摘要:

The skull of the primitive baenid turtleNeurankylusdemonstrates that it is distinct fromHayemysand is a primitive relative to the Baenodd. The course of the canalis caroticus lateralis in the Baenodd is reinterpreted and the identification of foramina altered accordingly.Neurankylusand the Baenodd share the derived features of a canalis caroticus lateralis that is smaller in diameter than the canalis caroticus internus and is located entirely within the pterygoid, rather than along the pterygoid-basisphenoid suture, a fully ossified hiatus acusticus, and a greatly reduced epipterygoid. A monophyletic taxon Paracryptodira including Baenidae and Pleurosternidae is supported by a greatly reduced perilymphatic fenestra.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011509

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Two jaw fragments of small tetrapods from the Turkey Branch Formation of the Richmond basin (Newark Supergroup; Upper Triassic: lower to middle Carnian) of Virginia have highly distinctive dentitions. The robust, transversely broadened, and bicuspid teeth ofGomphiosauridion baileyae, gen. et sp. nov. support its placement in the Procolophonidae. The two cusps are linked by a pronounced transverse ridge, which divides the occlusal surface of the crown into two deep fossettes. The cusps have strongly fluted enamel. The heterodont dentition ofXenodiphyodon petraios, gen. et sp. nov. comprises transversely broadened, tricuspid posterior teeth and transversely compressed anterior teeth with distinct apical ridges. The posterior teeth ofXenodiphyodonclosely resemble those of the alleged trilophosaurid taxaTricuspisaurus thomasiandVariodens inopinatusfrom Upper Triassic fissure-fillings in southwestern England and ?Trilophosaurus jacobsifrom the Upper Triassic Chinle Formation of Arizona. The latter is clearly distinct from the archosauromorphTrilophosaurus buettneriand is made the type species of the new genus,Chinleogomphius. All four genera may prove referable to the Procolophonia.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011510

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The Crocodylotarsi are a group erected by Benton and Clark (1988) for archosaurs that share the “crocodile-normal” ankle structure. In this study, the phylogeny of the Crocodylotarsi was re-examined based on study of most relevant fossil material of the early non–crocodyliform members of the clade. Relationships among the major archosaurian taxa (Ornithodira, Ornithosuchidae, and Crocodylotarsi) and their proximal outgroups (Proterochampsidae,Euparkeria) were also considered.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011511

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Adelobasileus cromptoniLucas and Hunt, 1990 is based on an incomplete skull from the lower part of the Tecovas Member of the Dockum Formation near Kalgary, Crosby County, Texas. Its age is late Carnian (Tuvalian), about 225 Ma, based on palynostratigraphy, ostracods, vertebrate biochronology, and sequence stratigraphy. This indicates thatAdelobasileusis at least 10 million years older than any previously described mammal.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011512

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Mookomys(?)bodeiWilson, from the Arikareean of California, is referred to the genusTenudomysRensberger, and two species previously referred only questionably to this genus,T. dakotensis(MacDonald) andT. basilarisKorth are definitely assigned to this genus, based on the association of upper and lower dental elements ofT. bodei.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011513

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Mammalian teeth show a considerable complexity in microstructure. The arrangement of decussated enamel prisms gives enamel the functional advantages of a composite material. This prism arrangement is genetically determined and altered throughout evolution. As the evolution of hypsodont molars implies a drastic alteration of the loading conditions and of the stress pattern in teeth, it can be expected that enamel microstructure is also affected. Equids and several other ungulates evolved the modified radial enamel in adaptation to these altered conditions. As the fossil record for the phylogeny of horses is available in considerable completeness, this group is suitable to investigate the correlation of morphologic evolution and the evolution of enamel microstructure. Indeed, the same patterns of evolutionary change previously known from the morphologic level can also be demonstrated on the microstructural level. Modified radial enamel is characterized by the orientation of the inter-prismatic crystallites, the thickness of the interprismatic matrix, and the radial prism arrangement. The three characters appear step by step in a phylogenetic context. First the orientation of the interprismatic crystallites perpendicular to the prisms occurs inMesohippus. InParahippus, all three characters appear together for the first time, but the location and the very small amount of modified radial enamel suggests that a function in strengthening the enamel is very unlikely. In all hypsodont equids, modified radial enamel appears in a considerable amount and obviously is an adaptation to the altered stress distribution in hypsodont molars.Hypohippusshows a further combination of two of the characters; the crystallite orientation and the thickness of the interprismatic matrix is similar to the modified radial enamel, but the prisms are not arranged in radial rows but in decussating layers. Because the characters of modified radial enamel appear stepwise and preadaptively, and because some other lineages that lack the development of these characters did not evolve hypsodont molars, it seems probable that enamel microstructure influences the potential for macromorphologic phylogenetic change.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011514

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Late Clarendonian and very early Hemphillian horse teeth from Florida previously identified as early members ofNannippus aztecus(=N. minor) are referred instead toN. westoni(Simpson).N. westoniwas originally assigned toMerychippusand thought to date from the early Miocene. The very low crown height in the teeth of the type specimen is the result of heavy attritional wear and is not of phylogenetic significance.N. westonidisplays a mixture of derivedNannippusand primitive hipparionine character states, both in its cheekteeth and metapodials.N. morgani, sp.nov. is described from a small sample of diminutive, isolated teeth and a medial metatarsal that occur in late early Hemphillian faunas together withN. aztecus. N. morganiis 15 to 20% smaller in dental parameters than mean values forN. aztecus, making it one of the smallest known hipparionines, with an estimated body mass of about 40 kg. Three similar-sized, diminutive equids,N. morgani, Pseudhipparion skinneri, andCalippus elachistus, lived contemporaneously in the very late Miocene of Florida.

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011515

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011516

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011517

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0272-4634    

DOI:10.1080/02724634.1993.10011518

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor