Allenypterus montanus was an unusual early coelacanth that lived during the late Carboniferous, around 324 million years ago, in a tropical bay covering what is now central Montana, USA.
Up to about 15cm long (~6"), its tapering tadpole-like body plan somewhat resembled that of modern knifefishes and featherbacks, with the top part of its tail fin highly elongated into a ribbon-like shape and the rest of its tail fins being vestigial. The distinctive humped shape of its back was also much more pronounced in larger, more mature individuals.
It was probably a fairly slow swimmer, and preserved gut contents suggest it mainly ate small soft-bodied prey.
Its closest known relative seems to have been the eel-like Holopterygius – but since around 60 million years and different continents separated them both, this suggests the existence of a whole ghost lineage of other tapering coelacanths yet to be discovered.
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References:
Friedman, Matt, and Michael I. Coates. "A newly recognized fossil coelacanth highlights the early morphological diversification of the clade." Proceedings of the Royal Society B: Biological Sciences 273.1583 (2006): 245-250. https://doi.org/10.1098%2Frspb.2005.3316
Lund, Richard, and Wendy Lund. "New genera and species of coelacanths from the Bear Gulch Limestone (Lower Carboniferous) of Montana (USA)." Geobios 17.2 (1984): 237-244. https://www.academia.edu/download/66985268/s0016-6995_2884_2980145-x20210504-8876-dzniic.pdf
Lund, Wendy L., Richard Lund, and G. Klein. "Coelacanth feeding mechanisms and ecology of the Bear Gulch coelacanths." Compte Rendus du Neuvième Congrès International sur la Stratigraphie et la Géologie du Carbonifère 5 (1985): 492-500. https://www.researchgate.net/publication/285577607_Coelacanth_Feeding_Mechanisms_and_Ecolqgy_of_the_Bear_Gulch_Coelacanths
Toriño, Pablo, Matías Soto, and Daniel Perea. "A comprehensive phylogenetic analysis of coelacanth fishes (Sarcopterygii, Actinistia) with comments on the composition of the Mawsoniidae and Latimeriidae: Evaluating old and new methodological challenges and constraints." Historical Biology 33.12 (2021): 3423-3443. https://doi.org/10.1080/08912963.2020.1867982
"Diamond in the Rough"
Stethacanthus/Allenypterus
Carboniferous, 318 million years ago, Bear Gulch
Allenypterus is a funny, stubby form of lobefin fish with the sense to armor the belly, where all the vitals are. It ate small, soft-bodied organsims.
Stethacanthus is a sharklike fish with, notably, what appears to be a back-mounted anvil for a dorsal fin (although I have no idea whether it's a true fin). This, and its head, had long, spiny denticles on its skin, seemingly present in males. As a ukiyo-e inspired piece, I took the liberty of giving it scales, like some old depictions of tiger sharks.
Living fish have been observed using sharks as mobile scratching posts. It's far from impossible that this phenomenon happened millions of years back as well.
This is part of my Perspectives series! Check out #perspectives on my blog for more.
The following is a digital doodle of a Allenypterus that I made. I did this as practice, I hope y'all like this drawing of this prehistoric Coelacanth.
Allenypterus – рід доісторичних лопатеперих риб, яка жила під час башкирського віку пізнього карбону, 318 мільйонів років тому). Скам’янілості були виявлені у вапняку Бер-Галч, штат Монтана, США. Рід був описаний в 1969 році.
