Miocene dugongid (Mammalia, Sirenia) diversity in the Indian Ocean, with description of a new genus and species from Kutch, Western India

A new dugongine (Kharisiren cristata gen. et sp. nov.) is described here based on a partial skull from the Lower Miocene of Kutch, Gujarat state, western India. The new taxon is characterized, among other features, by an anteriorly sloping frontonasal roof with a pair of ridges on either side of the midline suture, a massive, sub-horizontal nasal process of the premaxilla; rostral deflection of about 45°, pentagonal outline of the mesorostral fossa with a U-shaped posterior margin, and an upper incisor tusk with a lozenge- or kite-shaped cross section. The study also briefly describes key features in the partially encased endocast in this taxon. The new dugongine coexisted with four other dugongines—Bharatisiren indica, B. kachchhensis, Kutchisiren cylindrica, Domningia sodhae—suggesting considerable evolutionary diversification and specialized niche partitioning during the Early Miocene in the Indian Ocean region. The Miocene dugongids of the Indian Ocean, including dugongines from India and Madagascar, share morphological similarities that suggest potential paleobiogeographic influences on their diversification. This implies a close relationship between these faunas, likely due to their geographic proximity, and highlights the ability of early dugongids to cross large oceanic barriers.

本文基于采自印度西部古吉拉特邦库奇地区下中新统地层的部分头骨化石，记述了一个全新的儒艮亚科（Dugonginae）类群：*Kharisiren cristata* gen. et sp. nov.（新属新种）。该新类群的鉴别特征包括：沿中线缝合线两侧对称分布一对脊突的前倾斜额鼻区、粗壮且近水平的前上颌骨鼻突、约45°的吻部偏转角度、呈五边形且后缘为U形的中吻窝轮廓，以及横切面呈菱形或风筝形的上门齿獠牙。本研究还简要记述了该类群中部分被围岩包裹的颅内模（endocast）的关键形态特征。该新儒艮亚科类群与另外四种儒艮亚科类群——*Bharatisiren indica*（印度巴拉蒂海牛）、*B. kachchhensis*（卡奇巴拉蒂海牛）、*Kutchisiren cylindrica*（圆柱形库奇海牛）、*Domningia sodhae*（索达多明宁海牛）——伴生共存，这表明印度洋地区早中新世时期儒艮类群存在显著的演化分异与生态位特化分区现象。印度洋地区的中新世儒艮科（Dugongidae）化石类群，包括产自印度与马达加斯加的儒艮亚科类群，均共享诸多相似的形态特征，暗示古生物地理因素可能对其演化分化产生了潜在影响。这意味着上述化石动物群之间存在紧密的亲缘关系，这大概率源于它们的地理毗邻性，同时也凸显了早期儒艮科类群具备跨越大型海洋屏障的扩散能力。