Sunday, 25 May 2014

Fossil Romainvilliine Geese from the Late Eocene of Xinjiang Province, China.

The Romainvilliines are an extinct group of large Waterfowl known from Late Eocene and Early Oligocene of France, Belgium and England. They are thought to be members of the family Anatidae, which includes modern Swans as well as several groups of large Geese (the terms ‘Goose’ and ‘Duck’ are somewhat imprecise, being used for larger and smaller members of the Waterfowl order, Anseriformes, respectively). Romainvilliines vary in size from that of Dabbling Ducks, to that of large Geese, with one possible member of the group, Cygnopterus affinis, reaching sizes comparable to modern Swans.

In a paper published in the journal Verterata PalAsiatica on 21 January 2014, Thomas Stidham and Ni Xi-Jun of the Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, describe fragmentary remains of possible Romainvilliine Geese from the Late Eocene Irtysh River Formation of Jeminay County in Xinjiang Province in northwest China.

The material comprises two bone fragments, a partial distal right tarsometatarsus and a distal right femur, neither of which is assigned to species level, though the femur fragment is thought to show similarities to Cygnopterus.

The Xinjiang Anseriform tarsometatarsus in distal (A), lateral (B), dorsal (C), medial (D) and plantar (E) views. Abbreviations: di. distal interosseus canal; do. dorsal opening of the distal vascular foramen; g. groove on the plantar side distal to the distal vascular foramen; po. plantar opening of the distal vascular foramen; pr. ridge on the proximal plantar base of trochlea II; rs. rugose scar; t2. trochlea II; t3. trochlea III; t4. trochlea IV. The arrows indicate the plantar edges of the plantar opening of the distal vascular foramen highlighting the dorsoplantar offset between the proximal and distal sides of the foramen. Stidham & Ni (2014).

The Xinjiang Anseriform distal femur in caudal (A), medial (B), cranial (C), and lateral (D) views Abbreviations: fl. femoral ligamental attachment; ft. fibular trochlea; gl. presumed elongate tubercle for the origination of the gastrocnemialis lateralis; if. impression of the ansae iliofibularis; is. Intercondylar sulcus; lc. lateral condyle; mc. medial condyle; ml. ligament attachment (scar) on the medial side of the popliteal fossa; mp. medial pit; mr. medial rim of the intercondylar sulcus; pf. popliteal fossa; ps. popliteal fossa muscle scar; sc. Medial supracondylar crest and adjacent fossa. Stidham & Ni (2014).

The Irtysh River Formation comprises mudstones, siltstones and sandstones laid down in a river and lake system in the Late Eocene. It has produced numerous Fish and Crocodylians, but only a few Mammals, including fragmentary remains of Anthracotheriids, Brontotheriids, Perissodactyls and an unidentified Hyaenodontid. Only two fossil Birds are know from the Palaeogene of Xinjiang, neither from the Irtysh River Formation, and, despite the rich diversity of Chinese Mesozoic Bird Fossils, very few Chinese, or indeed Asian, Bird fossils are known from the Palaeogene at all.

Xiaerhete fossil locality and the Irthysh River Formation in Jeminay County. (A) Map showing the location of the Xiaerhete fossil locality in the Jeminay region within China adjacent to several other countries; (B) Detailed map showing the border region between Xinjiang and Kazakhstan and the location of the Xiaerhete fossil locality; (C) Panoramic view of the fossiliferous hills of the Irthysh River Formation that produced the Anseriform fossils. Stidham & Ni (2014).

During the Late Eocene Europe was separated from Asia by the Turgai Strait and Danish-Polish Trough, and the two areas had distinct Mammalian faunas (a distinction that broke down in the ‘Grande Coupure’ of the Early Oligocene when Europe was invaded by a variety of Asian Mammal groups). The Avian fauna of the period is less well known, so finding Birds from a group previously restricted to Western Europe in Central Asia is significant, though perhaps not that surprising since the fossils come from a group thought to have been both good fliers and good swimmers.

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