Cynodonts from the uppermost Burgersdorp Formation, South Africa, and their bearing on the biostratigraphy and correlation of the triassic Cynognathus assemblage zone
Cynodonts from the uppermost Burgersdorp Formation, South Africa, and their bearing on the biostratigraphy and correlation of the triassic Cynognathus assemblage zone
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DOI：
10.1671/0272-4634(2005)025
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发表时间：
2005-03-11
影响因子：
1.4
通讯作者：
Neveling, J
中科院分区：
文献类型：
--
作者：
Abdala, F;Hancox, PJ;Neveling, J
南非卡鲁盆地博福特群的伯格斯多普组记录了多样且丰富的脊椎动物群，从生物地层学角度被归入犬颌兽组合带。近期对该组的采集工作以及分类学和生物地层学研究，导致提议将犬颌兽组合带细分为三个非正式称为A、B和C的亚带。犬齿兽类化石是犬颌兽组合带最上部的C亚带动物群的重要组成部分。与中部的B亚带一样，犬颌兽类、冕齿兽类和三棱齿兽类在C亚带都有出现，尽管后一类群（而非冕齿兽）是优势分类单元。犬颌兽在三个亚带的动物群中都有出现，这证实了该属作为组合带的标志性分类单元是正确的选择。C亚带三棱齿兽类标本所达到的巨大体型是一个不寻常的特征。一个完整的头骨长160毫米，尽管其他标本的破碎残骸表明体型甚至更大。这些头骨长度远超过从较老的A和B亚带发现的三棱齿兽类所具有的100毫米特征长度。巨大的体型，特别是上部的丘齿型后犬齿呈卵形的整体形态，使得C亚带的三棱齿兽类标本能够被归入代谢克里克齿兽（Cricodon metabolus），此前它已知于坦桑尼亚的曼达组。南非的犬颌兽组合带被证明是冈瓦纳南部在时间上最完整的早 - 中三叠世非海相序列，并且是可用于与其他相似年龄序列进行比较的模板。
The Burgersdorp Formation in the Beaufort Group of the South African Karoo Basin records a diverse and rich vertebrate fauna that is referred biostratigraphically to the Cynognathus Assemblage Zone. Recent collecting efforts, and taxonomic and biostratigraphic studies on this formation, resulted in a proposed subdivision of the Cynognathus Assemblage Zone into three subzones informally known as A, B, and C. Cynodont fossils constitute an important component of the fauna of the uppermost subzone C of the Cynognathus Assemblage Zone. As in the middle subzone B, cynognathids, diademodontids, and trirachodontids are represented in subzone C, although the latter group--instead of Diademodon--is the dominant taxon. The presence of Cynognathus in the faunas of the three subzones confirms that this genus is the correct choice as the index taxon of the assemblage zone. The large size attained by trirachodontid specimens from subzone C represents an unusual characteristic. One complete skull measured 160 mm in length, although fragmentary remains of other specimens indicate even larger sizes. These skull lengths are well above the 100 mm that characterize trirachodontids recovered from the older subzones A and B. The large size, and particularly the ovoid overall pattern of the upper gomphodont postcanines allows the assignment of the trirachodontid specimens from subzone C to Cricodon metabolus, previously known from the Manda Formation in Tanzania. The Cynognathus Assemblage Zone of South Africa is shown to be the most temporally complete Early-Middle Triassic nonmarine sequence in southern Gondwana, and is the template against which other sequences of similar age may be compared.