Petalichthyida is an
extinct order of small, flattened
placoderm fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...
. 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 (especially in Germany), 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
Yunnan , () is a landlocked province in the southwest of the People's Republic of China. The province spans approximately and has a population of 48.3 million (as of 2018). The capital of the province is Kunming. The province borders the C ...
. 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 mouthparts.
Taxonomy
According to Zhu's 1991 redescription of ''Diandongpetalichthys'',
[Zhu, M. "New information on ''Diandongpetalichthys'' (Placodermi: Petalichthyida)." Early vertebrates and related problems of evolutionary biology. Science Press, Beijing (1991): 179-192.] 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'' (aside from having a much more square-looking skull).
In Zhu's redescription, "Quasipetalichthyidae" (comprising ''Quasipetalichthys'', ''
Eurycaraspis'', and possibly ''Neopetalichthys'') and "Macropetalichthyidae" (comprising all the other "advanced" petalichthyid genera not including ''Neopetalichthys'', or ''Diandongpetalichthys'') form a dichotomy, with ''Diandongpetalichthys'' as a sister taxon.
''Neopetalichthys'' is treated as an ''
incertae sedis
' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...
'' 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
The Lochkovian is one of three faunal stages in the Early Devonian Epoch. It lasted from 419.2 ± 3.2 million years ago to 410.8 ± 2.8 million years ago. It marked the beginning of the Devonian Period, and was followed by the Pragian Stage. It is ...
from: -411.2 till: -407 color:earlydevonian text: Pragian
from: -407 till: -397.5 color:earlydevonian text:Emsian
The Emsian is one of three faunal stages in the Early Devonian Epoch. It lasted from 407.6 ± 2.6 million years ago to 393.3 ± 1.2 million years ago. It was preceded by the Pragian Stage and followed by the Eifelian Stage. It is named after the ...
from: -397.5 till: -391.8 color:middledevonian text:Eifelian
The Eifelian is the first of two faunal stages in the Middle Devonian Epoch. It lasted from 393.3 ± 1.2 million years ago to 387.7 ± 0.8 million years ago. It was preceded by the Emsian Stage and followed by the Givetian Stage.
North American ...
from: -391.8 till: -385.3 color:middledevonian text:Givetian
The Givetian is one of two faunal stages in the Middle Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Eifelian Stage and followed by the Frasnian
The Frasnian is one of two faunal stages in the ...
from: -385.3 till: -374.5 color:latedevonian text:Frasnian
The Frasnian is one of two faunal stages in the Late Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Givetian Stage and followed by the Famennian Stage.
Major reef-building was under way during th ...
from: -374.5 till: -359.2 color:latedevonian text:Famennian
The Famennian is the latter of two faunal stages in the Late Devonian Epoch. The most recent estimate for its duration estimates that it lasted from around 371.1 million years ago to 359.3 million years ago. An earlier 2012 estimate, still used b ...
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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
color:earlydevonian bar:NAM2 from: -407 till: -397.5 text: Neopetalichthys
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
color:middledevonian bar:NAM12 from: -387.47 till: -385.3 text: Quasipetalichthys
color:latedevonian bar:NAM13 from: -378.1 till: -374.5 text: Epipetalichthys
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from: -416 till: -411.2 color:earlydevonian text:Lochkovian
The Lochkovian is one of three faunal stages in the Early Devonian Epoch. It lasted from 419.2 ± 3.2 million years ago to 410.8 ± 2.8 million years ago. It marked the beginning of the Devonian Period, and was followed by the Pragian Stage. It is ...
from: -411.2 till: -407 color:earlydevonian text: Pragian
from: -407 till: -397.5 color:earlydevonian text:Emsian
The Emsian is one of three faunal stages in the Early Devonian Epoch. It lasted from 407.6 ± 2.6 million years ago to 393.3 ± 1.2 million years ago. It was preceded by the Pragian Stage and followed by the Eifelian Stage. It is named after the ...
from: -397.5 till: -391.8 color:middledevonian text:Eifelian
The Eifelian is the first of two faunal stages in the Middle Devonian Epoch. It lasted from 393.3 ± 1.2 million years ago to 387.7 ± 0.8 million years ago. It was preceded by the Emsian Stage and followed by the Givetian Stage.
North American ...
from: -391.8 till: -385.3 color:middledevonian text:Givetian
The Givetian is one of two faunal stages in the Middle Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Eifelian Stage and followed by the Frasnian
The Frasnian is one of two faunal stages in the ...
from: -385.3 till: -374.5 color:latedevonian text:Frasnian
The Frasnian is one of two faunal stages in the Late Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Givetian Stage and followed by the Famennian Stage.
Major reef-building was under way during th ...
from: -374.5 till: -359.2 color:latedevonian text:Famennian
The Famennian is the latter of two faunal stages in the Late Devonian Epoch. The most recent estimate for its duration estimates that it lasted from around 371.1 million years ago to 359.3 million years ago. An earlier 2012 estimate, still used b ...
bar:era
from: -416 till: -359.2 color:devonian text: Devonian
References
Sources
* Long, John A. ''The Rise of Fishes: 500 Million Years of Evolution'' Baltimore: The Johns Hopkins University Press, 1996.
*
{{Taxonbar, from=Q147585
Early Devonian first appearances
Prehistoric fish orders
Late Devonian animals
Late Devonian extinctions