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The Osteolepiformes and Elpistostegalia are two crown groups of rhipidistians with respect to the tetrapods. [2] The development of skull roof and cheekbone patterns in these organisms match those found in the first tetrapods. Palatal and nasal skeletal features like choanae are present in these groups and are also observed in modern amphibians.
The term "marine mammal" encompasses all mammals whose survival depends entirely or almost entirely on the oceans, which have also evolved several specialized aquatic traits. In addition to the above, several other mammals have a great dependency on the sea without having become so anatomically specialized, otherwise known as "quasi-marine ...
Humans are mammals, but human migration, as commonly defined, is when individuals often permanently change where they live, which does not fit the patterns described here. An exception is some traditional migratory patterns such as transhumance , in which herders and their animals move seasonally between mountains and valleys, and the seasonal ...
Synapsida [a] is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant reptiles and birds).
For instance, descendants of the first reptiles include modern reptiles, mammals and birds; the agnathans have given rise to the jawed vertebrates; the bony fishes have given rise to the land vertebrates; a group of amphibians, the labyrinthodonts, have given rise to the reptiles (traditionally including the mammal-like synapsids), which in ...
While the early amniotes resembled their amphibian ancestors in many respects, a key difference was the lack of an otic notch at the back margin of the skull roof. In their ancestors, this notch held a spiracle , an unnecessary structure in an animal without an aquatic larval stage. [ 25 ]
[2] All mammals have some hair on their skin, even marine mammals like whales, dolphins, and porpoises that appear to be hairless. The skin interfaces with the environment and is the first line of defense from external factors. For example, the skin plays a key role in protecting the body against pathogens [3] and excessive water loss. [4]
In regards to males, the mammalian penis has a similar structure in reptiles and a small percentage of birds while the scrotum is only present in mammals. Regarding females, the vulva is unique to mammals with no homologue in birds, reptiles, amphibians, or fish. [10] [11] [12] The clitoris, however, can be found in some reptiles and birds. [13]