In January, I published a post in which I hypothesized that Dryptosaurus, a Late Cretaceous theropod found in Eastern North America, was misidentified. For the longest time, Dryptosaurus was believed to be a tyrannosaur, possibly a rather primitive one. However, with discoveries made within the past two decades, I came to question this taken-for-granted identification.
The megaraptorids are a weird bunch, since nobody knows for certain where exactly they fit. When the type species Megaraptor was found in Argentina by the paleontologist Fernando Novas, it was believed to be a giant dromaeosaur – hence the “raptor” name – measuring at least 25 feet long, which would have made it the largest raptor ever discovered up to that point.
Then in 2010, a study conducted by Benson, Carrano, and Brusatte claimed that the megaraptorids were more related to the allosaurs than the dromaeosaurs. Specifically, the study stated that the megaraptorids were very closely related to Neovenator. It certainly helped when a complete arm was discovered, which showed that the 15-inch long killing claw didn’t come from the foot, but actually came from the hand, similar to Baryonyx.
In 2012, Fernando Novas conducted his own study of Megaraptor and its relatives. He and his colleagues said that while Neovenator and the carcharodontosaurids were close relatives of each other, and that both belonged within the superfamily Allosauroidea, he also stated that Megaraptor and its ilk did not belong in this group. Instead, he stated that the megaraptorids were actually coelurosaurs, and were more closely related to the tyrannosaurs.
In 2014, more evidence to back up a connection between the megaraptorids and the tyrannosaurs came to light when a juvenile Megaraptor was described by J. D. Porfiri, Fernando Novas, and others. Porfiri even placed Eotyrannus, long thought to be a primitive tyrannosaur, as a member of Megaraptora. Because of this, the megaraptorids are thought of by some to be either close relatives of the tyrannosaurs or possibly even an offshoot of the tyrannosaur family.
As a result of learning all of this, I began to wonder if Dryptosaurus was actually a member of Megaraptora, and I published a post saying as much. However, Chase Brownstein, a paleontologist specializing in eastern North American dinosaurs who works at the Stamford Museum, and who I have been in contact with on a fairly regular basis, immediately challenged my hypothesis. He stated that while Dryptosaurus might have had some features that made it visibly look like a megaraptorid, the animal itself was not a member of the megaraptorid family. He put these physical similarities down to convergent evolution – when two different kinds of animals evolve in such a way that they look similar to each other. Convergent evolution is most often brought about by environmental conditions, which infers that both Dryptosaurus and the megaraptorids lived in similar environments, had similar lifestyles, or both.
I recently discovered that my hypothesis was not unique. An internet search showed that at least by 2014, other people had been looking at Drytposaurus with questioning eyes and were wondering if it was actually a megaraptorid. Damn, this happens all the time. Every time that I think I’ve come up with a new idea, it turns out that some has already thought of it before. Oh well.
While my assessment of Dryptosaurus as a megaraptorid may or may not be correct – we’ll never know the real answer until more Dryptosaurus specimens are found and analyzed – I feel that my drawing of Dryptosaurus is nevertheless accurate. A phylogenic analysis conducted in 2013 placed Dryptosaurus between Raptorex (which, according to some, is actually a misidentified juvenile Tarbosaurus) and Alectrosaurus. Both Raptorex and Alectrosaurus had similarly-shaped skulls, so I gave my rendition of Dryptosaurus a skull that was very similar to these two species. I gave it the massive thumb claws that are seen on the holotype specimen. I also gave my creation a mane of fibrous feathers, since many primitive three-fingered tyrannosaurs are known to have had feathers covering some or most of their bodies.
Figure 1. Skull of Alectrosaurus. Illustration by Tracy Ford (I think). http://www.paleofile.com/Dinosaurs/Theropods/Alectrosaurus.asp.
Figure 2. Skeleton of Raptorex. Photo by Kumiko (September 24, 2011). https://commons.wikimedia.org/wiki/File:Raptorex_vs_Psittacosaurus.jpg.
Figure 3. My own drawing of Dryptosaurus.