Biomedical subjects

Michael I Coates

Publications and source records attributed to Michael I Coates.

4 recordsLinked to original sources

PubMed2003

Early tetrapod relationships revisited.

In an attempt to investigate differences between the most widely discussed hypotheses of early tetrapod relationships, we assembled a new data matrix including 90 taxa coded for 319 cranial and postcranial characters. We have incorporated, where possible, original observations of numerous taxa spread throughout the major tetrapod clades. A stem-based (total-group) definition of Tetrapoda is preferred over apomorphy- and node-based (crown-group) definitions. This definition is operational, since it is based on a formal character analysis. A PAUP* search using a recently implemented version of the parsimony ratchet method yields 64 shortest trees. Differences between these trees concern: (1) the internal relationships of aïstopods, the three selected species of which form a trichotomy; (2) the internal relationships of embolomeres, with Archeria crassidisca and Pholiderpeton scut collapsed in a trichotomy with a clade formed by Anthracosaurus russelli and Pholiderpeton attheyi; (3) the internal relationships of derived dissorophoids, with four amphibamid species forming an unresolved node with a clade consisting of micromelerpetontids and branchiosaurids and a clade consisting of albanerpetontids plus basal crown-group lissamphibians; (4) the position of albenerpetontids and Eocaecilia micropoda, which form an unresolved node with a trichotomy subtending Karaurus sharovi, Valdotriton gracilis and Triadobatrachus massinoti; (5) the branching pattern of derived diplocaulid nectrideans, with Batrachiderpeton reticulatum and Diceratosaurus brevirostris collapsed in a trichotomy with a clade formed by Diplocaulus magnicornis and Diploceraspis burkei. The results of the original parsimony run--as well as those retrieved from several other treatments of the data set (e.g. exclusion of postcranial and lower jaw data; character reweighting; reverse weighting)--indicate a deep split of early tetrapods between lissamphibian- and amniote-related taxa. Colosteids, Crassigyrinus, Whatcheeria and baphetids are progressively more crownward stem-tetrapods. Caerorhachis, embolomeres, gephyrostegids, Solenodonsaurus and seymouriamorphs are progressively more crownward stem-amniotes. Eucritta is basal to temnospondyls, with crown-lissamphibians nested within dissorophoids. Westlothiana is basal to Lepospondyli, but evidence for the monophyletic status of the latter is weak. Westlothiana and Lepospondyli form the sister group to diadectomorphs and crown-group amniotes. Tuditanomorph and microbrachomorph microsaurs are successively more closely related to a clade including proximodistally: (1) lysorophids; (2) Acherontiscus as sister taxon to adelospondyls; (3) scincosaurids plus diplocaulids; (4) urocordylids plus aïstopods. A data set employing cranial characters only places microsaurs on the amniote stem, but forces remaining lepospondyls to appear as sister group to colosteids on the tetrapod stem in several trees. This arrangement is not significantly worse than the tree topology obtained from the analysis of the complete data set. The pattern of sister group relationships in the crownward part of the temnospondyl-lissamphibian tree re-emphasizes the important role of dissorophoids in the lissamphibian origin debate. However, no specific dissorophoid can be identified as the immediate sister taxon to crown-group lissamphibians. The branching sequence of various stem-group amniotes reveals a coherent set of internested character-state changes related to the acquisition of progressively more terrestrial habits in several Permo-Carboniferous forms.

Amphibians↗

PubMed2002

Analyzing developmental sequences within a phylogenetic framework.

Heterochrony is important as a potential mechanism of evolutionary change. However, the analysis of developmental timing data within a phylogenetic framework to identify important shifts has proven difficult. In particular, analytical problems with sequence (event) heterochrony revolve around the lack of an absolute time frame in development to allow standardization of timing data across species. An important breakthrough in this regard is the method of "event-pairing," which compares the relative timing of developmental events in a pairwise fashion. The resulting event-pair-encoded data can be mapped onto a phylogeny, which can provide important biological information. However, event-paired data are cumbersome to work with and lack a rigorous quantitative framework under which to analyze them. Critically, the otherwise advantageous relativity of event-pairing prevents an assessment of whether one or both events in a single event-pair have changed position during evolutionary history. Building on the method of event-pairing, we describe a protocol whereby event-pair transformations along a given branch are analyzed en bloc. Our method of "event-pair cracking" thereby allows developmental timing data to be analyzed quantitatively within a phylogenetic framework to infer key heterochronic shifts. We demonstrate the utility of event-pair cracking through a worked example and show how it provides a set of desired features identified by previous authors.

Animals↗

PubMedDate not supplied

Analyzing evolutionary patterns in amniote embryonic development.

Heterochrony (differences in developmental timing between species) is a major mechanism of evolutionary change. However, the dynamic nature of development and the lack of a universal time frame makes heterochrony difficult to analyze. This has important repercussions in any developmental study that compares patterns of morphogenesis and gene expression across species. We describe a method that makes it possible to quantify timing shifts in embryonic development and to map their evolutionary history. By removing a direct dependence on traditional staging series, through the use of a relative time frame, it allows the analysis of developmental sequences across species boundaries. Applying our method to published data on vertebrate development, we identified clear patterns of heterochrony. For example, an early onset of various heart characters occurs throughout amniote evolution. This suggests that advanced (precocious) heart development arose in evolutionary history before endothermy. Our approach can be adapted to analyze other forms of comparative dynamic data, including patterns of developmental gene expression.

Age Factors↗

PubMedDate not supplied

Fins to limbs: what the fossils say.

A broad phylogenetic review of fins, limbs, and girdles throughout the stem and base of the crown group is needed to get a comprehensive idea of transformations unique to the assembly of the tetrapod limb ground plan. In the lower part of the tetrapod stem, character state changes at the pectoral level dominate; comparable pelvic level data are limited. In more crownward taxa, pelvic level changes dominate and repeatedly precede similar changes at pectoral level. Concerted change at both levels appears to be the exception rather than the rule. These patterns of change are explored by using afternative treatments of data in phylogenetic analyses. Results highlight a large data gap in the stem group preceding the first appearance of limbs with digits. It is also noted that the record of morphological diversity among stem tetrapods is somewhat worse than that of basal crown group tetrapods. The pre-limbed evolution of stem tetrapod paired fins is marked by a gradual reduction in axial segment numbers (mesomeres); pectoral fins of the sister group to limbed tetrapods include only three. This reduction in segment number is accompanied by increased regional specialization, and these changes are discussed with reference to the phylogenetic distribution of characteristics of the stylopod, zeugopod, and autopod.

Animals↗