摘要：Some Middle Devonian (late Eifelian-early Givetian) fossil fish remains are described
from an outcrop of the Pimenteira Formation on the eastern border of the Parnaíba Basin (Picos
area, State of Piauí, northeast Brazil). These remains include a fin spine with ribbed ornament, a
bicuspid shark tooth similar to those of xenacanths and omalodontids, a badly-preserved
Machaeracanthus spine, and small indeterminate scales and fragments of what may be prismatically
calcified cartilage. The bicuspid tooth is the first record of its kind from the Devonian of Brazil and
the first unequivocal Devonian record from South America. Its principal cusps have widely spaced
cristae, like teeth of the Gondwanan Devonian elasmobranch Antarctilamna, but small intermediate
cusps are absent (as in Leonodus). The fin spine has comparable ornament to those of Ctenacanthus,
Antarctilamna, and Doliodus, but is too poorly preserved for accurate determination. Machaeracanthus
is the most widespread Devonian vertebrate in the Malvinokaffric Realm, and its spines are also
known from the Old World and Eastern Americas realms, although scales referred to the genus are
reported from outside these three regions. The occurrences of Machaeracanthus spines in the Parnaíba
and Amazon basins lends support to an earlier proposal based on the distribution of invertebrate
fossils that these basins provided maritime connections existed between the Malvinokaffric and the
Old World/Eastern Americas realms during the late Eifelian - early Givetian.
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