Day 24 (July 19, 2011) Microfauna—What the Tiniest Bones Tell Us

a pair of hands hold a tiny fossil frog bone fragment with forceps over a small, clear plastic storage box contained a label for Site 15 and 20-30 other fossil bones.
Remains of microfauna from Site 15
(Kathryn Ranhorn, Human Origins Program)

Ever try to find a needle in a haystack? How about a mouse bone in gravel? Jennifer Clark has. Her research, which focuses on microfauna, shows that sometimes big information comes in small packages.

 

Microfauna are tiny bones used to reconstruct paleoenvironments. Examples of microfaunal remains can include small mammals, fish, invertebrates, birds, and reptiles. The bones are so small, in fact, that they are often missed in standard excavation procedure. Instead, her research requires a much more complicated filtering process.

Nineteen piles of washed soil samples sit out in the sun, drying on a plastic sheet stretched across the ground. In the background, a man crouches over one pile as he sweeps
Richard Kinyua keeps the piles of wet sieved sample soil from the excavation site organized and labeled as they dry.
(Jennifer Clark, Human Origins Program, NMNH)

Jenny starts by collecting soil from the excavation site which has already been sieved through a screen with 1 millimeter openings ( see Day 19 ). Back at camp, she then uses water and 1 and 1/2 millimeter sieves to filter out even finer grains of soil, leaving only very small particles behind. This process is called wet-sieving.  After the wet sieve, the remaining soils are dried in the sun. She and other crew member then place the fine soil on a plate and comb over it with a small brush, picking out any tiny bones with forceps. All of the microfaunal remains are placed in a coin-sized plastic box and labeled.

 

Methodically speaking, that’s already a lot of work! However, finding the microfauna is only half the battle; she then has to analyze the findings!

A man sits under a canvas awning outside a green tent with a small paint brush and forceps searching for tiny fossils among small particles of soil scattered on a yellow plate
One of the crew members, Mang’ea Moki, meticulously picks through sediment in search of microfauna
(Kathryn Ranhorn, Human Origins Program)

The first step in analysis is to identify the critter in as much detail as possible. For most bones, she can easily identify the family, such as mouse or frog, by looking closely at it. Usually, it’s necessary to use a microscope or magnifying lens to get a better look at the specimen. It is more beneficial to identify the find to the most exact level in the biological spectrum – especially family, genus, and species, if at all possible.

 

Why is it important to identify the creature? By knowing which animals lived in the various layers of Olorgesailie in the past, we can determine what the environment was like and how the habitats changed from one layer to the next, over time. For example, there are some frogs which require a water source year round. On the other hand, there are some types of frogs which estivate, that is, they burrow in the ground when water is scarce. Determining which kinds of frogs were present at Olorgesailie gives us information about seasonal variation and rainfall.

A woman in floppy straw hat sits in the sun at a wooden table using a binocular microscope to look at tiny fossil bones and teeth.
Jenny uses a microscope to identify the family and genus and species of small microfaunal remains
(Kathryn Ranhorn, Human Origins Program)

After identification, Jenny then looks up what kind of environment that particular creature thrived in. Such a search yields vital information about the paleoenvironment, such as vegetation, temperature, or rainfall. In sum, microfauna are a big piece of the puzzle enabling our understanding of the environment in which our early hominin ancestors and relatives lived and evolved.