摘要:

From a simple experiment, it can be demonstrated that the curved path of a medial impression follows behind the track rows by a “lag distance”;, indicating the length between the mid‐point of the tracks of the posterior‐most left and right legs and the medial impression. An animal's movement direction may therefore be deduced by this relationship. Fossil trackways of arthropods, reptiles, and dinosaurs show similar relationships between the path of the medial impression and track rows to results obtained experimentally. From the experimental results, it is also possible to determine the unexposed parts of the track rows and medial impression from the “lag distance”;

ISSN:1042-0940    

DOI:10.1080/10420940009380143

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A previously unnoticed geometric pattern is present in the extremities of all tetrapods. Sets of straight and typically uninterrupted hinge lines pass through neighboring interphalangeal joints and across ungual tips. Four sets of these lines appear in basal polydactyl tetrapods, two medial sets, a transverse set and a lateral set. The two medial sets merge in primitive pentadactyl tetrapods. The resulting three line sets persist in later taxa, even when digits shrink and disappear. Primitively and typically the lines in each set are more or less parallel, but lines may converge, merge and shift as phalanges disappear or phalangeal proportions change. Confirming this geometric pattern, complex interphalangeal joint surfaces typically align with hinge lines and pad divisions parallel them. In addition, unguals rarely cross extensions of hinge lines and longer unguals may divert medially or laterally rather than cross them. Exceptions occur most commonly on ungual II. Line sets may exist because phalanges appear to flex and extend most efficiently in unison. Hinge line patterns appear to identify clades so they may, to a limited extent, be used taxonomically. Hinge lines also have predictive value in that missing phalanges, including unguals, can be reconstructed with confidence using hinge lines as size guides. Correct digit spread and metapodial configuration can also be determined in extinct taxa by seeking the appearance of continuous interphalangeal hinge lines in tested reconstructions.

ISSN:1042-0940    

DOI:10.1080/10420940009380144

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Several trace fossils of burrowing ophiuroids,Asteriacites lumbricalisvon Schlotheim 1820, occur on slabs of thinly‐bedded silty limestone in the lower Spathian part of the Lower Triassic Thaynes Formation in central Utah. This is the first record ofAsteriacitesin the Lower Triassic of North America. Their occurrence adds information to studies of the recovery of marine faunas following the Permian extinctions, including the oxygénation of benthic sediments.

ISSN:1042-0940    

DOI:10.1080/10420940009380145

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:1042-0940    

DOI:10.1080/10420940009380146

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:1042-0940    

DOI:10.1080/10420940009380147

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:1042-0940    

DOI:10.1080/10420940009380142

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor