Halecomorphi

Halecomorphi Temporal range: 251–94 Ma PreЄ Є O S D C P T J K Pg N
Cipactlichthys scutatus, a Cretaceous Halecomorph.
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Subclass:	Neopterygii
Infraclass:	Holostei
(unranked):	Halecomorphi

Halecomorphi is a taxon of bony fishes in the clade Neopterygii. The sole living Halecomorph is the bowfin (Amia calva), but the group contains many extinct species in several families, including Amiidae, Caturidae, Liodesmidae, Sinamiidae, and the orders Ionoscopiformes, and Parasemionotiformes). The Halecomorphi exhibit a combination of ancestral features, such as most heavily mineralized scales, but also by more derived or "modern" features, particularly in the structure of the skull (e.g. position and shape of preopercles).

Unique derived traits (synapomorphies) of the Halecomorphi include:^[1]

• Unique jaw articulation in which the quadrate and symplectrum participate in the joint.
• Lengthened dorsal fins
• Two biconcave vertebrae per segment in the posterior body region (a condition known as diplospondyly)
• Fan like arrangement of small bones (hypurals) in the tail.

On the systematic position of the Halecomorphi are two competing hypotheses:

• The Halecostomi hypothesis proposes Halecomorphi as a sister group of the major group (Teleostei) (rendering Holostei paraphyletic).^[2]
• The Holostei hypothesis proposes Halecomorphi as a sister group of gars (Lepisosteidae) and their fossil relatives together under the name Ginglymodi.^[3][4]

References

1. Ax, Peter [translated by Dr.Richard. E. Dunmur] (2010). "Halecomorphi — Teleostei". Multicellular Animals. Berlin: Gardners Books. pp. 207–210. doi:10.1007/978-3-662-08874-6_29. ISBN 978-3-642-05515-7.
2. Patterson C. Interrelationships of holosteans. In: Greenwood P H, Miles R S, Patterson C, eds. Interrelationships of Fishes. Zool J Linn Soc, 1973, 53(Suppl): 233–305
3. Olsen P. E. (1984). "The skull and pectoral girdle of the parasemionotid fish Watsonulus eugnathoides from the Early Triassic Sakemena Group of Madagascar with comments on the relationships of the holostean fishes". J Vert Paleontol 4: 481–499.
4. Grande, Lance; Bemis, William E. (1998). "A Comprehensive Phylogenetic Study of Amiid Fishes (Amiidae) Based on Comparative Skeletal Anatomy. an Empirical Search for Interconnected Patterns of Natural History". Journal of Vertebrate Paleontology 18 (sup001): 1–696. doi:10.1080/02724634.1998.10011114.

• Brian J. Gardiner, John G. Maisey, D. Tim J. Littlewood: Interrelationships of Basal Neopterygians. S. 117-146 in: Melanie L. J. Stiassny, Lynne R. Parenti, G. David Johnson (Hrsg.): Interrelationships of Fishes. Academic Press, 1996, ISBN 0-12-670950-5