Before There Were Dinosaurs, This Triassic 'Lizard King' Ruled Antarctica
Antes que houvesse dinossauros, este "Rei Lagarto" triássico governou a Antártida
Milhões de anos antes de o solo tremer sob os passos do T. rex - o chamado "rei dos dinossauros" -, a Antártida era lar de um "rei lagarto" do tamanho de uma iguana.
Esse antigo réptil era um arcossauro - parte do mesmo grupo que mais tarde incluiria dinossauros, pterossauros e crocodilianos. Cientistas descobriram recentemente um esqueleto parcial do lagarto que data de 250 milhões de anos atrás, época em que a Antártida estava explodindo de vida vegetal e animal.
O fóssil desse antigo "rei" não apenas fornece uma imagem mais nítida da paisagem da floresta na Antártida, como também ajuda a explicar a paisagem evolucionária após a maior extinção em massa da história da Terra, relataram cientistas em um novo estudo. [Antarctica: The Ice-Covered Bottom of the World (Photos)]
Though the lizard fossil was incomplete, researchers were able to tell
from the fused vertebrae that the animal was an adult reptile, and it
likely measured about 4 to 5 feet (1.2 to 1.5 meters) in length. They
dubbed it Antarctanax shackletoni: The first
part of its name comes from the Greek words for "Antarctic king;" the
second part is a nod to pioneering British polar explorer Ernest Shackleton, who named the Beardmore Glacier — where many Antarctic fossils, including Antarctanax, have recently been found — following an expedition in 1908.
Subtle features in the bones of the lizard's spine and feet indicated
that it was a new species, and its foot shape suggested that it lived on
the ground, scampering over the forest floor, lead study author Brandon
Peecook, a Meeker Postdoctoral Fellow at the Field Museum of Natural
History in Chicago, told Live Science.
"It doesn't have any adaptations in its feet that would make us think
it lived in the trees or that it's a burrower," Peecook said.
"Widespread forests"
Those trees might be hard to picture if you imagine Antarctica as it is today: a frozen, mostly lifeless, ice-covered desert.
But hundreds of millions of years ago, Antarctica hosted a warm, wet
environment where temperatures rarely — if ever — dipped below freezing,
the study authors reported.
"We have evidence of widespread forests all over the place, and big
rivers moving through those forests," Peecook said. Roaming among the
trees and rivers were amphibians, mammal relatives called cynodonts, other mammal-like predators called dicynodonts that had tusks and beaks, and reptiles like Antarctanax, he added.
But this fossil also contributes to an important evolution story. With
the discovery of this previously unknown ancient reptile, researchers
are piecing together the unexpected archosaur diversity that arose
shortly after the Permian mass extinction
— a cataclysmic event about 252 million years ago that wiped out around
96 percent of all marine species and approximately 70 percent of
terrestrial vertebrates. Scientists previously thought that after that
global extinction event, it took many millions of years for animals to
diversify and fill the planet's empty niches. But Antarctanax
shows that archosaurs began diversifying within just a couple of million
years after the Permian extinction, according to the study.
"If you look in the earliest rocks of the Triassic, archosaurs and
other groups are radiating explosively," Peecook told Live Science.
While Antarctanax's iguana-like body may not seem especially
dramatic, some Triassic reptiles evolved to soar through the skies as
pterosaurs, while others returned to the seas and eventually evolved
into enormous ichthyosaurs and plesiosaurs — and their ancestors were likely emerging at the same time as Antarctanax, he explained.
"The existence of Antarctanax in the early Triassic implies that
all these other crazy lineages must have existed at this point already,
even if we don't have a good fossil record of them from this time,"
Peecook said.
The findings were published online today (Jan. 31) in the Journal of Vertebrate Paleontology.
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