How long ago did ancient ‘beavers’ start ‘engineering’ Earths landscape?
-lecture report by Pauline Donaldson for an unpublished 2011 Whip-poor-will
More than 50 members of MVFN and the public were treated to a fascinating story packed with modern science details and enthusiastically told at our March lecture. Speaker Dr. Natalia Rybczynski, Canadian Museum of Nature paleobiologist, came to talk about our national animal, the beaver. When and why did this unique creature evolve? “How did evolution come up with this?” These are interesting questions from the perspective of the structure of our environment. How long have beavers been around cutting down trees and most significantly, re-engineering the very landscape they inhabit with their incredible dams?
Natalia explained that our Canadian beaver Castor canadensis and European beavers (Castor fiber) are the only surviving members of a diverse group of 18 genera of beaver ancestors which died out millions of years ago. These include ones with skulls much larger and much smaller than Castor ranging from the ‘infamous’ very large Castoroides, to the non-swimming burrowing beavers which dug with their teeth (forming, for the fossil record, mysterious, grooved tunnel structures known as devils corkscrews whose origins were earlier attributed to worms or thought to be channels from plant roots), to Agnotocastor which had a rather ‘boring’ rat-like tail.
To find out how long ago ‘beavers’ have been engineering the landscape, Dr. Rybczynski considered what features make a beaver the engineer it is. Swimming ability, wood-cutting talents and, of course, the ability to build dams; but how far back in the fossil record can one find evidence of these features, and which of Castors ancient relatives possessed them? As a paleobiologist Natalia studies the fossil record to better understand animals that live and that once lived. A key site Rybczynski and colleagues visit several times a year is ‘Beaver Pond’ on Ellesmere Island, an Early Pilocene peat deposit rich in fossils of bear, beaver and beaver-cut wood from a time when that arctic area enjoyed a lush, greener, warm period.
Fossil evidence suggests that beginning ~ 23 million years ago some of Castor’s ancestors could swim. Modern-day beaver are the most swimming adapted of rodents: closed ears, webbed feet, a streamlined body, and, last but not least, the characteristic flattened tail, an improvement which seems to have come about ~ 5-10 million years ago, and which is unique to Castor. This amazing tail (as we saw clearly in an underwater video clip) is not just a rudder for steering but, as the flapping rate showed, clearly contributes to the animal’s powerful underwater propulsion. The familiar flattened part is only part of the tail; there is a furry, muscular part closer to the body.
The next feature to consider is wood cutting. Once one knows how a beaver’s teeth cut wood, one can predict which of beavers ancestors had teeth that might work the same way. So, Dr. Rybczynski went undercover with some zoo beavers and made a movie of them cutting wood. They use their lower teeth only, and, turning their heads, they use only one lower tooth at a time! The cutting produces a characteristic gnawing pattern on two pieces of wood, an ‘A’ and a ‘B’ piece. Castor uses about 60% of the cutting edge of its incisor for cutting. At the Ellesmere Island site fossil evidence of beaver ancestor Dipoides was discovered with what could be wood-cutting teeth, although it likely used only 45% of its incisor surface. It was exciting to learn that there was fossilized Dipoides-cut wood to match. No fossil cut wood has yet been found to match the dentition of the mighty Castoroides ohioensis (shown in this early painting by O.M. Highley). When asked about the likelihood of it ever being found, Dr. Rybczynski says, yes, she thinks it will eventually be found.
So 23 million years ago there were creatures which could swim and cut wood. Perhaps this means our planets landscape has been engineered by beaver-like creatures for 23 million years. The final piece of the puzzle will, of course, be to determine when dam building actually began. The hope now is to find a fossil of an ancient beaver dam. Dr. Rybczynski speculates that ‘Beaver Pond’ on Ellesmere Island may actually be one. However, they will need to do more research to look at the sequence of deposition of materials there before they can be sure.
Mississippi Valley Field Naturalists
September 6, 2006
Submitted by Pauline Donaldson
Michael Runtz starts field naturalists’ lecture program with “Beaver Ponds in the Watershed”
Mississippi Valley Field Naturalists (MVFN) proudly presents the first lecture in their 2006-2007 public lecture series on Thursday September 14th., entitled “Beaver Ponds in the Watershed”.
Keynote speaker for the first seminar, Michael Runtz, is a well-known naturalist, award winning author and photographer, and an accomplished educator who has taught natural history at Carleton University for many years. Audiences have often been regaled with “beaver tales” from the man who is presently writing a book on them. This book follows others by Runtz which all feature aspects of his understanding of the natural world, such as “The Howls of August: Encounters with Algonquin Wolves, Moose Country and Wild Wings”. Runtz came to know and respect the natural world during years as interpreter/ researcher in Algonquin and other provincial parks.
It is fitting that the beaver, a natural watershed engineer, is the VIP for the first of a lecture series exploring the topic of the “watershed”. There is much to be learned about habitats and workings of the watershed by studying this quintessential Canadian mammal, Castor canadensis. In creating its own unique homes it not only takes care of its own family but creates homes for other creatures. Runtz’s presentation will explore the fascinating biological features of the animal which equip it for the life it leads, the well-known structures it builds and how in many ways its transformation of the environment gives life to other living things in the watershed.
MVFN’s 2006/07 series of speakers and presentations will focus on the theme “The Mississippi Valley Watershed”. The clubs’ new program committee, chaired by Joyce Clinton, is very enthusiastic about this years’ program. The series will include seven presentations, each looking at a different aspect of the watershed, including “diversity of habitats present”,” managing forests to protect the watershed”, “the effects of agriculture”, “development issues in the watershed”, “rehabilitation of shorelines”, and “factors affecting water quality”. One goal of the lecture series this year is to emphasize actions and practices individuals, organizations and communities can engage in to protect and enhance watershed conservation. The natural environment of the watershed faces many challenges. This lecture series will help us develop a better local understanding of the workings of our own Mississippi watershed.
Michael Runtz will be introduced by Cliff Bennett, Eastern Regional Director for Ontario Nature, who, as a local resident, was recently recognized by the Town of Mississippi Mills for his nature conservation efforts. The presentation by Michael Runtz takes place Thursday, September 14th at 7:30 pm at the Almonte United Church on Elgin St. All are welcome; following the presentation refreshments are available. MVFN members and children under 16 receive free admission to the lecture series. For others a non-member fee of $5 applies. MVFN memberships can also be purchased at the door. For more information on this lecture and others in the series, please contact MVFN Program Chair Joyce Clinton at 613-257-4879, or email or check the MVFN website at www.mvfn.ca