The Voracious Xiphactinus was More Widespread than Previously Thought

Xiphactinus (pronounced zee-fak-tin-us), was a fast swimming voracious predator of Cretaceous seas.  With a body length of up to six metres, this bony fish was one of the top predators associated with the Western Interior Seaway of North America.  It has a formidable reputation amongst palaeontologists, as several fossils have been found which show the undigested body parts of prey, preserved inside the stomach cavity.  Perhaps, the most famous specimen that documents predatory behaviour is the Xiphactinus (X. audax), with the complete skeleton of a 1.8 metre-long fish preserved inside its skeleton which is on display at the Sternberg Museum of Natural History (Kansas).

A Voracious Predator

A Bony Fish with a Fearsome Reputation

A team of scientists have reported this week the first occurrence of Xiphactinus from southern South America.  Writing in the academic journal “Alcheringa”, researchers from the Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” in collaboration with a colleague from Universidad Maimónides, both located in Buenos Aires, report the discovery of fragments of upper jaw bone (maxilla), as well as vertebrae from the Salamanca Formation (Chubut Province, Argentina).  It is estimated that this fish lived around 70 million years ago (Maastrichtian age of the Late Cretaceous).

Xiphactinus Geographically and Temporally Widespread

Xiphactinus has been widely reported from Upper Cretaceous strata throughout the Northern Hemisphere, although to date, equivalent discoveries in the Southern Hemisphere have been limited to a single fossil specimen consisting of elements from the skull and the spine from the Cenomanian aged limestones of the La Aguada Member, La Luna Formation, near Monay, Candelaria Municipality in western Venezuela.

A Life Reconstruction Xiphactinus

The picture (above) shows a CollectA Deluxe Xiphactinus model.

To view the CollectA Deluxe range of prehistoric animals: CollectA Deluxe Prehistoric Life Models.

This discovery extends the known geographical range for this genus and suggests that this teleost was widespread during the Cretaceous (Albian to Maastrichtian faunal stages).  It is related to the majority of fish species alive today, although the entire family of these types of predatory fish (Ichthyodectidae), became extinct at the end of the Cretaceous.

A Bony Fish with a Formidable Reputation

The scientific paper: “First record of the ichthyodectiform fish Xiphactinus (Teleostei) from Patagonia, Argentina” by Julieta J. De Pasqua, Federico L. Agnolin and Sergio Bogan published in Alcheringa: An Australasian Journal of Palaeontology.

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The First Juvenile Dromaeosaurid from Alaska

This blog has covered a lot of news stories about dinosaur fossil discoveries from Alaska, principally the remarkable Prince Creek Formation with its abundance of juvenile hadrosaurid remains.  A tiny partial lower jaw recovered from sediment screen washings indicates that dromaeosaurid dinosaurs were also present and from the size of the bone, complete with its two tiny teeth, it is likely that some dinosaurs were year-round residents and that they bred in the Arctic Circle.

A Flock of Dromaeosaurids Pursue Prey Under the Noses of Pachyrhinosaurs

Picture credit: Andrey Atuchin

A Juvenile Dromaeosaurid

Writing in the on-line academic journal PLOS One, researchers including Alfio Alessandro Chiarenza (Imperial College London) and Anthony R. Fiorillo (Southern Methodist University, Dallas Texas), report upon the discovery of the tiny jaw fragment that adds to a growing body of evidence that suggests Cretaceous Arctic dinosaurs of Alaska did not undergo long-distance migration, but rather they were year-round residents of these northern latitudes.

The fossil, which measures less than 1.5 cm in length, was collected from the Pediomys Point locality along the Colville River, some five miles (eight kilometres), upstream from the Liscomb bonebed with its abundant hadrosaurid remains.  Field team members had collected a large amount of bulk sediment over several field seasons and the specimen (specimen number DMNH21183), was recovered after screen washing and sorting of material conducted back at the Perot Museum of Nature and Science (Texas).

The Tiny Fossil Specimen (Assigned to a Saurornitholestinae Dromaeosaurid)

Picture credit: A. A. Chiarenza

Anatomical features such as the fibrous bone surface coupled with the small size of the fossil suggest a juvenile.

Dinosaurs of the Far North

Commenting on the significance of the fossil find, Anthony Fiorillo stated:

“Years ago, when dinosaurs were first found in the far north, the idea challenged what we think we know about dinosaurs.  For some time afterwards, there was a great debate as to whether or not those Arctic dinosaurs migrated or lived in the north year round.  All of those arguments were somewhat speculative in nature.  This study of a predatory dinosaur jaw from a baby provides the first physical proof that at least some dinosaurs not only lived in the far north, but they thrived there.  One might even say our study shows that the ancient north was a great place to raise a family and now we have to figure out why.”

What Type of Dromaeosaurid?

At least four different subclades of dromaeosaurid are known from the Late Cretaceous of North America (Dromaeosaurinae, Microraptorinae, Saurornitholestinae, and Velociraptorinae).  A phylogenetic assessment of the specimen suggests that this fossil represents a member of the Saurornitholestinae.  This subfamily consists of two species of Saurornitholestes and Atrociraptor, between them these dromaeosaurs, although restricted to the Late Cretaceous, do have a widespread palaeo-geographical range, with fossils found as far north as Alberta (Canada) and as far south as New Mexico in the USA.

The scientific paper: “The first juvenile dromaeosaurid (Dinosauria: Theropoda) from Arctic Alaska” by Alfio Alessandro Chiarenza , Anthony R. Fiorillo, Ronald S. Tykoski, Paul J. McCarthy, Peter P. Flaig and Dori L. Contreras published in the academic journal PLOS One.

To read our recent blog article about the hadrosaurids associated with the Prince Creek Formation: Is this the demise of a duck-billed dinosaur?

The Everything Dinosaur website: Everything Dinosaur.