Thoughts On Paleontology Topics, Issues And Debates

Did Theropods Hunt In Groups

This is one I really need to get off my chest. To put it simply, I think some Theropod species, to some degree, hunted together. Whether it was in a pack or a gang that lasted for a certain period of time, some Theropods probably hunted in groups, and I'll tell you why I think that.

First, some info. It has been theorized that some Theropod Dinosaurs may have hunted in packs, like wolves or lions. There are multiple fossil finds that been seen as evidence for pack hunting behavior, such as the Cleveland Lloyd Quarry and Albertosaurus Bone Bed. For years, this idea of pack hunting in Dinosaurs was supported by most researchers and often featured in Dinosaur depictions. As time has passed, however, the idea of group hunting in Dinosaurs has become a far more debated idea, with many leaning on the opposing side. For me, I think there is a middle ground in all this.

One of the main points that has been used against the idea of group hunting has a lot to do with the Dinosaurs' placement as Archosaurs. Many scientists say that group hunting in Dinosaurs is unlikely do to the lack of social behavior in birds and crocodiles, the closest living relatives to the Non-Avian Dinosaurs. This is a reasonable argument to make; if the Dinosaurs' closest living relatives don't show cooperative behavior, why would we think this wasn't the case for the Dinosaurs themselves.

I know what some of you might be thinking "We have found multiple sites that clearly show evidence of Theropod Dinosaurs being found together, proving they did hunt in packs", well that isn't quite the case. There have been sites that show multiple Theropods of the same species found together, but some scientists have contested that they are not evidence of pack hunting. One example is the Cleveland Lloyd Quarry, part of the Morrison Formation in Utah. There have been exactly 46 Allosaurus specimens found at the site. Many have interpreted the site as a natural predator trap along a large body of water (likely a lake): Herbivorous Dinosaurs would come to the water's edge to get a drink, only to get stuck in the dried mud. The Dinosaurs would try to free themselves, but their efforts would be in vain. The sounds of struggling animals would attract predators from miles around. The prospect of an easy meal could not be ignored by the Theropod Dinosaurs, so they would go in to feast. By the time they realized the danger, it was too late, and they too were stuck in the mud. Eventually, both predator and prey would die and continue to attract more victims. Out of all the Theropods found at the Cleveland Lloyd Quarry, Allosaurus is the most commonly found. Exactly 46 Allosaurus specimens have been found to date, compared to the one or two specimens of other Theropods, like Ceratosaurus or Torvosaurus. Many have attributed the numerous Allosaurus specimens found to be the result of a pack that was attracted by the cries of trapped Dinosaurs. They followed the sounds to find trapped herbivores, which could not fight back. The carnivores would go in to feast, only to become stuck themselves. A similar situation has been proposed for the numerous Dire Wolf and Smilodon (I only use Sabre Tooth Cat when talking about the group) found at the La Brea Tar Pits, which greatly outnumber the other carnivores found at the site. The Cleveland Lloyd Quarry finds do present a strong case for pack hunting in Allosaurus, but there is another view.

This other view sees these cases of mass Theropod groupings as representing a case more in line with the feeding habits crocodiles and Komodo Dragons. With these carnivores, they are normally solitary, but will gather and large animal kills. Adults eat first, and any individuals that break this hierarchy will be killed and, possibly, cannibalized. This can easily be applied to many of these types of fossil finds, like that of the Cleveland Lloyd Quarry. Most of these sites seem to lack juveniles of the species, which is unusual. With croc and komodo feedings, juveniles that try to eat before it's their turn are killed and, occasionally, cannibalized. This could explain the almost complete absent of juveniles at the sites.

Dromaoesaurs, or Raptors as they are more commonly known as, have often been interpreted as pack hunters. A fossil find where three Deinonychus, the real Velociraptors from Jurassic Park, were found alongside a Tenotosaurus has been seen as definitive proof of this. This too has been contested, with the same arguments being applied to it. There was also a study that found that the diets of adult and juvenile Deinonychus were different, disproving the idea of cooperative pack hunting in the species. How you may ask, well if Deinonychus lived like wolves, we would expect the adults and juveniles to be eating the same things. The difference in diets indicates that, at the very least, the juveniles were left to live on their own, away from the adults.

So this all seems depressing to anyone who supports the idea of Theropod group hunting, but there is still hope. I have a theory that may act as a middle ground. I think that some Theropods may have hunted together in a more gang like structure, not like the mammalian style of cooperative pack hunting. This kind of hunting would have a group of non related members, of the species mind you, that come together for a certain period of time and hunt prey in a mob like attack plan, attacking prey in an uncoordinated manner.

I see it this way for a few reasons. It is unlikely that Dinosaurs ever hunted together in the same way as some mammals, not impossible, but improbable. However, there are some birds and reptiles that indicate a different method of group hunting. Remember what I said that some think Dinosaurs didn't hunt together because birds and crocs don't that, well that's not entirely true. Contrary to what is often said, crocodiles are by far the most social of all reptiles in the world. Outside of mating, crocodiles often bask together and will tolerate other crocs. They don't form social groups, but to say that crocodiles are completely solitary would misguided. The only exception to this would be the Saltwater Crocodile, which is aggresive to others of its own kind all year round. Crocodiles have also shown to work together in order to capture prey, with one croc leading the target towards the jaws of another croc.

The same goes for birds. While most birds of prey are solitary, there are some species that hunt together. The Harris Hawk is the known for being among the very few modern Raptors that hunts cooperatively, working together to capture prey. So the Dinosaur's descendants aren't as solitary as they first appear. I think those Theropods that are said to hunt in groups likely hunted in a way similar to crocs and the Harris Hawk, uncoordinated group attacks on prey with each member working independently. A good example of this principle would be Allosaurus. CT scans of the brain case shown that the brain of Allosaurus was very similar to that of a crocodile. Seeing how sociable crocs can be, I'd imagine Allosaurus worked in a similar fashion. Allosaurus may have lived alone, but when taking down larger prey, such as sauropods, they would come together to bring it down. For one Allosaurus to take on a sauropod, let's say the childhood favorite Brontosaurus, it would be feasible for it to attack. The Brontosaurus is certainly bigger, but the size difference wasn't like that of a dog to an ant, more like a basketball player to you. A single Allosaurus could attack a Brontosaurus, whether it was successful is a different story. In this situation, it should be noted that it would never attack a healthy fit sauropod, a healthy animal is the never the target for a predator. If the individual is sick or injured, then it would have a chance at success.

I find it hard to believe that Allosaurus never hunted sauropods, considering they were a major part in the fauna of the Morrison. They would not have been regular food sources, that honor would go to the iguanodonts (ex. Camptosaurus) and stegosaurs (ex. Stegosaurus), but there would have been times where they hunted sauropods. This also applies to the Deinonychus. The size difference between a Deinonychus and Tenotosaurus was almost the same as that of a Lion and African Buffalo, a single raptor could take a weak or injured individual, and of course juveniles were always prime targets.

So there is my reasoning for why I think that some Theropods hunted in groups. I think it's arrogant to say all Theropods were solitary and never hunted together, there were likely some that did. Group hunting in predators is determined by a number of factors, what prey is available, how much food and resources are there, so many it can be hard to know for sure which extinct species hunted in packs or groups. I just wanted to give you something to think about, I've wanted this off my chest for a long time. Sorry for being so long winded.