Pseudopetalichthyida is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

order of lightly armored placoderms known only from rare fossils in Lower Devonian strata in

Hunsrück The Hunsrück () is a long, triangular, pronounced upland in Rhineland-Palatinate, Germany. It is bounded by the valleys of the Moselle-Saar (north-to-west), the Nahe (south), and the Rhine (east). It is continued by the Taunus mountains, past ...

, Germany. Like ''

Stensioella heintzi ''Stensioella heintzi'' is an enigmatic placoderm of arcane affinity. It is only known from the Lower Devonian Hunsrück slate of Germany. Anatomy ''Stensioella heintzi'' has an elongated body, a whip-like tail, and long, wing-like pectoral fin ...

'', and the

Rhenanida Rhenanida ("Rhine (fish)") is an Order (biology), order of scaly placoderms. Unlike most other placoderms, the rhenanids' armor was made up of a mosaic of unfused scales and tubercles. The patterns and components of this "mosaic" correspond to t ...

, the Pseudopetalichthids had armor made up of a mosaic of tubercles. Like ''

'', the Pseudopetalichthids' placement within

Placodermi Placodermi (from Greek πλάξ 'plate' and δέρμα 'skin', literally 'Plate (animal anatomy), plate-skinned') is a Class (biology), class of armoured prehistoric fish, known from fossils, which lived from the Silurian to the end of the Devoni ...

is suspect. However, due to a gross lack of whole, uncrushed, articulated specimens, there are no other groups that the Pseudopetalichthids could be, for a lack of a better word, pigeonholed into. On the other hand, according to anatomical studies done on the crushed specimens that have been found, those experts who do regard the Pseudopetalichthyida as placoderms consider them to be a group more advanced than the

Ptyctodont The ptyctodontids ("folded-teeth") are placoderms of the order Ptyctodontida, containing the family Ptyctodontidae. With their big heads, big eyes, reduced armor and long bodies, the ptyctodontids bore a superficial resemblance to modern day ch ...

s. And as such, pro-placoderm experts consider Pseudopetalichthyida to be the sister group of the

Arthrodires Arthrodira (Greek for "jointed neck") is an order of extinct armored, jawed fishes of the class Placodermi that flourished in the Devonian period before their sudden extinction, surviving for about 50 million years and penetrating most marine ec ...

+ Phyllolepida +

Antiarchi Antiarchi ("opposite anus") is an order of heavily armored placoderms. The antiarchs form the second-most successful group of placoderms after the arthrodires in terms of numbers of species and range of environments. The order's name was coin ...

trichotomy and the Acanthothoraci +

dichotomy A dichotomy is a partition of a whole (or a set) into two parts (subsets). In other words, this couple of parts must be * jointly exhaustive: everything must belong to one part or the other, and * mutually exclusive: nothing can belong simulta ...

. The best known species is the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

'' Pseudopetalicthys problematica''. Some experts have suggested that '' Paraplesiobatis heinrichsi'' is the same species as ''P. problematica'', but, due to the specimens of the latter species being crushed in a different position than the specimen of the former species, the anatomies of the two forms appear different (Moy-Thomas & Miles). However, this problem will be resolved only with more specimens. The anatomy of the specimens of '' Nessariostoma granulosum'' are sufficiently different from the other two pseudopetalichthyids to be recognized as a separate species. ''N. granulosum'' bears a superficial resemblance to ''

'', and it was this resemblance that originally led to the pseudopetalichthyids' grouping within Stensioellidae.

Timeline of genera

ImageSize = width:1000px height:auto barincrement:15px PlotArea = left:10px bottom:50px top:10px right:10px Period = from:-416 till:-359.2 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:5 start:-416 ScaleMinor = unit:year increment:1 start:-416 TimeAxis = orientation:hor AlignBars = justify Colors = #legends id:CAR value:claret id:ANK value:rgb(0.4,0.3,0.196) id:HER value:teal id:HAD value:green id:OMN value:blue id:black value:black id:white value:white id:paleozoic value:rgb(0.6,0.75,0.55) id:cambrian value:rgb(0.49,0.63,0.33) id:ordovician value:rgb(0,0.57,0.44) id:silurian value:rgb(0.70,0.88,0.71) id:devonian value:rgb(0.8,0.55,0.22) id:earlydevonian value:rgb(0.90,0.71,0.43) id:middledevonian value:rgb(0.96,0.81,0.51) id:latedevonian value:rgb(0.96,0.89,0.71) id:carboniferous value:rgb(0.4,0.65,0.6) id:mississippian value:rgb(0.4,0.56,0.4) id:pennsylvanian value:rgb(0.8,0.77,0.53) id:permian value:rgb(0.94,0.25,0.24) id:mesozoic value:rgb(0.38,0.77,0.79) id:triassic value:rgb(0.51,0.17,0.57) id:jurassic value:rgb(0.2,0.7,0.79) id:cretaceous value:rgb(0.5,0.78,0.31) id:cenozoic value:rgb(0.95,0.98,0.11) id:paleogene value:rgb(0.99,0.6,0.32) id:neogene value:rgb(0.999999,0.9,0.1) id:quaternary value:rgb(0.98,0.98,0.50) BarData= bar:eratop bar:space bar:periodtop bar:space bar:NAM1 bar:NAM2 bar:NAM3 bar:space bar:period bar:space bar:era PlotData= align:center textcolor:black fontsize:M mark:(line,black) width:25 shift:(7,-4) bar:periodtop 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 i ...

from: -411.2 till: -407 color:earlydevonian text:

Pragian The Pragian is one of three faunal stages in the Early Devonian Epoch. It lasted from 410.8 ± 2.8 million years ago to 407.6 ± 2.8 million years ago. It was preceded by the Lochkovian Stage and followed by the Emsian Stage. The most important La ...

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 s ...

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 Stage. It is named after the town of Givet in Fra ...

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:eratop from: -416 till: -359.2 color:devonian text:

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

PlotData= align:left fontsize:M mark:(line,white) width:5 anchor:till align:left color:earlydevonian bar:NAM1 from: -407 till: -403.83 text: Nessariostoma color:earlydevonian bar:NAM2 from: -407 till: -403.83 text:

Paraplesiobatis ''Paraplesiobatis heinrichsi'' is a lightly armored Pseudopetalichthyida, pseudopetalichthyid placoderm from the Hunsrück Slate, Hunsrückschiefer Lagerstätte of Early Devonian Germany. The Type specimen, type and only known specimen is an arti ...

color:earlydevonian bar:NAM3 from: -407 till: -403.83 text: Pseudopetalichthys PlotData= align:center textcolor:black fontsize:M mark:(line,black) width:25 bar:period from: -416 till: -411.2 color:earlydevonian text:

from: -411.2 till: -407 color:earlydevonian text:

from: -407 till: -397.5 color:earlydevonian text:

from: -397.5 till: -391.8 color:middledevonian text:

from: -391.8 till: -385.3 color:middledevonian text:

from: -385.3 till: -374.5 color:latedevonian text:

from: -374.5 till: -359.2 color:latedevonian text:

bar:era from: -416 till: -359.2 color:devonian text:

References

* Long, John A. ''The Rise of Fishes: 500 Million Years of Evolution'' Baltimore: The Johns Hopkins University Press, 1996. * Moy-Thomas, J. A. & Miles, R. S. ''Paleozoic Fishes'' (2nd ed)Chapman and Hall, London, 1971.

External links

Mikko's Phylogeny Archive
{{Taxonbar, from=Q3924915 Prehistoric fish orders