A skull fragment of a Devonian tetrapod with a unique lateral line morphology in the collection of the Museum fr Naturkunde Berlin

In the original description of the Devonian tetrapod Ventastega curonica Ahlberg et al., 1994, Oleg Lebedev mentioned his finding of an uncatalogued, presumed postorbital bone from the Late Devonian of Latvia in the collection of fossil fishes in the Museum f r Naturkunde in Berlin (Ahlberg et al. 1994). The bone bears a dermal sculpture of radially arranged ridges and furrows and is crossed by a partially enclosed lateral line canal. This specimen was collected at the right bank of the Venta river (former German name: Fluss Windau) near Ketleri hamlet by Walter Gross in 1931 together with a large amount of further vertebrate remains. Two years later, Gross (1933) described several of his findings that mainly consisted of ‘agnathans’, placoderms, chondrichthyans, actinopterygians and fish-like sarcopterygians. However, he neither described nor mentioned the postorbital bone from Ketleri. Ahlberg et al. (1994) gave a brief description of this bone, but did not provide an illustration. Based on the ‘tetrapod-like’ dermal sculpture of this bone, these authors suspected that it probably belongs to a tetrapod, possibly to Ventastega, remains of which have also been found at Ketleri locality. Because of the uncertainty of its taxonomic affinities, Ahlberg et al. (1994) did not incorporate this bone in their reconstruction of the skull of Ventastega. The Ketleri Formation, from which this bone is derived, is late Famennian (Late Devonian) in age. It is composed of unconsolidated sand, sandstones, clays and dolomitic marls, and was probably deposited in a shallow basin under brackish conditions (Lukševičs & Župins 2004). Lyarskaja & Savvaitova (1974) divided the Ketleri Formation into three members with the Ketleri locality belonging to the upper member, which is named Varkali Member. A diverse vertebrate fauna has been excavated at the Venta river near Ketleri (Gross 1933; Lukševičs 1991, 2001; Ahlberg et al. 1994) that comprises the placoderm Bothriolepis ciecere Lyarskaja, 1974 (in Lyarskaja & Savvaitova 1974), the acanthodians Devononchus tenuispinus (Gross, 1933) and D. ketleriensis Gross, 1947, the porolepiform Holoptychius cf. nobilissimus Agassiz, 1839, the osteolepiforms Cryptolepis grossi Vorobyeva, 1975 and Glyptopomus bystrowi (Gross, 1941), the dipnoan Orlovichthys cf. limnatis Krupina, 1980, the enigmatic Ventalepis ketleriensis Schultze, 1980, which is a possible holoptychiid (Schultze 1980), and the tetrapod Ventastega curonica. Ahlberg et al. (1994) pointed out that a large tristichopterid (eusthenopterid) probably also belongs to the fauna at Ketleri site.