Middle Ordovician – Late Ordovician
Heterorthina is an extinct genus of stationary epifaunal suspension feeder
Identification in Hand Sample:
- Traverse, planoconvex, unisulcate
- Hinge line long, nearly planoconvex profile
- Ventral interior with cordate to bilobed muscle scar
- Dorsal interior with lobate, medially cleft, widely divergent brachiophores
- Very wide, bilobed cardinal process
- Note that three species from the type Cincinnatian currently assigned to Damanella (D. bassleri, D. emacerata, and D. fultonensis) likely belong to Heterorthina, pending further study by Dr. Jisuo Jin.
Treatise on Invertebrate Paleontology, Part H, Vol. 3 (2000):
- Traverse, planoconvex, unisulcate, fascicostellate valves; ventral interior with cordate to bilobed muscle scar; dorsal interior with lobate, medially cleft, cardinal process and widely divergent brachiophores.
Harper et al.(1969):
- Heterorthina resembles typical heterorthinids in having a long hinge line and a nearly planoconvex profile. However, it has a relatively simple, non-flabellate muscle field in the pedicle valve unlike the flabellate muscle field of typical heterorthinids, and its very wide, bilobed cardinal process is unlike any in typical heterorthinids. Boucot, Gauri, & Johnson (1966, p.156-157) suggest that Heterorthina gave rise to the Proschizophoriinae. It could perhaps be assigned to the Proschizophoriinae, however, its long hinge line tends to preclude this possibility.
Because of its plano-convex profile and long hinge line, Heterorthina is, for the present, questionably assigned to the Heterorthinae, although further study may show that it is not directly related to the typical Heterorthinae.