美国西弗吉尼亚大学Ronald C. Meyer团队近日发现古马蹄蟹保存完好的卵巢。相关论文发表在2025年5月29日出版的《地质学》杂志上。

马蹄蟹是一种古老的水生螯合节肢动物，传统上被认为是“活化石”，在整个进化过程中表现出有限的形态变化。这一模式受到了古生代和中生代剑龙在非海洋环境中形态差异的挑战，它们显示出更大的前体甲壳形状变化。海洋马蹄蟹的进化史似乎较为保守，在石炭纪和侏罗纪时期，它们的体型明显增大。然而，对马蹄蟹进化趋势的解释是复杂的，因为不确定较小的古生代物种是代表成年还是幼年。

研究组描述了一种4.45亿年前的小型马蹄蟹（Lunataspis gundersoni sp. nov.），保留了原体中卵巢结构的细节。在剑龙目中独一无二的是，新种具有异常延长的原体，表明该类群的早期形态变异。然而，雌性的生殖系统似乎与现存的速叶虫相同。重要的是，卵的存在表明这些标本是成年的，而且在古生代马蹄蟹的体型要小得多。Lunataspis gundersoni显示了不同的外部和保守的内部解剖结构的混合物，揭示了马赛克进化模式，并阐明了海洋剑龙的早期形态变异。

附：英文原文

Title: Exceptionally preserved ovaries in an ancient horseshoe crab

Author: James C. Lamsdell, Amanda R. Falk, Thomas A. Hegna, Ronald C. Meyer

Issue&Volume: 2025-05-29

Abstract: Horseshoe crabs are an ancient lineage of aquatic chelicerate arthropods traditionally considered to be “living fossils” exhibiting limited morphological change throughout their evolution. This paradigm is challenged by the divergent morphologies of Paleozoic and Mesozoic xiphosurans in nonmarine environments, which show greater variation of prosomal carapace shape. Marine horseshoe crabs appear to exhibit a more conservative evolutionary history punctuated by marked increases in body size during the Carboniferous and Jurassic. However, interpretation of horseshoe crab evolutionary trends is complicated by uncertainty over whether the smaller Paleozoic species represent adults or juveniles. Here, we describe a diminutive 445-million-year-old horseshoe crab, Lunataspis gundersoni sp. nov., preserving details of ovarian structures in the prosoma. Unique among Xiphosura, the new species possesses an unusually prolongated prosoma, indicating early morphological variation within the group. However, the female reproductive system appears identical to that of extant Tachypleinae. Critically, the presence of eggs demonstrates that the specimens are adults and that horseshoe crabs were significantly smaller in size during the Paleozoic. Lunataspis gundersoni displays a mixture of divergent external and conserved internal anatomy that reveals mosaic evolutionary patterns and illustrates early morphological variation among marine Xiphosura.

DOI: 10.1130/G53317.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G53317.1/654867/Exceptionally-preserved-ovaries-in-an-ancient