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"Without a leg to stand on"; on the evolution and development of axial elongation and limblessness in tetrapods

Michael W. Caldwell
"Without a leg to stand on"; on the evolution and development of axial elongation and limblessness in tetrapods (in Studies on the evolution of vertebrates; papers in honour of Robert Lynn Carroll--Etudes sur l'evolution des vertebres; articles en l'honneur de Robert Lynn Carroll, Hans-Dieter Sues (editor), Alison M. Murray (editor) and Jason S. Anderson (editor))
Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre (April 2003) 40 (4): 573-588

Abstract

A review of the osteology of the axial and appendicular skeleton of fossil and extant tetrapods, in the context of tetrapod phylogenetic patterns, reveals common patterns of limb loss and axial elongation. A threshold number of 35-40 presacral vertebrae is linked to minor reductions in digit number and the phalangeal count. Presacral vertebral counts do not increase gradually, rather, presacral counts jump from 35-40 to 60-70. At this point, limb loss is extreme, with forelimbs being reduced to tiny appendages or lost altogether. Higher presacral counts (>90) are linked to total forelimb loss and radical rear-limb reductions culminating in total loss. A pattern of this sort is recognized in Paleozoic lepospondyls and Mesozoic to modern squamates. Developmental genetic models illuminate gene systems that are associated with morphogenesis and are linked to the evolution of limb reduction and leglessness in these tetrapods.


ISSN: 0008-4077
EISSN: 1480-3313
Coden: CJESAP
Serial Title: Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre
Serial Volume: 40
Serial Issue: 4
Title: "Without a leg to stand on"; on the evolution and development of axial elongation and limblessness in tetrapods
Title: Studies on the evolution of vertebrates; papers in honour of Robert Lynn Carroll--Etudes sur l'evolution des vertebres; articles en l'honneur de Robert Lynn Carroll
Author(s): Caldwell, Michael W.
Author(s): Sues, Hans-Dietereditor
Author(s): Murray, Alison M.editor
Author(s): Anderson, Jason S.editor
Affiliation: University of Alberta, Department of Earth and Atmospheric Sciences, Edmonton, AB, Canada
Affiliation: Carnegie Museum of Natural History, Pittsburgh, PA, United States
Pages: 573-588
Published: 200304
Text Language: English
Summary Language: French
Publisher: National Research Council of Canada, Ottawa, ON, Canada
References: 57
Accession Number: 2003-049557
Categories: Vertebrate paleontology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
Secondary Affiliation: Canadian Museum of Nature, CAN, CanadaUniversity of Toronto at Mississauga, CAN, Canada
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200316
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