New Fossil Crabs (Decapoda: Brachyura) from the La Meseta Formation (Eocene) of Antarctica: Paleogeographic and Biogeographic Implications
New Fossil Crabs (Decapoda: Brachyura) from the La Meseta Formation (Eocene) of Antarctica: Paleogeographic and Biogeographic Implications
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南极洲拉梅塞塔组（始新世）的新螃蟹化石（十足目：Brachyura）：古地理和生物地理意义
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发表时间：
1984
期刊：
影响因子：
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通讯作者：
W. Zinsmeister
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文献类型：
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作者：
R. Feldmann;W. Zinsmeister
在南极西摩岛的拉梅塞塔组发现了两个短尾目十足类甲壳动物新种，即Lyreidus anarcticus和Chasmocarcinus seymourensis。Lyreidus anaparticus与目前在新西兰上始新世地层中研究的该属标本相似。该属的南极和新西兰形式，与现代Lyreidus spp.的生态分布形成对比，适应近岸高能量环境在南极标本中，这种适应反映在腹部和行走腿的结构中，并由相关的动物群和沉积结构证实。现代的代表属被解释为已适应了更深的水，外架内坡栖息地与随之而来的形态变化。这种向低纬度和深水的过渡可能反映了对冷温带水条件的持续适应。Chasmocarcinus是第一次从化石记录中报道，似乎已经适应了类似的浅水，中等高能量的环境，就像该属的最近物种一样。这些螃蟹的发现只是第二次出现在南极洲的短尾龙。他们的存在证实了从解释的年龄和环境的La Meseta形成的沉积软体动物得出的结论。始新世晚期（40百万年前）气候条件温和可能反映了在南极洲和澳大利亚之间的深海分离发展以及随后的环南极洋流形成之前，太平洋、印度洋和大西洋的主要海洋环流对南大洋高纬度环流的影响。结果也是有意义的。学名Lyreidus anatomicus n. sp.与该属的现存和化石代表的比较，再次证实了La Meseta组的始新世时代，表明与新西兰已知的该属物种关系密切，并提供了该属现在适应于相对深水环境，以前占据近岸浅水栖息地的额外证据。Chasmocarcinus以前从未从化石记录中报道过，但似乎为La Meseta组的中等高能量浅水沉积环境提供了一些额外的文献。因此，本文的目的是描述两种新的短尾类，并将这两种类型的研究信息应用于La Meseta组的古生态学解释。此外，这两个新种的发现必然对南半球古生物地理的解释产生影响，这些影响也将在本文中讨论。
TWO new species of brachyuran decapod crustaceans, Lyreidus antarcticus and Chas- mocarcinus seymourensis, have been collected in close association with the recently reported first marsupial remains from the La Meseta Formation, Seymour Island, Antarctica. Lyreidus antarcticus is similar to specimens of that genus currently being studied from upper Eocene beds in New Zealand. Both the Antarctic and New Zealand forms of the genus, in contrast with the ecological distribution of recent Lyreidus spp., are adapted to nearshore, high energy regimes. In the Antarctic specimens, this adaptation is reflected in the architecture of the abdomen and walking legs and is confirmed by associated fauna and sedimentary structures. Modem representatives of the genus are interpreted to have adapted to a deeper water, outer shelf to inner slope habitat with concomitant morphological changes. This transition to lower latitudes and deeper water might reflect continued adaptation to cool temperate water conditions. Chasmocarcinus is reported, for the first time, from the fossil record and appears to have been adapted to a similar shallow water, moderately high energy environment as are recent species of that genus. Discovery of these crabs represents only the second occurrence of Brachyura from Antarctica. Their presence corroborates conclusions drawn from the interpretation of the molluscs regarding age and environment of deposition of the La Meseta Formation. Milder climatic conditions in the late Eocene (40 m.y.B.P.) may reflect the high latitude circulation of the southern oceans by the main Pacific, Indian, and Atlantic oceanic gyres prior to development of a deep oceanic separation between Antarctica and Australia and subsequent initiation of the circum-Antarctic current. tions result which are also of significance. Comparison of Lyreidus antarcticus n. sp. with living and fossil representatives of the genus provides reconfirmation of the Eocene age of the La Meseta Formation, suggests close relationship with species of the genus known from New Zealand, and provides additional evidence that the genus, now adapted to rel- atively deep water environments, previously occupied nearshore, shallow water habitats. Chasmocarcinus has never before been re- ported from the fossil record but does appear to provide some additional documentation for a moderately high energy, shallow water environment of deposition for the La Meseta Formation. The purpose of this paper, therefore, is to describe two new species ofbrachyurans, and to apply information from the study of these two forms to the interpretation of the paleo- ecology of the La Meseta Formation. Addi- tionally, recognition of these two new species inevitably has implications on the interpre- tation of the paleobiogeography of the south- ern hemisphere and those implications will also be discussed.