Wednesday, February 12th marked the 205th anniversary of Charles Darwin’s birth, but the Paleontological Research Institution in Ithaca, New York, has been celebrating all week long. PRI’s annual Darwin Days is a seven-day event commemorating the life and work of Darwin with lectures, movies, and fun activities around the city of Ithaca. Darwin Days serves to promote awareness of evolution and natural history, while tapping into the educational resources of the community. On Wednesday, Darwin’s birthday, PRI hosted a panel discussion at Cornell University asking one important question: What is your favorite fossil to use when teaching evolution?
Titled Illustrations of Evolution in the Fossil Record, the panel was comprised of Drs. Robert Ross of PRI, Linda Ivany of Syracuse University, and David Kendrick of Hobart and William Smith Colleges. Each was asked which fossil they find the most helpful when trying to illuminate the processes and presence of evolution.
Dr. Ivany’s fossil of choice was Tiktaalik, a Devonian fish nick-named the “fishapod” for its equally amphibian and piscine characteristics. Tiktaalik demonstrates the predictive power of the theory of evolution, which posits that amphibious tetrapods evolved from fish. Working from this knowledge, one can assume that at some point in the evolutionary process there must have been a creature existing in a half-fish half-amphibian state. Researchers located rocks of the age at which such a creature must have lived on Canada’s Ellesmere Island, where they found Tiktaalik fossils displaying the perfect transitional form, exactly as evolutionary theory predicted. Tiktaalik sports the gills, scales, and fins of a fish, the rib bones, mobile neck, and lungs of a tetrapod, and the joints and ears of something in between. Evolution assumed that it had to exist, and the fossil record provided the proof.
Dr. Kendrick selected Aglaophyton as his preferred educational fossil. Aglaophyton is a land plant of the Lower Devonian, around 410 million years ago. Found only in the Rhynie chert of Aberdeenshire, Scotland, Aglaophyton demonstrates an evolutionarily transitional stage much as Tiktaalik does. Within their life cycles, plants undergo an alternation between two generations: haploid and diploid. Within the diploid generation, spores are produced through asexual division. These spores germinate to become haploid gametophytes, which produce gametes. Gametes can then fuse with the gamete of another organism of the species to create a zygote, which develops into a diploid sporophyte and thus begins the cycle all over again. In simpler terms, plants alternate between periods of asexual and sexual reproduction. However, over time the dominant phase has shifted from the asexual to the sexual. This shift enables plants to develop proteins for lignin, which gives the rigidity of cellular structure necessary for supporting their own weight on land. In the water, primitive plants had no need for such a trait. When plants began to appear on land during the Silurian, they suddenly began to resemble contemporary land plants, which only undergo the asexual cloning phase on a very small scale (like within a few cells of the acorn of an oak tree), and can produce much more lignin. In the incredibly well preserved Rhynie chert, scientists have found Aglaophyton fossils in every stage of development, displaying both phases in equal force. As the scales of the two phases tipped, Aglaophyton represents the moment of equal balance. Like the Tiktaalik, Aglaophyton fossils from the Rhynie chert are perfectly preserved transitional organisims, showing physical evidence for what evolution suggests had to have been.
Tiktaalik. Image by Museum Victoria.
Dr. Ross chose his favorite fossil based on what is most commonly available but very unexpected in the Finger Lakes region of New York. He brought horn corals to the panel and passed them around, asking the audience to think critically about what they held. Using the abundant presence of corals in a region hundreds of miles from the sea, Dr. Ross demonstrated the necessity of perceiving our planet as a constantly changing environment. If the world did not shift drastically over time, there could be no logical explanation for the presence of so many corals in inland Ithaca, New York. As PRI’s Associate Director for Outreach, Ross frequently works with small children and visitors to PRI’s Museum of the Earth. He is concerned with presenting evidence that is accessible to everyone in the environment already around them, so that even our most local surroundings can open our eyes to the slow and steady working of evolutionary change.
Aglaophyton. Image by Francoise Gantet.
The Paleontological Research Institution, Ithaca, New York, is pleased to sponsor Paleontology content for This View of Life. Founded in 1932, PRI has outstanding programs in research, collections, and publications, and is a national leader in development of informal Earth science education resources for educators and the general public.