General history of dinoflagellates

Although the apparent primitive organization implies great age for the group, the acme of peridinalean history appears to have been reached in the Mesozoic and Cenozoic Eras. Dinosterane and 4a-methyl-24-ethylcholestane, two dinoflagellate biomarkers in samples of Upper Proterozoic and Cambrian age (Moldowan & Talyzina 1999), and RNA sequence data indicate the dinoflagellates diverged before the Foraminifera and the Radiolaria which both have a Cambrian fossil record. It is evident that Late Precambrian and Palaeozoic radiations of acritarchs may represent an earlier stage in dinoflagellate history, when non-tabulate forms thrived. The subsequent evolutionary history of the dinoflagellates

Structure Dinoflagellates

Protocentroidia

Change in swimi direction

Fig. 10.8 Possible evolutionary relationships amongst dinoflagellates. (Redrawn after Bujak & Williams 1981.'

Cyst Freshwater Dinoflagellates

Fig. 10.9 Photomicrographs of selected dinoflagellate cysts. (a) Gonyaulacysta jurassica (Deflandre 1938), x528. A proximate cyst ranging from the early Oxfordian to late Kimmeridgian. (b) Spiniferites mirabilis (Rossignol 1964), x611. Chorate cysts ranging from the Quaternary to Recent. (c) Wetzeliella articulata Eisenack 1939, x294. A proximochorate cyst ranging from the Ypresian to Rupelian. (d) Protoperidinium communis Biffe & Grignani 1983, x515. This is a proximate cyst with a cavate wall structure and shows the archeopyle. Range: Early Pleistocene. ((a) Reproduced from Riding & Thomas in Powell 1992, plate 2.17.3; (b) reproduced from Harland in Powell 1992, plate 5.3.2; (c) reproduced from Powell in Powell 1992, plate 4.6.10; (d) reproduced from Harland in Powell 1992, plate 5.1.6. All photomicrographs reproduced with permission from Kluwer Academic Publishers.)

Fig. 10.9 Photomicrographs of selected dinoflagellate cysts. (a) Gonyaulacysta jurassica (Deflandre 1938), x528. A proximate cyst ranging from the early Oxfordian to late Kimmeridgian. (b) Spiniferites mirabilis (Rossignol 1964), x611. Chorate cysts ranging from the Quaternary to Recent. (c) Wetzeliella articulata Eisenack 1939, x294. A proximochorate cyst ranging from the Ypresian to Rupelian. (d) Protoperidinium communis Biffe & Grignani 1983, x515. This is a proximate cyst with a cavate wall structure and shows the archeopyle. Range: Early Pleistocene. ((a) Reproduced from Riding & Thomas in Powell 1992, plate 2.17.3; (b) reproduced from Harland in Powell 1992, plate 5.3.2; (c) reproduced from Powell in Powell 1992, plate 4.6.10; (d) reproduced from Harland in Powell 1992, plate 5.1.6. All photomicrographs reproduced with permission from Kluwer Academic Publishers.)

has been reviewed by Bujak & Williams (1981; Fig. 10.8).

The earliest record of an equivocal peridinoid cyst is Arpylorus, from the Silurian. This has been interpreted as possessing tabulation, a cingulum and a precingular archaeopyle. The main dinoflagellate radiation, however, began in the mid- to Late Triassic with the appearance of genera such as Suessia (Figs 10.7f, 10.8). Proximate cysts were common throughout the Jurassic (e.g. Gonyaulacysta jurassica, Figs 10.3b, 10.9a), although chorate and proximochorate cyst types had all appeared by the Middle Jurassic.

Many Cretaceous forms are chorate (e.g. Hystricho-sphaeridium, Fig. 10.3d) or proximochorate (e.g.

Spiniferites ramosus, Figs 10.3e, 10.9b), and it was at this time that the greatest diversity of dinoflagellate cysts was reached.

Cavate peridinoid dinoflagellate cysts began to flourish in Aptian-Albian (e.g. Deflandrea, Fig. 10.3f, Wetzeliella, Figs 10.7e, 10.9c) and dominated many Tertiary assemblages until the Oligocene, almost dying out in the Pliocene. Proximate and chorate dinoflagellate cysts with complex processes occur in the Eocene and Oligocene, but simpler forms have prevailed since then. Dinoflagellate cysts first appeared in freshwater sediments during the Tertiary.

Was this article helpful?

0 0
Freehand Sketching An Introduction

Freehand Sketching An Introduction

Learn to sketch by working through these quick, simple lessons. This Learn to Sketch course will help you learn to draw what you see and develop your skills.

Get My Free Ebook


Post a comment