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Gueragama sulamerica. Credit: Julius Csotonyi
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University of Alberta paleontologists have
discovered a new species of lizard, named Gueragama
sulamericana, in the municipality of Cruzeiro do Oeste in Southern Brazil
in the rock outcrops of a Late Cretaceous desert, dated approximately 80
million years ago.
"The roughly 1700 species of iguanas
are almost without exception restricted to the New World, primarily the
Southern United States down to the tip of South America," says Michael
Caldwell, biological sciences professor from the University of Alberta and one
of the study's authors. Oddly however, iguanas closest relatives, including
chameleons and bearded dragons, are all Old World. As one of the most diverse
groups of extant lizards, spanning from acrodontan iguanians (meaning the teeth
are fused to the top of their jaws) dominating the Old World to non-acrodontans
in the New World, this new lizard species is the first acrodontan found in South
America, suggesting both groups of ancient iguanians achieved a worldwide
distribution before the final break up of Pangaea.
"This fossil is an 80 million year
old specimen of an acrodontan in the New World," explains Caldwell.
"It's a missing link in the sense of the paleobiogeography and possibly
the origins of the group, so it's pretty good evidence to suggest that back in
the lower part of the Cretaceous, the southern part of Pangaea was still a kind
of single continental chunk."
Distributions of plants and animals from
the Late Cretaceous reflect the ancestry of Pangaea when it was whole.
"This Gueragama sulamericana fossil
indicates that the group is old, that it's probably Southern Pangaean in its
origin, and that after the break up, the acrodontans and chameleon group
dominated in the Old World, and the iguanid side arose out of this acrodontan
lineage that was left alone on South America," says Caldwell. "South
America remained isolated until about 5 million years ago. That's when it bumps
into North America, and we see this exchange of organism north and south. It
was kind of like a floating Noah's Arc for a very long time, about 100 million
years. This is an Old World lizard in the new world at a time when we weren't expecting
to find it. It answers a few questions about iguanid lizards and their
origin."
The University of Alberta is a world
leader in paleontology. This study was a collaboration between the University
of Alberta and scientists in Brazil. Caldwell says of the collaboration,
"It's providing an opportunity for our students and research groups to
expand our expertise and interests into an ever-increasing diversity of
organisms within this group of animals called snakes and lizards."
The lead author of the paper is Caldwell's
PhD student, Tiago Simoes, a Vanier scholar. "As with many other
scientific findings, this one raises a number of questions we haven't
previously considered," says Simoes. "This finding raises a number of
biogeographic and faunal turnover questions of great interest to both
paleontologists and herpetologists that we hope to answer in the future."
In terms of next steps, Caldwell notes
"Each answer only rattles the questions harder. The evolution of the group
is much older than has been previously thought, which means we can push an
acrodontan to 80 million years in South America. We now need to focus on much
older units of rock if we're going to find the next step in the process."
The findings, "A stem acrodontan
lizard in the Cretaceous of Brazil revises early lizard evolution in
Gondwana," were published in the journal Nature Communications, one of the
world's top multidisciplinary scientific journals.
Citation
Tiago R. Simões, Everton Wilner, Michael
W. Caldwell, Luiz C. Weinschütz, Alexander W. A. Kellner. A stem acrodontan
lizard in the Cretaceous of Brazil revises early lizard evolution in Gondwana. Nature Communications, 2015; 6: 8149
DOI: 10.1038/ncomms9149