Anthroposaurus
Did a Dinosaur Have the Attributes that Let Humans Evolve?
Abstract
Contents Updated: Wednesday, December 15, 1999
"It is tempting to hope that the most original achievements of the mind are also the most recent."
…but a Thinking Dinosaur
Dr Brian Stableford is a biology graduate and lecturer in sociology at the University of Reading, England, but is better known as a writer of science fiction. He writes in The Science in Science Fiction:
Certain difficulties stand in the way of the ever popular lizard men who figure so frequently as science fictional villains. Reptiles, having no internal temperature control, are rather limited in the amount of brain activity they can indulge in.
That may be true of lizard men but not of dinosaur-men or dinosauroids, to use the word coined by Dale Russell of the National Museum of Natural Sciences in Ottawa, Canada. Dinosauroids are intelligent creatures evolved from dinosaurs, and because dinosaurs had a physiology superior to lizards and in many ways superior to mammals, Dr Stableford’s complaint does not hold water. Our anthroposaur and Russell’s dinosauroid are Dr Stableford’s lizard-men precisely because they are all lizard-men could be.
Anthroposaur is the better term: it is more descriptive than Russell’s word, and Russell’s conception of dinosaur evolution was vastly different from that considered here. Russell imagined how dinosaurs might have evolved had they survived the Cretaceous-Tertiary (K-T) extinction and remained alive until today. They didn’t survive, so they couldn’t evolve. But the anthroposaurs could have evolved before the K-T catastrophe, as we shall see.
Stableford informally lists the characteristics of an intelligent organism: If human beings did not walk upright, freeing their forelimbs to develop hands instead of paws, they could not have developed the kind of intelligence they have. Similarly intelligent beings must be sociable, because intelligence arises out of the need to communicate. The fact that most mammals and birds show a degree of intelligence not seen in reptiles is connected with the fact that they generally have more complicated social relationships, especially in connection with the rearing of young. The more sociable animals are, and the more able they are to interfere with and transform their environment, the more intelligent they become.
Stableford’s characteristics tally respectably with those deduced from our study of mankind’s emergence.
The ones which we have some chance of assessing rationally 65 million years after the death of the dinosaurs other than warm-bloodedness, are: intelligent terrestrial animals are bipedal, have an erect stance; are equipped with grasping hands having sensitive fingers and opposable thumbs; are equipped with binocular vision; own a large brain; are subject to social and parental guidance in childhood; are able to speak; are aggressive.
How do the dinosaurs measure up?
Bipedal
From what Bakker and Ostrom discovered during the 1970s, dinosaurs offer remarkable possibilities for the development of intelligence. We have seen that dinosaurs fulfilled the requirement of bipedalism early on—the reason for their supremacy was their upright, bipedal stance. Bipedalism gave dinosaurs a head start on mammals in the race for intelligence because it was the very basis of their evolutionary emergence. Like the hominids, having discovered that they could run on their hind legs, they must eventually have realized that their forelimbs were freed for the manipulation of objects.
Manipulative hands
What, then, of grasping hands? To be of maximum use this means that one of the digits, the thumb, should be opposed enabling its tip to touch the tip of the other digits. Is there evidence that the dinosaurs were able to grasp things? The answer is that opposed digits were very common in dinosaurs. Even the Tyrannosaurids and other large carnivores had an opposed toe rather like perching birds, but T—rex’s forelimbs, we noted, had degenerated into crutches to help it get out of bed.
The feathered dinosaur, the archaeopteryx, certainly had grasping hands, as did its near relatives the coelurosaurs, and surely used them for grasping insects and climbing trees. A related but later dinosaur that seemed to have evolved a high degree of coordination of hands and arms was the deinonychus. Its “hands [were] better adapted for grasping and holding than any other dinosaur” (Desmond). Deinonychus had long, grasping hands with wrist joints that rotated so that the hands could turn towards each other enabling the animal to grasp its prey in both hands. Wilford’s comment is that “only humans and certain other mammals can do this”.
The Late Cretaceous, the period we are chiefly interested in, was full of examples. Some descendants of deinonychus formed a whole group called the dromaeosaurs all of which had opposable fingers and were obviously capable of a high degree of coordination.
One of the descendants of deinonychus was a dinosaur discovered by Dale Russell called the stenonychosaurus. This animal had manipulating fingers, but also had a complex of advanced features, including binocular vision, that make it rather special. Plainly some dinosaurs combined a bipedal gait with sensitive, manipulative hands.
Binocular vision
Binocular vision is, you will recall, the ability to direct both eyes simultaneously at an object. In considering the evolution of man it was coupled with manipulating hands in early primates and is considered basic to the development of intelligence. The importance of this ability for the growth of the brain is that it allows a better judgment of distance, valuable for leaping and throwing. It stimulates three dimensional thinking. The evolution of manufacturing levels of intelligence requires the development of hand and eye coordination. Without the ability to see stereoscopically, it seems unlikely that it would be possible to think stereoscopically and thereby to erect structures in the mind prior to building them on the ground. Many creatures alive today besides man have binocular vision, birds of prey like the owl, for instance, but they do not often combine it with grasping hands.
Binocular vision in tyrannosaurus was facilitated by the snout being very narrow so as not to impair its line of sight. But tyrannosaurus, as we have seen, had atrophied arms and the real evolutionary advantage comes when the binocular vision is combined with skillful hands. The stenonychosaurus had binocular vision combined with manipulative hands and fingers. Its eyes were large and well developed like the eyes of the ostrich—which has the largest eyes of any terrestrial creature alive today. This in itself is an interesting feature because it suggests that these dinosaurs were nocturnal or that they had evolved not long before from a nocturnal form.
Two points from this. First, it is further evidence, should anyone need convincing, that the dinosaurs were warm-blooded, because cold-blooded animals must be inactive at night. Second, what would they be hunting at night time that needed speed, agility, keen vision and grasping hands? None other than our predecessors, the mammals. “It was not until the Cretaceous that we find signs that the mammals were hounded even into the night. They were terrorized, moreover, by creatures more cunning than themselves,” as Desmond puts it. Yes, the mammals were small, but these dinosaurs were also small by dinosaur standards—stenonychosaurus was only about five feet long including its long tail. Here then is a dinosaur with keen senses, nimble and agile enough to hunt, by night, the supposedly superior mammals!
Brains
Let us turn now to the size of the dinosaurian brain. Carl Sagan writes:
The entire evolutionary record on our planet, particularly the record contained in fossil endocasts, illustrates a progressive tendency toward intelligence.
This is Marsh’s Law—brains grow from generation to generation. But it is not true of cold blooded animals. Whereas a modern cat of the same body size as a sabre toothed tiger of 30 million years ago has twice the brain volume, a modern crocodile has just the same volume of brain matter as an ancestor of comparable size 200 million years ago. The brains of even advanced cold bloods like crocodiles violate Marsh’s law. But Marsh formulated his law from studying dinosaur brains!
The popular idea that the dinosaurs were dim witted, with brains no bigger than a ping pong ball is only partly true. It appertains to the huge sauropods, ceratopsians and some carnosaurs—the dinosaurs well known to the layman. A triceratops’s body weighed 9000 times more than its brain, a hadrosaurus’s body weighed 20,000 times more, and an apatosaurus’s weighed 100,000 times more. But it is not true of many others dinosaurs, the ones noted above with the grasping hands and binocular vision, the smaller, agile coelurosaurs and dromaeosaurs that lived late into the Cretaceous period. Knowing what we do about these, it is not so surprising that they had evolved large brains to coordinate their sophisticated movements and vision.
Deinonychus had the odd but effective habit of standing on one leg while slashing its victim with a vicious talon on the other. Such balancing tricks, even accepting that the creature would have its prey firmly in its grip, required remarkable brain development. The descendants of deinonychus, the family of dromaeosaurs, were agile, skilful predators with large brains. Few good fossils have been found but it has been conjectured that they were more common, and more successful, than the fossil record suggests, their habitats not being conducive to fossilization—just like the apes and hominids, mankind’s ancestors!
The body to brain ratio of the stenonychosaurus was 1000. This doesn’t signal much intelligence compared with a human being whose ratio is about 50, but it is comparable to a living flightless bird like the emu. It is also within a factor of about six of the ratio for a chimpanzee. Yet a bird-mimic dinosaur, the dromiceiomimus, had a brain bigger than an ostrich’s.
Birds, despite the derogatory expression “bird brain”, are remarkably intelligent. They are caring parents and often have a hierarchical social system epitomized by their “pecking order”. Large brained flightless birds such as the ostrich live together in flocks and also had some social organization suggesting that the dromiceiomimus did likewise.
Pterosaurs were flying “dinosaurs”. In modern day birds, the ability to fly has required substantial development of their brains, particularly in the cerebellum region at the back of the brain and the cerebral region at the front of the brain. The cerebellum controls movement and balance while the cerebral region looks after coordination, both plainly important to a flying creature. The fascinating aspect of the pterosaurs was that their brains had developed exactly these features by convergent evolution. Like birds their olfactory sense had atrophied and instead they had well developed optic lobes. The optic lobes had been pushed by the growth of the cerebellum and cerebral regions to the sides and rear of the brain. Exactly the same had occurred in birds!
Even more similarities between the physiology of pterosaurs and birds could be listed but they are not relevant here. Suffice it to say that some pterosaurs were as small as a sparrow and that would be impossible for a cold blooded or a naked warm-blooded creature. A cold blooded vertebrate could hardly have generated the energy needed to fly. External insulation was needed for a warm-blood to maintain its high internal temperature. Pterosaur fossils have been found with clear impressions of fur on them. They must have looked like a cross between a fledgling bird and a bat, and they succeeded in holding their own against the birds for 90 million years until the cataclysm that marked the end of the Cretaceous era. But despite their obvious intelligence and fur coats, bat-like dinosaurs were not principle contenders for the honor of developing any sort of technology.
Parental care
Dale Russell, in a paper in the Canadian Journal Of Earth Sciences in 1972, discussing the bird mimic, dromiceiomimus, suggested that parental care seemed likely in animals with such intelligence and with evidence of a social organization. But even Sagan writing in 1977 thought it unlikely that the dinosaurs “actively protected either eggs or young”. Typical reptiles!
Nile crocodiles are reptilian enough but, we’ve already seen, are caring parents, having quite a sophisticated social and family life:
- the male is territorial
- he courts the female
- she builds a nest
- she lays about 40 eggs
- when the young are ready to hatch they warn mom from the egg using piping sounds audible several yards away
- mom carefully digs them out and carries them tenderly in batches in her jaws to a nursery near the river or swamp
- while the young learn how to live by hunting frogs and fish, the parents dutifully keep watch over them
- after several months they are able to fend for themselves.
If cold blooded crocs are as doting as this why shouldn’t warm blooded dinosaurs have been?
More familiar are birds, which lay eggs and devote an astonishing amount of parental care to them. Bakker tells us that birds are living dinosaurs. If so, dinosaurs must have been just as attentive to their eggs and as indulgent to their hatchlings.
Dinosaur eggs are quite rare. None were found until in midsummer 1923, Roy Chapman Andrews and his team exploring the Gobi desert found nests of dinosaur eggs, some of which contained the fossil embryos of a dinosaur, protoceratops, a precursor of the giant ceratopsians of the Late Cretaceous. Yet eggs have a hard exterior and would be expected to be easily fossilized. When the dinosaur’s ancestors emerged from the swamps, one of the advantages they had over their competitors, the amphibians, was the hard exterior of their eggs. Amphibians laid soft eggs like those of modern frogs and newts. These would be unsuitable for an animal that had ambitions of living on dry land. Amphibians had to have water nearby—not so, the dinosaurs. Their hard eggs enclosed a watery fluid in a sac called the amnion. Within this the embryo developed, feeding on its self-contained food supply in the yolk. Foetuses of mammals including humans are similarly enclosed in a sac of amniotic fluid which bursts shortly before birth.
In summer 1978 in Montana, two fossil hunters found a nest of fifteen fossilized baby dinosaurs each about three feet long. They were not hatchlings because their teeth were worn showing that they had been eating for some time. Further work exposed a whole treasure trove of dinosaurs’ nests, a veritable hadrosaurs’ roost of 300 eggs and over 60 skeletons of dinosaurs of all ages from embryos to adults. The nests, which were about six or seven feet across, were about 20 feet apart leaving sufficient room for the bulky parents to gain access. Some of the nests contained only broken shells, the nestlings presumably having left the nest, but some contained immature skeletons of varying sizes, presumably because the nest had been abandoned for some reason and the young hadrosaurs had starved to death. The physiology of the skeletons confirmed that dinosaur babies grew rapidly from a very small size. The eggs were oval shaped with a maximum dimension of about eight inches, providing enough room for hatchlings only about 15 to 20 inches long. Such small, vulnerable animals, growing rapidly, must have been warm blooded. The remains often included eight feet long juveniles alongside 20 feet long adults suggesting that parents and young stayed together until the young were mature. The ratio of juveniles to adults seems to have been about two to one.
The following year nests of another dinosaur, the hypsilophodont, were found containing up to two dozen eggs, and about fifteen skeletons of juveniles were found nearby. As John Noble Wilford puts it:
dinosaurs … had a sense of family life and community.
Why had baby dinosaurs not been found before? They had! But the experts had classified them as new species of small dinosaurs rather than seeing them as juveniles of species already identified. Furthermore, mental fix had led dinosaur hunters into looking in particular types of strata to make their finds. These were rocks laid down on lowland plains or in shallow bays or estuaries. The Montana dinosaur colonies were on dryer rockier outcrops where the nests were perhaps safer from predators.
Must all dinosaurs have laid eggs?
Not even all modern reptiles lay eggs. Snakes, skinks, some amphibians (salamanders) and even some fish (sharks, guppies and sea horses) keep their eggs within themselves until birth.
- The sea snakes of the Indian Ocean give birth to live young (viviparity). They do not have a placenta like the mammals to nourish the embryo while it is developing, but nevertheless they do keep their eggs within their bodies until they are hatched.
- Rattlesnakes are even more advanced. They retain their eggs and have even dispensed with a hard shell. The embryo not only gets nutriment from a yolk but also by diffusion of sustenance from the mother across the thin outer membrane of the egg, a support system very suggestive of a placenta. At birth the mother continues to look after the young.
- One species of frog, gastrotheca, keeps its young in a pouch until they hatch into tadpoles when they are released into the water, but another species keeps them in its pouch until they emerge as baby frogs.
- A West African toad, nectophrynoides, retains its eggs in its oviduct. When the tadpoles hatch they feed upon particles released from the walls of the oviduct and at the next wet season live baby toads are born, the mother having provided a pseudo pond for them within her oviduct.
- Amazingly, the coelacanth, a fish thought to have been extinct for 70 million years until found again in 1938, gives birth to live young. This creature is believed not to have evolved in any significant way for hundreds of millions of years indicating that creatures had live offspring before the dinosaurs even appeared on earth.
Following a discovery made by an assistant in 1947 in New Mexico, Edwin Holbert found several fossilized skeletons of a small early dinosaur called coelophysis. Coelophysis was an early type of coelurosaurus living at the end of the Triassic period about 210 million years ago. A remarkable graveyard of these specimens was found in New Mexico. Bones were weathering out of a rock stratum in a hillside and some had been recovered by a collector as long ago as 1881. Thus the species had been known for 60 years but previous specimens had been poor: these were excellent. When the site was rediscovered it was agreed to dig away the overlying strata and look at the layer containing the fossils. An amazing lode of coelophysis bones was found, young and old together. The amazing feature of one of them, Colbert noted, was that it seemed to have inside it the bones of a tiny juvenile. Colbert could not accept the obvious inference that the dinosaur gave birth to live young, especially as the pelvic bones seemed too narrow. He deduced that the “baby” was actually the adult’s last meal.
Live birth did occur in ichthyosaurs, the dolphin like dinosaurs. At first, paleontologists, faced with the idea of sea-dinosaurs, thought they must leave the sea to lay their eggs like turtles. But the ichthyosaurs were far too whale like for that to happen. An ichthyosaur would be no more able to crawl up a beach than a porpoise or a killer whale—on land it would be literally stranded. It also seemed odd that no ichthyosaur eggs could ever be found. Even though masses of ichthyosaur fossils were found at Holzmaden in Germany there were no signs of any eggs. And this despite the discovery of fossilized ichthyosaur droppings—called coproliths—that would plainly have been less suitable for fossilization than eggs.
The answer came from our friend, the noted amateur, Bernard Hauff, who owned those productive quarries in Holzmaden and made a name for himself by the skill he put into the delicate process of extracting the imprint from the rock matrix. He conclusively showed that some of the ichthyosaurs had smaller specimens inside them. As we might expect, this triggered off a controversy about the “baby” ichthyosaurs. “They are not unborn babies but part of the larger creature’s last dinner”, was the cry. It is far from unknown for vertebrates, especially fish, to eat their own young. The small specimens inside the body of the larger specimen were always facing forwards, in the direction of motion of the larger fossil. “If the animal were to be born it would have its head to the rear—animals are always born head first”, pronounced the critics. “What’s more, a swimming creature being pursued and finally swallowed by another would be swallowed tail first and would be bound to be “head forward” in the predator’s stomach”.
Hauff countered by showing what the larger ichthyosaurs had had for dinner—mainly a variety of types of swimming shelled molluscs having a lifestyle similar to modern squids.
The experts remained unmoved. Hauff responded by providing the ultimate proof. He had had a slab of rock needing cleaning for a long time but had constantly sidelined it as more promising finds were brought to him. When he did remove the extraneous rock, he was amazed to find that the impression was one of an ichthyosaur in the act of giving birth. The smaller specimen was hanging below the body of the parent yet with its foreparts still evidently within the mother’s body. It is now known that whales give birth in this fashion, tail first, to allow the tail of the foetus to get strong in the stream of water flowing over the mother’s body. The infant whale will dangle thus for four to six weeks, the birth only being completed when the baby is strong enough to swim alongside its mother. Once again the similarity of function in similar environments and lifestyles demonstrates itself. Efficient evolution into a particular ecological niche generates the same solution to problems of adaptation. We shall have reason to remember this when the question of the evolution of intelligence is considered in more detail.
The sauropods like apatosaurus also could have given birth to live young. Tracks of sauropods indicate that they moved about in groups, if not herds. Bakker has found that dinosaur herds were structured such that the young were protected in the middle by a surrounding circle of adults, showing that the young were evidently cared for after birth, viviparous or otherwise. Yet, if they laid eggs, there are several problems to answer. Did the herd stop in one locality while the eggs hatched? If they did, would not such dim witted animals trample all over the eggs before they had time to hatch. If not, how did the young rejoin the herd, which had presumably moved on after the egg laying? Furthermore, eggs cannot be larger than a certain maximum size since beyond that size they would either collapse under their own weight or they would have to be so tough that the hatchling would not be able to crack the shell to emerge. The maximum size is small for such huge dinosaurs as apatosaurus and its relatives, which reached 50 tons or more at maturity. Even if the eggs were three feet across like those of the extinct bird, the aepyornis, the hatchlings would be still likely to be crushed underfoot.
All these problems are answered if the young were carried until they had reached a reasonable level of maturity. At birth they would then have been able to keep up with the wanderings of the herd and avoid the clumsy feet of their elders. They would also have been big enough not to lose heat to their surroundings. Bakker believes the sauropods’ live young weighed as much as 500 pounds at birth, solving most problems, but if they were smaller the problems remained.
Could sauropods have carried their young in pouches rather like a kangaroo? The problem then is what they could have fed on. Kangaroos are mammals with teats to provide nourishing milk. One assumes that we are on safe ground in believing that not even hot blooded dinosaurs had mammalia! Could the young have snuggled into a pouch near to the sauropod’s tail feeding upon the parent’s dung? Since they were too small to avoid rapid heat loss, they would also be kept warm by their mother’s body heat. The large herbivorous dinosaurs probably had to allow their food to ferment in their stomachs because the cycads and ferns they ate were tough and fibrous. Their droppings would therefore be effectively predigested food for the infants. Many smaller creatures live on the dung of larger ones and some, like rabbits and mole rats, eat their own to make sure no nutrition is wasted. Perhaps some of the many dinosaurs that undoubtedly did lay eggs also carried their young like marsupials, particularly to keep them from dying of heat loss when they were tiny. The upright posture of many dinosaurs is reminiscent of the posture of the kangaroo and wallaby. Though marsupials do not necessarily adopt this erect stance, it might be convenient for erect animals to adopt a marsupial method of protecting their young. Admittedly there has been no quoted instances of this, but the dinosaurs were still vigorously adapting even shortly before their final demise. Is it possible that they anticipated other vertebrate systems for protecting their young, millions of years ago? The marsupial system? The human system?
What of the pterosaurs of the Cretaceous period? Bakker scorns the experts, authors of the “most commonly used twentieth-century paleontology textbook”. They concluded that the pterosaurs were “failures in everything they did”. For these experts the pterosaur could not fly and could not walk. Its wings were too floppy and tore too easily. On the ground it was clumsy and ungainly. It is amazing that the poor creatures survived at all, let alone that they existed in large numbers in the Jurassic and Cretaceous periods.
In reality their success was obvious to those who correctly read the fossil evidence. They were superbly adapted to their aerial home, as earlier and wiser men like Baron Cuvier and Professor Seeley, who wrote the seminal work, Dragons of the Air in 1901, knew. Excellent fossils found in the 1970s showed that the wing was supported by cartilaginous membranes tensioned by strong muscles along their arms, and not by the extended fourth digit alone. There was continuous control over the whole of the surface of the wings. Pterodactyls also had powerful muscles in their breasts like birds, indicated by their deep breast bone. In all respects the pterosaur’s whole anatomy can be shown to be dedicated to its commitment to powered flight.
But did they, like birds, look after their young? The pelvis of the female pterosaurs was too narrow to permit live births unless the foetus was born in an immature state. If so its tiny size would have necessitated parental care especially since it would have difficulty keeping warm despite its fur coat. More likely, eggs were laid. A family structure like that of birds would then have been needed, to hatch the eggs, to feed the immature young and to guide them in taking to the wing.
Whether dinosaurs of all types laid eggs or gave birth to live young it is certain that they were often caring parents.
Sounds and speech
Let us come to the important question of vocal communication. Could the dinosaurs communicate by sounds?
All dinosaurs had sensitive middle ear bones and a notch in their skull where the tight ear drum stretched. Crocodiles and birds, both of which are related to the dinosaurs, have keen hearing so it is not surprising that dinosaurs also had acute hearing. Would they then make sounds? Birds do. And present day crocodiles can recognize each other by night by making a barking noise. There seems no reason to doubt that dinosaurs, known to have acute hearing, would also have done this.
But they had nothing akin to a larynx to enable them to make the sort of speech we do. Why should they? The cetaceans, our whales and porpoises, have sophisticated communication systems based on a host of sounds not made in the human way. Many of the hadrosaurs had distinctive crests protecting their elaborately long nasal passages. Philip Currie of Alberta’s Tyrrell Museum suggests that these could have acted as a resonant chamber allowing the hadrosaurs to make sounds rather like a French horn. It is surmised that Charles Sternberg’s edmontosaurus had an inflatable sac on its snout that acted as a resonator enabling calls and signals to be made to other members of the herd to attract them or warn them. Elephant seals have a similar sort of arrangement. The nesting maiasaur of Montana could have made a deep base like sound by blowing air through its nasal passages.
Hunting
Meat, being concentrated protein, we saw, is an important factor in the development of intelligence. The animal needs less bulky food and needs less time eating. So, it has more thinking time, time free to become cultural and inventive.
Tracks of up to six carnivorous dinosaurs all moving in parallel suggests that some of them hunted in packs. If, as Washburn suggested in man, sophisticated communication and language originated to coordinate group hunting activities, intelligent dinosaurs should be looked for among those types that hunted together. Carnivores also had the other attributes of intelligence discussed in this chapter. The hadrosaurs which could surely make conspicuous noises were not carnivores but, if herbivores could make sounds, hunting dinosaurs could also have developed a sophisticated range of whistling sounds for communication—like birdsong, perhaps.
Washburn’s hunting hypothesis is, of course, far from convincing but, if it were correct, it could apply equally to dinosaurs as to mankind. Plainly, the predatory dinosaurs were aggressive enough, if that were an important attribute for technological success. The skulls of the dinosaurs show that many had very well developed senses. The structure of their ears, indicates excellent hearing and the ability to hear high pitched noises, possibly initially the calls of their young and later the sounds of communication. Brain casts show highly developed olfactory bulbs showing the sense of smell was often good. Large orbits and pronounced optic lobes tell of excellent vision. Some were caring parents possibly having live young, had stereoscopic vision and manipulating hands. Many walked upright and some later dinosaurs had large and growing brains. Some also were fierce hunters and presumably correspondingly aggressive.
Some dinosaurs somewhere had each of the attributes considered necessary for man to evolve. The only conclusion is that some dinosaur somewhere could have had them all and become intelligent before Adam. But how? Could the same feature have evolved twice in vastly different types of animal? Certainly. Features have evolved repeatedly. We have already met several instances, ichthyosaurs and dolphins, for example. The mechanism is convergent evolution.
Some possibilities for the precursors of the intelligent dinosaurs.
Compsognathus was a small—two feet long—dinosaur about the weight of a hen from the end of the Jurassic, 140 million years ago. It was clearly fast and could catch nimble creatures as its prey. Its hand only had two digits and its forelimbs were short, putting its grasping abilities in doubt, but in the time period up to the end of the Cretaceous its descendants could have well adapted along the required lines.
Ornitholestes lived about the same time as compsognathus but was bigger and had a more powerful head. Its arms were long and it had three digits two of which were long and the other, the thumb, short but opposed. It would have been quite good at grasping and could have diversified into even better forms.
The coelurosaurs were small, lightly built fast running predators. They had small heads with sharp teeth, moderately long necks and long arms with grasping hands. Animals of this type must have been abundant during the 140 million years reign of the dinosaurs but because of their slightly built physiology they decayed and their bones were scavenged quickly so that few specimens have been found. The dromaeosaurids, which seemed to have evolved from coelurosaurs, lived at the end of the Cretaceous.
The ornithomimosaurs had three digit hands, long arms, large brains and opposed thumbs. Oviraptorosaurs which fall into the same category had grasping hands. Saurornithoidids like stenonychosaurus could have hunted the mammals into the night and sharpened their intelligence against that of our distant ancestors. These dinosaurs were thought by Dale Russell capable of evolving intelligence.
