Petalichthyida


Petalichthyida is an extinct order of small, flattened placoderm fish. 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 Early Devonian and were found throughout the world, particularly in Europe, North America, Asia, South America, and Australia. The petalichthids Lunaspis and Wijdeaspis are among the best known. The earliest and most primitive known petalichthyid is Diandongpetalichthys, which is from earliest Devonian-aged strata of Yunnan. The presence of Diandongpetalichthys, along with other primitive petalichthyids including Neopetalichthys and Quasipetalichthys, 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 mouth parts.

Taxonomy

According to Zhu's 1991 redescription of Diandongpetalichthys, that genus represents the most basal petalichthyid known, as it has a comparatively elongated head, and shares certain anatomical features with acanthothoracids and primitive arthrodires such as the actinolepids. Quasipetalichthys, in turn, strongly resembles Diandongpetalichthys.
In Zhu's redescription, "Quasipetalichthyidae" and "Macropetalichthyidae" form a dichotomy, with Diandongpetalichthys as a sister taxon. Neopetalichthys is treated as an incertae sedis within Petalichthyida that may or may not be placed within or near Quasipetalichthyidae.

Timeline of genera


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from: -416 till: -411.2 color:earlydevonian text:Lochkovian
from: -411.2 till: -407 color:earlydevonian text:Pragian
from: -407 till: -397.5 color:earlydevonian text:Emsian
from: -397.5 till: -391.8 color:middledevonian text:Eifelian
from: -391.8 till: -385.3 color:middledevonian text:Givetian
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from: -416 till: -359.2 color:devonian text:Devonian
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color:earlydevonian bar:NAM1 from: -416 till: -411.2 text: Diandongpetalichthys
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color:earlydevonian bar:NAM3 from: -407 till: -397.5 text: Notopetalichthys
color:earlydevonian bar:NAM4 from: -407 till: -397.5 text: Shearsbyaspis
color:earlydevonian bar:NAM5 from: -407 till: -391.8 text: Wijdeaspis
color:earlydevonian bar:NAM6 from: -400.67 till: -397.5 text: Lunaspis
color:middledevonian bar:NAM8 from: -397.5 till: -391.8 text: Xinanpetalichthys
color:middledevonian bar:NAM9 from: -397.5 till: -385.3 text: Macropetalichthys
color:middledevonian bar:NAM10 from: -387.47 till: -385.3 text: Ellopetalichthys
color:middledevonian bar:NAM11 from: -387.47 till: -385.3 text: Eurycaraspis
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from: -416 till: -411.2 color:earlydevonian text:Lochkovian
from: -411.2 till: -407 color:earlydevonian text:Pragian
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from: -397.5 till: -391.8 color:middledevonian text:Eifelian
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