The tail of the Ordovician fish Sacabambaspis.
The tail of the earliest known articulated fully skeletonized vertebrate, the arandaspid Sacabambaspis from the Ordovician of Bolivia, is redescribed on the basis of further preparation of the only specimen in which it is most extensively preserved. The first, but soon discarded, reconstruction, which assumed the presence of a long horizontal notochordal lobe separating equal sized dorsal and ventral fin webs, appears to have considerable merit. Although the ventral web is significantly smaller than the dorsal one, the presence of a very long notochordal lobe bearing a small terminal web is confirmed. The discrepancy in the size of the ventral and dorsal webs rather suggests that the tail was hypocercal, a condition that would better accord with the caudal morphology of the living agnathans and the other jawless stem gnathostomes.
Pradel
Alan
A
UMR 5143 du CNRS, Paléobiodiversité et Paléoenvironnements, Departement Histoire de la Terre, CP38, Museum National d'Histoire Naturelle, 8 rue Buffon, 75005 Paris, France.
Sansom
Ivan J
IJ
Gagnier
Pierre-Yves
PY
Cespedes
Ricardo
R
Janvier
Philippe
P
D000818:Animals; D005399:Fishes / Q000033:anatomy & histology*; D005580:Fossils; D013623:Tail / Q000033:anatomy & histology*