摘要:

In Rowe (1988), 158 characters of the skull and postcranial skeleton distributed among Placentalia, Marsupialia, Monotremata, Multituberculata, Morganucodontidae, Tritylodontidae, andExaeretodonwere analyzed with PAUP. Mammalia, defined by Rowe as comprising the most recent common ancestor of living monotremes, marsupials, and placentals, was distinguished from its nearest extinct relatives by 37 osteological synapomorphies, including 24 characters of the cranium and dentition. Within Mammalia, Multituberculata was identified as the sister taxon of Marsupialia plus Placentalia.

ISSN:0272-4634    

DOI:10.1080/02724634.1991.10011372

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Fusion of caudal vertebrae in the sauropod dinosaursApatosaurus, Diplodocus, andCamarasaurusis explained as the result of ossification of ligaments spanning consecutive centra. The ossification does not involve the intervertebral space or the annulus fibrosus of the disc and therefore represents true bridging. This is verified by not only the gross external appearance, but also by the use of CAT scans and longitudinal section of a fused pair ofDiplodocuscaudal vertebrae. Fusion of caudal vertebrae inCamarasaurusis reported here for the first time. It is concluded that the fusion is the result of the physiological phenomenon called diffuse idiopathic skeletal hyperostosis (DISH) and therefore is not a pathological response or due to a physical injury. Various proposed hypotheses to explain the function of the fused caudals, such as defense and postural support, are considered untenable. Fusion of caudal vertebrae probably aided in keeping the tail elevated and undoubtedly served a functional role, though the specific nature of that function is presently unknown. Survey of North American specimens indicates that fusion of caudal vertebrae occurs in 50% of the individuals ofApatosaurusandDiplodocusin which the requisite portion of the tail is preserved, whereas this figure forCamarasaurusis about 25%. For this reason it is suggested that fusion of caudal vertebrae may be a sexually dimorphic feature.

ISSN:0272-4634    

DOI:10.1080/02724634.1991.10011373

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Two specimens collected recently from the middle Wichita Group (Wolfcampian–Leonardian Series, Early Permian) of Baylor and Archer Counties, Texas, represent a new sphenacodontid pelycosaur,Ctenorhachis jacksoni, gen. et sp. nov. The type includes of an articulated column of 31 vertebrae (presumably numbers 4 through 34) and an attached, nearly complete pelvis; the second specimen consists primarily of dorsal vertebrae. The vertebrae are typically sphenacodontid, with well-developed keels in the cervical and anterior dorsal series and pronounced pits on the lateral surface of the neural arch above elongated transverse processes. The pelvis is very similar to, if not indistinguishable from,Dimetrodon. Ctenorhachisis distinguished from all other sphenacodontids by neural spines that are only modestly heightened and uniformly blade-like antero-posteriorly. These spines are more primitive than those ofDimetrodonandSecodotosaurusand possibly more primitive than those ofCtenospondylus. A survey of sphenacodontid taxa from the Wichita Group of North–Central Texas indicates that existing classifications are handicapped by fragmentary type specimens that may be generically indeterminate and by a reliance upon size differences that are largely unquantified and upon stratigraphie data of questionable significance.

ISSN:0272-4634    

DOI:10.1080/02724634.1991.10011374

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

“Temnocyon” venatoris not related toTemnocyonof the Family Amphicyonidae; as shown by auditory structure, it is a true canid that is dentally convergent withTemnocyon. “T.”venatorcan be placed within the canid genusMesocyon, as a derived species of presumably hypercarnivorous ?solitary predator, with reduced M1–2, and trenchant M1–M2M. venatorhas generalized, catlike cervical vertebrae and pelvis, short,Gulo-like limbs, and a sub-digitigrade manus with a long pollex.Temnocyonis not related, andM. venatoris not closely related, toSpeothos (=Icticyon), Cuon, orLycaon, living convergent, hypercarnivorous canids which have reduced upper molars and a trenchant M1.

ISSN:0272-4634    

DOI:10.1080/02724634.1991.10011375

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The subfamily Leporinae probably had its origin from the Archaeolaginae in the North American Clarendonian (late Miocene) and include the following genera and species from late Miocene Clarendonian to latest Pliocene Blancan:Alilepus hibbardi, sp. nov.,A. vagus, A. wilsoni, sp. nov.,Pratilepus kansasensis, Aluralagus bensonensis, A. virginiae, Nekrolagus progressas, Aztlanolagus agilis, Sylvilagus hibbardi, Lepus, cf.L. californiens, Pronotolagus apachensis, gen. nov.,Notolagus velox, N. lepusculus, andParanotolagus complicatus. Two specimens ofHypolagus parviplicatusfrom the late Barstovian of Saskatchewan have two shallow grooves in the enamel of the lingual side of P3that may be incipient anterointernal and posterointernal reentrants, suggesting a precursor to the ancestry of the Leporinae.

ISSN:0272-4634    

DOI:10.1080/02724634.1991.10011376

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The braincase of the Early Cretaceous birdEnaliornisis indicative of a primitive avian brain with a relatively large medulla oblongata, a small cerebellum, small cerebral hemispheres broadly separated from the labyrinth, and a strong basilordotic bend of the whole brain, the latter being characteristic of an airencephalic skull. The reduction of the dorsal pneumatic recess, the large size of the auricular fossa, and possibly the lack of interfoliar ridges on the roof of the cerebellar fossa suggest diving habits and thus support the association of the braincases with the type tarsometatarsus ofEnaliornis. The braincase ofEnaliornisis most similar to those ofHesperornis, Phaethon, Diomedeidae andFregata. Most of the similarities to these taxa are primitive for birds.

ISSN:0272-4634    

DOI:10.1080/02724634.1991.10011377

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

At least 33 vertebrate taxa from the lower and middle Siwalik Group (middle and late Miocene) of southern and western Nepal compare well with assemblages from the lower and middle Siwaliks of Pakistan and India. Localities low in the Nepal section contain the suidConohyus, the hominoidSivapithecus, the rhinocerotidBrachypotherium, and typical lower Siwalik artiodactyls, carnivorans, and proboscideans. Several stratigraphically higher localities yieldHipparion, as well as artiodactyls characteristic of the middle Siwaliks.

ISSN:0272-4634    

DOI:10.1080/02724634.1991.10011378

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0272-4634    

DOI:10.1080/02724634.1991.10011379

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0272-4634    

DOI:10.1080/02724634.1991.10011380

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0272-4634    

DOI:10.1080/02724634.1991.10011381

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor