Did Dakotaraptor Really Face Off Against Tyrannosaurus?

Dakotaraptor pulls feathers from Ornithomimus it killed. Art by Emily Willoughby.
Dakotaraptor pulls feathers from Ornithomimus it killed. Art by Emily Willoughby.

By now you’ve probably heard about the giant “raptor” uncovered in South Dakota. The dinosaur’s discovery came as quite a shock. For the past century Tyrannosaurus rex has dominated our imaginations as the sole apex predator of the Hell Creek Formation, but Dakotaraptor steini, as Robert DePalma and coauthors dubbed the dinosaurs, was large enough to compete for flesh with young tyrannosaurs.

With scenes from the Jurassic Park franchise still stomping through our imaginations, it’s tempting to pit packs of 18-foot-long Dakotaraptor against the heavyweight champion T. rex, mobbing the bulky carnivore off its kills. DePalma has suggested as much, calling Dakotaraptor “the most lethal thing you can possibly throw into the Hell Creek ecosystem.”

But before we get too carried away and start commissioning murals of giant raptors slashing the flesh of Tyrannosaurus Age of Reptiles style, it’s worth thinking about what the world of dinosaurs was really like.

The known elements of Dakotaraptor and a reconstructed skeleton. From DePalma et al., 2015.
The known elements of Dakotaraptor and a reconstructed skeleton. From DePalma et al., 2015.

Dakotaraptor ups the diversity of dinosaurs known from the Hell Creek Formation. It’s an increase of one new species. And finding a new species means that there must have been a population of these big dromaeosaurids running around that paleontologists have missed up until now. (Although the idea of cooperative raptor packs rests on only the barest sliver of evidence right now.) But this doesn’t mean that where there was Tyrannosaurus, Dakotaraptor followed. What I’m getting at is a concept ecologists call species evenness.

Let’s take an avian dinosaur’s-eye view of the big Hell Creek Formation carnivores. We’ll cover Tyrannosaurus first. This dinosaur is known from about 50 partial-to-nearly-complete skeletons found in rocks between 68 and 66 million years old spanning Saskatchewan to New Mexico, at the very least. Dakotaraptor, on the other hand, is only known from a partial adult individual found near the top of the Hell Creek Formation in South Dakota and a smattering of other isolated elements from that area.

The fossil record is biased, of course. What’s preserved in the rocks is not a perfect record of life as it once was, and there are various other reasons why Dakotaraptor is so rare. Perhaps the dinosaur was the wrong size to be preserved as often as Tyrannosaurus. Maybe teeth and other pieces of this dinosaur were found before but could not be recognized as belonging to a giant raptor until now. Or the commercial fossil market could have snaffled up some of the relevant bones, making them inaccessible to paleontologists.

Future finds will inform what we know about the abundance and distribution of Dakotaraptor. But what if it took so long to find this predator because it truly was a rare animal with a relatively limited range? In terms of species evenness, in other words, the current spread of what we know is heavily imbalanced. Tyrannosaurus was extremely abundant and widespread while Dakotaraptor seems elusive, even by mid-size dinosaur standards.

This isn’t a knock against Dakotaraptor. Quite the opposite. If the dinosaur’s rarity isn’t stemming from a biased fossil record or a problem with sampling, then Dakotaraptor might eventually yield some new information about Hell Creek Formation ecology.

"Jane" is our best look at a juvenile T. rex. Photo by Brian Switek.
“Jane” is our best look at a juvenile T. rex. Photo by Brian Switek.

Up until now, Hell Creek Formation carnivores seemed to be widely split. There wasn’t a gradient from the small to the gargantuan as there was in the Late Jurassic Morrison Formation, but a wide gap between little nippers like Acheroraptor and the lone giant, Tyrannosaurus. What was in the middle, then, were juvenile Tyrannosaurus – lithe, leggy youngsters that had jaws better-suited to stripping flesh than to delivering crushing bites.

Dakotaraptor changes that picture. At least one other mid-sized predator was able to evolve and survive within the domain of Tyrannosaurus. Yet Dakotaraptor may have been so elusive because Tyrannosaurus still maintained a disproportionate presence on the landscape, or perhaps because Dakotaraptor typically lived in upland environments that weren’t preserved as often as the wet lowlands Tyrannosaurus frequented. So even though it’s possible, even probable, that Dakotaraptor and young Tyrannosaurus faced off over carcasses from time to time, it’s not as if Hell Creek Formation time was an era of constant shrieks, roars, and ruffled feathers.

Ceratosaurus was rare compared to Allosaurus. Photo by Brian Switek.
Ceratosaurus was rare compared to Allosaurus. Photo by Brian Switek.

This wouldn’t be the first time carnivorous dinosaur tallies have come out uneven. At the Late Jurassic Cleveland-Lloyd Dinosaur Quarry, for example, the remains of at least 48 Allosaurus have been uncovered while the same site has yielded only a single Ceratosaurus, a few Torvosaurus bones, and single-digit counts of the medium-sized carnivores Marshosaurus and Stokesosaurus. This pattern holds at a wider, rougher view, as well. Allosaurus was the most common large carnivore of the Morrison Formation with Ceratosaurus trailing behind in count and range, followed by even rarer and more restricted Torvosaurus, Stokesosaurus, and Marshosaurus. So, with a count of at least five, we can say that the upper part of the Morrison Formation had a diverse array of mid- to large-sized carnivorous dinosaurs, but that their numbers were not at all even.

Why different dinosaurs were unevenly spread in a given habitat or formation isn’t something that’s well-understood. It’s difficult to study an ecosystem that’s been dead for at least 66 million years. Answers could range from how we sample the fossil record to instances of niche partitioning like habitat preference or seeking particular food sources. There’s still plenty of rock to shift and dinosaurs to count. But if we’re ever going to fully understand dinosaurs, we need to step back from the carnivore vs. carnivore fights we used to imagine in the sandbox and try to understand them as animals that were each part of ever-shifting ecosystems. Dinosaurs weren’t monsters stalking around on unimportant backdrops. The endpoint of raising their bones in the first place is to envision how they fit into lost worlds.

Reference:

DePalma, R., Burnham, D, Martin, L., Larson, P., Bakker, R. 2015. The first giant raptor (Theropoda: Dromaeosauridae) from the Hell Creek Formation. Paleontological Contributions. doi: 10.17161/paleo.1808.18764

10 thoughts on “Did Dakotaraptor Really Face Off Against Tyrannosaurus?

  1. Palaeosaniwa, a 3.5 meter long LIZARD, probably was the dominant mid-range predator in the area, since it is certainly more common than Dakotaraptor.

    1. Palaeosaniwa was not anywhere near 3.5 meters long. It was between 1.5 and 2 meters at the most. It was far more likely to be a nest raider, considering it’s affinity with extant Heloderma.

  2. Perhaps Dakotaraptor cremated their dead? Or, more likely, ate them. Though I see no cranial bones on that diagram, so we are just guessing about the head, I presume?

  3. Dakotaraptor was a predator that combined the stealth and agility of a leopard with the stamina and talons of an eagle, while tyrannosaurs were hyena-like pursuit hunters. Tyrannosaurs can’t fill every predatory niche there is. Their specialty is wearing down prey in open country, not tacking proportionately gigantic prey or launching a leaping attack.

  4. “Tyrannosaurus was extremely abundant…”

    Ed, surely you jest?

    “We’ll cover Tyrannosaurus first. This dinosaur is known from about 50 partial-to-nearly-complete skeletons found in rocks between 68 and 66 million years old spanning Saskatchewan to New Mexico, at the very least.”

    Only “about 50 partial-to-nearly-complete skeletons” of T-rex have ever been found yet they were “extremely abundant”? And what do you mean by “at the very least”?

    “The fossil record is biased, of course. What’s preserved in the rocks is not a perfect record of life as it once was…”

    Yeah, and there are other things to consider, such as the randomness/chance of fossils being exposed at the surface of the ground, how well an area is searched (even exposed fossils are often easy to miss), how accurately the found fossils are identified, etc., etc., etc. The Horner et al. article doesn’t verify squat about the actual number or relative abundance of T-rexes or anything else during the time span of the deposition of the Hell Creek Fm.

    Do you or others actually believe that T-rexes were “extremely abundant” and as abundant or more abundant than all other dinosaurs during the time span of the deposition of the Hell Creek Fm.? If so, what did they mostly eat, other T-rexes?

    1. It was made very clear several times in the article that Brian was talking about carnivores, not dinosaurs in general.

      The “extremely abundant” quote was in a paragraph and after a paragraph that set up plenty of acknowledgement that the fossil record we have is possibly misleading. Brian had already covered “how accurately the found fossils are identified” with “Maybe teeth and other pieces of this dinosaur were found before but could not be recognized as belonging to a giant raptor until now.” Your other two points were only covered by “how we sample the fossil record” but even you couldn’t be bothered to cover all the different subtleties of the problem and resorted to “etc., etc., etc.”

      What I understood by “at the very least” is that the fossils we know of may come from more individuals, if some parts were mistakenly thought to be from one tyrannosaur.

    2. You realize 50 specimens (even partial) is a lot by Dinosaur standards. Fossilization is a difficult process and the vast majority doesn’t have a chance to be fossilized.

  5. I’ve been doing research on the Dakotaraptor, going on the idea of it traveling in family groups or packs. Since the environment in Cretaceous South Dakota was supposed to have been swampy. I have my doubts that a pack of raptors who need to stay in tip top condition would seek out and attack a tyrannosaur. Unless of course they had to protect territory and ‘chicks’. I can see them mobbing juveniles rexes if need be. Of course that is just speculation and basing on the behaviors of animals that exist today.

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