Cladistic Classification of Class Sarcopterygii

Sarcopterygii or the lobe-finned fishes (coelacanths and lungfishes) were usually classified as either a class or a subclass of Osteichthyes based on the traditional Linnaean classification. The group are grouped together based on several characteristics, such as the presence of fleshy, lobed, paired fins, which are joined to the body by a single bone.[1] This is in contrasts to the other bony fish group Actinopterygii which have lepidotrichia, or ray-fins made of bony rods. Regardless the two bony fish groups were classified in Osteichthyes for a while and as a whole were seen as the sister group to the tetrapods (mammals, birds and reptiles, and amphibians).

The extensive fossil record and numerous morphological and molecular studies have shown, however, that lungfish and some fossil lobe-finned fish are more closely related to tetrapods than they are to coelacanths; as a result tetrapods are nested within Sarcopterygii.[2][3] This abides to cladistics in that in order for a clade to be monophyletic, it must have an ancestral species and all descendants of that common ancestor based on shared characteristics. As such mammals, birds and reptiles, and amphibians are highly derived lobe-finned fish despite looking nothing like the standard sarcopterygian anatomically speaking.

Below is shows the taxonomy of the extant members of class Sarcopterygii at the ordinal level. While this does reflect the evolutionary relationships within the group, it also retains the rankings seen in the Linnaean classification as suggested by some scientists.[4] The evolutionary sequences are based from current phylogenetic work on the various subclades.[5][6][7][8][9][10][11][12]

Class Sarcopterygii (Romer, 1955)

See also

References
  1. Clack, J. A. (2012). Gaining ground: the origin and evolution of tetrapods. Indiana University Press.
  2. Tudge, C. (2000). The variety of life. Oxford: Oxford University Press.
  3. Pough, F. H., Janis, C. M., & Heiser, J. B. (2005). Vertebrate life. Pearson/Prentice Hall.
  4. Nelson, J. S., Grande, T. C., & Wilson, M. V. H. (2016). Fishes of the World. John Wiley & Sons.
  5. Crawford, Nicholas G., et al. "More than 1000 ultraconserved elements provide evidence that turtles are the sister group of archosaurs." Biology letters 8.5 (2012): 783-786.
  6. Wang, Z. et. al. (2013). The draft genomes of soft-shell turtle and green sea turtle yield insights into the development and evolution of the turtle-specific body plan. Nature Genetics, 45(6), 701-706.
  7. Lee, M. S. Y. (2013). Turtle origins: insights from phylogenetic retrofitting and molecular scaffolds. Journal of Evolutionary Biology, 26(12), 2729-2738.
  8. McCormack, J. E., Harvey, M. G., Faircloth, B. C., Crawford, N. G., Glenn, T. C., & Brumfield, R. T. (2013). A phylogeny of birds based on over 1,500 loci collected by target enrichment and high-throughput sequencing. PLoS One, 8(1), e54848.
  9. Jarvis, E. D. et. al. (2014). Whole-genome analyses resolve early branches in the tree of life of modern birds. Science, 346(6215), 1320-1331.
  10. Prum, R. O., Berv, J. S., Dornburg, A., Field, D. J., Townsend, J. P., Lemmon, E. M., & Lemmon, A. R. (2015). A comprehensive phylogeny of birds (Aves) using targeted next-generation DNA sequencing. Nature.
  11. May-Collado, L. J., Kilpatrick, C. W., & Agnarsson, I. (2015). Mammals from ‘down under’: a multi-gene species-level phylogeny of marsupial mammals (Mammalia, Metatheria). PeerJ, 3, e805.
  12. Tarver, J. E. et. al. (2016). The Interrelationships of Placental Mammals and the Limits of Phylogenetic Inference. Genome Biology and Evolution, evv261.
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