"Drop Crocs!!" Plunging Onto Prey From The Trees

 

By Margherita Bassi - Smithsonian Magazine

Paleontologists Unearthed Australia’s Oldest Known Crocodile Eggshells. The eggshells belonged to an extinct group of crocs, some members of which were “drop crocs” that plunged onto prey.

As if the wildlife in Australia today isn’t intimidating enough, tens of millions of years ago, visitors would have had to deal with an additional nightmarish scenario—crocs jumping out of trees.

“It's a bit of a joke when you talk about Australia having drop crocs. But the reality is, we appear to have had them,” Mike Archer, a paleontologist at the University of New South Wales Sydney (UNSW), tells the Australian Broadcasting Corporation’s Angus Randall. The ancient reptiles “spent time in the trees, probably jumping out on their prey. And these same weird crocodiles weren't behaving like normal crocodiles. They weren't sitting in the water.”

In a study published November 11 in the Journal of Vertebrate Paleontology, Archer and his colleagues describe the oldest known crocodile eggshells discovered in Australia. They belonged to mekosuchine crocodiles—an extinct group of crocs that inhabited the continent’s inland waters 55 million years ago.

Some mekosuchines seem to have been at least semi-arboreal, “like a leopard croc, jumping on top of you from the trees, not leaping up from river systems,” Archer tells the Canberra Times’ Lloyd Jones.

The fossilized eggshells probably didn’t belong to a drop croc, but an earlier relative, per the Australian Broadcasting Corporation. Namely, the fragments may have come from species of Kambara—an especially old genus of mekosuchines, Michael Stein, a paleoecologist at UNSW and co-author of the study, writes for the Conversation. Kambara species could grow to over six feet long and likely ate fish and softshell turtles, he adds.

Researchers unearthed the eggshells in a rancher’s backyard in the small Queensland town of Murgon—one of the oldest fossil sites in Australia. The fragments are now shedding light on the crocs’ reproduction, adaptation and environment.

The fossil site at Murgon Mina Bassarova

“They preserve microstructural and geochemical signals that tell us not only what kinds of animals laid them, but also where they nested and how they bred,” Xavier Panadès I Blas, lead author of the study and a researcher at the Catalan Institute of Paleontology Miquel Crusafont, says in a UNSW statement.

The shells’ microstructure indicates that the crocs laid their eggs on the edge of a lake and that they were adapting their reproductive strategies to a changing environment. The remains also feature little evidence of bacterial degradation, Stein writes for the Conversation, suggesting that the nest may have gone through dry periods because of the fleeting nature of forest-lined wetlands surrounding Murgon.

“We're quite convinced we're talking about a kind of a temporary, shallow, freshwater lake in which these crocodiles came in, perhaps only once a year, to a crocodile, you know, egg-laying fest,” Archer tells the Australian Broadcasting Corporation. They “probably retreated after that back into the forest to gobble up animals that didn't expect to be eaten by crocodiles in the middle of the forest.”

Mekosuchine crocs might have eventually lost a significant portion of their inland habitat to spreading dryland, forcing them to retreat to diminishing waterways, where competition for food was fierce. Nevertheless, they highlight that especially ancient crocodiles “did a lot more than they do in modern ecosystems,” Matthew McCurry, a vertebrate paleontologist at the Australian Museum who did not participate in the study, tells the Guardian’s Donna Lu. Australia’s modern crocs arrived just 3.8 million years ago.

Ultimately, the study provides a window into the ecosystem of Australia tens of millions of years ago, back when the island continent was still attached to South America and Antarctica.