Tuesday, 26 August 2014

Fossil Owls from the Early Pliocene of Langebaanweg, South Africa.

Owls (Stringiformes) first appear in the fossil record in the Palaeocene and become quite common in the fossil record in the Eocene and Oligocene of Eurasia and North America. The modern Owl families Strigidae and Tytonidae first appear in the fossil record in the Miocene and Eocene respectively. Like all Birds, Owls have rather delicate, lightweight skeletons well suited to flying, but with rather poor preservational potential. However the leg bones of Owls are somewhat more robust, being used to strike an subdue prey, and most fossil Owls are known entirely from their legs. 

In a paper published in the journal Acta Palaeontologica Polonica on 13 June 2014 Marco Pavia of the Dipartimento di Scienze della Terra at the Università degli Studi di Torino, Albrecht Manegold of the Senckenberg Forschungsinstitut und Naturmuseum and the Staatliches Museum für Naturkunde Karlsruhe, and Pippa Haarhoff of the West Coast Fossil Park, describe a series of Owl remains from the Early Pliocene Upper Varswater Formation at Langebaanweg in Western Cape, South Africa. The Langebaanweg deposits have produced over 90 species of Birds in 35 families, making them the most important pre-Pleistocene deposits for the study of Avian faunas in Africa and one of the most important in the world. They are also important in that they are a mixture of coastal and near-coastal river deposits, whereas most locations with rich Avian faunas are karsts (limestone cave systems), which tend to produce rather different assemblages.

The first fossils described are placed within the Barn Owl genus Tyto, and placed in a new species, richae, named in honour of Patricia Vickers-Rich, who carried out the first work on the Avian fauna of Langebaanweg in 1980, and who has made significant contributions to the study of fossil Birds in Africa. The new species is described from the distal end of a right tarsometatarsus (in anatomy the distal end of a bone is the end furthest from the head), a complete left coracoid, the distal end of a left ulna, the distal ends of two left tibiotarsi and the distal end of a right tibiotarsus.

Tyto richae from the Upper Varswater Formation at Langebaanweg, South Africa; Early Pliocene. (A) Left coracoid in dorsal (A1), lateral (A2), medial (A3), and ventral (A4) views. (B) Left ulna in dorsal (B1), caudal (B2), ventral (B3), and cranial (B4) views. (C) Left tibiotarsus in cranial (C1), lateral (C2), caudal (C3), medial (C4), and distal (C5) views. (D) Left tibiotarsus in cranial (D1), lateral (D2), caudal (D3), medial (D4), and distal (D5) views. (E) Right tarsometatarsus in dorsal (E1), lateral (E2), plantar (E3), medial (E4), proximal (E5), and distal (E6) views. Pavia et al. (2014).

Barn Owls first appear in the fossil record of Europe in the Middle Miocene, with most known fossil species from Europe, the Mediterranean and North Africa (including several species from Mediterranean islands with very restricted distributions). The modern Barn Owl, Tyto alba first appears in the fossil record in Morocco in the latest Pliocene or earliest Pleistocene, while the African Grass Owl, Tyto capensis, first appears in the latest Pleistocene in Tanzania. An as yet undescribed species of Tyto is also known from the Early Pliocene of Ethiopia, and two further undescribed species from the early Pleistocene of Kromdraai and Swartkrans in South Africa.

The second species described is placed in the Little Owl genus Athene and given the specific name inexpectata, meaning ‘unexpected’. To date the earliest known Little Owl is a specimen from Bulgaria from the Late Pliocene, which has not been assigned to a specific species (a claimed specimen from the Miocene of Hungary is not generally accepted); and the closest relatives in the fossil record are thought to be fossils from the Pliocene of Idaho, Kansas and Nebraska. The modern Little Owl, Athene noctua first appears in the Early Pleistocene in Italy, and several apparently endemic species are known from Mediterranean islands in the Pleistocene. As such Athene inexpecta is both the oldest member of the genus, and the first recorded specimen from Africa, raising questions about our understanding of the history of the genus. This is not entirely a surprise, as the Langebaanweg deposits have produced other fossils with apparent close affinities to Northern Hemisphere faunas, notably the Bear Agriotherium africanum and the Wolverine Plesiogulo monspessulanus

Athene inexpectata from the Upper Varswater Formation at Langebaanweg, South Africa; Early Pliocene , (A, C–F, H) and Athene noctua, Recent (B). (A) Left tibiotarsus in cranial (A1), lateral (A2), caudal (A3), medial (A4), and distal (A5) views. (C) Left scapula in medial (C1), cranial (C2) and lateral (C3) views. (D) Right in dorsal (D1), caudal (D2), ventral (D3) and cranial (D4) views. (E) Right tibiotarsus in cranial (E1), lateral (E2), caudal (E3), medial (E4), and proximal (E5) views. (F) Right tarsometatarsus in dorsal (F1), lateral (F2), plantar (F3), medial (F4), proximal (F5), and distal (F6) views. (H) Right humerus in cranial (H1), dorsal (H2) caudal (H3), ventral (H4), and distal (H5) views. (B) Reversed right tibiotarsus in cranial view (B1), left tarsometatarsus in dorsal view (B2). Pavia et al. (2014).

Athene noctua is described from two complete right tarsometatarsi, the cranial part of a sternum (the cranial part being the part closest to the cranium), the cranial end of a right scapula, the distal half of a right humerus, the distal half of a right ulna, an almost complete left tibiotarsus, lacking the distal end, the proximal end of a right tibiotarsus (the proximal end being closest to the body), the distal end of a right tibiotarsus, and the distal half of a left tarsometatarsus.

Thirdly the distal end of a left tibiotarsus is assigned to the genus Bubo (Eagle Owls), but not assigned to a specific species, the material being too fragmentary. The oldest members of this genus previously described have been Pleistocene in age, though this includes specimens from Laetoli and Olduvai in Tanzania.

Bubo sp., left tibiotarsus in cranial view, from the Upper Varswater Formation at Langebaanweg, South Africa; Early Pliocene. Pavia et al. (2014).

Fourthly the shaft of a left tibiotarsus and distal end of a right tibiotarsus assigned to the genus Asio (Long-eared Owls), but again not assigned to a specific genus. Asio first appears in the fossil record in the Early Miocene of Germany, and the genus appears to have become widespread by the Plio-Pleistocene, with several species recorded from Europe and North America, and as well as Laetoli in Africa.

Asio sp., right tibiotarsus in cranial (A1), lateral (A2), caudal (A3), medial (A4), and distal (A5) views, from the Upper Varswater Formation at Langebaanweg, South Africa; Early Pliocene. Pavia et al. (2014).

Finally the distal end of a left tibiotarsus is recorded and assigned to the Strigidae (the family which includes all modern Owls except Barn Owls), but not to any specific genus or species.

Unassigned left tibiotarsus in cranial view from the Upper Varswater Formation at Langebaanweg, South Africa; Early Pliocene. Pavia et al. (2014).

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