Tomoyuki Mikami

• Doctor of Philosophy
• National Museum of Nature and Science

The ammonites in spherical carbonate concretions often preserve their original three-dimensional (3D) shell shapes and detailed fragile structures. However, the formation process of spherical ammonite concretion is not fully understood. Herein, the ammonite concretions identified in the Cretaceous (Campanian) Osoushinai Formation, Yezo Group, Japan...

Tullimonstrum gregarium , also known as the Tully monster, is a well‐known phylogenetic enigma, fossils of which have been found only in the Mazon Creek Lagerstätte. The affinities of Tullimonstrum have been debated since its discovery in 1966, because its peculiar morphology with stalked eyes and a proboscis cannot easily be compared with any know...

Glendonite is generally accepted as a calcite pseudomorph after ikaite (CaCO3·6H2O) and is commonly preserved in spherical carbonate concretions known as glendonite concretions in marine sedimentary rocks. Although they have widely attracted attention as environmental indicators, the detailed geochemical process underlying glendonites formation is...

The internal architecture of chambered ammonoid conchs profoundly increased in complexity through geologic time, but the adaptive value of these structures is disputed. Specifically, these cephalopods developed fractal-like folds along the edges of their internal divider walls (septa). Traditionally, functional explanations for septal complexity ha...

An organism cannot be fully optimized for all tasks that are needed for its survival because of the existence of intrinsic trade‐offs among those tasks. It was recently proposed that an economics‐originated theory, the Pareto theory, is a general theory explaining the rules of phenotypic evolution under such trade‐offs. To date, many phenotype data...

Nipponites is a heteromorph ammonoid with a complex and unique morphology that obscures its mode of life and ethology. The seemingly aberrant shell of this Late Cretaceous nostoceratid seems deleterious. However, hydrostatic simulations suggest that this morphology confers several advantages for exploiting a quasi-planktic mode of life. Virtual, 3D...

Nipponites is a heteromorph ammonoid with a complex and unique morphology that obscures its mode of life and ethology. The seemingly aberrant shell of this Late Cretaceous nostoceratid seems deleterious. However, hydrostatic simulations suggest that this morphology confers several advantages for exploiting a quasi-planktic mode of life. Virtual, 3D...

Ectocochleate cephalopods have external shells filled with divider walls called septa. Ammonoid cephalopods had complex, marginally frilled septa that have been subjected to many hypotheses regarding possible biological functions. Among these hypotheses is the retention of chamber liquid via surface tension. The relative amount of liquid retained b...