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Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found in most fish, in mammals such as whales, and in extinct ancient marine reptiles such as ichthyosaurs. Most have only one dorsal fin, but some have two or three.
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]
There are two dorsal fins: a large triangular first dorsal fin and a low rectangular or depressed second dorsal fin. For defense, some chimaeras have a venomous spine on the front edge of the dorsal fin. [4] In many species, the bulbous snout is modified into an elongated sensory organ, capable of electroreception to find prey.
One of the largest living gecko species, these bright and beautiful reptiles are known for their vibrant grey coloring with orange and blue spots. However, they do have a reputation for having ...
Tetrapod limbs which have evolved into fin-like structures are usually (but not always) called "flippers" rather than fins. The dorsal structure on cetaceans is called the "dorsal fin" and the large cetacean tails are referred to primarily as flukes but occasionally as "caudal fins"; neither of these structures are flippers.
As of May 2023, about 12,000 living species of reptiles are listed in the Reptile Database. The study of the traditional reptile orders, customarily in combination with the study of modern amphibians, is called herpetology. Reptiles have been subject to several conflicting taxonomic definitions.
Marine reptiles are reptiles which have become secondarily adapted for an aquatic or semiaquatic life in a marine environment. Only about 100 of the 12,000 extant reptile species and subspecies are classed as marine reptiles, including marine iguanas , sea snakes , sea turtles and saltwater crocodiles .
The evolution of tetrapods began about 400 million years ago in the Devonian Period with the earliest tetrapods evolved from lobe-finned fishes. [1] Tetrapods (under the apomorphy-based definition used on this page) are categorized as animals in the biological superclass Tetrapoda, which includes all living and extinct amphibians, reptiles, birds, and mammals.