This article is an extract from a longer article published in the August 1997 edition of The Magpie. Steve Brady discusses Steven Spielberg’s blockbuster films and their probably biological accuracy.
Spielberg’s dinosaurs mostly look plausible enough. Though the Tyrannosaurus
rex varies in size from scene to scene if you watch closely! At one point it
treads on a hapless human whose scrunched cadaver then sticks to its foot like
a bit of chewing gum to a shoe, necessitating a foot over six feet long, twice
its actual size, and twice the size of its footprint seen earlier in the film.
The stegosaurs seem a bit on the large size to me. Also an argument has broken
out amongst palaeontologists as to whether Stegosaurus
could physically swing its spiked tail about with quite the dexterity
Spielberg’s one shows, though it doesn’t look too implausible to me as a
layman. But there is less of the ‘demonisation’ of
dinosaurs noticeable in
Spielberg has followed what is now the general consensus among palaeontologists in depicting his dinosaurs, even more than
in
That dinosaurs should have been active - and evidence of fossil nest sites indicates in at least some important respects behaved - like birds is not surprising since it is also now generally believed that birds are dinosaurs. They are thought to be descended from coelurosaurs, little dinosaurs in the same group, the theropods, as the big meat-eaters like T. rex. Spielberg’s depiction of dinosaurian biology, with pair bonding and parental care of offspring resembling that in most modern birds, is entirely credible. Indeed there is fossil evidence that dinosaurs guarded and (by piling on and taking off rotting vegetation rather than sitting on, for obvious reasons!) regulated the incubation temperature of their eggs as modern crocodilians and birds do. And that they also fed and cared for their hatchlings like today’s birds. Some fossil baby dinosaurs have largely cartilaginous skeletons making walking impossible, like the altricial, nest-bound, babies of such birds as blackbirds and sparrows. Like which they clearly spent some time helpless in a nest fed and protected by their parents. Others hatched with largely ossified skeletons and could run about soon afterwards, precocial like hen chicks. The economics of nest and baby care tends to demand the participation of both parents, as in birds, which in turn implies pair bonding.
Spielberg’s depiction of a pair of Tyrannosaurus rex guarding their nest and jointly defending a territory much in the manner of predatory birds such as eagles is thus quite believable. But fossil dinosaur nests contain several eggs or babies, like those of most birds, not the solitary baby with which Spielberg endows his tyrannosaur and stegosaur families. Laying clutches of eggs is an advantage if you are a big animal since it enables you to breed quite rapidly if opportunity arises. One problem with conserving big mammals like rhinos, whales etc. is that they have only one baby and that only after a long gestation period, so their population takes a long time to recover even if protected. The evidence is that big dinosaurs could produce several babies in the time it takes a rhino or an elephant to have one, a useful advantage.
It also seems more likely that tyrannosaur hatchlings were helpless and altricial like predatory bird chicks such as those of hawks, eagles, owls etc. rather than active and precocial as in the film. This is because precocial chicks are usually found in species such as hens and pheasants which eat food such as seeds and insects pecked up off the ground and easily accessible to very young chicks. Species where food needs catching or has to be flown to get tend to keep their chicks nestbound until they can fly, since they cannot accompany the adults feeding nor feed themselves. Fossil evidence seems to indicate that dinosaur hatchlings operated by similar rules, though as far as I know no nests or small young of any of the big theropods, of which T. rex is one, have been found to prove the point. Possibly if a dinosaur hatchling was removed from the nest its parents would search for it,at least if, as in the film, it was emitting distress cries. Among birds these are restricted to active precocial chicks, which can wander off and get lost. Helpless altricial ones can only fall from the nest whereupon they are as good as dead anyway. But an altricial dinosaur baby can’t fall out of its nest - we can be pretty confident that 7-tonne theropods did not nest up trees, not even giant redwoods! If it is outside its nest it has presumably been siezed by a predator, so being able to emit a judicious alarm call to bring Mummy and Daddy to the rescue would be entirely reasonable.
But even Spielberg’s own expert advisor Dr. Horner admits his T.rexes’ subsequent revenge attack on the "kidnappers
of their baby" by kicking their vehicle over a cliff is wholly
implausible. Very few mammals, even, think things through to that extent. And,
whilst dinosaurs are no longer regarded as quite as intellectually challenged
as they once were, their brain size and structure gives little hint of immense
brainpower. Tyrannosaurus rex was probably as bright as the average chicken. Or
eagle, which is no more intellectually endowed but sounds more impressive!
Albeit possibly a very old chicken with a lot of remembered behaviour
patterns. Analysis of bone growth patterns indicates that dinosaurs, like
modern birds, had longer life spans in relation to body weight than mammals. A
canary lives over twice as long as a mouse of the same size, and a tyrannosaur
apparently could live for well over 100 years, a big sauropod
("Brontosaurus" type beast) twice that. An old dinosaur would
probably have seen and survived nearly everything that could happen to it and
could as birds do simply repeat from memory what it did last time - deep
thought would seldom be called for anyway. Certainly few if any dinosaurs would
have had the problem-solving ability of a brighter bird such as a crow or a
parrot (the small, very latest Cretaceous troodonts
might have come near that) so the cunning, handle-twisting, door-opening
‘raptors of
Also rather absurd biologically is the curious interest shown in both films by big carnivorous dinosaurs in small, scrawny human adults, let alone children, as a food source. However useful it might be for dramatic purposes, for a 7-tonne tyrannosaur to spend any time at all chasing a 70 kg human is just a waste of the dinosaur’s effort! Remember that any animal must "show a profit" from feeding - it must get more energy out of its food than it puts in to getting it, or it will simply starve. For a tyrannosaur or a dromaeosaur pack to go chasing humans is not worth it for them. A single dromaeosaur ‘raptor might snap up a human if one was going begging, but a whole pack would not spend ages besieging a couple of people in a building, chasing them over rooftops etc. as they do in the film. An instinctive behavioural program saying "not worth chasing, let it go and see if we can find a nice medium sized (about 5 ton!) dinosaur instead" would kick in pretty quickly however lustily the heroine screamed from the rafters! ‘Raptors, incidentally, had skeletons showing they were fast plains runners, no more able to climb and jump about the roofbeams than a racehorse, or the combination of cheetah and wolf which would be their mammal equivalent. While a T. rex would no more hunt humans than a lion hunts mice, and for the same reason - it’s not worth the effort: the return doesn’t justify the expenditure. Not that the predator works that out - natural selection gives it instincts such that piffling little creatures don’t stimulate its hunting appetite, unless it is starving. It makes for boring films, but leave a tyrannosaur alone and it would probably leave you alone! Unless you got close to its nest, where you’re just the right size to be a little egg-stealing beastie like Oviraptor, for which T.rex would doubtless have evolved a suitably nasty instinctive reception!
Equally peculiar is the ravening hunger for human flesh attributed by Spielberg to the smallest, as well as the largest, carnivorous dinosaurs. Small chicken-sized coelurosaurs, now thought to be ancestral to modern birds, are depicted swarming antlike over humans and devouring them despite their victims strangling and squashing a few in the process. This is absurd from basic principles of evolutionary biology. The only animals which attack much larger prey like ants regardless of losses sustained are eusocial insects like ants. They do it because the colony, not the sterile worker individual, is the passer on of genes and the unit on which natural selection acts. If the colony loses 0.2 grams of worker to get 20 grams of prey it may make a net gain in colony fitness justifying that (and ants, such as army ants, that do regularly swarm over much larger prey tend to have queens that produce vast numbers of eggs to replace squashed workers quickly!) But a non-social vertebrate that regularly gets itself killed so that even related individuals will get more food will kill off the genes for such suicidal altruism with itself. Only if the rest of the pack are very closely related would such behaviour occur. That would only happen if coelurosaurs, like naked mole-rats, were as eusocial as ants, complete with queen and sterile workers. Mole rats evolved this because of their very odd lifestyle (in fact evolutionary biologists predicted the naked mole-rat’s social structure form its life-style before either was discovered in the field!). Coelurosaurs almost certainly were not eusocial and therefore could not in principle have evolved the behaviour Spielberg depicts (and which his advisor Dr. Horner admits is wrong). In practice we know what these little dinosaurs did eat from fossils. The exact, if remarkably obscure, species named in Lost World, Procompsognathus triassicus, is known only from one badly-preserved skeleton, but it is very similar to the later, and possibly its direct descendant, genus Compsognathus. Fossils of these have been found in the Solnhofen lithographic limestones with gut contents fossilised too, from which we know they ate lizards and insects (in fact the Jurassic lizard Bavarisaurus is known only from a half-digested skeleton found inside a fossil Compsognathus!) Spielberg’s killer coelurosaurs are as ridiculous as depicting flocks of homicidal hens rampaging the modern Bucks countryside, swarming over hapless humans and pecking them to death!