Stensioella heintzi

From Palaeos

The suspect placoderm Stensioella heintzi, from the Early Devonian Hunsrück. Here, one of the beasts is settling down with the starfish Helianthaster rhenanus, while a Phacops ferdinandi trilobite explores a forgotten orthocone nautiloid shell.

Thelodonti
|--+--Furcacaudiformes
|  `--Thelodontida
`--+--+--Katoporida 
   |  `--Cephalaspidomorphi
   `--+--Loganiidae
      `--Gnathostomata
         |--PLACODERMI
         |  |?--Stensioellida
         |  |==Acanthothoraci
         |  |--Arthrodira
         |  |  |--Actinolepidoidei
         |  |  `--Phlyctaenioidei
         |  |     |--Phlyctaenii
         |  |     `--Brachythoraci
         |  |--+--Petalichthyida
         |  |  `--Ptyctodontida
         |  `--+--Rhenanida
         |     `--Antiarchi
         `--Eugnathostomata
            |--Chondrichthyes
            `--Teleostomi 

Stensioella heintzi was an enigmatic fish of arcane affinity. It is 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 contempary in Hunsrück). Like Gemuendina, it had armor made up of a complex mosaic of tubercles.

It is tentatively placed within Placodermi, 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. However, aside from this, coupled with superficial similarities in skull plates, and gross, superficial similarities between its tubercles, and the tubercles of the rhenanids, 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 then the holocephalids (chimaeras, iniopterygians, petalodonts, et al) diverged from sharks before the Chondrichthyan Carboniferous radiation.

External Links

Reconstruction [2]

Wikipedia [3]

References

Long, John A. The Rise of Fishes: 500 Million Years of Evolution Baltimore: The John Hopkins University Press, 1996. ISBN 0-8018-5438-5