Stensioella heintzi
Encyclopedia
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. heintzis placement in Placodermi. The paleontologist, Philippe Janvier
http://tolweb.org/onlinecontributors/app?service=external/ContributorDetailPage&sp=488&sp=X suggests that it was actually a holocephali
d, and not a placoderm at all. However, if this is true, then the holocephalids (chimaera
s, 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.
Hunsrück
The Hunsrück is a low mountain range in Rhineland-Palatinate, Germany. It is bounded by the river valleys of the Moselle , the Nahe , and the Rhine . The Hunsrück is continued by the Taunus mountains on the eastern side of the Rhine. In the north behind the Moselle it is continued by the Eifel...
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
Chimaera
Chimaeras are cartilaginous fish in the order Chimaeriformes, known informally as ghost sharks, ratfish , spookfish , or rabbitfishes...
-stargazer
Stargazer
The stargazers are a family Uranoscopidae of perciform fish that have eyes on top of their heads . The family includes about 50 species in 8 genera, all marine and found worldwide in shallow waters....
, 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
Placodermi
Placodermi is a class of armoured prehistoric fish, known from fossils, which lived from the late Silurian to the end of the Devonian Period. Their head and thorax were covered by articulated armoured plates and the rest of the body was scaled or naked, depending on the species. Placoderms were...
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. heintzis placement in Placodermi. The paleontologist, Philippe Janvier
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 contributed to the Tree of Life phylogeny project...
http://tolweb.org/onlinecontributors/app?service=external/ContributorDetailPage&sp=488&sp=X suggests that it was actually a holocephali
Holocephali
The subclass Holocephali is a taxon of cartilaginous fish, of which the order Chimaeriformes is the only surviving group.Holocephali has an extensive fossil record that starts during the Devonian period. However, most fossils are teeth, and the body forms of numerous species are not known, or, at...
d, and not a placoderm at all. However, if this is true, then the holocephalids (chimaera
Chimaera
Chimaeras are cartilaginous fish in the order Chimaeriformes, known informally as ghost sharks, ratfish , spookfish , or rabbitfishes...
s, iniopterygians, petalodonts, et al.) diverged from sharks before the Chondrichthyan Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
radiation.
Aside from a similar bodyplan to primitive holocephalids like Menaspis
Menaspis
Menaspis is an extinct genus of holocephalian cartilaginous fish from the Permian.-References:*Aquagenesis: The Origin and Evolution of Life in the Sea by Richard Ellis*Rocks and Fossils: A Visual Guide by Robert R. Coenraads...
, critics to Janvier's idea say that there is very little else in common with S. heintzi and holocephalids.