| Pseudopetalichthyida Temporal range:Emsian | |
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| Artist's reconstructions | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | †Placodermi |
| Order: | †Pseudopetalichthyida Denison 1975 |
| Family: | †Paraplesiobatidae Berg 1940 |
| Species | |
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Pseudopetalichthyida is anorder of lightly armoredplacoderms known only from rare fossils in Lower Devonian strata inHunsrück, Germany. LikeStensioella heintzi, and theRhenanida, the Pseudopetalichthids had armor made up of a mosaic of tubercles. LikeStensioella heintzi, the Pseudopetalichthids' placement withinPlacodermi 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 thePtyctodonts. And as such, pro-placoderm experts consider Pseudopetalichthyida to be the sister group of theArthrodires +Phyllolepida +Antiarchitrichotomy and theAcanthothoraci +Rhenanidadichotomy.
The best known species is thetype speciesPseudopetalicthys problematica. Some experts have suggested thatParaplesiobatis heinrichsi is the same species asP. 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 ofNessariostoma granulosum are sufficiently different from the other two pseudopetalichthyids to be recognized as a separate species.N. granulosum bears a superficial resemblance toStensioella heintzi, and it was this resemblance that originally led to the pseudopetalichthyids' grouping within Stensioellidae.
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