Sabre-Toothed Squirrel – Fanged Beast of the Cretaceous Night

The Cretaceous strata of southern Argentina may be associated with some of the most spectacular dinosaur fossils ever found, huge monsters such as the fearsome Mapusaurus and the herbivorous Argentinosaurus but fossils found in Patagonia have shed light on a bizarre, primitive mammal that scurried around these leviathans and shared their home.

In a “truth is sometimes stranger than fiction”  moment, this little mammal superficially resembles “Scat” the buck-toothed, acorn chasing squirrel from the Ice Age films.  The animal has been formally named Cronopio dentiacutus.  It had extremely long teeth, a narrow snout and large eye sockets.  The large orbits in the skull (eye sockets), suggest that  it probably had a nocturnal habit or it lived in dense undergrowth, either of which would have been sensible strategies to employ as at a little over fifteen centimetres long it was about the size of a single Mapusaurus tooth.

Mesozoic “Scat” – Cronopio dentiacutus

Sabre-Toothed Mammal that lived amongst Dinosaurs

Picture Credit: Associated Press

The fossil was found in the Patagonian province of Rio Negro,  in a bed of sediment that also has produced a variety of much larger dinosaur bones.  The strata has been dated to around 93 million years ago (Cenomanian faunal stage).  The two partial skulls and jawbones bridge a sixty-million-year gap in the mammalian fossil record, according to the research paper’s authors – Sebastian Apesteguia, Leandro Gaetano and Guillermo Rougier, who describe their study in the latest edition of the scientific journal “Nature”.

Commenting on what has already been termed “a major palaeontological event”,  as this is the first mammal fossil found in Cretaceous aged rocks from the Cenomanian of South America, Christian de Muizon, (Paris Museum of Natural History) expressed excitement about the find.

De Muizon stated:

“It’s the first mammal from the late Cretaceous period of the Mesozoic era ever found in South America.”

The scientists have classified this small creature as a member of a primitive group of mammals known as Dryolestoids.  These type of mammals are believed to be ancestral to placental mammals and marsupials.  As a group, their fossil record is extremely poor with the majority of Dryolestoids known from teeth and fragments of jawbone.  It is believed they had their evolutionary origins in the Mid Jurassic, surviving beyond the Mesozoic into the early Cenozoic in South America.

Cronopio dentiacutus  was named after a type of character in the books of Argentine author Julio Cortazar.

It is likely that the long teeth at the front of the jaws helped Cronopio dentiacutus catch fast moving insects, it may superficially resemble the nut loving squirrel from the Ice Age animated movies but it is probably more closely related to marsupials like opossums than rodents.

One of the researchers (Sebastian Apesteguia – researcher at Maimonides University in Buenos Aires) stated:

“During the age of the dinosaurs, no mammal was bigger than a mouse, and they could do what they wanted, but under ground or at night — out of sight of the dinosaurs.”

It is surprising that such a statement has been made.  The size of mammals during the Mesozoic is often mis-represented in this manner.  It is indeed true that mammals were very small, especially in relation to their reptilian contemporaries during the Mesozoic but some mammals were surprisingly big, especially towards the end of the Cretaceous.  The marsupial Didelphodon, fossils of which are associated with Upper Cretaceous strata of Montana (United States) indicate an animal over a metre long – the size of a Springer Spaniel.

Christian de Muizon added:

“Such discoveries of remarkably complete Mesozoic fossils always represent giant steps” in mammalian palaeontology.  In fact, one reasonably preserved Mesozoic mammalian skull in a critical stratigraphic and geographic position can be more relevant to our understanding of mammalian evolution and bio-geography than hundreds of isolated teeth — even if teeth are the most common (and sometimes the only) remains palaeontologists work with.”

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