A second lamprey from the Lower Carboniferous (Namurian) of Bear Gulch, Montana (U.S.A.)

Abstract

A second fossil lamprey is described from the Lower Carboniferous (Namurian) locality of Bear Gulch (Montana, U.S.A.), which had already yielded the type specimen of Hardistiella montanensis, the oldest and, probably, the most primitive of all known lampreys. This new specimen, which may possibly belong to the latter species, is badly preserved, but clearly shows the impressions of four to six branchial pouches which are relatively small and closely set, like those of the other Carboniferous lamprey Mayomyzon pieckoensis. They differ thus from extant lampreys, in which the branchial apparatus extends relatively far behing the eyeballs. This concentration of the branchial apparatus in early lampreys is regarded here as a primitive condition, which is also met with in many anaspids, as evidenced from their closely-set external branchial openings. The presence of an impression which recalls the loop of the trabecles in larval extant lampreys suggests that this specimen was a larval individual.