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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.
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 ...
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.
Eotetrapodiformes is a clade of tetrapodomorphs including the four-limbed vertebrates ("tetrapods" in the traditional sense) and their closest finned relatives, two groups of stem tetrapods called tristichopterids and elpistostegalids.
Limb evolution in Devonian tetrapodomorphs from pectoral fins to forelimbs. From left to right: Eusthenopteron , Panderichthys , Tiktaalik , Elpistostege , Acanthostega Polydactyly in stem-tetrapods should here be understood as having more than five digits to the finger or foot, a condition that was the natural state of affairs in the earliest ...
Ventastega (Venta referring to the Venta River at the Ketleri Formation where Ventastega was discovered [2]) is an extinct genus of stem tetrapod that lived during the Upper Fammenian of the Late Devonian, approximately 372.2 to 358.9 million years ago. [2]
This implies that the evolution of the braincase during the transition from fish-tetrapod was very rapid and seems to display the same timing as the evolution of the pelvic girdle. In general, Panderichthys demonstrates that the braincase structure evolved much more slowly than the external skull morphology that created the tetrapod-like ...
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]