by John Conway
Science and speculation are happy bedfellows, so long as we remain grounded in our speculations, and so long as we state the core evidence we have in the first place. When it comes to the reconstruction of fossil animals, there will always be a great many aspects of anatomy, behaviour and lifestyle that will remain unknown, and for which a modicum of reasonable speculation will be allowed, and even necessary. Enjoy the ride.
All Yesterdays
What images come to mind when you hear the word "dinosaur"? Perhaps you picture enormous lumbering animals, lurking in the swamps of old; or maybe you imagine lithe predatory dinosaurs sprinting on lean muscular legs, perfect killing machines with mouths agape in perpetual screams. In recent years, these views have become opposing stereotypes, putting prehistoric animals in straightjackets of appearance and behaviour.
We wanted a way out – a way that would show dinosaurs (and the other extinct animals of the Mesozoic Era) as plausible, real animals that engage in such complicated behaviours such as play, courtship, and the expression of curiosity.
While it is reasonable to think that the predominant purpose of palaeontological art is to display the latest knowledge about extinct animals, it can also serve as an arena for the proposal of new hypotheses, rather than the repetitive drawing of proven theories. In the history of palaeontology, out-of-the-norm images have been crucial in popularizing new ideas about the appearances and behaviours of extinct animals.
While we are well aware that some of our reconstructions will probably be falsified, some may actually "hit the spot," or may even look modest when compared to new fossil discoveries. Only time will tell!
Carnotaurus and Other Arm-Waggling Abelisaurs
Perhaps owing to its "bull-like" horns, Carnotaurus has become one of the more popular predatory dinosaurs in public knowledge. A member of an unique lineage of mostly Southern Hemisphere predators known as abelisaurids, Carnotaurus had a short, deep skull, heavy-set limb bones and very short arms. Although Carnotaurus is known from reasonably complete remains, almost every feature of this animal's body is surrounded by a cloud of theories and debates. Visible yet frustratingly unknown, Carnotaurus is the perfect palaeontological enigma.
This reconstruction was conceived as we tackled of the more interesting anatomical details of Carnotaurus, namely, its comically stunted hands. Although short dinosaur arms immediately remind one of Tyrannosaurus, Carnotaurus and other abelisaurids independently evolved a wholly different and even stranger set of arms, which still bore a full set of four fingers. The upper arm bones (or humeri) were long and straight while the lower arm bones were bizarrely short. The head of the humerus was rounded and ball-like, a feature indicating that substantial motion was possible at the shoulder joint. It seems that Carnotaurus and kin could stick their arms out sideways in a manner completely unlike that of other large predatory dinosaurs.
What was the reason for this arrangement, and why was it maintained across abelisaurids rather than fading away? Perhaps the baby arms still had a function, albeit a social one. Palaeontologists Phil Senter and J. M. Parrish suggested exactly this, proposing that Carnotaurus and its relatives most likely waved their arms and hands around when displaying to mates or rivals.17 We have to note that we came up this idea independently of that study, and only learnt about its existence after creating the artwork you see here. It's difficult to think of a better role for such weird structures.
Here, you can see a bull Carnotaurus and a related form, Majungasaurus, in full display, flashing brightly-colored arms and facial wattles to potential mates, or rivals. Seen head on, Carnotaurus looks more like a science-fiction creature rather than a dinosaur, yet it must be remembered that the sideways-facing depictions we are accustomed to are artifacts of scientific illustration, laid out for maximum visibility and clarity. Real-life animals would have been more complex, more three-dimensional.
Elasmosaurus in a Neck-Swinging Contest
Even if, one day, we had access to perfectly preserved fossils, a vital aspect of animal life would still elude our grasp. Behaviour is almost entirely lost in the fossil record. Imagine the richness and strange wonder of animal life today. The eerie, ululating songs of whales, the elaborate middens of bowerbirds and the surreal spectacle of a peacock’s display could never be deduced from inanimate remains.
Likewise, some of the most spectacular sights of the past will never be seen, or even guessed. In this painting, we have imagined one such piece of behaviour, in this case as applied to elasmosaurs, long necked marine reptiles that lived during the Cretaceous period. Although they feature in many books about dinosaurs, elasmosaurs were not members of the dinosaur family. Instead, they belonged to a distinct lineage of marine reptiles known as plesiosaurs.
This particular group of male elasmosaurs are out in the open sea, trying to see who is the toughest by lunging up from the depths and waving their necks. While old depictions mistakenly portrayed elasmosaurs as holding their necks swan-like above the water surface, these animals actually had very dense bones and heavy necks that could probably not be lifted out of the water when the animal was in its standard, horizontal pose.16 Accordingly, the stunt seen here would have been very difficult and energy-demanding, and could not be sustained for more than a few seconds. What better way is there for males to prove their strength than through rigorous, energy-intensive bouts of a ridiculously pointless activity? No record of such behaviour could possibly exist – it is wholly and unashamedly speculative – and yet things equally spectacular must have happened throughout the history of life.
A Giant Centipede Snatches an Anurognathid
Pterosaurs are everybody's favorite prehistoric flyers. Anurognathus was a member of an extraordinary group of pterosaurs known as anurognathids. Members of this group were characterized by extremely small size, short, broad wings and wide, frog-like mouths. They are further unusual in possessing short tails, an independently-evolved feature elsewhere seen only in the larger, more "advanced" pterosaurs called pterodactyloids. Judging from their wing and skull shape, anurognathids are thought to have lived like today's insect-eating bats.
Small-bodied animals like bats and anurognathids are rarely preserved in the fossil record. Although only several anurognathid specimens are known to science, there may have been hundreds, even thousands, of different anurognathid species living in the lost forests, caves and islands of the past. These animals must have lived in a world of danger, where they were vulnerable to predation, not just from dinosaurs, birds and other pterosaurs, but also from smaller animals like mammals, insects, spiders and centipedes.
Our illustration depicts the death of an anurognathid at the formidable, jaw-like maxillipeds of a large scolopendrid centipede. Centipedes have a poor fossil record, but scolopendrids are known from the Cretaceous: in fact, some Cretaceous centipedes are virtually indistinguishable from modern ones. It is wholly plausible that large scolopendrids were snatching small, flying animals during Mesozoic times, just as they do today.18
Allosaurus fragilis and Camptosaurus dispar
Palaeontology aims to obtain a clear, natural view of the past, but gratuitous acts of predation and vicious monsters are an undeniable factor in attracting people to the study of dinosaurs. The tradition of palaeoart is full of such epic battles, almost as canonical as the clash of heroes in classical mythology. No children's book is complete without scenes of Tyrannosaurus attacking Triceratops, matched in miniature by a Velociraptor locked in mortal combat with a Protoceratops, and so on.
While predation is indeed a vital (and violent) fact of nature, not all predator-prey encounters end in cinematic bloody struggles. More often than not, hunters give up on chasing their quarry. Predators regularly ignore animals that won't be worth the energy to pursue them, and herbivores may cautiously approach meat-eaters while seeking common resources such as water. Curiosity, fear, intimidation and exhaustion make predator-prey rel
ationships far more complicated than we typically picture them to be.
In this scene, set in the Late Jurassic, a herbivorous Camptosaurus is seen approaching a resting Allosaurus in what appears to be a curious social gesture. While Allosaurus was certainly a regular predator of Camptosaurus, this encounter seems to be a peaceful exception to the norm. In today's ecosystems, predatory big cats and herbivores have also been observed interacting in similarly non-violent ways.
Tenontosaurus tilletti Takes a Stroll
Like mythical figures cast into tragic roles, some dinosaurs suffer terrible fates in palaeoart, experiencing the same deaths over and over again. Tenontosaurus - a horse-sized member of the same group as Iguanodon that lived in North America during the Early Cretaceous-was one such dinosaur. Because its remains were found in association with the meat-eating Deinonychus, scientists have argued that Tenontosaurus was a frequent prey of the vicious, bird-like predators.19
While this assumption is possibly correct, it has become a cliché in fact, it is almost impossible to find a reconstruction of Tenontosaurus where it isn't being viciously torn apart by a pack of Deinonychus. Relegated to the role of "stock fodder," many unique features of Tenontosaurus, such as its unusually long tail and interesting position within the iguanodontian family tree, have been mostly overlooked by the general audience.
In real-world ecosystems, predators are far less common than their quarry. It is thus absolutely likely that Tenontosaurus spent most of its time feeding and resting, not fending off Deinonychus attacks. To illustrate this point, we depict Tenontosaurus happily walking along, without a single Deinonychus in sight. This surely happened on a regular basis.
Hypsilophodon foxii Eating a Millipede
Much like wildlife art, prehistoric art has unconsciously cast roles for animals and their behaviour. Predators are always on the hunt, giants are always seen in majestic repose, while small herbivores, depicted as meek and innocent, are either shown grazing or in hurried flight from some terrible hunter.
With small, herbivorous dinosaurs, this type-casting has a risk of falling short of reality. To begin with, herbivorous animals are not "innocent" of occasional predatory acts. Modern herbivores eat, or will at least try to eat, a wide variety of things. Deer and sheep have been observed chewing the heads and legs off seabirds,20, squirrels often eat bird hatchlings for an extra helping of protein, and it turns out that even cattle will eat bird's eggs and nestlings if they find them.21 Moreover, one can only draw general connections between anatomy and dietary adaptations in fossil animals. There is no doubt many of these are correct assumptions but, then again, we may be overlooking some fascinating possibilities.
Here, we see Hypsilophodon, generally known as the ultimate small dinosaurian herbivore. This particular Hypsilophodon is unaware of future speculations on its remains, and is happily supplementing its plant diet with small animals. However, this snack will give it a nasty surprise-millipedes often cover their bodies with foul-tasting chemicals.
Citipati osmolskae and Stegosaurus stenops : Giant Penises and Violent, Confused Sexuality
Reproduction is one of the most important, if not the most important driving force in evolution. Sexual display and sexual attraction have resulted in the peacock’s dazzling tail feathers, the musical songs of birds, and the various horns, crests and frills that adorn animals of every size and shape. Socio-sexual display behaviours may even have contributed to the evolution of language and human intelligence.
With reproductive acts playing such a vital role in the evolution of life, it is surprising that the issue has not received more attention in palaeoart. If we assume that the sex habits of Mesozoic dinosaurs were similar to those of their modern descendants (the birds), then a dazzling, even bizarre, range of possibilities reveal themselves.
Among modern birds, ducks lead notoriously rough sex lives, involving aggressive mobbing and gang-rape. In some duck lineages, female vaginal canals and male penises have entered a bizarre sexual “arms race”,22 one of the results being that the males of some species have penises that can sometimes be as long as the head, neck and body combined.23,24 We have imagined a similar scenario in this particular reconstruction of Citipati, an oviraptorosaurian maniraptoran theropod from the Late Cretaceous. This Citipati has expired after a particularly rough season of mating, but at least its genes have been safely passed on to the next generation.
Another possibility we have considered is interspecies mating. When sexually aroused, excited or unable to find available members of their own kind, animals mate with members of other species with surprising regularity. Incidents of this sort are probably more common than generally realised, and there is evidence from the modern world that they occur increasingly during times of environmental stress or as populations become reduced or brought together due to changing conditions. When the species concerned are closely related, hybrid babies can be the result: numerous such cases are known from the modern world. However, matings between distantly-related species also occur in the wild. These seem to serve no function other than to relieve the frustration or boredom of at least one of the participants. As unsettling as they may seem, such acts may even be considered to be part of the animal's play behavior. In one especially celebrated recent case, an apparently frustrated Antarctic fur seal (Arctocephalus gazella) copulated with a King penguin (Aptenodytes patagonicus).25 It is well known that modern elephants are prone to a sort of seasonal sexual madness when they go through a phase of heightened sexual aggression termed musth. While in musth, elephants have been observed trying to forcefully mate with members of different species, such as rhinos.
We combined ideas about interspecies mating events with both the possibility of oversized sexual organs and of a seasonal 'sexual madness'. The result: a bull Stegosaurus trying to mount an innocent Haplocanthosaurus. In order to mate with females bearing a phalanx of dangerous spines and armored plates, we imagined male stegosaurs to have developed some of the largest and most frighteningly dextrous penises of the dinosaur world.
Stegosaurus trying to mount an innocent Haplocanthosaurus.
Stegosaurus stenops skeletal
Glorious Mud— Camarasaurus grandis
Of all the kinds of behaviour that animals can engage in, it's probably play that been depicted the most rarely. Plenty of pieces of art show dinosaurs running, jumping, attacking or defending themselves from other dinosaurs, and some even show dinosaurs mating and defecating, but almost none show them playing. Celebrated artist Luis Rey might be unique, then, in having published a scene where dromaeosaurids and troodontids are shown playfully sliding down a snowy slope in a Late Cretaceous winter,26 a speculation inspired by behaviour seen in living magpies and crows. Other than Rey’s work, no artist seems to have thought of dinosaurs in play. This lack of interest is no doubt maintained through the idea that only “smart” animals such as birds and mammals engage in play behaviour.
Interestingly enough, it is now known that play behaviour is not limited to birds and mammals. Monitor lizards, turtles, crocodiles and even fish and cephalopods have been reported to engage in behaviours that do not seem to serve any other purpose than simply having fun.27,28 If all these animals could play, we are certain that Mesozoic dinosaurs could, too. Here a sub-adult Camarasaurus is shown enjoying the soothing feeling and antiparasitic properties of a good roll in the mud.
Camarasaurus was a large sauropod dinosaur from the Late Jurassic of North America. Well-known for its boxy skull and stout proportions, it is considered by some experts to be among the ugliest of all sauropods.
Sleepy Stan— Tyrannosaurus rex
If popular depictions are to be believed, Tyrannosaurus spent most of its life charging at hapless victims while roaring at the top of its lungs. This image, immortalized by movie and comic book depictions, is false on both fronts. To begin with, predators almost never roar or scream while attacking. Stealt
h is vital in nature. A hunter like Tyrannosaurus must have waited silently, and kept as quiet as possible as it hunted. Even the slightest noise could have scared its prey away. The only things its victims would have heard would be the crashing of the vegetation as the giant predator charged towards them.
Secondly, as we saw before with Allosaurus, hunts take up only a minor part of a predator's lifetime. Most hunting animals spend long days resting, either in order to conserve energy, or while digesting the food acquired from a fresh kill. Like most warm-blooded modern predators, the fearsome T. rex may have spent most of its time asleep.
Here, we portrayed a large specimen of Tyrannosaurus with an unusually large head, also known as "Stan." In this picture, Stan has just finished a big meal and is sleeping soundly as he digests his fill. A Tyrannosaurus like Stan was probably capable of eating tonnes of flesh in a single hunt, and would have eaten relatively infrequently. It could have taken Stan several days to sleep off the exhaustion and torpor of a meal.
The sleeping poses of tyrannosaurs have also been an interesting area of speculation. Resting poses have been depicted for tyrannosaurs before: Lawrence Lambe imagined tyrannosaurs lying flat on their bellies, partly due to their boot-shaped pubic bones.29 Combine this with the idea that giant animals cannot lie on their sides due to their excessive weight and an artistic meme was born whereby tyrannosaurs were never shown sleeping on their sides. As demonstrated by elephants, however, even tyrannosaur-sized animals can and do recline on their sides and sleep deeply.30 How, when and where other big dinosaurs slept remains a fascinating area of speculation.
