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Sacabambaspis janvieri
Sacabambaspis janvieri (after Gagnier et al. 1986)
Sacabambaspis is an early, jawless fish that lived during the Ordovician period (495-420 mya), in shallow waters on the margins of Gondwanaland. Sacabambaspis is in the phylum Chordata, the class Pteraspida, the order Arandaspidiformes, and the family Arandaspidae. The type species S. janvieri was found in in Sacabamba in Cochabamba Dept. of Bolivia, in a group of over 30 fossil specimens in a small area, probably caught in a mudslide or large storm (Gagnier et al. 1986). It is named for the village of Sacabamba, plus -aspis, "shield," and for the paleontologist Philip Janvieri. Other species have been found in Argentina, Oman, and Australia, showing a global distribution around Gondwanaland.
Sacabambaspis, with a body length of 25 cm, is the best known genus of the arandaspid family. It is related to Astraspis. Its body had long strap-like scales, and its tail consists of relatively large dorsal and ventral webs.
Sacabambaspis had characteristic, frontally positioned eyes, like head lamps, and a head shield with a large upper (dorsal) plate rising to a slight ridge in the midline, and a curved lower (ventral) plate. Near the front of the upper head shield, behind the eyes, were small pineal openings. Fossils of Sacabambaspis and Astraspis show clear evidence of a sensory structure known as a lateral line system. The arrangement of these organs in regular lines allows the fish to detect the direction and distance of outside movement in the water.
Between
the frontal eyes are traces of two small nostrils, and a mouth armed
with thin oral plates. The nostrils are surrounded by what is thought
to be endoskeletal bone. It also had narrow branchial
plates along the sides, covering the gill area. The
mouth of Sacabambaspis janvieri was lined with nearly 60 rows of small, bony oral plates used for eating.
References:
Gagnier, Blieck & Rodrigo, 1986.
Janvier, Philippe 1997. Arandaspida. The Tree of Life Web Project.
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