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| Borelis matsudai Bassi, Iryu, Kinoshita, Fujita & Pignatti, 2023 |
Highlights:
• Shell structures circumscribe a new Borelis species.
• The ancestor of the new species is Borelis pulchra.
• The new species appeared from the Middle Pleistocene in the southern Ryukyu Islands.
• The new species followed the northward Kuroshio dispersal route.
• This is the northernmost Borelis record in the western Indo-Pacific Warm Pool.
Abstract
Only three species of alveolinoidean larger foraminifera occur in present-day tropical shallow-water marine settings. Alveolinella quoyi thrives in the Central Indo-Pacific and Eastern Indo-Pacific, Borelis pulchra in the Central and Eastern Indo-Pacific and in the central Atlantic, whereas Borelis schlumbergeri inhabits the Indo-Pacific Ocean. The northernmost record is that of Alveolinella quoyi from the shallow-water settings in Okinawa (central Ryukyu Islands, Japan). A new porcelaneous larger foraminiferal species, Borelis matsudai sp. nov. (Alveolinoidea, Borelinae), is established herein, based on specimens discovered in present-day shallow-water sediments from Sekisei Lagoon, southern Ryukyu Islands (Japan). This is the northernmost record of the genus in the western Indo-Pacific Warm Pool. The architectural characters of this species suggest its phylogenetic relationship with the Borelis pulchra group. A comprehensive literature survey of fossil and modern records of Borelis pulchra over the past 30 million years shows that the Middle Miocene constriction of the Indonesian Seaway and the Late Miocene–Early Pliocene restriction of the Indonesian Throughflow impacted the species-level dispersal of this species in the Indo-Australian Archipelago. Driven by the Kuroshio dispersal route Borelis matsudai sp. nov. likely appeared in the southern and central Ryukyu Islands at least from the Chibanian (Middle Pleistocene). This species represents a marginal part of a population in significant contact with its ancestor (B. pulchra), which is widespread southward since the Oligocene (Philippines). With ongoing global warming possible occurrences of Borelis matsudai sp. nov. in the northern Ryukyu Islands, where it has not yet been found, are expected. The Sekisei Lagoon represents, therefore, a biogeographical stepping stone relay station in northward migration of the shallow-water benthic organisms along the Kuroshio dispersal route.
Keywords: Biogeography, Kuroshio, Ryukyu Islands, Indo-Pacific Ocean, Oligocene–Miocene, Recent
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| SEM photos of Borelis matsudai sp. nov.; megalospheric specimens (A-forms), paratypes; Sekisei Lagoon, southern Ryukyu Islands; Recent. Institute of Geology and Paleontology, Graduate School of Science, Tohoku University (Sendai, Japan). The apertural face is characterized by a single row of rimmed apertures (pr, peristomal rim) with upright masks (um). Septula (sept), dividing the chamberlets (cl), are aligned from chamber to chamber. |
Borelis matsudai sp. nov.
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| Borelis matsudai sp. nov.; holotype, megalospheric specimen (A-form); Sekisei Lagoon, southern Ryukyu Islands; Recent. Institute of Geology and Paleontology, Graduate School of Science, Tohoku University (Sendai, Japan); IGPS Coll. Cat. No. 112751. Micro-computed tomographic scanning 3-D rendered models with shell removed (rendering by S.K.). A–E. The sub-ellipsoidal megalospheric shell showing the large proloculus (prol; prol-ap, proloculus aperture) enveloped by the flexostyle (flex). Note the thick columella (col) in the axial region. F–H. The first and second whorls (green) are strepstospiral. I–K. Chamberlets (cl) are aligned from chamber to chamber with apertures in a single row and only preseptal passage (p-sept) present. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) |
Davide Bassi, Yasufumi Iryu, Shunichi Kinoshita, Kazuhiko Fujita and Johannes Pignatti. 2023. A New Species of the larger porcelaneous Foraminifer Borelis provides Novel insights into Neogene to Recent western Pacific Palaeobiogeographical Dispersal Patterns. Palaeogeography, Palaeoclimatology, Palaeoecology. 628, 111764. DOI: 10.1016/j.palaeo.2023.111764
Researchers Discover a New Species of Larger Benthic Foraminifer from the Ryukyu Islands
