Evolution Caught in the Act: Evidence from Microfossil Morphology

• Published in: The Paleontological Society Special Publications
• Main Author: Culver, Stephen J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1999
• Subjects: Planktonic foraminifera
• Online Access: http://dx.doi.org/10.1017/s2475262200014064; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S2475262200014064

Microfossils are of prime importance in documenting patterns of evolution due to their great abundance (often tens of thousands to millions of specimens in a hand sample) and widespread distribution (in both time and space) in the fossil record. The term “microfossil” is often used for paleontological material that requires a microscope for its study, no matter what its biological affinities. For the purposes of this article we will be looking at the remains of protists (single-celled organisms). The several examples I discuss in this chapter are of three groups of planktonic (floating) protists, the calcareous nannoplankton (tiny plant-like protists whose single cell is covered in minute calcitic scales), the radiolaria (animal-like protists with siliceous shells) and the planktonic foraminifera (animal-like protists with calcitic shells). These organisms have been the subject of extensive study because the material from which they are often extracted, cores of deep-sea sediments, are usually comprised of a more complete sedimentological record ( i.e. , fewer breaks) than shallow shelf deposits. Hypotheses of evolutionary history have been constructed for many groups (lineages) of microfossils using specimens from deep-sea cores. Ancestor-descendent relationships have been recognized by tracking shape and form (morphologic) changes through time. This approach to reconstruction of evolutionary history provides an empirical record of morphologic evolution; that is, a record based on observations.