Rosa Rubicondior: Creationism Refuted - Why Snakes, Like Creationists, Don't Have A Leg To Stand On

Najash rionegrina

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An ancient snake's cheekbone sheds light on evolution of modern snake skulls | Faculty of Science

Creationism is the art of ignoring evidence while pretending to be interested in it. Creationists continually demand that science provide supporting evidence for their childish parodies of evolution, abiogenesis, the Big Bang, and other scientific explanations; then, when the evidence is provided, they either ignore it, misrepresent it, or move the goalposts.

This is neatly illustrated by a paper published in Science Advances in 2019 by an international team of palaeontologists, including researchers from Argentina, the University of Alberta and McGill University. The paper provides creationists with something they are forever pretending to ask for — a transitional fossil — while also undermining another of their favourite assertions: that evolutionary change must always involve adding something new, and that loss or reduction cannot contribute to evolution.

The fossil in question belongs to Najash rionegrina, a rear-limbed fossil snake from Argentina. The presence of hind limbs is striking enough, but it is not the most important point of the paper. The fossil also shows that, during snake evolution, legs were not the only structures to be reduced or lost. The skull of Najash still retained a cheekbone — the jugal bone — which has almost entirely disappeared in living snakes.

That matters because it helps refine our understanding of how the modern snake skull evolved. Rather than appearing suddenly, fully formed and magically snake-like, the snake body plan was assembled over time through a series of anatomical changes, including elongation of the body, reduction of limbs, modification of the skull, and the loss or reduction of bones that were present in earlier ancestors. In other words, this is exactly the kind of transitional evidence creationists claim not to have seen, and exactly the kind of evolutionary reduction they claim cannot happen.

Background^ Gondwana’s early snakes. The “ancient lineage of snakes” referred to in the report is best described as Gondwanan basal snakes — early branches of the snake family tree that lived across the southern supercontinent of Gondwana and its later fragments. These were not modern snakes, but extinct relatives close to the evolutionary base of the snake lineage. The 2019 Science Advances study recovered Najash, Dinilysia and madtsoiid snakes as Mesozoic Gondwanan forms lying outside the modern snake crown group. [1]

These snakes are important because they show that early snake evolution was not a simple, sudden leap from lizard to modern snake. Najash rionegrina, from Cretaceous Patagonia, still had well-developed hind limbs and a pelvis, yet it was already recognisably a snake. The new skull material also showed that it retained a jugal, or cheekbone, which is almost entirely absent in living snakes. [2]

The broader Gondwanan snake fauna included forms from what are now South America, Africa, Madagascar, India and Australia, with some later dispersal into parts of Europe. One important extinct group, the madtsoiids, were primarily Gondwanan terrestrial snakes with a fossil record stretching from the Late Cretaceous into the Late Pleistocene — a span of about 100 million years. [3]

Madtsoiids varied greatly in size. Some were relatively modest snakes, while others became among the largest snakes known. A recently described Indian species, Vasuki indicus, has been estimated at about 11–15 metres long, making it one of the largest snakes ever reported. Like large boas and pythons, giant madtsoiids were probably powerful constricting ambush predators rather than fast, active hunters. [3]

For the evolution of snakes, the significance is clear: early snakes were not necessarily tiny burrowing animals, as was once often assumed. The Najash fossils support the idea that some ancestral snakes were relatively large-bodied, wide-mouthed predators, and that hind limbs persisted for a long period before modern limbless snakes appeared. [2]

The significance of this fossil in refining our understanding of snake evolution — by filling a gap in the fossil record and correcting earlier assumptions based on more limited evidence — is explained in a University of Alberta Faculty of Science news item by Katie Willis. As the report explains, the fossil shows that nearly 100 million years ago, these legged snakes still possessed a jugal bone, a feature that has all but disappeared in their modern descendants.

An ancient snake's cheekbone sheds light on evolution of modern snake skulls
100-million-year-old legged snake fossil provides critical insight into how the heads of modern snakes evolved.
New research from a collaboration between Argentinian and University of Alberta palaeontologists adds a new piece to the puzzle of snake evolution.

The researchers examined a strikingly well-preserved fossil of the rear-limbed snake Najash rionegrina, found in Argentina. The study shows that nearly 100 million years ago, these legged snakes still had a cheekbone-also known as a jugal bone-that has all but disappeared in their modern descendants.

Our findings support the idea that the ancestors of modern snakes were big-bodied and big-mouthed-instead of small burrowing forms as previously thought. The study also reveals that early snakes retained their hindlimbs for an extended period of time before the origin of modern snakes which are for the most part, completely limbless.

Fernando F. Garberoglio, lead author.
CONICET, Área de Paleontología
Fundación de Historia Natural Félix de Azara
CEBBAD, Universidad Maimónides
Buenos Aires, Argentina.

For decades, paleontologists' understanding of snake evolution was hampered by the limited fossil record. The new fossils presented in this study are crucial for reconstructing the early steps in the evolutionary history of modern snakes.

The fine details of the well-preserved fossil show that nearly 100 million years ago, these legged snakes still had a cheekbone-also known as a jugal bone-that has all but disappeared in their modern descendants.
Photo: Fernando Garberoglio.

This research revolutionizes our understanding of the jugal bone in snake and non-snake lizards. After 160 years of getting it wrong, this paper corrects this very important feature based not on guesswork, but on empirical evidence. This research is critical to understanding the evolution of the skulls of modern and ancient snakes.

Professor Michael Caldwell, co-author.
Department of Biological Sciences and Earth and Atmospheric Sciences
University of Alberta
Edmonton
Alberta, Canada.

The nearly 100 million year old fossil snakes described in this study, found in Northern Patagonia, are closely related to an ancient lineage of snakes that populated the southern hemisphere continents of Gondwana, and appear to be related to only a small number of obscure, modern snakes. The researchers used micro-computed tomography (micro-CT) scanning to visualize the skull structures within the specimen, examining the pathways of nerves and blood vessels as well as the skeletal structure that would be otherwise impossible to see without damaging the fossil.

Publication:
Fernando F. Garberoglio et al.
New skulls and skeletons of the Cretaceous legged snake Najash, and the evolution of the modern snake body plan.
Sci. Adv. 5, eaax5833 (2019). DOI: 10.1126/sciadv.aax5833

Abstract
Snakes represent one of the most dramatic examples of the evolutionary versatility of the vertebrate body plan, including body elongation, limb loss, and skull kinesis. However, understanding the earliest steps toward the acquisition of these remarkable adaptations is hampered by the very limited fossil record of early snakes. Here, we shed light on the acquisition of the snake body plan using micro–computed tomography scans of the first three-dimensionally preserved skulls of the legged snake Najash and a new phylogenetic hypothesis. These findings elucidate the initial sequence of bone loss that gave origin to the modern snake skull. Morphological and molecular analyses including the new cranial data provide robust support for an extensive basal radiation of early snakes with hindlimbs and pelves, demonstrating that this intermediate morphology was not merely a transient phase between limbed and limbless body plans.

Fig. 1 Najash specimens from LBPA.

(A) MPCA 500, skull with atlas-axis in right lateral view. (B) MPCA 591, partial skull with articulated vertebrae in right lateral view. (C) MPCA 581, partial skull with atlas in left lateral view. (D) MPCA 564, articulated specimen with partial skull and postcranium in ventral view. (E) MPCA 419, dentary and associated vertebrae and ribs. (F) MPCA 480, partial skull with atlas in dorsal view. (G) MPCA 536, partial skull in ventral view. (H) MPCA 386, partial skull in ventral view. bo, basioccipital; ti, tibia.

Fig. 2 CT scan reconstructions of the articulated skull of Najash (MPCA 500).

(A) Right lateral view. (B) Left lateral view. (C) Dorsal view. (D ) Ventral view. II, optic foramen; V, trigeminal foramen; aiaf, anterior inferior alveolar foramen; amf, anterior mylohyoid foramen; at, atlas-axis; ang, angular; bo, basioccipital; cb, compound bone; co, coronoid; cri, crista interfenestralis; crt, crista tuberalis; d, dentary; ept, ectopterygoid; fr, frontal; iof, infraorbital foramen; j, jugal; mf, mental foramina; mx, maxilla; n, nasal; ot, otoccipital; pa, parietal; pbs, parabasisphenoid; pal, palatine; pmx, premaxilla; pof, postfrontal; prf, prefrontal; pro, prootic; pt, pterygoid; q, quadrate; smx, septomaxilla; so, supraoccipital; sp, splenial; st, supratemporal; stf, stapedial footplate; vo, vomer.

Fig. 3 Snake phylogeny and cranial evolution.

(A) Majority-rule consensus of Bayesian inference analyses of dataset 1 (morphology-only). pol, postorbital loss; crcf, presence of full crista circumfenestralis (continuous system of bony crests surrounding the fenestra ovalis and the lateral aperture of the recessus scalae tympani, formed by prootic and otoccipital). Colored branch indicates Gondwanan radiation of basal snakes of Mesozoic origin as shown in the map (B) Gondwana during the Mesozoic, with the distribution of the fossil taxa in the analysis [1: Najash and Dinilysia (Patagonia, Argentina); 2: Menarana (Madagascar); 3: Sanajeh (India); 4: simoliophiids (Middle East); 5: Cenozoic madtsoiids of Cretaceous origin (Australia)]; (C) otic region of Najash, showing the absence of crista circumfenestralis in basal snakes; and (D) otic region of Anilius, showing the presence of full crista circumfenestralis in Serpentes (crown or modern snakes) consisting of crista interfenestralis (cri), crista prootica (crp), and crista tuberalis (crt). bt, basal tubera; rst, lateral aperture of the recessus scalae tympani.

Fig. 4 Snake phylogeny and divergence times.

Relaxed-clock Bayesian inference analysis of dataset 2 (combined evidence). Majority-rule consensus tree of the major diapsid and squamate lineages, with region of interest (blue square, see complete tree in fig. S4) zoomed in, showing snakes and closer clades against a geological time scale. Colored branch indicates Gondwanan radiation of basal snakes. Numbers at nodes indicate the median value for the divergence time estimates for each clade.

Fernando F. Garberoglio et al.
New skulls and skeletons of the Cretaceous legged snake Najash, and the evolution of the modern snake body plan.
Sci. Adv. 5, eaax5833 (2019). DOI: 10.1126/sciadv.aax5833

Copyright: © 2019 The authors.
Published by American Association for the Advancement of Science. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

So, once again, the fossil record has done exactly what creationists insist it never does: it has provided a transitional form in precisely the place evolutionary theory says such forms should be found. Najash rionegrina was not a modern snake, nor was it a lizard. It was an early snake retaining anatomical features that later snakes lost — hind limbs, a pelvis, and a skull bone almost entirely absent from living snakes. It is a snapshot of evolutionary change in progress.

It also illustrates something creationists routinely try to deny: evolution is not always about gaining new structures. It can also proceed by modifying, reducing, repurposing or losing existing structures. The snake body plan was not created in a single magical act; it was assembled over deep time by ordinary biological processes acting on inherited anatomy. Limbs were reduced, skull bones were remodelled, feeding structures changed, and the result was the highly specialised modern snake.

For creationists, this is doubly awkward. They demand transitional fossils, then ignore them when they are found. They claim loss of information cannot be evolutionary, then look away when evolution produces successful lineages by reduction and simplification. And they insist their Bronze Age mythology explains life better than science, while science continues to uncover fossils that fit evolutionary expectations and contradict creationist dogma at every turn.

Najash is therefore not just another ancient reptile from Cretaceous Patagonia. It is another reminder that the history of life is written in stone, bone and deep time — not in the pages of a creation myth written by people who knew nothing of fossils, genes, plate tectonics or evolution.

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