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

It may be the latest but it won't be the last.  I'm sure that just like those back in the fifties they're getting close to something natural. This should last 70 years just like the old scheme, with plenty of differing options in the interim.  

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.

Cephalopod Phylogenetics

The more things are found to be the same the more they are found to be different. It may never end

Pohle et al. BMC Biology (2022) 20:88 https://doi.org/10.1186/s12915-022-01284-5

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.