[D] Texacephale langstoni [dG]
Longrich, Sankey, & Tanke 2010
Cretaceous Late Campanian
Ornithischia Genasauria Cerapoda Marginocephalia Pachycephalosauria Pachycephalosauridae Nomina Dubia
Aguja Formation, Texas, US
(Jasinski & Sullivan 2011) A reassessment of the newly named taxon Texacephale langstoni demonstrates that it is not based on diagnostic material and, therefore, is a nomen dubium.
Based on two frontoparietal domes. Texacephale langstoni gen. et sp. nov. is diagnosed by a tall, arched nasal boss, flange-like processes articulating the dome with the peripheral elements, and a low pedicel separating the cerebral fossa from the skull roof. The skull dome is composed largely of the fused frontals and parietals, with limited participation of the peripheral elements, and the supratemporal fenestrae remain open. Phylogenetic analysis indicates that Texacephale langstoni is a basal member of the Pachycephalosauria.
The discovery of Texacephale supports previous suggestions that the dinosaur fauna of Texas was distinct from that of contemporary assemblages to the north. The phylogenetic analysis presented here indicates that the Asian pachycephalosaurs form a monophyletic group, deeply nested within the Pachycephalosauridae, and that the basal members of the group are all North American. This finding indicates that pachycephalosaurids originated in North America, rather than Asia, as previously believed. The high diversity of North American pachycephalosaurs and the late appearance of pachycephalosaurs in Asia are consistent with this hypothesis.
The biology of Texacephale and other Pachycephalosauridae are also discussed. The morphology of the dome in Texacephale and other pachycephalosaurs supports the hypothesis that pachycephalosaurids engaged in intraspecific combat, while the occurrence of Texacephale and other pachycephalosaurs in nearshore deposits argues that the pachycephalosaurs were not restricted to inland habitats.
LSUMNS 20010, fused frontoparietals.
LSUMNS 20012, incomplete frontoparietal dome.
In honor of Wann Langston, for his contributions to the vertebrate palaeontology of the Big Bend region.
Locality and horizon
Holotype LSUMNS 20010, was recovered from site WPA-1, a site which lies low in the upper shale member of the Aguja Formation . WPA-1 is a quarry in a multitaxon bonebed dominated by the ceratopsian Agujaceratops mariscalensis and hadrosaurs (Lehman, 1982; Davies and Lehman, 1989; Lehman, 2007); nodosaur remains are also present. The bonebed lies above the Terlingua Creek sandstone member, and within the lower part of the upper shale member of the Aguja (Lehman, 1989).
This accumulation is located in a grey claystone that is thought to represent an interdistributary marsh (Lehman, 1989). The referred specimen was recovered east of the bonebed, less than a kilometer away, and several tens of meters above WPA-1 in section. It was found as part of a deflation lag, along with numerous other dinosaur scraps that had weathered from an ironstone-cemented conglomerate. The only other diagnostic fossil recovered from this site is a parietal fragment from Agujaceratops.
Medium-sized pachycephalosaurid characterized by the following autapomorphies: (1) parietal articulating with postorbital via a series of flange-like processes, (2) tall, narrow nasal boss with a dorsal margin that is convex in lateral view, (3) skull roof elevated above the roof of the braincase by a low pedicel. These characters are unique to Texacephale among the Pachycephalosauridae and allow this animal to be distinguished from all previously described pachycephalosaurs. Texacephale is further distinguished from Colepiocephale and Gravitholus by the absence of prominent lateral lobes of the parietal; from Stegoceras by the inflation of the supraorbital lobes of the frontal and by low postorbitals; and from Hanssuesia by the low postorbitals, low supraorbitals, open supratemporal fenestrae, and the tall nasal boss. Texacephale is distinguished from Sphaerotholus, Prenocephale and the Pachycephalosaurini by the following characters: open supratemporal fenestrae, limited contribution of the postorbitals to the dome, a large contact between supraorbital 1 and the frontal, and a tall nasal boss. Thus, even without considering the autapomorphies described above, the frontoparietal dome of Texacephale is distinct from any previously described pachycephalosaurid dome.