摘要:

A new Late Cretaceous neosuchian crocodylomorph,Gilchristosuchus palatinusgen. et sp. nov., is described on the basis of a partial skull from the basal Campanian or uppermost Santonian Milk River Formation of southern Alberta. This species is diagnosed primarily by the posterior extension of the palatine well beyond the suborbital fenestra, leading to a posterior shift of the choana. The primitive entrance of the palatines into the choana excludesG. palatinusfrom the Eusuchia. The posteriorly positioned choana and the presence of the postorbital/parietal contact, however, indicate that the species is the most derived non-eusuchian crocodylomorph.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011497

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The recent discovery of a nearly complete ceratopsid skull in the Aguja Formation of southwest Texas supports previous conclusions that the Aguja ceratopsid represents a distinct species,Chasmosaurus mariscalensis. The diagnostic features ofC. mariscalensisinclude an extensive anteromedian projection of the nasal between the premaxillae, erect supraorbital horns, and laterally rounded squamosal. Nine cranial features that vary amongChasmosaurusspecies,Pentaceratops sternbergii, and other chasmosaurines are analyzed.Chasmosaurus mariscalensisappears to be most closely related to northern species ofChasmosaurus (C. belli, C. russelli), which also exhibit a transversely flattened nasal horn and modifications of the anterior margin of the external naris. The genusChasmosaurus, in turn, appears to be most closely related to the other southern chasmosaurine,Pentaceratops sternbergii. The biogeographic history inferred from these relationships suggests that the biogeographic exchange between northern and southern chasmosaurines cannot be explained by a single dispersal event to the south.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011498

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

In previous phylogenetic analyses the hypothesis of homology of the furcula of birds and some other maniraptorans with the clavicles of ancestral archosaurs has been protected from the test of congruence through ad hoc hypotheses of non-preservation. Cladistic evaluation of the distribution of the evidence for clavicles and furculae within the Dinosauria casts some doubt on the homology of the furculae and clavicle-like structures that characterize various clades within the Maniraptora with the plesiomorphic archosaurian clavicle. Depending on the degree to which the absence of clavicles in particular clades is accepted as real, the test of congruence using the currently accepted phylogenetic relationships within the Ornithodira suggests that the loss of clavicles may be plesiomorphic within Dinosauria. This raises the possibility that the furcula of birds may be a neomorph, or may represent the reappearance of a “lost” structure. The test of congruence depends on acceptance of negative evidence for clavicles in particular clades. Preference for the alternative explanation of non-preservation seems to be based, at least in part, on a priori acceptance of the very homology statement that one wishes to test. Provisional acceptance of the absence of structures in fossils forms the basis for hypotheses that are subject to falsification and provides the only means whereby certain homologies can be tested via congruence.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011499

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The anatid genusChendytescomprises two species from the Pleistocene and early Holocene of California: the comparatively largeC. lawiand the smaller (poorly represented)C. milleri. Osteological comparisons confirm thatChendytesis a member of the Mergini, probably most closely related to the eiders (Somateria). Peculiarities of the pectoral skeleton ofC. lawiinclude features of the humerus, ulna, and carpometacarpus.C. lawiexceeded the largest extant seaduck, the Common Eider (Somateria mollissima), in most dimensions of the skull and pelvic limb. Pectoral reduction inC. lawiwas among the most extensive known for Anseriformes; reductions inC. milleriwere of lesser magnitude. Distal wing elements ofC. lawihad undergone the greatest shortening, whereas the elongate pelvic limb ofC. lawiwas characterized by disproportionately short femora and long tibiotarsi. Based on femur lengths and body masses of modern Mergini, estimated body masses ofC. lawiandC. milleriare 2,550–3,700 g and 1,820–2,650 g, respectively. Based on mean wing areas and skeletal wing lengths of modern Mergini, and shortening of remiges in flightlessAnas, an estimate for the wing area ofC. lawiis 190 cm2. The ‘minimal’ estimate of body mass and approximated wing area yield an estimated wing-loading of 13.4 g cm−2forC. lawi, a figure which exceeds those of extant Anseriformes (including flightless species) and the theoretical maximum wing-loading permitting flight (2.5 g cm−2).K-means clustering of 44 femora ofC. lawiindicated that differences in skeletal dimensions between provisional sex groups approximated those of extant Mergini, and led to estimated mean body masses of 2,820–4,055 g and 2,360–3,430 g for males and females, respectively. Multivariate analyses of extant Mergini andC. lawidemonstrate the importance of the statistics employed to quantify body size in fossil species. Flightlessness ofChendytesis compared to those of other foot-propelled dividing birds and considered with respect to ontogeny, probable paleoecology, and extinction of the genus.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011500

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

New, well-preserved specimens of the Upper Pennsylvanian synapsidHaptodus garnettensisfrom Garnett, Kansas, represent more mature individuals than those available previously and indicate thatH. garnettensisis diagnosed by several autapomorphies: septomaxilla with small facial exposure; prefrontal pocket shallow; pineal ridge present; supratemporal notched; anterior end of angular overlapped dorsally and ventrally by splenial; robust, chisel-shaped teeth; teeth present on palatal ramus of premaxilla. A phylogenetic analysis of early synapsids indicates thatH. garnettensisis not a sphenacodontid.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011501

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A striking diversity in limb morphology among fossil sloths suggests that the traditional distinction between extant “tree” sloths and fossil “ground” sloths merits closer scrutiny. Morphologically, xenarthrans (sloths, anteaters, and armadillos) are divergent from other mammalian orders. However, morphological shape indices of aspects of the elbow, hip, and knee joints that clearly discriminate locomotor modes in primates, carnivores, and bovids also succeed in differentiating the fully arboreal, semiarboreal, and terrestrial genera of anteaters. When compared to this extant data base, fossil sloths from both the Pleistocene radiation of the Antilles and the Santacrucian radiation of Argentina exhibit a range of values for these indices comparable to those of primates and anteaters. These results indicate that the diversity of limb structure in fossil sloths is associated with variation in posture and locomotor habits including arboreality, semiarboreality, and terrestriality.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011502

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The southernmost Uintan (middle to late middle Eocene) vertebrate faunas in North America occur in Trans-Pecos Texas and in the Texas Gulf Coast province at Laredo. Small rodents, mainly represented by isolated teeth, are among the most abundant faunal elements. These rodent faunas show high endemism and a Uintan refugium in Texas for some forms which fail to persist in the better-known coeval faunas of the Northern Interior. Two new species ofPauromys(P. texensis, sp. nov. andP. simplex, sp. nov.) are described, as well as other small Sciuravidae, extending the known range ofPauromyssouthward to the Gulf Coast and late into the Uintan.Pauromyswas the ecological equivalent of modernPeromyscusorMusin being small, abundant, and with several syntopic species.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011503

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011504

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011505

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011506

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor