Standard snake evolution story stymied by spate of fossil discoveries
Note: two updates to this article, supplementing rather than contradicting the findings discussed in it, are appended at the end: 1) 5 December 2016, on the status of Tetrapodophis amplectus; 2) 12 December 2019, about a reported new analysis of Najash fossils.
Until early 2015, the ‘earliest’ date reported for a fossil snake was less than 100 Ma old. In January, a team led by University of Alberta (Canada) paleontologist Professor Michael Caldwell described fossils of four new species, in Nature Communications, which they claimed extended the snake fossil record backwards by about 70 Ma to the Middle Jurassic.1
‘Earliest’ snake fossils
The new species reported were:
- Parviraptor estesi (from Dorset, England)—145–140 Ma
- Diablophis gilmorei (from Colorado, USA)—155 Ma
- Portugalophis lignites (from Guimarota, Portugal)—157–152 Ma
- Eophis underwoodi (from Oxfordshire, England)—167 Ma.
The skull anatomy of all four of these ‘ancient’ snakes, they say, is similar to that of both modern snakes and other fossil snakes. Of course, this is unexpected. However, the skull structure of previously reported fossil snakes, Pachyrhachis problematicus and Haasiophis terrasanctus, also surprised evolutionary researchers, resembling that of modern boas and pythons (deemed ‘advanced’).
Furthermore, the latter two species were preserved with actual fossilized hind limbs (considered a ‘primitive’ condition).2 It was anticipated that fossils of earlier snakes would turn out to have more pronounced hind legs as well as front legs. So what of the four species reported by Caldwell’s team?
Reuters published artistic renditions of three of the species, picked up by media outlets globally.3 Diablophis gilmorei was pictured with diminutive hind legs and forelegs and Portugalophis lignites as a colourful tree climber with the suggestion of tiny forefeet.
Unknown to most readers of the popular new reports was that these limbs and feet were sheer artistic licence. No trace of limbs or feet was reported by Caldwell et al., neither was there any trace of pectoral or pelvic girdles!
The systematic description of skeletal and dental specimens for Diablophis gilmorei included little of the backbone itself—just some precloacal4 vertebrae and “one possible sacral vertebra”.5 Similarly, Portugalis lignites was reconstructed solely from fragmentary jaw remains. In fact, the fossil material of all four species was acknowledged to be so incomplete6 that “we cannot ascertain the shape, length, form and so on of any aspect of the body of the earliest snakes (~167 Myr ago) reported herein [emphasis added]”.
This did not prevent the researchers speculating that “all four may have had some form of reduced forelimbs and hind limbs”.2
New insights and a new story?
There have long been two competing ideas for the origins of snakes. Some researchers have held that snakes are descended from monitor lizards which, in turn, descended from mosasaurs (an aquatic origin). The other view (a terrestrial origin), has gained ascendancy, with land lizards being deemed the snake ancestors.7 Commenting on these oldest fossil snakes, the writer for Reuters exclaimed: “The remarkable fossils … rewrite the history of snake evolution.”3 Caldwell et al. were more cautious but did claim that the new fossils “provide insights on snake evolution”.1
In fact, the dates assigned to the new fossils posed something of a dilemma, as Caldwell acknowledged: “Importantly, there is now a significant knowledge gap to be bridged by future research, as no fossils [sic] snakes are known from between 140 to 100 Ma ago”8 (but see later).
If mature, biologically diverse snakes (with ‘advanced’ crania) already existed by 167 Ma ago (the ‘age’ of the oldest fossil), evolutionary paleontologists now had little option but to argue for an even earlier origin for snakes. One of Caldwell’s colleagues, Sebastián Apesteguía (from the National Scientific and Technical Research Council, Argentina), believes snakes must have first appeared about 190 Ma ago.3
The evolutionary story was further stymied by the lack of hard evidence for limbs or limb girdles.9
Caldwell’s team advanced the ‘revolutionary’ view that the snakes evolved their characteristic skull morphology long before losing their legs.10 They had little choice in taking this step for two reasons: (1) the modern-looking skulls of all four of these ‘oldest’ snakes; (2) the fact that much ‘younger’ snakes (such as the 94-Ma-old Eupodophis11) had small hind limbs. It wouldn’t do to argue for an evolutionary reversal having occurred (the loss, then regaining of limbs over millions of years violating Dollo’s Law12), so although these early snakes appear to have been limbless (based on the fossils alone) it is presumed that they possessed legs, front and back. During the 70 Ma of time between Eophis underwoodi and the younger hind-limbed snakes, snakes were envisaged to have been diversifying geographically and biologically, principally by virtue of elongation of the body and reduction in size of the legs.
First four-legged snake
In July, a further species of fossil snake was reported in Science:13
- Tetrapodophis amplectus (from Brazil)—113 Ma.
A complete skeleton of the animal is preserved (figure 1), in contrast to the much more fragmentary fossil remains of the four ‘older’ species. The creature possessed 160 spinal and 112 tail vertebrae and beautifully preserved hind limbs and forelimbs.
Ironically, this exquisite fossil has created a quandary for researchers in this field—confusion rather than clarity. Some are even cautious about whether Teptrapodophis is actually a true snake, with Michael Caldwell (author of the earlier 2015 paper1) even suggesting it may belong to an extinct amphibian group.14
Nevertheless, the media proclaimed it a four-legged snake. Evolutionary developmental biologist Prof. Martin Cohn claimed: “this could be one of the most important fossils ever found. The combination of snakelike body with complete forelimbs and hindlimbs is like a snake version of Archaeopteryx.”15
Even accepting it as a true snake, Tetrapodophis is somewhat problematic for the conventional evolutionary view. Yes, it partially narrows the approx. 40 Ma ‘time gap’ mentioned earlier.
However, Tetrapodophis is certainly not morphologically transitional between those ‘earliest’ (limbless) snakes and the later snake fossils with hind limbs; namely Pachyrhachis problematicus, Haasiophis terrasanctus and Eupodophis descouensi—notwithstanding that evolutionists will have to claim that the ‘earliest’ fossil snakes also had four limbs—and larger ones at that. Speaking of the limbs of Tetrapodophis, one of the authors of the Science paper, Dr Nick Longrich (University of Bath, UK), says they were “far from being ‘vestigial’ evolutionary leftovers, dangling uselessly”.16
Instead, it is believed that Tetrapodophis used its long, clawed fingers and toes for grasping onto its prey, conveyed by the species name amplectus, meaning ‘embrace’. This was portrayed in artistic reconstructions of the creature. Even the preserved remains of its last meal were fossilized, some sort of small vertebrate.
The five ‘ancient’ snake species reassessed
However the debate on this fascinating little creature pans out, the fact remains that, from an evolutionary perspective, the fossils fail to furnish the evidence for their story. The ‘earliest’ snake fossils appear mature, ‘advanced’, and limbless. Fifty-four Ma after their first appearance in Eophis underwoodi, Tetrapodophis amplectus turns up with four fully functional legs and feet!
It is now imperative that evolutionary paleontologists find much ‘older’ fossil snakes (about 190 Ma) showing much more developed hind legs and forelegs (and associated pelvic and pectoral girdles respectively) than observed in Tetrapodophis amplectus. In addition, such creatures should show much less body elongation than in ‘later’ snakes.
Evolutionary paleontologists will continue to seek fossils which definitively answer the conundrum of snake origins. The snake fossil record still says no to evolution! From a creationist perspective, the four oldest fossils are likely the remains of the types of snakes we would readily recognize in today’s world.
Tetrapodophis is part of the rich antediluvian diversity that is now lost to us; assuming some of its kind passed (via the Ark) into the post-Flood world, they appear to have long since gone extinct. Its limbs exhibit clear evidence of purposeful design. Even if they were diminished in size from an ancestral condition, this would be devolution. The loss of legs (gradually or quickly) in snakes or lizards no more poses a challenge to biblical biology than does the loss of functional wings in flightless insects17 or birds.18
Update, 12 December 2019
In November 2019, new snake skull and skeletal fossils of the genus Najash were published in Science Advances.1 While the age for these fossils is not stated, Figure 4 of the paper seemingly gives a date of 91 Ma for Najash rionegrina, first published in 2006.2 The authors of the newer, 2019 paper used ‘Relaxed-clock Bayesian inference analysis’ on a large dataset of snake species to arrive at a divergence date of 171.55 Ma for snakes; this was rounded down to 170 Ma in popular media reports. One news outlet in November 2019 typically claimed that the new study of fossils of Najash and other species, “revealed they possessed hind legs during the first 70 million year of their evolution” (i.e. from ca. 170 to 100 Ma).3 However, this is unsubstantiated hype.
Fossils of the first four species discussed in the CMI article above (Parviraptor estesi, Diablophis gilmorei, Portugalophis lignites and Eophis undewoodi), though presumed to have had hind limbs, were not found with any, not even traces of pelvic girdles—these ranged in ‘age’ from 167–140 Ma. And these fossil species don’t even get a mention in the Science Advances paper, perhaps because they provide zero evidence for the longed-for pelvis, let alone hind legs. Yet, these snake species lie smack bang in the middle of this claimed 170–100 million year time period.
Furthermore, several fossil snakes are dated as ‘older’ than Najash, by evolutionary palaeontologists themselves: <100 Ma for Haasiophis terrasanctus, 98 Ma for Pachyrhachis problematicus and 94 Ma for Eupodophis descouensi. Thus, one cannot help but wonder, why all the fuss about Najash sp., a genus that has been known about for 13 years? Bona fide fossil snakes with definite hind limbs are absent ‘before’ 100 Ma on the evolutionary timescale. Even discounting the controversial fossil Tetrapodophis sp. (see previous Update box, 5 December 2016) this still leaves evolutionary palaeontologists keen to find much ‘older’ snakes that actually document the existence of hind legs in their 170–100 Ma time frame.
References and notes
- Garberoglio, F.F. et al, New skulls and skeletons of the Cretaceous legged snake Najash, and the evolution of the modern snake body plan, Science Advances 5(11), 20 November 2019 | DOI: 10.1126/sciadv.aax5833.
- Apesteguía, S., A Cretaceous terrestrial snake with robust hindlimbs and sacrum, Nature 440(7087):1037–1040, May 2006 | DOI: 10.1038/nature04413.
- Caldwell, S. & Palci, A., This Fossil Find of an Ancient ‘Snake With Legs’ Tells an Incredible Story…, sciencealert.com, 21 November 2019.
Update, 5 December 2016
As discussed in this article, the identification of Tetrapodophis amplectus as a true snake has not been without controversy. For instance, some researchers suspect it was a marine lizard rather than a terrestrial snake. An article in the 4 November 2016 issue of Science gives an opposing view.19 Most frustratingly, for all concerned, it has come to light that this “missing link in the snake evolutionary tree” (Carolyn Gramling’s words in the new Science article) cannot be studied any more. When the slab containing the fossil was split open, one half showed the animal’s features much more clearly than the other (the ‘counterpart’). The better slab (upon which last year’s paper was based) reportedly is no longer available for study. This has greatly irritated the critics of the ‘Tetrapodophis is a snake’ advocates! The Bürgermeister-Müller Museum, which housed the fossil on behalf of a private owner, is no longer permitting access to the fossil, including the original researchers—there is speculation that this may be due to damage caused during the fossil’s analysis. Since, in principle, the original research findings cannot be checked by other experts, University of Cambridge palaeontologist Dr Jason Head says “Tetrapodophis is no longer science. … It’s not repeatable, it’s not testable.”
References and notes
- Caldwell, M. W. et al., The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution, Nat. Comm. 6:5996, January 2015 | doi:10.1038/ncomms6996. Return to text.
- Whitehouse, D., Discovery challenges snake origins, news.bbc.co.uk, March 2000; accessed June 2015. Return to text.
- Dunham, W., Remarkable fossils push back snake origins by 65 million years, uk.reuters.com, January 2015; accessed February 2015. Return to text.
- The cloaca is the shared opening for the expulsion of faecal matter and urine, also used during copulation. Precloacal vertebrae are those back bones which are close to, but in front of, the cloaca. Return to text.
- See ref. 1. The sacral part of the backbone is the region where a pelvic girdle would be supported if there was one. Return to text.
- The photographs and illustrations appearing in the paper’s illustrations are restricted to details of skull and jaw elements (plus teeth) and comparisons of vertebral bones. One can be sure that any pelvic or limb elements would have taken pride of place, had they been found. Return to text.
- Bell, P., Of snakes, lizards and mosasaurs—evolutionists puzzle over snake origins, Creation 31(3):15–17, 2009; creation.com/snakes. Return to text.
- University of Alberta, The world’s oldest known snake fossils: rolling back the clock by nearly 70 million years, sciencedaily.com, January 2015; accessed February 2015. Return to text.
- The best they could offer was “one potential sacral vertebra in Parviraptor estesi” (in contrast to most other snakes) and “another in the vertebral specimens referred to Diablophis gilmorei …”. That these were robust led them to speculate about “the possible presence of robust pelvic girdles and hind limbs”. Return to text.
- This is the opposite of the conclusion of a recent paper on the fossil snake Coniophis precedens; Longrich, N.R., Bhullar, B.–A.S. and Gauthier, J.A., A transitional snake from the Late Cretaceous period of North America, Nature 488(7410):205–208, 2012 | doi:10.1038/nature11227. Return to text.
- Sarfati, J., Another leggy snake? What should creationists think?, 29 April 2008; creation.com/another-leggy-snake. Return to text.
- Dollo’s Law is named after Belgian biologist Louis Dollo. Another example of a violation of this ‘law’ relates to the alleged evolutionary loss, reappearance and loss (again) of the wings of stick insects; Bell, P., Evolution revolution, Creation 25(3):31, 2003; creation.com/evo-revo. Return to text.
- Marthill, D.M., Tischlinger, H. And Longrich, N.R., A four-legged snake from the Early Cretaceous of Gondwana, Science 349(6246):416–419, July 2015 | doi: 10.1126/science.aaa9208. Return to text.
- Perkins, S., Four-legged snake fossil stuns scientists—and ignites controversy, news.sciencemag.org, July 2015. Return to text.
- Christakou, A., Four-legged fossil snake is a world first, nature.com/news, July 2015. Return to text.
- Webb, J., Four-legged snake ancestor ‘dug burrows’, bbc.co.uk/news, July 2015. Return to text.
- Catchpoole, D. and Wieland, C., Researchers: Evolution of insect flight?, 19 June 2012; creation.com/insect-flightlessness. Return to text.
- Cosner, L. and Sarfati, J., The birds of the Galápagos, Creation 31(3):28–31, 2009; creation.com/galapagos-birds. Return to text.
- Gramling, C., ‘Four-legged snake’ may be ancient lizard instead, Science 354(6312):536–537, 2016. Return to text.