Realistic raptors: pop-culture dromaeosaurs vs current science, part 1

Recently, I shared this image of our greyhound, Beau, next to a Velociraptor* skeleton on social media. Twitter quickly lit up with likes and comments...

We test-mounted a Velociraptor skeleton yesterday, allowing comparison with our greyhound, Beau. She's a large-ish dog (27kg), and we all know Vel. was no giant, but it's surprising to see the skeleton so dwarfed by a common family pet. Puts a new spin on Velociraptor for me. pic.twitter.com/c2OPBv7qJC

— Mark Witton (@MarkWitton) March 1, 2020

...many of which remarked on how, despite being dwarfed by a big, but not exceptionally large dog, Velociraptor was still a formidable animal that would turn Beau into mincemeat should the two ever meet in real life. Poor old Beau. She doesn't deserve that: she's barely a risk to a bag of kibble.

*Probably 'velociraptorine', to be honest: there's some uncertainty about the identification of the specimen this replica was cast from.

Reading through the comments on this tweet reinforced how Velociraptor-like dinosaurs have been mythologised in popular culture. Thanks largely to Jurassic Park, Raptor Red and other 1990s palaeo media, these dinosaurs are regarded as some of the fastest, most vicious and meanest creatures of all time. Commonly discussed aspects of their savagery include razor-sharp claws capable of ripping into and disembowelling prey; strong legs for delivering rapid slashing attacks; ferocious bites and flesh-rending teeth; cheetah-like speed and agility; and high intelligence. They sound, from this description, like some of the most terrifying predators to have ever existed.

As is often the case, our pop culture takes on Velociraptor and co. have not always aligned with scientific thinking. A case can be made for Velociraptor-like dinosaurs having attained a near-fantastical public reputation reminiscent of Western pop-culture takes on ninjas. Both are genuine historical entities capable of awesome and fascinating feats, but both are also so fundamentally and unrealistically overhyped by popular culture that they bear little resemblance to the real deal.

To attempt to shed some real light on what these famous but often misrepresented dinosaurs were like, I want to compare our pop-culture takes on Velociraptor and similar dinosaurs with some of our more robust recent science on these animals. My intention is not to provide a tried and tested "what Jurassic Park got wrong about Velociraptor-type post" or to discuss basic stuff you can read about elsewhere, like the undoubted presence of extensive feathering in these dinosaurs (Turner et al. 2007; DePalma et al. 2015), but to focus on aspects of lifestyle, biomechanics and ecology. There's a lot to talk about here, so I'm dividing this article into two posts.

The 1993 Jurassic Park Velociraptor, a Hollywood creation that introduced much of the world to dromaeosaurid dinosaurs, and which probably remains the chief point of public reference for their appearance and behaviour. There is, of course, a slew of well-known anatomical issues with the JP Velociraptor that conflict with science published in the last few decades, but that's not what I want to talk about here. Image © Universal, I'm not sure who originally put it online.

Before we begin we need to quickly discuss some aspects of terminology. Firstly, exactly what group of dinosaurs are we focusing on here? Velociraptor is a member of Dromaeosauridae, a group of bird-like feathered theropods generally characterised by large, sickle-shaped claws on their second toes; long, stiffened tails; and narrow, lightweight skulls lined with sharp, serrated teeth. Fossils show that their feathering was broadly comparable to living birds such that, in life, they probably looked like long-tailed, toothy avians. But dromaeosaurs were a diverse bunch which, in addition to Velociraptor-like forms, also included the long-skulled, long-legged unenlagiines, the small-bodied and sometimes 'four winged' microraptorines, and the newly identified Halszkaraptorinae, an enigmatic group containing the semi-aquatic Halszkaraptor. The "raptors" of popular convention - mid- to large-sized dromaeosaurs with large foot claws - are perhaps best matched among palaeontological classifications by Eudromosauria, a group generally considered to include several household names: Velociraptor, Deinonychus, Utahraptor, Dromaeosaurus and others. Eudromaeosauria is not a universally recognised group as the exact composition and arrangement of Dromaeosauridae remains the subject of ongoing study. However, it's a neat match for the public perception of dinosaurian "raptors" and will serve us well in our discussion, regardless of whether it's a true taxonomic group or merely a collection of anatomically similar, but unrelated species.

Secondly, a qualifier on the word "raptor". While "raptor" has been synonymous with "birds of prey" for about two centuries, it has increasingly been used to refer to dromaeosaurids and similar non-avian dinosaurs since the Jurassic Park franchise introduced it as shorthand for Velociraptor (see Farquhar 2017 for the complex history of this word). While some purists dislike the latter use (myself included, to be honest), technical palaeontological literature has started to adopt "raptor" as a colloquialism for Dromaeosauridae as well. Miserable old-fashioned folks like myself thus need to concede that "raptor" has grown to encompass members of Dromaeosauridae even though this complicates discussions where raptorial birds and dromaeosaurs are mentioned simultaneously. Thus, to avoid confusion, my use of "raptor" here is meant in the traditional avian sense of the word, unless otherwise specified.

These points in place, let's get moving through pop-culture takes on eudromaeosaurs to see how they stand up to scientific scrutiny.

Pop-culture concept. Eudromaeosaur species are basically all the same animal expressed at different body sizes.

It's difficult to mention dromaeosaurs online without discussion turning to the real taxonomic identity of the Velociraptor featured in the Jurassic Park series. Deinonychus and Utahraptor are often mentioned as the actual basis for the animals featured in those films*. These discussions imply that all eudromaeosaurs were generally similar in appearance to Deinonychus or Velociraptor: fairly gracile animals with long-ish limbs, large claws, long tails and low, slender skulls, and that size was their main distinguishing feature.

*It's worth taking a moment to give some additional information on this oft-discussed point. The preface of Robert Bakker's 1995 novel Raptor Red gives a behind-the-scenes insight on this matter, acknowledging that the size of the Jurassic Park Velociraptor was not based on anything other than the desires of the filmmakers, and that their scaling of these animals to sizes beyond those of Deinonychus - the biggest dromaeosaur known until 1993 - was cause for concern among some involved in the film. The Jurassic dromaeosaurs were made vastly bigger than both Velociraptor and Deinonychus because the real size of these animals wasn't considered intimidating enough. The 1993 discovery of Utahraptor, while giving the filmmakers a reprieve for making their dromaeosaurs so big, didn't fully justify their scaling either as this animal was initially thought to be around 7 m long: about twice the size of those in the film (Kirkland et al. 1993). The man-sized Jurassic 'raptors' thus lacked a good size match among Dromaeosauridae in the early 1990s and, in my view, are best viewed as 'generic' eudromaeosaurs shaped to the requirements of the film, rather than being based on any particular genus.

Not all eudromaeosaurs were variants on Velociraptor. Utahraptor ostrommaysorum sits at the other end of their anatomical range, being a large (5-6 m long), 300-500 kg predator with a proportionally large head, stout limbs and enormous claws. It almost resembles a dromaeosaur wanting to revert to a more traditional theropod body plan, without sacrificing some key dromaeosaur adaptations.

A fair degree of anatomical variation has been apparent in Eudromaeosauria since at least the early 1990s, however. Though sharing a similar body plan, eudromaeosaurs differ in attributes of limb length, limb bone proportions, head size, jaw depth, dental configuration, claw sizes, tail flexibility and many other smaller anatomical components (e.g. Turner et al. 2012; Paul 2016). They ranged from smallish animals less than 1.5 m in length and perhaps just 5 kg in weight (Bambiraptor) to grand species some 5-6 m long and exceeding 300 kg (Utahraptor). At least some of these large-bodied species, such as Utahraptor and Achillobator, were stocky, large-headed creatures with deep jaws, heavy hips, stout limbs, large sickle claws, and relatively powerful bites (above). Other giant eudromaeosaurs were not especially robust however, with Dakotaraptor being of similar build to Deinonychus-like morphs despite being one of the largest dromaeosaurs (DePalma et al. 2015). Smaller eudromaeosaurs were also anatomically varied, with genera such as Dromaeosaurus and Atrociraptor bearing short, deep snouts and robust teeth, instead of the long, slender jaws of Deinonychus-like species. Some real oddballs are also known, such as Adasaurus mongoliensis: a smallish eudromaeosaur with a somewhat reinforced posterior skull and a vastly reduced sickle claw (Turner et al. 2012).

The wimpy sickle claw of Adasaurus, as illustrated by Turner et al. 2012.

Although these differences are undeniably small compared to the disparity of theropods as a whole, they would surely be very obvious should we have seen these animals in life. Eudromaeosaurs were not merely differently-scaled variants on Velociraptor, but differently adapted species with a range of functional morphologies and behaviours. Eudromaeosauria was a widespread and long-lived group and these distinctions probably reflect adaptations to the range of prey species, as well as environmental and climatic regimes experienced by its members. We should probably view eudromaeosaurs as having a similar anatomical and ecological range to some living carnivore groups, such as felids or raptorial birds, which range from tiny hunters of small animals to heavyset predators of larger game. As with cats and raptors, those concerned with the accurate conveyance of eudromaeosaur biology have to be careful not to over-generalise details of their anatomy and appearance.

Pop culture concept. Eudromaeosaurs were lightning fast, streaking after their prey at speeds comparable to the fastest living land animals.

The silver-screen Velociraptor of Jurassic Park has, time and again, been shown as an incredibly swift animal. Described as having cheetah-like speed in the first film (which equates to a maximum speed of 109.4–120.7 kph, or 68.0–75.0 mph), we've since seen them running down hadrosaurs in Jurassic Park III and leading jeeps and motorcycles in Jurassic World. These pop-culture depictions align with energetic names and artwork associated with these animals for almost a century. Deinonychus was, of course, a poster child of the dinosaur renaissance and an animal which helped change thinking about dinosaur metabolism and activity rates. Robert Bakker's famous sprinting Deinonychus reconstruction (below, first published in Ostrom 1969) is a famous and influential palaeoartwork demonstrating eudromaeosaurs as fast, agile creatures. The names of classic eudromaeosaur taxa - Dromaeosaurus ("running lizard"), Velociraptor ("fast thief") - emphasise their swiftness and raptorial nature, implying speed and agility above the dinosaurian average.

Bakker's sprinting Deinonychus antirrhopus from Ostrom (1969). Now over 50 years old and dated in many respects, it remains an iconic image of the Dinosaur Renaissance and conveys the important message that dinosaurs - including dromaeosaurs - were fast, powerful creatures.

Perhaps surprisingly given their reputation, studies show that eudromaeosaurs weren't exactly speed-demons. A caveat here is that it's actually pretty difficult to know exactly how fast extinct animals could move because speed is influenced by a range of factors which are challenging to predict reliably from fossils. These include animal mass, muscle fractions, muscle speed, bone strength, stride length and others. Trackways can give an idea of velocity for a given individual - and they are known for dromaeosaurs - but they may not record animals moving at their maximum speeds. We can, however, make decent assessments of extinct animal speed from their limb proportions and by searching for anatomies that are common to fast runners today. From these, we've known for at least half a century that eudromaeosaurs were not among the quickest dinosaurs (Ostrom 1969; Paul 1988; Kirkland et al. 1993; Carrano 1999; Persons and Currie 2016), despite contrary claims in popular works and their treatment in some scientific literature.

What slows eudromaeosaurs down is that, in contrast to cursorial (= fast running) animals, they lack elongated distal limb segments, reduced and streamlined toe anatomy, and narrowed, fused metatarsals. Studies suggest that eudromaeosaur hindlimbs, although clearly well-muscled, sacrificed speed for strong, grasping foot anatomy (Ostrom 1969; Fowler et al. 2011). Biomechanical studies show that appendage strength and running speed are something of an adaptive fork in the road as they exert conflicting demands on muscle distribution, limb length and bone robustness. Close relatives of eudromaeosaurs, including the unenlagiines and troodontids, adapted towards greater cursorial abilities at the expense of foot power and were probably far nimbler, faster creatures than equivalently-sized eudromaeosaurs (Carrano 1999; Persons and Currie 2016).

Eudromaeosaurs were probably not the fastest dinosaurs, but they were lightly built, well-muscled animals that could surely move at a reasonable speed for at least a short amount of time to catch their prey. Here, Velociraptor chases down Zalambdalestes.

This all said, no-one thinks eudromaeosaurs were exactly slowpokes. As generally smallish, lightly built dinosaurs with somewhat elongated and well-muscled hindlimbs, eudromaeosaurs were probably capable of moving quickly at times, just not for sustained periods or at record-breaking speeds. Their stiffened tails are clear hallmarks of rapid locomotion, being ideally suited to facilitating quick changes in direction at speed (Ostrom 1969; Persons and Currie 2012). It seems reasonable to assume that eudromaeosaurs were adept at ambushing prey, relying on a short burst of speed and agility to catch fleeing animals from a covered position, but that target species might have had an advantage if a long pursuit was involved.

Certain eudromaeosaurs, such as the large-bodied Utahraptor, were probably not especially quick animals, however. Their hindlimb proportions are even less suited to running than other eudromaeosaurs and their tails were not significantly stiffened, suggesting lessened agility as well as speed (Kirkland et al. 1993). Judging from their proportions, it looks like these species compromised their running capabilities to facilitate greater body mass, hindlimb power and head size. Hopefully, as we learn more about these very large eudromaeosaur species we'll develop more insights into their locomotion.

Pop culture concept. Eudromaeosaurs had tremendously strong bites.

An idea popularized in at least the Jurassic Park novel is that eudromaeosaurs, in addition to being blade-wielding superninjas, were also armed with a bite that would make an alligator feel inadequate. In this book Velociraptor literally chews through steel bars in a noble but ultimately futile effort to kill one of fiction's most irritating characters, Ian Sodding Malcolm. While this doesn't seem to be a particularly widespread popular assumption about eudromaeosaurs, responses to the Beau vs. dromaeosaur tweet certainly included a few comments about powerful bites.

Terrifically preserved skull of Velociraptor mongoliensis showing the low, narrow, lightly built skull construction typical of most eudromaeosaurs. These are not the skulls of powerful biters, but of lightweight, fast-moving animals with teeth suited to rapid tearing of flesh. From Turner et al. (2012).

Dromaeosaur bite strength is something that we've addressed on this blog before so I won't dwell on it long here. Deep bite marks on a Tenontosaurus fossil have been attributed to Deinonychus and promoted as evidence for a powerful, alligator-grade bite in this genus by one set of authors (Gignac et al. 2010), but virtually all other studies conducted on the skull strength and bite forces of eudromaeosaurs have drawn conflicting conclusions (Therrien et al. 2005; Sakamoto 2010; Fowler et al. 2011). Eudromaeosaur skulls are generally lightweight structures composed of thin bars and sheets of bone, and were thus poorly suited to powerful biting. In all likelihood, those Tenontosaurus bones were bitten by another animal. Therrien et al. (2005) predicted the bite force of Deinonychus as being comparable to that of a 30 kg wolf, a value which seems impressive until we remember that Deinonychus was about twice that size (c. 80 kg). This difference likely reflects the fact that canids are adapted for chewing into bone, while eudromaeosaurs have the slender teeth and relatively delicate jaws of dedicated flesh-eaters. They surely ate around or swallowed skeletal elements whole so as not to damage their teeth chewing into bones. Thus, while it would not be wise to put your hand in a eudromaeosaur's mouth, there are plenty of other animals out there that could bite you harder. An unknown quantity here is how powerful the bite of something like Utahraptor was: there is good reason to think these animals had large, relatively strong skulls that may have allowed for greater bite forces, but we need more substantial fossils of these giant dromaeosaurs to understand their bite performance.

Pop culture concept. Eudromaeosaurs attacked their prey with razor-sharp claws, slicing deep into their flesh to leave long, bloody lacerations.

The eudromaeosaurs I knew from my childhood dinosaur books - both educational and fiction - were imagined as having ferociously sharp claws which could be deployed in an especially gory, grotesque fashion to dispatch prey. Palaeoart fans will not need to be reminded of the glut of 1990s dinosaur art showing this: swarms of dromaeosaurs using their claws to clamber over prey species, tearing into their hides to leave long, deep gashes. I have no doubt that these predatory scenarios were a major part of why dromaeosaurs became a firm favourite among dinosaur fans and the public alike. My own childhood sketchbooks were certainly full of bloody, gory dromaeosaur art inspired by these ideas.

Page from the 1993 comic serial Age of Reptiles showing Deinonynchus bringing down a sauropod with slashing, razor-sharp claws. Though portrayed in a comic book, this is pretty close to how dromaeosaur claw function was predicted by scientists in the early 1990s. Art by Ricardo Delgado, borrowed from Dark Horse Comics.

Flesh-ripping dromaeosaur claws have some actual basis in science, this being the accepted interpretation of sickle and hand claw function in the mid to late 20th century (e.g. Ostrom 1969; Bakker 1986, 1995; Paul 1988; Kirkland et al. 1993). Their deep, bladed nature and large flexor tubercles (the part of the claw anchoring flexing musculature) of dromaeosaur hand and sickle claws give this idea some credibility, and the size of most eudromaeosaurs claws is undeniably remarkable: there's no doubt that they were paramount to their predatory behaviour.

However, this concept has come under fire in recent years as we've started to assess the lifestyles of eudromaeosaurs in a more detailed and biomechanics-led fashion. It's quite well established, for instance, that while dromaeosaur claws are narrow, they aren't quite knife-like enough to facilitate easy cutting of skin and muscle tissue. Their cross-sections are somewhat like a stretched, inverted pear (below) with a narrow but distinctly rounded inner margin (Carpenter 2000; Farlow et al. 2011). It is also unlikely that their claws were shaped into razor-like cutting edges by keratinous sheaths, unless they had a sheath-claw bone relationship unlike anything seen in birds and reptiles today (Carpenter 2000; Manning et al. 2006). These are major problems for the slashing hypothesis because, as many of us know from personal dining experiences, it can be challenging to cut animal skin and flesh without a well-sharpened blade (Carpenter 2000). That dromaeosaurs could hone and maintain a razor-like claw edge against routine abrasion and wear is a naive assumption: claw tips can be sharpened by the removal of abraded and ragged sheath layers (as the trashed furniture of many cat owners will attest) but it's harder to hone the edge of an entire claw without dedicated technology (Carpenter 2000).

Eudromaeosaur claw shape as illustrated by Carpenter (2000). Note the width of the claws and lack of bladed cutting edges along their inner margins.

A further problem for the slashing hypothesis is the amount of force eudromaeosaurs could transmit to their sickle claws during kicks or other attacks with extended legs. Many of us are familiar with artwork of aggressive dromaeosaurs posed in this way, but it turns out that outstretched legs are actually the weakest configuration for application of claw force (Farlow et al. 2011; Bishop 2019). Eudromaeosaur hindlimbs actually delivered a lot more power through their sickle claws when the leg was crouched or otherwise flexed (Fowler et al. 2011; Bishop 2019) and, perhaps surprisingly, the overall force achieved at the claw tips was not great relative to the strength of prey animal tissues (Manning et al. 2006; Bishop 2019). Thus, even under optimal conditions, it's unlikely that eudromaeosaurs had sufficient strength to create long, deep wounds in animal flanks. Neither claw shape nor our understanding of hindlimb mechanics corroborates the use of eudromaeosaur claws as ripping and slashing structures.

A counterargument to this might be the commonality of foot slashing behaviour by sparring birds. Many avian species, including those with formidable claws for raptorial or perching behaviour, kick and slash at each other when settling disputes in a manner not entirely unlike that traditionally predicted for predatory dromaeosaurs. Might not similar movements, scaled up to the size of large eudromaeosaurs, have been effective means to bring prey down? In my mind, the behaviour of modern sparring birds might actually be further evidence against claws inflicting major injury through kicking actions. In all but the most serious bouts - where slashing and kicking turns to wrestling, pecking and eye-gouging, or where circumstances do not allow for escape for a weakened bird - avian sparring rarely leads to more than superficial injuries. In some species, including those with large talons and curved claws like eagles and seriemas, talon clashing is even employed in non-aggressive acts such as courtship and between parents and juveniles (e.g. Silva et al. 2016). The fact that birds can endure kicks from clawed feet without great concern is further evidenced by brutish humans equipping cockfighting roosters with artificial spurs - metal blades and so on - to allow them to inflict deeper, more critical wounds when sparring**. Though not a perfect analogue for eudromaeosaur slashing predation, these avian behaviours demonstrate that simply having large claws on powerful legs does not turn animals into deadly bladed assassins, and seemingly concurs with the predicted weak performance of claws in kicking or slashing. There's more to say on how dangerous bird claws can be when employed aggressively, and we'll return to this topic in the next article.

**In what might be seen as poetic justice, the addition of artificial spurs to fighting chickens turns them into animals that are also deadly to humans. At least three people have been recorded as dying after attacks or accidents involving sparring cockerels with razors added to their legs.

The flexed left foot of Deinonychus as illustrated by Fowler et al. (2011). I find this image absolutely compelling evidence of the powerful grip provided by these feet in life, and more than a little intimidating. Note the lateral flexion of the fourth toe afforded by the ball and socket-like joint at the end of the metatarsal. Scale bar is 100 mm.

So if they weren't for cutting and tearing, what were eudromaeosaur sickle claws for? A breakthrough interpretation of their function has stemmed from realising that we should focus on eudromaeosaur feet as a whole, and not just the impressive sickle claws on digit II (Fowler et al. 2011). Armed with this perspective, it becomes apparent that their whole foot structure is well adapted to piercing and powerful gripping. Their claws are mechanically strong against the forces associated with puncturing skin (Manning et al. 2009) and, although ill-suited to ripping flesh, physical modelling implies a great ability to dig into and hold bunched animal tissues (Manning et al. 2006, though see Fowler et al. 2011 for a critique of this research). Articulating well-preserved eudromaeosaur feet shows that they could form a formidable-looking 'fist' in which the middle toes (the sickle claw and digit III) clenched tightly in line with the long bones of the foot, and the lateral toes (the hallux, and a relatively mobile fourth digit) gripped from opposing sides (Fowler et al. 2011). This gripping function benefits enormously from the short, wide and unfused metatarsus of the eudromaeosaur foot as this provides room for multiple strong ligaments and gives a robust, strain-resistant base to the clenching digits. Presumably, this gripping adaptation is the payoff for reduced eudromaeosaur running speed (Fowler et al. 2011). An ability to form a tight fist with the foot is shared with many living raptors, and studies have found numerous hitherto unappreciated similarities between the feet of these species, with eagles among the best modern analogues (Fowler et al. 2009, 2011).

This revelation that dromaeosaur feet are more about gripping than slashing has important implications for how we imagine the ecology of these animals, and suggests many of our traditional concepts of eudromaeosaur prey apprehension are unlikely. It seems that the formidable claws of these animals were not quite the be-all and end-all of eudromaeosaur predation that we once thought, and that they were instead part of a prey immobilisation strategy that involved their entire bodies. Exactly what that predatory strategy might have been is something we'll get to in the second part of this series.

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