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Reptiles (Late Latin for creeping or crawling) do not have an aquatic larval stage, and in this way are unlike amphibians. Most reptiles are oviparous, although several species of squamates are viviparous , as were some extinct aquatic clades [ 25 ] — the fetus develops within the mother, contained in a placenta rather than an eggshell .
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 ...
The oldest known animal that may have been an amniote is Casineria (though it may have been a temnospondyl). [35] [36] [37] A series of footprints from the fossil strata of Nova Scotia dated to 315 Ma show typical reptilian toes and imprints of scales. [38] These tracks are attributed to Hylonomus, the oldest unquestionable reptile known. [39]
Scutes (left) and skeletal components (right) of a turtle's plastron Pleurodires have an extra scute known as the intergular. It is mostly absent in cryptodires . The turtle shell is a shield for the ventral and dorsal parts of turtles (the order Testudines), completely enclosing all the vital organs of the turtle and in some cases even the ...
The oldest known animal that may have been an amniote, a reptile rather than an amphibian, is Casineria [3] [4] (though it has also been argued to be a temnospondyl amphibian). [5] A series of footprints from the fossil strata of Nova Scotia, dated to 315 million years, show typical reptilian toes and imprints of scales. [6]
Comparative anatomy studies similarities and differences in organisms. The image shows homologous bones in the upper limb of various vertebrates.. Comparative anatomy is the study of similarities and differences in the anatomy of different species.
A skeleton is the structural frame that supports the body of most animals.There are several types of skeletons, including the exoskeleton, which is a rigid outer shell that holds up an organism's shape; the endoskeleton, a rigid internal frame to which the organs and soft tissues attach; and the hydroskeleton, a flexible internal structure supported by the hydrostatic pressure of body fluids.
The hemipenis is the intromittent organ of Squamata, [4] which is the second largest order of vertebrates with over 9,000 species distributed around the world. They differ from the intromittent organs of most other amniotes such as mammals, archosaurs and turtles that have a single genital tubercle, as squamates have the paired genitalia remaining separate. [5]