bild 3 lecture 10

bild 3 lecture 10 - Morphological species or morphospecies...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
Morphological species or morphospecies are groups of organisms that show clear and consistent phenotypic differences. Morphospecies can be described on the basis of morphological criteria. The change from one morphospecies to another can sometimes be seen clearly in marine deposits. Foraminifera are tiny one-celled marine protozoa that float and multiply in the upper layers of the oceans. When they die their shells fall in uncounted numbers to the ocean floor, where they build up in thick layers of ooze that can remain undisturbed in the darkness of the deep for tens of millions of years. When cores are drilled into the sea bottom they reveal an uninterrupted record of changes in foraminiferan populations. Such records are far more complete than terrestrial fossil records, which tend to be broken up by tectonic movements and partially destroyed by erosion. The figure below shows details of the skeletons of two of these foraminiferan species, Globorotalia plesiotumida which lived from ten to five million years ago in the southern Indian Ocean, and G. tumida , which replaced it about five million years ago and has survived down to the present day.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Globorotalia plesiotumida Globorotalia tumida The next figure, an analysis of the cores, shows that this replacement was gradual rather than sudden, taking about half a million years.
Background image of page 2
Millions of years before present G. tumida G. plesiotumida Expanded view of period of most rapid change The core has also preserved much smaller but significant changes in the population. Many small environmental fluctuations affected the Globorotalia population throughout this ten million year period, causing repeated alterations and sometimes temporary reversals in size and shape. What selective pressures drove this phenotypic change? We do not yet know, but the major increase in size of these foraminiferans, starting 5.5 million years ago, coincided with the Miocene-Pliocene boundary and the onset of a global cooling trend that eventually resulted in a series of severe glaciations that have lasted down to the present time. At the same time as G. tumida evolved, many other animal and plant species that resemble present-day species appeared around the world for the first time. The foraminiferans preserved in the South Indian Ocean deep-sea cores have provided a detailed glimpse of one small part of a global burst of speciation.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Morphological species differences depend, literally, on the eye of the beholder. Some of these beholders are taxonomists called lumpers , who do not think that slight morphological differences are important, and tend to lump similar individuals together into a single species. Others are splitter taxonomists, who put great weight on slight differences in appearance, and tend to split the same set of individuals into different species or subspecies. Disagreements between lumpers and splitters are common and often contentious, because different taxonomists emphasize different aspects of morphology even within a
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 11/05/2008 for the course BILD BILD 3 taught by Professor Woodruff during the Spring '08 term at UCSD.

Page1 / 17

bild 3 lecture 10 - Morphological species or morphospecies...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online