The purpose in writing this short missive is to issue a rejoinder to a recent article George Dvorsky has written on a subject near to my heart: dinosaurs. I have long, long been fascinated by dinosaurs and cannot remember a time when I wasn’t. In particular the twists and turns of their evolution is an obsession of mine, even more so given the modern view that they didn’t really die out all those millions of years ago but in fact went on and now live amongst us as the birds. Birds are an enormously successful class of vertebrate animal and it’s perhaps not a hugely fanciful vision to consider that the age of dinosaurs actually still continues to date because of them.
In George’s article, Do Advanced Dinosaurs Rule Other Planets? Uh No, he seems to characterize the dinosaur world like something from King Kong; all about enormous carnivores such as Spinosaurus and Tyrannosaurus. Instead of this fantasy ecosystem, dinosaur studies show that they had a very large range of sizes and body forms, just as diverse as the flourishing of mammal types that followed the end of the Cretaceous.
Dinosaurs evolved into a multiplicity of body forms rather than a restricted selection as George's article implies. Dinosaur types were of many different types and evolved in a broad range of habitats. It would be useful to at least summarize some of this radically differing morphology to make the point – indeed the striking and perhaps even bizarre diversity of dinosaurs is one of the things that makes them so interesting.
Dinosaurs quickly diverged from the basic two legged type during the early to mid Triassic period (say 225 million years ago) into differing forms. Many people will be familiar with the large lumbering plant eaters often referred to (incorrectly) as brontosaurs but there were types of this class of dinosaur that went about at least some of the time on two legs. Some of these animals, known as sauropods, such as Ampelosaurus sported strange spikes and plates on their bodies to provide at least some protection from predators. The sauropods ranged in size from modest sized creatures the size of a family car to the largest land living animals ever, well over twice the length of a double decker bus.
The meat eating dinosaurs also greatly ranged in size from the very smallest, about the size of a duck, to Spinosaurus, itself about the length of a double decker bus. Some of them it is now believed had feathers including perhaps Tyrannosaurus. It is also generally considered that birds evolved from species within the meat eating dinosaurs and that birds themselves are a type of dinosaur. The diversity of bird types can only add to the richness of the dinosaurs if that is correct.
Some of the meat eating dinosaurs, such as Spinosaurus itself, had large spines on their backs, possibly to help regulate body temperature. A very successful group of the meat eaters were around the size of ostriches, emus or smaller and in this group we find the well known Velociraptor of Jurassic Park fame. It has been suggested they hunted in packs and had sickle shaped claws on their feet to attack their prey with. There is also within the meat eaters the gigantic and rather odd Therizinosaurus with its enormous claws.
Many people will be familiar with the Stegosaurus and its large plates on its back but the family which it belonged to had several variations on this theme. There were also low lying ankylosaurs with armoured plates lying on their backs and a hefty club on the end of the tail to thwack an attacker. The horned dinosaurs are also very familiar and again a fascinating variety on the basic design can be seen with different shapes of horns and crests, for example Pentaceratops. Some of these were possibly two legged such as Leptoceratops.
Some of the greatest diversity can be seen in what are commonly referred to as the duck billed which arose towards the end of the Cretaceous period. Some had crests, horns or spines on their head and it is possible these developed to attract a mate. The range of sizes from the modest to the enormous is yet again a feature as well as the astonishing variation in species and sub-species. It is known from fossils of nesting sites that some of these cared for their young after they were hatched. There were also the similar iguanodonts and hypsilophodonts which add further to the diversity. A sister family of dinosaurs to these is the dome headed species, the pachycephalosaurs.
This enormously concise overview of the dinosaurian must show how varied they were and are. Their morphology was not shaped just by predatory pressures – much of the variety may also be attributed to sexual selection. Even during the Jurassic and Cretaceous, birds had also diversified into a number of forms. If George is going to characterize the pressures on dinosaur evolution as being either Flight or Fight, it’s difficult to see, applying this analysis, how mammalian evolution (including primate) has been any different.
Not all authorities accept categorise Tyrannosaurus and Spinosaurus as super-predators, as described in the article. There has long been discussion about whether Tyrannosaurus and its cousin species actively hunted – many dinosaur experts take the view that instead it scavenged on dead dinosaurs already brought down by smaller, more active hunters. Spinosaurus may also have had a fish based diet based on the shape of its jaws, although it may have also scavenged as well like Tyrannosaurus. It is not clear then that these two types can definitely be said to be aggressively preying on other dinosaur types in the way George suggests.
The historical, popular view of dinosaurs is of enormous, lumbering beasts with brains the size of walnuts. It is fair to say that many of the dinosaurs did not have large brains either absolutely or proportionately to their body size. That by itself of course did not stop them becoming widely successful animals; just as in more modern periods intelligence was not a prerequisite to success. The vast majority of living organisms do not show any great degree of intelligence and yet are very successful in evolutionary terms.
Yet there were some dinosaurs that simply do not fit this view. In particular we may examine the small meat eating dinosaurs, the coelurosauria, and uncover some types that proportionately had large brains for their body size. Attention has previously been focused on the species Troodon which had a brain size that was in a similar proportion to its body size as birds, which is rather more impressive than many other types of dinosaur.
This may not be a remarkably large amount of intelligence compared to a mammalian population but the point is that it is misleading to imply that all dinosaurs were as dumb as each other and therefore very dumb indeed. Troodon and its cousins evolved towards the end of the Mesozoic (that is the age of dinosaurs as it is generally considered) so it is possible to suggest an evolution towards greater brain size.
Speculation has been made that if all non-bird dinosaurs had not been wiped out at the end of the Cretaceous then Troodon or a similar species may have ultimately evolved into an intelligent, bipedal animal which would have been a dinosaur equivalent to a human – the “dinosauroid” as it is called. This is of course guess work – but tantalising none the less. Troodon had a certain degree of depth perception as its eyes were slightly forward facing and it also had forelimbs with semi-manipulative fingers; factors (along with brain size) which to the imaginative mind might suggest it was on a track of evolution leading to Dinosauria sapiens. There is a rather wonderful article that suggests dinosaur evolution leading to intelligence would take a much less anthropomorphic route and lead to a more dinosaur or avian looking intelligent creature. Although perhaps more plausible this is still ultimately speculation.
It is just as much speculation to suggest that if the non-bird dinosaurs had not been wiped out then there is no chance intelligence would have emerged amongst the continuing dinosaur population. There is no way to know. This is just negative speculation as much as the dinosauroid is positive speculation.
It must also be borne in mind that drawing conclusions from the fossil record, as palaeontology does, is fraught with difficulty and an area where caution must be applied. The fossil record is a small proportion of all the living organisms that lived at that time. We only find fossils of things that were lucky enough to be fossilized. It is very likely that a number of prehistoric species will never be available to us as they failed to have any fossilized remains. If, for argument’s sake, a race of sapient dinosaurs had evolved somehow during the Mesozoic, we might never know about it if they only survived for a short period and failed to leave remains in the fossil record before becoming extinct.
The second limb of George’s argument suggests that human intelligence had enough “elbow room” to evolve in the absence of super-predators such as the large carnivorous dinosaurs. Whilst allowing some role for the predation of sabre-toothed tigers George suggests that predatory pressures were not as high as they were during the Mesozoic and this enabled human intelligence some valuable time in which to emerge.
Some anthropologists take the view that in fact the early ancestors of humans were regularly preyed on and this was a pervasive evolutionary pressure on our evolution. Leopards are the prime suspects here although other potential offenders are crocodiles and hyenas. Early humans were fairly small and somewhat defenceless creatures, having no natural armour or efficient weapons and being poor at running. The fossil record suggests predation rates on early human ancestors ran at about six to ten per cent, similar to that on gazelles and ground dwelling monkeys on the African savannah at present. (see http://news.wustl.edu/news/Pages/4582.aspx)
All diurnal primates (including humans) live in permanent social groups and this is generally taken to be as a primary defence against predators. If you are a defenceless primate, like an early human ancestor, living in a group is one of the few ways you have to combat predators such as a leopard. This theory suggests that social existence, language and human cooperation may have evolved in response to predation by the super-predators of our original habitat. Many of those factors that we think of as making us human, including perhaps intelligence itself, may have arisen to ensure we stayed alive in the face of some very active, cunning and powerful carnivores that wanted to eat us.
In contrast to the doubtful nature of Tyrannosaurus and Spinosaurus feeding habitats, it is clear that leopards and other hunters ate a large amount of our ancestors. Much of our nature is, in this theory, attributable to this evolutionary background as being the hunted rather than, as previously thought, the hunter.
So, my hope is this brief article illustrates some counter-points to the propositions outlined in George’s article and I would be pleased to read any comments about all of this in the hope of further illumination and enlightenment.
Please do read George’s site at www.sentientdevelopments.com and follow him on twitter at@dvorsky to be both informed and enlightened on many subjects and also entertained. Being in contact with George in this way has made me aware of many new and fascinating subjects and I am very grateful to him.
