| 概要 |
The Oligocene Yoshinotani Formation of Takeo, Saga Prefecture, Japan, yielded several distinct footprints without any track maker at the end of its trail. The most well-preserved trackway, consisting ...of eight left footprints and seven right ones, is described in this paper. Each footprint has four'fingers'and a bifurcate'heel'. The right and left footprints are arranged symmetrically. An average stride length, 25.8 cm, is nearly equal to an average track breadth, 24.6 cm. All left footprints are nearly equal in form and size, averaging 6.2 cm long and 3.4 cm wide. All right ones, 5.4 cm in length and 3.7 cm in width, are also identical with each other. This evidence suggests that the trackway was made by a pair of left and right legs of the track maker, which moved both left and right legs simultaneously. These footprints have been compared with the trails of bipedal vertebrates, including birds and turtles, but the manner of occurrence and the morphology of footprints suggest that they are probably undertracks formed by the pushing appendages of a limulid, i.e. the paired sixth cephalothracical appendage with four blades. Although no fossil limulid has been reported from Japan, the trackway of the Yo shinotani Formation, i. e. Kouphichnium sp., suggests that Japanese limulids should go back to the Oligocene age. It is predicted that limulid body fossils will be found from the Yoshinotani Formatiom, which is important in considering the origin of the living Japanese limulid, Tachypleus tridentatus続きを見る
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