Pelycosaurs were a dominant group of tetrapods that emerged in the Late Carboniferous and were replaced by therapsids in the Late Permian. Ranging in size from a large mouse to larger than an elephant, they exploited various roles as herbivores, insectivores, and carnivores. Pelycosaurs were the first successful amniotic group, able to colonize continental interiors, and were the ancestors of mammals. They became extinct before the end of the Permian.
The pelycosaurs (from the Greek pelyx meaning “bowl” and sauros meaning “lizard”) are an order of tetrapods that emerged during the Late Carboniferous, flourished during the Early Permian, then were replaced by their descendants, the therapsids, during the Late Permian . This primitive group was the dominant form of terrestrial life for about 40 million years, 3/5 the duration of the mammalian dominance, and was among the first amniotes (non-amphibian tetrapods) to evolve. It is one of the most primitive groups of tetrapods, after the basal tetrapods and the first amphibians.
Pelycosaurs ranged in size from a large mouse to a wolf to larger than an elephant. As the dominant form of terrestrial life, they have evolved to exploit numerous roles, including herbivores, insectivores, and carnivores. Some resembled robust lizards, others were more alien, such as the iconic Dimetrodon grandis, an apex predator 3 1/2 meters (11 feet) long, with huge vertebral extensions that created a large, skin-covered sail. This animal had a somewhat dragon-like appearance. Other pelycosaurs shared the rear sail, which is believed to have been used to raise the animal’s temperature. Another pelycosaur, Cotylorhynchus, was a titanic barrel-shaped herbivore with a small head and a total length exceeding 6 m (20 ft). It would have been longer and heavier than the largest elephants alive today.
Pelycosaurs were among the first amniotes, meaning they had well-developed eggs, allowing them to venture away from water: Amphibians need to stay moist and lay their eggs in water. Pelycosaurs were the first successful amniotic group, able to colonize continental interiors that had been reached by plants and insects tens of millions of years earlier. However, the period in which pelycosaurs were successful, the Early Permian, was also a time of great deserts, as all of the world’s continents had merged into the supercontinent Pangea, which included virtually all of the world’s land mass. The interior of Pangea would have been the largest desert the world had ever seen. For this reason, art depicting reconstructions of pelycosaurs often show them against a desert backdrop, even though many groups of pelycosaurs probably lived in forests.
Pelycosaurs are occasionally grouped with dinosaurs, especially when simplifying things for children, but adults should know that there is no relationship between dinosaurs and pelycosaurs, except that both were the dominant life form on Earth for a period. Despite their occasionally reptilian appearance, pelycosaurs were synapsids, not sauropsids (reptiles), and actually the ancestors of mammals. A group of pelycosaurs, the therapsids, acquired characteristics very typical of mammals and, after more than a hundred million years, produced the first true mammals. All pelycosaurs became extinct before the end of the Permian, sparing them from the massive extinction at the end of the Permian.
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