摘要:

We recognize at least 22 taxa of vertebrates from the Paleocene Cannonball Formation, which records the last marine incursion into central North America. These include 12 elasmobranchs, two chimaeroids, five actinopterygians, and three reptiles. All but three taxa are described and illustrated for the first time for the formation. One species is new,Dasyatis concavifoveus. Teeth ofCarcharias taurusare most frequently found; other vertebrate fossils are relatively uncommon or rare. Cannonball vertebrates are known from 72 localities, most from southwest-central North Dakota.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011484

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Previously undescribed frog and salamander bones from the Morrison Formation, at Quarry Nine, Como Bluff, Wyoming, are reported. One anuran ilium is diagnostically discoglossid and forms the basis ofEnneabatrachus hechti, gen. et sp. nov. A second ilium is diagnostically pelobatid and is the earliest record for the family Pelobatidae, although it is indeterminate below family level. Salamander vertebrae appear to represent two morphological types but neither can be diagnosed critically. The previously described anuran taxaEobatrachus agilisMarsh andComobatrachus aenigmatisHecht and Estes and the salamanderComonecturoides marshiHecht and Estes are all based on non-determinate elements and must be considered nomina dubia at our present state of knowledge.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011485

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

In extant turtles and lepidosaurs, the astragalus forms from a single ossification center in a tarsale proximale resulting from fusion of originally separate chondrogenic condensations in the proximal tarsus. In crocodiles, the astragalus also ossifies from a single center although the cartilaginous precursors of astragalus and calcaneum do not fuse to form a tarsale proximale. Developmental stages of the parareptilianMesosaurusdocument a similar ossification pattern, as do ontogenic series of a number of fossil diapsid reptiles. There is no consistent evidence of ontogenetic fusion of a “tibiale,” intermedium, and centrale to form the astragalus ofCaptorhinus. The development of the amniote astragalus contrasts with variable patterns of fusion of originally separate proximal tarsal ossifications in anthracosaurian amphibians and inDiadectes. It is concluded that the reptilian (and probably also the mammalian) astragalus is a neomorph, which resulted from ontogenetic repatterning and is diagnostic of the Amniota (or Reptilia, respectively). Instances of incongruence in the formation of the astragalus from a single ossification center include microsaurs of problematical status.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011486

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The laterosphenoid is an ossification of the pila antotica neurocranial cartilage in the anterior sidewall of the braincase of crocodylians and birds. Contrary to published reports, the bone is present in the basal archosauriformsProterosuchus fergusi, Euparkeria capensis, and Erythrosuchidae, taxa that diverged prior to the origin of the archosaurian crown group. Its presence is thus a synapomorphy of Archosauriformes rather than of Archosauria. The bone appears to have been induced by shifting jaw muscle origins from the skull roof to the anterolateral wall of the braincase. Additional innovations in the archosauriform feeding apparatus, such as a mandibular fenestra, appear to reflect changes in jaw muscles that may, in turn, facilitate predaceous habits. We review the historical development of the names of bones in the anterior sidewall of the amniote braincase and argue for the use of the term laterosphenoid, rather than either pleurosphenoid or orbitosphenoid, for this bone in all Archosauriformes.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011487

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Much of a skeleton ofDibothrosuchus elaphrosfrom the Lower Lufeng Group (Lower Jurassic) of Yunnan, China permits a detailed review of the anatomy and relationships of sphenosuchian crocodylomorphs. The skull is strongly built, akinetic, and monimostylic. The quadrate shows three dorsal processes that are firmly sutured to the skull roof and the braincase. The otic capsule is essentially crocodilian, and the tympanic pneumaticities are more elaborate than in extant forms. The animal possessed refined hearing ability and was probably vocal. The coracoid has an extremely elongated, posteriorly directed postglenoid process. The humerus bears an oval depression anteriorly near the head, and the radiale and ulnare are longer than the metacarpals. The limbs are long and slender, adapted for quadrupedal terrestrial gait. The estimated total length was 1.3 m. Phylogenetic analysis of 65 characters indicates the monophyly of the Sphenosuchia. Within the Sphenosuchia,Saltoposuchus(=Terrestrisuchus),Pseudhesperosuchus, Hesperosuchus, andSphenosuchusare successively closer relatives toDibothrosuchus. The Sphenosuchia, in turn, are the sister-group of Crocodyliformes.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011488

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A new crocodilian from the Miocene of northwestern Queensland is described asTrilophosuchus rackhami, gen. et sp. nov. This is a small crocodilian reminiscent ofOsteolaemusandPaleosuchus. However, resemblance to these forms appears to be the result of convergence on a short-snouted adaptive form.Trilophosuchusalso resembles extinct taxa such asNotosuchus, Araripesuchus, Libycosuchus, Theriosuchus, andProtosuchus.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011489

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The bone microstructure of three third metatarsals and two tibiae of differing sizes fromTroodon formosuswas examined. Bone inT. formosuspassed through three ontogenetic stages: rapid fibro-lamellar, moderate lamellar-zonal, and slow avascular lamellar growth. Highly-vascularized fibro-lamellar bone accounted for the majority of growth, with adult size possibly being reached in 3 to 5 years. No significant growth occurred afterT. formosusreached a body weight of roughly 50 kg (femur: tibia length 310:425 mm). Abundant vasculature together with dense Haversian bone suggestsT. formosushad a relatively high metabolism. Other gross morphological features (large brain, large eyes, cursorial adaptations including high tibia: femur ratio) would indicateT. formosuswas very active and possibly endothermic.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011490

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A diverse therian fauna is present in the Dakota Formation of Cenomanian age. Two pediomyid-like taxa are described on the basis of upper molars, but may be deciduous molars of nonpediomyid taxa. A new genus and species of marsupial-like tribothere is described and named (Dakotadens morrowi). A new family of marsupials (Alphadontidae) is established forAlphadon-like genera. The range ofAlphadonis extended back into the Cenomanian, two new species are named (A. clemensi, A. lillegraveni), and a possible third new species is described. The range ofProtalphadonis also extended back into the Cenomanian. Possible upper molars ofPariadens kirklandiare described and the diagnosis of the genus is revised based on unsheared lower molars; placement of this taxon in the Stagodontidae remains problematic. Upper molars of all therians recovered from the Dakota Formation have relatively broad stylar shelves; collectively, they include a wide range of stylar cusp configurations, although a cusp or cusps in the position of stylar cusp C is present on most upper molars. As such, the absence of cusps in the C position may not be primitive for marsupials. The marsupial-like tribothere described here, together with several other tribotheres, share derived characters with marsupials and may be part of an early diversification of the Metatheria. The divergence of metatherian and eutherian lineages may have occurred in the earliest Cretaceous (Neocomian).

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011491

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Analysis of a recently discovered partial skeleton ofProlimnocyon atavus, an early Eocene creodont (Hyaenodontidae, Limnocyoninae), from the Willwood Formation of the Bighorn Basin, Wyoming, demonstrates that its postcranial skeletal anatomy was most similar to that of extant scansorial procyonid, viverrid, and mustelid Carnivora. Its anatomical traits (including reduced greater tuberosity, prominent and sharp deltopectoral crest, well-developed entepicondyle and brachial flange, ovoid radial head and gently concave, laterally oriented radial notch, moderately deep, laterally compressed ungual phalanges, medially projecting lesser trochanter, flattened talar trochlea with high lateral rim, helical proximal cuboid facet) are commonly associated with joint mobility and abducted limb posture which, in extant mammals, are characteristic of scansorial and ambulatory locomotion. These features resemble those of some early Eocene proviverrine hyaenodontids and, to a lesser extent, miacid Carnivora, but contrast with those of more terrestrially adapted oxyaenids, certain other hyaenodontids, and viverravid Carnivora.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011492

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011493

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor