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

ABSTRACTWe describe a new capitosauroid temnospondyl, <i>Antarctosuchus polyodon</i>, 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 <i>Antarctosuchus</i> 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 <i>Antarctosuchus</i> within a clade of derived Triassic stereospondyls as the sister taxon to <i>Paracyclotosaurus crookshanki</i> from the Triassic Denwai Formation of India. To date, the upper Fremouw Formation has yielded two endemic temnospondyl species (viz., <i>Kryostega collinsoni</i> and <i>Antarctosuchus polyodon</i>), although indeterminate remains referred to benthosuchids and a cranial fragment assigned to <i>Parotosuchus</i> sp. have also been noted. In contrast to the broadly distributed therapsid taxa recognized from the Middle Triassic of Antarctica (e.g., <i>Cynognathus</i>, <i>Diademodon</i>), 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：我们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，描述一种新的大头鲵型类（capitosauroid）离片椎类（temnospondyl）新属新种——多齿南极鲵（Antarctosuchus polyodon）gen. et sp. nov.。该新种以具大量极其细小的上颌骨、腭骨及外翼骨牙齿为典型特征，这种齿列形态暗示其特化捕食小型猎物，可能为无脊椎动物。该类群同时具有延伸至鼻后孔（choana）后方甚远的鼻后孔齿列，以及紧邻中线排布的枕髁。扁平头骨、低矮枕部与发育良好的感觉管等一系列特征的组合，均表明其具备水生生活习性。

我们将该类群加入近期的大头鲵类（Capitosauria）分支系统学分析，以探讨其系统发育关系。修订后的数据集涵盖27个分类单元与53个形态特征。分析结果显示，多齿南极鲵（Antarctosuchus polyodon）隶属于衍生的三叠纪离片椎类支系，为产自印度三叠系登瓦组（Denwai Formation）的歪旋螈（Paracyclotosaurus crookshanki）的姊妹群。

截至目前，上弗里莫组已产出两种特有离片椎类物种，即科林逊冰原螈（Kryostega collinsoni）与多齿南极鲵（Antarctosuchus polyodon），不过此前也曾报道过归属似贝氏螈科（benthosuchids）的未定属种遗骸，以及一块被归为副托勒密螈（Parotosuchus）sp.的头骨碎片。

与南极洲中三叠世已发现的广泛分布的兽孔类类群（如犬颌兽（Cynognathus）、双冠兽（Diademodon））不同，该离片椎类动物群显示其与其他同期南部泛古陆盆地（如卡鲁盆地、卢安瓜盆地、鲁胡胡盆地、沃特伯格盆地）的物种交流更为有限。

补充数据：本文的补充材料可通过http://www.tandfonline.com/UJVP免费获取。