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

Gorgosaurus: Beast of the Week

Today we will look at a famous meat-eater known from lots of well-preserved fossils that has helped us understand a lot about tyranosaurs over the years.  Check out Gorgosaurus libratus!

Gorgosaurus was a meat-eating dinosaur that lived in what is now Alberta, Canada, and Montana, USA, during the late Cretaceous period, between 76.6 and 75.1 million years ago.  From snout to tail adults could grow up to 30 feet (9 meters) long.  The genus name translates to "Dreadful Reptile".  The species name, libratus, translates to "balanced".

Life reconstruction in watercolors by Christopher DiPiazza of a pair of Gorgosaurus libratus.

Gorgosaurus was a member of the tyrannosaurid family, often described as a slightly smaller, more gracile relative of Tyrannosaurus.  Like all tyrannosaurids, Gorgosaurus had a series of chisel-like teeth in the frontmost portion of its jaws that are rounded in the front, but flat in the back, giving them a D-shaped cross section.  These could have been an adaptation for scraping meat off bones.  The rest of Gorgosaurus' teeth were curved, thick in cross section, and serrated for cutting flesh.  Gorgosaurus possessed large, round eye sockets and likely had good vision in life.  It also had rough textured bone running down the top of its snout and a small, forward-facing, horn over each eye.  There was likely keratin growing over these parts of the skull in life, giving the dinosaur a more ornamented look than the skull shows.  The presence of horns on the snout and over the eyes is actually a trait common to many tyrannosaurs.  We don't know exactly what these structures were for in life, but they very well may have been for some kind of interaction within the species, either for display only or perhaps some sort of physical combat for dominance between rivals.  

Gorgosaurus skeleton on display at the Royal Tyrell Museum in Alberta, Canada.

Like all tyrannosaurids, Gorgosaurus had proportionally short arms and only two functional fingers on each hand.  It's legs, however were proportionally long and powerful, implying it was a strong distance walker and probably a fast runner in life.  Since we also have juvenile Gorgosaurus specimens on the fossil record, we know that when younger, the legs were even longer, proportional to the body, implying the younger individuals were even faster.  Because there are relatively numerous Gorgosaurus specimens in the fossil record of varying life stages, scientists were able to figure out just how fast this dinosaur grew.  It turns out that tyrannosaurids, like Gorgosaurus, continued to grow their entire lives, but went through extremely rapid growth spurts during certain parts and slowed down once reaching mature adult sizes, the fastest of these spurts they would have gained about 110 pounds in a single year!  It was also found out that Gorgosaurus spent about half of its life at juvenile size.  This has supported the idea that tyrannosaurids specialized in hunting smaller faster prey when young, and then moved on to slower, but tougher, prey when fully mature.  This also helps explain the lack of small-medium sized predators in communities where tyrannosaurids are found, because it was likely the tyrannosaurids were filling more than one predator niche depending on their maturity. 

Skeleton of a juvenile Gorgosaurus on display at the American Museum of Natural History in New York.  Note the long, slender legs.

Gorgosaurus is one of the few fossil dinosaurs scientists have been able to recover skin impressions from.  The patch of skin from Gorgosaurus would have been on the tail and shows fine, slightly raised bumps.  There is no way to tell if Gorgosaurus also had feathers or not in life since different forms of body covering can exist on different parts of an animal's body and also preserve under different conditions (for instance we have numerous dinosaur fossils that preserve feathers but no scales, yet we can infer they also had scales on certain parts of the body), but given that it is from the branch of dinosaurs that includes birds, called coelurosaurs, it very well could have.  

Photograph of Gorgosaurus skin impressions from Bell's 2017 paper.

Throughout the course of it's living on earth, Gorgosaurus would have coexisted with, and probably hunted, lots of other dinosaurs, including, but not limited to hadrosaurs, like Parasaurolophus, Lambeosaurus, and Corythosaurus, ankylosaurs, like Eouplocephalus and Anodontosaurus, and ceratopsians, like Chasmosaurus and Styracosaurus.

That is all for this week!  Feel free to leave a comment below!

References

Bell, Phil R., et al. “Tyrannosauroid Integument Reveals Conflicting Patterns of Gigantism and Feather Evolution.” Biology Letters, vol. 13, no. 6, 2017, p. 20170092., https://doi.org/10.1098/rsbl.2017.0092.

Erickson, Gregory M., GM; Makovicky, Peter J.; Currie, Philip J.; Norell, Mark A.; Yerby, Scott A.; Brochu, Christopher A. (2004). "Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs". Nature. 430 (7001): 772–775.

Lambe, Lawrence M. (1914). "On a new genus and species of carnivorous dinosaur from the Belly River Formation of Alberta, with a description of Stephanosaurus marginatus from the same horizon". Ottawa Naturalist. 28: 13–20.

Holtz, Thomas R. (2004). "Tyrannosauroidea". In Weishampel, David B.; Dodson, Peter; Osmólska Halszka (eds.). The Dinosauria (Second ed.). Berkeley: University of California Press. pp. 111–136.

Russell, Dale A. (1970). "Tyrannosaurs from the Late Cretaceous of western Canada". National Museum of Natural Sciences Publications in Paleontology. 1: 1–34.

Voris, Jared T., Zelenitsky, Darla K., Therrien, Francois, Ridgely, Ryan C., Currie, Phillip J., Witmer, Lawrence M. Two exceptionally preserved juvenile specimens of Gorgosaurus libratus (Tyrannosauridae, Albertosaurinae) provide new insight into the timing of ontogenetic changes in tyrannosaurids. Jou Ver Pal (2022).

Amargasaurus: Beast of the Week

This week we will be checking out a sauropod with a truly striking style!  Introducing Amargasaurus cazaui! 

Amargasaurus was a plant-eating dinosaur that lived in what is now Argentina during the early Cretaceous period, roughly 130 million years ago.  It measured about 33 feet (10 meters) long from snout to tail.  It's name translates to "Amarga reptile" in reference to La Amarga, the geological formation as well as the town near where this dinosaur's bones were discovered in Argentina.  "Amarga" in Spanish means "bitter". 

Watercolor reconstruction of Amargasaurus by Christopher DiPiazza

The most unique and striking feature about Amargasaurus is the fact that it had two rows of upward-facing spines down its neck and part of its back.  These spines were actually part of the animal's vertebrae!  The spines growing out of this dinosaur's neck were pointed and spike-like, but as they go further down the back, they become blunter and flatter.  Nobody is exactly sure what purpose these structures would have served in life.  However, many think they were most likely some sort of display adaptation within the species.  Reconstructions of these spines have varied over the years as scientists studied the fossils and came up with more updated ideas.  The oldest versions had skin connecting the spines, like a pair of fins running down the back.  Then it was argued they were more likely not covered in skin, but individually covered in keratin, forming a series of spikes.  The latest study from 2022 examined the spines more closely, finding that their texture and the growth rings in their cross section suggests that there were fibers connecting them in life, and they were likely covered in some sort of soft tissue, forming a sail-like structure.    

Amargasaurus skeletal mount.

Other interesting features about Amargasaurus is that it actually had a relatively shorter neck proportionally when compared to other sauropod dinosaurs.  Like its relatives, however, it likely possessed a set of teeth concentrated at the front of the mouth that were peg-shaped.  This is a good mechanism for raking leaves and other foliage off of branches while feeding. Only part of the skull was found, unfortunately.  This is common for sauropods with their big, bulky bodies and tiny, delicate heads that are easily destroyed during fossilization.

In 2014, a team of paleontologists actually scanned the inside of the part of Amargasaurus' skull that was found, which included the braincase.  They were able to see the space that would have held the dinosaur's inner ear canals, which would control the sense of balance.  The shape of the inner ears plus how the vertebra fit together suggest that Amargasaurus actually would have held its neck horizontally out in front, rather than upright, as sauropods are often imagined.  The head also would have also been oriented with the snout facing directly downwards.  This doesn't mean that Amargasaurus wasn't capable of moving its head and neck around in different poses depending on its behavior, of course, but rather a suggestion on its most comfortable default resting position.  

That's it for this week!  As always feel free to comment below!

References

Cerda, Ignacio A.; Novas, Fernando E.; Carballido, José Luis; Salgado, Leonardo (March 24, 2022). "Osteohistology of the hyperelongate hemispinous processes of Amargasaurus cazaui (Dinosauria: Sauropoda): Implications for soft tissue reconstruction and functional significance". Journal of Anatomy: joa.13659.

Novas, Fernando E. (2009). The age of dinosaurs in South America. Bloomington: Indiana University Press. ISBN 978-0-253-35289-7.

Paulina Carabajal, A.; Carballido, J.L.; Currie, P.J. (2014). "Braincase, neuroanatomy, and neck posture of Amargasaurus cazaui (Sauropoda, Dicraeosauridae) and its implications for understanding head posture in sauropods". Journal of Vertebrate Paleontology. 34 (4): 870–882.

Upchurch, P., Barrett, P.M, & Dodson, P. 2004. Sauropoda. In: Weishampel, D.B., Dodson, P., & Osmolska, H. (Eds.). The Dinosauria (2nd Edition). Berkeley: University of California Press. Pp. 259–322.