A evolução precoce dos répteis diapsidas é marcada por um profundo contraste entre nosso conhecimento da origem e evolução precoce dos arquissauros (crocodilos, dinossauros aviários e não-aviários) ao dos lepidosauromorfos (escamos (lagartos, cobras) e esfenodoncianos (tuataras)). Considerando que as primeiras incluem centenas de espécies fósseis através de várias linhagens durante o período Triássico1, estes últimos são representados por um registro fóssil extremamente irregular que compreende apenas um punhado de fósseis fragmentários, a maioria dos quais têm afinidades filogenéticas incertas e estão confinados à Europa1,2,3. Aqui relatamos a descoberta de um crânio réptil tridimensionalmente preservado, atribuído comoTaytalura alcoberigen. et sp. nov., da época triássica tardia da Argentina que é robustamente inferido filogeneticamente como o primeiro lepidosauromorpha em evolução, usando vários tipos de dados e critérios de otimização.
Tomografias microcomputadas deste crânio revelam detalhes sobre a origem do crânio lepidosauriano a partir de diapsidas precoces, sugerindo que vários traços tradicionalmente associados com esfenodontas de fato se originaram muito antes na evolução do lepidosauromorpha.Taytalurasugere que a arquitetura do crânio fortemente conservada evolutivamente dos esfenodoncianos representa a condição plesiomórfica para todos os lepidosauros, que os lepidosauros de caule e coroa foram contemporâneos por pelo menos dez milhões de anos durante o Triássico, e que os lepidosauromorfos primitivos tinham uma distribuição geográfica muito mais ampla do que se pensava anteriormente.
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.
The origin of squamates revealed by a Middle Triassic lizard from the Italian Alps
Modern squamates (lizards, snakes and amphisbaenians) are the world’s most diverse group of tetrapods along with birds1
and have a long evolutionary history, with the oldest known fossils
dating from the Middle Jurassic period—168 million years ago2,3,4.
The evolutionary origin of squamates is contentious because of several
issues: (1) a fossil gap of approximately 70 million years exists
between the oldest known fossils and their estimated origin5,6,7;
(2) limited sampling of squamates in reptile phylogenies; and (3)
conflicts between morphological and molecular hypotheses regarding the
origin of crown squamates6,8,9.
Here we shed light on these problems by using high-resolution
microfocus X-ray computed tomography data from the articulated fossil
reptile Megachirella wachtleri (Middle Triassic period, Italian Alps10).
We also present a phylogenetic dataset, combining fossils and extant
taxa, and morphological and molecular data. We analysed this dataset
under different optimality criteria to assess diapsid reptile
relationships and the origins of squamates. Our results re-shape the
diapsid phylogeny and present evidence that M. wachtleri is the oldest known stem squamate. Megachirella
is 75 million years older than the previously known oldest squamate
fossils, partially filling the fossil gap in the origin of lizards, and
indicates a more gradual acquisition of squamatan features in diapsid
evolution than previously thought. For the first time, to our knowledge,
morphological and molecular data are in agreement regarding early
squamate evolution, with geckoes—and not iguanians—as the earliest crown
clade squamates. Divergence time estimates using relaxed combined
morphological and molecular clocks show that lepidosaurs and most other
diapsids originated before the Permian/Triassic extinction event,
indicating that the Triassic was a period of radiation, not origin, for
several diapsid lineages.
