New record of the Early Jurassic myriacanthid holocephalan Myriacanthus paradoxus AGASSIZ, 1836 from Belgium by Christopher J. Duffin (*) and Dominique Delsate (**) Abstract: A right upper posterior ("palatine") toothplate from the Grès de Florenville ( bucklandi zone, Lower Sinemurian, Early Jurassic) of Clairefontaine (Belgian Lorraine) is described and identified as Myriacanthus paradoxus AGASSIZ, 1836. This, the first record in Belgium, extends the known palaeogeographical range of the species. Key words: Chondrichtyes, Holocephali, Myriacanthid, Jurassic, Belgium. Résumé: Le Grès de Florenville (Zone à bucklandi , Sinémurien inférieur, Jurassique inférieur) de Clairefontaine (Lorraine belge) a livré une plaque dentaire postéro-supérieure droite ("palatine") de Chimère. Elle est ci-décrite et attribuée à Myriacanthus paradoxus AGASSIZ, 1836. Cette espèce est signalée pour la première fois en Belgique. Son extension paléogéographique connue s'en trouve ainsi élargie. Mots-clefs: Chondrichtyes, Holocephali, Myriacanthid, Jurasique, Belgique. Kurzfassung: Eine rechtse oberposteriore ("palatine") Zahnplatte von dem Grès de Florenville (Bucklandi-Zone , Unteres Sinemurium, Unter-Jurassicum) von Clairefontaine (belgische Lothringen) wird beschrieben und bestimmt als Myriacanthus paradoxus AGASSIZ, 1836. Dieser erste Fund in Belgien vergrößert die paläontologische Reichweite dieser Art. Schlüsselwörter: Chondrichtyes, Holocephali, Myriacanthid, Jurassicum, Belgiën. (*) Dr. C. DUFFIN, 146 Church Hill Road, Sutton, Surrey SM3 8NF, England. (**) Dr. D. DELSATE, 5 Rue du Quartier, 6792 Battincourt, Belgium. Introduction The myriacanthoids are an extinct group of holocephalans ranging from the Late Triassic (Rhaetian) to the Late Jurassic (Tithonian). They are most commonly represented by isolated toothplates, dorsal fin spines and frontal clasper spines, although some articulated specimens are known from the Lower Lias (Sinemurian) of Lyme Regis, Dorset, England (WOODWARD, 1891), Osteno in Lombardy, Italy (DUFFIN, 1992; DUFFIN & PATTERSON, in press), the Posidonienschiefer (Toarcian) of Holzmaden, Germany (FRAAS, 1910; DUFFIN, 1983), and the Plattenkalk of Solnhofen, Germany (ZITTEL, 1887). Holocephalan specimens are relatively rare components of most Jurassic vertebrate faunas, and the geographical and stratigraphical ranges of most taxa seem to be very limited. This is almost certainly due to the scarcity of material. Myriacanthus is the type genus of the family, and M. paradoxus is the type species of the genus by monotypy. It is currently known only from the "Lower Lias" of Lyme Regis, and the Westbury Beds (Penarth Group (Rhaetian, Late Triassic) of Aust Cliff, Avon (DUFFIN, 1994). An upper anterior ("vomerine") tooth plate from the Hettangian of France (TERQUEM, 1855) may pertain to this species, but anterior upper tooth plates are not well known in myriacanthids. Indeed, the upper anterior tooth plates of M. paradoxus from Lyme Regis and Halonodon warneri DUFFIN, 1984 from the Belgian Sinemurian are virtually indistinguishable. The purpose of the present paper is to extend the known palaeogeographical range of Myriacanthus paradoxus into southern Belgium. Geological background The Lorraine (southern Belgium and Grand Duchy of Luxembourg) consists of a sequence of cuestas of Early Mesozoic clastic sedimentary rocks. Three cuestas form the Belgian Lorraine; the Sinemurian, Pliensbachian and Bajocian cuestas.