摘要:

A new genus and species of heterostracan jawless vertebrate is described from early Wenlockian (Silurian) beds of the Delorme Group, Mackenzie Mountains, Northwest Territories, Canada. The age of the fossil is based on conodonts and other fossils in the same and in nearby correlated sections. The new vertebrate is significant as the oldest heterostracan and one of the oldest vertebrates preserved as complete, articulated skeletons. It is also one of the few heterostracans of any age for which mouth parts, branchial scales and platelets, body scales, and tail are all preserved.

ISSN:0272-4634    

DOI:10.1080/02724634.1990.10011825

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The pterygoid plates and inner bones of the lower jaw ofDiabolepiswere further prepared and sections made of one dental plate to examine additional features of the dentition and to relate macrostructure to histology and growth. These observations confirm the position ofDiabolepiswithin dipnoans. The growth pattern inferred from these observations is compatible with the general model for the growth of dipnoan tooth plates proposed by Smith (1988). New teeth are added from the anterolateral margin, the older posteromedial teeth are retained until worn flat, and the worn surface is repaired by new tissue forming as a blister superimposed on the old tissue. It is proposed that the dentition inDiabolepisis the most primitive for dipnoans. These primitive features include 1) paired dental plates consisting of radial rows of teeth that converge on the posteromedial corner, 2) radial tooth rows in which the teeth gradually increase in size from posteromedial to labial, 3) tooth patches of graded size teeth on the shortened premaxilla and dentary, and 4) a complete cover of denticles and teeth on the palate and the inner bones of the lower jaw. New observations support a previous suggestion that the entopterygoid and prearticular in dipnoans may incorporate the dermopalatine, ectopterygoid, and coronoids.

ISSN:0272-4634    

DOI:10.1080/02724634.1990.10011826

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The taxonomy of the North American cheetah-like cats is unresolved as they have been assigned at different times toFelis, Puma, orAcinonyx. A recently discovered, nearly complete skeleton of a large, slender-limbed cat of Irvingtonian age from West Virginia prompted this study of their relationships. We describe the new specimen and compare it with the living puma (Puma concolor) and cheetah (Acinonyx jubatus) as well as with the extinct Old World cheetah (A. pardinensis) and New World cheetah-like cats most recently assigned toAcinonyx trumaniandA. studeri. The new specimen appears to be a member of the earlier of the two North American species, previously known asA. studeri, here calledMiracinonyx inexpectatusbased on the priority of Cope's (1895) name. A cladistic analysis suggests that the New and Old World forms are distinct at the generic level and we remove the North American taxa fromAcinonyxand place them in the genusMiracinonyx. The two genera are distinguished by a minimum of ten features of the skull and postcranial skeleton.Miracinonyxdiffers fromPumaprimarily in limb proportions, slenderness of the long bones, and aspects of the nasomaxillary region of the skull. A review of the fossil record suggests that the extinction ofM. inexpectatuspreceded the appearance of both the cursorialM. trumaniand the shorter-limbedPuma concolor. Thus,M. inexpectatuscould have given rise to both of these taxa in the middle Pleistocene.

ISSN:0272-4634    

DOI:10.1080/02724634.1990.10011827

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Histological study of the ribs in two archaeocetes,Basilosaurus cetoidesandZygorhiza kochii, reveals conspicuous pachyostosis, with hyperostosis of periosteal cortices and absence of a free medullary cavity. In addition, abundant remains of calcified cartilage matrix, associated with extensive globular ossification, exist within the medulla. Among Cetacea, these features seem to be unique to the archaeocetes. Conversely, the structural peculiarities of bone in these animals are identical to those of the Sirenia and would arise from similar causes: inhibition of the chondroclastic and endosteal osteoclastic resorptions, and prolongation of subperiosteal osteogenesis during ontogeny, exemplifying morphological adaptation to aquatic life via heterochrony. The possible hormonal mechanisms of these features, as also their supposed adaptive consequences for the buoyancy of the archaeocetes, are discussed in relation to data already available for the Sirenia.

ISSN:0272-4634    

DOI:10.1080/02724634.1990.10011828

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The Lufeng hominoid locality, China, yields two murid taxa,Progonomys yunnanensis, sp. nov., andYunomys wui, gen. et sp. nov.P. yunnanensisis more advanced thanP. debruijnifrom the Dhok Pathan Formation of Pakistan and slightly more advanced thanP. cathalaifrom the Vallesian of Europe. It suggests a middle Baodean age (=middle Turolian, MN 12 equivalent) and a somewhat younger age than 8 Ma for the Lufeng fauna.Yunomys wuiis closely related to theKarnimata-Parapelomyscomplex of Neogene south Asian murids. Both murids have affinities with subtropical elements ranging from the Mediterranean region through East Africa and across southern Asia.

ISSN:0272-4634    

DOI:10.1080/02724634.1990.10011829

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Numerous remains ofMesopithecushave recently been recovered from the late Miocene mammalian localities of Macedonia, northern Greece. Three mandibles from the early Turolian are identified asM. delsoni, sp. nov., probably ancestral toM. pentelicusof Pikermi. Others, dated to the latest Turolian, differ fromM. pentelicus, but most of the teeth are so worn that they must be identified asMesopithecus, aff.M. pentelicus. A last set, coming also from the latest Turolian, could possibly be attributed toMesopithecus, cf.M. monspessulanus. The evolution of the genusMesopithecuscan be used as a biostratigraphic tool in late Miocene continental deposits.

ISSN:0272-4634    

DOI:10.1080/02724634.1990.10011830

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

New records ofAtopomys salvelinusfrom West Virginia and Florida, and additional remains ofA. texensisfrom Texas are reported. A partial mandible ofA. salvelinuswith M1–2from Alachua County, Florida, is the first record of the genus from that state, and the most complete specimen ofAtopomysknown. Although M3s ofA. texensishave not been recovered, three M3s ofA. salvelinusare now known from Hamilton Cave, West Virginia. These teeth, as well as the others, are similar to those of the Blancan arvicoline genusNebraskomys. These similarities support Hibbard's (1970) suggestion thatNebraskomyswas ancestral toAtopomys.

ISSN:0272-4634    

DOI:10.1080/02724634.1990.10011831

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The association of eggshell with embryonic remains and nestbound hatchlings in the Upper Cretaceous (Campanian) Two Medicine Formation of Western Montana allows us to positively correlate eggshell morphology with specific dinosaur taxa in North America. Eggshell material from the nesting sites at Willow Creek Anticline, Egg Mountain, and Egg Island are described; they show the presence of four morphotypes. Two of these morphotypes can be assigned toOrodromeus makelai, a hypsilophodontid, andMaiasaura peeblesorum, a hadrosaurid based on embryonic remains and nestbound hatchlings. The third morphotype probably belongs to a ?Troodon, based on contained embryonic remains. A very small isolated egg of ornithoid morphotype was found without associated fossil material; it is probably avian.

ISSN:0272-4634    

DOI:10.1080/02724634.1990.10011832

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0272-4634    

DOI:10.1080/02724634.1990.10011833

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0272-4634    

DOI:10.1080/02724634.1990.10011834

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor