The postcranial skeleton of Vagaceratops irvinensis (Dinosauria, Ceratopsidae)

Abstract

Abstract:The postcranial skeleton of Vagaceratops (= Chasmosaurus) irvinensis (CMN 41357), lacking only the tail, most of the left front and left hind limbs, and portions of the pelvis, is preserved in articulation. It is one of the most complete, best articulated ceratopsid skeletons known. Both the manus and vertebral column exhibit conspicuous pathologies, possibly an indication of advanced age at the time of death. The vertebral column comprises a syncervical, six additional cervical vertebrae, and 12 dorsals. A partial synsacrum is represented by two dorsosacrals, four sacrals, two caudosacrals, and a partial third caudosacral centrum. The ribcage, although crushed, is nearly complete. The sternum is unusually wide compared with other ceratopsids. As in other chasmosaurines, the humerus bears a prominent deltopectoral crest that forms the anterior edge of the broad, rectangular proximal humeral expansion. The medial tuberosity is separated from the dorsal surface of the humerus by a distinct notch. The insertion for the latissimus dorsi is conspicuous. The deltopectoral crest extends a full half of the distance to the distal end of the humerus. Epipodials of the forelimb are relatively short compared to the corresponding propodial. The ulna has a long, distinctly triangular olecranon, broadly rounded anterolateral process, prominent medial process, and a deeply concave trochlear notch. The terminal phalanges on the fourth and fifth manual digits are relatively large, and unlike other ceratopsids have distinct distal (possibly articular) facets. The fourth trochanter of the femur is relatively proximal in position. This study and other recent studies of ceratopsid postcrania suggest that potentially useful taxonomic variation is present in the number of dorsosacrals, size of the groove on the ventral surface of the sacrum, morphology of the last dorsal and dorsosacral ribs, morphology of the scapula and proximal expansion of the humerus, morphology of the ulna, ratio of humerus/epipodium, morphology of the fifth manual digit, and position of the fourth trochanter of the femur.

Temporal range extension and evolution of the chasmosaurine ceratopsid ‘Vagaceratops’ irvinensis (Dinosauria: Ornithischia) in the Upper Cretaceous (Campanian) Dinosaur Park Formation of Alberta

“…However, based on the location of the parietal-squamosal suture, they identified the three medialmost pairs as epiparietals, the fourth pair as epiparietosquamosals, and the fifth pair as episquamosals for this taxon. As the parietal-squamosal suture is difficult to discern in the holotype of C. irvinensis, likely as a result of advanced age for this individual (Holmes 2014), Sampson et al (2010) concluded that it probably lies below the fourth epiossification, as in Figure 1. Regional map of localities producing 'Vagaceratops' irvinensis specimens (solid black stars; CMN 41357, TMP 1987.045.0001, TMP 1998.102.0008, and TMP 2011 and 'V.'…”

Spiclypeus shipporum gen. et sp. nov., a Boldly Audacious New Chasmosaurine Ceratopsid (Dinosauria: Ornithischia) from the Judith River Formation (Upper Cretaceous: Campanian) of Montana, USA

“…Statistical support for this or any other topology is currently weak, likely reflecting issues of missing data and character conflict. Besides determined fieldwork and the pursuit of more complete specimens, we would likewise encourage the search for new and phylogenetically informative characters, particularly in the braincase (e.g., [ 25 ]) and postcranium (e.g., [ 39 , 44 ]), which are traditionally overlooked. Explicit and illustrated character state definitions would also help to ensure compatibility between studies, which is presently concerning.…”

“…We further modified the matrices as follows: (1) character 24 (presence/absence of forked distal end of posteroventral process of premaxilla) was recoded as ‘present’ for Vagaceratops ; (2) character 49 (curvature of postorbital horncore in anterior view) was recoded as ‘laterally curved’ for Kosmoceratops (previously miscoded as ‘straight’); (3) character 69 (length of squamosal relative to parietal) was recoded as ‘squamosal slightly shorter than parietal, posterolateral-most margin of frill formed by the parietal’ for Vagaceratops ; (4) character 70 (squamosal forms part of posterior margin of frill) was recoded as ‘absent’ for Vagaceratops ; (5) characters 76–78 (relating to the shape of the posterior parietal bar) were recoded for Chasmosaurus belli , C . russelli , and Vagaceratops following Campbell et al [ 37 ]; (6) character 100 (episquamosal S2 shape) was recoded as ‘low raised D‐shaped process’ for Vagaceratops ; (7) character 103 (marginal ossification crossing squamosal‐parietal contact) was recoded as ‘absent’ for Vagaceratops , and as ‘absent’ for Anchiceratops (the previously coded polymorphism for Anchiceratops arguably reflects an ontogenetic transformation, which is inadvisable; see Hennig [ 38 ]); (8) character 104 (shape of marginal ossification crossing squamosal‐parietal contact) was recoded as ‘-‘ (not applicable) for Vagaceratops ; (9) character 105 (number of epiparietals per side) was recoded as ‘five or more’ for Vagaceratops , and as polymorphic for Chasmosaurus belli ; (10) codings for character 111 (presence/absence of epiparietal P1) were corrected in the traditional homology matrix ( Pachyrhinosaurus was recoded as ‘absent’, chasmosaurines mistakenly coded as ‘absent’ were instead coded as ‘present’) (11) characters 112–114 (relating to the morphology of epiparietal 1) were recoded as ‘-‘ (not applicable) for Albertaceratops and Pachyrhinosaurus because epiparietal P1 is missing in these taxa; (12) postcranial characters 163–165 and 172 were coded for Vagaceratops (after description of Holmes [ 39 ]). Character 33 (adult nasal ornamentation type) was specified as ordered.…”