The Silurian and Devonian vertebrates of Bolivia

Silurian and Devonian vertebrate remains are described from various localities in Bolivia. Most of the material occurs in concretions in the marine Devonian of the Altiplano and Subandean area, and some isolated specimens have been found in sandstones and lutites. The jawless vertebrates are known only from isolated thelodont scales which occur in the Uppermost Silurian or Lower Devonian of Seripona, Chuquisaca. All the other vertebrate remains belong to gnathosthomes, in particular to the acanthodians, placoderms, chondrichthyans and actinopterygians. The acanthodians are represented by some ischnacanthid dentigerous jaw bones and climatiid spines and shoulder girdles. They are fairly abundant and show no marked differences from acanthodian remains known elsewhere in the Siluro-Devonian of Europe and North America. However, some isolated spines are suggestive of the genus Sinacanthus, known from the Lower Devonian of China. The placoderms are represented only by the rhenanid Bolivosteus chacomensis Goujet et al., known from two well preserved braincases. This genus closely resembles Gemuendina (Lower Devonian of Germany) with respect to the overall shape of the braincase, but its shoulder girdle differs substantially. The chondrichthyans are the most abundant vertebrates in the Devonian of Bolivia. They are represented by isolated spines and endoskeletal elements lined with prismatic calcified cartilage. Among them, some peculiar occipital regions of braincases are referred here to Pucapampella rodrigae n.g., n.sp. These brain-cases differ from all other known Devonian chondrichthyan braincases in showing a ventrally continuous occipital fissure which completely separates the occiput from the rest of the brain-case. The strongly vaulted ventral surface of these braincases is rather suggestive of chimaeroids, and they may belong to some early bradyodont. The actinopterygians are represented by a few isolated scales suggestive of Moythomasia. The most abundant vertebrate remains in the Devonian concretions of Bolivia are peculiar “pan-flute”-like bony plates-which are referred here to Zamponiopteron n.g. These plates, which have never been described anywhere else than in Bolivia, may be interpreted as anchylosed paired fins of some unknown chondrichthyan. Three form-species have been recognized in this genus. Any wide-sweeping palaeobiogeographical interpretation of this vertebrate fauna would be premature. However, one should note that it contains a mixture of widespread forms (rhenanids, some acanthodians, Moythomasia-like actinopterygians), forms with specific transpacific affinities (Sinacanthus-like acanthodians), and possibly endemic forms (Pucapampella, Zamponiopteron).