National Geographic News
A fossilized dinosaur egg with insect cocoons.

The possible wasp cocoons found inside a fossilized dinosaur egg (coin shown for scale).

Photograph courtesy Jorge Genise

A wasp cocoon.

A cocoon from a modern wasp. Photograph courtesy Jorge Genise

Charles Q. Choi

for National Geographic News

Published July 19, 2011

Wasps may have once roosted within rotting dinosaur eggs, an idea suggested by the discovery of exceptionally well-preserved fossils of insect cocoons.

Scientists were recently investigating several roughly 70-million-year-old titanosaur eggs found in the Patagonia region of Argentina.

Titanosaurs belonged to a group of gigantic plant-eaters that included the heaviest creatures to ever walk the Earth. Titanosaur eggs were similarly large—up to almost 8 inches (20 centimeters) long.

(Related: "Eggs Hold Skulls of Titanosaur Embryos.")

Within one of the broken fossil eggs from Argentina, researchers found eight tiny, sausage-shaped structures about an inch (two to three centimeters) long and nearly a half-inch (just over a centimeter) wide.

The strange structures appear to be fossilized insect cocoons that are similar in size and shape to cocoons belonging to a number of modern wasp species.

Bugs Key to Cleaning Dino Nests

The study authors suggest that the ancient egg was somehow cracked open before it hatched. Scavengers such as crickets might have fed on the yolk, and spiders later dined on the scavengers.

Wasps might have attacked either the initial scavengers or the spiders, laying their eggs in the bodies of those creatures. The wasp offspring then spun their cocoons inside the rotting egg. (Related: "'Zombie' Roaches Lose Free Will Due to Wasp Venom.")

The finding could be the first evidence of invertebrates such as crickets scavenging on dinosaur eggs, since it's "the first time that [wasp] cocoons are associated with a dinosaur egg," said study co-author Jorge Genise, an entomologist at the Argentine Museum of Natural Sciences.

(Related pictures: "Snake vs. Dinosaur in New Fossil Find.")

Although the bugs profited off the death of this particular egg, the critters were probably key in keeping titanosaur nests clean overall, added co-author Laura Sarzetti, another entomologist at the museum.

By devouring rotting matter, the scavenging insects cleared the nest of potentially dangerous microbes.

The newfound fossil cocoons are described in the July issue of the journal Palaeontology.



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