''Stensioella heintzi'' is an enigmatic

placoderm Placoderms (from Ancient Greek πλάξ 'plax'', ''plakos'''Plate (animal anatomy), plate' and δέρμα 'derma'''skin') are vertebrate animals of the class (biology), class Placodermi, an extinct group of prehistoric fish known from Pal ...

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, whic ...

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. The

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

is named after

Erik Stensiö Prof Erik Helge Osvald Stensiö HFRSE (2 October 1891 – 11 January 1984), né Andersson, was an influential Swedish paleozoologist and founder of the so-called "Stockholm School" of vertebrate paleontology. He later took his new surnam ...

, the species name honours Anatol Heintz.

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 (not to be confused with rattails), spookfish, or rabbit fish; the last two names are also applied to Opisthoproctidae and Siganidae, r ...

. Like the

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

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

tubercle In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal. In plants A tubercle is generally a wart-like projectio ...

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 paleontology, paleontologist, specialising in Palaeozoic vertebrates, who currently works at the Muséum national d'Histoire naturelle, Museum National de l’Histoire Naturelle in Paris. He has written several books an ...

suggests that it was actually a

holocephali Holocephali (Sometimes spelled Holocephala; Romanization of Greek, Greek for "complete head" in reference to the fusion of Palatoquadrate, upper jaw with the rest of the skull) is a Subclass (biology), subclass of Chondrichthyes, cartilaginous fi ...

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

chimaera Chimaeras are Chondrichthyes, cartilaginous fish in the order (biology), order Chimaeriformes (), known informally as ghost sharks, rat fish (not to be confused with rattails), spookfish, or rabbit fish; the last two names are also applied to B ...

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

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

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 "blueprin ...

to primitive holocephalids like '' Menaspis'', 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 Hunsrück Slate fossils {{Placoderm-stub