestes toevsi, sp. nov., and Turgidodon russelli). Paracimexomys propriscus and Turgidodon russelli are probably conspecific with Judithian forms that did not survive to the Lancian. Leptalestes toevsi and Nidimys occultus are taxa unique to the ‘Edmontonian’ but may represent lineages that separated from their closest relatives prior to the Judithian. Lack of Lancian-aspect mammals contrasts sharply with other ‘Edmontonian’ faunas, including an older fauna recovered from the Williams Fork Fm of Colorado, suggesting that the replacement of Judithian mammals by Lancian forms was a complex transition. We tentatively suggest that the Lancian fauna may have expanded into the northern part of the Western Interior in response to the appearance of new terrestrial habitats as sea level fell.
... 2012). The topology and paired appearance of these morphotype B elements strongly suggests that they fit an identification as clavicles better than morphotype A. Such an interpretation would also match previous findings of similarly shaped clavicles in ceratopsian dinosaurs (Chinnery & Weishampel, 1998:Fig. 6; Vickaryous & Hall, 2010:Fig. ...
Article
Ossified gastralia, clavicles and sternal ribs are known in a variety of reptilians, including dinosaurs. In sauropods, however, the identity of these bones is controversial. The peculiar shapes of these bones complicate their identification, which led to various differing interpretations in the past. Here we describe different elements from the chest region of diplodocids, found near Shell, Wyoming, USA. Five morphotypes are easily distinguishable: (A) elongated, relatively stout, curved elements with a spatulate and a bifurcate end resemble much the previously reported sauropod clavicles, but might actually represent interclavicles; (B) short, L-shaped elements, mostly preserved as a symmetrical pair, probably are the real clavicles, as indicated by new findings in diplodocids; (C) slender, rod-like bones with rugose ends are highly similar to elements identified as sauropod sternal ribs; (D) curved bones with wide, probably medial ends constitute the fourth morphotype, herein interpreted as gastralia; and (E) irregularly shaped elements, often with extended rugosities, are included into the fifth morphotype, tentatively identified as sternal ribs and/or intercostal elements. To our knowledge, the bones previously interpreted as sauropod clavicles were always found as single bones, which sheds doubt on the validity of their identification. Various lines of evidence presented herein suggest they might actually be interclavicles - which are single elements. This would be the first definitive evidence of interclavicles in dinosauromorphs. Previously supposed interclavicles in the early sauropodomorph Massospondylus or the theropods Oviraptor and Velociraptor were later reinterpreted as clavicles or furculae. Independent from their identification, the existence of the reported bones has both phylogenetic and functional significance. Their presence in non-neosauropod Eusauropoda and Flagellicaudata and probable absence in rebbachisaurs and Titanosauriformes shows a clear character polarity. This implicates that the ossification of these bones can be considered plesiomorphic for Sauropoda. The proposed presence of interclavicles in sauropods may give further support to a recent study, which finds a homology of the avian furcula with the interclavicle to be equally parsimonious to the traditional theory that furcula were formed by the fusion of the clavicles. Functional implications are the stabilizing of the chest region, which coincides with the development of elongated cervical and caudal vertebral columns or the use of the tail as defensive weapon. The loss of ossified chest bones coincides with more widely spaced limbs, and the evolution of a wide-gauge locomotor style.
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The development of the vertebral column has been studied extensively in modern amniotes, yet many aspects of its evolutionary history remain enigmatic. Here we expand the existing data on four major vertebral developmental patterns in amniotes based on exceptionally well-preserved specimens of the early Permian mesosaurid reptile Mesosaurus tenuidens: (i) centrum ossification, (ii) neural arch ossification, (iii) neural arch fusion, and (iv) neurocentral fusion. We retrace the evolutionary history of each pattern and reconstruct the ancestral condition in amniotes. Despite 300 million years of evolutionary history, vertebral development patterns show a surprisingly stability in amniotes since their common ancestor. We propose that this stability may be linked to conservatism in the constraints posed by underlying developmental processes across amniotes. We also point out that birds, mammals, and squamates each show specific trends deviating from the ancestral condition in amniotes, and that they remain rather unchanged within these lineages. The stability of their unique patterns demonstrates a certain homogeneity of vertebral developmental constraints within these lineages, which we suggest might be linked to their specific modes of regionalization. Our research provides a framework for the evolution of axial development in amniotes and a foundation for future studies.
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Here we report a new articulated skeleton of Yamaceratops dorngobiensis (MPC-D 100/553) from the Khugenetjavkhlant locality at the Shine Us Khudag (Javkhlant Formation, ?Santonian-Campanian) of the eastern Gobi Desert, Mongolia, which represents the first substantially complete skeleton and the first juvenile individual of this taxon. The specimen includes a nearly complete cranium and large portions of the vertebral column and appendicular skeleton. Its skull is about 2/3 the size of the holotype specimen, based on mandibular length. Its juvenile ontogenetic stage is confirmed by multiple indicators of skeletal and morphological immaturity known in ceratopsians, such as the long-grained surface texture on the long bones, the smooth external surface on the postorbital, open neurocentral sutures of all caudal vertebrae, a large orbit relative to the postorbital and jugal, the low angle of the lacrimal ventral ramus relative to the maxillary teeth row, narrow frontal, and straight ventral edge of the dentary. Osteohistological analysis of MPC-D 100/553 recovered three lines of arrested growth, implying around 3 years of age when it died, and verified this specimen’s immature ontogenetic stage. The specimen adds a new autapomorphy of Yamaceratops , the anteroventral margin of the fungiform dorsal end of the lacrimal being excluded from the antorbital fossa. Furthermore, it shows a unique combination of diagnostic features of some other basal neoceratopsians: the ventrally hooked rostral bone as in Aquilops americanus and very tall middle caudal neural spines about or more than four times as high as the centrum as in Koreaceratops hwaseongensis , Montanoceratops cerorhynchus , and Protoceratops andrewsi . The jugal with the subtemporal ramus deeper than the suborbital ramus as in the holotype specimen is also shared with A. americanus , Liaoceratops yanzigouensis , and juvenile P. andrewsi . Adding 38 new scorings into the recent comprehensive data matrix of basal Neoceratopsia and taking into account the ontogenetically variable characters recovered Y. dorngobiensis as the sister taxon to Euceratopsia (Leptoceratopsidae plus Coronosauria). A second phylogenetic analysis with another matrix for Ceratopsia also supported this position. The new phylogenetic position of Y. dorngobiensis is important in ceratopsian evolution, as this taxon represents one of the basalmost neoceratopsians with a broad, thin frill and hyper-elongated middle caudal neural spines while still being bipedal.
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North America is known for its rich uppermost Cretaceous record of dinosaur egg remains, although a notable fossil gap exists during the lower Maastrichtian. Here we describe a diverse dinosaur eggshell assemblage from the St. Mary River Formation of southern Alberta that, in conjunction with recently described eggs from the same formation in Montana, helps fill this gap and sheds light on the dinosaur diversity in this poorly fossiliferous formation. Three theropod eggshell types (Continuoolithus cf. C.canadensis, Montanoolithus cf. M.strongorum, and Prismatoolithus cf. P.levis) and one ornithopod (Spheroolithus cf. S.albertensis), are reported from Albertan exposures of the St. Mary River Formation, increasing the ootaxonomic diversity of the formation from two to five ootaxa. The taxonomic composition of the eggshell assemblage is consistent with the dinosaurian fauna known from the St. Mary River Formation based on skeletal remains. Spheroolithus eggshells constitute the majority of identifiable eggshells in our assemblage, a trend also observed in several other Upper Cretaceous formations from North America. Continuoolithus is shown to be synonymous with Spongioolithus, thus expanding the Maastrichtian geographic range of the ootaxon to include Utah. The St. Mary River eggshell assemblage supports a general trend of increase in eggshell thickness among theropod ootaxa from the uppermost Santonian through the Maastrichtian, which is inferred to reflect an increase in body size among some clades of small theropods through the Upper Cretaceous. Eggshell preservation in the St. Mary River Formation may be related to the semiarid climatic and environmental conditions that prevailed.
Article
Two closely associated egg types occur at the same locality in the Upper Cretaceous (Maastrichtian) St. Mary River Formation in north central Montana. These specimens represent the first fossil eggs described from this formation. At least fifteen small ovoid eggs or egg portions are scattered through a 25 cm interval of rock. Five significantly larger, round eggs overlie these smaller eggs and are in close proximity to one another on a single bedding plane. The best preserved egg of the smaller size measures 36 mm × 62 mm and exhibits the prismatic, two-layered eggshell structure of a theropod egg. The dispersed distribution and inconsistent angles of these small eggs likely resulted from disturbance by subsequent nesting activity and/or possibly nest predation. At least twelve additional small prismatic eggs also occur at this site. We assign the small eggs as a new oogenus and oospecies, Tetonoolithus nelsoni, within the Prismatoolithidae. The large round eggs measure 130 mm in diameter and the eggshell displays substantial diagenetic alteration. These eggs likely belonged to a hadrosaur due to their similarity in egg size, shape, and eggshell thickness to Maiasaura eggs from the stratigraphically lower Two Medicine Formation. Eggs at different stratigraphic levels at this site indicate that conditions favorable to both dinosaur species persisted for an extended period of time. However, determining whether these dinosaurs occupied the nesting site at the same or different years remains beyond the resolution of the rock record.
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The discovery of the smallest Triceratops skull (UCMP 154452) provides a new ontogenetic end member for the earliest stage of ceratopsid (Centrosaurinae plus Chasmosaurinae) cranial development. The lack of co-ossification among the parietal, squamosals, postorbitals, quadratojugal arch, and the braincase preserves sutural contacts and bone surfaces that later become obscured in adults. The ability to document the early development and morphology of the horns and frill in Triceratops allows a reevaluation of their functional roles. UCMP 154452 shows that the cranial ornamentation of the frill and the postorbital horns were not restricted to adults, but began at an early age in this species. This evidence supports the hypothesis that the function of ceratopsid horns and frills was potentially important for visual communication and species recognition because in this young form it could not have functioned in sexual display. Although some features of UCMP 154452 anticipate or mimic the adult character states, some braincase characters recapitulate the juvenile and adult stages of more basal neoceratopsians.
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The cranial anatomy of ceratopsian (“horned”) dinosaurs is well understood, but the postcranial skeleton has been largely ignored in previous studies of phylogeny, evolution, and function. In order to study morphological differences among ceratopsian postcranial elements and to compare evolutionary patterns, multivariate (Principal Components Analysis) and bivariate methods were used to analyze linear measurement data, and the shape methods Resistant-Fit Theta-Rho Analysis (RFTRA), Least-Squares Theta-Rho Analysis (LSTRA), and Euclidean Distance Matrix Analysis (EDMA) were applied to biological landmark data. Results of the analyses show that size is the primary change through ceratopsian skeleton evolution. Elements display positive allometry, and increasing structural support is evident, especially in the radius and fibula. Phylogenetic distribution of ceratopsian postcrania agrees with the skull material included in recent cladistic analyses. Psittacosaurus elements are in many ways derived relative to those of non-ceratopsid neoceratopsians, and evidence suggests that Psittacosaurus was bipedal, while non-ceratopsid neoceratopsians were not, except maybe for Udanoceratops. With increasing body size, neoceratopsian limbs bowed laterally. The variety of methods allows for unbiased interpretation of results, provides more information than any one method, and provides controls for each other. However, sample sizes are not ideal, and all results should be treated with caution at this time.
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The sequence of neurocentral suture closure is one criterion for the determination of ontogenetic stage in extant crocodylians. This pattern is frequently used to assess ontogeny for a variety of fossil archosaurs that may or may not follow the same sequence and timing of suture closure. Phytosaurs are one of the few basal archosaur groups with a sample size large enough to help test whether the crocodylian pattern of suture closure is plesiomorphic for Pseudosuchia and Archosauria. Analysis of a large sample of North American phytosaur specimens confirms that phytosaurs share the crocodylian state of closure, and so this pattern is probably plesiomorphic for the Pseudosuchia. An additional independent ontogenetic trend observed in phytosaurs is that the lateral fossae on cervical vertebrae in phytosaurs deepen with ontogeny. A preliminary survey indicates that there is considerable variation of both the sequence and timing of neurocentral suture closure in other archosaur clades. Therefore, it is unwise to apply a priori the crocodylian pattern to other archosaur groups to determine ontogenetic stage. Currently, apart from histological data, there are few if any reliable independent criteria for determining ontogenetic stage. I propose that histology be integrated with independent ontogenetic criteria (such as neurocentral suture closure) and morphometric data to provide a better understanding of archosaur ontogeny.
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We present a reinterpretation of the bones previously identified as ossified hyoid elements in the Asian Late Cretaceous ceratopsian dinosaur Protoceratops andrewsi Granger and Gregory, 1923. Comparisons with other ceratopsian skeletons indicate that the tetraradiate bone tentatively regarded as a first ceratobranchial is actually an incomplete middle cervical rib, and the larger, flattened elements identified as second ceratobranchials are partial sternal plates. As in nearly all other ornithischian dinosaurs for which this area of the skeleton is known, the ossified hyoid apparatus of P. andrewsi probably consisted of a pair of rod-like first ceratobranchials; two additional, splint-like or sheet-like bones that are most frequently interpreted as ceratohyals may also have been present.
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Shallow marine, nearshore strata of earliest Campanian (Gonioteuthis granulataquadrata belemnite Zone) and latest Early Campanian (informal Belemnellocamax mammillatus belemnite zone) age in the Kristianstad Basin, southern Sweden, have yielded isolated leptoceratopsid teeth and vertebrae, representing the first record of horned dinosaurs from Europe. The new leptoceratopsid occurrence may support a European dispersal route for the Leptoceratopsidae, or may represent an entirely endemic population. The presence of leptoceratopsid teeth in shallow marine deposits contradicts previous hypotheses suggesting that basal neoceratopsians mainly preferred arid and/or semi-arid habitats far from coastal areas.
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Among recent discoveries of new neoceratopsian material in North America are teeth from the Cedar Mountain Formation of Utah (Albian-Cenomanian boundary) and the Arundel Formation of Maryland (late Aptian). These teeth are determined to belong to Neoceratopsia on the basis of gross morphology. A character suite, which includes a bulbous, convex non-enameled crown surface, deep indentations, a well-developed cingulum, and secondary ridges that end within the cingulum, distinguishes neoceratopsian from similar ornithopod teeth. These characters, when studied in combination with other morphological traits, can be confidently used for identification of isolated neoceratopsian teeth. The early and continent-wide appearance of Neoceratopsia in North America necessitates a reevaluation of the biogeography of the clade.
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A new centrosaurine ceratopsid, Albertaceratops nesmoi, is described from the lower Oldman Formation (Upper Cretaceous) of southern Alberta, and is based on a single, almost complete skull. Referred material is described from equivalent beds in the Judith River Formation of north-central Montana. A limited phylogenetic analysis of the Ceratopsidae places the new taxon as the basal member of the Centrosaurinae and indicates that robust, elongate postorbital horncores that form a synapomorphy of (Ceratopsidae + Zuniceratops) are also present in Centrosaurinae.
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: A new basal neoceratopsian dinosaur, Helioceratops brachygnathus gen. et sp. nov., is described from the Quantou Formation (late Early Cretaceous or early Late Cretaceous) in the Liufangzi locality (Jilin province, China). Helioceratops differs from other basal neoceratopsians with its deep dentary ramus, its steeply-inclined ventral predentary facet, its heterogeneous dentary crowns, and by the denticles and secondary ridges asymmetrically distributed on either side of the primary ridge on its dentary teeth. Along with Auroraceratops and Yamaceratops, Helioceratops represents one of the most derived non-coronosaurian neoceratopsians. The palaeogeographical distribution of basal neoceratopsians appears limited to northern China and southern Mongolia in the current state of our knowledge. It is therefore probable that this region constituted the birthplace for more advanced, Late Cretaceous Coronosauria.
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Kerberosaurus manakini, gen. et sp. nov. (Dinosauria, Hadrosauridae) is described on the basis of disarticulated skull elements from the Maastrichtian Tsagayan Formation of Blagoveschensk, Far Eastern Russia. This flat-headed hadrosaur is characterized by a unique morphology of the lateral wall of the braincase, a particularly narrow frontal, a depressed rostral margin of the parietal, a strong, wide and flattened crest around the circumnarial depression, and a very prominent hook-like palatine process on the maxilla. A phylogenetic analysis, based on 21 cranial characters, indicates that, among hadrosaurines, Kerberosaurus is the sister taxon of a monophyletic group formed by Prosaurolophus and Saurolophus. Several independent hadrosaurid lineages migrated from western North America to eastern Asia, probably by late Campanian to early Maastrichtian time. At the end of the Maastrichtian, completely different dinosaur faunas developed in both regions, indicating some kind of geographical or paleoecological barrier.
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The recent discovery of a nearly complete ceratopsid skull in the Aguja Formation of southwest Texas supports previous conclusions that the Aguja ceratopsid represents a distinct species, Chasmosaurus mariscalensis. The diagnostic features of C. mariscalensis include an extensive anteromedian projection of the nasal between the premaxillae, erect supraorbital horns, and laterally rounded squamosal. Nine cranial features that vary among Chasmosaurus species, Pentaceratops sternbergii, and other chasmosaurines are analyzed. Chasmosaurus mariscalensis appears to be most closely related to northern species of Chasmosaurus (C. belli, C. russelli), which also exhibit a transversely flattened nasal horn and modifications of the anterior margin of the external naris. The genus Chasmosaurus, in turn, appears to be most closely related to the other southern chasmosaurine, Pentaceratops sternbergii. The biogeographic history inferred from these relationships suggests that the biogeographic exchange between northern and southern chasmosaurines cannot be explained by a single dispersal event to the south.
Article
Ceratopsian dinosaurs were characterized by a number of peculiar features that set them apart from all other tetrapods. The development of these features, reflected to varying degrees in the array of North American genera, constituted the major evolutionary trends within the group. Some of these have been noted before, others have not. The most conspicuous evolutionary developments were 1) extreme enlargement of the head, 2) two divergent trends of frill enlargement, 3) the development of large turtle-like beaks, 4) the perfection of unique shearing dentitions, 5) a general tendency for increased size, 6) increased quadrupedalism, and 7) development of either brow or nasal horns. The first four of these are related directly to problems of food-gathering or preparation, and are considered in detail here. The origin and enlargement of both long (Torosaurus type) and short (Triceratops type) parieto-squamosal frills is correlated with extreme enlargement of the jaw muscles (M. adductor mandibulae externus) that attached to the coronoid process. The resultant magnification of jaw power is believed to have been related to the unusual shearing dentition of advanced ceratopsians. Perfection of the shearing dentition involved 1) development of a long edentulous anterior jaw segment behind the beak, 2) a progressive increase in the number of tooth positions in the tooth row, 3) longitudinal compaction of tooth rows to unite individual teeth into long, continuous dental batteries, 4) increase in tooth replacement rate, 5) enlargement of tooth size, 6) increased transverse curvature of tooth root and crown, 7) lateral displacement of upper teeth relative to lower teeth, 8) increase in size of the central carina of tooth crowns, and 9) a progressive backward displacement of the entire tooth row. Except for Leptoceratops, all post-Protoceratops taxa reflect each of these modifications to varying degrees. Associated with these changes were structural alterations in the design of the mandibular lever. The short-frilled line is shown to have been characterized by progressive improvement in the jaw mechanics, resulting in progressively greater leverage for the jaw muscles in successive forms. This was effected by an increased height of the coronoid process, increased depression of the jaw articulation, and lowering of the angle of muscle application. The long-frilled line cannot now be analyzed completely, because of a lack of critical material of the latest members of the lineage, but limited analyses indicate that this line may not have been characterized by comparable mechanical improvements in the mandibular lever. This may be the reason for the development of much longer parieto-squamosal frills in the Torosaurus line, reflecting the greater size of the external adductor muscles. Exclusive shearing dentitions, efficient and powerful jaw mechanics, and extremely large jaw muscles equipped these reptiles to feed on a peculiar unknown diet. Whatever this diet was, it clearly was very resistant and probably very fibrous-perhaps like the fronds of cycads, or palms.
Article
Well preserved skulls of Triceratops are extremely abundant in Maastrictian rocks from western North America. Although ossification obscures sutural and structural details in many skulls, others reveal much previously undescribed morphology. The circumnarial area includes enlarged nares and a complex narial fossa. A nasal horn of varying size, augmented by an epinasal ossification, caps the snout. The anterodorsal orbital margin is formed by the lacrimal and the supraorbital, which has fused to the lateral side of the prefrontal. This thick and laterally extensive orbital rim restricted forward vision in Triceratops. The ossified braincase completely surrounds the brain cavity, and is overlain by a deep frontal and cornual sinus complex. These sinuses probably acted as shock absorbers to counteract stresses placed on the postorbital horns during intraspecific interactions. The frill is heavily vascularized, lacks fenestrae, and is well buttressed by expansive paroccipital processes. Endocasts reflect all twelve cranial nerves, major structures of the brain, and some arterial and venous drainage systems.
Article
The history of discoveries of new species of euornithopod dinosaurs, merychippine horses, and hominid primates is analyzed using cladistic analyses. Using decade-by-decade additions of newly discovered species, these analyses were used to evaluate changes in tree topology and completeness of the fossil record of each clade. Most discoveries have been assimilated by and thus have strengthened prior phylogenetic patterns. Discoveries have also overthrown prior tree topologies. In addition, new species have either widened or closed previously-recognized stratigraphic gaps implied by phylogeny, or in some cases even revealed new gaps. In this way, discoveries can increase the patchiness of the fossil record. Such gaps may disclose aspects of yet undiscovered, but deducible diversity from the Earth's past biotas.
Article
Two new ceratopsid dinosaurs, Einiosaurus procurvicornis and Achelousaurus horneri, are described from the Two Medicine Formation (Upper Cretaceous) of Montana. E. procurvicornis is known from three skulls and numerous cranial and postcranial elements from two bonebed assemblages. A. horneri is based on three skulls, one with associated postcranial elements. A phylogenetic review of the subfamily Centrosaurinae reveals two clades, one containing Centrosaurus and Styracosaurus and the other Pachyrhinosaurus plus the two new taxa from Montana. Diagnostic traits for resolving within-group relationships are found only in the skull roof in association with what appear to be secondary sexual characters, probably the result of sexual selection. In addition to illuminating the pattern of ceratopsian evolution, these taxa suggest an increased rate of evolution that may correlate with the late Campanian transgression of the Bearpaw Sea.
Article
Chasmosaurus mariscalensis is a new species of ceratopsian dinosaur (Ornithischia; Ceratopsia) from the upper part of the Aguja Formation (late Campanian, Judithian) in Big Bend National Park, Brewster County, Texas. This species is distinguished from other species of Chasmosaurus by its relatively short and broad squamosal bearing six very large epoccipitals, maxilla without pronounced lateral shelf, premaxilla without posterodorsal extension, and very long supraorbital horncores in adults. A bone bed accumulation comprising disarticulated remains of 10–15 juvenile, subadult, and fully adult individuals forms the hypodigm of C. mariscalensis, and allows the first full description of the postcranial skeleton for the genus. Males and females are separated on the basis of brow horncore orientation. This is the most advanced species of Chasmosaurus and is morphologically intermediate with Pentaceratops in several characters.
Article
A new species of psittacosaur, Psittacosaurus xinjiangensis, is based on one articulated skeleton and additional disarticulated material from several individuals. Diagnostic features of the species include an anteriorly flattened jugal horn, an unusually high denticle count on maxillary and dentary crowns, a proportionately narrow iliac postacetabular process, and ossified tendons that extend along the tail.
Article
The ceratopsid dinosaur genus Chasmosaurus from the Judith River Formation (Campanian; Judithian) of western Canada shows considerable variability in cranial morphology due in part to an unusually long ontogenetic trajectory. Nevertheless, two more or less distinct morphs can be identified. Allometry and sexual dimorphism cannot be invoked to account for this variability, leaving the presence of two species as the most likely explanation. In C. belli, the posterior margin of the parietal frill shows little or no emargination and bears one large triangular epoccipital on each posterolateral corner. Additional epoccipitals may be present, but are much less prominent. Chasmosaurus Canadensis, Chasmosaurus kaiseni, and Chasmosaurus brevirostris also show this morphology, and are here considered junior synonyms of Chasmosaurus belli. Chasmosaurus russelli is characterized by a deeply emarginated posterior parietal margin. On each side, the posterior margin of the frill forms a broad arch, bearing three triangular epoccipitals of approximately equal size. The reduced lateral parietal bar is incomplete in all but one specimen, allowing the squamosal to form part of the margin of the parietal fenestra. Other variable cranial characters that had previously been used to diagnose Chasmosaurus species (orbital and nasal horncore length, orbit shape, number of squamosal epoccipitals), show a mosaic distribution within these two closely related species, and are attributed to postmortem distortion, intraspecific ontogenetic variation, or sexual dimorphism. Both species appear to be sexually dimorphic in the length of the orbital horncores.
  • Gilmore C. W.
1-300. Monograph. United States Geological Survey 49I-XXIX
  • J B Hatcher
  • O C Marsh
  • R S Lull
  • Gilmore C. W.