A new fossil lizard from the Lower Cretaceous Sasayama Group of Hyogo Prefecture, western Honshu, Japan

An assemblage of lizards from the Early Cretaceous of Japan

“…Moreover, new squamate material has recently been recovered from slightly younger (early Albian) deposits in Hyogo Prefecture. In addition to the Pachygenys adachii jaw mentioned above (Ikeda et al, 2015), the "Lower Formation" of the Sasayama Group in Hyogo Prefecture has yielded several isolated "scincomorph" dentaries (Ikeda and Saegusa, 2013). One of these (Hyogo Type A) shows some resemblance to Sakurasaurus shokawensis, but the others are distinct and show no obvious affinity to the taxa described herein in their combination of dental and mandibular characters.…”

“…The lizard species Sakurasaurus shokawensis was first described from Shokawa (Evans and Manabe, 1999b), and the same locality has yielded more fragmentary remains of one or more additional lizard taxa. More recently, squamate remains have also been recovered from the slightly younger (early Albian) Sasayama Group of Hyogo Prefecture (Ikeda and Saegusa, 2013;Ikeda et al, 2015). Shiramine has been more productive, with a diverse squamate assemblage (Evans and Manabe, 2000) that includes Sakurasaurus sp.…”

“…Pachygenys was based on two mandibles from Early Cretaceous deposits in Shandong Province, China. Recently, however, closely similar jaws were recovered from the Sasayama Group of Hyogo Prefecture, Japan (Ikeda et al, 2015), dated as early Albian (112 Ma, Kusuhashi et al, 2013) and named Pachygenys adachii. As in Hakuseps imberis, the dentary of Pachygenys thlastesa is curved and has small number of teeth (eight) concentrated at the anterior end of the dentary.…”

“…Small reptile (preserved dentary length 9.75 mm) that differs from all known squamates, living and extinct, in having dentary with alveolar margin ending abruptly roughly halfway along the bone and leaving thick, strongly curved, edentulous border between posteriormost tooth and coronoid facet; somewhat resembles Early Cretaceous Pachygenys spp. from China (Gao and Cheng, 1999) and Japan (Ikeda et al, 2015) in edentulous margin and in short dentary tooth row (10 tooth positions versus 8 in Pachygenys), but differs in having heterodont dentition with unicuspid anterior teeth and bicuspid posterior teeth (versus homodont series of bluntcrowned teeth in Pachygenys), dentary dorsal and ventral margins fused without suture to enclose FIGURE 12. The phylogenetic position of Asagaolacerta tricuspidens gen. et sp.…”

“…The two genera could be related, but given that both are represented only by partial mandibles, their phylogenetic position within Squamata is difficult to ascertain. Pachygenys has been referred to "scincomorphs" (Gao and Cheng, 1999) or lacertoids (Ikeda et al, 2015). Hakuseps imberis was not included in the phylogenetic analyses as it preserves too few codable characters.…”