How do we know about past environments?

Historic and precontact archaeological and palaeoenvironmental sites from across Alberta tell us much about people and past environments. But how can we learn the details about that environment? This blog post will tell you how we use environmental indicators, especially macrofossils, to reconstruct what conditions were like at sites in the past.

It may seem reasonable to assume that the environment when an archaeological site was inhabited by people was generally the same as it is now, and this is sometimes the case. However, the archaeological record in Alberta goes back at least 13,000 years , to the end of the last major glaciation and its transition to our present epoch (the Holocene). Given this long and varied history, it’s obvious some considerable changes have occurred.

In addition to sedimentary and geologic indicators of past environments (the things soil scientists and geologists study), the remains of plants and animals buried in these sediments can also help us understand specific environmental conditions in the past. Many studies use pollen, often preserved in sediments on lake bottoms, to reveal what plants were growing in the area long ago. Because pollen can travel great distances from its parent plant, and is transported by wind, weather, and water, it helps tell a sweeping story about an area’s general conditions and plant communities on a regional scale. To tell the story of the environment at a particular site, local indicators are more appropriate; macrofossils are one example.

What is a macrofossil?

Macrofossils include all plant and animal remains that are visible to the naked eye. Sometimes, especially for older specimens, minerals eventually replace some or all of the macrofossil’s organic remains. However, macrofossils also include specimens where organic tissues or structures are preserved relatively unaltered, despite exposure to various degrees of physical and/or chemical weathering. These are most common class of macrofossil used to study historic or archaeological sites. At the Royal Alberta Museum’s Quaternary Environments lab, although we sample for and study macrofossils like wood, insects, and leaves, most of our focus is on plant seeds and shells from molluscs like snails and clams.

How do we find macrofossils?

Given that the material we study, though “visible to the naked eye”, is still quite small, detection is not always straightforward. However, the most macrofossil-rich layers of sediment are normally those that clearly contain increased organic content. These layers are usually darker, sometimes showing preserved plant matter or other organisms, and may even have a greasy or fibrous feel if rubbed between your fingers. Otherwise, shellbeds, conspicuous by the presence of many (usually) white mollusc shells, are good sources of material. Shellbeds are found especially in the bottoms of river valleys or in places where ponds have previously dried up and been buried.

Most of the samples we study are collected through professional archaeological or palaeontological investigations. Still, the interpretation of these ancient remains relies on our knowledge of modern organisms. Sometimes modern specimens can be seen in the drift at the high-water mark along a river’s edge or on a lake shore. These accumulations often include shells and plant material brought downstream and deposited in shallows or after a flood. Material found along larger streams and rivers is usually environmentally representative of the upstream area, giving insight into the living conditions required by the organisms present. Collecting from drift deposits is a great way to build our collective knowledge of modern plants and animals that are likely to be preserved as macrofossils.

You can contribute your observations of the modern biota to sites like iNaturalist, even without collecting specimens. In this way, your results become available to researchers around the world. Another advantage of this platform is that, if your identifications need some work, more experienced individuals are usually quick to come to your aide and offer their own suggestions. Just remember, if you come across macrofossils, make sure to respect Alberta’s Historical Resources Act (click here for information on permitting, excavation, and the Historical Resources Act). Even for modern specimens, permits are needed to collect in National Parks, Provincial Parks, and other protected areas. Because of these considerations, the best policy is to observe, record, and report any finds you make.

If you see a promising shellbed or buried vegetation-rich layer, the Quaternary Environments section of the Royal Alberta Museum and the Archaeological Survey are always interested. To preserve the most information, the layer shouldn’t be disturbed. Instead, take pictures of the site and its context, including at least one close-up of the contents (especially if macrofossils are visible) and record the location (on a map, with a GPS, or a GPS-enabled smart phone). Information about finds can be sent to the Archaeological Survey’s Report a Find service. By reporting finds and recording observations you can make meaningful contributions to the understanding of ancient environments in archaeological or palaeontological contexts.

How do we identify macrofossils?

Identification of macrofossils is best done under a dissecting microscope, like the one pictured, with tools such as fine forceps and artist’s paintbrushes, so as not to damage the often delicate specimens. If you don’t have access to a microscope, however, many features can be seen with a good hand-lens that has at least 10x magnification.

Aside from a steady hand and the tools to manipulate and view the specimens, identification of macrofossils relies on comparative material and published descriptions against which to compare your specimens and help build your “mental catalogue” of identification criteria. The Royal Alberta Museum has reference collections of modern and macrofossil seeds and shells. These collections have been growing since the 1970s and we continue to add samples to them. For an idea of the collection scope, the Seed Reference Collection contains specimens from more than 1000 different taxa. These collections are used not only by museum staff but are also accessed by interested scholars and visiting researchers.

There is an incredible diversity of plants and animals known from Alberta, with more than 40 species of aquatic snails, nearly 60 shelled land snails, and more than a thousand species of vascular plants. How can one person be expected to have the knowledge to identify all these species? Luckily, in our experience, the Pareto principle (i.e., the 80/20 rule) applies to macrofossils. By being able to identify the most common taxa (e.g., the top 20%), presuming the environmental conditions they represent are well known, you will already have the information to detect at least 80% of the environmental signal encoded in any complete macrofossil assemblage. And beyond that, you already know 80% of the terminology and possess all the basic skills required to identify the remaining taxa!

A starting point for macrofossil identification

Considering this, we have drafted an “identification guide” for some of the most common macrofossils we’ve found in samples from the banks of rivers in southwestern Alberta. Our PDF guide is freely available as part of the Archaeological Survey of Alberta Occasional Paper series. This guide contains photographs of both fossil and modern specimens from the Quaternary Environments collection, detailed descriptions of the characteristics of the seeds and shells, and a glossary of important terms used for their identification. Armed with a solid foundation of knowledge about the most common terms and taxa, any interested person, including prospective researchers or students of archaeology or natural history, can begin exploring the fascinating world of small-scale macrobiology and the rich macrofossil record in Alberta. Identifying macrofossils is a crucial step towards understanding how environments in the province have changed over thousands of years.

Written by: Matthew Bolton, Quaternary Environments Assistant and Flood Sample Analyst, Quaternary Environments, Royal Alberta Museum and Alwynne Beaudoin, Head Curator of Earth Sciences and Curator of Quaternary Environments, Royal Alberta Museum.

Header photograph: Potamogeton spp. (pondweed) fruits from Alberta (photographs by M. Bolton).