Contents Updated: Tuesday, August 24, 1999
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.
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 brontosaurus 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 brontosaurus 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.
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.