Editing Placoderm (section)

====Stensioellida ====
[[File:Stensioella heintzi.png|thumb|upright|''[[Stensioella heintzi]]'']]
[[Stensioellida]] ("[Heintz's] little [[Erik Stensio|Stensio]]") contains another problematic placoderm of uncertain affinity, known only from the [[Lower Devonian]] [[Hunsrück]] slates of Germany. ''Stensioella'' was a thin fish that, when alive, looked vaguely like an elongated [[chimaeridae|ratfish]], or a skinny ''[[Gemuendina]]'' with thin, strap-like pectoral fins. Similar to those of the Rhenanida, its armour was a complex mosaic of small, scale-like tubercles. The shoulder joints of its armour are similar to other placoderms, and there are superficial similarities in skull plates, and even more superficial similarities between its tubercles and the tubercles of the [[rhenanids]]. It is tentatively placed within Placodermi as a primitive placoderm, though some paleontologists believe the rationale for the placement is inadequate. The paleontologist [[Philippe Janvier]], as well as other paleontologists, has suggested that ''Stensioella'' is not a placoderm, but instead is a [[holocephali]]an.<ref>{{Cite web |last=Carr |first=Robert K. |display-authors=etal |date=2010 |title=The ancestral morphotype for the gnathostome pectoral fin revisited and the placoderm condition |url=https://www.academia.edu/48849838 |website=Academia}}</ref><ref>{{Cite web | url=http://tolweb.org/onlinecontributors/app?service=external/ContributorDetailPage&sp=488&sp=X | title=Philippe Janvier Tree of Life Contributor Profile}}</ref> If this is true, then the holocephalians diverged from sharks before the [[Chondrichthyes|Chondrichthyan]] [[Devonian]] radiation. Critics of Janvier's position say that aside from a [[bodyplan]] superficially similar to primitive [[holocephali]]ans, the two groups have little else in common anatomically.