ISSN:0272-4634    

DOI:10.1080/02724634.1997.10011012

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0272-4634    

DOI:10.1080/02724634.1997.10011013

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Some specimens of the Late Cretaceous lamniform shark,Cretoxyrhina mantelli(Agassiz), from the Niobrara Chalk in Kansas are represented by partial skeletons. The vertebral and neurocranial structures ofC. mantellisuggest its placement in Lamniformes. The pectoral fins ofC. mantellimay be plesodic, possibly indicating that the taxon is an “advanced” lamnoid. The total vertebral count ofC. mantelli, approximately 230, is a unique number among lamniforms, supporting the view based on tooth-based taxonomy that this taxon is a distinct species. The total length of largeC. mantelliis estimated to be 5 m. Very large C.mantellipossibly attained a total length of about 6 m or slightly more.Cretoxyrhina mantellipossessed a conical head with a blunt snout and large eyes. The body form ofC. mantellicould have resembled that of extantCarcharodon carcharias.

ISSN:0272-4634    

DOI:10.1080/02724634.1997.10011014

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A new tristichopterid,Cabonnichthys burnsigen. et sp. nov. from the Upper Devonian Mandagery Sandstone near Canowindra, New South Wales, Australia, is the second tristichopterid to be described from this locality. The first,Mandageria fairfaxi, was interpreted as the sister group of the Laurussian taxonEusthenodon. Cabonnichthys burnsigen. et sp. nov. is similar to these two taxa in possessing a posterior supraorbital extending ventrally behind the orbit to exclude the postorbital from the orbital margin, a posteriorly positioned pineal surrounded by kite or teardrop shaped bones, and an enlarged fang-like tooth at the anterior end of the premaxillary tooth row.Cabonnichthys burnsidiffers fromMandageriaandEusthenodonin retaining a contact between the intertemporal and posterior supraorbital, and in possessing “horn-like” processes on the postparietal shield that notch into the posterior margin of the postorbital. The Tristichopteridae is a clade characterized inter alia by the possession of postspiracular bones. A phylogenetic analysis of the Tristichopteridae yields the topology [Tristichopterus [Eusthenopteron [Jarvikina [Platycephalichthys [Cabonnichthys [Mandageria+Eusthenodon]]]]]]. This topology is consistent with the biostratigraphy of the group, and with a number of morphological trends including size increase and elaboration of the anterior dentition. It also suggests that the group has a northern origin and dispersed into Gondwana during the Upper Devonian.

ISSN:0272-4634    

DOI:10.1080/02724634.1997.10011015

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A new procolophonid,Libognathus sheddi, gen. et sp. nov. is reported from the Cooper Canyon Formation (Dockum Group; Upper Triassic: lower Norian) near Post, Texas. This is the first published description of an unequivocal procolophonid from the Upper Triassic of the southwestern United States. Some of the distinctive characters ofLibognathusare the deep dentary, large anteriorly directed foramen on the lateral dentary surface, and the forward projecting coronoid.Libognathusprovides a good example of tooth replacement and implantation, which are poorly known in procolophonids. The implantation is protothecodont, with the teeth set in sockets and firmly anchored by spongy bone of attachment. The stages of replacement are of the typical reptilian pattern.Libognathusis closely related toHypsognathusfrom the Passaic Formation (Norian) of New Jersey, and correlative strata in Connecticut and Nova Scotia.

ISSN:0272-4634    

DOI:10.1080/02724634.1997.10011016

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A review of all described species referred toLeidyosuchusrecognizes six valid taxa:Leidyosuchus canadensis, L. multidentatus, L. sternbergii, L. formidabilis, L. wilsoni, andL. acutidentatus. Leidyosuchus riggsiis a nomen dubium,L. gilmoreiis a junior synonym ofL. canadensis, andDiplocynodon stuckeriis a junior synonym ofL. wilsoni. Phylogenetic analysis of 164 morphological characters indicates a basal position within Alligatoroidea forL. canadensis. The nameListrognathosuchusis established forL. multidentatus, which is an alligtoroid, but difficult to characterize further because of its incompleteness. The remaining taxa form a clade herein namedBorealosuchus;this group is related to, but not within, a monophyletic group that includes Alligatoroidea and Crocodyloidea. A close relationship between these taxa andDiplocynodonis rejected. Although presently known only from the Tertiary of Europe, taxa closer toDiplocynodonthan to Alligatoridae are expected to occur in the Late Cretaceous.

ISSN:0272-4634    

DOI:10.1080/02724634.1997.10011017

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A previously unrecognized partial skeleton ofChirostenotes pergracilisGilmore, 1924 from the Upper Cretaceous Horseshoe Canyon Formation of Alberta (Canada) includes parts of the skull, much of the pelvic girdle, and elements from all regions of the vertebral column. It provides much new information concerning the skeletal structure of this unusual theropod dinosaur. Close structural correspondence between the maxilla of this specimen and the mandible ofCaenagnathus collinsiR. M. Sternberg, 1940 indicates that the latter taxon should be considered a subjective junior synonym ofChirostenotes pergracilis. “Ornithomimus” elegansParks, 1933 is probably also referable toChirostenotes. The family-level taxon Elmisauridae Osmólska, 1981 is regarded as a subjective junior synonym of Caenagnathidae R. M. Sternberg, 1940. The newly recognized specimen ofChirostenotes pergracilisprovides important new evidence for referring Caenagnathidae to Oviraptorosauria. Preliminary phylogenetic analysis indicates a sister-group relationship between Oviraptorosauria and Therizinosauroidea.

ISSN:0272-4634    

DOI:10.1080/02724634.1997.10011018

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A skull of the oldest described argyrolagid,Proargyrolagus bolivianus(late Oligocene of the Salla Beds, Bolivia) allows an assessment of the phylogeny of this group and a reconstruction of its paleobiology. Several aspects of the cranial anatomy of theMonodelphis-sizedProargyrolagusserve to support the hypothesis that argyrolagids are marsupials: the palate has large vacuities, the angular process is medially inflected, the auditory bulla is composed of a wing of the alisphenoid, and the dental formula includes four molars. Like Argentine Plio-Pleistocene argyrolagids,Proargyrolagushas an unfused symphysis, and a phaneric and almost vertically oriented ectotympanic in the shape of a flattened ring.Proargyrolagusis more primitive in having a less globular braincase, smaller orbits, and a shallower mandible. The dental formula is 4/3.1/1.3/2.4/4 or 4/4.1/0.3/2.4/4 (vs. 2/2.0/0.1/1.4/4 forArgyrolagus). Large infraorbital foramina transmitted nerves and vessels of the snout. The snout is long with the nasals projecting well forward of the incisors and with a strong antorbital fossa for facial muscles. It can be inferred that this animal had well-developed vibrissae and a mobile proboscis, and relied heavily on its rostrum to gather tactile information. Food manipulation was assisted by an elongate, procumbent lower incisor that occluded with three sharply-edged upper incisors, as in living phalangeriform marsupials. Like Plio-Pleistocene argyrolagids and extant elephant shrews,Proargyrolagushas prismatic and high crowned cheek teeth suggesting an abrasive diet consisting perhaps of seeds.

ISSN:0272-4634    

DOI:10.1080/02724634.1997.10011019

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We analyzed 108 adult lower third premolars and 38 upper second premolars of leporids from the late Barstovian (ca. 13 Ma) Valentine Railway quarries in north-central Nebraska. Remains of two species of the archaeolagine genusHypolagusare overwhelmingly abundant in four of five quarry samples. Both the large, primitiveHypolagus parviplicatusand the smaller, more derivedH. fontinalisare represented by larger samples than have previously been available, including upper and lower jaws. At a fifth site remains of leporines, including a new species ofPronotolagusand a probable new species ofAlilepus, outnumber those ofHypolagus. The leporines are characterized by lingual reentrants and/or an enamel lake on p3 and, possibly, by three anterior reentrants on P2. The newPronotolagusis less derived than the oldest leporine previously known,P. apachensisof Clarendonian age (ca. 10 Ma), and probably descended from an earlier population ofH. parviplicatus. The unnamedAlilepus, on the other hand, shows closer affinity toH. fontinalis. The existence of two well-differentiated leporine species in the late Barstovian of the Great Plains strongly supports a North American rather than Palaearctic origin for the Leporinae, the oldest Eurasian representatives of which are at least five million years younger than the Valentine species. The abundance of brachydont ungulates at the leporine-rich Valentine site indicates a more wooded paleoenvironment than those represented at the remaining archaeolagine-rich sites, suggesting that the Leporinae may have first evolved in a forested environment.

ISSN:0272-4634    

DOI:10.1080/02724634.1997.10011020

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The giant otterEnhydritherium terraenovae, a New World taxon thought to be related to both the Old World otterEnhydriodonand the extant sea otterEnhydra, was originally described on the basis of relatively limited material, mostly dental. However, an incomplete skeleton ofE. terraenovaerecovered from the early Hemphillian Moss Acres Racetrack site in northern Florida includes a skull, mandible, part of the axial skeleton, and most of both the fore- and hindlimbs, adding greatly to knowledge of this animal. On the basis of this new material, the osteology of this species is described in detail for the first time, with its diagnosis revised accordingly. This new osteological information, along with information about the nature of the Moss Acres Racetrack site, allows such paleoecological and functional aspects ofE. terraenovaeas habitat preference, mode of swimming, and diet to be inferred or interpreted in a detail previously impossible.E. terraenovae:1) was a habitat generalist rather than a marine specialist, as previously thought; 2) was reasonably competent for terrestrial locomotion; 3) extensively used its forelimbs during swimming like living otariid seals, in contrast to the hindlimb-specializedEnhydra;and 4) had a generalized diet, potentially including soft items such as fish, as well as hard items, such as thick-shelled molluscs.

ISSN:0272-4634    

DOI:10.1080/02724634.1997.10011021

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor