New research highlights influence of intraspecific variability on biodiversity studies

Jan 18, 2013
New research highlights influence of intraspecific variability on biodiversity studies
Reconstruction of the study object, Erbenoceras from the Early Emsian (Early Devonian) of Morocco. Credit: Christian Klug

(Phys.org)—A study of around 100 newly collected specimens of early ammonoids (marine invertebrates with distinctive coiled shells) suggests that the number of species they belong to might have been over-estimated due to the large variability in size and shape within each species.

Recognizing this intraspecific variability is important for biodiversity studies as failing to do so might artificially inflate the number of species known from a certain time or place.

Like dogs and various other organisms, ammonoids – a group of externally shelled cephalopods related to Nautilus, squids and octopods – show extremely large ranges in intraspecific variability in size and shape.

They have often been used to study changes in biodiversity, and extinction events in Earth history due to their high taxonomic and , wide , high evolutionary rates and preservable shell, as well as their successful on the Earth for over 300 million years.  They survived multiple , only to go extinct together with the dinosaurs at the end of the .

Dr Kenneth De Baets of the University of Bristol, with Dr Christian Klug (University of Zürich) and Dr Claude Monnet (University of Lille), studied the intraspecific variability through ontogeny (development of an organism) in early ammonoids, which has rarely been attempted before.  Ammonoids are ideal for this type of study as they hold a record of growth from embryo to adult in their accretionary shell.

Dr De Baets said: "It took more than three years to collect and prepare around 100 Devonian ammonoid specimens from the same geological layer in the same region of Morocco."

New research highlights influence of intraspecific variability on biodiversity studies
Dr Kenneth De Baets holding a full-grown manticoceratid (Manticoceras) from the Late Devonian of Morocco, one of the largest known ammonoids from this time. Credit: Christian Klug

The earliest ammonoids (Anetoceratinae) are known from the Early Devonian and are still loosely coiled with not, or only partially, in contact.  A fairly high number of genera (eight) and species (twenty-four) of Anetoceratinae have been defined, which might be due to considerable intraspecific variability in conch geometry and rib spacing.

Dr De Baets's study, published in Paleobiology, could quantitatively demonstrate a large intraspecific variability in ribbing and shell shape in these early ammonoids.  Only two species could be separated rather than the four previously recognized in Morocco and the range of multiple, previously defined, global species fell within the range of a single species.  Hence, the number of currently valid species of ammonoids is probably much too high in the Devonian and in general.  Despite this large intraspecific variability, different species could still be separated using their entire ontogeny. 

This is important because underestimating or ignoring intraspecific variability can lead to 'taxonomic oversplitting' where specimens that are actually of the same species are identified as belonging to different species.  This significantly biases taxonomy and diversity counts.  For example, the effect of the Frasnian-Famennian extinction, one of the Big Five mass extinctions in Earth history, on ammonoids might have been significantly overestimated as it is based on the diversity of manticoceratids like Manticoceras, an extinct genus of ammonoid, which was artificially inflated by oversplitting. 

Dr De Baets, now a Swiss National Science Foundation (SNF) postdoctoral fellow at the University of Bristol, said: "Our study does not only demonstrate the need to integrate intraspecific variability to avoid artificial fluctuations of diversity in , but also more generally in all other fossil groups."

Explore further: Why there are so many spiders in Britain's homes this year

More information: De Baets, K. et al., Intraspecific variability through ontogeny in early ammonoids. Paleobiology. www.bioone.org/doi/abs/10.1666/0094-8373-39.1.75

add to favorites email to friend print save as pdf

Related Stories

Species loss tied to ecosystem collapse and recovery

Jan 10, 2011

The world's oceans are under siege. Conservation biologists regularly note the precipitous decline of key species, such as cod, bluefin tuna, swordfish and sharks. Lose enough of these top-line predators (among ...

Ups and downs of biodiversity after mass extinction

Dec 21, 2012

The climate after the largest mass extinction so far 252 million years ago was cool, later very warm and then cool again. Thanks to the cooler temperatures, the diversity of marine fauna ballooned, as paleontologists ...

Nautilus survives 500 million years -- until humans fancy it

Jul 23, 2012

No matter how well adapted an animal may be, it can spell evolutionary doom to have feathers or even shells that become coveted by human beings. Take the nautilus, a creature that pulled easily through the asteroid impact ...

Recommended for you

'Red effect' sparks interest in female monkeys

Oct 17, 2014

Recent studies showed that the color red tends increase our attraction toward others, feelings of jealousy, and even reaction times. Now, new research shows that female monkeys also respond to the color red, ...

Roads negatively affect frogs and toads, study finds

Oct 17, 2014

The development of roads has a significant negative and pervasive effect on frog and toad populations, according to a new study conducted by a team of researchers that included undergraduate students and ...

All in a flap: Seychelles fears foreign bird invader

Oct 17, 2014

It was just a feather: but in the tropical paradise of the Seychelles, the discovery of parakeet plumage has put environmentalists in a flutter, with a foreign invading bird threatening the national parrot.

User comments : 0