First egg from Antarctica is big and might belong to an extinct sea
lizard

Date:
June 17, 2020
Source:
University of Texas at Austin
Summary:
An analysis has found that a mysterious fossil discovered in 2011 is
a giant, soft-shell egg from about 66 million years ago. Measuring
in at more than 11 by 7 inches, the egg is the largest soft-shell
egg ever discovered and the second-largest egg of any known animal.



FULL STORY ==========================================================================
In 2011, Chilean scientists discovered a mysterious fossil in Antarctica
that looked like a deflated football. For nearly a decade, the specimen
sat unlabeled and unstudied in the collections of Chile's National Museum
of Natural History, with scientists identifying it only by its sci-fi
movie- inspired nickname -- "The Thing."

==========================================================================
An analysis led by researchers at The University of Texas at Austin has
found that the fossil is a giant, soft-shell egg from about 66 million
years ago.

Measuring in at more than 11 by 7 inches, the egg is the largest
soft-shell egg ever discovered and the second-largest egg of any known
animal.

The specimen is the first fossil egg found in Antarctica and pushes the
limits of how big scientists thought soft-shell eggs could grow. Aside
from its astounding size, the fossil is significant because scientists
think it was laid by an extinct, giant marine reptile, such as a mosasaur
-- a discovery that challenges the prevailing thought that such creatures
did not lay eggs.

"It is from an animal the size of a large dinosaur, but it is completely
unlike a dinosaur egg," said lead author Lucas Legendre, a postdoctoral researcher at UT Austin's Jackson School of Geosciences. "It is most
similar to the eggs of lizards and snakes, but it is from a truly giant relative of these animals." A study describing the fossil egg was
published in Nature on June 17.

Co-author David Rubilar-Rogers of Chile's National Museum of Natural
History was one of the scientists who discovered the fossil in 2011. He
showed it to every geologist who came to the museum, hoping somebody had
an idea, but he didn't find anyone until Julia Clarke, a professor in
the Jackson School's Department of Geological Sciences, visited in 2018.



==========================================================================
"I showed it to her and, after a few minutes, Julia told me it could be
a deflated egg!" Rubilar-Rogers said.

Using a suite of microscopes to study samples, Legendre found several
layers of membrane that confirmed that the fossil was indeed an egg. The structure is very similar to transparent, quick-hatching eggs laid by
some snakes and lizards today, he said. However, because the fossil egg
is hatched and contains no skeleton, Legendre had to use other means to
zero in on the type of reptile that laid it.

He compiled a data set to compare the body size of 259 living reptiles
to the size of their eggs, and he found that the reptile that laid the
egg would have been more than 20 feet long from the tip of its snout
to the end of its body, not counting a tail. In both size and living
reptile relations, an ancient marine reptile fits the bill.

Adding to that evidence, the rock formation where the egg was discovered
also hosts skeletons from baby mosasaurs and plesiosaurs, along with
adult specimens.

"Many authors have hypothesized that this was sort of a nursery site
with shallow protected water, a cove environment where the young ones
would have had a quiet setting to grow up," Legendre said.

The paper does not discuss how the ancient reptile might have laid
the eggs.

But the researchers have two competing ideas.

One involves the egg hatching in the open water, which is how some species
of sea snakes give birth. The other involves the reptile depositing the
eggs on a beach and hatchlings scuttling into the ocean like baby sea
turtles. The researchers say that this approach would depend on some
fancy maneuvering by the mother because giant marine reptiles were too
heavy to support their body weight on land. Laying the eggs would require
the reptile to wriggle its tail on shore while staying mostly submerged,
and supported, by water.

"We can't exclude the idea that they shoved their tail end up on shore
because nothing like this has ever been discovered," Clarke said.


========================================================================== Story Source: Materials provided by University_of_Texas_at_Austin. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Lucas J. Legendre, David Rubilar-Rogers, Grace M. Musser, Sarah
N. Davis,
Rodrigo A. Otero, Alexander O. Vargas, Julia A. Clarke. A giant
soft- shelled egg from the Late Cretaceous of Antarctica. Nature,
2020; DOI: 10.1038/s41586-020-2377-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200617150011.htm

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