Search results
Results From The WOW.Com Content Network
The stem tetrapods may also include one or both of Temnospondyli and Lepospondyli, depending on author. This is due to the uncertain origin of the modern amphibians , whose position in the phylogenetic tree dictates what lineages go in the crown group Tetrapoda.
These early "stem-tetrapods" included animals such as Ichthyostega, [2] with legs and lungs as well as gills, but still primarily aquatic and poorly adapted for life on land. The Devonian stem-tetrapods went through two major population bottlenecks during the Late Devonian extinctions, also known as the end-Frasnian and end-Fammenian extinctions.
It is unclear whether polydactylous tetrapods survived to the Carboniferous. Crassigyrinus, from the fossil-poor Romer's gap in the early Carboniferous, is usually thought to have had five digits to each foot. The anthracosaurs, which may be stem-tetrapods [7] [8] or reptiliomorphs, [9] retained the five-toe pattern still found in amniotes.
Baphetidae is an extinct family of stem-tetrapods. Baphetids were large labyrinthodont predators of the Late Carboniferous period (Namurian through Westphalian) of Europe. Fragmentary remains from the Early Carboniferous of Canada have been tentatively assigned to the group.
The informal variant of the name, "reptiliomorphs", is also occasionally used to refer to stem-amniotes, i.e. a grade of reptile-like tetrapods that are more closely related to amniotes than they are to lissamphibians, but are not amniotes themselves; the name is used in this meaning e.g. by Ruta, Coates and Quicke (2003). [6]
The Tetrapodomorpha contains the crown group tetrapods (the last common ancestor of living tetrapods and all of its descendants) and several groups of early stem tetrapods, which includes several groups of related lobe-finned fishes, collectively known as the osteolepiforms.
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 ...
Stem tetrapods are the animals belonging to the lineage leading to tetrapods from their divergence from the lungfish, our nearest relatives among the fishes. In addition to a series of lobe-finned fishes , they also include some of the early labyrinthodonts .