Eukritta- Beast of the Week

 This week we will be checking out a beast that is named after one of the most iconic movie monsters.  Watch out for Eucritta melanolimnetes!

Eucritta was an early tetrapod (animal with four limbs or that evolved from a four limbed ancestor...basically any vertebrate that's not a fish) that lived in what is now Scotland during the Carboniforous period, between 344 and 331 million years ago.  It measured about 10 inches (25.4cm) long from snout to tail and would have been a meat-eater when alive.  The genus and species name together, Eucritta melanolimnetes, translates to "True Creature from the Black Lagoon", after the famous 1954 monster movie.  This is in reference to how, like the movie monster, Eukritta exhibited features from multiple different kinds of other animals and would have spent time on both land and in the water when alive.

Life reconstruction of Eucritta in watercolors by Christopher DiPiazza.

When Eucritta was alive, none of the land vertebrates we are familiar with today were around yet.  The ones that did exist would have had the most in common with modern amphibians but were still pretty different even from them.  Eucritta stands out among these ancient animals because it possessed a number of features associated with multiple different varieties of early land creatures that were evolving around that time, placing it somewhere between the early ancestors of the first reptiles and the amphibian-like temnospondyls.  

Eucritta is known from several skeletons so we actually know quite a bit about its anatomy.  It possessed a wide, semi-circular skull and its eye sockets were proportionally large and round, suggesting it had good vision in life, and it possessed many small pointed teeth, ideal for grabbing and swallowing small prey.  The top of its mouth also possessed small tooth-like protrusions, which would have helped ensure live prey did not escape once grabbed.  Despite its amphibian-like skull, it also possessed a bony pallet on the roof of its mouth separating its mouth from its nose, which is something amphibians do not have, but an ancestral trait to the group of animals that would become the first reptiles.  It's arms were short and robust, and its legs were proportionally longer and also powerfully built, suggesting that Eucritta could have spent considerable time walking around outside the water.  Sadly its tail was never found so we do not know if it was stubby or longer and possibly paddle-shaped to aid in swimming. 

Photograph of the skull and shoulder girdle of Eucritta from the paper by Clack et. al. referenced below.

Eukritta's low flat skull and short, straight ribs, give us clues as to how it breathed.  Modern ampbibians, like frogs and salamanders have the same traits and get their oxygen by buccal pumping, which is when they use muscles in their throat to pump air into their bodies. (Ever notice how the skin under a frog's chin is always moving up and down? that's buccal pumping in action.)  This is because they do not have a diaphragm, a muscle which other land animals (including us) use to breathe instead. Animals with diaphragms also have longer ribs that curve around their torso to better support their organs. 

References

Clack, J. A. (March 2001). "Eucritta melanolimnetes from the Early Carboniferous of Scotland, a stem tetrapod showing a mosaic of characteristics". Earth and Environmental Science Transactions of the Royal Society of Edinburgh. 92 (1): 75–95.

Clack, Jennifer A. (2 July 1998). "A new Early Carboniferous tetrapod with a mélange of crown-group characters". Nature. 394 (6688): 66–69.