Donald B. Brinkman

Paleooecology of the Judith River Formation (Campanian) of Dinosaur Provincial Park, Alberta, Canada: Evidence from vertebrate microfossil localities

Abstract A survey of the stratigraphic disriubtion of 34 taxa of vertebrates in Judith River Formation (Campanian) of Dinosaur Provincial Park, Alberta, Canada, based on screenwashed samples from 25 vertebrate microfossil localities showed that many vertebrates have a non-random distribution in these beds. Amiidae gen. unident., holostean A, Coriops, teleost D, teleost gen. unident., Scapherpeton Opisthotriton, and frogs decrease in abundance through all or most of the stratigraphic interval exposed in Dinosaur Park; Myledaphus, Atractosteus, holostean B, Belonostomus, Champsosaurus, Leidyosuchus, and ceratopsians increase in abundance through this interval; Hybodus, Basilemys, and Paratarpon are found only in the upper part of the exposures; Thescelosaurus is restricted to the lower exposures; Troodon is encountered more frequently in localities low in section, and Paralbula and Aspideretes increase in abundance in channel deposits. These stratigraphic distributions reflect ecological zonation of the coastal plain in which the beds were laid down; the animals that have their horizons of greatest abundance in the upper beds would have been members of a zone located near the shoreline, and the animals that have their horizon of greatest abundance low in section would have been members of a zone located relatively more inland. These two paleoecological assemblages can be further subdivided into aquatic and terrestrial paleocommunities according to interpretations about the mode of life of the individual taxa. The terrestrial paleocommunities are similar to those of the Late Maastrichtian in that ceratopsians occupied the most near-shore areas of the coastal plain and hypsilophodonts were present in the areas of the coastal plain farthest from shore.

SMALL THEROPOD AND BIRD TEETH FROM THE LATE CRETACEOUS (LATE CAMPANIAN) JUDITH RIVER GROUP, ALBERTA

Abstract A collection of over 1,700 small theropod teeth from the Judith River Group (Campanian; ∼79.5–74 Ma) allows our understanding of the diversity and variation of small theropods in this assemblage to be refined. In addition to the previously recognized taxa, a series of morphologically distinct groups are recognized that may represent distinct taxa in some cases. Teeth with the Paronychodon-like features of a flat surface with longitudinal ridges on one side are resolved into a few discrete morphotypes. Two of these are included in Paronychodon lacustris and two additional morphotypes are hypothesized to represent distinct taxa, here referred to as ?Dromaeosaurus morphotype A and Genus and species indet. A. The teeth of Paronychodon lacustris and ?Dromaeosaurus morphotype A share a distinctive wear pattern that suggests tooth functioning involved contact between the flat surfaces of opposing teeth. Two species of Richardoestesia, R. gilmorei and R. isosceles, are present in the assemblage. Additionally, bird teeth are identified in the assemblage and are described in this review. Bivariate plots were used to document the variation in the theropod teeth, especially in the features that distinguish between Richardoestesia gilmorei, R. isosceles, Saurornitholestes, and Dromaeosaurus. Considerable overlap is present in all plots, so although the teeth are morphologically distinct, they are not easily distinguished by quantitative means.

The paleogeographic and stratigraphic distribution of ceratopsids (Ornithischia) in the upper Judith River Group of Western Canada

Articulated remains and teeth preserved in vertebrate microfossil localities are used as independent lines of evidence to quantify the relative abundances of dinosaurs along a 250-km transect extending from the paleogeographically more inland Dinosaur Provincial Park area (Alberta), through the South Saskatchewan River area, to the more coastal Unity, Saskatchewan locality. A comparison of articulated dinosaur remains along chronostratigraphically equivalent horizons from the Dinosaur Provincial Park and South Saskatchewan areas indicate that ceratopsid dinosaurs are more abundant in the South Saskatchewan River area, whereas the converse is true for ankylosaur and pachycephalosaur dinosaurs. In the case of ceratopsid dinosaurs, the same distributional pattern is reflected in data amassed from vertebrate microfossil assemblages from these areas. In addition, vertebrate microfossil assemblages show that ceratopsids increase in relative abundance moving upsection in both the Dinosaur Park and South Saskatchewan River areas. In these same sections ankylosaurs and pachycephalosaurs decrease in abundance in the Dinosaur Park area, but their abundances show no change up through the section in the South Saskatchewan River area. These paleogeographic and stratigraphic patterns further support the existing hypothesis that ceratopsids were relatively more abundant in coastal areas, rather than inland areas, during the Campanian. They also provide tentative support for the hypothesis that ankylosaurs and pachycephalosaurs were, in general, more prominent members of inland communities.

Size-independent criteria for estimating relative age in Ophiacodon and Dimetrodon (Reptilia, Pelycosauria) from the Admiral and lower Belle Plains formations of west-central Texas

ABSTRACT The relationship between size and age is central to many problems of diversity within genera of pelycosaurs and needs to be quantified before the age structure of a population can be interpreted. The degree of ossification of the limb elements provides a basis for interpreting relative age independent of size in pelycosaurs. The pattern of ossification of the humerus of Ophiacodon and of the humerus, femur, and ulna of Dimetrodon are described and stages in the development of these bones are defined. When materials from the Admiral and lower Belle Plains formations are lumped together, size correlates poorly with developmental stage. This is interpreted as a result of the presence of two species of different size within each genus. There is no evidence for a difference in the habitat selection of juveniles and adults of these genera.

Morphology and Evolution of Turtles

The unquestioned unity of the Chelonia provides a necessary basis for establishing their interrelationships and determining the evolutionary history within the group. On the other hand, the host of uniquely derived features of the oldest known turtles make it extremely difficult to establish their ancestry among more primitive amniotes. This is illustrated by the great diversity of taxa that continue to be proposed as putative sister-taxa of turtles without general acceptance of any. Nearly every major clade of early amniotes from the late Paleozoic and early Mesozoic has been proposed as a possible sister-taxon of turtles, from synapsids to anapsids and diapsids, including pelycosaurs, captorhinomorphs, procolophonids, pareiasaurs, aquatic placodonts and crocodiles, but none possess derived characters that could be synapomorphic with the unique skeletal structure and patterns of development of the chelonian skull, carapace or plastron, which had reached an essentially modern configuration by the Late Triassic. Numerous molecular biologists have attempted to establish the closest sister-group of turtles through analyses of a host of living species, but there is no way for them to preclude turtles from having evolved from one or another of the Paleozoic or early Mesozoic clades that have become extinct without leaving any other living descendants. On the other hand, recent studies of the genetic and molecular aspects of the development of the carapace and plastron imply unique patterns of evolutionary change that cannot be recognized in any of the other amniote lineages, living or dead. This, together with the retention of a skull without temporal fenestration implies a very early divergence from a lineage that probably retained an anapsid skull configuration. This problem may be resolved by more detailed study of the enigmatic genus Eunotosaurus, from the Late Permian of South Africa.

Faunal assemblages from the upper Horseshoe Canyon Formation, an early Maastrichtian cool-climate assemblage from Alberta, with special reference to the Albertosaurus sarcophagus bonebedThis article is one of a series of papers published in this Special Issue on the theme Albertosaurus.

The faunal assemblage from the early Maastrichtian portion of the Horseshoe Canyon Formation is described on the basis of four new vertebrate microfossil localities and remains from the Albertosaurus bonebed. All of the localities sampled were deposited during a cool, dry climate at a palaeolatitude of ∼58°N. Thus, these assemblages provide insight into a northern cool-climate assemblage in the early Maastrichtian of western North America. This fauna is characterized by the presence of taxa with more northern affinities, such as Holostean A, champsosaurs, Troodon, and toothed birds. Warm-climate taxa, such as crocodylians, large and diverse turtles, and albanerpetontids are notable in their absence. The Albertosaurus bonebed locality at the top of unit 4 of the Horseshoe Canyon Formation was deposited during the initial stages of a trend to a warmer and wetter climate that is represented in unit 5. The bonebed shares many taxa with the underlying vertebrate microfossil localities. However, a notable diffe...

Cretaceous Esocoidei (Teleostei); early radiation of the pikes in North American fresh waters

ABsTRAcr-Contrary to ideas that Cretaceous fresh waters contained few teleosts, there were several taxa of Esocoidei (pikes and relatives) in North American Cretaceous rivers. Dentaries and palatines of Campanian to Maastrichtian age all have C-shaped tooth bases and other distinctive features of shape and foramina. The fossils include at least three distinct kinds, two of which are described here as new genera and species in the Esocidae: Estesesoxfoxi n. gen. and sp. and Oldmanesox canadensis n. gen. and sp. These old, diverse, and apparently primitive specimens show that pikes radiated when Eurasia and North America were still joined. Some references in the literature to the Cretaceous fish Platacodon Marsh are based on referred dentaries that are here identified as esocoid fossils. The Esocidae are the first example of a family of Recent North American freshwater teleosts that has been shown to have speciated in Cretaceous fresh waters and survived the terminal Cretaceous extinction.

Anatomy and relationships of the turtle Boremys pulchra (Testudines: Baenidae)

ABSTRACT An associated skull, neck and carapace provides the first evidence concerning the structure of the skull in Boremys pulchra. The relationships of Boremys and its species-level diversity are re-evaluated based on this specimen, together with a series of shells and isolated skulls collected from the Judith River Formation. Boremys pulchra and Boremys grandis are recognized as valid species. Boremys is the sister taxon of Eubaena within the Eubaeninae based on six derived and shared cranial characters. We conclude that the derived characters of the carapace and plastron that had previously defined the subfamily but are not present in Boremys have arisen independently within the subfamily. These are the subdivision of the cervical scale into four small scales and the reduction in the number of suprapygal bones to one.

New exceptional specimens of Prognathodon overtoni (Squamata, Mosasauridae) from the upper Campanian of Alberta, Canada, and the systematics and ecology of the genus

ABSTRACT Currently known from the early Campanian to late Maastrichtian, Prognathodon constitutes a group of mosasaurine mosasaurs that typically possessed massive jaws. Only four articulated skulls are known to date and the information concerning their postcrania remains minimal. Moreover, the early to middle Campanian specimens of the taxon are extremely rare and fragmentary. Two new specimens of Prognathodon overtoni from the early late Campanian (ca. 74.5 Ma) Bearpaw Formation exposed near Welling, southern Alberta, Canada, provide the first fully articulated skeletons of the genus. Detailed morphological assessment of these and pre-existing specimens indicates that many cranial characters are shared between P. overtoni and the generic type P. solvayi from the early Maastrichtian, including (1) short premaxillary-maxillary suture; (2) short triangular frontal with marked anterior constriction; and (3) distinct, blind-ended median opening on medullary floor of basioccipital. These are interpreted as generically diagnostic characters, and the first character in particular distinguishes Prognathodon from Liodon and other long-snouted mosasaurines. The postcranium of P. overtoni is lightly built, and differs very little from that of Clidastes, a basal mosasaurine. Marginal teeth are carinate with fine crenulations, indicating their proposed opportunistic predatory behavior. Additionally, most of the fully erupted teeth exhibit a similar degree of apical wear, which is interpreted as indicating that the taxon regularly handled prey items that involved crunching. To augment these dietary inferences, gut contents from one of the new specimens include fragments of a large and a small fish, a sea turtle, and possibly a cephalopod.

A NEW TURTLE FROM THE ARUNDEL CLAY FACIES (POTOMAC FORMATION, EARLY CRETACEOUS) OF MARYLAND, U.S.A.

Abstract A new paracryptodiran turtle, Arundelemys dardeni, gen. et sp. nov., is described on the basis of an isolated, nearly complete skull from the Early Cretaceous Arundel Clay facies of Maryland, USA. The basicranial region exhibits the paracryptodiran condition of a single foramen for the canalis caroticus internus located midway along the basisphenoid. As revealed by CT scans, the basicranial region of Arundelemys is unusual in that the right and left canales carotici interni merge just before reaching the sella turcica and the canalis caroticus lateralis is very small or absent. A phylogenetic analysis places Arundelemys dardeni as the basal-most member of the Paracryptodira. Within the Paracryptodira, Arundelemys dardeni is most similar to Compsemys victa in general proportions.