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Paleontology and Mineral History

  • ITO Yasuhiro, Professor
  • ‡ The Kyushu University Museum
Our laboratory aims at frontier researches on paleontology and mineral history. In paleontology laboratory, our current goal is settled to elucidate fossilization mechanism in geologic time scale, i.e., taphonomy. Our research starts from a very primitive question “How and why were fossils made?” But it provides an essential bridgehead for all fields of paleontology, and gives rise to innovation in sciences about the history of life. From this unique viewpoint, our laboratory leads this field in Japan, and the chief is now active as the president of the Palaeontological Society of Japan.
Besides, detailed analyses on meteorites have been carried out in the mineral history laboratory, while it is temporary closed because of retirement of the faculty.

By field-oriented research, we have collected several tons of fossil materials not only from Japan but also from various areas in the world.

1. Extraordinarily preserved fossils

Discovery of phosphatized minute ostracod-like animals showing 3D soft-part preservation in fecal pellets from the Cambrian Orsten deposits substantiated our new hypothesis of preservation of animal soft-tissues about 500 million years ago (Fig. 1). Our laboratory acts as a research center of extraordinarily preserved fossils (=fossil Lagerstätten) in Japan.

Figure 1. Phosphatocopines (extinct Arthropoda; in left- and right circles) entombed in numerous fecal pellets in the Swedish Cambrian Orsten (Maeda et al., 2011, in PALAIOS). Phosphatized animal carcasses with their eyes, mandibles (B) and appendages (C) retain tremendous original morphology in 3D. Fecal pellets played an important role as phosphorous source as a “cesspool”. This study was selected as a featured article of the volume. By courtesy of SEMP.

2. Revision and updating ammonoid taxonomy:

Another emphasis of our laboratory is on ammonoid paleoecology and systematics. Close investigation revealed the existence of a dimorphic pair within a single species (e.g., male and female; Fig. 2). Such dimorphs are quite different in appearance, and have been designated to different taxa. This results cast doubts on traditional scheme of typological taxonomy, and triggered off revision of the systematics.

Figure 2. Dimorphism in a Cretaceous ammonoid species Yokoyamaoceras ishikawai (Jimbo). The macroconch supposed to female is three times larger than the microconch (Maeda, 1993). Peculiar apertural modification appear only in micoroconchs. By courtesy of the Palaeontological Society of Japan.

3. Ammonoid taphonomy:

To reconstruct paleoecology of extinct animals like ammonoids, detailed observation about modes of fossil occurrence is essential. Bed-by-bed observation on the Cretaceous strata inspires us an new idea that an empty large ammonoid shell triggers off accumulations of small ammonoid carcasses, shell fragments and plant remains like a “trap” on the sea floor. Abundant examples showing similar occurrence in outcrops support this view.

Figure 3. Sheltered preservation caused by an large empty ammonoid shell (Maeda and Seilacher, 1996). As light-weight material less than 1.2 g/cm3 density, smaller ammonoid shell, shell fragments and plant remains are swept by very weak bottom current and trapped by the large ammonoid shell. By courtesy of Plenum Press.