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Ray-finned fish, class Actinopterygii, differ from lobe-finned fish in that their fins consist of webs of skin supported by spines ("rays") made of bone or horn. There are other differences in respiratory and circulatory structures. Ray-finned fish normally have skeletons made from true bone, though this is not true of sturgeons and paddlefish ...
Major groups of fish evolved during this period, often referred to as the age of fish. [39] See Category:Devonian fish. D e v o n i a n: Early Devonian: Early Devonian (419–393 Ma): Psarolepis: Psarolepis (speckled scale) is a genus of extinct lobe-finned fish that lived around 397 to 418 Ma.
Evolutionary theory predicted that since amphibians evolved from fish, an intermediate form should be found in rock dated between 365 and 385 million years ago. Such an intermediate form should have many fish-like characteristics, conserved from 385 million years ago or more, but also have many amphibian characteristics as well.
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 idea of a tree of life arose from ancient notions of a ladder-like progression from lower into higher forms of life (such as in the Great Chain of Being).Early representations of "branching" phylogenetic trees include a "paleontological chart" showing the geological relationships among plants and animals in the book Elementary Geology, by Edward Hitchcock (first edition: 1840).
This chart displays one of the first published attempts at a paleontological "Tree of Life" by Geologist Edward Hitchcock. (1840) 1843, distinction between homology and analogy (the latter now referred to as homoplasy), Richard Owen, precursor concept. Homology is the term used to characterize the similarity of features that can be ...
The GNC hypothesis or GNC-SNS primeval genetic code hypothesis refers to a hypothesis about the origin of genes. It suggests the universal genetic code originated not from a three-amino acid system, but from a four-amino acid system. It is this GNC code encoding [GADV]-proteins which is the most primitive genetic code.
Fishes are a paraphyletic group and for this reason, the class Pisces seen in older reference works is no longer used in formal taxonomy.Traditional classification divides fish into three extant classes (Agnatha, Chondrichthyes, and Osteichthyes), and with extinct forms sometimes classified within those groups, sometimes as their own classes: [1]