Rhenanid
| Rhenanida Temporal range: Emsian - Upper Frasnian |
|
|---|---|
 |
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| Gemuendina stuertzi | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | †Placodermi |
| Order: |
†Rhenanida Broili, 1930 |
| Genus | |
|
?Ohioaspis † |
|
?Ohioaspis †
Asterosteus †
Nefudina †
Gemuendina †
Jagorina †
Bolivosteus †
Rhenanida ("Rhine (fish)") is an 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 the plates of armor in other, more advanced placoderms, suggesting that the ancestral placoderm had armor made of unfused components, as well.
All rhenanids were flattened, ray-like, bottom-dwelling predators that lived in marine environments.
The rhenanids were once presumed to be the most primitive, or at least the closest to the ancestral placoderm, as their armor was made up of a mosaic of tubercles, as opposed to the solidified plates of "advanced" placoderms, such as antiarchs and arthrodires. Through comparing the skull anatomies of Jagorina pandora with those of antiarchs, the rhenanids are considered to be the sister group of the antiarchs (together with their respective Acanthothoracid relatives).
The fossil record of Rhenanida is very sparse, with most fossils being isolated tubercles and skull fragments that are identified as being similar to Gemuendina stuertzi, the most well-known rhenanid, known from several specimens from the Hunsruck slates. Given the rhenanids' worldwide distribution, this paupacity probably did not reflect a scarcity of living individuals (when the order was alive), but reflects the fact that rhenanid armor disintegrated into isolated fragments, and scattered soon after the owner's demise. Most fossils of rhenanids are from the Early Devonian, primarily in the United States and Germany. The recently discovered Nefudina qalibahensis is known from Northeastern Saudi Arabia. Asterosteus stenocephalus is known from Mid Devonian Ohio. Another species of rhenanid was Bolivosteus chacomensis, of the Lower to Middle Devonian Malvinokaffric Fauna of Western Gondwana, in what is now Bolivia, South America. The youngest rhenanid, Jagorina pandora is known from Upper Devonian Germany.
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