Giant Clawed Dinosaur from Utah- Discovery Interview with Expert Lindsay Zanno

July 17, 2009

I hope you saw the Discovery News story earlier this week about a giant, clawed dinosaur unearthed in Utah.

(Nothronychus graffami eating; Credit for this and all images: Victor Leshyk 2009)

Today I'd like to share with you my interview with Dr. Lindsay Zanno, John Caldwell Postdoctoral Fellow in the Department of Geology at the Field Museum. She's the lead author of the Proceedings of the Royal Society B paper that describes the new dinosaur.

JV: Please provide a brief physical description of the new dinosaur, mentioning its most noteworthy characteristics. Please also clarify the age of the dinosaur in years. And how can a dinosaur be called "predatory" if it wasn't necessarily a predator?

LZ: Nothronychus graffami is a large-bodied dinosaur belong to a group known as Therizinosauria.  Therizinosaurs, including Nothronychus graffami, are unusual in that they have small heads with a keratinous beak at the front of the mouth (the same material as the beak of modern birds) and small leaf-shaped teeth.  Their bellies are proportionally enormous supporting large guts.  They have greatly enlarged claws on their hands, short legs and tails, and four toed feet.  Your second question gets to the heart of our research.  The broader group of dinosaurs that therizinosaurs belong to are known as theropods.  With few potential exceptions, Theropods include all known carnivorous dinosaurs (think T-rex, Velociraptor, Allosaurus, Carnotaurus, Spinosaurus etc...).  Because of this theropods have commonly been refered to as predatory dinosaurs.

 

We've known about toothless (beaked) theropod dinosaurs for a very long time, but because they lacked teeth and were members of an almost exclusively predatory group there was little evidence suggesting they might represent herbivores or omnivores.  Recently paleontologists have uncovered dozens of new species of theropod dinosaurs belonging to the group Maniraptora (birds and their closest extinct relatives), some of which are very primitive members of these lineages still possessing teeth.  These teeth do not look like your typical predator teeth.  On top of that recent studies on therizinosaurs have demonstrated that they also belong to this group of maniraptoran theropods.  Our study suggests they are the most primitive maniraptoran lineage.  All this put together suggests that this particular group of theropods or "predatory" dinosaurs had a much more diverse diet than we have thus far appreciated.  When we traced the evolution of anatomical features related to herbivory in maniraptorans we discovered that they evolved very early, suggesting that their ancestors had already switched from an exclusively predatory lifestyle.  Thus, to call theropods "predatory" dinosaurs is missing a huge part of their evolutionary story.

JV: Do you think N. graffami only ate plants, or could it have been an omnivore? If it was solely herbivorous, what do you think it did with those scary-looking claws and its more carnivore-associated features?

LZ: Nothronychus graffami is an advanced therizinosaur, it has many adaptations that are correlated with a plant-based diet, so we can speculate that it was predominantly consuming plant-material.  One aspect of our study was to correlate adaptations present in fossil taxa preserving direct evidence of a plant-eating (such as stomach contents) with other species that do not to infer diet.  However, there is no way to know if Nothronychus graffami only ate plants and other plant fodder.  It may have supplemented its diet with small animals, insects, or aquatic animals.  It is also very difficult to say what these beasties were doing with their claws.  They still had to defend themselves against predators, yet the claws of more advanced species aren't well suited for this purpose so they may have functioned during feeding or may have been used for display or intimidation.  We don't see any good anatomical evidence that they were used for digging.

 

JV: Although this dinosaur appears to have been an early maniraptoran dinosaur, do you think it represents a sort of half-way point in the evolution of this particular lineage, to where a carnivore was evolving into an herbivore? Or would it have been the other way around, an herbivore evolving into a carnivore, given the mention that "iconic predators like Velociraptor may have evolved from less fearsome plant-eating ancestors?"

 

LZ: It is not accurate to say that Nothronychus graffami represents an early maniraptoran dinosaur.  What our study shows it that the group to which Nothronychus belongs (Therizinosauria) is a primitive maniraptoran lineage--meaning that this group split off before other maniraptoran lineages and thus can tell us something about the common ancestor of Maniraptora.  Nothronychus is a highly evolved maniraptoran dinosaur that lived over 60 million years after the earliest maniraptorans.  Nothronychus does represent a half-way point in the evolution of this lineage, but it likely does not represent a half-way point in the evolution of plant-eating in the group.  That transition would have occurred much earlier in therizinosaurs.  The statement "iconic predators like Velociraptor may have evolved from less fearsome plant-eating ancestors" stems from the idea that at least one group of maniraptoran dinosaurs appear to be highly evolved predators (dromaeosaurs such as Velociraptor).  If our research is correct and the earliest maniraptorans were omnivores and not exclusively carnivores, than these dinosaurs had to re-evolve carnivory.  Therizinosarus meanwhile, appear to have been on a different trajectory, evolving into dominant herbivores.

JV: Why do you think it would benefit a carnivore at that time to have switched to an all-veg diet, or vice versa as the case may be?

 

LZ: This is an interesting question and one we really can't answer at this point.  Our current thoughts are that in gaining the ability to eat more than just meat, maniraptorans may have been able to invade new "niches" in the ecosystem that were unavailable to them before.  In other words they may have been able to find a new way of living in the ecosystem and new resources to exploit that gave them an advantage and allowed them to diversify into new forms.  However, this idea needs to be tested and we hope to do that in the future.

JV: Is it unusual (a first?) to find such a well-preserved skeleton at a site that was once at least 60 miles from the nearest shoreline? Maybe a first for Utah discoveries?

LZ: This is unusual in terms of Utah discoveries, however, these types of remains are known.  At least a handful of relatively complete dinosaur skeletons have been recovered in the seaway.  Paul V. Heinrich from the Louisiana Geological Survey has hypothesized that they may have rafted out into the sea on floating islands after storms.

Comments

[Clifton Goodwin]

Unless a Velociraptor is in the same genepool as a Sloth, you might want to rethink this one..