Pictures: Oldest Reptile Embryos Discovered

Short Incubation

Image courtesy Graciela Piñeiro

A fossil of a mesosaur skeleton is seen in a recent photograph. The black bar at bottom right indicates a scale of ten millimeters.

Piñeiro suspects some mesosaur species gave birth to live young, while others laid eggs but kept those eggs in their uteruses for a long time.

In the latter scenario, a mother mesosaur may have laid her eggs near water, where the baby would have hatched following a short incubation period of a few days or mere hours, she said.

(See "'Sea Monster' Fetus Found—Proof Plesiosaurs Had Live Young?")

Published April 17, 2012

"Exquisite" Embryo

Illustration courtesy Gustavo Lecuona

An illustration shows what a baby mesosaur might have looked like inside its egg. The tiny nub on its snout is an egg tooth, which the youngster would've used to break out of its shell.

The fossil embryos found in Uruguay were "exquisitely preserved" by the salty, low-oxygen lagoon in which they were trapped, Piñeiro noted.

With little oxygen, the lagoon lacked the bacteria that rapidly decompose dead organisms, she said.

(See "Dinosaur 'Death Pits' Created by Giant's Footprints?")

Published April 17, 2012

Fossil Jumble

Images courtesy Graciela Piñeiro

Pieces of an adult mesosaur skeleton are seen jumbled with the skull, vertebrae, and other bones of a baby mesosaur in a recent photograph. An edited picture, reworked for clarity, is shown at right.

Such an arrangement—found elsewhere in the Uruguayan site—suggests to Piñeiro and her team that mesosaurs may have cared for their young.

The juvenile's scattered bones likely mean the animal was not contained inside a shell when it died—suggesting the little one was hanging out with its parent.

This evidence makes mesosaurs the "oldest known probable case of parental care in reptiles," Piñeiro said.

(See "Dinosaur Dads Played 'Mr. Mom'"?)

Published April 17, 2012

Mesosaur Fossil

Photograph by Chris Howes, Wild Places Photography/Alamy

An adult mesosaur fossil from Brazil—dated to between 299 to 251 million years ago, and not part of the recent study—is seen in a file photograph.

For Piñeiro, the recent finds culminate more than a decade of work searching for mesosaur fossils.

"I was euphoric," she said, "and almost crying for the emotion of [having] discovered so much important specimens."

Published April 17, 2012

More Pictures: Record-Breaking Dinosaur Nests >>

Illustration courtesy Julius Csotonyi

Published April 17, 2012