Halecomorphi
Clade of fishes
Halecomorphi is a taxon of ray-finned bony fish in the clade Neopterygii. The only extant Halecomorph species are the bowfin (Amia calva) and eyespot bowfin (Amia ocellicauda), but the group contains many extinct species in several families (including Amiidae, Caturidae, Liodesmidae, Sinamiidae) in the order Amiiformes, as well as the extinct orders Ionoscopiformes, Ophiopsiformes, Panxianichthyiformes, and Parasemionotiformes. The fossil record of halecomorphs goes back at least to the Early Triassic epoch.
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:
- Unique jaw articulation in which the quadrate and symplectic participate in the joint.
- Lengthened dorsal fins (in some species)
- 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.
01Systematics and phylogeny
On the systematic position of the Halecomorphi, there are two competing hypotheses:
- The Halecostomi hypothesis proposes Halecomorphi as the sister group of Teleostei, the major group of living neopterygians, rendering the Holostei paraphyletic.
- The Holostei hypothesis proposes Halecomorphi as the sister group of Ginglymodi, the group which includes gars (Lepisosteidae) and their fossil relatives, rendering the Halecostomi paraphyletic.
The latter hypothesis is more widely accepted.
| Neopterygii |
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The following cladogram summarizes the evolutionary relationships of extinct (indicated with a dagger, †) and living orders of Halecomorphi.
| Halecomorphi |
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Sources and credits
This article is adapted from the Wikipedia article “Halecomorphi”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
Images, from Wikimedia Commons:
- Cipactlichthys scutatus holotype.png by Paulo M. Brito and Jesus Alvarado-Ortega, CC BY 3.0
- Watsonulus eugnathoides.png by GleisReis, CC BY-SA 4.0
- Ionoscopus cyprinoides 387.jpg by Ghedoghedo, CC BY-SA 4.0
- Strobilodus giganteus.JPG by Ghedoghedo, CC BY-SA 3.0
- Enneles audax.JPG by Ghedoghedo, CC BY-SA 3.0
- Sinamia.JPG by Laikayiu, CC BY-SA 3.0
- Amia skull.jpg by Terhaaed, CC BY-SA 4.0
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