Errivaspis

Taxobox
name = "Errivaspis"


fossil_range = Early Devonian
regnum = Animalia
phylum = Chordata
classis = Heterostraci
familia = Pteraspidae
genus = "Errivaspis"

"Errivaspis" is an extinct genus of pteraspid heterostracan that lived in the Early Devonian period.

Description

"Errivaspis" had large dorsal plates and ventral plates, the linking branchial plate, as well as a cornual plate at the side, an orbital plate around the eye. A rostral plate formed a pointed ‘snout’, several small plates around the mouth, and a dorsal spine pointing backwards. The rest of the body was covered with small scales that look more like modern fish scales than the bony plates of early forms. The tail was fan-shaped.

Characteristics

More analytically, "Errivaspis" had a pair of external lateral gill openings, emptying from several gill pouches. The exoskeleton consisted of head covered in dermal armor consisted of plates of dentine and aspidine, generally with a honeycomb-like structure, covering the branchiocephalic region and body with large scales covering the trunk and tail. The eyes were lateral, extremely small without sclerotic ring. Also the two movable paired fins were absent; anal fin absent; tail internally hypocercal, externally often symmetrical; perhaps two olfactory capsules (diplorhinal condition) with only an internal opening into the mouth area.

Species with interlocking tesserae in the dermal armor are known as the tessellated pteraspidiforms or heterostracans. Maximum length is 1.5 m, usually much smaller. Pteraspidiforms are well known from the Lower Silurian to the Late Devonian. Taxa of uncertain affinities, of which some are not definitely known to be heterostracans.

References

* Michael J. Benton, "Vertebrate Palaeontology" 3rd Edition, p. 48 - 49 (Blackwell Publishing, 2005)