A distinctive new archosaur from the Middle Triassic (Los Chanares Formation) of Argentina
A distinctive new archosaur from the Middle Triassic (Los Chanares Formation) of Argentina
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DOI：
10.1080/02724634.1998.10011046
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发表时间：
1998-03-01
影响因子：
1.4
通讯作者：
Marsicano, CA
中科院分区：
文献类型：
--
作者：
Arcucci, A;Marsicano, CA
Chafiares动物群是最丰富和最多样化的大陆中生代爬行动物组合之一（Romer, 1973; Bonaparte, 1978）。自从1964年发现这个地方以来，已经描述了十多个分类群。值得注意的是，这一组合包括了恐龙（Sereno and Arcucci, 1994）和哺乳动物（Crompton and Jenkins, 1979）的近亲。Los Chafiares组是Agua de La Pefia群中最低的四足动物单元。这些三叠纪陆相沉积物构成了充填Ischigualasto-Villa Union盆地（位于阿根廷西北部的圣胡安和拉里奥哈省）的大部分沉积物。Los Chanares组不适应地位于Los Tarjados组的河流红相上，并整合向上进入Los Rastros组的湖相沉积。化石层对应于该单元的下部，在Los Chafiares类型地区（La Rioja省），脊椎动物遗骸丰富，关节程度不同，但大多数保存完好。标本主要出现在结节中，但一些物质，如本文所述的物质，保存在结节外的沉积物中。地貌学分析表明，下部岩石层的沉积代表了一个中等能量的洪泛平原，随着古土壤的发育，具有季节性的干旱期（Rogers et aI）。, 1993)。最近几年在Los Chafiares地区发现的大量标本中，有一些是一种有甲爬行动物的遗骸，它不同于同一层次的所有其他已知分类群。Romer （1971a）提到并描绘了来自Los Chafiares地区的两种骨皮（MCZ 4076）的碎片，他认为这两种骨皮属于Lupero-suchus，这是在Los Chanares地区记录到的最大的祖龙。他的定位仅仅基于鳞片的大尺寸，因为这些碎片保存得太差，不能被认为是一个已知的分类群，而且，它们与其他骨骼遗骸没有直接联系（Romer, 197Ia）。1990年，其中一位作者（AA）在里约热内卢Gualo地区的Los Chafiares组中发现了几个几乎完整的鳞片（PULR 063），并与椎骨碎片相关。此外，1993年，当另一位作者（CM）在哈佛大学审查阿根廷三叠纪藏品时，她发现了一种未描述的中型爬行动物的鳞片碎片（MCZ 9319）的装饰头骨遗骸，该碎片是由罗默的工作人员在b里约热内卢Chafiares地区的Los Chafiares水平收集的。在目前的讨论中，对上述所有材料都进行了详细的描述。考虑到前面提到的所有鳞片都有相同的结构和纹饰，后者也出现在头骨表碎片上，我们认为所有的遗骸都代表同一个分类群。此外，在同一层次记录的任何已知分类群中都没有这种类型的纹饰，这表明存在一个新的分类群。机构缩写- uplr， La Rioja大学古生物博物馆；哈佛大学比较动物学博物馆MCZ；AMNH，美国自然历史博物馆。
The Chafiares fauna is one of the richest and most diverse continental Mesozoic reptile assemblages (Romer, 1973; Bonaparte, 1978). Since the discovery of this locality, in 1964, more than a dozen taxa have been described. It is important to note that this assemblage includes the closest relatives of both Dinosauria (Sereno and Arcucci, 1994) and Mammalia (Crompton and Jenkins, 1979). The Los Chafiares Formation represents the lowest tetrapod-bearing unit of Agua de La Pefia Group. These Triassic continental deposits comprise most of the sediments filling Ischigualasto-Villa Union Basin (San Juan and La Rioja Provinces, northwestern Argentina). The Los Chanares Formation rests uncomformably on fluvial red facies of Los Tarjados Formation and grades conformably upward into the lacustrine deposits of Los Rastros Formation. The fossiliferous level corresponds to the lower part of the unit, and in Los Chafiares type locality (La Rioja Province), the vertebrate remains are abundant and occur in different degrees of articulation but, in most cases, are well preserved. The specimens occur primarily in nodules but some of the materials, like the ones described herein, are preserved in the sediment out of the nodules. Taphonomic analysis suggests that the deposits of the lower lithosome represent a flood plain of medium energy with seasonal periods of drought with the development of paleosols (Rogers et aI., 1993).Among the numerous specimens recovered from Los Chafiares locality in the last few years are some remains of an armored reptile, which differs from all other known taxa from the same levels. Romer (1971a) mentioned and figured fragments of two types of osteoderms (MCZ 4076) from Los Chafiares locality that he attributed to Lupero-suchus, the largest archosaur recorded from Los Chanares levels. His assignation was based only on the large size of the scutes as the fragments were too poorly preserved to be recognized as representing a known taxa and, moreover, they were not found in direct association with other skeletal remains (Romer, 197Ia). In 1990, one of the authors (AA), found in Los Chafiares Formation in Rio Gualo area several almost complete scutes (PULR 063) associated with fragmentary vertebrae. Moreover, in 1993 when the other author (CM) was reviewing Argentinian Triassic collections at Harvard University she found ornamentated skull remains in association with a scute fragment (MCZ 9319) of an undescribed medium sized reptile, collected by Romer's crew in Los Chafiares levels in Rio Chafiares area. In the present discussion, a detailed description of all materials mentioned above is given. Taking into account the fact that all the scutes previously mentioned share the same structure and ornamentation, this latter also present on the skull table fragment, we consider all the remains to represent the same taxon. Furthermore, the absence of this type of ornamentation in any of the known taxa recorded in the same levels suggests the presence of a new taxon. Institutional Abbreviations-UPLR, Museo de Paleontologia Universidad de La Rioja; MCZ, Museum of Comparative Zoology, Harvard University; AMNH, American Museum of Natural History.