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Evolution of fish to tetrapods. The basic body plan has been phylogenetically constrained. Most terrestrial vertebrates have a body plan that consist of four limbs. The phylogenetic inertia hypothesis suggests that this body plan is observed, not because it happens to be optimal, but because tetrapods are derived from a clade of fishes (Sarcopterygii) which also have four limbs.
The principle of phylogenetic reconciliation was introduced in 1979 [14] to account for differences between genes and species-level phylogenies. In a parsimonious setting, two evolutionary events, gene duplication and gene loss were invoked to explain the discrepancies between a gene tree and a species tree.
The phyllosoma larva of spiny lobsters has a long planktonic life before metamorphosing into the puerulus stage, which is the transitional stage from planktonic to a benthic existence. [ 3 ] [ 4 ] Despite the importance of larval survival to predict recruitment, not much is known about the biology of phyllosoma larvae. [ 5 ]
Biological constraints are factors which make populations resistant to evolutionary change. One proposed definition of constraint is "A property of a trait that, although possibly adaptive in the environment in which it originally evolved, acts to place limits on the production of new phenotypic variants."
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.
These evolutionary lineages can thereby be portrayed through a phylogenetic tree, or cladogram, where varying relatedness amongst species is evidently depicted. Through this tree, organisms can be categorized by divergence from the common ancestor, and primitive characters, to clades of organisms with shared derived character states.
A phyllosoma larva of the spiny lobster Palinurus elephas, from Ernst Haeckel's Kunstformen der Natur. The larvae of the Achelata (slipper lobsters, spiny lobsters and furry lobsters) are unlike any other crustacean larvae. The larvae are known as phyllosoma, after the genus Phyllosoma erected by William Elford Leach in 1817. They are flattened ...
A few species from other phyla; the nemertean pilidium larva, the larva of the phoronid species Phoronopsis harmeri and the acorn worm larva Schizocardium californicum, do not depend on Hox genes in their larval development either, but need them during metamorphosis to reach their adult form.