A new capitosauroid temnospondyl from the Middle Triassic upper Fremouw Formation of Antarctica

ABSTRACTWe describe a new capitosauroid temnospondyl, Antarctosuchus polyodon, gen. et sp. nov., on the basis of a large and relatively complete skull from the upper Fremouw Formation of Antarctica. The new species is characterized by its possession of numerous, extremely small maxillary, palatine, and ectopterygoid teeth, a dental pattern that suggests specialization on small prey items, possibly invertebrates. The taxon is also characterized by a parachoanal tooth row that extends far posterior to the choana and occipital condyles set close to the midline. A combination of features, including a flat skull and low occiput together with well-developed sensory canals, suggests an aquatic lifestyle. We address the phylogenetic relationships of Antarctosuchus by adding it to a recent cladistic analysis of Capitosauria. The revised data set includes 27 taxa and 53 characters. The results of this analysis place Antarctosuchus within a clade of derived Triassic stereospondyls as the sister taxon to Paracyclotosaurus crookshanki from the Triassic Denwai Formation of India. To date, the upper Fremouw Formation has yielded two endemic temnospondyl species (viz., Kryostega collinsoni and Antarctosuchus polyodon), although indeterminate remains referred to benthosuchids and a cranial fragment assigned to Parotosuchus sp. have also been noted. In contrast to the broadly distributed therapsid taxa recognized from the Middle Triassic of Antarctica (e.g., Cynognathus, Diademodon), the temnospondyl fauna suggests more limited interchange with other coeval southern Pangean basins (e.g., Karoo, Luangwa, Ruhuhu, Waterberg).SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at http://www.tandfonline.com/UJVP.

摘要：本文基于采自南极洲上弗里莫组（upper Fremouw Formation）的一具大型且相对完整的头骨，记述了一种新的巨头螈超科（capitosauroid）离片椎类（temnospondyl）——安塔克特多齿螈（Antarctosuchus polyodon），新属新种（gen. et sp. nov.）。该新种的鉴别特征为拥有大量极其细小的上颌骨（maxillary）、腭骨（palatine）以及外翼骨（ectopterygoid）牙齿，这种牙齿形态暗示其可能以小型猎物（大概率为无脊椎动物）为食。该类群还具有延伸至鼻门（choana）后方很远的鼻门旁齿列，以及紧靠中线排列的枕髁（occipital condyles）。头骨扁平、枕部低平且具发育良好的感觉管等一系列特征，表明其具有水生生活习性。我们通过将该属加入近期的巨头螈超科分支系统学分析（cladistic analysis），探讨了安塔克特多齿螈的系统发育关系。修订后的数据集包含27个分类单元（taxa）与53个形态特征。分析结果显示，安塔克特多齿螈位于演化程度较高的三叠纪全椎类（stereospondyls）演化支（clade）中，作为印度三叠纪登瓦组（Denwai Formation）的克罗尚克环螈（Paracyclotosaurus crookshanki）的姊妹群（sister taxon）。截至目前，上弗里莫组已发现两种特有离片椎类物种，即科林松冻螈（Kryostega collinsoni）与安塔克特多齿螈（Antarctosuchus polyodon），不过也有报道称发现了归属未定的底栖螈科（benthosuchids）遗骸，以及一枚归入帕托托螈未定种（Parotosuchus sp.）的头骨碎片。与在南极洲中三叠世发现的分布广泛的兽孔类（therapsid）类群（如犬颌兽Cynognathus、冠齿兽Diademodon）不同，该离片椎类动物群与其他同期泛古陆（Pangean）南部盆地（如卡鲁盆地、卢安瓜盆地、鲁胡胡盆地、沃特伯格盆地）的物种交流较为有限。补充数据——本文的补充材料可通过http://www.tandfonline.com/UJVP免费获取。