How Did Allosaurus Kill Its Prey?

Now you've probably heard of Allosaurus - aside from T-rex, it was, for the longest time, the second-most-famous big theropod (it's still in the Big Five, along with T-rex, Spinosaurus, Giganotosaurus and Carnotaurus). In addition, due to the fact it is known from a huge amount of fossils, we know more about it than most other Jurassic theropods.

Now this popularity is all a tad misleading - because, y'see, Allosaurus is pretty... weird - especially when it comes to a single question. How did it kill its prey?

Allosaurus, despite having a strong skull with high bone density (able to withstand up to 55,000N), had a surprisingly weak bite for its size; only approximately 2150 newtons, similar to that of a modern leopard, despite being several times the size. This was considerably less than that of other large theropods (such as T-rex) or even alligators. Many theories have been articulated in order to explain this dissonance, drawing on multiple aspects of the morphology of the skull. They are as follows:

1. The skull is relatively lightweight, despite its surprising strength.

2. The jaw is narrow, with a wider gape (Allosaurus was capable of opening its jaws at a 79o angle), allowing them to deliver extreme soft tissue trauma, powered by the incredibly strong neck muscles.

3. The jaw was powered by large jaw muscles, inferred by the presence of large fenestral openings, which indicates significant muscle mass. 

4. Unlike T-rex, its teeth are a mitigating fact as they are relatively small, laterally compressed and serrated; perfectly suited to cutting, rather than crushing.

Many theories have been articulated to explain this - most famously, Bakker (1998), through comparisons between Allosaurus and various sabre-toothed Cenozoic predatory mammals, interpreted these features as adaptations for a wide gape and use of the neck musculature in head elevation and depression, which in turn would allow allosaurs to use their skull and teeth in what he called a "Samoan war-club" attack, where they prey was violently hit by a downward motion of the skull and neck. (Now, this is drawn from an anachronistic interpretation of how sabre-toothed cats killed their prey - we now know they killed their prey with bites to the throat).

More recently, Rayfield et al (2001) used Finite Element Analysis (FEA) to study the constructional morphology of an Allosaurus skull and found that it was capable of withstanding large vertical forces, despite having weak jaw adductors. They concluded that this combination of features implied the involvement of a non-muscular force - which they interpreted as the use of the inertia of the predator's rush towards its prey, which has been compared to a hatchet. This scenario was most famously depicted in the 2011 documentary series "Planet Dinosaur" (as seen below).

However, when I researched this for a presentation as part of my undergrad degree, I found that the hatchet jaw attack had its own issues. Anton et al, (2003) was particularly useful in this regard. 

Firstly, the theory argues that Allosaurus' skull was "over-engineered"... according to what metric? Rayfield et al (2001) did not compare Allosaurus' skull with other theropods or even modern predators that use muscle-powered bites without hatchetting.

The hatchet analogy doesn't quite work - the comparison would only really be valid if the person with the hatchet was running towards the victim and the hatchet struck harder because the person was running. The claim that the inertia of the allosaur's dash toward prey could be incorporated into the bite is contradicted by the fact that the allosaur would be running forwards - if the allosaur were to benefit from this, the teeth and maxilla would have to have an anterior orientation, not a ventral one. A more valid analogy would be a soldier with a bayonet.

Another issue is that, for a theropod its size, Allosaurus' teeth were comparatively small - would hitting the size of a large sauropod with such a set of teeth (with the jaws nearly at the point of dislocation) would cause a devastating injury of any kind? There'd also be a high risk of tooth breakage/loss. Even if the teeth were continually replaced throughout life (as most non-avian theropods did), it would still be pretty counterproductive for a predator to break a large portion of its tooth row every time it was hunting. The enormous gape necessary to clear the mandible from the path of the cranium is also problematic, since, given the greatest strengthening of the cranium was at the central maxillary dentition, it would require a gape of over 90 degrees (which Allosaurus id not have).

I thought there was a much simpler explanation based on the factors above...

What do I think?

My personal take on all this is that Allosaurus' relatively weak bite was a trade-off for a wider gape (Allosaurus had a gape wider than most other theropods its size), which, combined with powerful neck muscles, enabled it to deliver muscle-powered, shearing bites in order to slice chunks of flesh off their prey, killing it through shock and blood loss, similar to the Komodo dragon today. 

This would enable Allosaurus to "punch above its weight", as it were, and hunt prey much larger than itself - including the many large sauropods it existed alongside. (Now, there's an interesting implication for behaviour here, but that's for another day).

Given predators use different methods to hunt different prey, I'd imagine that Allosaurus did the same. Prey closer to Allosaurus' own size - mid-sized ornithopods such as Camptosaurus - were probably subdued with the forelimbs and killed by multiple bites to the throat (to crush the trachea), whilst larger prey (such as stegosaurs or young sauropods) were brought down by multiple, muscle-powered bites designed to shear off chunks of flesh

Now, perhaps interestingly, Allosaurus is part of the same group - the allosauroids - that contain the carcharadontosaurs. In carcharadontosaurs, like Giganotosaurus and Carcharadontosaurus, we see roughly similar mechanics to Allosaurus (wide gape, blade-like teeth), indicating a similar killing method (shearing off chunks of flesh, with the prey dying via shock and blood loss), only taken to extreme levels.