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Thomas A. Hegna, Ph.D

On the 5th day of my true love gave to me, Angustidontus seriatus Cooper, 1936 (Woodruff Fm, Nevada, USA). Originally described as an actinopterygian fish from isolated claw material (though others thought the fossils to be eurypterid chelicerae), complete fossils like this one revealed the true nature of these claws.
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Devonian crustacean, Angustidontus seriatus
Dec 05, 2022, 05:26 PM·Public·Web
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Thomas A. Hegna, Ph.D

The maxilliped claws were evidently quite robust—they are known as fossils from a number of localities without accompanying body fossils. The maxillipeds have interesting patterns of teeth in alternating sizes.
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Maxilliped claw from the Devonian crustacean Angustidontus seriatus
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Thomas A. Hegna, Ph.D

They have been suggested to be a sistergroup to the decapods (Gueriau et al 2014), or related to the Devonian decapod Palaeopalaemon, and thus within the crown-group Decapoda (Jones et al., 2018). Images from Rolfe & Dzik, 2006.
Rolfe, W. D. I., and J. Dzik. 2006. Angustidontus, a Late Devonian pelagic predatory crustacean. Transactions of the Royal Society of Edinburgh: Earth Sciences 97: 75-96.
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Reconstruction of Devonian crustacean Angustidontus seriatus
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Jo Wolfe

@Thomashegna stronger evidence of sister group to decapods also by @pgueriau biorxiv.org/content/10.1101/20

bioRxivExceptional Late Devonian arthropods document the origin of decapod crustaceansWith over 15,000 extant species, Decapoda—or ten-legged crustaceans such as crabs, shrimp, lobsters, and relatives— are among the most speciose and economically important group of crustaceans. Despite of their diversity, anatomical disparity, and remarkable fossil record extending back to the Late Paleozoic, the origins of Decapoda and their phylogenetic relationships with eumalacostracans remains elusive and inconclusive. Molecular dating suggests that decapods originated in the Late Ordovician (~450 Mya), but no reliable fossil crown groups are found until the Late Devonian. Moreover, there is no consensus on which lineages belong to stem groups, obscuring our understanding of the roots of the ten-legged decapod body plans as a whole, and how they relate to other non-decapod crustaceans. We present new, exceptional fossils from the Late Devonian of Czech Republic and Poland that belong to †Angustidontida, an odd shrimp-looking crustacean with a combination of anatomical features unlike those of any crown eumalacostracan known—extinct or extant. Our phylogenetic analyses, including representatives of all major lineages of crown eumalacostracans plus †Angustidontida, identify angustidontids as the only known stem-group decapod, and give hints about the transformation series, polarity of change, and evolutionary pathways leading to the modern decapod body plans seen today. ### Competing Interest Statement The authors have declared no competing interest.
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Thomas A. Hegna, Ph.D

@jopabinia I did not know about this. Nor did I know that @pgueriau was lurking on Mastodon.

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