Meraxes: Beast of the Week

 Today we'll be checking out a recently described dinosaur that was a giant meat-eater!  Make way for Meraxes gigas!

Meraxes was a large theropod that lived in what is now Argentina during the late Cretaceous period, between 95 and 94 million years ago.  From snout to tail it would have measured about 36 feet (almost 11 meters) long.  The genus name is actually after a dragon from the popular A Song of Ice and Fire fantasy novels. (what the show, Game of Thrones is based on.)  The species name, gigas, translates to "giant" because...this dinosaur was big.  

Watercolor life reconstruction of Meraxes gigas by Christopher DiPiazza.  Note the proportionally small arms and long claw on the second toes.

Meraxes was a member of the family of theropods called carcharodontosaurids, which are characterized by having large, narrow skulls lined with serrated blade-like teeth. (hence the family name which translates to "shark tooth reptiles") Other examples of carcharodontosaurids were the earlier Acrocanthosaurus and Concavenator, and the more famous and slightly larger Giganotosaurus. Meraxus is particularly important because it is the most complete skeleton known of a large charcharodontosaurid, which helps us understand more about their anatomy as a group.  

Like most of its kin, Meraxus had a long, tall skull, filled with blade-like serrated teeth, ideal for slashing and cutting huge chunks of flesh off bone. It also possessed ridges of rough-textured bone on the top of the snout and over the eyes, suggesting it had horn-like crests growing there in life.  These bony crests are actually common in various forms among many kinds of large theropods and may have been for some kind of intraspecies communication or even combat.  

Photoraph of recovered skull material from Meraxus from the 2022 paper by Canale.

Meraxus had three fingers with sharp claws on each hand, but extremely short arms proportional to the body.  Scientists note that despite how Tyrannosaurus is so famous for having tiny arms, this feature is actually not that rare among different kinds of theropods.  In fact, it was noted that proportionally small arms must have evolved at least four different times in theropods, present in tyrannosaurs, abelisaurs (like Carnotaurus), carcharodontosaurs, and the smaller bird-like alvarezsaurs.  If you count modern birds with tiny wings, like Kiwis, it's evolved even more times!  

Possibly the most unique feature about this dinosaur is the fact that it had an elongated claw on the second toe of each foot.  Unlike the specialized toes of dromaeosaurs and troodontids, these claws weren't retractable, so it seems they may have been more similar to the elongated claws on some modern bird feet, like cassowaries.  What purpose these claws served is currently a mystery, but they could have been to help Meraxus pin down a carcass or struggling prey as it tore chunks off with its jaws. (similar to what many modern predatory birds do today with their toe claws) It also could very well have been another instrument in fighting members of its own species. 

Photograph of the foot of Meraxus.  Note the long second toe claw.

Feet of the living Cassowary(bird).  Note the enlarged second claw convergently similar to that of Meraxus.  Unlike Meraxus, Cassowaries eat fruit and seeds, and mostly use their claws for defense.

Lastly before we go, scientists were able to examine certain bones from Meraxes and determine roughly how old it was when it died.  Turns out that individual was over 50 years old at the time of its death!  That makes it the oldest recorded fossil dinosaur known to science! They also were able to determine that like many modern reptiles, even though this Meraxes was an adult, it was still growing at a slow pace right up until it died.  This is a process called indeterminate growth, and it's been observed in a number of fossil dinosaurs, many modern reptiles, but not in modern birds.  

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

References

Canale, J.I.; Apesteguía, S.; Gallina, P.A.; Mitchell, J.; Smith, N.D.; Cullen, T.M.; Shinya, A.; Haluza, A.; Gianechini, F.A.; Makovicky, P.J. (7 July 2022). "New giant carnivorous dinosaur reveals convergent evolutionary trends in theropod arm reduction". Current Biology.

Cullen, Thomas M.; Canale, Juan I.; Apesteguía, Sebastián; Smith, Nathan D.; Hu, Dongyu; Makovicky, Peter J. (25 November 2020). "Osteohistological analyses reveal diverse strategies of theropod dinosaur body-size evolution". Proceedings of the Royal Society B: Biological Sciences. 287