京都大学21世紀COEプログラム 活地球圏の変動解明 アジア・オセアニアから世界への発信

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Seminar Series of Active Geosphere #31

T. Satomura

Paleontological Analysis of the Dinosaur Foot-prints, at the Chat Trakan National Park, northeast of Phitsanulok

by
Takeshi Setoguchi & Kazuhiro Kiyoto
Graduate School of Science, Kyoto University

By the preliminary analysis of the foot-prints at the Chat Trakan Nationhal Park, it is concluded that the foot-prints have been left by some kinds of bi-pedal animals, not by quadra-pedal animals. All the tracks are arranged in the narrow transverse distance. The tracks are composed of two rows. The distances from one print to the contiguous print in the same row are nearly constant in both the right and left rows and a print is situated nearly at the mid-point between the contiguous prints of the opposite row. These kinds of prints can be left only by bi-pedal animals.
An another slub of the sandstones which is also reclined at the angle of nearly 70 degree is recognized. On the under-surface of the reclining slub, many foot-prints are observable. The outlines of the foot-prints on the sandstone surface have been faded because of weathering, but more clearly preserved foot-prints are observable on the under-surface of the reclining slub: the latter is the counterpart mold of the former cast. The foot-prints clearly show that the animal had four digits anterior to their foot: three outer digits (Digits U-W) are facing front-laterally and the rest (Digit T) is facing medially. This condition of Digit T indicates that this animal is surely a dinosaur, because birds are diagnosed by its reflexed Digit T (Hallux) facing posteriorly rather than medially. Among mammals, no bipedal types have been evoluved during the Cretaceous and Tertiary.
Alexander (1976) provided the key to deriving estimates of dinosaur gait and speed from trackways. From observations of modern animals, he derived a general relationship between an animal's speed of locomotion (v) and its hip height (h) and its stride length (SL), which is

v = 0.25*g0.5*SL1.67*h-1.17

Alexander also pointed out that this formula could be applied to dinosaur trackways since the stride length can be measured directly and the hip height could be estimated from the size of the foot prints. The stride length si the distance between successive prints of the same foot. Alexander estimated from a range of dinosaur skeletons that the hip height ranged from 3.6 to 4.3 times the foot length and h=4*foot print length has become widely used as a convenient and easily remembered rule of thumb. But several workers have pointed out that different types of dinhosaur had slightly different relationships between foot lengthand hip height and Thulborn (1990) has suggested that the following approximations could be used for bipedal dinosaurs;

FL less than 0.25m FL greater than 0.25m
small theropods h=4.5*FL large theropods h=4.9*FL
small ornithopods h=4.8*FL large ornithopods h=5.9*FL
small bipedal dinosaur in general h=4.6*FL large bipedal dinosaurs in general h=5.7*FL

On the sandstone slubs, three trackways were recognized. The above equations are applied for these three trackways. The results are as folloows:

foot length(cm) stride length (cm) hip height (cm) speed (km/h)
track A 4.6 25.4 21.1 1.8
track B 3.2 16 14.6 1.3
trakc C 4.5 32.8 20.9 2.7

The hip height of the animal is estimated as nearly 20 cm; a turkey size. It is safely concluded that the animal left the foot-prints on the sandstone slub at the Chat Trakan National Park was a small bipedal dinosaur of a turkey size indicating the stratigraphic position of the Formation as the Upper Cretaceous.

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