Search results
Results from the WOW.Com Content Network
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.
The term tetrapod, meaning "four feet," refers to all land vertebrates. The earliest ones, the stem tetrapods, spawned evolutionary lineages that led to true amphibians, reptiles and mammals.
The earliest evidence for life on Earth includes: 3.8 billion-year-old biogenic hematite in a banded iron formation of the Nuvvuagittuq Greenstone Belt in Canada; [30] graphite in 3.7 billion-year-old metasedimentary rocks in western Greenland; [31] and microbial mat fossils in 3.48 billion-year-old sandstone in Western Australia.
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.
The history of life on Earth traces the processes by which living and extinct organisms evolved, from the earliest emergence of life to the present day. Earth formed about 4.5 billion years ago (abbreviated as Ga, for gigaannum) and evidence suggests that life emerged prior to 3.7 Ga. [1] [2] [3] The similarities among all known present-day species indicate that they have diverged through the ...
The universal tetrapod characteristics of front limbs that bend backward at the elbow and hind limbs that bend forward at the knee can plausibly be traced to early tetrapods living in shallow water. [18] Panderichthys is a 90–130 cm (35–50 in) long fish from the Late Devonian period (380 Mya). It has a large tetrapod-like head.
Traditionally, Ichthyostega was considered part of an order named for it, the "Ichthyostegalia". 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 ...
Acanthostega is a partially aquatic tetrapod with developed limbs that shares features common with the earlier tetrapods, Panderichthys and Eusthenopteron. [3] Like Panderichthys , the humerus of Acanthostega is flattened dorso-ventrally, the intermedium terminates level with the radius, and the endoskeleton can be divided into stylopodium ...