We reviewed the history of studies and conservation efforts related to terrestrial mammals in the central and southern Ryukyu Archipelago in Japan, covering six orders, 11 families, 20 species, and six subspecies, with 77% endemic and 62% of species classified as threatened. The most significant feature is that phylogenetically ancient species have survived alongside humans, who have inhabited the islands for approximately 30 000 years. This coexistence is unique to this region and not found in other parts of Japan, making it a globally rare phenomenon. In 2021, four islands in the region were designated as Natural World Heritage Sites, marking a conservation milestone, although challenges remain. Island biodiversity is crucial to global biodiversity because of its high endemism. Island biol ogy provides an essential biogeographical perspective to understand evolution and shape conservation strategies. The region has become a focal point of interest due to its unique biota and distinctive island ecosystems. We concluded that a comprehensive re-evaluation of the islands is essential, focusing on biogeography, ecology, and species interactions. Conservation measures should be tailored to each island by incorporating insights from ethnography, sociology, and economics. It is our responsibility to protect the region's endangered species and the biodiversity for future generations.

The Ryukyu long-furred rat, Diplothrix legata (Muridae) is an endangered large arboreal species endemic to the central Ryukyus, Japan. Previous studies have recorded the food habits of this species through direct observations. However, its observation records are limited. Here, we aimed to clarify the food habits of D. legata using DNA metabarcoding of its stomach contents. The ITS2 intergenic regions in plant nuclear genomes and the COI gene regions in animal mitochondrial genomes were used as DNA markers to identify the prey species of D. legata based on its stomach contents. We successfully identified 63 plant and 36 animal species as the prey species of D. legata. Finally, 84 plant and 46 animal species are listed as food menu in total. Thus, a greater number of its animal prey species were identified in this study than in previous observation-based studies. As this species is omnivorous, the conservation of a wide array of ecological habitats is necessary for maintaining its population. Regardless of the limited sample size and unknown parts consumed, slight differences in food items were observed between different sex- and age-based groups. Relatively more detailed DNA reference databases for the local fauna and flora are required for further analysis.

The Amami rabbit (Pentalagus furnessi) and the Ryukyu long-furred rat (Diplothrix legata) are rare, endemic mammals of the Ryukyu Islands. So far, knowledge about their basic ecology is limited. This study aims to expand data on their feeding ecology by dental microwear texture (DMT) analysis using skull specimens (n = 20 for each species) collected as roadkill. DMT data were compared with those from laboratory-reared rodents in controlled feeding experiments, to infer the physical properties of their diets. The results indicated no sexual difference in DMT for either species, suggesting similar diets between males and females. However, a significant seasonal variation was observed in the Ryukyu long-furred rat, with increased DMT roughness in winter, suggesting a dietary shift from more abundant and less mechanically demanding summer foods like soft-bodied invertebrates to harder foods such as acorns. In contrast, the Amami rabbit showed consistently less rough DMT throughout the year. Microwear patterns suggested that the Amami rabbit consumes plants with toughness comparable to bamboo and dry grass. These findings highlight the importance of seasonal dietary shifts in the Ryukyu long-furred rat and the consistent diet of the Amami rabbit, providing insights into their ecological adaptations.

In the northern part of Okinawajima Island, a large nest box equipped with an automatic camera trap was set up at a height of 5.2 m above the ground from April 2022 to March 2023 to study the reproductive ecology of the Ryukyu long-furred rat Diplothrix legata. This species is endemic to the central Ryukyus and is the largest arboreal murid species in Japan. Videos captured between October and February showed that D. legata was carrying branches and leaves into the nest box and nesting. Calls of newborn rats, sometimes overlapped between different individuals, were recorded from late February to early March, indicating that multiple rats were born in the nest box. These observations suggest that large nest boxes are useful for studying the nesting behavior of D. legata. However, habu snakes Protobothrops flavoviridis were observed entering the nest box and preying on newborns, resulting in no newborns being observed leaving the nests. Although previous studies have recorded the predation of D. legata by habu snakes, this study is the first to provide direct evidence of habu snakes attacking the nesting site and preying on newborns of D. legata.

Bone histology is a valuable tool for studying growth patterns and life history traits in animals. This study examines four Japanese sika deer (Cervus nippon) populations-mainland (Hokkaido and Chiba) and insular (Yakushima and Kerama Islands)-using femoral and tibial histology to investigate growth patterns and sexual dimorphism. Growth curves based on lines of arrested growth (LAGs) revealed slower growth rates in insular populations, supported by extensive parallel-fibered bone (PFB) development and reduced vascularity. Earlier external fundamental system (EFS) formation and epiphyseal fusion in mainland populations (three to four years) compared to insular populations (5.5 to 7.5 years) further support this finding. Sexual dimorphism was pronounced in mainland populations, with males exhibiting delayed EFS formation, epiphyseal fusion, and extensive bone remodeling than females. In contrast, the Kerama population showed no significant sex-related differences in remodeling, which may influence unique growth patterns. These findings highlight the influence of insularity, such as resource limitation and predator-free environments on life history traits, which could associate slower growth rates and delayed maturity in insular deer. This study underscores the utility of bone histology in understanding adaptive strategies of endemic and endangered mammals.

The Amami rabbit (Pentalagus furnessi), endemic to Amami-Oshima and Tokunoshima Islands, exhibits distinct life history traits compared to mainland lagomorphs, yet its growth patterns remain largely unexplored. This study conducted bone histological analysis of Amami rabbit limb bones to uncover its growth and ecological adaptations. Results indicate rapid growth until about two years old, followed by gradual growth until approximately five years old, when growth ceases with epiphyseal closure. This delayed maturation contrasts sharply with mainland species like the Japanese hare (Lepus brachyurus), which matures within a year. This slower growth and delayed maturation in the Amami rabbit aligns with previous observations suggesting a shift toward a K-strategy in its reproductive traits. Additionally, the Amami rabbit's dense limb bones with thick cortices and a small medullary cavity, provide bone robustness suited for its steep, rugged habitat-contrary to other lagomorphs which adapted to leaping locomotion. These findings suggest that the Amami rabbit's growth and skeletal structure respond to unique island ecological conditions, with limited predation and resources, highlighting adaptive strategies in insular mammals and emphasizing the Amami rabbit's unique ecological adaptations.

The osteohistology of Andrias spp. is a pivotal analogue for large fossil non-amniotes (e.g., Temnospondyli), and the endangered status of this taxon underlines the importance of gathering information on its growth. We here present the first osteohistological study by petrographic thin sections of an ontogenetic series of humeri and femora of eight individuals of varying sizes (28.5-104 cm) and ages (2.5-32 years) of Andrias japonicus from the Hiroshima City Asa Zoological Park, Japan. In addition, two individuals of A. cf. davidianus of unknown age but of different size (62 cm and 94 cm) were studied. All samples of Andrias spp. show a primary avascular periosteal cortex made of parallel-fibred tissue around the ossification center in the petrographic thin sections. Mainly in small individuals, the fibers forming this tissue are very coarse and loosely organized. With increasing size and age, the coarse tissue is irregularly intermixed and later replaced with finer and better organized fibers. This histologic change is accompanied by a change from diffuse annuli in the inner cortex to distinct lines of arrested growth (LAGs) in the outer cortex. We interpret these changes in tissue and the appearance of distinct growth marks as indicating the onset of active reproduction. The lack of primary vascularization around the ossification center in our Andrias spp. sample is striking and contradicts other observations. Vascularity may be prone to plasticity and further studies are necessary. We hypothesize that the large osteocyte lacunae and the dense networks of canaliculi observed in our sample may have nourished the tissue instead of primary vascular canals. We measured the size of osteocyte lacunae of Andrias spp. in comparison to other Lissamphibia, and found them to be significantly larger throughout ontogeny. The periosteal cortex contains a high amount of thick Sharpey's fibers all around the midshaft cross sections. The two samples of Andrias cf. davidianus show tissue and growth mark distribution similar to that observed in A. japonicus. However, the large individual of A. cf. davidianus differed in its extremely osteosclerotic condition and the retention of a small layer of calcified cartilage in the endosteal region of the femur. It remains unclear whether these differences are related to plasticity, taxonomy, sex, exogenous factors, or attributable to a regenerated but fully regrown leg. Although the present study is based on zoo-kept and not wild, animals, it yields important insights into osteohistological plasticity and growth patterns in giant salamanders.

Of the four main Japanese islands, Late Cretaceous dinosaur fossils have been discovered in Hokkaido, Honshu, and Kyushu. Here, we report the first Late Cretaceous dinosaur from the remaining main island Shikoku, an isolated dorsal vertebra from the upper Campanian Hiketa Formation (Izumi Group) in Sanuki, Kagawa Prefecture. The vertebra is incomplete, comprising a robust centrum with a subrectangular profile that is generally characteristic of dinosaurs. Histological examination of the centrum reveals moderately packed trabecular bone and the complete absence of pneumatic structures, which precludes referral of the specimen to Saurischia or Pterosauria. Instead, we interpret it as a hadrosauriform ornithischian based on the slightly expanded anterior articular surface of the centrum; heart-shaped outline of the intervertebral surface, resulting from its dorsally wide and ventrally narrow shape; ventral keel; and neural canal partially embedded into the centrum. As the ventral positioning of the neural canal is common to Bactrosaurus and higher taxa within Hadrosauriformes, we tentatively refer the specimen to Hadrosauroidea. This discovery provides additional evidence that hadrosauriforms had dispersed into present-day Japan by the Campanian and highlights the potential of the Hiketa Formation to provide additional evidence to improve our understanding of the dinosaur diversity at the extreme eastern continental margin of Eurasia.