Friday, 7 July 2017

Another Gap Closes. No God Found!

Asiatic Yellow-striped Caecilian (Ichthyophis kohtaoensis)
Photo credit: cowyeow (via Flickr)
Stem caecilian from the Triassic of Colorado sheds light on the origins of Lissamphibia

Scientists working for the Department of Integrative Anatomical Sciences at the Keck School of Medicine of USC have closed another one of those gaps in science that creationists scrabble around in, desperately searching for as somewhere to fit their god.

Although no serious biologist these days sets out to confirm evolution or to refute creationism, papers such as this one do that quite incidentally because they report on the reality of the natural world and objectively assess the evidence. Quite naturally, this refutes any notions such as creationism which are not based on real-world evidence.

Like every other gap in the history of human knowledge, when examined closely and closed, no god was found. Did anyone seriously ever expect one? This gap was the details of how and when one of the most elusive and least understood groups of amphibians, the caecilians or Lissamphibia, diverged from the other amphibians.

Guess what the gap-closing find was. It was another of those 'non-existent transitional forms' that creationists are forever telling us about! It has been given the taxonomic name Chinlestegophis jenkinsi.

Caecilians are a group of some 200 or more carnivorous species of legless amphibians that live almost entirely underground in moist, tropical areas of Africa, Southeast Asia and South America. Many are entirely eyeless or have reduced eyes covered by moist skin. They can range in size from about six inches to five feet in length. The gap in evolutionary biology was just how caecilians connect with the other amphibians.

Research into modern amphibian origins is increasingly focusing on the limbless caecilians, a poorly studied group whose pre-Cenozoic fossils are limited to two species. We describe tiny fossils from the Triassic of Colorado with a mixture of traits found in caecilians and extinct Permian–Triassic temnospondyls: Stereospondyli. Computed 3D tomography shows how skull bones organized around internal structures, and we suggest how these may have become fused or simplified in caecilians. The fossils’ association with burrows highlights ecological diversity of Triassic amphibians as well as when and how burrowing evolved in the stereospondyl ancestors of caecilians. Our narrative for research on amphibian origins highlights the importance of stereospondyls, the most numerous and anatomically diverse amphibian group of the Triassic.

The origin of the limbless caecilians remains a lasting question in vertebrate evolution. Molecular phylogenies and morphology support that caecilians are the sister taxon of batrachians (frogs and salamanders), from which they diverged no later than the early Permian. Although recent efforts have discovered new, early members of the batrachian lineage, the record of pre-Cretaceous caecilians is limited to a single species, Eocaecilia micropodia. The position of Eocaecilia within tetrapod phylogeny is controversial, as it already acquired the specialized morphology that characterizes modern caecilians by the Jurassic. Here, we report on a small amphibian from the Upper Triassic of Colorado, United States, with a mélange of caecilian synapomorphies and general lissamphibian plesiomorphies. We evaluated its relationships by designing an inclusive phylogenetic analysis that broadly incorporates definitive members of the modern lissamphibian orders and a diversity of extinct temnospondyl amphibians, including stereospondyls. Our results place the taxon confidently within lissamphibians but demonstrate that the diversity of Permian and Triassic stereospondyls also falls within this group. This hypothesis of caecilian origins closes a substantial morphologic and temporal gap and explains the appeal of morphology-based polyphyly hypotheses for the origins of Lissamphibia while reconciling molecular support for the group’s monophyly. Stem caecilian morphology reveals a previously unrecognized stepwise acquisition of typical caecilian cranial apomorphies during the Triassic. A major implication is that many Paleozoic total group lissamphibians (i.e., higher temnospondyls, including the stereospondyl subclade) fall within crown Lissamphibia, which must have originated before 315 million years ago.

The scientists used 3D X-rays to analyse the fossil remains of two speciments. The first consisted of parts of the skull, spinal column, ribs and legs and the second of only the skull. This expands the known history of amphibians by at least 15 million years and connects the caecilians to the stereospondyls, the most diverse amphibian group during the Triassic era but which were previously thought to have been an evolutionary dead end.

Twenty to 30 years ago, we weren’t even sure of the origins of birds, now we are solving some of the final remaining mysteries when it comes to what sorts of animals the major vertebrate groups evolved from. Caecilians, turtles and some fish are the only major vertebrate groups that paleontologists still have questions about.

Jason Pardo, lead author.
Doctoral candidate, Faculty of Veterinary Medicine
University of Calgary in Alberta, Canada.
Quoted by Zen Vuong in UCS News.
The burrows these fossils were preserved in were about two inches wide and the skulls were about an inch long so they may have been about the size of a small modern salamander, maybe between six inches and a foot long. It probably ate insects. The temperature in what is now Colorado during the Triassic would have been too hot even for the larger dinosaurs such as Tyrannosaurs, so these moisture-dependent amphibians would have lived deep in the soil close to the water table.

The scientific significance of this find, apart from closing another gap, is that it increases our knowledge of vertebrate evolution and so that of our own evolution.

For creationism, this is simply another problem for their superstition for which they will need to employ the standard disinformation techniques, or simply ignore altogether. For any proper science, finds like this would normally be fatal for a hypothesis which depends on the absence of transitional species, but creationism is about as far from a proper science as it is possible for any human enterprise to get. Creationism is about maintaining a delusion in the face of contrary evidence.

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