Search results
Results from the WOW.Com Content Network
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.
Early fossil tetrapods have been found in marine sediments, and because fossils of primitive tetrapods in general are found scattered all around the world, they must have spread by following the coastal lines — they could not have lived in freshwater only. Fossil Illuminates Evolution of Limbs from Fins Scientific American, 2 2 April 2004.
Tulerpeton is one of the early transition tetrapods – a marine animal capable of living on land. The separation of the pectoral-shoulder girdle from the head allowed the head to move up and down, and the strengthening of the legs and arms allowed the early tetrapods to propel themselves on land. Tulerpeton is important in the study of dactyly.
An informal term with a broader meaning is stem tetrapod, a stem group consisting of all species more closely related to modern tetrapods than to lungfish, but excluding the crown group. This group includes both traditional "labyrinthodonts" as well as more basal tetrapodomorph fish, though its total content is a matter of some uncertainty, as ...
Other factors that caused aquatic tetrapods to spend more time on land caused the development of terrestrial hearing with the development of a tympanum within an otic notch and developed by convergent evolution at least three times. [10] There was also a change in the dermal bones of the skull in the aquatic tetrapods. [5]
In most analyses, the group as traditionally imagined is actually an evolutionary grade, the last "fishes" of the tetrapod stem line, though Chang and Yu (1997) treated them as the sister clade to Tetrapoda. [15] [16] Elpistostegalia was re-defined as a clade containing Panderichthys and tetrapods. [7] Below is a cladogram from Swartz, 2012. [7]
However, this group represents a paraphyletic grade of primitive stem-tetrapods and is not used by many modern researchers. Phylogenetic analysis has shown Ichthyostega is intermediate between other primitive stegocephalian stem-tetrapods. The evolutionary tree of early stegocephalians below follows the results of one such analysis performed by ...
For specialists who prefer a neontological definition of tetrapods (i.e., only in the context of modern life), alternative terms for non-crown tetrapods include "stem-tetrapod" or "stegocephalian". Hynerpeton hails from the Red Hill fossil site, which, during the Late Devonian, was a warm floodplain inhabited by a diverse ecosystem of aquatic ...