T. Rex Revisited: Fast, Slow, or Pack Hunter?

There has been a lot written in the scientific literature on the speed of Tyrannosaurus rex since the Hollywood glory days of one just barely being beaten out by a 1992 Jeep Wrangler in the movie Jurassic Park. Apparently moving at a 40 mph clip, T. rex was fast, agile, and definitely a solitary hunter, unlike the velociraptors which hunted in packs. That first film and several sequels later, T. rex and the velociraptors haven’t changed much in Hollywood. But that’s show biz for you.

Raptors Might Not Have Been Pack Hunters?

The popular write-up of the study also pointed out that they likely didn’t care for their young much beyond the hatchling age.

In the world of paleontology, there has been a dramatic shift for both. First of all the Jurassic Park and Jurassic World (hereafter abbreviated JP and JW) velociraptors were not based on real velociraptors, which are the size of a turkey. They were based on another raptor, Deinonychus antirrhopus, the “terrible claw” dinosaur that was about the size of a human. Plus there has been recent research which suggests that raptors did not hunt in packs. The verdict was based on different diets between young, middle-aged, and older raptor teeth fossils. The popular write-up of the study also pointed out that they likely didn’t care for their young much beyond the hatchling age.1 (That pretty much kills the plotlines of JP, JPIII, and JW.)

Also the perception of raptors being pack hunters was/is primarily based on mass-burial fossil finds, especially Deinonychus antirrhopus (mostly teeth) and Tenontosaurus tilletti partial or full skeletons having been found in over a dozen sites together.2 The two most-noted examples of this with partial or complete skeletons are several Deinonychus around a single Tenontosaurus tilletti and multiple Utahraptors with the herbivore Hippodraco. But in the former case, it has been shown that at least one juvenile Deinonychus appears to have been killed by another member of the same species, possibly suggesting a feeding frenzy rather than a pack hunt.3 However in both of these cases, scavenging a lone carcass would not be out of the question, and of course all of the animals were buried rapidly in a watery catastrophe or, as some researchers postulate, died while mired in quicksand.4 But the global flood could have produced both of the above scenarios by sweeping the animals from the continent and burying them together or burying them together as they were either eating or entrapped in waterlogged sand from a previous inundation. In this latter case, this could have been similar to how ice age animals died in the La Brea Tar Pits. A herbivore would get stuck and its distress cries would alert carnivores that would come for a free meal but also get stuck in the muck.5

The only other evidence for pack hunting among raptors comes from a set of trackways in Shandong Province, China, made by two raptors: Dromaeopodus shandongensis and Velociraptorichnus sichuanensis (which run parallel in a single direction). Curiously enough, there are several other dinosaur footprints nearby all going in the opposite direction. The entire bedding plane is made of sandstone, but there are several places where mud is present with ripple marks.6 All of these trackways could be more reasonably explained by some dinosaurs moving away from rising water during the Noachian flood and by raptors going towards the water after hearing distress cries from drowning animals. In any event, the tracks themselves do not necessitate pack-hunting behavior.

But what about T. rex? There is new research that claims T. rex was a pack hunter. There have also been revisions of the speed at which it could “run” in the scientific literature since as early as 1995. As mentioned above, in the early 1990s T. rex was considered to be an apex predator with the ability to run down prey at speeds up to 45 mph (72 kph).

The Bigger They Are the Harder They Fall

Additionally because of its small arms, if a T. rex were to trip, it would be dead: its internal organs would rupture on contact with the ground and its skull (hitting the ground from 11 ft. high (3.3 meters) would likely be crushed.

In 1995, James Farlow from the Museum of the Rockies examined one of the (then) recent fossils finds of an almost complete T. rex skeleton. Using CT scans, they were able to determine bone density and strength and determined that T. rex bones were significantly weaker than the leg bones of a white rhino. In extant animals, the white rhino is the heaviest one to be able to gallop. Anything larger (Asian and African elephants) can only walk fast (what we would call power-walking in humans). After running computer simulations, they determined that if a T. rex was running at 43–5 mph (72 kph) and tried to suddenly stop and skidded 10 ft. (3 meters), the torso would experience a horizontal force of 7 g’s (“g” here stands for gravitational force, defined as the force of gravity or acceleration on a body). The resulting net force of both the horizontal and vertical vectors would put 9 g’s of stress on the torso and 16 g’s for the head. Most trained fighter pilots can withstand 9 g’s but anything higher without protective gear could be fatal. A 9 g torso and 16 g head stress would almost certainly be lethal for the dinosaur. Additionally because of its small arms, if a T. rex were to trip, it would be dead: its internal organs would rupture on contact with the ground and its skull (hitting the ground from 11 ft. high (3.3 meters) would likely be crushed. They concluded that the maximum speed for a T. rex would be 22 mph (36 kph) and only for short bursts.7

Slowing T. rex’s Roll

Then in 2002 Stanford graduate student researcher John Hutchinson and postdoctoral researcher Mariano Garcia decided to investigate the biomechanics of very large animals. What they found was that the bigger an animal is, the more leg muscle mass it needs to run fast. But all that extra leg muscle can weigh you down, which in turn makes it harder to run. According to a press release, when Hutchinson ran the numbers (with input from Scott Delp, co-chair of Stanford's Biomechanical Engineering Division), his model suggested that in order to run at 45 miles per hour, a T. rex would need 86 percent of its weight to be leg muscles. That would leave just 14 percent for all the other muscles, plus skin, skeleton, organs, teeth, which of course is biologically untenable. They concluded that a range of 10 to 25 miles per hour (16–40 kph) was much more feasible.8

Larsson also mentioned that tyrannosaurs likely had great endurance due to their energy efficiency when walking.

The most recent study into T. rex speed, as well as possible pack hunting, used different biometric analyses from previous studies to determine speed. They compared several bipedal dinosaurs' hip height, total body length and limb bone length of both the upper leg (femur) and lower leg bones (tibia and fibula) then added total body mass estimates. This allowed them to estimate energy requirements for bipedal dinosaurs at top running speed as well as walking speeds. The results showed that up to a certain weight ~ 2,200 lbs. (1,000 kg) bipedal dinosaurs will have higher absolute speeds due to their absolutely longer leg length, but once they exceed that weight limit, their body size limits speed and acceleration potential even allowing for longer leg length.9 However, larger dinosaurs showed greater energy conservation, with T. rex showing the best energy conservation at 2 m/s speeds (approx. 4.5 mph).10 One of the study’s coauthors, Hans Larsson estimated top running speed of T. rex at 12 mph (20 kph), which is yet a further speed downgrade. But Larsson also mentioned that tyrannosaurs likely had great endurance due to their energy efficiency when walking.11

Pack Hunting T. rex?

So how does this equate to T. rex being a pack hunter? Well now we move from estimates of body mass, measurements of body and leg length, as well as laws of motion, kinematics, and laws of scaling to conjecture about prey types and how this would have affected (according to their paradigm) tyrannosaurs’ “evolution.” Noting that slow-moving sauropods (a large herbivorous quadrupedal dinosaur) were rare in those communities where tyrannosaurs existed, with only a single taxon from North America known—and it lived in the southernmost portion of Tyrannosaurus’ range—the researchers believe that T. rex had to target faster prey like hadrosaurs (duck-billed dinosaurs) and ceratopsians (like Triceratops). Because hadrosaurs and ceratopsians are smaller and not as calorie-dense as sauropods, they reasoned that T. rex had “pressure for obtaining more kills due to the fact that each kill provides less resources, thus necessitating minimizing energy expenditure per hunt and maximizing resource extraction per kill, especially if that kill is shared amongst a group, [and which therefore] influenced selection for longer limbs in Tyrannosauridae.”12

Since T. rex was not built for speed, to the researchers this suggested that pack hunting was their likely methodology for capturing prey.

Hunting the relatively smaller and faster hadrosaurs and ceratopsians may also have been facilitated by group behavior in tyrannosaurids, something previously documented by track and body fossils in large theropods. Juveniles, less than 10–15 years of age, would still be in the zone where their long legs could be used to maximize top speed, potentially helping run down faster prey items. Beyond this it has been shown that amongst pack-hunting animals employing strategy or communication between individuals can allow them to capture prey that is faster than any one individual. Combining these factors we find that pack hunting would only increase the. energetic savings differential even more dramatic between tyrannosaurs compared to allosauroids13

Keep Away From Turnaround Sue

While acknowledging that T. rex. also likely occasionally obtained meat from scavenging, they pointed to another study which had shown that tyrannosaurs were able to pivot remarkedly quickly for their size and in a smaller radius than other theropods, making it very likely they were active hunters and not scavengers only.14 The researchers believe that “when coupled with the evidence that tyrannosaurids were, at least on occasion, living in groups as well as the fact their primary prey was on average smaller and more elusive . . . this paints a picture where efficiency would be a major evolutionary advantage.”15

We would not dispute that tyrannosaurs were active hunters (in addition to scavenging), nor would we deny that there have been examples found of active predation attempts, notably tyrannosaur teeth or toothmarks on both hadrosaurs16 and a triceratops’17 horn that had healed over, proving that those particular cases were not a result of scavenging. Ironically though, both of these healed injuries testify to the “meal that got away” and argue against pack-hunting behavior among tyrannosaurs. But we would dispute that evolution had anything to do with it. All dinosaurs were created on day 6 of creation week and were initially herbivores, with carnivory only occurring sometime after man’s fall in Genesis 3.

The majority of their research was either direct observational science done with fossil bones, comparison to extant large animal mobility, and using math and physics to provide reasonable hypotheses.

Aside from the researchers looking to tack “evolution” onto their study, the majority of their research was either direct observational science done with fossil bones, comparison to extant large animal mobility, and using math and physics to provide reasonable hypotheses. But the diet of tyrannosaurs is inferred based upon their evolutionary paradigm not solely from fossil data, and their interpretation of pack hunting is another assumption predicated upon those assumptions. Based on the reasoning above, one could just as easily conclude that T. rex ate other T. rex, at least in a scavenging role (and possibly active predation) since we have bone bite marks testifying to it.18 And another tyrannosaurid, Daspletosaurus shows evidence of active predation of their own kind, with healed bite marks.19

Can We Really Determine Pack Hunting from Preferred Prey Species?

To look at predator-prey relationships and to then infer the mode of hunting is very tenuous. Both pack-hunting African wild dogs and solitary leopards will kill gazelle, and both group-hunting lions and leopards will kill and eat zebra. Some animals may gather in one place to hunt collectively but eat their own catch only (think grizzly bears during a salmon run). Then there are some animals that hunt alone but share the kill with other members of the group (some coyotes and chimpanzees). Even within the same species of animal, there are different hunting strategies. Non-dominant male lions, once they leave the pride, are often solitary hunters but will sometimes team up with one of their siblings.

And then there’s the irony of mass burials with several raptors and a potential-prey species not being accepted by some secular researchers as evidence of pack-hunting (although we would agree that some fossil sites might better be explained by “distress hunting”), yet the belief that T. rex was a pack hunter based on nothing more than assuming predator/prey relationships, foot speed, and energy conservation needs—and this in spite of the scant fossil evidence, much of which is not supportive of the hypothesis.

Furthermore, as creation researchers are quick to point out, mixed fossil assemblages do not necessarily reflect whether certain animals lived together, hunted each other, or formed herds together. The only thing it does tell us is that they were buried together. And whether they were trapped in quicksand or simply swept away by water and buried together in sediment, both processes are more readily explained by the worldwide flood of Genesis 6–8.