The First Report of the Acrotretoid Brachiopod Hadrotreta from the Tsinghsutung Formation Cambrian (Series 2, Stage 4), Guizhou, South China

SIMPLE SUMMARY: A number of well-preserved fossils of Hadrotreta were found in the Tsinghsutung Formation of Cambrian Series 2, Stage 4 in Jianhe, Guizhou, south China by etching rocks with 2–3% acetic acid. This is the first report of Hadrotreta in south China. According to the global palaeogeographical distribution of Hadrotreta shows an expanding trend from the Cambrian Age 4 to the Miaolingian Epoch, and this genus was mainly found at low latitudes. In the Cambrian Epoch 2, Age 4, Hadrotreta only appeared in south China and the Laurentia palaeocontinent, and was mostly associated with deep-water continental shelf environments. Later, Hadrotreta expanded its distribution to become virtually cosmopolitan during the Miaolingian Epoch and is mostly preserved in shallow-water platform environments. ABSTRACT: Hadrotreta is a worldwide acrotretoid brachiopod reported from the Cambrian Series 2 to Miaolingian. Here, a number of well-preserved fossils of Hadrotreta, identified as Hadrotreta cf. H. timchristiorum, were found in the Protoryctocephalus arcticus Zone of the Tsinghsutung Formation of Cambrian Series 2, Stage 4 in Jianhe, Guizhou, south China. This is the first report of Hadrotreta in China, which enriches its global palaeogeographical distribution. Hadrotreta is very similar to acrotretoids such as Kostjubella, Vandalotreta, Linnarssonia, and Eohadrotreta. It differs from them with its well-developed ventral boss-like apical process, apical pits, and dorsal median sulcus. In view of the palaeogeography of Hadrotreta, this genus was mainly distributed in low-latitude regions. Hadrotreta was only found in south China and Laurentia during the Cambrian Age 4, then expanded its distribution to other regions such as Siberia, Baltica, the Kazakh Terranes, the Far East, and Gondwana Pange during the Miaolingian Epoch. Hadrotreta seems to have shifted from deeper water to shallow-water environments during the period from the Cambrian Series 2 to the Miaolingian.