| Petalichthyida Temporal range: EarlyLochkovian -Frasnian | |
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| Lunaspis | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | †Placodermi |
| Order: | †Petalichthyida Jaeckel, 1911 |
| Families | |
Petalichthyida is anextinctorder of small, flattenedplacodermfish. They are typified by their splayed pectoral fins, exaggerated lateral spines, flattened bodies, and numerous tubercles that decorated all of the plates and scales of their armor. They reached a peak in diversity during the EarlyDevonian and were found throughout the world, particularly in Europe (especially in Germany), North America, Asia, South America, and Australia. The petalichthidsLunaspis andWijdeaspis are among the best known. The earliest and most primitive known petalichthyid isDiandongpetalichthys, which is from earliest Devonian-aged strata ofYunnan. The presence ofDiandongpetalichthys, along with other primitive petalichthyids includingNeopetalichthys andQuasipetalichthys, and more advanced petalichthyids, suggest that the order may have arisen in China, possibly during the late Silurian.
Because they had compressed body forms, it is speculated they were bottom-dwellers that chased after or ambushed smaller fish. Their diet is not clear, as none of the fossil specimens found have preserved mouthparts.
According to Zhu's 1991 redescription ofDiandongpetalichthys,[1] that genus represents the most basal petalichthyid known, as it has a comparatively elongated head, and shares certain anatomical features withacanthothoracids and primitive arthrodires such as theactinolepids.Quasipetalichthys, in turn, strongly resemblesDiandongpetalichthys (aside from having a much more square-looking skull).
In Zhu's redescription, "Quasipetalichthyidae" (comprisingQuasipetalichthys,Eurycaraspis, and possiblyNeopetalichthys) and "Macropetalichthyidae" (comprising all the other "advanced" petalichthyid genera not includingNeopetalichthys, orDiandongpetalichthys) form a dichotomy, withDiandongpetalichthys as a sister taxon.[2]Neopetalichthys is treated as anincertae sedis within Petalichthyida that may or may not be placed within or near Quasipetalichthyidae.
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