Dakosaurus: Beast of the Week

You may know that we have reviewed a Godzilla dinosaur on here before.  This week we will be looking at yet another prehistoric beast with connections to the "King of the Monsters."  Check out Dakosaurus andiniensis!

Dakosaurus andiniensis lived in the oceans that once covered what is now Argentina during the Late Jurassic to the Early Cretaceous, between 145 and 140 million years ago.  Dakosaurus was a meat-eater in life, and measured about fifteen feet long from snout to tail.  The genus name, Dakosaurus, translates to "biter lizard/reptile" in reference to the creature's formidable teeth.  There are actually a few species within the Dakosaurus genus, but I want to focus specifically on the species, Dakosaurus andiniensis.  

Dakosaurus andiniensis by Christopher DiPiazza.

Dakosaurus was an extinct genus of crocodilian that belonged to the family called Metriorhynchidae.  Metriorhynchids were prehistoric crocodiles that were specially adapted to living in the ocean during the middle Jurassic through the early Cretaceous periods.  Their limbs were like flippers and their flattened tails even independently evolved flukes like those of sharks, dolphins, and their fellow reptiles, the ichthyosaurs and mosasaurs.

Fossilized skull of Dakosaurus andiniensis.  It looks mean!

Dakosaurus andiniensis had a uniquely short snout compared to the other species within its genus, giving it a particularly menacing look, to the scientists who studied it.  It is because of this unusually short, and boxy face, that this species of Dakosaurus was nicknamed "Godzilla" among the scientists who worked with it.

Dakosaurus' teeth were unique in that they were both laterally compressed and serrated.  This is a feature more commonly seen in certain kinds of meat-eating dinosaurs.  In fact, when the isolated teeth of Dakosaurus were first discovered, they were initially believed to have been from a Megalosaurus, not a crocodile.  The skull of Dakosaurus had openings towards the back, called fenestrae, that would have anchored powerful jaw muscles in life.  This, combined with the fact that its teeth were deeply rooted within the jaws, means that Dakosaurus would have been able to bite down with extreme force.  It is likely that an adult Dakosaurus would have been a top predator and was able to hunt most other animals it shared its habitat with, including other marine reptiles. 

Nobody is exactly sure how Dakosaurus would have reproduced.  There is specific fossil evidence that other prehistoric marine reptiles, like mosasaurs and ichthyosaurs, gave birth to live young in the water.   Dakosaurus' group, the crocodilians, however, only lay eggs in nests, however.  In fact, even broadening this group to all of archosauria, which includes crocodilians, in addition to dinosaurs and several other reptile groups, all we know of is egg-laying so far.  Going off this information alone, using closest relatives as a reference, Dakosaurus would have needed to haul out on land to lay its eggs.  However, a study looking at the anatomy of a more completely known metriorhynchid showed that the anatomy of the pelvis was more similar to that of other kinds of marine reptiles that we know gave birth to live young.  Despite that all known archosaurs lay eggs, it wouldn't be unheard of for one group of marine crocodilians to have evolved live birth, since we already can confirm it has happened multiple independent times in other groups of reptiles.

Closeup photo of the tail of a Dakosaurus, including imprints of skin.  You can also see scars the animal had in life left on its skin from external parasites, like barnacles, perhaps.  Photo from Spindler et al.'s research paper published in 2021.

Lastly we have fossil evidence of what the skin of Dakosaurus probably looked like!  Since it was a crocodilian, one might assume it had chunky chainmail like armor and scaly skin, like its modern relatives, but this wasn't the case.  It appears, thanks to a beautifully preserved specimen discovered in Germany, that Dakosaurus had smooth skin that lacked any visible scales or scutes.  This is consistent with other lineages of reptiles that evolved fully marine lifestyles, like ichthyosaurs and plesiosaurs.  This may have been an adaptation to be as streamlined as possible to better maneuver in the water.  

That is all for this week!  As always feel free to comment below.

References

Gasparini Z, Pol D, Spalletti LA. 2006. An unusual marine crocodyliform from the Jurassic-Cretaceous boundary of Patagonia. Science 311: 70-73.

Herrera, Y.; Fernandez, M.S.; Lamas, S.G.; Campos, L.; Talevi, M.; Gasparini, Z. (2017). "Morphology of the sacral region and reproductive strategies of Metriorhynchidae: a counter-inductive approach". Earth and Environmental Science Transactions of the Royal Society of Edinburgh: 1–9. 

Spindler, Frederik, et al. “The Integument of Pelagic Crocodylomorphs (Thalattosuchia: Metriorhynchidae).” Palaeontologia Electronica, 2021, doi:10.26879/1099.

Vignaud P, Gasparini ZB. 1996. New Dakosaurus (Crocodylomorpha, Thalattosuchia) from the Upper Jurassic of Argentina. Comptes Rendus de l'Académie des Sciences, Paris, 2 322: 245-250.