Fósseis de cobras gigantes de 47 milhões de anos
retirados de minas na Índia podem ser a maior cobra de todos os tempos,
ultrapassando potencialmente a Titanoboa em cerca de 4,5 metros.
A cobra recém-descoberta era muito mais longa do que qualquer cobra viva, incluindo esta anaconda verde. (Crédito da imagem: WaterFrame / Alamy Stock Photo)
Cientistas na Índia descobriram os restos fossilizados de uma antiga cobra que pode ser a maior serpente conhecida que já existiu.
A enorme serpente pode ter medido 15 metros de comprimento – ultrapassando o atual detentor do recorde, Titanoboa, em cerca de 2 metros.
A espécie recém-identificada, chamada Vasuki Indicus
, leva o nome do gênero do mítico rei das serpentes do hinduísmo, que é
frequentemente representado enrolado no pescoço de uma das principais
divindades do hinduísmo, Shiva.
Um total de 27 vértebras
fossilizadas da enorme cobra foram desenterradas na mina de linhita
Panandhro, no estado de Gujarat. Os fósseis datam de cerca de 47
milhões de anos atrás, durante a época do Eoceno (56 milhões a 33,9
milhões de anos atrás). Os autores acham que os fósseis vieram de um
adulto totalmente crescido.
A equipe estimou o comprimento total
do corpo da serpente usando a largura dos ossos da coluna vertebral da
cobra e descobriu que V. indicus poderia ter variado entre 11
e 15 m (36 pés e 50 pés) de comprimento, embora reconheçam que pode
haver um possível erro associado com sua estimativa. Eles publicaram
suas descobertas na quinta-feira (18 de abril) na revista Scientific Reports .
Os pesquisadores usaram dois métodos para chegar a possíveis faixas de comprimento do corpo de V. indicus
. Ambos usaram cobras atuais para determinar a relação entre a
largura das vértebras de uma cobra e seu comprimento – mas diferiram nos
conjuntos de dados que usaram.
Um
deles usou dados de cobras modernas da família Boidae, que inclui jiboias e pítons e contém as maiores cobras vivas atualmente. O outro
conjunto de dados utilizou todos os tipos de cobras vivas.
" Vasuki
pertence a uma família extinta de cobras, remotamente aparentadas com
pítons e sucuris, e portanto, quando você usa cobras existentes para
estimar o comprimento do corpo, pode haver incertezas", disse o coautor
do estudo, Debajit Datta , pesquisador de pós-doutorado no Instituto Indiano. Instituto de Tecnologia Roorkee, disse ao Live Science.
O limite superior de suas estimativas tornaria a V. indicus ainda maior que a Titanoboa cerrejonensis
, a maior cobra já descoberta até agora, que viveu há cerca de 60
milhões de anos e foi descoberta em 2002 no nordeste da Colômbia.
V. indicus
pertence a um grupo de cobras conhecido como Madtsoiidae, que apareceu
pela primeira vez no final do período Cretáceo (100,5 milhões a 66
milhões de anos atrás), na América do Sul, África, Índia, Austrália e
sul da Europa.
Observando os locais onde as costelas se fixavam às vértebras, os investigadores pensam que V. indicus
tinha um corpo largo e cilíndrico e vivia principalmente em terra. As
cobras aquáticas, em comparação, tendem a ter corpos muito planos e
aerodinâmicos.
Devido ao seu grande tamanho, os pesquisadores
dizem que a cobra era provavelmente um predador de emboscada, subjugando
suas presas por constrição, semelhante às sucuris modernas.
Os cientistas estimam que V. indicus
prosperou num clima quente com uma média de cerca de 82 graus
Fahrenheit (28 graus Celsius) – significativamente mais quente do que
hoje.
“Ainda há muitas coisas que não sabemos sobre Vasuki. Não
sabemos sobre seus músculos, como ele os usava ou o que comia”, disse
Datta.
Sunil Bajpai
, coautor do estudo e paleontólogo de vertebrados do IIT Roorkee, disse
que a equipe espera que os fósseis sejam analisados quanto ao seu
conteúdo de carbono e oxigênio, o que pode revelar mais sobre a dieta da
cobra.
quinta-feira, 21 de novembro de 2019
Fóssil de cobra com patas encontrado na Argentina confirma teoria de Darwin
Concepção artística da cobra cujo fóssil foi encontrado na Argentina
Pesquisadores da Universidade de Flinders, Austrália, encontram na
Argentina um esqueleto de serpente com patas traseiras, o que seria uma
das melhores provas da teoria da evolução de Darwin.
A Najash rionegrina
tem seu nome derivado da palavra Nahash (cobra em hebraico) e por seu
esqueleto ter sido encontrado na província argentina de Río Negro.
O fóssil
possui restos de patas traseiras, o que mostraria o quanto o corpo das
cobras evoluiu até se tornar mais flexível como as atuais. Elas seriam
uma evolução de antigos lagartos.
Durante os primeiros 70 milhões de anos de evolução, o animal ainda se movia sobre um par de patas traseiras.
De
acordo com Alessandro Palci, pesquisador da Universidade de Flinders,
além do desaparecimento das patas traseiras, outras mudanças na
estrutura do animal teriam surgido ao longo do tempo, como indicaria o
fóssil.
"A Najash tem o crânio mais completo, tridimensionalmente preservado
de uma serpente antiga. Isto está nos fornecendo uma grande quantidade
de novas informações sobre como a cabeça das serpentes evoluiu. Tem
algumas, mas não todas as juntas flexíveis encontradas no crânio de
serpentes modernas. Sua orelha é intermediária entre a dos lagartos e
das cobras atuais, e diferente destas, tem o osso da face bem
desenvolvido, que também é remanescente dos lagartos", afirmou Palci.
Ainda
segundo Mike Lee, pesquisador do Museu do Sul da Austrália e da
Universidade de Flinders, a "Najash encontrada mostra como as cobras
evoluíram dos lagartos em passos evolutivos, tal como Darwin predisse".
Com informação da Science Advances, com ilustração de Raúl O. Gómez, da Universidade de Buenos Aires.
domingo, 3 de junho de 2018
This 240-Million-Year-Old Reptile Is the "Mother of All Lizards"
By Mindy Weisberger, Senior Writer |
About 240 million years ago, Megachirella wachtleri trod the vegetation in what is now the Dolomites region of northern Italy.
Credit: Davide Bonadonna
HBO's "Game of Thrones" features a "Mother of Dragons," but a fossil
that's hundreds of millions of years old was recently identified as the
"mother of all lizards" (and snakes, too).
This ancient lizard was the direct ancestor of approximately 10,000
species alive today that have inhabited the planet for more than 240
million years.
Paleontologists initially described the tiny reptile, Megachirella wachtleri, in 2003. But recent scans revealed features in the fossil that were hidden, enabling scientists to identify Megachirella as the oldest known ancestor in the squamate lineage — the reptile group that includes lizards and snakes. Megachirella, which predates the fossils previously thought to
belong to the earliest squamates by around 75 million years, bridged
the gap between the oldest known squamates and the estimated origins of
this reptile group derived from molecular data, researchers reported in a
new study. [In Photos: Amber Preserves Cretaceous Lizards]
The Megachirella fossil was found in the Alps in northern
Italy. It was estimated it to be about 240 million years old and
scientists thought it belonged to a lepidosaur, a type of primitive
reptile. But certain lizard-like features
hinted that the fossil might provide valuable and unique clues about
squamates, lead study author Tiago Simões, a doctoral candidate in
biological sciences at the University of Alberta in Edmonton, Canada,
told Live Science in an email.
"It deserved further attention — especially in the form of CT [computed
tomography] scanning — to provide greater anatomical details and an
improved data set, to understand its placement in the evolutionary tree
of reptiles," Simões said.
Scientists found a preserved specimen of Megachirella wachtleri in northern Italy and described it in 2003.
Credit: MUSE Science Museum
The researchers used CT scans to build 3D computer models of the fossil reptile, and found a number of features linking Megachirella
to squamates. Two of those features were unique to the squamate group: a
part of the braincase and a collarbone structure. Together, those
elements identified Megachirella as "the first unequivocal squamate from the Triassic," according to the study published online today (May 30) in the journal Nature.
Molecular and skeletal clues also indicated that geckoes, rather than
iguanians (which includes iguanas, anoles and chameleons), made up the
earliest squamate group to arise, the researchers reported.
Their evidence provided a critical and "really satisfying" missing
piece of an evolutionary puzzle, by providing fossil evidence to support
what molecular data suggests about squamate origins,
Chris Raxworthy, curator-in-charge of the Department of Herpetology at
the American Museum of Natural History in New York City, told Live
Science.
"Scientists always love it when we see different types of data coming
up with the same answer," said Raxworthy, who was not involved in the
study.
However, a large gap persists in the fossil record between Megachirella, which lived 240 million years ago, and other fossil squamates
that appeared no earlier than 168 million years ago. This leaves much
to be unraveled about the diversity of these ancient snakes and lizards
and what they may have looked like, Simões said.
"What we are discovering is the tip of the iceberg, and much further
work needs to be done to understand the early evolution of squamates,"
he said. Original article on Live Science.
quinta-feira, 26 de abril de 2018
Photos: Weird 4-Legged Snake Was Transitional Creature
By Laura Geggel, Senior Writer |
Snakes used to have four legs, according to a roughly
120-million-year-old fossil from northeastern Brazil. These legs likely
weren't used for movement, but perhaps helped the snake mate or grasp
prey, the researchers of the new study said. Like other snake fossils
from the Cretaceous, this one is from Gondwana, suggesting that snakes
originated on the southern supercontinent. [Read the full story on the four-legged snake] Wrestling match
An artist's interpretation of the four-legged snake, dubbed Tetrapodophis amplectus,
just after it caught a small mammal for its next meal. Paleontologists
have yet to find fossil remains of mammals in the Crato Formation in
northeastern Brazil, but "we know that they're in South America" during
the Early Cretaceous, said co-researcher David Martill, a professor in
paleobiology at the University of Portsmouth. It's likely that Tetrapodophis fed on lizards and small frogs in the tropical forests of Gondwana, he added. (Image credit: Julius T. Csotonyi.) Stunning snake
The entire skeleton of Tetrapodophis, with its head ending in a
curly-q on the left. The specimen was on exhibit at the Solnhofen
Museum in Germany, but its stunning feet escaped the notice of the
scientific community until Martill spotted them during a visit to the
museum. (Image credit: Dave Martill | University of Portsmouth.) Foot photo
This close-up photo shows Tetrapodophis' rear feet. (Image credit: Dave Martill | University of Portsmouth.) Little hands
The hands of Tetrapodophis. (Image credit: Dave Martill | University of Portsmouth.) Ancient battle
An illustration of Tetrapodophis capturing an ancient lizard in the genus Olindalacerta. (Image credit: James Brown | University of Portsmouth.) Digestion central
The fossilized stomach contents of Tetrapodophis contain bits
of bones, suggesting that the 7.8-inch-long (20 centimeters) critter ate
ancient vertebrates. (Image credit: Helmut Tischlinger.) Skull shot
The skull of Tetrapodophis. Notice its short snout and long braincase. (Image credit: Dave Martill | University of Portsmouth.)
Mistaken identity? debate over ancient 4-legged snake heats up
Identidade equivocada? Aquece o debate sobre a antiga serpente de 4 patas
By Laura Geggel, Senior Writer |
The, entire skeleton of Tetrapodophis with its head ending in a curly-q on the left. Credit: Dave Martill | University of Portsmouth
SALT LAKE CITY — A critter heralded as the first four-legged fossil
snake on record may actually not be a snake, according to new research.
Instead, the 120-million-year-old creature is likely a dolichosaurid, an
extinct four-legged marine lizard with an elongated, snake-like body, a
new analysis of the specimen finds.
"Tetrapodophis doesn't show any of those features that you would expect to see in a snake,"
said Michael Caldwell, a professor and chair of biological sciences at
the University of Alberta in Edmonton, Canada, who is leading the new
investigation into the enigmatic fossil.
For instance, Tetrapodophis amplectus doesn't have hooked
teeth like a snake does, nor does it have a snake-like skull and
skeleton, Caldwell said. Other anatomical details that have been found
in ancient and modern snakes are also missing, including the subdental
ridge in the mouth and zygosphenes, which are special joints that are
found between snake vertebrae, he said. [See Photos of the Four-Legged, Snakelike Creature]
Rather, the creature is likely a dolichosaurid, which falls under the
squamate (scaly reptile) umbrella, he said. It's unclear exactly how
dolichosaurids are related to snakes, but some evidence suggests they
are a sister group to the slithery reptiles, Caldwell said.
Uma criatura anunciada como a primeira cobra fóssil de quatro patas registrada pode na verdade não ser uma cobra, de acordo com uma nova pesquisa. Em vez disso, a criatura de 120 milhões de anos é provavelmente um dolichosaurid, um extinto lagarto marinho de quatro patas com um corpo alongado semelhante a uma cobra, uma nova análise dos achados do espécime.
"Tetrapodophis não mostra nenhuma das características que você esperaria ver em uma cobra", disse Michael Caldwell, professor e presidente de ciências biológicas da Universidade de Alberta, em Edmonton, Canadá, que está liderando a nova investigação sobre o assunto. fóssil enigmático.
Por exemplo, Tetrapodophis amplectus não tem dentes como uma cobra, nem tem um esqueleto e uma caveira, disse Caldwell. Outros detalhes anatômicos que foram encontrados em cobras antigas e modernas também estão faltando, incluindo a crista subdental na boca e os ziggosfénos, que são articulações especiais que são encontradas entre as vértebras de serpentes, disse ele. [Veja as fotos da criatura de quatro patas e uma cobra]
Em vez disso, a criatura é provavelmente um dolichosaurid, que cai sob o guarda-chuva squamate (escamosa réptil), disse ele. Não está claro exatamente como os dolichossaurídeos estão relacionados às cobras, mas algumas evidências sugerem que eles são um grupo irmão dos répteis escorregadios, disse Caldwell.
Paleontologist Michael Caldwell took a selfie with his finger next to Tetrapodophis amplectus to illustrate the specimen's small size.
Credit: Michael Caldwell
He even pointed to the bones of prey that were preserved in the specimen's gut — the animal's last meal before it died.
These are likely fish bones — a theory that fits the dolichosaurid
interpretation, because dolichosaurids lived in the water, Caldwell
said.
Brazilian fossil
T. amplectus made a big splash last year when a study published in the journal Science
in July 2015 announced that the fossil was the so-called missing link,
which showed that snakes evolved from four-legged lizards. The
researchers reported that the 7.8-inch-long (20 centimeters) specimen
probably descended from terrestrial burrowers (rather than marine
animals), and that it likely used its tiny limbs for grasping prey for
hunting and holding mates while reproducing.
David Martill, a co-researcher of the 2015 study and a professor of
paleobiology at the University of Portsmouth in England, came across the
fossil while he was on a field trip with his students at the Solnhofen
Museum (formerly known as the Bürgermeister-Müller-Museum) in Germany.
The exhibit featured fossils from the Crato Formation in northeastern Brazil, and one specimen, titled "Unknown fossil," caught Martill's eye.
It looked like a snake, but it had four exquisitely small limbs — a
feature that had never before been seen in a snake. Martill asked the
museum if he could study it, and eventually he and his colleagues named
it Tetrapodophis amplectus (which means, literally, four-legged snake).
Brewing controversy
Within two months of the 2015 study's publication, Caldwell and his
colleague Robert Reisz, a paleontologist at the University of Toronto,
traveled to Germany to see the specimen for themselves. [7 Shocking Snake Stories]
They brought two microscopes with them — a digital and a dissecting
microscope — so that they could take photos of the small critter at 200
times the magnification of the naked eye, Caldwell said.
The specimen comprises a part and counterpart — which are basically the sides of the two rocks that held the creature.
When the rock was split in two, the "part" retained some pieces of the
skull and most of the creature's body, and the "counterpart" retained
the other part of the skull. When they were studied together, there were
myriad clues that the animal was not a snake, Caldwell said.
However, Caldwell and Reisz may be the last scientists to examine the
specimen in person. The fossil is privately owned, and it has since been
removed from the museum, meaning other paleontologists can't study it,
Caldwell said.
An image taken at 200x magnification showing the teeth of Tetrapodophis amplectus.
A new analysis suggests that the teeth were not recumbent (pointing
backward) like a snake's, but were simply displaced after the animal
died. In contrast, the original analysis describes the teeth as
recumbent.
Credit: Michael Caldwell
Moreover, the specimen doesn't have a reported provenance, so it's
unknown when and where it was found, as well as who sold and bought it,
he said. In Brazil, it has been illegal since 1942 to remove holotype fossils
(holotypes are the first described specimen of a newfound species) from
the country, and there's also a ban on removing paratypes (subsequently
found specimens of a known species) without a permit. It's unclear
whether T. amplectus was discovered before or after
that law went into effect, Caldwell and his colleagues said. However, if
it was discovered after 1942, it was likely smuggled out of the
country, Caldwell said.
Tiago Simões, a doctoral candidate of vertebrate paleontology at the
University of Alberta, who is working with Caldwell, noted that the
fossil is from a region containing limestone that was quarried in the
1960s and 1970s for commercial purposes. Some fossils were found before
then, but the vast majority were discovered after the 1942 ruling, said
Simões, who is from Brazil.
"It's highly likely that the material was collected after the 1960s and 1970s," Simões told Live Science. [6 Strange Species Discovered in Museums]
When placed together, the part
and counterpart fossils (top two) form an entire skull (bottom) that is
not snakelike, the authors of the new research said.
Credit: Michael Caldwell
Given its mysterious past and current out-of-reach status, it might be best to "strike Tetrapodophis from the record of snake evolution
until more specimens can be found or that specimen comes back [from the
private collector] and can be put in the public trust," said Jason
Head, a lecturer in zoology and curator of vertebrate paleontology at
the University Museum of Zoology at the University of Cambridge in
England, who was not involved with either the 2015 study or the new
research.
"[In] the original description, the analysis was not very convincing to
begin with," Head said. "It was a very problematic study. Certainly the
work that Dr. Caldwell presented today illustrates a lot of the
ambiguities of the animal."
But, whether the specimen is a snake remains a mystery.
"We're never going to know whether or not the original analysis was
right or wrong, or whether or not Dr. Caldwell's work was right or
wrong, because we can't replicate either observation," Head said.
Supersnake
The authors of the original study are defending their work, and said that it's clear that T. amplectus is a four-legged snake.
"I don't think Caldwell has made a case for Tetrapodophis not
being a snake," Martill told Live Science in an email. "Some of his
observations, such as saying that the teeth are not recumbent [pointing
backward], are plain wrong."
He added that, "Tetrapodophis has a single row of belly scales; Tetrapodophis has
snake vertebral articulations (although a couple of lizard groups do
have these). There are many more snake features, too, based on skull
anatomy."
Martill's colleague and co-author Nicholas Longrich, a senior lecturer
in evolutionary biology at the University of Bath, in England, said, "I
would happily bet a million dollars it’s a snake." Longrich contested
the assessment that the specimen didn't have a subdental ridge or
visible zygosphenes, as well as myriad other features that Caldwell and
his colleagues listed as missing. Moreover, the prey in the animal's gut
likely aren't fish bones, unless it's a Tiktaalik (a fish with limbs), "because the bones in the gut include leg bones," Longrich said.
"I’m as confident of Tetrapodophis being a snake as I have ever been of anything in my scientific career," Longrich wrote in an email to Live Science.
Questions about snake limbs remain a popular subject among scientists. Two studies published last week
found that snakes likely sported limbs up until about 150 million years
ago, when genetic mutations caused them to lose the ability to develop
arms and legs. But, if T. amplectus loses its snake status,
there will be zero fossil evidence that snakes once had four limbs,
"which is a real bummer," Caldwell said.
The research, which has yet to be published in a peer-reviewed journal,
was presented Wednesday (Oct. 26) at the 2016 Society of Vertebrate
Paleontology meeting. Original article on Live Science.
quinta-feira, 18 de janeiro de 2018
Phylogenetic
inference and divergence dating of snakes using molecules, morphology
and fossils: new insights into convergent evolution of feeding
morphology and limb reduction
Bayesian divergence time analyses were used
to simultaneously infer the phylogenetic relationships and date the
major clades of snakes including several important fossils that have not
previously been included in divergence dating analyses as terminal
taxa. We also explored the effect of using fossilized birth–death (FBD)
and uniform tree priors for divergence dating with terminal
calibrations. Nonclock and relaxed clock analyses of the combined
morphology and molecular data set supported previous molecular
phylogenetic hypotheses for the major clades of snakes, including the
paraphyly of the traditionally recognized Scolecophidia and
Macrostomata. Tip-dating analyses using either a uniform tree prior or
FBD prior that assume that all fossils are tips and that extant lineages
are randomly sampled resulted in older ages than those inferred using a
FBD prior assuming diversified sampling of extant lineages and those
estimated by previous studies. We used Bayesian ancestral state
reconstruction methods to map the evolution of the ability to consume
large prey and the loss of limbs onto our inferred time-calibrated
phylogeny. We found strong support for early evolution of the ability to
consume large prey, indicating multiple independent losses of this
ability. We also found strong support for retention of external
hindlimbs until relatively late in snake evolution, indicating multiple
independent losses of hindlimbs.
quarta-feira, 20 de maio de 2015
Data Suggests Legs and Toes in Ancestor of Living Snakes
Photo
An artist’s rendering of the
most recent common ancestor of all living snakes. Its small hind legs
probably served no purpose in locomotion.Credit
Julius Csotonyi
From
the robust boa constrictor to the venomous rattlesnake, all of the more
than 3,400 snake species that slither today may have descended from the
same prehistoric forest prowler, whose sinuous body had two small hind
legs with toes and ankles, researchers reported on Tuesday.
After
analyzing data gathered through fossils, genetic sequencing and
anatomical comparisons of 73 snake and lizard species, a team of
paleontologists from Yale University has constructed what it calls the
most comprehensive snake “family tree” to date. The findings provide an
answer to longstanding questions about when, where and how modern snakes
originated.
“Having
that tree as a backbone let us draw a ton of conclusions for what the
ancestral snake would have been like,” said Daniel J. Field, a doctoral
candidate in evolutionary biology and an author of the study. The team
concluded that the most recent common ancestor of all living snakes was
nocturnal, thrived 128.5 million years ago in the Southern Hemisphere
and devoured relatively large prey whole using its sharp, hooked teeth
as a hunting tool.
To
reach this conclusion, the team’s first step was to reconstruct the
snake’s family tree from tips to its trunk. To better understand when
certain characteristics — like the ability to constrict prey or hunt at
night — first appeared, the researchers used the genetic and
morphological data they collected to piece together how different groups
of living snakes are related to one another.
After
mapping the relationships among distinct snake groups, the
herpetologists used a series of algorithms to fill in when each trait
first arose, in a process called ancestral state reconstruction. Mr.
Field and his team identified 11 characteristics that they wanted to
place onto the snake’s tree of life. Each trait would answer a question
about snake evolution that scientists often debate: Did ancient snakes
dwell in the water or on land? Originate from the Northern or the
Southern Hemisphere? Ambush their prey or forage for food?
Using
the tree, team members could rule out the traits that could not have
belonged to the most recent ancestor of living snakes and generate a
model of what traits it did exhibit. They found that it did not
constrict prey like boas and pythons, but did have remnants of hind
legs, which Mr. Field said were most likely vestigial structures that
served no purpose in locomotion.
“I
was most amazed by how strongly we inferred that the common ancestor
retained hind limbs,” he said. The team published its tree of life for
snakes in the journal BMC Evolutionary Biology.
The
team’s ancestral reconstruction is not without its limitations, Mr.
Field said. Because there are no fossil records of the most recent
common ancestor of living snakes, Mr. Field and his team have no way of
confirming that the creature they recreated with their models is
correct.
“Sometimes
evolution plays out in unexpected and strange ways,” he said. “We think
we’ve got a strongly supported idea, and based on the mathematical
reconstruction it is what is most likely to be true.”
Christopher J. Raxworthy,
a herpetologist at the American Museum of Natural History in New York,
who was not involved in the study, called the work fantastic and said he
was impressed by how strongly the genetic and fossil data supported the
authors’ findings. But he said he was not surprised that the common
ancestor of all living snakes had hind legs, because several living
snakes have vestigial hind limbs and pelvic girdles.
Dr.
Raxworthy added a caveat to the work. He said that herpetology, like
most of evolutionary biology, is on the cusp of a genomic revolution,
and that many snake groups most likely will have their entire genomes
sequenced in coming years. Because of that influx of genetic
information, “it’s almost inevitable that there will be changes to this
evolutionary history of snakes,” he said.
PALEONTOLOGIA 2015
Origem das serpentes
The Origin of Snakes: revealing the Ecology, Behavior, and Evolutionary History of Early Snakes - using Genomics, Phenomics, and the Fossil Record
Reconstruction of the ancestral crown-group snake, based on the new study.
Artwork by Julius Csotonyi.
Abstract
Background
The highly derived morphology and astounding diversity of snakes has
long inspired debate regarding the ecological and evolutionary origin of
both the snake total-group (Pan-Serpentes) and crown snakes
(Serpentes). Although speculation abounds on the ecology, behavior, and
provenance of the earliest snakes, a rigorous, clade-wide analysis of
snake origins has yet to be attempted, in part due to a dearth of
adequate paleontological data on early stem snakes. Here, we present the
first comprehensive analytical reconstruction of the ancestor of crown
snakes and the ancestor of the snake total-group, as inferred using
multiple methods of ancestral state reconstruction.
We use a
combined-data approach that includes new information from the fossil
record on extinct crown snakes, new data on the anatomy of the stem
snakes Najash rionegrina, Dinilysia patagonica, and Coniophis precedens,
and a deeper understanding of the distribution of phenotypic
apomorphies among the major clades of fossil and Recent snakes.
Additionally, we infer time-calibrated phylogenies using both new
‘tip-dating’ and traditional node-based approaches, providing new
insights on temporal patterns in the early evolutionary history of
snakes.
Results
Comprehensive ancestral state reconstructions reveal that both the
ancestor of crown snakes and the ancestor of total-group snakes were
nocturnal, widely foraging, non-constricting stealth hunters. They
likely consumed soft-bodied vertebrate and invertebrate prey that was
subequal to head size, and occupied terrestrial settings in warm,
well-watered, and well-vegetated environments. The snake total-group –
approximated by the Coniophis node – is inferred to have originated on
land during the middle Early Cretaceous (~128.5 Ma), with the
crown-group following about 20 million years later, during the Albian
stage. Our inferred divergence dates provide strong evidence for a major
radiation of henophidian snake diversity in the wake of the
Cretaceous-Paleogene (K-Pg) mass extinction, clarifying the pattern and
timing of the extant snake radiation. Although the snake crown-group
most likely arose on the supercontinent of Gondwana, our results suggest
the possibility that the snake total-group originated on Laurasia.
Conclusions
Our study provides new insights into when, where, and how snakes
originated, and presents the most complete picture of the early
evolution of snakes to date. More broadly, we demonstrate the striking
influence of including fossils and phenotypic data in combined analyses
aimed at both phylogenetic topology inference and ancestral state
reconstruction.
Keywords: Serpentes, Phylogeny, Ancestral state reconstruction, Divergence time estimation, Combined analysis, Fossil tip-dating
Allison Y Hsiang, Daniel J Field, Timothy H Webster, Adam DB Behlke,
Matthew B Davis, Rachel A Racicot and Jacques A Gauthier. 2015. The
Origin of Snakes: revealing the Ecology, Behavior, and Evolutionary
History of Early Snakes using Genomics, Phenomics, and the Fossil
Record. BMC Evolutionary Biology. DOI: 10.1186/s12862-015-0358-5.
