Other therapods in the time of Tyrannosaurus rex?

[Bulldog Psion]

This is something I've been wondering about for some time, but I don't have time to research it as thoroughly as I'd like right now. So, I'll pick the brains of any kind people here who might know the answer and be willing to share.

Were there other therapod dinosaurs contemporaneous with T. rex in North America, occupying the same ranges? Anything allosaurus-sized, say?

In modern faunal assemblages, there are various sizes of predator, all the way down to insectivore. You can have, say, foxes, bobcats, lynx, coyotes, wolves, black bears, and puma, all living in the same region and taking slightly different prey, etc.

What I'm wondering is if there was a complete predatory faunal assemblage in the T. rex's western U.S. habitat, or if the T. rex distorted this in some way (outcompeting medium-large therapods, for example).

Like I said, I could dig this up if I had time, but that's of the essence right now, so...

Thanks in advance for any info you might have!

[Emperordaniel]

According to this site, Tyrannosaurus lived from 85 to 65 mya during the Senonian epoch of the Cretaceous, which makes it roughly contemporary with the following North American Allosaurus-sized theropods:

• Albertosaurus (76-74 mya)
• Daspletosaurus (76-72 mya)
• Gorgosaurus (76-68 mya)

However, Wikipedia places the Tyrannosaurus at only 68-66 mya, which would make it barely contemporary with Albertosaurus, which Wikipedia places at 71-68 mya (Daspletosaurus and Gorgosaurus being placed at 77-74 mya and 76.6-75.1 mya, respectively).

Hope this helped!

[Closet_Skeleton]

Technically, there wasn't a Western north America for most of the Cretaceous period.

T.Rex is just one species of Tyranosaurid, so it had contemporaries for some time of its existence, the three Emperordaniel mentioned and Albertosaurus are all Tyranosaurids so they're more like comparing a lion to a leopard than to a bear. T.Rex was the last known species of Tyranosaurid but there would have been a period where other related animals were still alive (like how for most of homo sapiens existence it wasn't the only hominid). Some Tyranosaurids weren't around in North America.

Whether or not Tyranosaurus was actually one species or not is something palaeontologists argue about but can't really answer due to all the missing soft tissue.

Unless you meant 'did Tyranosaurids have similar contemporaries' which is a slightly different question and not one I know the answer to.

[Bulldog Psion]

Thanks guys!

It almost sounds like tyrannosaurus rex didn't have any predatory contemporaries -- no cheetahs, leopards, or hyenas to its lion, so to speak. Which is pretty weird.

[VoxRationis]

For some time, it was believed that T. rex outcompeted all other major large predators in its habitat, by virtue of having an unusually long adolescence—the juveniles were capable predators in their own right, but in niches different from that of the adult form. Thus, by spending a lot of time in each state, a single species got to fill most predator niches above a certain small size, so there wouldn't be much in the way of other major theropods around.
However, the recent discovery of Dakotaraptor, which would have shared the same time and place as T. rex, is casting doubt on this hypothesis. Dakotaraptor was a dromeosaur, rather similar to Deinonychus, but on a larger scale, only slightly smaller than Utahraptor. It's possible, I have read, that Dakotaraptor occupied a position as ambush predator, while the long-legged T. rex juveniles focused on pursuit predation.

[Bulldog Psion]

For some time, it was believed that T. rex outcompeted all other major large predators in its habitat, by virtue of having an unusually long adolescence—the juveniles were capable predators in their own right, but in niches different from that of the adult form. Thus, by spending a lot of time in each state, a single species got to fill most predator niches above a certain small size, so there wouldn't be much in the way of other major theropods around.
However, the recent discovery of Dakotaraptor, which would have shared the same time and place as T. rex, is casting doubt on this hypothesis. Dakotaraptor was a dromeosaur, rather similar to Deinonychus, but on a larger scale, only slightly smaller than Utahraptor. It's possible, I have read, that Dakotaraptor occupied a position as ambush predator, while the long-legged T. rex juveniles focused on pursuit predation.

Very interesting! Thank you!

[WolfLordBran]

Based on modern predators, I would venture to say that T. rex did have one predatory competitor: other larger T. rexes. There is evidence of cannibalism in therapods (Majungatholus) and it's entirely possible that larger specimens may have reacted aggressively towards smaller/weaker members of the species, possibly even cannibalizing remains afterwards since meat is meat.

[lsfreak]

It almost sounds like tyrannosaurus rex didn't have any predatory contemporaries -- no cheetahs, leopards, or hyenas to its lion, so to speak. Which is pretty weird.

Part of this has to do with biodiversity. Unless I'm mistaken, as far as we can tell, animals have become increasingly good at niche partitioning. One type hunt mostly in the open valleys while another is on the wooded hills, one hunts animals in this specific weight range while another in this one, one is diurnal and one is nocturnal, one goes after animals that can run at this speed and another at this speed, and so on. The farther back in time you go the broader the range of situations a single species dominates, and thus, the fewer species you have.

[Closet_Skeleton]

It almost sounds like tyrannosaurus rex didn't have any predatory contemporaries -- no cheetahs, leopards, or hyenas to its lion, so to speak. Which is pretty weird.

The thing is, we have a lot of Tyrannosaurus fossils. We can therefore tell how long the species lasted quite well.

We don't have a lot of specimens of similar sized dinosaurs. So its totally possible that various other species survived quite far into the period of T.Rex's apparent dominance, but their bones didn't survive. Probability tells you that since a tiny amount of skeletons ever get fossilized, more animals equals more fossils so the amount of skeletons could very well reflect there having been more T.Rex than similar dinosaurs but since we're talking about a quite small sample size (50-60 skeletons) compared to how many Tyrannosaurs would have lived over the million year period the species was existent for so that could still just be a fluke. Albertosaurus on the other hand has just over half as many (maybe 30-40?) specimens known, which makes it harder to tell how long it lasted and to what degree it might have over-lapped with T.Rex.

The thing about Lions and Cheetahs is that they have similar habitats but lions are a lot bigger. Tigers, who are closer in size to Lions, don't generally live in the same areas. Tyrannosaurus Rex is quite a bit bigger than Albertosaurus, but had similar sized contemporaries on other continents.

Its also vaguely possible that Tyranosaurids were close enough to interbreed, so the other species like Albertosaurus and Gorgosaurus could have been absorbed into the T.Rex genius like might have happened to Neanderthals (and potentially to Polar Bears if their habitat vanishes since they've proven to be capable of interbreeding with other bear species).

[Dire Moose]

The other tyrannosaurids mentioned were not contemporaneous with Tyrannosaurus rex for the most part. And the correct timeframe is from 69-65 Ma.

The earliest T. rex fossils known are from around 69 Ma in Utah and Texas. This is around the same timeframe as the youngest known Albertosaurus from farther north. However, by the time T. rex starts showing up in the better-known localities of Montana, the Dakotas, and southwest Canada, Albertosaurus is gone. If there was any overlap between the two, it was likely a case of the bigger theropod moving in and outcompeting the smaller one.

There are a few theropods contemporaneous with T. rex. A couple of ornithomimids (Struthiomimus and Ornithomimus) are known from the same formations, as is the large oviraptorosaur Anzu, but these all had smaller heads with toothless beaks and occupied a different ecological niche from the top predator.

There are also a couple of dromaeosaurs, Acheroraptor and Dakotaraptor. The former was a fairly small animal about the size of Velociraptor; the latter was in between Deinonychus and Utahraptor in size. Neither one was in the same league as T. rex.

Another name that gets brought up a lot is Nanotyrannus, allegedly a smaller lighter species of tyrannosaur with more teeth that lived alongside T. rex. This one is still controversial, but it seems most likely that the relevant specimens are actually juvenile T. rex, which changed a lot as it grew up. A big problem here is that many proponents of the " Nanotyrannus is different" hypothesis rely on fossils that are in private collections for their evidence, and these cannot be examined by legitimate scientists.