Date Published: May 8, 2019
Publisher: Public Library of Science
Author(s): Anna Ayvazyan, Davit Vasilyan, Madelaine Böhme, Jürgen Kriwet.
We studied 4 Ma old isolated pharyngeal teeth from lake sediments of Çevirme (Tekman Palaeolake, Erzurum Province). Based on shape characters defined for 3D models of modern species, we found that the Pliocene lake constitutes sympatric occurrence of four Capoeta species (C. cf. umbla, C. cf. baliki, C. cf. sieboldi and C. sp. sevangi/capoeta), whose modern relatives belong to a monophyletic clade inhabiting today three different drainage systems of this region (Euphrates River, Kura River and Black Sea). We interpreted this high local diversity of closely related species in terms of the species-flock model. The Tekman palaeolake was a part of an unrecognized extended late Miocene to Pliocene palaeolake system in the present-day Armenian Highland, which has been disrupted by Pliocene tectonic activities. Surface uplift of the Armenian Highland contributed to the very characteristic biogeographic distribution and endemism of Capoeta in West Asian drainage systems. Thus, we proposed a species-flock scenario for the evolution and dispersal of the cyprinid genus Capoeta in a huge unrecognized palaeolake system in the present-day Armenian Highland.
Tigris and Euphrates are the largest rivers in Western Asia, both have a rich and diverse aquatic fauna which includes seven endemic fish genera (two of the Cobitidae family and five of the Cyprinidae family) . In southern Caucasus, the Kura-Araxes River Basin is the major river system with many tributaries . It is also characterized by several endemic fish species . Among them, the cyprinid genus Capoeta shows phylobiogeographical pattern and it is widely distributed in Western Asia and the Ponto-Caspian region (Euphrates, Tigris, Araxes, Kura and Orontes) with 30 valid species [4, 5]. The distribution of the Capoeta species within Western Asian and Ponto-Caspian water basins provides an excellent basis for the analyses biogeographical evolution of the main drainage systems of this region.
The studied fossil fish material is collected from 1965–1969 during the prospection of Neogene lignite deposits of Turkey . The material contains 247 isolated pharyngeal teeth (Table 1, Fig 5A–5U) collected from the early Pliocene locality Ҫevırme in Eastern Anatolia, Turkey. From the same horizon, 41 isolated pharyngeal teeth of Leuciscinae (Leuciscus sp.) and some amphibian and reptile bones are also founded . The studied fossil material already housed in the Bundesanstalt für Geowissenschaften und Rohstoffe, Hannover (BGR collection numbers) and no additional excavation of fossils was undertaken. The studied isolated fossil pharyngeal teeth are photographed under the Leica DVM5000 digital microscope, Leica M50 stereomicroscope and LEO Model 1450 VP scanning electron microscope (SEM). Recent comparative material (pharyngeal bones) is represented by adult individuals and comes from following collections: Bavarian State Collection for Anthropology and Palaeoanatomy Munich (SNSB), Palaeontological Collection of Tübingen University (GPIT), Senckenberg Naturmuseum Frankfurt (SMF) and National Museum of Natural Sciences of Madrid (MNCN) (Table 2). Both fossil and extant specimens publicly deposited in the above-mentioned collections and accessible by others in a permanent repository.
In our fossil samples, we record eight shape classes where the genus diagnostic shape class “C” dominates the assemblage (53%). Identified shape classes as species or clade diagnostic (A, J, R, M) compose 10% of the assemblage (S1 Fig).
For the first time, a detailed study of the isolated fossil pharyngeal teeth of the genus Capoeta (n = 247) is provided. The description and identification of the fossil material from Ҫevırme (Erzurum Province, Tekman district) is based on the methodology introduced by Ayvazyan et al. 2018. We show that our methodology is applicable to the fossil record of the genus Capoeta and allows identification of the isolated fossil pharyngeal teeth at species level. Within the studied fossil material eight shape classes are distinguished, four of them are species or clade diagnostic and indicate the presence of the four sympatric Capoeta species (C. cf. sieboldi, C. cf. umbla, C. cf. baliki and C. sp. capoeta/sevangi) in the Tekman Palaeolake at 4 Ma. These four species belong to a monophyletic clade of the genus and today they are distributed in different water basins (Euphrates/Kura/Black Sea) of Western and Ponto-Caspian region. We interpret this high local diversity of closely related species in terms of the species-flock model.