Hidden morphological diversity among early tetrapods

  title={Hidden morphological diversity among early tetrapods},
  author={Jason D. Pardo and Matt Szostakiwskyj and Per Erik Ahlberg and Jason S. Anderson},
Phylogenetic analysis of early tetrapod evolution has resulted in a consensus across diverse data sets in which the tetrapod stem group is a relatively homogenous collection of medium- to large-sized animals showing a progressive loss of ‘fish’ characters as they become increasingly terrestrial, whereas the crown group demonstrates marked morphological diversity and disparity. [] Key Result Digital dissection reveals extremely primitive cranial morphology, including a spiracular notch, a large remnant of the…

The smallest known Devonian tetrapod shows unexpectedly derived features

Brittagnathus is described from a single complete right lower jaw ramus recovered from the Acanthostega mass-death deposit in the upper part of the Britta Dal Formation of Stensiö Bjerg, Gauss Peninsula, East Greenland and suggests that diversification of ‘Carboniferous-grade’ tetrapods had already begun before the end of the Devonian and that the group was not greatly affected by the end-Devonian mass extinction.

A Mississippian (early Carboniferous) tetrapod showing early diversification of the hindlimbs

A new East Kirkton tetrapod with an unusual hindlimb morphology reminiscent of that of several stem- and primitive crown amniotes is named and described, with a unique ilium with two slender and elongate processes and a 5-digit pes with a long, stout metatarsal IV and a greatly elongate digit IV.

A Late Devonian actinopterygian suggests high lineage survivorship across the end-Devonian mass extinction.

An exceptionally preserved fossil from 7 Myr before the extinction that reveals unexpected anatomical features is reported and a revised model matches more complex patterns of divergence, survival and diversification around the Devonian/Carboniferous boundary in other vertebrate clades.

The phylogeny of early amniotes and the affinities of Parareptilia and Varanopidae

A new amniote phylogeny excludes varanopids as stem-line mammals, nests Parareptilia within Diapsida and suggests that temporal fenestration evolved fewer times than previously thought.

Multiple paths to morphological diversification during the origin of amniotes.

Evidence for an early burst, comprising high rates of anatomical change that decelerated through time, giving way to a background of saturated morphological evolution is found, demonstrating the importance of variation in modes of phenotypic divergence during a major evolutionary radiation.

Fossil bone histology reveals ancient origins for rapid juvenile growth in tetrapods

Patterns of growth throughout the lifetime of an animal reflect critical life history traits such as reproductive timing, physiology, and ecological interactions. The ancestral growth pattern for

Early amphibians evolved distinct vertebrae for habitat invasions

Living tetrapods owe their existence to a critical moment 360–340 million years ago when their ancestors walked on land. Vertebrae are central to locomotion, yet systematic testing of correlations

Snake-like limb loss in a Carboniferous amniote

A new taxon of molgophid recumbirostran from the Carboniferous of Illinois, Nagini mazonense, suggests that the forelimb-first pattern of limb reduction that characterizes modern snakes also occurs early on in amniote evolution.

Early tetrapod cranial evolution is characterized by increased complexity, constraint, and an offset from fin-limb evolution

It is found that bone loss across the origin of tetrapods is associated not only with increased complexity of bone-to-bone contacts but also with decreasing topological diversity throughout the late Paleozoic, which may be related to developmental and/or mechanical constraints.

High lineage survivorship across the end-Devonian Mass Extinction suggested by a remarkable new Late Devonian actinopterygian

This revised model matches more complex patterns of divergence, survival, and diversification around the Devonian-Carboniferous boundary in other vertebrate clades and fundamentally recalibrates the onset of diversification early in the history of this major radiation.



A uniquely specialized ear in a very early tetrapod

Ichthyostega's braincase and ear region defied interpretation, such that conventional anatomical terms seemed inapplicable, and can now be seen to form part of a highly specialized ear, probably a hearing device for use in water.

Cranial Morphology of the Carboniferous-Permian Tetrapod Brachydectes newberryi (Lepospondyli, Lysorophia): New Data from µCT

The morphology of the skull of a partial growth series of the lysorophian Brachydectes newberryi is studied using x-ray micro-computed tomography and reveals similarities between the braincase of BrachydECTes and brachystelechid recumbirostrans, corroborating prior work suggesting a close relationship between these taxa.

New information on Lethiscus stocki (Tetrapoda: Lepospondyli: Aistopoda) from high-resolution computed tomography and a phylogenetic analysis of Aistopoda

High-resolution computed tomography provides an alternative to serial sectioning and other destructive tech - niques of studying fossils (data available at http://www.DigiMorph.org). This technology

Cranial anatomy of ophiderpetontid aı̈stopods: Palaeozoic limbless amphibians

Oestocephalus, an ophiderpetontid from the Middle Pennsylvanian of both Europe and North America provides the best known basis for evaluating the relationships of the aistopods. All aistopods are

An early tetrapod from ‘Romer's Gap’

Pederpes is the earliest-known tetrapod to show the beginnings of terrestrial locomotion and was at least functionally pentadactyl, bridging the temporal, morphological and phylogenetic gaps that have hitherto separated Late Devonian and mid-Carboniferous tetrapOD faunas.


An anatomical study of Microbrachis reveals inaccuracies in previous studies, especially in the palate and cranial proportions, which corroborates previous suggestions that lissamphibians are part of a clade that includes the taxa classically referred to as “lepospondyls,” and that seymouriamorphs and temnospONDyls are not part of Tetrapoda.

The Devonian tetrapod Acanthostega gunnari Jarvik: postcranial anatomy, basal tetrapod interrelationships and patterns of skeletal evolution

Comparison between axial skeletons of primitive tetrapods suggests that plesiomorphic fish-like morphologies were re-patterned in a cranio-caudal direction with the emergence of tetrapod vertebral regionalisation.

Dates, nodes and character conflict: Addressing the Lissamphibian origin problem

Tests of different crown topologies show that placement of amphibians within lepospondyls is not a significantly worse fit for the whole character set than a close temnospondyl‐lissamphibian relationship, and the latter phylogenetic hypothesis best captures the most coherent assembly of derived lissampshibian apomorphies.

Late to the table: diversification of tetrapod mandibular biomechanics lagged behind the evolution of terrestriality.

The substantial temporal gap between the origin of postcranial features associated with terrestriality, such as limbs with functional elbow/knee and wrist/ankle joints capable of weight-bearing, and the onset of divergence in jaw biomechanics provides a compelling example of "functional modularity" during a major adaptive radiation.


Details of Cranial anatomy contradict a previous model of cranial kinesis by severely limiting the skull's potential mobility and three species are recognised within the family Phlegethontiidae.