Prehistoric Crocodile – Machimosaurus rex

A team of international scientists including researchers from the University of Bologna (Italy), the University of Alberta (Canada) and the Office National Des Mines, Service Patrimoine Géologique (Tunis, Tunisia), have announced the discovery of the fossilised bones of a huge prehistoric marine crocodile, the largest member of the Teleosauridae (marine crocodyliforms), described to date.  The ancient crocodile provides proof that these types of marine reptile did not become extinct at the end of the Jurassic.

An Illustration of the Super-sized Marine Crocodile (Machimosaurus rex)

Probably preyed on turtles.

Picture credit: Davide Bonadonna

Marine Crocodile Fossil Remains

The fossil material which includes a nearly complete skull plus post cranial elements such as ribs, cervical and dorsal vertebrae plus one bone from the forelimbs, comes from Lower Cretaceous rocks of Tataouine (southern Tunisia).  The giant crocodile, named Machimosaurus rex was probably an ambush predator of the lagoonal environments on the shores of the Tethys Ocean.  It lived approximately 130 million years ago in the Early Cretaceous (Barremian faunal stage of the Cretaceous).

A Scale Drawing of M. rex Showing the Fossil Material Found

A scale drawing showing known fossil material and close up of the skull (dorsal view).

Picture credit: Marco Auditore

Marine Crocodile

At an estimated ten metres in length, and perhaps weighing more than three tonnes, not only is this the largest marine crocodile known to science, but it is also the largest crocodylomorph known from the Barremian faunal stage.  There are larger crocodiles known from the fossil record, Deinosuchus of North America and Sarcosuchus from Africa for example, but these animals lived later in the Mesozoic.  Machimosaurus rex with its skull measuring 160 centimetres in length, was certainly bigger than any extant crocodile.

The relatively short snout and the shape of the teeth (blunt and bullet shaped), suggest that this big “croc”, like many other members of the Machimosaurus genus, specialised in hunting turtles, but it may also have ambushed unwary dinosaurs and other animals should they have got too close to the water’s edge.

PNSO have added a marine crocodile replica to their Age of Dinosaurs model range: PNSO Age of Dinosaurs Figures.

Field Team Members Pose with the Skull in Situ

The field team pose with the fossilised skull.

Picture credit: Federico Fanti

A Skull Bigger than Tyrannosaurus rex

The Machimosaurus genus contains a number of species, most of which were named and described in the 19th century.  Their fossils are widespread with specimens having been recorded from Switzerland, France, Germany and England, although the Tunisian specimen is the only one known from Cretaceous strata.

University of Alberta PhD student Tetsuto Miyashita, a co-author of the scientific paper that was published this week in the journal “Cretaceous Research” stated:

“These teeth weren’t for cutting or piercing flesh.  They were built for crushing bones.”

Hence the speculation that along with other machimosaurs, this crocodile specialised in hunting and eating turtles.

Unexplored and Fieldwork is Challenging

This part of Tunisia remains relatively unexplored and fieldwork was difficult as the region is politically unstable.  However, the scientists hope to be able to return to the area in the near future to look for more post cranial material and to search for evidence of other vertebrates that shared this crocodile’s watery habitat.

Commenting on the significance of the discovery, lead author, palaeontologist Dr Federico Fanti (University of Bologna) said:

“The fossils indicate that M. rex belonged to a group of crocodiles that inhabited the sea and coastal areas around the end of the Jurassic Period, but the species is not directly related to modern-day crocodiles.”

Surviving into the Cretaceous

It had been thought that the teleosaurids had died out at the end of the Jurassic, but the discovery of Machimosaurus rex refutes this hypothesis.  It seems likely that the paucity of the fossil record for these types of crocodiles from Gondwana may have skewed the data to suggest that these marine crocodiles became extinct at the end of the Jurassic.  Although, local extinction events may have occurred, it seems likely that more fossils of crocodylomorphs that get assigned to the Machimosaurus genus will be found in Cretaceous-aged rocks.

Dr Fanti added:

“Therefore, this discovery sheds new light on the hypothesised mass extinction event at the end of the Jurassic, a biological crisis currently much less understood than the famous extinction at the end of the Cretaceous that wiped out the dinosaurs.” 

A Picture of Machimosaurus spp. Cranial Material

Typical skull material assigned to the Machimosaurus genus and line drawing (below).

Picture credit: Wikipedia Commons

Palaeontology can Sometimes be a Dangerous Business

This part of Tunisia remains politically unstable and field work has been hampered, but members of the research team are hopeful that they will be able to return to complete their survey of the area.  Sadly, barely a week after the field team left Tunis then ISIL inspired terrorists attacked the Bardo National Museum in Tunis (18th March 2015), killing more than twenty people and injuring a further forty-two.

Reflecting on the current troubles in that part of the Arab world, Tetsuto Miyashita said:

“Sometimes we are reminded that our endeavour to unlock the ancient mysteries is only possible through peace, freedom and sheer goodwill of people.  We were touched by the kindness and hospitality of Tunisians when we were there.  Nothing could make me happier than us working together again to get to that big monster.”

A Dinosaur Goes a Wooing?

The link between the Dinosauria and birds is well established.  However, to what extent can we view the behaviour of our feathered friends today and infer behaviours in the long extinct dinosaurs?  Thanks to some new research published this week in the academic journal “Scientific Reports”, palaeontologists may have  gained an insight into the courtship and mating behaviours of theropod dinosaurs.

Courtship and Mating Behaviours of Theropod Dinosaurs

The research team, which included scientists from South Korea, China, Poland as well as the United States, conclude that trace fossils consisting of gouges and scrapes preserved in sandstone strata that is estimated to be around 100 million years old, preserve evidence of dinosaurs engaging in courtship and mating behaviours similar to extant birds.  The scrapes, gouges and scratches, some of which cover an area the size of a bathtub, have been interpreted as being similar to “nest scrape display” as seen in modern Aves.

Dinosaurs Displaying and Undertaking Ritualised Courtship Displays

An artist imagines the Cretaceous courtship scene.

Picture credit: (Lida Xing and Yujiang Han / University of Colorado, Denver)

Dance of the Dinosaurs

The study was led by Professor Martin Lockley (University of Colorado) a highly respected specialist in dinosaur tracks and footprints (ichnologist).  The team interpret the trace fossils as evidence of courtship behaviour in theropod dinosaurs as the dinosaurs demonstrated their ability to make suitable mates by excavating pseudo nests.  Various trace fossil sites were studied and mapped, most of which are associated with the Upper Cretaceous deposits of the Dakota sandstone and mudstone formation of western Colorado.

Professor Lockley explained:

“These are the first sites with evidence of dinosaur mating display rituals ever discovered, and the first physical evidence of courtship behaviour.  These huge scrape displays fill in a missing gap in our understanding of dinosaur behaviour.”

Scientists Provide a Sense of Scale to the Scrape Marks

Martin Lockley (right) and  co-author Ken Cart pose beside large theropod dinosaur scrapes in western Colorado.

Picture credit: University of Colorado

Could They Be Signs of Digging for Water or Food?

In their review of the trace fossil evidence, the scientists dismiss the idea that the marks could have been made by meat-eating theropod dinosaurs looking for food.  Back in 2010, Everything Dinosaur reported on a remarkable trace fossil found in Utah which suggested that a deinonychosaurid dinosaur had been digging out a potential prey animal from its burrow.  However, no evidence of burrows or other signs of prey were found in association with the scrapes.

To read about the evidence of a dinosaur potentially digging mammals out of their burrow: Trace Fossils Suggest a Dinosaur Digging for its Supper.

Not “Scratch Digging”

As for whether the marks represent dinosaurs digging for water, after all much of the Dakota sandstone and mudstone was laid down in association with rivers and streams, the researchers conclude that this is unlikely.  Whilst elephants and other terrestrial vertebrates do dig into dried up river beds to find water, the authors conclude that these marks are not “scratch digging” as any attempt to dig to the level of the water table would produce a pooling of water which would have washed away any scrape marks made in the sediment.

A Map of One of the Study Sites (Club Gulch – Western Colorado)

Map of Club Gulch site (a) prepared in Photoshop CS5 by MGL, with natural colour photogrammetic image (b) at same scale by RTM and LGB. Coloured image (inset in a) shows three large scrapes, together covering 5 m. Digging traces are classified as paired (bilobed) or single, with or without scratch marks and adjacent sand aprons.

Picture credit: Scientific Reports

Dance of the Dinosaurs in “Leks”

The display arenas, also referred to as “leks” were found in two National Conservation Areas (Dominguez-Escalante and Gunnison Gorge) on property permitted by the Bureau of Land Management near Delta, Colorado.  The biggest site had approximately sixty preserved scrapes, located in a single bed of sandstone covering an area of 750 square metres.  The scientists also studied potential dinosaur mating/courtship fossil sites at the Dinosaur Ridge, a National Natural Landmark, just west of the city of Denver.

It is assumed that the males competed with each other to impress the females.  The females, choosing the most impressive male performers as their consorts.  Similar mating selection behaviours are common in tetrapods alive today, however, until now scientists could only speculate about dinosaur mating behaviour although in theropods at least, it had been assumed it might be similar to that of their modern avian relatives.

Dinosaurs Strutting Their Stuff

The discovery of a number of feathered varieties including oviraptorids with ornate tail feathers has led a number of palaeontologists to speculate that some theropod dinosaurs performed elaborate displays in order to win a mate or to gain status amongst the flock.  Research from the University of Alberta (Canada), proposed that some dinosaurs had compressed tail vertebrae that formed a pygostyle, as seen in many extant birds.  This structure would have enabled the dinosaurs to shake their tail feathers.

To read an article that provides more detail on this research: Dinosaurs Shaking Their Tails.

Commenting on this new study, Professor Lockley stated:

“The scrape evidence has significant implications.  This is physical evidence of pre-historic foreplay that is very similar to birds today.  Modern birds using scrape ceremony courtship usually do so near their final nesting sites.  So, the fossil scrape evidence offers a tantalising clue that dinosaurs in ‘heat’ may have gathered here millions of years ago to breed and then to nest nearby.”

A Line Drawing with Key of One of the Trace Fossil Sites Studied

The coloured image shows three large scrapes.

Picture credit: Scientific Reports