The history of research of the Kobiwako Group is reviewed, including the fossils occurring in each formation, and the significance of the vertebrate fossils (excluding fish). The first report of vertebrate fossils from the Kobiwako Group was a fossil elephant (Stegodon orientalis) that was found in Otsu City and described by E. Naumann in 1881. Lists of the terrestrial vertebrate fossils of the group were published in 1979 and 1991, which made it possible to more fully appreciate the vertebrate faunas of the Kobiwako Group. Fossil vertebrates from the lowest Ueno Formation are species that are thought to have lived in warm climates, and these are the same as those of the Ajimu fauna reported from Oita Prefecture, Kyushu Island. In the Gamo Formation, deposited during a period of declining global temperatures, well-preserved elephant (S. aurorae) fossils belonging to the same individual were excavated in 1993, and these are now mounted as a whole skeleton. A recent comprehensive paleoenvironmental survey at the site revealed that during this time there were cool temperate mixed forests consisting of coniferous and deciduous broad-leaved trees. Other vertebrate fossils, including elephants and deer, have been reported from the Katata Formation, the upper formation of the Kobiwako Group. The age of the Kobiwako Group has been established by tephra and paleomagnetic stratigraphy, and vertebrate fossils discovered from it are extremely valuable as they show a transition of the fauna spanning four million years.

　Lake Biwa is known as an ancient lake with some endemic species. It is necessary to understand the paleo-water system changes in order to examine the formation of the present aquatic fauna. There are five important periods for transition of paleo-water system around paleo-lake Biwa basin. Their periods are depositional period of the lower Ueno Formation, Ayama-Koka F., lower Gamo F., Kusatsu F. and the Katata F. In period of the Ueno to the Koka Formation (4.4 - 2.6 Ma), paleo-lake Biwa basin was connected water system with Ise Bay area to the Chubu Mountains. The paleo-lake Biwa basin might be composed same sedimentary basin with Ise Bay area in the period of the Ueno Formation. This basin was connected with Kyoto-Nara area in a period between upper Koka Formation and lower Gamo Formation. There was water system from Chubu Mountains to Osaka area through this basin in the period of the Gamo to the Kusatsu Formation (2.6 - 1.4 Ma). It was separated between the paleo-lake Biwa basin and the Ise Bay area in approximately 1 Ma. These paleo-water system transitions correspond to the structural activities and topographical changes around widely area of this basin in five million years.

　Lake Biwa, the largest lake in Japan, is a typical ancient lake in temperate Asia. It harbors more than two thousand animal and plant species, including about 70 indigenous freshwater fish species/subspecies with 16 endemic or semi-endemic forms. Lake Biwa is more than 4 million years old, but acquired its current form, including its unique environments (pelagic, deep, and rocky zones), 0.4 million years ago. Endemic fishes in Lake Biwa are traditionally divided into old“relict”species and new species that evolved within the lake ; the latter are assumed to have evolved through adaptations to the present lake environment. Our molecular phylogenetic/population genetic analyses have revealed that many species considered to have evolved in Lake Biwa in fact have origins that are older than the present lake, although other species likely evolved in response to the present environment. The historical demographic patterns of many endemic and non-endemic species, on the other hand, suggested that their populations expanded after the development of the present lake environment. Lake Biwa appears to have functioned as a reservoir for species and genetic diversity in western Japan, and this may have facilitated further diversification and adaptation of freshwater fishes in Lake Biwa and adjacent waters.

　A summary of the fossil footprints from the Plio-Pleistocene Kobiwako Group is given, together with the results of surveys of modern footprints in Southeast, South and East Asia. Five kinds of footprints, namely elephants, rhinoceroses, artiodactyls (considered to be deer), crocodiles and birds (similar to large cranes or storks), are dominant in Plio-Pleistocene sediments, including the Kobiwako Group. This is because elephants, deer and rhinoceroses are large animals that can make well-defined and deep footprints due to the large load per unit of ground area. Additionally, as they walk, the fore and hind feet of these animals step on the same place, deepening the footprints. Crocodiles and birds also tend to leave footprints with well-defined toes and claws because their toes are narrow.

　Based on plant macrofossil assemblages from the Plio-Pleistocene Kobiwako Group outcropping around Lake Biwa, Shiga, central Japan, the types of vegetation in forests inhabited by Proboscidea were determined. Stegodon miensis inhabited mixed forests of deciduous conifers and deciduous broad leaved trees, including warm-temperate taxa, such as the broad leaved evergreens Lauraceae and Cyclobalanopsis, during the period 4.4 Ma to 2.5 Ma. Stegodon aurorae, from 2.5 Ma to 1 Ma, inhabited forests dominated by deciduous broad leaved trees mixed with evergreen and deciduous conifers, and in wetland forests dominated by Metasequoia glyptostrobides and Glyptostrobus pensilis, with deciduous broad leaved trees, such as Alnus, Salix and Fraxinus, and hydrophyte herbs, such as Carex and Cyperus. Mammuthus protomammonteus, from 1.1 Ma to 0.7 Ma, inhabited mixed forests consisting of the deciduous broad leaved trees Quercus serrata, Hamamelidaceae gen. et sp. indet., Corylus heterophylla, and Carpinus, and the evergreen conifers Tsuga and Picea, including warm-temperate taxa, such as Caesalpinia sepiaria and the evergreen broad leaved tree Distylium.