The answer to this question is the straightforward part of this post: palaeontology is the study of fossils and micropalaeontolgy is the study of microfossils. Alas, that’s the easy bit done… what then, are microfossils?
I’ll assume that we all know what a fossil is (if not, I recommend starting here) so a microfossil must be a small fossil, right? Actually, this is a harder question to answer than you might think so here are some thoughts on how large a microfossil is, how old they are and how we manage them at the Museum.
There is no agreed size below which a fossil stops being a large fossil and starts becoming a microfossil. Some people arbitrarily say that if you need to use a microscope to view a fossil then you are looking at a microfossil. However, some fossils we consider microfossils measure more than a couple of centimetres in diameter. The rocks that were used to construct the pyramids in Egypt contain microfossils that can be as large as a ten pence piece!
Photo of Egyptian pyramid courtesy of Bobbie Molloy.
This size delimiting definition also gets slightly difficult to use when you are studying the microscopic parts of a larger organism, for example the fossilised scales of a fish or a minute example of something that is usually larger like a gastropod (e.g. a snail). Most people studying these topics would consider themselves microvertebrate workers or gastropod workers and not micropalaeontologists. However, many micropalaeontologists, like me also study microscopic remains of larger organisms like fish that they find during laboratory preparations for other microscopic remains.
Some people try to restrict micropalaeontology to particular biological groups that are commonly considered microfossils. This can also be open to personal opinion, for example, palynologists study microscopic organic remains like spores, pollen and oceanic plankton – all microscopic in size – but some of them would consider themselves palynologists rather than micropalaeontologists. The Micropalaeontological Society defines its specialist groups to reflect biological classifications of organisms commonly accepted as microfossil groups.
As with size, there is no agreed age beyond which something stops being recently dead and becomes a fossil. With specimens in this narrow window of age (ie 0-10,000 years old) it is virtually impossible to tell how old a microfossil specimen is without carrying out some sort of destructive chemical analysis on it.
At the Museum, we mainly follow the Micropalaeontological Society's definition of a microfossil and in the Palaeontology Department we have collections of Foraminifera, Ostracoda, conodonts, Radiolaria, nannofossils and various palynological groups such as the dinoflagellates and spores. In future posts I will introduce each of these microfossil groups as I highlight projects that are currently happening here at the Museum.
My job is to manage all of these collections which number over 750,000 objects. It would be impossible to count the exact number of specimens because some slides and residues contain hundreds of thousands of specimens.
The lack of clarity over what age makes a microfossil causes problems sometimes with deciding where to store specimens in the Museum collections. In the Palaeontology Department we have all the extant (modern) Foraminifera as well as the fossil specimens, so no problem there. However, ostracods are split between our department and the Zoology Department, with us holding the fossils and Zoology the recent (extant) forms. In practise it is very difficult to draw the line between fossil and recent and we certainly have some ostracods that could be in the Zoology Department and probably vice versa.
The majority of the microfossil collections are Foraminifera, which are unicellular animals with a foramen (i.e. an opening, sometimes multiple) that form small shells of calcium carbonate, silica or organic materials. Examples of Foraminifera are shown below, where the field of view of the slide from the Heron-Allen Collection is about 2cm.
The Heron-Allen Collection
I mentioned that some micropalaeontologists like me also work on microscopic fragments of fish (microvertebrates). At the Museum these are kept with the fish collections so they do not come under my ‘jurisdiction’. However, I still study them and some of my most important discoveries have been on this subject as you will find out in the next post to the blog.