Monday, July 9, 2012


The Family PRIONITIDAE is a nightmare of taxonomy.  The amount of intraspecific variation, or even intrageneric variation is overwhelming.  Most generic assignments are based on the shape, size, amount, and/or lack of ribs, bullae, nodes, whether they cross the venter or stop short, whether the nodes are mid flank or start near the umbilicus, whether the inner whorls or the outer whorls are smooth.  A lot of specific and generic assignments are arbitrary, a slightly arched venter instead of a flat venter is cause for different generic assignment of forms that basically look exactly alike. 

Tozer, 1994, in his monograph of Canadian Triassic Ammonoids, discussed the differences between Population Taxonomy and Typological Taxonomy and admitted that his classification, especially of the Prionitidae, was arbitrary, and to use a strictly typological taxonomy would mean almost every specimen was a seperate species.  He also talked about using the typological method just to show what the taxon looked like.

To see a Prionitid, it is easily assigned to the Prionitidae, and the beds containing it are easily assigned to the Late Smithian, and usually to the biozone and/or beds known for the Prionitidae.  Is it really necessary to split them into a bunch of different species or genera?  I suppose I could live with a few nominal species divided amongst a few genera for the time being, at least until the family is revised and a more natural classification determined.  Still, what a Prionite-mare.

For references see THIS old post, along with an old rant of the same topic. ;)

Wednesday, April 4, 2012

When Ammonites Fly

Along the lines of reverting to aquatic dinosaurs as has been seen in the geoblogosphere of late, I give you Duria Antiquior (above), and it's lithographic byproduct (below).  Floating on the surface of the water are ammonites with wings (or sails as conjectured some).

Clearly showing that ammonites could fly


Or could they?

A lot of science has been done since the art above was first seen.  Back then about the only creature known to compare the ammonites to was the Argonaut, one of the group of octopus that are known for a lot of webbing between their arms (such as this Blanket Octopus).  The "wings" of argonauts are specially modified arms used to secrete a calcium carbonate shell used to hold eggs (best seen in the top photo here).  We now compare ammonite shells more closely to the Pearly Nautilus and the animal itself to the ten armed cephalopods.  Hopefully we can advance as we learn, .