Morphocoenoclines, character combination, and environmental gradients: a case study using symbiont-bearing benthic foraminifera

Author(s)

Johann Hohenegger

Abstract

Abstract.-The species-characteristic combination of morphological characters that depend on an

environmental gradient can be used to determine the frequency distribution of the species along

the gradient. All functional characters of a phylogenetically closely related species group demonstrate

overlapping intervals along an environmental gradient. The gradual change in character

composition along the gradient is called a morphocoenocline. Based on transfer functions, a morphocoenocline

can be used for gradient values estimation (proxies) in the historical or geological

past, similar to a coenocline based on species (democoenocline).

Transforming the empirical frequency distributions of characters and character states along the

gradient to probability distributions enables calculating a probability density function of any subset

of characters of the morphocoenocline. Because a species is distinguished by a specific combination

of characters that are functionally related to the gradient, the distribution of this species

along the gradient can be estimated using the probability density functions of combined characters.

Assuming ''functional uniformitarianism'' this estimation can be extended into the geologic past

for all fossil species, as long as their functional characters are homologous or analogous to those

found among Recent forms. When a morphocoenocline is based on a compound environmental

gradient, such as depth, which represents a combination of single environmental factors, the gradient

estimation reflects only a specific combination of single factors.

A morphocoenocline for test characters of symbiont-bearing benthic foraminifera from theWest

Pacific was established for water depth. This compound environmental gradient represents tropical

open sea conditions at a slope where the water is highly transparent (low inorganic nutrients and

sediment input). Depth distributions based on probability density functions were compared with

empirical distributions to prove the accuracy of this method, and were used to estimate the depth

distribution of other living species that had not been included in the determination of the morphocoenocline

because they live in other regions. The method was also applied to fossil species

that are closely related to Recent forms (Nummulites, Assilina from the Eocene) and to fossil species

that are more distantly related to the living species (Orbitoides from the Upper Cretaceous).

Organisation(s)

Department of Palaeontology

Journal

Paleobiology

Volume

32

Pages

70-99

No. of pages

30

ISSN

0094-8373

Publication date

2006

Peer reviewed

Yes

Austrian Fields of Science 2012

105118 Palaeontology

Portal url

https://ucrisportal.univie.ac.at/en/publications/bf6ede5b-2c1c-4c7f-92ad-ec4a0c078db8