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The morphology and systematic position of the capitosauroid amphibian “Parotosuchus” africanus (latest Early(?)–earliest Middle Triassic, Middle Cynognathus Subzone, Karoo Basin, South Africa) are re-evaluated on the basis of a nearly complete, hitherto undescribed, skull from the Museum of Paleontology, University of California. The attribution of the UCMP specimen to “P.” africanus is based on direct comparison with the holotype. This species is shown to be markedly advanced over the Parotosuchus level in the structure of the tabulars and the postglenoid division of the lower jaw, in the shape of the posterior rim of the mandibular adductor fossa, and in the strong development of the medial plate of the surangular. This pattern of the cranial structure is combined with a set of primitive characters lost in true Parotosuchus, such as the broad nasals, weakly developed interorbital projections of the frontals, elliptic choanae, short palatal exposure of the parasphenoid cultriform process, and a curved interchoanal tooth row. On this evidence, “P.” africanus is distinguished as a new genus, Xenotosuchus, gen. nov.
The first phylogenetic analysis of the Euramerican Early Cretaceous–Miocene genus Albanerpeton is presented based on 16 characters of the jaws, frontals, and inferred body size scored for the seven recognized species in the genus and three other albanerpetontid taxa. Monophyly of Albanerpeton is corroborated and nested sets of synapomorphies yield the following hypothesized relationships: A. arthridion ((A. cifelliiA. galaktionA. gracilis) (A. nexuosus (unnamed late Paleocene species A. inexpectatum))). Osteological modifications identified in Albanerpeton initially involve the frontals, then shift largely to the jaws. Many of these changes are interpreted to be associated with broadening the head and strengthening the snout and jaws, presumably for feeding and burrowing. The first half or more (latest Aptian/earliest Albian to late Paleocene) of the known record for Albanerpeton and six of the seven species are restricted to the North American Western Interior. These occurrences and the phylogenetic framework proposed here suggest that the evolutionary history of Albanerpeton was centered in the Western Interior of North America.
Dentary and maxillary fragments represent the first documented evidence of a bolosaurid reptile, Bolosaurus grandis, sp. nov., from the Lower Permian (Leonardian) fissure fills of the Dolese Quarry, near Richards Spur, Oklahoma. The discovery of bolosaurid remains at this unique site, characterized by the preservation of exclusively terrestrial tetrapods, is of particular interest because they bridge the temporal gap in the evolutionary history of bolosaurids between the Wolfcampian Bolosaurus striatus of Texas and the much younger, Upper Permian (Kazanian) Belebey of southern Russia. They also provide new information about the mandibular and dental anatomy of this enigmatic group of early amniotes.
A new taxon of Cretaceous short-necked plesiosaur, Edgarosaurus muddi, gen. et sp. nov., is described. The specimen consists of a complete skull, 34 vertebrae including the entire series of 26 cervicals, and a nearly complete forelimb. The new taxon occurs in marine sediments of the Thermopolis Shale (late Albian), deposited during an early transgression of the Western Interior Seaway. The skull of Edgarosaurus is the oldest, and one of the best preserved plesiosaur specimens from the Cretaceous Western Interior of North America described to date. Edgarosarus differs from the morphologically and stratigraphically close short-necked taxon Plesiopleurodon wellesi in a number of cranial characters. In the absence of an established phylogenetic framework, the new plesiosaur is placed in the Polycotylidae, as recently defined by Carpenter in 1996. It is plesiomorphic with respect to other polycotylids in that it possesses a relatively robust and moderately elongated rostrum, a pineal foramen, caniniform teeth, a shorter mandibular symphysis, and a relatively high number of cervical vertebrae.
Soft tissues associated with the cranial crest are described in a specimen of Germanodactylus rhamphastinus from the Solnhofen Limestone of southern Germany. The soft tissues covered, and extended upward from, the bony premaxillary crest, more than doubling the height of the crest, and were probably composed of cornified epidermis. Comparison of this specimen with other Solnhofen pterodactyloids with premaxillary crests suggests that all had soft tissues increasing the size of the crest in life.
A new Early Cretaceous enantiornithine bird, Eocathayornis walkeri, gen. et sp. nov. is reported from Liaoning, northeast China. It is about the size of Cathayornis but is more primitive. Teeth are present on the jaws. Claws are retained on three wing digits, but that of the minor digit is reduced. The width of the radius is nearly three-fourths that of the ulna. The sternum is relatively short, with a pair of long caudo-lateral processes and a low and caudally distributed keel. The coracoid is strut-like and caudally concave, typical of enantiornithine birds. The advanced features of the scapula and the wing suggest a powerful flapping flight capability. This bird is referred to the family Cathayornidae based on a few shared derived characters with Cathayornis.
A nearly complete, well-preserved maxilla of an abelisaurid theropod from the early Late Cretaceous (middle Cenomanian-Turonian) Lower Member of the Bajo Barreal Formation of Chubut, Argentina represents the first definitive member of the abelisaurid clade from pre-Senonian (Coniacian–Maastrichtian) deposits. The new maxilla shares derived characters with the maxillae of Carnotaurus and Majungatholus, and with AMNH 1955, a maxilla previously referred to Indosuchus, suggesting that it pertains to the abelisaurid subclade Carnotaurinae. Abelisaurus shares apomorphic characters with Carnotaurinae, but many of these characters are also found in the carcharodontosaurid allosauroid Giganotosaurus. As it is known only from cranial material lacking carnotaurine synapomorphies, Abelisaurus may represent a late-surviving carcharodontosaurid derivative.
The presence of the Bajo Barreal predator in the early Late Cretaceous indicates that the origin of Abelisauridae had occurred by then. The occurrence of the new maxilla is nearly concurrent with the accepted interval of tectonic divergence between South America and Africa. Its discovery thus weakens support for the recent hypothesis that the abelisaurid clade could not have penetrated Africa. The known occurrence of Abelisauridae may reflect a former pan-Gondwanan distribution, and is thus of limited utility in the support of Late Cretaceous paleogeographic hypotheses.
A sub-adult Allosaurus fragilis (MOR 693) was discovered in 1991 in the Upper Jurassic Morrison Formation of Big Horn County, Wyoming. Examination of the specimen reveals pathological conditions on five dorsal ribs, gastralia, cervical vertebra, three dorsal vertebrae, caudal vertebra, chevron, scapula, manus phalanx, ilium, two metatarsals, and two pes phalanges. Detailed description of these bones includes classification according to probable cause (i.e., traumatic; infectious; traumatic-infectious; developmental; idiopathic). In addition to the paleopathological analysis of MOR 693, descriptions and interpretations are given from a study in progress of pathological abnormalities in the Cleveland-Lloyd Dinosaur Quarry collection. This study provides a model for future paleopathological analyses, emphasizing that description of the location, extent, and texture of an abnormality is crucial, since interpretations are subject to change.
This analysis discusses physiological implications of the abnormalities in MOR 693 and suggests probable behaviors and environmental influences resulting in injury and infection. Lifestyle and behaviors that likely predisposed allosaurs to injury and infection include pursuit of prey, intra-specific competition for mates, and intra- and inter-specific rivalry for carcasses and territory. Ultimately, paleopathological analysis of a large sample of dinosaur bones may reveal that certain abnormalities characterize taxa, and are diagnostic of specific behaviors, environmental influences, and physiology.
A survey of mosasaur material from the Eutaw Formation (Santonian) and Selma Group (Late Santonian–Late Maastrichtian) of western and central Alabama has revealed significant stratigraphic segregation among taxa. Three distinct biozones are recognized based on this survey: the Tylosaurus Acme-zone (from the base of the Tombigbee Sand Member of the Eutaw Formation to approximately 12 m above the base of the Mooreville Chalk), the Clidastes Acme-zone (from approximately 12 m above the base of the Mooreville Chalk to the base of the Demopolis Chalk), and the Mosasaurus Acme-zone (from the base of the Demopolis Chalk to the K-T boundary at the top of the Prairie Bluff Chalk). In each case, the biozone is named for the genus comprising the majority of the specimens examined from that horizon. The previously-recognized Globidens alabamaensis Acme-zone, including the Arcola Limestone Member of the Mooreville Chalk, has been abandoned. The transition from the Tylosaurus biozone to the Clidastes biozone has been interpreted primarily as an artifact of paleoecology, reflecting habitat preference; additional support for this interpretation has come from the mosasaur fauna of the Blufftown Formation (?Late Santonian–Early Campanian) of eastern Alabama and western Georgia. The transition from the Clidastes biozone to the Mosasaurus biozone appears to represent the local expression of a reorganization within North American mosasaur communities. The uppermost portion of the Selma Group, comprised of the Ripley Formation and Prairie Bluff Chalk, has been tentatively included in the Mosasaurus Acme-zone on the basis of poorly-known faunas.
Pachyrhachis problematicus is an early Upper Cretaceous snake with legs from the Middle East. The taxon is involved in an increasingly controversial debate about the origin and higher-level interrelationships of snakes. Its status is problematic because it combines characters of advanced (macrostomatan) snakes with plesiomorphic squamate traits. Two competing hypotheses of relationships have consequently been proposed: (1) Pachyrhachis is the sister group of all other snakes, and links Serpentes with Mosasauroidea; and (2) Pachyrhachis is related to the advanced macrostomatan snakes and has no bearing on the issue of snake origins. In a recent paper published in this journal, Caldwell critically reviewed the status of Pachyrhachis as the sister-taxon of macrostomatan snakes, and concluded that Pachyrhachis is the sister-group of all other snakes instead. In the present paper, we review several aspects of character delimitations as proposed by Caldwell, and corroborate the macrostomatan affinities of Pachyrhachis.
Extant camelids (llamas and camels) are unique among wild mammals in their regular employment of a pacing gait. They also have a unique foot morphology, assumed to be an adaptation for this mode of locomotion: their feet are secondarily digitigrade, with the loss of hooves and the addition of a broad foot pad. We examined 22 measurements of the metapodials and phalanges of camelids and ruminants with bivariate and multivariate analyses, including 18 genera of extinct camelids from the Tertiary of North America. Extant camelids and ruminants were clearly distinguishable from each other. Most extinct camelids showed some morphological features typical of extant forms, five out of eighteen clustered with the extant camelids. Pacing may have evolved independently within the subfamilies Camelinae and Protolabinae. Additionally, evolutionary change towards a condition resembling that of extant camelids also occurred within the subfamilies Stenomylinae and Miolabinae. These parallel changes in camelid locomotor anatomy occurred in the late Oligocene or early Miocene, preceding the formation of widespread open grassland habitats in the late Miocene.
The hyracoid Antilohyrax pectidensRasmussen and Simons, 2000 from quarry L-41 in the Fayum, Egypt displays many interesting features, including a comb-like, pectinate lower first incisor similar to that of the dermopteran Cynocephalus. Antilohyrax was originally described as lacking upper incisors, and having retracted nasal bones and selenodont cheek teeth, functionally resembling characters found in bovid artiodactyls. Analysis of cranial and postcranial material led to the hypothesis that Antilohyrax was a cursorial browser.
Recent expeditions have recovered additional material that contributes greater detail about cranial and dental morphology and allows for the reassessment of characters previously unknown or misinterpreted. Among these is the presence of at least two pairs of upper incisors, the central pair of which form tusks as in all other hyracoids, and a slender nasal bone which projects anteriorly to the level of the premaxilla. There is evidence of a pad on the premaxilla that occludes with the pectinate lower incisors. In the mandible, a second pair of incisors has been recovered that are sickle shaped, lack pectinations, and occlude with the upper tusks. Other notable characters preserved in the new specimen include the presence of a complete postorbital bar, a large, round, and blunt postorbital boss, a lateral flange on the zygomatic arch, a deep antorbital groove of the frontal bone, a lambdoid crest, a long paroccipital process, and a unique nuchal region. Comparisons with newly recovered and as yet undescribed cranial material of Titanohyrax reveal more characters shared by these genera, strengthening the case for their inclusion as sister taxa within the Titanohyracinae. Examination of characters relevant to paenungulate phylogenetics confirm earlier observations that extant hyracoids have changes in cranial proportions that result in some character states not representative of early hyracoids. Functional inferences lend further support to the suggestion that Antilohyrax was a folivorous browser.
Spermophilus cf. howelli, Spermophilus sp., Castor or Dipoides sp., Geomys cf. adamsi, Symmetrodontomys daamsi, sp. nov., Bensonomys hershkovitzi, sp. nov., Ogmodontomys pipecreekensis, sp. nov., and Pliophenacomys koenigswaldi n. sp. are reported from the Pipe Creek Sinkhole of Grant County, Indiana. The Geomys sample demonstrates a variable sulcus morphology of the upper incisor, suggesting it stands near the Geomys—Pappogeomys boundary. Symmetrodontomys daamsi is characterized by its short lower molars and small mandible. Bensonomys hershkovitzi has a unique m1, with an anteroconid that with little wear connects deeply with the labial cingulum, and a mesolophid. O. pipecreekensis, with relatively low dentine tracts and no enamel atoll on m1, may be related to both Ogmodontomys sawrockensis and Ogmodontomys poaphagus, although it is probably not ancestral to either of them. Ogmodontomys Hibbard is considered an endemic North American genus distinguished from Mimomys Forsyth Major on the basis of a suite of dental features, including absence of a full lamellar enamel layer on leading edges of the molar triangles. The dentition of Pliophenacomys koenigswaldi exhibits a set of features suggesting a close relationship with Pliophenacomys finneyi of the early Blancan Fox Canyon local fauna of Kansas. Together with the rhinoceros Teleoceras, the rodent assemblage collectively suggests an early Pliocene (latest Hemphillian) age for the Pipe Creek biota. This is the first report of a late Neogene rodent fauna from Indiana.
The late Early Miocene locality of Shanwang, China is known for its rich and well preserved fossils. Here new suid material is described and previously published material is revised. Hyotherium shanwangense, sp. nov. is described based on a partial skull and includes the M3 from the site that was previously assigned to Palaeochoerus cf. pascoei. A right lower jaw is referred to Sinapriculus linquensis, gen. et sp. nov., a primitive suid. The type material of Hyotherium penisulus is assigned to Listriodontinae. The Chinese Hyotherium seems to lie close to the ancestry of tetraconodonts. The more primitive suid Sinapriculus linquensis may represent a survival of an earlier suid radiation in East Asia and the Shanwang suid community as a whole could be seen as a sample of a previously unsuspected East Asian early suid diversity. Such a view would be concordant with the record of late Eocene and early Oligocene suoids from China and Thailand.
Among living carnivorans, the degree of sexual dimorphism in canine tooth size is correlated with breeding system. Monogamous pair-bonding species and those that form multi-male, multi-female groups tend to be less dimorphic than uni-male, group living species. This correspondence between social behavior and dental dimensions suggests that the inference of sexual dimorphism in extinct carnivorans could shed light on their breeding structure. In this paper, we estimate level of sexual dimorphism in skull length, canine tooth size, and lower molar length for two extinct species, the dire wolf, Canis dirus, and the sabertooth cat, Smilodon fatalis. Three methods are employed to estimate sexual dimorphism: extrapolation from coefficients of variation, division of the sample about the mean, and finite mixture analysis. Results indicate that dire wolves were similar to most canids in their low level of sexual dimorphism, suggesting a pair-bonded breeding structure. Smilodon fatalis appears to have been significantly less dimorphic than living or fossil lions and more comparable to solitary living felids in canine and skull size dimorphism. Thus it seems unlikely that S. fatalis had a polygynous breeding structure like lions in which males compete intensely for access to females. Instead, if S. fatalis lived in groups, these would have been composed of a monogamous pair and their offspring from current and perhaps previous years.