Otero Rodrigo A
Red Paleontológica U-Chile, Laboratorio de Ontogenia y Filogenia, Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, RM, Chile.
Millennium Nucleus Early Evolutionary Transitions of Mammals, ANID-Milenio, Santiago, RM, Chile.
PeerJ. 2025 Sep 5;13:e19996. doi: 10.7717/peerj.19996. eCollection 2025.
The Paleogene chondrichthyan diversity of the southern hemisphere is mostly known in Antarctica, southernmost South America and New Zealand, but records from the southeastern Pacific remain sparse to date. Among these, lamnid sharks (the lineage of the great white shark) are one of the scarcer groups in the southern hemisphere prior to the Eocene; moreover, their occurrences prior to the Neogene remained unreported in the southeastern Pacific. This contribution presents new Paleogene chondrichthyans recovered from two different horizons at Loanco, central Chile, including the first local records of lamnids, with the description of a new species of the genus .
Sections of two geologic units were studied. These provided new teeth of chondrichthyans, as well as a single associated tooth set plus fragments of jaw cartilage and vertebrae. The material was taxonomically identified and compared with other local occurrences and other coeval assemblages from the southern hemisphere.
This research recognizes a lower Paleocene-lower Eocene assemblage including material referable to sp., sp. and Hexanchidae indet., the latter being the oldest known record in the southwestern Pacific. In addition, material from upper Eocene-lower Oligocene levels include dental pieces referable to the lamnids Leriche, and to a new species, sp. nov., the latter represented by an exceptional specimen preserving a dental set, mandibular cartilage and vertebrae. Although discrete, this fauna shows the presence of Paleocene- lower Eocene elements commonly present in Antarctica and the Austral Basin, suggesting a typical Weddellian distribution during that timespan. On the contrary, the presence of the genus reinforces the evidence of vertebrate interchange with the north Atlantic between the upper Eocene-lower Oligocene, previously suspected by the shared presence of blochiid billfishes. Evidence of such marine interchange is also present during the late Paleocene, based on the previous reports of , , and , genera with similar known geographic occurrences. The new records of and also represent the oldest known record of Lamnidae in the southwestern Pacific, proving its early presence previous to its widespread and abundant occurrence during the Neogene.
南半球古近纪软骨鱼类的多样性在南极洲、南美洲最南端和新西兰最为人所知，但迄今为止，东南太平洋的记录仍然稀少。其中，鼠鲨科鲨鱼（大白鲨的谱系）是始新世之前南半球较为稀少的类群之一；此外，在东南太平洋，新近纪之前它们的出现情况尚未见报道。本文介绍了从智利中部洛安科两个不同层位发现的新的古近纪软骨鱼类，包括鼠鲨科的首个本地记录，并描述了一个新属种。
研究了两个地质单元的剖面。这些剖面提供了软骨鱼类的新牙齿，以及一组相关牙齿加上颌骨软骨和椎骨碎片。对这些材料进行了分类鉴定，并与其他本地发现以及南半球其他同期组合进行了比较。
本研究识别出一个古新世早期至始新世早期的组合，包括可归入 属、 属和六鳃鲨科未定种的材料，后者是西南太平洋已知最古老的记录。此外，始新世晚期至渐新世早期层位的材料包括可归入鼠鲨科的勒氏 和一个新种 属新种的牙齿碎片，后者由一个保存了一组牙齿、下颌软骨和椎骨的特殊标本代表。尽管该动物群不连续，但显示出古新世至始新世早期常见于南极洲和澳大利亚盆地的元素，表明在该时间段内具有典型的威德尔分布。相反， 属的存在加强了始新世晚期至渐新世早期与北大西洋脊椎动物交换的证据，此前由于布洛奇科旗鱼的共同存在而受到怀疑。基于此前对 属、 属和 属的报道，这些属具有相似的已知地理分布，在晚古新世也存在这种海洋交换的证据。 属和 属的新记录也是西南太平洋鼠鲨科已知最古老的记录，证明了它在新近纪广泛且大量出现之前就已早期存在。
