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Caldwell, M. W.

Publications and source records attributed to Caldwell, M. W..

2 recordsLinked to original sources

Cryptovaranoides is not a squamate

Accurate reconstruction of the timescale of organismal evolution requires placement of extinct representatives among living branches. In this way, the fossil record has the capacity to revise hypotheses of organismal evolution by producing representatives of clades that far pre-date the age of the clade inferred using phylogenies built from molecular data and previous fossil calibrations. Recently, one fossil with the potential to drastically change current understanding surrounding the timescale of reptile diversification was described from Triassic fissure-fill deposits in the United Kingdom. This taxon, {dagger}Cryptovaranoides microlanius, was originally placed deep within the squamate crown clade, suggesting that many lineages of living lizards and snakes must have appeared by the Triassic and implying long ghost lineages that paleontologists and molecular phylogeneticists have failed to detect using all other available data. Our team challenged this identification and instead suggested {dagger}Cryptovaranoides had unclear affinities to living reptiles, but a crown-squamate interpretation was later re-iterated by the team that originally described this species. Here, we again challenge the morphological character codings used to support a crown squamate affinity for {dagger}Cryptovaranoides microlanius and illustrate several empirical problems with analyses that find this taxon is a crown squamate. Our analyses emphasize the importance of stringency in constructing hypodigms of fossils, particularly when they may be key for proper time calibration of the Tree of Life.

paleontology↗

Megaevolutionary dynamics in reptiles and the role of adaptive radiations in evolutionary innovation

Adaptive radiations are long believed to be responsible for the origin of phenotypic diversity and new body plans among higher clades in the fossil record. However, few studies have assessed rates of phenotypic evolution and disparity across broad scales of time to understand the evolutionary dynamics behind the origin of major clades, or how they relate to rates of molecular evolution. Here, we provide a total evidence approach to this problem using the largest available data set on diapsid reptiles. We find a strong decoupling between phenotypic and molecular rates of evolution, with many periods of accelerated phenotypic evolution or expansion of phenotypic disparity at the origin of major reptile clades and body plans that do not correspond to periods of adaptive radiation. We find heterogeneous rates of evolution during the acquisition of similarly adapted functional types, and that the origin of snakes is marked by exceptionally high evolutionary rates.

evolutionary biology↗