Monday, July 17, 2023
Devonian Orthocones
Monday, May 8, 2023
Early Triassic Stomatopod
Saturday, September 10, 2022
More Taxonomy
A new paper just out trying to update the nomenclature and authorship of ammonoids:
The higher taxonomic nomenclature of Devonian to Cretaceous ammonoids and Jurassic to Cretaceous ammonites including their authorship and publication
Hoffmann, René; Howarth, Michael K.; Fuchs, Dirk; Klug, Christian; Korn, Dieter
Thursday, July 21, 2022
Paris Biota Decapods
The Paris Biota decapod (Arthropoda) fauna and the diversity of Triassic decapods
Abstract
We describe here the early Spathian (Early Triassic) Paris Biota decapod fauna from the western USA basin. This fauna contains two taxa of Aegeridae (Dendobranchiata), namely Anisaeger longirostrus n. sp. and Aeger sp. that are the oldest known representatives of their family, thus extending its temporal range by 5 Myr back into the Early Triassic. This fauna also includes two representatives of Glypheida (Pleocyemata) with Litogaster turnbullensis and Pemphix krumenackeri n. sp., confirming for the former and extending for the latter the temporal ranges of their respective superfamilies back to the Early Triassic. Overall, the Paris Biota decapods are some of the oldest known representatives of Decapoda, filling in an important gap in the evolutionary history of this group, especially during the Triassic that marks the early diversification of this clade. Additionally, we compile and provide overviews for all known Triassic decapods, which leads to the revision of four species of Middle and Late Triassic Aegeridae, and to a revised family assignment of a Middle Triassic Glypheida. Based on this refined dataset, we also investigate decapod diversity throughout the Triassic. We show that the apparent increase in decapod taxonomic richness is probably driven by the heterogeneity of the fossil record and/or sampling effort, and that the decapod alpha diversity is actually relatively high as soon as the Early Triassic and remains rather stable throughout the Triassic.
Friday, April 15, 2022
Cephalopod Phylogenetics
Wednesday, March 9, 2022
Ammonite Chamber Internal Mold
An internal mold of an ammonite chamber. Left, lateral view, right, apertural view |
Two views of an internal mold of one of the chambers from the phragmocone of an ammonite (Prionocyclus macombi Meek 1876). The chamber was hollow and probably filled with gas and a little liquid while the animal was alive, and was probably empty of any solids after it died. How long it sat empty on the seafloor, and while it was being buried under sediment is unknown. Eventually, it was filled with what we have here, dark sparry calcite crystals. I imagine the crystals grew from the inner walls of the chamber towards the center until it was completely filled. You can see the siphuncle at the top of the chamber (the keel here is missing), and on the bottom, in the apertural view, you can see a notch where the keel of the preceding whorl would have fit.
Ammonites preserved in limestone or concretions are more often found this way because the surrounding shell was preserved uncrushed as the matrix around the shell hardened. Those found in sandstone or shale many times have the phragmocone and most of the chambers crushed unless the chambers were filled with sediment.
Sunday, December 5, 2021
The Canadian System (Period) as proposed by Flower (1957)
Because the Cephalopods were so different, Rousseau H. Flower wrote proposing the Canadian System with four divisions of unspecified rank (Flower 1957 p. 17). Quoting from Flower:
"Faunally, the Canadian is relatively isolated from the Ordovician above and is characterized by stocks of its own. In the cephalopods..., the Canadian-Ordovician boundary involves changes never lower than of generic rank, and generally of the rank of families and orders."
Someone looking at only, or mostly Cephalopod fossils could see the column this way. The four divisions are areas where Flower collected cephalopods. The Cassinian from the Ft. Cassin area in Vermont, the Jeffersonian from the Adirondacks in NY, the Demingian from the Florida Mts. in New Mexico, and the Gasconadian from the Ozark Mt. area of Missouri. I don't think his later collections in Utah and Nevada changed anything. His boundary is just above Zone K, which is basically the Hesperonomiella minor bed (e.g. Li and Droser 1999) or the base of the Whiterockian Stage of the Ordovician.
Chart modified from Flower 1964 (p. 23, fig. 3) Ross-Hintze Zones on the right. |
These days, the Canadian System of Flower (later referred to as the Canadian Series) has been replaced with the Ibexian Series (Ross et al., 1997) and the Lower Ordovician Series of the ICS.
Flower, R.H., 1957, Studies of the Actinoceratida, Memoir 2, New Mexico Bureau of Mines and Mineral Resources, Socorro, NM.
Flower, R.H., 1964, The Nautiloid Order Ellesmeroceratida (Cephalopoda), Memoir 12, New Mexico Bureau of Mines and Mineral Resources, Socorro, NM.
Li, X., and Droser, M.L., 1999, Lower and Middle Ordovician Shell Beds from the Basin and Range Province of the Western United States (California, Nevada, and Utah) PALAIOS, V. 14.
Ross, R.J., Jr, Hintze, L.F., Ethington, R.L., Miller, J.F., Taylor, M.E. & Repetski, J.E., 1997, The Ibexian, lowermost series in the North American Ordovician. United States Geological Survey Professional Paper, 1579-A.
Monday, November 8, 2021
Wiping the smile off the face of the horizontal Nautiloid
Needless to say, I now have to re-arrange the thoughts of horizontal nautiloids having smiles and put the smile on the vertical nautiloid.
This might be just as hard as giving up the Geosynclinal Theory I was taught back in 1972.
:)