When I was a lad, I was fond of dinosaurs. However, my school library was stocked with books from, at the most recent, the 1970s. Thus, they were filled with the slow, lumbering, dull-witted depictions of dinosaurs. They also contained information on various other prehistoric creatures: pterosaurs, icthyosaurs, plesiosaurs, and a big, ugly, nasty prehistoric fish called Dinicthys.
Okay, flash forward 10 years or so. I’m reading a shiny new dinosaur book, and I get to the sectrion on big, ugly, nasty prehistoric fish, and there’s a big picture of Dinicthys. However, it’s labelled, “Dunkleosteus”. What gives? Are they two different, but similar animals? Or are they the same animal, with a different name?
If they are the same animal, why the name change? Was it something similar to the Brontosaurus/Apatosaurus deal?
Dunkleosteus was (probably) the biggest member of the family Dinichthyidae (“terrible fishes”) from the Late Devonian period, about 400 million years ago. Generally speaking, Dunkleosteus is considered synonymous with Dinichthys.
Your guess is as good as mine on this one.
I googled the two names and got a variety of sources. This site, predominantly for children, indicates that Dinichthyidae was the family of placoderms that grew to record size, with Dinichthys as the type genus of the family and Dunkleosteus as the record-largest genus in the family. Other sites, such as here (page down for the Dinichthys text) suggest [by lines such as “Dunkleosteus (=Dinichthys)”] that the names are synonymous with Dunk having priority.
I think they are two separate extinct placoderm fish. Placoderm translates to “tablet skin” after the thick bony plates on the head. Dinicthys and Dunkleosteus are two very large placoderms and considered by some to be two separate genera of family Dinicthyidae “terrible fishes”, though I think we have only their skulls to go by. Some believe that the respective skulls are different age classes of the same species. You may find the following links helpful:
http://www.palaeos.com/Vertebrates/Units/Unit060/060.000.html
http://www.taylorstudios.com/models/Dunk.htm
This fellow seems to have put a lot of thought into this sort of question, though his site includes a disclaimer: “Caution: Please, don’t use this page as a scientific reference. This site is not peer-reviewed, and any alleged information contained herein may in fact represent whim, caprice, bias, speculation, ignorance, or simply typographical error, rather than science.”
Mikko’s Phylogeny Archive
He also is undecided about whether the two names describe the same or different fishes. Here’s the relevant part of his taxonomic chart:
|–o †Dinichthyidae Newberry, 1885
| |-- †Bruntonichthys multidens U. Dev. Aus.
| |-- †Bullerichthys fasadens U. Dev. Aus.
| |–o †Dinichthys [Ponerichthys] U. Dev. NA. [jr. synon. to Dunkleosteus??]
| | -- †D. canadensis [nomen dubium, type lost] [Hanke, Stewart & Lammers, 1996] | |--o †Dunkleosteus U. Dev. Eu. EEu. NAf. NA. | | – D. telleri
Just for the record, Placodermi is a (possibly invalid) class, on a level with jawless fishes, bony fishes, and sharks/rays/chimaeras; the order that the Dinichthyidae fall into are the Arthrodira.