Robert B. Holmes

The first articulated skeleton of Dendrerpeton acadianum (Temnospondyli, Dendrerpetontidae) from the Lower Pennsylvanian locality of Joggins, Nova Scotia, and a review of its relationships

ABSTRACT The discovery of the first articulated, well-preserved specimen of Dendrerpeton acadianum makes it possible to describe this taxon completely for the first time, and reassess its phylogenetic relationships. Large, laterally facing orbits, large, rounded squamosal embayments, absence of lateral line sulci, a short presacral column of only 24 vertebrae that is less than twice the length of the skull, and large stout limbs all suggest a terrestrial lifestyle distinct from the aquatic and semiaquatic adaptations of most contemporary Carboniferous amphibians. Although Dendrerpeton bears a general resemblance to the highly terrestrial dissorophoid temnospondyls and even shares with them a large squamosal embayment supported ventrally by the quadratojugal and a quadrate process, phylogenetic analysis does not support a sister-group relationship. Rather, Dendrerpeton is best considered the primitive sistergroup of a clade of temnospondyls including trimerorhachoids, “eryopoids” (Eryops, Parioxys, and Scl...

PLIOPLATECARPUS PRIMAEVUS (MOSASAURIDAE) FROM THE BEARPAW FORMATION (CAMPANIAN, UPPER CRETACEOUS) OF THE NORTH AMERICAN WESTERN INTERIOR SEAWAY

ABSTRACT One almost complete mosasaur skeleton and much additional material from the Upper Cretaceous Bearpaw Formation of South Central Saskatchewan permits the first adequate description and diagnosis of Plioplatecarpus primaevus Russell. It possesses the following unique (within mosasaurs) characters: 11 maxillary teeth; a large shield-shaped septomaxilla forming a median internarial septum; a posterodorsally directed iliac process; and no obturator foramen. It can be distinguished from Plioplatecarpus marshi in the possession of a modest sized coracoid foramen, and both P. houzeaui and P. marshi in the possession of an unreduced presacral column of 30 vertebrae, all bearing functional zygapophyses, indicating that P. primaevus is the primitive sistergroup to these two taxa. Although extremely similar to UNO 8611-2, an unnamed specimen from Alabama, the lack of an eminence on the posterior surface of the quadrate shaft in the latter establishes UNO 8611-2 as the primitive sister group of P. primaevus +...

Variation in the Skull of Anchiceratops (Dinosauria, Ceratopsidae) from the Horseshoe Canyon Formation (Upper Cretaceous) of Alberta

ABSTRACT Anchiceratops is a chasmosaurine ceratopsid from the Upper Cretaceous Horseshoe Canyon Formation (HCF) of Alberta. It is distinguished primarily by its unique parietosquamosal frill ornamentation and possibly by the presence of a ventrally flexed olfactory bulb of the brain. Although Anchiceratops is known from at least ten partial skulls, only two of these have been formally described. These skulls are not stratigraphically segregated, but they differ markedly in their proportions (e.g., supraorbital horncore and frill dimensions), causing previous authors to account for this disparity with reference to either interspecific or sexual differences. Both of these hypotheses assume that variation in Anchiceratops is dimorphic; however, this assumption has never been tested with reference to all available material. The present study describes all material from the HCF that can be positively attributed to Anchiceratops, and tests the assumption of dimorphism by subjecting this material to a series of morphometric analyses. We find no compelling evidence for dimorphism in Anchiceratops, although sample size is still too small for convincing statistical support. We conclude that there is a single, variable species of Anchiceratops, A. ornatus. Average sedimentation rates for the HCF suggest that A. ornatus is a particularly long-lived species compared with other ceratopsids (∼1.5–2.0 Ma), and the paleoecological implications of this are discussed. A cladistic analysis that includes the new data presented here indicates that Anchiceratops is more closely related to Chasmosaurus than to Triceratops, in contrast with previous studies.

A revision of the late campanian centrosaurine ceratopsid genus Styracosaurus from the Western Interior of North America

Abstract The centrosaurine ceratopsid genus Styracosaurus is known from multiple specimens and a multigeneric bone bed in the upper 30 m of the Late Cretaceous Dinosaur Park Formation of southern Alberta, and a single specimen (S. ovatus) from approximately time equivalent sediments of the Two Medicine Formation of Montana. Key cranial elements (nasals and postorbitals) of Styracosaurus appear to undergo similar ontogenetic changes as documented in Centrosaurus. Although all adult-sized centrosaurines except Centrosaurus apertus are known to possess spike-like parietal ornamentation at the P3 position on the parietal, only Styracosaurus has the P4 ornamentation expressed as a well-developed spike. Styracosaurus shows intraspecific variation in the shape of the more anteriorly placed P5–P7 ornamentation that are either the typical unmodified crest-shaped epoccipitals of other centrosaurines or are developed as short spikes. S ovatus from Montana is retained as a valid species based on the autapomorphic convergence of the P3 spikes toward the midline.

New information on the Skull of Keichousaurus hui (Reptilia: Sauropterygia) with Comments on Sauropterygian Interrelationships

Abstract Newly prepared material of Keichousaurus hui demonstrates that the nasals are very reduced and do not contribute to the margins of external nares, the quadrate lacks a posterior condylar process, the premaxilla and anterior dentary teeth are enlarged and procumbent, the maxilla has a pair of ‘canines,’ the vomers are co-ossified, the suborbital fenestrae are very reduced or lost, a distinct coronoid process is present, and both the mandibular symphysis and retroarticular process are elongated. The presence of an ectopterygoid could not be confirmed. The shape of the prefrontal, length of the quadrate ramus of the squamosal, and length of the quadrate and quadratojugal all indicate that the skull profile of Keichousaurus is much lower than previously thought. A new reconstruction attributes a distinctly eusauropterygian gestalt to the skull. A phylogenetic analysis, although equivocal, suggests that Keichousaurus is more appropriately considered a basal nothosauroid rather than a pachypleurosauroid, and that the Eusauropterygia is paraphyletic.

AN UNUSUAL TYLOSAURINE MOSASAUR FROM NEW ZEALAND: A NEW SKULL OF TANIWHASAURUS OWENI (LOWER HAUMURIAN; UPPER CRETACEOUS)

Abstract Recently collected materials of a tylosaurine mosasaur from Haumuri Bluff, New Zealand, are assigned to Taniwhasaurus oweni Hector, 1874. Previously described tylosaurine mosasaur specimens from Haumuri Bluff that were assigned to other taxa are re-evaluated here and assigned to T. oweni. Taniwhasaurus is diagnosed as a tylosaurine based on the possession of a premaxillary rostrum and anterior edentulous process of the dentary. However, Taniwhasaurus also exhibits a prefrontal-maxillary contact in which the prefrontal forms a portion of the naris, thus precluding the frontal-maxillary contact characteristic of all other tylosaurines with the possible exception of Hainosaurus bernardi. The distribution of the frontal-maxillary contact in mosasaurs suggests that it may be correlated with snout elongation.

A Juvenile Chasmosaurine Ceratopsid (Dinosauria, Ornithischia) from the Dinosaur Park Formation, Alberta, Canada

ABSTRACT An articulated, 1.5 m long skeleton of a juvenile Chasmosaurus, lacking only the front limbs, pectoral girdles, and terminal caudal vertebrae, was collected from the Dinosaur Park Formation in Dinosaur Provincial Park, Alberta. The short, tall skull has a narrow frill that lacks a posterior embayment. Many of the cranial bones are co-ossified in spite of the small size of the specimen. The nasals form an incipient horncore, and the short, knob-like postorbital horncore lacks sinuses. The palpebral is not fused to the rest of the skull. The frontal fontanelle is keyhole-shaped. The triangular squamosal extends to the back of the parietals. Epiossifications are lacking, although the squamosal margin is thick and scalloped. The parietal has a pronounced midline sagittal crest. Parietal fenestrae, if present, would have been narrow and elongate. There are only 18 maxillary tooth positions. The syncervical comprises three co-ossified, but distinct vertebrae. Anterior caudal vertebrae support unfused caudal ribs. Ossified tendons in the neck, trunk, and sacrum do not extend into the tail. Hind limb proportions are comparable to those of adult ceratopsids. The pedal unguals are distally acute. Skin impressions are similar to those of mature chasmosaurines. Phylogenetic analysis, if all characters are coded as they are seen, suggests that the specimen is a basal chasmosaurine. When size or age dependent characters are recoded as ‘?,’ the specimen groups with other Chasmosaurus. These characters should only be used in phylogenetic analyses when all specimens are mature.

Kinetic Limitations of Intracranial Joints in Brachylophosaurus canadensis and Edmontosaurus regalis (Dinosauria: Hadrosauridae), and Their Implications for the Chewing Mechanics of Hadrosaurids

The highly specialized tooth morphology and arrangement of the dental battery of hadrosaurids has led to much speculation surrounding the chewing mechanics of this successful group of herbivorous dinosaurs. Pleurokinesis, a long established hypothesis explaining the ornithopod chewing mechanism, proposes a transverse power stroke in hadrosaurids that was accommodated by vertical adduction of the mandible, lateral rotation of the maxilla at the maxilla‐premaxilla joint, lateral rotation of the jugal‐maxilla complex at its contact with the lacrimal, and posterolateral rotation of the quadrate at its contact with the squamosal. A secondary series of movements were also thought to have occurred as a consequence of these primary movements. In this article, the intracranial joint morphology is described for both Brachylophosaurus canadensis and Edmontosaurus regalis and their permissive kinematics are established. Based on this evidence, the movements associated with pleurokinesis are not accommodated in these hadrosaurine dinosaurs. Rather, the movements that seem most likely to have produced the observed dental wear patterns are those associated with the mandible about the jaw joint. The structure of this joint appears well‐suited to have accommodated some translation as well as rotation of the mandible about the quadrate condyle. Three‐dimensional modeling of the alternate mandibular movements reveals that not all the combined labiolingual width of the lingual and buccal facets of the tooth row was involved in the power stroke. Rather, limits on the degree of mandibular long axis rotation suggest that only the lingual facet and the more medial portion of the buccal facet were utilized. Anat Rec, 2012.

Agamid lizard (Agamidae: Uromastycinae) from the lower Oligocene of Egypt

Agamid lizards are currently found in Africa, Asia, the eastern Mediterranean region and Australia. Together with the Chamaeleonidae and some extinct basal forms, they comprise the Acrodonta, lizards with acrodont dentition. The Acrodonta have been suggested to have a Gondwanan origin, with the oldest members found in the Triassic of India. The first agamids are known from the Late Cretaceous of Asia, and the group is widely distributed in the northern hemisphere throughout much of the Paleogene. However, the fossil history of Acrodonta on the Afro-Arabian plate is extremely limited: a single jaw fragment bearing acrodont dentition, possibly attributable to Agamidae, has been reported from the Paleogene of Morocco, and material identified as agamid was reported from the Oligocene of Oman. We here add to the African record the first clear evidence of Agamidae, represented by several jaws with attached teeth from earliest Oligocene deposits of the Jebel Qatrani Formation in the Fayum Depression, Egypt. Characters of the teeth, including very rounded labial surface, shearing edges concave lingually, shearing tip crescentic and accessory cusps absent, are similar to those of Uromastyx. Species of Uromastyx currently inhabit the Saharan and Somalian regions of Africa and adjacent Arabia.

The anatomy and homologies of the ceratopsid syncervical

The Ceratopsidae and all other members of the Ceratopsia, except Psittacosaurus and Hongshanosaurus (Family: Psittacosauridae), comprise the order of Neoceratopsia (sensu Sereno, 2000). All members of this group can be distinguished from psittacosaurids and other members of the Ornithischia by fusion of the anterior-most vertebrae (Fig. 1). The resulting structure is called the syncervical (Ostrom and Wellnhofer, 1986) or cervical bar (Langston, 1975). This fusion probably occurred in order to stabilize the neck region so that it could support the relatively larger heads characteristic of neoceratopsians (Hatcher et al., 1907). In all neoceratopsians, the presacral column consists of the syncervical, six free cervical vertebrae, and 12 dorsal vertebrae. The presacral count varies only in more basal ceratopsians: Psittacosaurus mongoliensis has 21 or 22 vertebrae (13 or 14 dorsal vertebrae) (Sereno, 1987); P. neimongoliensis has 22 (14 dorsal vertebrae) (Russell and Zhao, 1996); and Leptoceratops gracilis has 22 (13 dorsal vertebrae) (Sternberg, 1951). Vertebral count is therefore a potentially useful character for phylogenetic analysis. If the composition of the derived neoceratopsian syncervical can be established, it will then be possible to compare presacral counts throughout the Ceratopsia. The specific composition of the syncervical is uncertain, but two competing hypotheses have been advanced. The first, and original hypothesis, advanced by Hatcher (in Hatcher et al., 1907), states that the syncervical is composed of three vertebrae: the atlas, the axis, and the third cervical vertebra (Fig. 1). The second, proposed by Lull (in Hatcher et al., 1907:fig. 50), states that the structure comprises four vertebrae: the atlas, axis, third, and fourth cervical vertebrae. Opinions concerning the composition of the syncervical have been divided between the two interpretations; in recent years, however, the majority of experts adhere to the latter hypothesis of four vertebrae (e.g. Ostrom and Wellnhofer, 1986; Dodson, 1996; You and Dodson, 2004, Dodson et al., 2004; the former is supported by Brown, 1917; Lull, 1933; Lehman, 1989). However, no justifications have been given, and no attempts have been made to return to the original arguments, or to compare the syncervical of ceratopsids to the atlas-axis of basal amniotes.