Trace Fossils Show Evidence of Dinosaur Digging for Mammals in their Burrow

For us, the concept of digging up dinosaurs is not unusual, we have had the opportunity to be involved in a number of vertebrate fossil excavations including Dinosauria.  However, a paper published in the scientific journal “Geology” discusses a remarkable find in Utah (USA) that provides Late Cretaceous evidence of a dinosaur turning the tables and digging up mammals.  This amazing trace fossil (a trace fossil preserves evidence of behaviour and/or activity) provides an insight into the hunting behaviour of a small theropod dinosaur.

Described as an “ancient crime scene”, the 77-million-year-old dinosaur claw marks and scratches were discovered next to a series of mammal burrows in the Dixie National Forest by Edward Simpson, a geologist at Kutztown University (Pennsylvania).  Some of the burrows were made by rabbit sized mammals, others were much smaller, perhaps the homes of shrew-like creatures.  However, it appears that one little dinosaur was attempting to dig out the residents, aiming to turn the mammalian burrow dwellers into lunch.  This is the first instance of this behaviour being found in the fossil record.

Commenting on the discovery, Simpson stated:

“It appears a dinosaur was digging down and trapping rodent-like mammals in a similar way to coyotes hunting prairie dog burrows today.”

A co-author of the paper that has been published in the journal “Geology” Simpson and his colleagues describe the study of this newly discovered trace fossil of signs of digging and scratch marks found in association with mammalian burrows as evidence of a predator/prey relationship.

The fossils are actually three component elements that together can be interpreted as evidence of dinosaur hunting behaviour.  All the fossils occur within a floodplain siltstone-mudstone bed of the Upper Cretaceous Wahweap Formation in southern Utah.  The strata and the fossils they contain have been dated to Campanian faunal stage and although the dinosaur cannot be specifically identified, the scientists suggest that the marks indicate a maniraptoran theropod, possibly a dromeosaurid or a troodontid.  The team conclude that the close proxmity of the digging scratches and marks to the mammalian burrows suggests that dinosaurs used excavation techniques to prey on mammals.

A study of the strata and surrounding fossil matrix paints a picture of a sparsely vegetated, dry and exposed sandy plain, crossed by meandering streams.  The trace fossil evidence was preserved when it was suddenly covered by a flood and sand was deposited  covering the tell-tale signs of dinosaur and mammalian activity.  The fossils were eventually re-exposed at the bottom of a cliff face and discovered by the geological team.

Dinosaur trace fossil expert (ichnologist) Martin Lockley of the University of Colorado agreed with Simpson and his team’s interpretation of the fossils.

He went on to state:

“Hopefully, this will encourage palaeontologists to look for more of this type of evidence.”

Although trace fossils provide extremely important “in situ” evidence of behaviour such as digging for prey, it is difficult to associate the trace fossil evidence with any known specific dinosaur genera.  However, the size of the claw marks and an assessment of the curvature has led the authors to conclude that the culprit was a one metre tall maniraptoran theropod, possibly a dromaeosaurid such as Dromaeosaurus or maybe Saurornitholestes.  The claw marks may also have been made by a member of the Troodontidae such as Troodon.

Although it is difficult to ascribe this behaviour to any known genus, it is very easy to imagine a keen eyed maniraptoran spotting a burrow entrance and then starting to dig out the hole to get to the small mammal cowering inside.

To view a large range of articulated “raptor” models including dromaeosaurids and troodontids: Beasts of the Mesozoic Models and Figures.