Cienciaes.com: Psittacosaurus, el lagarto loro.

by time news

2018-03-23 09:50:12

About 110 million years ago, at the beginning of the Cretaceous, the climate was warmer than it is today. Although it snowed in winter, the poles were free of ice, and extensive forests covered the mid-latitudes. An arm of the sea separated Europe from Asia. In this last continent lived Psittacosaurus, the parrot lizard. It is a distant relative of ceratopsians or horned dinosaurs like Triceratops, although not its direct ancestor, among other things because Psittacosaurus has four fingers and toes, while ceratopsians retain the original five fingers of terrestrial vertebrates.

The head of Psittacosaurus is reminiscent of that of a parrot: The skull is tall and short, with large, far-forward eyes, and a robust beak, which was probably covered in life with a sharp keratin sheath to cut down the plants on which it feeds. . The structure of the beak, with the lower part that fits inside the upper part, is also adapted to break seeds or nuts, which could be an important part of their diet. The teeth inside the mouth are sharpened by rubbing against each other; They serve, like the beak, to cut. But it lacks the crushing teeth of later ceratopsians. Instead it has to resort to gastroliths: swallow stones that work like a mill to grind food. These stones, which can number up to several dozen, are safely stored in a gizzard, as in modern birds.

The Psittacosaurus brain is relatively large; and smell, sight and balance are highly developed. Several projections, resembling small horns, project around the eyes; there is also one on each side of the skull, the so-called jugal horn.

One specimen has been preserved with the skin, so we know that the body is covered in scales for the most part. There are large scales, irregularly distributed, and smaller ones that cover the gaps between the large ones. Adjacent to the jugal horn is a dark structure that may be a keratin shield or a skin fold.

The study of melanosomes, the organelles that give color to the skin, indicates that the belly is lighter than the back, and that the hind legs are adorned with spots or stripes, camouflage techniques currently used by many animals. The color distribution, with a smooth transition from a light belly to a darker back, indicates that Psittacosaurus is adapted for camouflage in dense forest with low light. It is also heavily pigmented on the face, shoulders, and cloaca. The latter, probably due to the bactericidal effects of melanin.

Psittacosaurus is a bipedal dinosaur. The front legs are just over half the length of the hind legs; they are too short to reach the ground in locomotion. They are also short for digging or for bringing food to the mouth; although it can use them to transport construction material and food to the nest. Up to three years of age, the front legs grow faster than the hind legs, and the young may be quadruped up to six years. This suggests that perhaps the ancestor of Psittacosaurus was quadrupedal, and the hatchlings retain that primitive trait. The smallest surviving hatchlings measure just over four inches in length. Growth is quite fast for a reptile, although slower than that of birds; at three years old they still weigh less than a kilo, but at nine they already weigh twenty. It is estimated that their longevity reaches between ten and eleven years.

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The hind legs are attached to the tail by a membrane, like in bats. Along the top of the tail base is a row of hollow bristles about six inches long, grouped in sets of three to six, which were probably keratinized, like scales. Its structure is similar to that of the protofeathers of other dinosaurs, and to certain modified feathers developed by some current birds.

Since many of the remains of Psittacosaurus have been found in lake sediments and the eyes and nostrils are quite high on the head, some authors have proposed that Psittacosaurus was a semi-aquatic animal, capable of swimming by propelling itself with its legs and lateral movements of its arms. the tail, in which they imagine a skin membrane covering the bristles, like a fin. Although it is not the general opinion of paleontologists.

Psittacosaurus ranged through what is now Siberia, Mongolia, China, and perhaps as far south as Thailand. It is one of the best known dinosaur genera; Since its discovery in 1922, the fossil remains of several hundred individuals have been found, many of them complete, and representatives of all stages of growth, from hatchlings to adults. About ten species have been described based on differences in size, the number and position of the small bumps on the head, and certain skeletal characteristics, although they are all similar in general terms. The largest reach two meters in length, while the smallest do not exceed one meter.

Based on the structure of the eyes, it is assumed that Psittacosaurus alternate short periods of activity and rest throughout the day and night. Based on the fossils, we know that at least the young live in groups, probably to protect themselves from predators. Although from a very young age they are capable of feeding themselves, it is possible that the adults take care of the young; one fossil shows a six-year-old lying on thirty-four young, although there are doubts as to the interpretation of the whole. In any case, as we already saw in the episode entitled “The big mammal eats the small dinosaur”, we know that Psittacosaurus hatchlings could be preyed on by carnivorous mammals of the time, such as Repenomamus. And, of course, adults had to beware of large meat-eating dinosaurs, like the feathered Tyrannosauroid Yutyrannus, which we also talked about here a few years ago.

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