Tiny dinos perished in footprint death pits

27 January 2010 by Jeff Hecht
Magazine issue 2745.

FOLLOWING in someone's footsteps was a bad idea for a few unlucky dinosaurs. A rare fossil haul of feathered dinosaurs suggests they perished after falling into the deep muddy footprints of larger beasts.

David Eberth of the Royal Tyrrell Museum in Drumheller, Alberta, Canada, found partial skeletons of 18 small two-legged dinosaurs in the 160-million-year-old sediments from an ancient marsh in China. They were stacked on top of each other, apparently after becoming trapped in roughly circular swampy pits.

The pits contain distinctive red fragments of crust mixed into the mud. The palaeontologists reckon this is the result of large, heavy sauropod feet breaking through a crusty surface layer to watery mud beneath. A thin crust would have formed hiding the trap from an unsuspecting small dinosaur but unable support its weight.

Fifteen of the fossils were Limusaurus inextricabilis, an odd bipedal dinosaur with short arms and a beak. It appears to have eaten plants, although it belonged to a group of predators.

The victims were less than 1 metre tall and 1 to 3 metres long, says Eberth, so they would have been too short to push against the bottom, which was 1 or 2 metres beneath the surface of the watery mud. Their arms would have been covered with mud-slicked feathers and too small to pull them out of the hole (PALAIOS, DOI: 10.2110/palo.2009.p09-028r). "Finding any fossil remains like these, whose presence depends on the behaviour of other dinosaurs is bizarre," Eberth says.

There are few small dinosaur fossils from the period. "It's a really interesting find," and expands the known behaviours of two-legged dinosaurs, says David Fastovsky of the University of Rhode Island, Kingston.

http://www.newscientist.com/article/mg20527454.100-tiny-dinos-perished-in-footprint-death-pits.html
(Submitted by Tim Chapman)