Home » Paleontology » Dryptosaurus: A possible North American megaraptorid? – part 2

Dryptosaurus: A possible North American megaraptorid? – part 2

Categories

Archives

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.

 

Dryptosaurus

Figure 3. My own drawing of Dryptosaurus.

 

Advertisements

4 Comments

  1. The large reptile tree nested traditional megaraptorids basal to tyrannosaurus, which is a nontraditional nesting.

  2. Chase says:

    Hi there and excellent follow-up to the previous post. I’d like to note that I work at the Stamford Museum and my last name is “Brownstein” not “Bernstein”, haha. As I noted, the thing about Dryptosaurus aquilunguis is that any resemblances between it and megaraptorans are superficial. Dryptosaurus has small arms with huge hands and claws whereas the forelimbs of megaraptorans are long as a whole. Secondly, multiple anatomical features from elsewhere on the body of Dryptosaurus are extremely dissimilar with the morphology of the same elements within megaraptorans (e. g. the presence of a most likely arctometatarsalian pes on Dryptosaurus). These different forelimb proportions not only show that D. aquilunguis and megaraptorans cannot be united on the basis of forelimb anatomy but also suggest each was doing something different with their forelimbs.

    Secondly, no megaraptorans are known from North America (the only analysis to include on taxon -Siats meekorum- within megaraptora found the entire group to fall within allosauroidea), and remains from the Turonian of New Jersey indicate that Appalachian tyrannosauroids were endemic to the landmass (I’ve got a paper in the works on this). Superficial resemblances and the possibility that megaraptorans may be tyrannosauroids or tyrannosauroid relatives (this classification should be thought of as equivocal especially in light of recent phylogenies) is not any indication that the New Jersey taxon has any affinities with megaraptorans.

    Also, I’d like to make a note about your comment that “we’ll never know the real answer until more Dryptosaurus specimens are found and analyzed”. You could argue this for basically any dinosaur from Appalachia or otherwise. However, as scientists, we must concur with the hypothesis that currently is congruent with the majority of the information we have. Note that there isn’t any evidence to support that any other Appalachian tyrannosauroids (Appalachiosaurus montgomeriensis and a couple of indeterminate and not properly named but possibly distinct taxa) share any affinities with megaraptorans, which seem to be an exclusively southern clade.

    I would like to say that I’m glad you’ve been writing about D. aquilunguis. These dinosaurs remain in need of more study and the Appalachian dinosaur paleocommunity is in need of growth. Therefore any attention to these dinosaurs is super important.

    Regards,

    Chase

    • jrabdale says:

      Hi. I’m sorry about mispelling your name and being incorrect on which museum you worked at. I changed those points in the article.

      So, my hypothesis was wrong, and my drawing was wrong too. The head may possibly be the correct shape, but the arms are too long, and the body needs to be a bit “meatier”. Did Dryptosaurus have two fingers on each hand or three? Was it likely that Dryptosaurus had feathers on its body as a fully-grown adult? If so, how much feather covering would it have had?

      It’s a shame. I was really proud of this drawing – I thought the resulting animal reconstruction looked cool. Oh well. Next time it will be better.

      • Chase says:

        The drawing is very good, and as I’m said I am glad you’ve given the ol’ eagle-clawed tearing lizard some attention. In moderation, speculation can be a healthy thing when dealing with prehistoric animals. See my email on your questions.

        Regards,

        Chase

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: