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I've recently heard about a Ctenacanthiform genus named Pyknotylacanthus from the Triassic of what is now Nevada and Idaho. The Ctenacanthiform genus consists of two species (P. spathianus and P. humboldtensis). What makes this genus so interesting is that while I've mostly heard that there is a gap in the fossil record between Permian and the Cretaceous where Ctenacanthiform fossils are recorded, this genus bridges that gap (if only by a little bit). G. Guinot, et al. (2013). Cretaceous stem chondrichthyans survived the end-Permian mass extinction. Nature Communication. 4:2669 doi: 10.1038/ncomms3669 https://www.nature.com/articles/ncomms3669 P. Davidson (1919). A cestraciont spine from the Middle Triassic of Nevada. University of California Publications, Bulletin of the Department of Geology 11(4): 433-435 R. J. Mutter and H. Rieber. (2005). Pyknotylacanthus spathianus gen et sp nov, a new ctenacathoid from the Early Triassic of Bear Lake (Idaho, USA). Revista Brasileira de Paleontologia 8(2): 139-148 There is also more recently another unnamed Ctenacanthiform recorded from the Triassic Arrow Rock section of the Oruatemanu Formation of New Zealand (this record also somewhat bridges the Permian-Cretaceous gap in Ctenacanthiform records). Grant-Mackie, & Yamakita, Satoshi & Matsumoto, & Hori, Rie & Takemura, & Aita, Yoshiaki & Takahashi, Satoshi & Campbell, Hamish. (2014). A probable shark dorsal fin spine fragment from the Early Triassic of the Arrow Rocks sequence, Whangaroa, northern New Zealand. New Zealand Journal of Geology and Geophysics. 57. 10.1080/00288306.2014.889722. https://www.researchgate.net/publication/265606171_A_probable_shark_dorsal_fin_spine_fragment_from_the_Early_Triassic_of_the_Arrow_Rocks_sequence_Whangaroa_northern_New_Zealand Iris Feichtinger, Andrea Engelbrecht, Alexander Lukeneder & Jürgen Kriwet (2020). New chondrichthyans characterised by cladodont-like tooth morphologies from the Early Cretaceous of Austria, with remarks on the microstructural diversity of enameloid, Historical Biology, 32:6, 823-836, DOI: 10.1080/08912963.2018.1539971 https://www.tandfonline.com/doi/abs/10.1080/08912963.2018.1539971?journalCode=ghbi20 What I'm really wondering is why has this Ctenacanthiform genus and it's confirmed presence in the Early Triassic been overlooked by most of the public (especially since the discovery of the Cretaceous Ctenacanthioform fossils in Europe in 2013 and 2020)?

Oldest 'fish-lizard' fossils ever found suggests these sea monsters survived the 'Great Dying' By Harry Baker, LIveScience, March 18, 2023 The fossilized remains of an ichthyosaur dating back to shortly after the Permian mass extinction suggest that the ancient sea monsters emerged before the catastrophic event Oldest sea reptile from Age of Dinosaurs found on Arctic island Uppsla University, March 13, 2023 The paper is: Kear, B.P., Engelschiøn, V.S., Hammer, Ø., Roberts, A.J. & Hurum, J.H., 2023: Earliest Triassic ichthyosaur fossils push back oceanic reptile origins. Current Biology 33(5), R1-R2 Yours, Paul H.

I've been fascinated with the Eugeneodontids (the buzz-saw chondrichthyans) and how they managed to practically become the apex predators of most oceanic environments from the Carboniferous to the Permian with famous members like Edestus and Helicoprion. Two genus of this extraordinary group even survived the Permian-Triassic Extinction 252 Million Years ago - Fadenia and Caseodus! http://www.fossilworks.org/cgi-bin/bridge.pl?a=taxonInfo&taxon_no=34456 http://www.fossilworks.org/cgi-bin/bridge.pl?a=taxonInfo&taxon_no=34451 But by the Olenekian stage of the Triassic, the group disappeared. I can understand why the more specialized members of the group like Helicoprion went extinct (ecological specialists and top predators don't do well in events like the Permian-Traissic Extinction event), but what caused the extinction of Fadenia and Caseodus? What occurred in the Triassic that ended the reign of the Eugeneodontids?

Why did trilobites go extinct? By Donavyn Coffey, Live Science, November 2020 https://www.livescience.com/why-trilobites-went-extinct.html The open access paper is: Jonathan L. Payne, Alexandra V. Turchyn, Adina Paytan, Donald J. DePaolo, Daniel J. Lehrmann, Meiyi Yu, and Wei, Calcium isotope constraints on the end-Permian mass extinction. PNAS May 11, 2010 107 (19) 8543-8548 https://www.pnas.org/content/107/19/8543 A totally unrelated article is: The role of cat eye narrowing in cat-human communication by Ellie Bennett, Snippet Science, November 2020 https://www.snippetscience.com/the-role-of-cat-eye-narrowing-in-cat-human-communication The open access paper is: Humphrey T, Proops L, Forman J, Spooner R and McComb K. The role of cat eye narrowing movements in cat-human communication. Sci Rep. 2020 Oct. 10, 16503 https://doi.org/10.1038/s41598-020-73426-0 Yours, Paul H.

https://phys.org/news/2020-11-large-volcanic-eruption-largest-mass.html?fbclid=IwAR0kx9loMz4DZP-V2K4ASrxZxqBP5E_ciswktcaUonT1QrYUCFGvmhzEOt8 Kunio Kaiho et al. Pulsed volcanic combustion events coincident with the end-Permian terrestrial disturbance and the following global crisis, Geology (2020). DOI: 10.1130/G48022.1

New evidence suggests volcanoes caused biggest mass extinction ever Mercury found in ancient rock around the world supports theory that eruptions caused 'Great Dying' 252 million years ago. University of Cincinnati, Science Daily, April 15, 2019 https://www.sciencedaily.com/releases/2019/04/190415122249.htm The open access paper is: Jun Shen, Jiubin Chen, Thomas J. Algeo, Shengliu Yuan, Qinglai Feng, Jianxin Yu, Lian Zhou, Brennan O’Connell, Noah J. Planavsky. Evidence for a prolonged Permian–Triassic extinction interval from global marine mercury records. Nature Communications, 2019; 10 (1) https://www.nature.com/articles/s41467-019-09620-0 Yours, Paul H.