What 15 million years ago was very bad for Australian marsupials is now very good for paleontologists: Researchers have uncovered a death trap, an underground limestone cave where hundreds of animals stumbled to their demise.

A paper published today in Journal of Vertebrate Paleontology details the resulting fossil menagerie, which includes an extinct wombat-like marsupial known as Nimbadon lavarackorum.

Karen Black of the University of New South Wales led the excavation and says in a press release that her team has already uncovered 26 Nimbadon skulls. The varying ages of the skulls detail the Nimbadon’s whole life cycle from “suckling pouch” to “elderly adults.”

“This is a fantastic and incredibly rare site,” says Dr. Black [regarding the cave]. “The exceptional preservation of the fossils has allowed us to piece together the growth and development of Nimbadon from baby to adult.” [Society of Vertebrate Paleontology]

See a photo gallery of the excavation and fossil processing below the jump.

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Researchers believe that there are even more fossils deeper in the Queensland cave, known officially as AL90. They also suspect that finding so many of the same animal might mean the Nimbadon exhibited “mob” behavior–traveling in large groups–as seen with today’s grey kangaroos.

The skulls are relatively large, but researchers think Nimbadon didn’t have much in the way of brains. Perhaps that’s not surprising, given the animals fell into a hole en masse.

“We think it needed a large surface area of skull to provide attachments for all the muscle power it required to chew large quantities of leaves, so its skull features empty areas, or sinus cavities,” said study team member Mike Archer of the University of New South Wales (UNSW) in Sydney. “Roughly translated, this may be the first demonstration of how a growing mammal ‘pays’ for the need to eat more greens—by becoming an ‘airhead.’” [Society of Vertebrate Paleontology]

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