Page 238 - Introduction to Paleobiology and The Fossil Record

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(c)

(a)
(b)
(d)

(e) (f) (g) (h)

Figure 9.16 A prasinophyte (a) and some dinoflagellate taxa (b–h): (a) Tasmanites (Jurassic), (b)
Cribroperidinium (Cretaceous), (c) Spiniferites (Cretaceous), (d) Defl andrea (Eocene), (e) Wetzeliella
(Eocene), (f) Lejeunecysta (Eocene), (g) Homotryblium (Eocene), and (h) Muderongia (Cretaceous).
Magnifi cation ×250 (a, d, e), ×425 (b, c, f, g, h). (Courtesy of Jim Smith.)

chorate cyst is smaller than the theca and the have suggested that a number of Paleozoic
cysts are contained within the theca, intercon- acritarch taxa may in fact be dinofl agellates.
nected by various appendages and spines, Multiplated forms such as Rhaetogonyaulax
which are related to the external tabulation and Suessia appearing in the Late Triassic
of the theca. In cavate morphs there is a gap characterize dinocyst fl oras ranging from
between the cyst and the theca at the two Australia to Europe. Nannoceratopsis cysts
poles. with characteristic archeopyles and tabula-
tion are common in Early Jurassic fl oras,
Evolution and geological history while Ceratium-like forms appeared fi rst
during the Late Jurassic and diversified in the

Dinoflagellate biomarkers have been identi- Cretaceous. Many precise zonation schemes

fied in Upper Proterozoic and Cambrian for Mesozoic and Cenozoic strata are based
rocks. Moreover the Late Precambrian and on dinocyst distributions. However, during

Paleozoic diversifications of the acritarchs the Eocene the global biodiversity of the group
may mark an early phase in dinofl agellate began a steady decline.
radiation, involving non-tabulate forms. To
date, however, the oldest dinofl agellate cyst is
probably Arpylorus from the Ludlow (Upper Ciliophora
Silurian) rocks of Tunisia; the cyst has feeble The Ciliophora today consist of some 8000
paratabulation and a precingular archeopyle. species of single-celled organisms that swim
Oddly, there is a long gap after this record by beating their cilia, minute hair-like organs.
until the Early Triassic, when Sahulidinium Two fossil groups, the calpionellids and tin-
appears off northwest Australia. Some authors tinnids, may belong here. Calpionellids are a