Pseudopetalichthyida is an

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

of lightly armored

placoderm Placoderms (from Ancient Greek πλάξ 'plax'', ''plakos'''Plate (animal anatomy), plate' and δέρμα 'derma'''skin') are vertebrate animals of the class (biology), class Placodermi, an extinct group of prehistoric fish known from Pal ...

s known only from rare fossils in Lower Devonian strata in

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

, Germany. Like '' Stensioella heintzi'', and the Rhenanida, the Pseudopetalichthids had armor made up of a mosaic of tubercles. Like '' Stensioella heintzi'', the Pseudopetalichthids' placement within

Placodermi Placoderms (from Ancient Greek πλάξ 'plax'', ''plakos plate' and δέρμα 'dermaskin') are vertebrate animals of the class Placodermi, an extinct group of prehistoric fish known from Paleozoic fossils during the Silurian and the De ...

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 Ptyctodonts. And as such, pro-placoderm experts consider Pseudopetalichthyida to be the sister group of the Arthrodires + Phyllolepida + Antiarchi trichotomy and the Acanthothoraci + Rhenanida

dichotomy A dichotomy () is a partition of a set, 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: nothi ...

. The best known species is the

type species In International_Code_of_Zoological_Nomenclature, 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 spe ...

'' 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 '' Stensioella heintzi'', 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 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 410.62 ±1.95 million years ago to 393.47 ±0.99 million years ago. It was preceded by the Pragian Stage and followed by the Eifelian Stage. It is named after ...

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

from: -385.3 till: -374.5 color:latedevonian text: Frasnian from: -374.5 till: -359.2 color:latedevonian text:

Famennian The Famennian is the later of two faunal stages in the Late Devonian epoch. The most recent estimate for its duration is that it lasted from around 371.1 to 359.3 million years ago. An earlier 2012 estimate, still used by the International Commis ...

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

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

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

from: -397.5 till: -391.8 color:middledevonian text: Eifelian from: -391.8 till: -385.3 color:middledevonian text:

from: -385.3 till: -374.5 color:latedevonian text: Frasnian 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 Placoderm orders Monotypic vertebrate orders