New ornithopod footprints from the Lower Cretaceous Kitadani Formation, Fukui, Japan: Ichnotaxonomical implications

Abstract

Two ichnogenus of “large-sized” ornithopods are found from the Lower Cretaceous (Aptian) Kitadani Formation in central Japan. Caririchnium isp. is characterized by the longer pes print than its width with strong mesaxony. Amblydactylus isp. is characterized by the wider pes print than its length with weak mesaxony. In the northern hemisphere, Caririchnium-type footprints are known from the Berriasian–Cenomanian strata, whereas Amblydactylus-type footprints are known from the Barremian–Maastrichtian strata. It is consistent with the temporal and geographic distribution of non-hadrosauroid iguanodontians and basal hadrosauroids. It suggests that footprint length-width ratio and mesaxony are important factors to indicate trackmakers (basal iguanodontian or hadrosauroid). Two “large-sized” ornithopod ichnogenus from the Kitadani Formation is also consistent with two iguanodontians from same site. It indicates a high diversity of the Kitadani ichnofauna and its importance to elucidate the ecosystem of the Kitadani Formation.