RESEARCH PAPER Revision of Isanodus paladeji (Elasmobranchii, Hybodontiformes) from the Lower Cretaceous of Thailand Suchada Khamha 1 • Gilles Cuny 2 • Komsorn Lauprasert 1 Received: 25 April 2015 / Accepted: 14 December 2015 Ó Pala ¨ontologische Gesellschaft 2015 Abstract Microremains from the Lower Cretaceous Phu Phan Thong locality, Nong Bua Lam Phu Province, northeastern Thailand, yielded ten tooth morphotypes of the freshwater shark genus Isanodus, which allow the revision of this genus. Two new morphotypes assigned to anterolateral and posterolateral teeth possess shared char- acters with anterior and posterior teeth of Isanodus paladeji whereas its former anterolateral and posterolateral teeth appear to belong to a new species, Isanodus nongbualam- phuensis sp. nov. The pattern of ornamentation in some teeth of I. paladeji and I. nongbualamphuensis is quite similar to that observed in the genus Heteroptychodus, suggesting these two genera are closely related. Keywords Isanodus Á Elasmobranchii Á Hybodontiformes Á Lower Cretaceous Á Thailand Kurzfassung Mikro-U ¨ berreste aus der Unterkreide von Phu Phan Thong Ort, Nong Bua Lam Phu Province, Thailand, ergaben zehn Zahnmorphotypen der Su ¨ßwasser Hai-Gattung Isanodus, die eine Revision dieser Gattung erlauben. Zwei neue Morphotypen besitzen gemeinsame Merkmale mit vorderen und hinteren Za ¨hnen von Isanodus paladeji und werden als anterolaterale oder posterolaterale Za ¨hne betrachtet. Die Za ¨hne, die fru ¨her als anterolaterale oder posterolaterale Za ¨hne von I. paladeji identifiziert wurden, scheinen in der Tat zu einer neuen Art, Isanodus nongbualamphuensis sp. nov., zu geho ¨ren. Zwei Morpho- typen ko ¨nnen nicht zu einer dieser beiden Arten geho ¨ren und zeigen die Anwesenheit einer dritten Art. Das Orna- mentations-Muster in einigen Za ¨hnen von I. paladeji und I. nongbualamphuensis sp. nov. ist ziemlich a ¨hnlich dem in der Gattung Heteroptychodus beobachteten, was eine eng Verwandtschaft dieser beiden Gattungen andeutet. Schlu ¨ sselwo ¨rter Isanodus Á Elasmobranchii Á Hybodontiformes Á Unterkreide Á Thailand Introduction In February 2006, more than a ton of sediments were collected from the Phu Phan Thong locality (Nong Bua Lam Phu Province, Sao Khua Formation, Barremian). Many taxa, including hybodont sharks, actinopterygians, turtles, crocodiles and dinosaurs, were identified among the thousands of microremains retrieved. Six taxa of hybodont sharks were identified based on isolated teeth by Cuny et al. (2006), including Isanodus paladeji, a species showing an important heterodonty. Its heterodonty pattern was reconstructed based on a comparison with Lissodus nodosus (Duffin 1985). All material from the Phu Phan Thong locality was completely sieved, but thus far only 250 kg of concentrated sediments has been sorted under a stereomicroscope. More teeth belonging to Isanodus have been retrieved, some of which possess shared characters with anterior and posterior teeth of I. paladeji. However, anterolateral and posterolateral teeth thus far attributed to this species, in fact, appear to belong to a different species & Komsorn Lauprasert lauprasert@gmail.com 1 Department of Biology, Faculty of Science, Mahasarakham University, Khamrieng, Kantharawichai District, Maha Sarakham 44150, Thailand 2 UMR CNRS 5276 LGLTPE ENS, Universite ´ Claude Bernard Lyon 1, 2, rue Raphae ¨l Dubois, 69622 Villeurbanne Cedex, France 123 Pala ¨ontol Z DOI 10.1007/s12542-015-0282-4