Superfamilies: Orbitodacea, Spirillinacea, Duostominacea and Robertinacea

Lecture 10

Superfamily OrbitodaceaSuperfamily Orbitodacea The The orbitoidsorbitoids are a are a Late CretaceousLate Cretaceous to Miocene to Miocene

group of "larger foraminifera" which originated group of "larger foraminifera" which originated in tropical Americas.in tropical Americas.

Their tests are Their tests are radial hyalineradial hyaline and and perforateperforate, with , with a discoidal mode of growth, the chambers being a discoidal mode of growth, the chambers being arranged in arranged in annular cyclesannular cycles rather than plane rather than plane spirals.spirals.

A median (equatorial) layer of chambers is A median (equatorial) layer of chambers is differentiated from the lateral chambers, seen differentiated from the lateral chambers, seen most clearly in axial thin sections (most clearly in axial thin sections (DiscocyclinaDiscocyclina).).

Superfamily SpirillinaceaSuperfamily Spirillinacea The wall consists of a single crystal of The wall consists of a single crystal of

calcite. They are small benthic forms often calcite. They are small benthic forms often found adhering to algae and other hard found adhering to algae and other hard substrates.substrates.

SpirillinaSpirillina has a long, planispiral second has a long, planispiral second chamber and terminal aperture.chamber and terminal aperture.

PatellinaPatellina has a trochospiral to biserial test in has a trochospiral to biserial test in which the chambers are subdivided by a which the chambers are subdivided by a scroll-like median septum and numerous scroll-like median septum and numerous transverse transverse septulaeseptulae..

Spirillina

Patellina

Superfamily DuostominaceaSuperfamily Duostominacea

The The Duostominacea Duostominacea are an extinct group are an extinct group that may be intermediate in development that may be intermediate in development between certain between certain EndothraceaEndothracea and most and most RotaliinaRotaliina..

This is suggested by the wall structure This is suggested by the wall structure which consists of both optically radial which consists of both optically radial and and microgranularmicrogranular calcite. calcite.

In In DuostominaDuostomina (M. Triassic) the (M. Triassic) the lowlow trochospiraltrochospiral test has a basal aperture test has a basal aperture divided into two by a flap.divided into two by a flap.

Duostomina

Superfamily RobertinaceaSuperfamily Robertinacea

The The RobertinaceaRobertinacea have optically radial bilamellar walls have optically radial bilamellar walls composed of composed of aragonite instead of calcitearagonite instead of calcite, although , although this may revert to the latter mineral with time in the this may revert to the latter mineral with time in the fossil state. fossil state.

The aperture is typically a basal slit extending up the The aperture is typically a basal slit extending up the face of the last chamber. face of the last chamber.

In In RobertinaRobertina the test is high the test is high trochospiraltrochospiral, each , each elongate chamber subdivided by transverse partitions. elongate chamber subdivided by transverse partitions.

CeratobuliminaCeratobulimina (Upper Cretaceous)(Upper Cretaceous) has a moderately has a moderately low trochospiral test whilst that of low trochospiral test whilst that of HoeglundinaHoeglundina (M. (M. Jurassic-Recent)Jurassic-Recent) is provided with a keel and is provided with a keel and peripheral slits marking the primary and relict peripheral slits marking the primary and relict (supplementary) apertures(supplementary) apertures..

Robertina Ceratobulimina

Hoeglundina