Stensioella heintzi

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iStensioella heintzi

Extinct (fossil)

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Subphylum:	Vertebrata
Class:	Placodermi
Order:	?Stensioellida
Family:	Stensioellidae
Genus:	Stensioella
Species:	Stensiolla heintzi

Stensioella heintzi was an enigmatic placoderm of arcane affinity. It is only known from the Lower Devonian Hunsrück slates of Germany, where the only specimens have been found.

In life, it was a blocky-looking fish that resembled either a squat, pug-nosed combination chimaera-stargazer, or an uncompressed Gemuendina (Gemuendina also happened to be its contemporary in Hunsrück), with broad, wing-like pectoral fins. Like Gemuendina, it had armor made up of a complex mosaic of tubercles.

It is tentatively placed within Placodermi as being among the most primitive of all placoderms, as from what can be discerned from the few whole specimens 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. heintzi's placement in Placodermi. The paleontologist, Philippe Janvier [1] suggests that it was actually a holocephalid, and not a placoderm at all. However, if this is true, then the holocephalids (chimaeras, iniopterygians, petalodonts, et al) diverged from sharks before the Chondrichthyan Devonian radiation.

Aside from a similar bodyplan to primitive holocephalids like Menaspis, critics to Janvier's idea say that there is very little else in common with S. heintzi and holocephalids.