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LIFE ON LAND - ectothermy as the obsolete...

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LIFE ON LAND The amniote lineage (the first truly terrestrial vertebrates that did not need to return to water to lay eggs), especially the fossils, often are classified based on the number of openings in the skulls. These openings allow for muscle attachment and have traditionally been used to separate the "reptiles" into several groups, including the anapsids, synapsids, and diapsids. The anapsids, which include the turtles, lack any openings. Synapsids include the mammals and their predecesssor and related groups the pelycosaur (the non-mammalian synapsids). Diapsids, with two openings on each side of their skulls, include the birds, dinosaurs, and most of the traditional reptile groups. The synapsids used to be called the mammal-like reptiles. Recent studies suggest that many animals in this group were not so strongly reptilian (such as
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Unformatted text preview: ectothermy) as the obsolete term "mammal-like reptiles" implied. The amniotes that had appeared during the late Carboniferous diversified from the protothyrid stock along two lineages: one leading to the quadrupedal pelycosaurs (stem synapsids) of the Carboniferous-Permian and then to the therapsids (advanced synapsids) of the Permian-Triassic; and the other leading to the bipedal thecodonts of the Permian-Triassic. Dimetrodon, shown above, was a member of the pelycosaurs, or non-mammalian therapsids. By the end of the Permian the therapsids had developed, a group possibly characterized by some degree of endothermy (warm-bloodedness). The early mammals of the Triassic period are possibly an offshoot or descendant group of the therapsids....
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