Megaraptor started out only being known from very scant remains, and has gradually become closer to being more completely known over the years since its discovery. Initially only one of its gigantic sickle-shaped claws was discovered. Upon seeing this, most scientists assumed it was the second toe claw of a dromaeosaur, much like Velociraptor or Deinonychus, just a heck of a lot bigger. In fact, it would have been the biggest dromaeosaur known if that was the case, so it was named Megaraptor which translates to "Giant Thief/Hunter". The claw, itself, was just under a foot long!
Years later a few more bits and pieces were found from this dinosaur including some of the arm and hand. In addition, a dinosaur, named Australovenator, was discovered, which bore striking similarities to the known parts of Megaraptor. Because of this, it was determined that the monster claw did not belong on the foot but on the first digit of the hand which is what Australovenator had. Megaraptor wasn't a dromaeosaur at all. Instead, it may have been from the same group of theropods that includes Allosaurus. Even amongst other large theropods, many of which had enlarged first claws on their hands, like Baryonyx (name actually translates to "heavy claw"), the claw of Megaraptor was proportionally the largest.
|One of Megaraptor's hand claws. If it were to give you a wedgie, you'd die.|
But there's more! In 2014 even more material from Megaraptor was discovered. A juvenile specimen preserved even more bones, including part of the skull. We now know that at least as juveniles, Megaraptor would have had very long, low snouts, with proportionally small teeth. The teeth themselves curved towards the back of the mouth. It is because of the teeth that some paleontologists propose Megaraptor wasn't an allosauroid either, but rather a kind of tyrannosauroid, similar to Eotyrannus or Dryptosaurus. (which also possessed huge hand claws)
|Section of the upper jaw of a juvenile Megaraptor. Image from Porfiri et al. 2014.|
So which is it? What was Megaraptor!? The definite answer to that is...we don't know. We have some choices! But we don't know anything for sure for now. And that's okay! This happens a lot in paleontology. In some ways it is the unsolved mysteries and multiple possible truths and different ideas put forth by different individuals that make this field so much fun.
Benson, R.B.J., Carrano, M.T., Brusatte, S.L., 2010. A new clade of archaic large-bodied predatory dinosaurs (Theropoda: Allosauroidea) that survived to the latest Mesozoic. Naturwissenschaften 97, 71-78.
Calvo, J. O.; Porfiri, J.D.; Veralli, C.; Novas, F.E.; Poblete, F. (2004). "Phylogenetic status of Megaraptor namunhuaiquii Novas based on a new specimen from Neuquén, Patagonia, Argentina". Ameghiniana 41: 565–575.
Novas, F.E. (1998). "Megaraptor namunhuaiquii, gen. et sp. nov., a large-clawed, Late Cretaceous theropod from Patagonia". Journal of Vertebrate Paleontology 18: 4–9.
Porfiri, J. D., Novas, F. E., Calvo, J. O., Agnolín, F. L., Ezcurra, M. D. & Cerda, I. A. 2014. Juvenile specimen of Megaraptor (Dinosauria, Theropoda) sheds light about tyrannosauroid radiation. Cretaceous Research 51: 35-55.