Wednesday, January 9, 2008

Churkites vs Arctoceras

Churkites noblei Jenks 2007

The ornamentation is exactly like Arctoceras tuberculatum, the only difference is the shape of the venter. These have an acute venter, becoming almost oxyconic in large shells and Arctoceras has a well rounded venter (almost semi-circular). This could be sexual dimorphism with the round ventered forms being female and the acute ventered forms male.

Of course there are two different sizes found in the Confusion Range, the small 100-180mm and the large 300mm, perhaps these are dimorphs of Churkites and Arctoceras isnt congeneric.

Jenks, J. F., 2007, Smithian (Early Triassic) Ammonoid Biostratigraphy at Crittenden Springs, Elko County, Nevada and a New Ammonoid From the Meekoceras Gracilitatis Zone, in, Lucas S. G. and Spielmann, J. A. eds., Triassic of the American West, New Mexico Museum of Natural History and Science Bulletin 40

1 comment:

  1. These may be a different species than C. noblei, these are more involute than C. noblei.