PRESS RELEASE - Recent studies bring fossils and genes together to piece together evolutionary history

November 7, 2012
DEERFIELD, ILLINOIS (November, 2011) – Paleontology, with its rocks and fossils, seems far removed from the world of developmental genetics, with its petri dishes and embryos. Whereas paleontology strives to determine "What happened in evolution?", developmental genetics uses gene control in embryos to try to answer "How did it happen?" Combined, the two approaches can lead to remarkable insights that benefit both fields.

In the current issue of the Journal of Vertebrate Paleontology, Hans Thewissen, Ingalls-Brown Professor at Northeast Ohio Medical University (NEOMED), and his colleagues review recent studies that have used modern genetic techniques to shed light on fossils, and vice versa. "It is a very exciting time to be an evolutionary scientist. So many researchers are investigating evolution, either by finding new fossils or by figuring out the genes that underlie changes in evolution. Now it is possible to combine those two fields and go beyond what each field could have accomplished on its own," said Dr. Thewissen.

Their review discusses the profound evolutionary changes that brought about some of the more spectacular animals of today and the past, including dolphins, whales, snakes, bats, elephants, and dinosaurs. For instance, although the transition from a four-legged ancestor to something with only two forelimbs, like a dolphin, or no limbs at all, like a snake, may seem like a big leap, transitional fossils have been discovered that bridge these gaps. Additionally, using developmental genetics, researchers have come to understand that these large changes in shape involved relatively small changes in the working of just of few genes.

Perhaps even more fascinating, recent research has discovered that similarly shaped organisms may not have experienced similar developmental changes in their past. Cetaceans (whales and dolphins) and snakes both lost limbs independently from their respective ancestors through evolution, but they did so in different ways. Snakes lost their forelimbs by basically getting rid of their neck region and leaving no room for forelimbs. During snake embryonic development, no limb buds form in that region of the body. Snakes do still develop hind limb buds as embryos, but the genes that control their growth have been knocked out through the course of evolution, so hind limbs do not develop (except for small stubs in some snakes like pythons). This demonstrates that different developmental mechanisms can be at work even in the evolutionary
history of a single animal. Whales and dolphins lost their hind limbs in a process similar to that of snakes.

Dr. Thewissen says, "For me personally, as someone who has spent most of his life studying fossil whales, it is very exciting to be able to use information from the development of living mammals, and use it to teach me about how whale evolution happened, 50 million years ago."

Scientists can even modify the genetic code of living animals to replicate changes that have been observed in the fossil record. As explained in the paper, it has been shown that heightened activity of a particular gene in mouse embryos causes their teeth to grow larger. A similar change occurred during the course of elephant evolution - early elephants had teeth less than an inch long, while modern elephants have teeth over a foot in length. The genetic changes that brought about this increase in size in elephants may have resembled the ones induced in lab mice.

This sort of cross-pollination of biological disciplines was once rare but is increasingly common. The paper was co-authored with Lisa Noelle Cooper, also of NEOMED, and Richard R. Behringer of the Department of Genetics at the University of Texas MD Anderson Cancer Center. Dr. Cooper said, "At a time when most of science is hyper-specialized, my hope is that the newest generations of scientists are able and unafraid to approach research questions using a variety of techniques."



About the Society of Vertebrate Paleontology
Founded in 1940 by thirty-four paleontologists, the Society now has more than 2,300 members representing professionals, students, artists, preparators, and others interested in VP. It is organized exclusively for educational and scientific purposes, with the object of advancing the science of vertebrate paleontology.

Journal of Vertebrate Paleontology The Journal of Vertebrate Paleontology (JVP) is the leading journal of professional vertebrate paleontology and the flagship publication of the Society. It was founded in 1980 by Dr. Jiri Zidek and publishes contributions on all aspects of vertebrate paleontology.

Thewissen, J.G.M., L.N. Cooper, and R.R. Behringer. 2012. Developmental biology enriches paleontology. Journal of Vertebrate Paleontology 32(6):1-12.

J.G.M. Thewissen
Department of Anatomy and Neurobiology
Northeast Ohio Medical University
Rootstown, OH 44272, U.S.A.

Lisa Noelle Cooper
Department of Anatomy and Neurobiology
Northeast Ohio Medical University
Rootstown, OH 44272, U.S.A.

Richard R. Behringer
Department of Genetics
University of Texas MD Anderson Cancer Center
Houston, TX 77030, U.S.A.

Other Experts Not Associated with this Study
Hans Larsson
Redpath Museum
McGill University
(514)398-4086 ext. 089457

Martin Cohn
Department of Biology
University of Florida

Michael Bell
Department of Ecology and Evolution
Stony Brook University

Scott Gilbert
Department of Biology
Swarthmore College


Figure 1 - Mounted skeletons of the extinct whales Ambulocetus and Pakicetus, both found in Pakistan, respectively 48 and 49 million years old. (source: Thewissen-Lab, NEOMED)

Figure 2 - The embryo of the pantropical spotted dolphin Stenella attenuata in the fifth week of development. The hind limbs are present as small bumps (hind limb buds) near the base of the tail. The pin is approximately 1 inch long. (source: Thewissen-Lab, NEOMED)

Figure 3 (JVP Cover Image) - A bat and dolphin embryo illustrate the process of forelimb enlargement and hind limb reduction, respectively, in the orders Chiroptera and Cetacea. The fossil record shows that Eocene whales (Ambulocetus natans) still had hind limbs, but the earliest known bats looked much like modern Carollia perspicilata (images thanks to T. Hieronymus and K. Sears)