The Ruditayoj-Tunasniyoj fossil area (Chuquisaca, Bolivia): a Triassic chirotheriid megatracksite and reinterpretation of purported thyreophoran tracks

The South American tetrapod track record is highly diverse and well known mainly from Argentina, Brazil, Bolivia, Chile and Peru. To date, many tracksites are known from Bolivia, most studied during the past century. From the Jurassic-Cretaceous La Puerta Formation of the Tunasniyoj locality (Incapampa-Icla syncline) thyreophoran trackways have previously been described. New geological studies related with the Central Atlantic Magmatic Province in Bolivia recognised the track-bearing unit as the Ipaguazú Formation, dated as Late Triassic in age. In this significantly new context, we present here a new track-bearing locality: Ruditayoj, neighbour to Tunasniyoj, near Icla, Chuquisaca, Bolivia. A detailed study of the trackways from this new site allowed new interpretations consistent with the geological context. Hundreds of <i>Brachychirotherium</i> trackways are present at the site with a wide diversity of preservational types. Behavioural issues such as gregariousness and grouping around ponds are suggested. Trackway parameters, track size and shape support large ‘rauisuchid’ or aetosaur pseudosuchian producers. Previous assignations to thyreophoran producers are discussed. This is the first record of <i>Brachychirotherium</i> from Bolivia, filling the lack of information about suchian fossils, well known in other South American sites.

南美洲四足类足迹化石记录极为多样，且主要以阿根廷、巴西、玻利维亚、智利和秘鲁的产出最为学界熟知。迄今为止，玻利维亚已发现多处足迹点，其中多数于过去一个世纪间得到研究。此前曾在位于因卡帕姆帕-伊克拉向斜的图纳斯尼约赫产地的侏罗纪-白垩纪拉普埃尔塔组中，报道过覆盾甲类（Thyreophora）足迹行迹。针对玻利维亚中大西洋火成岩省（Central Atlantic Magmatic Province）的最新地质研究，将该含足迹地层修订为伊帕瓜苏组（Ipaguazú Formation），其地质年代被限定为三叠纪晚期。在此全新的地质背景下，本文报道一处新的含足迹化石产地：鲁伊塔约赫（Ruditayoj），其毗邻图纳斯尼约赫产地，地处玻利维亚丘基萨卡省伊克拉附近。对该新产地的足迹行迹开展的详细研究，得出了与地质背景相符的全新解释。该产地产出数百件短手兽足迹属（Brachychirotherium）足迹行迹，其保存类型丰富多样。研究表明该类群存在群居习性，并倾向于在水塘周边集群活动。足迹行迹参数、足迹大小与形态均支持造迹者为大型劳氏鳄科（Rauisuchidae）或链鳄亚目（Aetosauria）伪鳄类（Pseudosuchia）动物。本文同时讨论了此前将该类足迹归因为覆盾甲类造迹者的相关观点。本次研究是玻利维亚境内短手兽足迹属的首次记录，填补了该地区关于副鳄类（Suchia）化石记录的空白——这类化石在南美洲其他产地已有较为充分的报道。