Polydactyly in the earliest known tetrapod limbs

  title={Polydactyly in the earliest known tetrapod limbs},
  author={Michael I. Coates and Jennifer Alice Clack},
NEW specimens of the earliest known tetrapod limbs shows them to be polydactylous. The forelimb of Acanthostega has eight digits and the hindlimb of Ichthyostega has seven. Both of these come from the Upper Devonian of East Greenland, complementing the only other known Devonian tetrapod limb, that of Tulerpeton from Russia1, which has six digits. The morphology of the specimens suggests that limbs with digits may have been adaptations to an aquatic rather than a terrestrial environment. The… 

Urodelans, Ichthyostega and the origin of the tetrapod limb

It is suggested that the fin type ancestral to terrestrial limbs was asymmetrical biserial, possessed a short axis, unbranched jointed preaxial radials deviating from the distal mesomeres of the axis in two or more radials.

The axial skeleton of the Devonian tetrapod Ichthyostega

A new reconstruction of Ichthyostega is shown based on extensive re-examination of original material and augmented by recently collected specimens and reveals hitherto unrecognized regionalization in the vertebral column.

Palaeontology: A polydactylous amniote from the Triassic period

It is discovered that a preaxial form of polydactyly, in which extra digits are positioned anterior to the first digit, has unexpectedly re-emerged in a marine reptile from the Early Triassic period about 242 million years ago.

Evidence for an amphibian sixth digit

It is proposed here that the prehallux seen in various species of amphibians generally represents a rudimentary sixth digit, as is evident from anatomical features, development, and molecular marker expression.

A history of digit identification in the manus of theropods (including Aves)

The history of research into the identification of avian and dinosaurian digits remains one of the major controversies in vertebrate evolution, dating from approximately 1825 to 2009.

Hypothesis: hemimelia and the maintenance of pentadactyly?

  • C. Hayes
  • Biology
    Journal of theoretical biology
  • 2001
The abnormal gait and torsion of the limb caused by the hemimelia is acting as a stabilizing force to maintain the dactyly of the tetrapod limb with five or fewer digits.

The Fish–Tetrapod Transition: New Fossils and Interpretations

  • J. Clack
  • Geology
    Evolution: Education and Outreach
  • 2009
Study of modern vertebrates, especially the evolutionary developmental genetics of Hox genes, are beginning to provide clues to the origin of digits, and these include new tetrapod-like fish and very primitive tetrapods that help to resolve questions of the sequence of acquisition of Tetrapod characters.

Fish fingers: digit homologues in sarcopterygian fish fins.

Evidence suggests that Neoceratodus fin radials and tetrapod digits may be patterned by shared mechanisms distinct from those patterning the proximal fin/limb elements, and in that sense are homologous.

A complete primitive rhizodont from Australia

The new evidence shows that rhizodonts are more remote from tetrapods than are osteolepiform and elpistostegid lobe-fin fishes and the pectoral fin of Sauripteris should not be used as a model limb precursor.



Ontogeny of the limb skeleton in Alligator mississippiensis: Developmental invariance and change in the evolution of archosaur limbs

An analysis of the early development of the crocodilian limb skeleton and a hypothesis in which the derived skeletal patterns found in crocodilians and birds have originated by a heterochronic process of paedomorphosis is proposed.

Two Perspectives on the Evolution of the Tetrapod Limb

A re-analysis of the limb characters advocated by Rosen et al. (1981) does not support their contention that lungfishes are the sister group of tetrapods, but instead suggests that rhipidistian fishes of the family Osteolepidae are the closest relatives of the tetrapoda.

IX.—The Postcranial Skeleton of Ensthenopteron foordi Whiteaves

A functional analysis of the skeleton of Ensthenopteron is attempted, suggesting that it resembled the pike in its mode of life and that it may have been capable of short journeys “walking” overland.


A recent review by Rosen et al. (1981) claims that Dipnoi (lungfish) are the sister‐group of the Tetrapoda, that Osteolepiformes is a non‐taxon and that Eusthenopteron is more distant from tetrapods than are Dip noi, coelacanths and probably the fossil Porole piformes, are refuted by use of the same cladistic technique.

The Carboniferous Amphibian Proterogyrinus scheelei Romer, and the Early Evolution of Tetrapods

Proterogyrinus scheelei Romer, from the Upper Mississippian of Greer, West Virginia, is one of the earliest known members of the amphibian infraorder Embolomeri, and has no undisputed synapomorphies with reptiles either, making it impossible to support close relationship between the two groups.


The problem of the origin and evolution of the paired appendages and girdles has been considered as if it could be settled by itself, but the cumulative result of more than a century of investigation is now quite rapidly revealing the broad outlines, although there is still great need for more precisc knowledge of details.

The postcranial skeletal anatomy of the carboniferous tetrapod Greererpeton burkemorani Romer, 1969

A cladistic analysis indicates that Greererpeton burkemorani shares a more recent common ancestor with the anthracosaur Proterogyrinus scheelei than it does with either Crassigyrinus scoticus or Ichthyostega sp.

The earliest known reptile

The discovery of a much earlier amniote skeleton from the Brigantian (Lower Carboniferous) of Scotland, which thus represents the earliest occurrence of amniotes in the fossil record.


This paper shall attempt to define the idea of a “developmental constraint” more precisely by examining the vertebrate limb from three viewpoints and suggest a more precise operational definition of “ developmental constraints” on morphological evolution.