Ancient lizards that roamed the Earth hundreds of millions of years ago could be covered with hair. At least the genes for "hair" proteins in the DNA of modern lizards and birds are present - and in almost the same form as in mammals. Why they need them and where they came from, remains a mystery
Even in the most fantastic scripts of films about dinosaurs, the authors did not "experiment" much with the veils of their wards. Size, color of scales, spines and ridges - everything that was enough for imagination, adjusted for historical plausibility.
Nature, as usual, turned out to be more original - Leopold Eckhart and his colleagues from the universities of Vienna, Bologna and Padua showed that the genome of lizards contains genes encoding structural proteins of hair.
As it turned out, the popular among animal lovers lizard Anolis carolinenis, which became the first reptile with a deciphered DNA sequence a few years ago, has six genes encoding mammalian "hairy" keratins. They almost certainly have them in birds, whose ancestors separated from the reptiles later than the ancestors of animals.
Therapsids (Therapsida), formerly known as "bestial reptiles" - a detachment of the class of synapsids. They appeared in the early Permian period.
Traditionally, therapsids were classified as reptiles, but they possessed a number of features characteristic of mammals, primarily related to the structure of teeth. In addition to the structure of the teeth, the terapsid (or rather, the entire synapsid) branch of the tetrapods was probably initially different in the structure of the skin. Hard scales never developed in this group. It is known that primitive therapsids had smooth, scaleless skin. Perhaps the skin carried numerous glands. The question of the time of the appearance of the coat has not yet been finally resolved. Vibrissae ("whiskers") could appear quite early (it is not excluded that even dicynodonts have them).
Most of the therapsids became extinct during the Permian catastrophe; a few representatives survived until the Triassic period, after which they became extinct. The exception was the cynodonts, which were part of the periodont group - mammals descended from them. The Cynodonts survived to the Early Cretaceous. It is also possible that the dicynodonts survived until the beginning of the Cretaceous era in Australia.
There is nothing surprising in the fact that reptiles have keratins. It is they who form dense formations, like claws and some outer plates. However, scientists have found almost "human" proteins in anolis. Why they need them is still a mystery.
A curious, at first glance, discovery will seem more significant if we consider that the integument of the body is the most specific characteristic of each class of vertebrates. Suffice it to recall the placoid scales in cartilaginous and bony scales in bony fish, the bare "breathing" skin of amphibians and the strong scales that make up the armor of reptiles. And the most narrowly adapted classes of the vertebrate type - birds and mammals - acquired, respectively, feathers and wool.
In addition, the integument is also a defining feature. Unlike many other adaptations, on the one hand, they limit the habitat, and on the other hand, they allow achieving maximum evolutionary progress in the given climatic and geographical conditions.
However, when animals learned to grow hair is still a mystery. And although Eckhart's work does not have sufficient power to assess this point from genetic evidence, based on the publication in the Proceedings of The National Academy of Sciences, hair could have arisen somewhat before the selection of animals in a separate class.
For a long time, animals did not trust milk to take care of their offspring. As Swiss scientists have shown, for 200 million years they retained a backup option - the accumulation of yolk in the egg, and only 30-70 million years ago our ancestors finally lost this opportunity.
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An omelet is a very nutritious breakfast, but most people still prefer either milk or eggs. The same choice was made by nature, which deprived mammals of the opportunity to feed their children with yolks about 30–70 million years ago. Swiss scientists were able to follow step by step how the animals moved to feeding their cubs exclusively with milk - a strategy used by the most successful representatives of the fauna to date.
At the embryonic stage, a developing organism needs especially a lot of nutrients and energy, because in a matter of days one cell grows tens and hundreds of times. Over the long millions of years of evolution, nature has tried various options for meeting this need.
The most ancient organisms were limited to leaving the cubs with a supply of nutrients once and for all, accumulating enough "food" in the egg to form a full-fledged organism. If an egg has a hard shell, then we usually call it an egg, and the supply of nutrients in it is an egg yolk.
This hypothesis is supported by recent results regarding other traits previously considered unique to mammals. Firstly, this is heterodontics - “different teeth” that have appeared in reptiles, which allow you to significantly expand your diet or follow the path of specialization, as did herbivorous ungulates or canine predators. Secondly, the ability to use the yolk, which was preserved in animals 200 million years after the appearance of the placenta and the unique ability to feed the cubs with milk.
Recent results seem to reaffirm another old hypothesis.
The skull of one of the first dinosaurs who refused to kill for the sake of grass was found in Africa. The animal retained its fangs of prey, but its main food was plants. The youth of the dinosaur proves that he did not need fangs for hunting, but in order to dilute a dull diet from time to time with something meaty.
Life is often unfair to the smallest, even if these little ones are dinosaurs. During life they had to constantly hide and run away, and after death they get much less attention than, say, aggressive tyrannosaurs and ichthyosaurs or bizarre platypuses. Perhaps the approach of educated paleontologists is not very different from the behavior of children, who first look at giant skeletons and models in a museum and only then bend over individual small bones and fossils.
For example, the tiny skull described in the latest issue of the Journal of Vertebrate Paleontology was recovered from African soil in the 60s of the last century and has since been gathering dust in the storerooms of the Cape Town Museum.
It probably would still be lying on the shelves if not for Laura Porro from the University of Chicago, who visited the museum as part of her project to study heterodontosaurs. This group of reptiles is one of the most mysterious among the known inhabitants of the Triassic and Jurassic. Until now, paleontologists all over the world have only two skulls of adults, which differ from other dinosaurs in various, as their name implies, teeth - a feature characteristic of mammals, and not of amphibians, reptiles, and even more so birds.
The "rediscovered skull", with a total length of only 45 millimeters, appears to have belonged to a very young member of this group. According to paleontologists' calculations, the specimen weighed only 200 grams, but the dinosaur could easily feed on its own.
It was the issue of nutrition that made this finding important.
Adult heterodontosaurs had fangs, like those of carnivores, and flat back teeth, like those of herbivores. Scientists have no doubt that the lush vegetation of the time was the basis of the diet, but why then fangs? One of the hypotheses is a demonstration of strength and weapons in the fight against predators and with their male relatives. But in this case, long and sharp teeth would appear during maturation, and the young should not have them.
Now scientists are confident that the fangs of heterodontosaurs are proof of their transitional status between carnivorous and herbivorous reptiles. The ancestors of all dinosaurs, and the rest of the reptiles, were active predators, but the origin of herbivores was still a mystery. In addition, the time of occurrence of heterodontosaurs is the Triassic (although the "youth" refers to the early Jurassic period, the previous ones date from the end of the Triassic), so that heterodontosaurs, and their descendants, had enough time to settle across the whole Pangea before its split.
There is also a second feature that brings these reptiles closer to mammals.
As it became clear from the X-rays, the baby did not have the rudiments of the second, third, and so on teeth, characteristic of the vast majority of even modern reptiles, not to mention the predators of that time. After all, losing a tooth or two for the vast majority of predators is tantamount to death. By the way, the lack of oral hygiene is considered one of the reasons for the short life of even our immediate ancestors - Cro-Magnons.
Judging by their teeth, heterodontosaurs from time to time diluted their mostly plant-based diet with animal flesh: fangs could be used for protection from enemies, and for hunting small animals, for example, insects. // Natural History Museum
So the teeth of the heterodontosaurus grew very slowly, if at all, and besides, there were tight contacts between them, again characteristic of mammals.
Of course, it is possible to finally judge the taste preferences only by observing the animal or by dissecting its intestines, but the analysis of the teeth and jaws is also quite a reliable criterion. Of course, it is difficult to imagine how two to three kilogram adults chased through the forest for dessert - large insects and small mammals, although this adds color to the already vivid picture of the Jurassic period.
She suggests that the engine of evolutionary change in the appearance of animals was the selection of suitable genes from the DNA sequences still available in reptiles. At the same time, the number of newly formed genes is minimal, and they are mainly associated with the development of immunity.
The fact that at the same time mammals have learned to use the capabilities inherent in the reptile genome much more efficiently, Eckhart and his colleagues have clearly demonstrated.