''Stensioella heintzi'' is an enigmatic placoderm of arcane affinity. It is only known from the

Lower Devonian The Early Devonian is the first of three epochs comprising the Devonian period, corresponding to the Lower Devonian series. It lasted from and began with the Lochkovian Stage , which was followed by the Pragian from and then by the Emsian, w ...

Hunsrück slate 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 ...

of Germany.

Anatomy

''Stensioella heintzi'' has an elongated body, a whip-like tail, and long, wing-like pectoral fins. In life, the animal would have looked vaguely like an elongated

ratfish Chimaeras are cartilaginous fish in the order Chimaeriformes , known informally as ghost sharks, rat fish, spookfish, or rabbit fish; the last three names are not to be confused with rattails, Opisthoproctidae, or Siganidae, respectively. At o ...

. Like the

sympatric In biology, two related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter one another. An initially interbreeding population that splits into two or more distinct species sh ...

Gemuendina ''Gemuendina stuertzi'' (named for Gemünden, Rhein-Hunsrück, Gemünden from where it was discovered) is a placoderm of the order Rhenanida, of the seas of Early Devonian Germany. In life, ''Gemuendina'' resembled a scaly ray with an upturned he ...

'', ''S. heintzi'' had armor made up of a complex mosaic of small, scale-like tubercles.

Taxonomy

''Stensioella'' is tentatively placed within Placodermi as being among the most basal of all placoderms, as from what can be discerned from the only whole specimen found, the shoulder joints of its armor appear to be very similar to other placoderms. Despite this detail, coupled with superficial similarities in skull plates, and gross, superficial similarities between its tubercles, and the tubercles of the rhenanids, some paleontologists believe that there are very few concrete reasons for ''S. heintzis placement in Placodermi. The paleontologist,

Philippe Janvier Philippe Janvier is a French paleontologist, specialising in Palaeozoic vertebrates, who currently works at the Museum National de l’Histoire Naturelle in Paris. He has written several books and scientific papers on Palaeozoic vertebrates and ...

suggests that it was actually a

holocephali Holocephali ("complete heads"), sometimes given the term Euchondrocephali, is a subclass of cartilaginous fish in the class Chondrichthyes. The earliest fossils are of teeth and come from the Devonian period. Little is known about these primiti ...

d, and not a placoderm at all. However, if this is true, then the holocephalids (

chimaera Chimaeras are cartilaginous fish in the order Chimaeriformes , known informally as ghost sharks, rat fish, spookfish, or rabbit fish; the last three names are not to be confused with rattails, Opisthoproctidae, or Siganidae, respectively. At ...

iniopterygians Iniopterygiformes ("Nape Wing Forms") is an extinct order of chimaera-like cartilaginous fish that lived from the Devonian to Carboniferous periods (345–280 million years ago). Fossils of them have been found in Montana, Indiana, Illinois ...

petalodont Petalodontiformes ("thin-plate teeth") is an extinct order of marine cartilaginous fish related to modern day chimaera found in what is now the United States of America and Europe.Lund, Richard, E. D. Grogan, and M. Fath. "On the relationships ...

s, et al.) diverged from sharks before the Chondrichthyan

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 ...

radiation. Aside from a superficially similar

bodyplan A body plan, ( ), or ground plan is a set of morphological features common to many members of a phylum of animals. The vertebrates share one body plan, while invertebrates have many. This term, usually applied to animals, envisages a "bluepr ...

to primitive holocephalids like ''

Menaspis ''Menaspis'' is an extinct genus of holocephalian cartilaginous fish from the Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years from the end of the Carboniferous Perio ...

'', critics to Janvier's idea say that there is very little else in common ''S. heintzi'' has with holocephalids.

References

External links

Mikko's Phylogeny Archive
Placoderm genera Placoderms of Europe Devonian placoderms Early Devonian fish of Europe Emsian life {{Placoderm-stub Hunsrück Slate fossils