2020-02-13 12:35:31
About 42 million years ago, in the middle of the Eocene, the first Carnivores appeared in North America. I do not mean by this that before that date there were no animals that ate meat, I am talking about the order of Carnivores, the group of mammals that includes hyenas, mongooses, genets and civets, felids, canids, bears, raccoons and coatis, mustelids , skunks, sea lions, walruses, seals… Strictly, the order of Carnivores is made up of the last common ancestor of dogs and cats and all their descendants. It is a bit confusing that in Spanish we call the animals that eat meat the same as this group of mammals, because not all animals that eat meat, such as the Tyrannosaurus, belong to the order Carnivores, nor do all species of the order of Carnivores eat meat: the panda bear, for example, is almost exclusively herbivorous. To avoid confusion, we will call members of the order Carnivores “true carnivores.”
Before true Carnivores were the dominant predators, other groups of mammals played that role. One of these groups was that of the Creodonts.
Creodonts appeared in the Paleocene, about 63 million years ago, in North America, where they became the dominant terrestrial predators. At the end of that period, about 61 million years ago, they spread to Africa, and in the Eocene they reached Europe and Asia. At the end of the Oligocene they became extinct in Europe and North America, but they survived in Africa and Asia until the end of the Miocene. They never reached South America, which was an island at the time, nor, of course, Oceania. During the Eocene, between 56 and 33 million years ago, they were the dominant predators in the Old Continent and North America, until they were replaced by true Carnivores. Although their position on the mammalian evolutionary tree is not entirely clear, their closest living relatives appear to be pangolins.
The creodonts are divided into two large groups, the oxyenids and the hyenodontids. The first, oldest, appeared in North America, and spread to the Old Continent during the Eocene. The hyenodontids, for their part, spread to Eurasia and North America from Africa. The first creodonts were small, about the size of a cat, and were probably omnivorous, opportunistic animals that fed on eggs, birds, small mammals, insects, and even plants. Towards the end of the Paleocene, the first large carnivorous creodonts already appeared in North America, such as Dipsalidictis, the size of a puma.
The creodont skull is long and narrow, with a characteristic narrowing behind the eyes. The brain is small. The sagittal crest, a bony extension at the top of the skull that supports the jaw muscles, is large. In many species, the head is quite large in relation to the size of the body. Creodonts have relatively short legs, with five clawed toes.
The canine teeth are always long and pointed. The lateral incisors are large, while the central ones are usually small. The premolars are simple. Creodonts have two or three pairs of carnass molars, large teeth that are constantly sharpened by rubbing and that cut through flesh and bone like shears, though usually only one pair is functional. In oxyenids, the carnass teeth are the upper first and lower second molars, while in hyenodontids they are the upper second and lower third molars. In this they differ from true Carnivores, whose carnassal teeth are the last upper premolar and the first lower molar. At least in hyenodontids, milk teeth were replaced more slowly than in true carnivores.
Throughout their evolution, creodonts explored many of the forms that true Carnivores would later repeat. Among the creodonts we find species similar to dogs, cats, bears, wolverines, pumas, saber-toothed tigers, hyenas… Although there are also original forms: Apterodon was a semi-aquatic burrower similar to an otter, although with strong front legs to dig, like those of a badger, which lived on the coasts of Africa from the mid-Eocene to the Oligocene, and fed on invertebrates such as crustaceans and shelled molluscs.
There were also species larger than today’s largest carnivores: The largest known oxyenid, Sarkastodon, reached 10 feet in length and 1800 pounds in weight, and was the size and appearance of a large bear. It lived in Mongolia in the late Eocene, 35 million years ago, and probably stalked large prey, such as brontotheres, callicotherines, and rhinos. Among the hyenodontids there are even larger species: Simbakubwa, Swahili for “great lion”, which lived in Kenya at the beginning of the Miocene, 23 million years ago, weighed more than a thousand kilos and was bigger than a polar bear. It probably fed on rhinos and mastodons.
The last creodonts went extinct about eleven million years ago. The last genus was Dissopsalis, a predator two meters long, including a 90-centimeter tail, half a meter high at the withers and about thirty kilos in weight, which lived in Asia, from Pakistan to China. Several reasons can explain the defeat of the creodonts before the true Carnivores: their brains were smaller, their teeth limited them to consuming meat exclusively, and their locomotor system was less efficient, and with less mobility, so that they could only use the jaw to catch its prey. The latter may be the reason for the larger relative size of the head in creodonts. Although it is not clear if their extinction was due to direct competition with the true Carnivores, or they simply took advantage of their disappearance.
CONSTRUCTION OF GERMAN FERNÁNDEZ:
reticular infiltrate
Reticular Infiltrator is the first novel in the trilogy The Saga of the Borelians. Do you want to see how it starts? Here you can read the first two chapters.
The Karnak file. Ed.Rubeo
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