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.

Elephant Fossils Found in Brazil

When people today are asked about elephants they associate these members of the Class Proboscidea (animals with trunks) with Africa and India.  Those extant species that survive today are strongly associated with the African Savannah and the Indian sub-continent.  However, the elephant lineage is long and the fossil evidence indicates that over the course of the Cenozoic these animals have existed in some form or other over much of the globe.

For example, the United Kingdom has its fair share of prehistoric elephant fossils, perhaps most notably the West Runton elephant.  Partial remains including elements of the pelvis, skull and tusks of an enormous prehistoric elephant (Mammuthus trogontherii) were discovered eroding out of the sea cliffs at West Runton, near Cromer on the Norfolk coast in 1990.  A complete excavation took place in 1995 and evidence of a ten tonne giant elephant was revealed.

A report from Brazil states that scientists have described a fossil tooth, that could only belong to an elephant in the Amazon jungle.  The existence of elephants in South America in prehistory is not disputed, especially when one considers the excellent fossil material of Cuvieronius that has been found in Argentina and Bolivia.  This elephant genus was originally named and described by that great French scientist and anatomist Georges Cuvier back in 1808.  These fossils and those of another member of the Gomphotheridae – Stegomastodon (Stegomastodon platensis) indicate that a number of elephant genera were present in South America.

What is unusual about this fossil tooth from the Amazon, is that it has been dated to just 45,000 years ago, indicating the presence of elephants in South America during the Pleistocene Epoch, whereas the elephant fossils found to date are from the earlier geological Epoch, the Pliocene.

Scientists from Brazil say that this fossil tooth, proves the presence of pachyderms in South America as recently as 45,000 years ago.  The tooth had been discovered in the early 1990s, around the time of the excavation work on the West Runton elephant, but it was only recognised as a tooth from an elephant after a close examination by a University student from the Federal University of Minas Gerais.

Commenting on the find, palaeontologist Mario Cozzuol of Federal University stated:

“Only elephants and capybaras have teeth with this kind of laminate structure, but those of capybaras are no longer than five centimetres, while the fossil measured twelve centimetres.”

Earlier fossil discoveries had indicated that ancient elephants were present in Central America during the Pleistocene, but there was an absence of evidence to indicate that elephants from North America had migrated further south.  Both the African and Indian elephant are very much at home in enclosed forest environments, so the existence of ancient elephant species in the forested Amazon basin would not be entirely surprising.

A Trio of Papo Woolly Mammoth Models

A “Memory” of Elephants.  The collective noun for a collection of elephants.  A trio of Papo Woolly Mammoth models.  Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

To view a model of a prehistoric elephant (Woolly Mammoth) and lots of dinosaur replicas: Papo Dinosaur and Prehistoric Animal Models.

Australian Discovery Provides Evidence of “Mob” Behaviour in Ancient Marsupials

By the Eocene, Australia had become isolated from the rest of the world.  Here in splendid isolation, its primitive mammals, especially the marsupials were allowed to evolve unheeded without the frequent migration of other types of creature into Australian habitats.  In contrast to their South American cousins, which were usurped from many environmental niches by more modern placental mammals from North America, the Australian marsupials survived as the dominant group in this part of the world.  Researchers have been analysing a large number of marsupial fossils.

Discovery of a Cave

Scientists from the University of New South Wales have reported on the discovery of a cave which contains a substantial number of prehistoric marsupial fossils.  Their findings are reported in the scientific publication “The Journal of Vertebrate Palaeontology”, analysis of the fossils indicate that they are approximately 15 million years old (dating to the middle of the Miocene Epoch).

The cave is located in the northwest of Queensland, near to the famous Riversleigh site, an area famous for its prolific quantities of Cenozoic mammal fossils.  Riversleigh is a relatively remote area, with few townships and lots of ranches.  Evidence for Australian marsupials ranging from 23 million years ago to less than 20,000  years old have been found.

Fossils have been excavated from the Riversleigh area for more than 100 years but the real breakthrough which put this relatively obscure part of Australia firmly on the palaeontological map occurred in 1983 when a few weathered blocks of Riversleigh limestone revealed more than 30 new species of mammal.

For much of the Miocene and Pliocene Epochs this part of Australia was a lush lowland rain forest that was teeming with life.  One particular site at Riversleigh has been recorded as one of the most vertebrate fossil rich locations known.  In 1983, a two cubic metre block of limestone yielded 58 new mammal species.  The Riversleigh area is a limestone terrain which in the Miocene had a lot of surface water.  These were ideal conditions for bone preservation.

Marsupial Fossils

The cave system contains a number of complete prehistoric marsupials skeletons, their discovery has revealed some surprising similarities between these ancient creatures and extant species of modern-day kangaroos and koalas.

The cave has kept the fossils beautifully preserved.  The fossil find includes 26 skulls from an extinct, wombat-like marsupial called Nimbadon (N. lavarackorum).  The herbivorous Nimbadon was approximately the size of a sheep, but with giant claws.

Co-author of the study, University of New South Wales palaeontologist Mike Archer commented:

“It’s extraordinarily exciting for us.  It’s an extra insight into some of the strangest animals you could possibly imagine.”

The cave was found in the mid 1990s and has been extensively explored.  The scientists were amazed at how well preserved the fossils were and the large number of fossilised bones discovered at the site.  The number of skulls found together (twenty-six) suggests that these particular marsupials may have travelled as a group or to use an appropriate collective noun a “mob”.

The scientists remain unsure as to how all the animals ended up in the cave.  One theory put forward suggests that the mob of kangaroos fell into the cave through a whole in the roof that had been obscured by overgrowing vegetation.  These poor animals would have either been killed by the fall or become trapped and starved to death.

The Remains of Joeys

The fossil bones include the remains of joeys still in their mother’s pouches.  This gives the researchers an insight into how these ancient marsupials developed.  The skulls of the babies reveal that the bones at the front of the face developed quite quickly, this would have allowed the joey to suckle from its mother at an extremely young age.

Karen Black, the expedition’s leader, commented that the Nimbadon joeys developed in a similar way to extant kangaroos today, probably being born after a month’s gestation and crawling into their mother’s pouch for the remainder of their development.

The large claws indicate a potential arboreal existence, with Nimbadon climbing trees in a similar way to modern Koalas.  With large marsupial predators in the area, animals such as the carnivorous kangaroo Ekaltadeta and the marsupial “tiger” the Thylacine, being able to climb trees may have been a very effective strategy for defence.

Discussing this significant discovery, palaeontologist Liz Reed of Flinders University (South Australia) stated:

“To find a complete specimen like that and so many from an age range is quite unique.  It allows us to say something about the behaviour and growth and a whole bunch of things that we wouldn’t normally be able to do.”

Australia may be well known today for its unique fauna and flora but it seems back in the Miocene the unusual life in the Riversleigh area would have given today’s strange Australian natives a run for their money.

To view models and replicas of prehistoric mammals: Replicas of Prehistoric Mammals.