In the shallows near shore, Tetrapodophis amplectus glides through a tangle of branches from the conifer Duartenia araripensis that have fallen into the water, sharing this habitat with a water bug in the family Belostomatidae and small fish (Dastilbe sp.).
Image credit: Julius Csotonyi
In a very nice example of the self-correcting nature of science, a paper published three days ago in the Journal of Systematic Palaeontology, scientist led by University of Alberta palaeontologist Michael Caldwell, produce evidence refuting an earlier claim to have identified a fossil of a 'missing link' between snakes and lizards, from which snakes are assumed to have evolved, with a detailed reassessment showing that the fossil was not of a snake but in fact a highly adapted aquatic lizard.
This is the sort of science which will gladden the heart of any dedicated creationist trying desperately to ignore the evidence of the very many other 'missing' link fossils which turn up almost routinely in the scientific literature - until, that is, it dawns on them that this willingness to reassess and revise is exactly what gives the scientific method its great power to reveal the truth of the natural world as opposed to the theological method which looks for reasons not to change one's mind but to reinforce the sacred dogmas - like the Creationist insistence that there are no missing link fossils.
So, we can expect the professional Creationist frauds like Ken Ham to trumpet this finding as yet another example of how science changes its mind and gets things wrong, leaving their scientifically illiterate dupes to fill in the assumption that this proves science is unreliable and so fall for the unspoken false dichotomy fallacy that therefore the locally-popular god did it, neatly leaving Ham, et al with no need to produce any evidence that such a god exists or is capable of creating anything.
Embarrassingly for Creationist frauds, this publication also gives the lie to their claim that scientists are not permitted to publish anything that refutes anything to do with evolutionary biology.
The finding of the University of Alberta-led team is explained in the Taylor & Francis press release announcing this new paper:
Details of their findings and why they believe the fossil is a highly adapted marine lizard, not an early snake, are given in the abstract to their free access paper in the Journal of Systematic Palaeontology:It has long been understood that snakes are members of a lineage of four-legged vertebrates that, as a result of evolutionary specializations, lost their limbs. Somewhere in the fossil record of ancient snakes is an ancestral form that still had four legs. It has thus long been predicted that a snake with four legs would be found as a fossil.Filling in the links of the evolutionary chain with a fossil record of a "snake with four legs" connecting lizards and early snakes would be a dream come true for palaeontologists. But a specimen formerly thought to fit the bill is not the missing piece of the puzzle, according to a new Journal of Systematic Palaeontology study led by University of Alberta palaeontologist, Michael Caldwell.
Professor Michael Caldwell, lead author
Departments of biological sciences and earth and atmospheric sciences. Alberta University, Edmonton, Alberta, Canada.
Missing link discovered?
In a paper published in the journal Science in 2015, a team of researchers reported the discovery of what was believed to be an example of the first known four-legged snake fossil, an animal they named Tetrapodophis amplectus.
If correctly interpreted based on the preserved anatomy, this would be a very important discovery. There are many evolutionary questions that could be answered by finding a four-legged snake fossil, but only if it is the real deal. [However], [t]he major conclusion of our team is that Tetrapodophis amplectus is not in fact a snake and was misclassified. Rather, all aspects of its anatomy are consistent with the anatomy observed in a group of extinct marine lizards from the Cretaceous period known as dolichosaurs.Caldwell explained that the new study of Tetrapodophis revealed a number of mischaracterizations of the anatomy and morphology of the specimen — traits that initially seemed to be shared most closely with snakes, suggesting this might be the long-sought-after snake with four legs.
When the rock containing the specimen was split and it was discovered, the skeleton and skull ended up on opposite sides of the slab, with a natural mould preserving the shape of each on the opposite side. The original study only described the skull and overlooked the natural mould, which preserved several features that make it clear that Tetrapodophis did not have the skull of a snake — not even of a primitive one.
Professor Michael Caldwell
[…]
The clues to this conclusion, Caldwell noted, were hiding in the rock the fossil was extracted from.Part and counterpart of Tetrapodophis amphlectus.
Image Credit: Michael Caldwell
Although Tetrapodophis may not be the snake with four legs that paleontologists prize, it still has much to teach us, said study coauthor Tiago Simões, a former U of A PhD student, Harvard post- doctoral fellow and Brazilian paleontologist, who pointed out some of the features that make it unique.
Abstract
The origin of snakes remains one of the most contentious evolutionary transitions in vertebrate evolution. The discovery of snake fossils with well-formed hind limbs provided new insights into the phylogenetic and ecological origin of snakes. In 2015, a fossil from the Early Cretaceous Crato Formation of Brazil was described as the first known snake with fore- and hind limbs (Tetrapodophis amplectus), and was proposed to be fossorial, to exhibit large gape feeding adaptations (macrostomy) and to possess morphologies suggesting constriction behaviours. First-hand examination of T. amplectus, including its undescribed counterpart, provides new evidence refuting it as a snake. We find: a long rostrum; straight mandible; teeth not hooked zygosphenes/zygantra absent; neural arch and spines present and tall with apical epiphyses; rib heads not tubercular; synapophyses simple; and lymphapophyses absent. Claimed traits not preserved include: braincase/descensus parietalis; ‘L’-shaped nasals; intramandibular joint; replacement tooth crowns; haemal keels; tracheal rings; and large ventral scales. New observations include: elongate retroarticular process; apex of splenial terminating below posterior extent of tooth row; >10 cervicals with hypapophyses and articulating intercentra; haemapophyses with articulating arches; reduced articular surfaces on appendicular elements; rows of small body scales; and reduced mesopodial ossification. The axial skeleton is uniquely elongate and the tail with >100 vertebrae is not short as previously claimed, although overall the animal is small (∼195 mm total length). We assessed the relationships of Tetrapodophis using a revised version of the original morphological dataset, an independent morphological dataset, and these two datasets combined with molecular data. All four were analysed under parsimony and Bayesian inference and unambiguously recover Tetrapodophis as a dolichosaur. We find that Tetrapodophis shows aquatic adaptations and there is no evidence to support constricting behaviour or macrostomy.
Note that there are no doubts expressed in this paper that there would have been just such a link at some point in the evolutionary history of snakes, only this specimen isn't it. The scientists are in no doubt that snakes evolved out of lizards and have a very clear understanding of just what a 'transitional' ancestor would have looked like. The same cannot be said of Creationists who deny that evolution occurs at all. They would run a mile rather than take the risk of describing what a transitional fossil such as is proposed by science would look like, in case just such a fossil is ever found.
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