Phoebodus was recognized as the earliest elasmobranch known from articulated remains, a group which constitutes most modern cartilaginous fish comprising sharks, skates and rays. Its elongate body, the presence of two dorsal fins with fin spines, and the elongate head had already been described. Based on spectacularly well-preserved fossils, we add new anatomical information on its exact body proportions, the paired and caudal fins, the dermal denticles, the skull morphology, the endocast, and the gill skeleton. These new skeletons from the Famennian (Upper Devonian) of Morocco (c. 367 Ma) permit a much-improved reconstruction of the anatomy of Phoebodus. The new materials comprise the oldest elasmobranch specimens preserving the complete head in three dimensions. Additionally, the new materials yield information about growth and diet and thus position in the trophic network. Despite the newly coded characters, the phylogenetic position of the genus Phoebodus with the oldest teeth dating to the early Givetian remains that of the oldest stem-elasmobranch in the Bayesian analyses.

Key words: Chondrichthyes, Elasmobranchii, Famennian, ontogeny, exceptional preservation, Fossillagerstätten.

Christian Klug [chklug@pim.uzh.ch; ORCID: https://orcid.org/0000-0002-4099-7453], Merle Greif [merle.greif@uzh. ch; ORCID: https://orcid.org/0000-0001-5519-017X], Jonathan Pople [jonathan.pople@pim.uzh.ch; ORCID: https:// orcid.org/0009-0001-0029-0656], and Linda Frey [linda.frey@web.de; ORCID: https://orcid.org/0000-0001-6110- 0548], Paläontologisches Institut, Universität Zürich, Karl-Schmid-Strasse 4, 8006 Zürich, Switzerland. Alexander Pohle [alexander.pohle@rub.de; ORCID: https://orcid.org/0000-0001-6979-1048], Geowissenschaften, Ruhr-Universität Bochum, 44801 Bochum, Germany. Michal Ginter [m.ginter@uw.edu.pl; ORCID: https://orcid.org/0000-0002-7210-7312], Faculty of Geology, University of Warsaw, Żwirki i Wigury 93, 02-089 Warsaw, Poland. Michael I. Coates [mcoates@uchicago.edu; ORCID: https://orcid.org/0000-0003-2843-1075], Department of Organismal Biology and Anatomy, University of Chicago, 1027 E. 57th Street, Chicago, IL 60637, USA. Wahiba Bel Haouz [wahiba.belhaouz@gmail.com; ORCID: https://orcid.org/0000-0002-4799-9697], Géosciences, Géomatique, Planétologie and Environnement (GEOPEN) laboratory, Department of Geology, Faculty of Sciences Ain Chock, Hassan II University, Km 8 Route d’El Jadida, 20100, Casablanca, Morocco. Abdelouahed Lagnaoui [Abdelouaed.lagnaoui@uhp.ac.ma; ORCID: https://orcid.org/0000-0002-4176-1987], Laboratory of Education, Sciences and Training – LEST, Higher School of Education and Training Berrechid (ESEFB), Hassan First University, Route de Casablanca Km 3.5, BP 539, 26100, Berrechid, Grand-Casablanca, Morocco. Laboratory of Stratigraphy of Oil-and-Gas Bearing Reservoirs, Department of Paleontology and Stratigraphy, Institute of Geology and Petroleum Technologies, Kazan (Volga Region) Federal University, Kremlyovskaya Str. 18, Kazan, 420008, Russia.