Graptolite biozones are usually the most trusted ones, but we will also analyse the behaviour of biozones based on conodonts and chitinozoans, and also on less 'authoritative' groups of fossils such as ostracodes and 'microvertebrates' (mostly thelodont and acanthodian
Don and Eldon collected skull roofs of haplolepidid fishes and a fin-spine of a small acanthodian
fish (Gyracanthus) that Don later described in detail (Baird 1962a, 1978a).
But armed with new data on what the earliest sharks and bony fishes looked like, Coates and colleagues re-examined fossils of Acanthodes bronni, the best-preserved acanthodian
In addition, acanthodian
fish scales and a portion of a fin spine, and numerous actinopterygian and sarcopterygian fish scales and tips of actinopterygian teeth from the MNSC were identified by Kenaga and Sellepack (1995).
These substages correspond to the acanthodian
zones established by Valiukevicius .
Also interesting are the results of a close study of the acanthodian
scales within the excrement.
2002); very rare acanthodian
scales may occur in a few samples.
Another peculiarity highlighted by the data at hand is the sudden appearance of several acanthodian
taxa in the Nar Formation on Gotland.
According to a report in National Geographic News, the specimen is of a 415-million-year-old Ptomacanthus, which is only the second known example of a braincase from an Acanthodian
, a long-extinct group of fossil fish.
Gagnier, Paris, acanthodian
expert and member of expedition to Canadian Arctic islands in 1994.
and an acanthodian
of Gomphonchus sandelensis-type.
On the other hand, the acanthodian
species Diplacanthus gravis is only known to occur in the Arukula Regional Stage (Mark-Kurik 2000; Valiukevicius 2000).