In 2004, paleontologist Neil Shubin made the discovery of a lifetime: A fossil, later named Tiktaalik, that appeared to bridge the gap between ocean dwelling fish and land walking amphibians. As explained in NOVA: Your Inner Fish
, the discovery of Tiktaalik reveals evidence of the shared ancestry of humans with ancient fish.
In NOVA: Your Inner Reptile, Dr. Shubin uses the discoveries of other fossils, and the laboratory study of embryos, to demonstrate our links to early reptiles. In particular, fossils of ancestors such as the fierce predator Gorgonopsid, an early “mammal-like” reptile, Thrinaxodon, a burrow-living, nocturnal animal that likely had hair, and Hadrocodium, the earliest known mammal species, demonstrate the origins of our teeth, skin, hair, and inner ear bones.
Dr. Shubin takes the viewer to diverse locations such as the Bay of Fundy in Nova Scotia, home to the largest tidal variation on earth, and a South African “bone yard” located in the Karoo, the “land of thirst”, where paleontologist Dr. Roger Smith unearths the remarkable fossils of early mammal-like creatures.
The importance of our linkage to early reptiles is demonstrated through the use of ultrasound imagery of a pregnant mother revealing the presence of a vestigial yolk sac, a feature of reptilian eggs; the work of Dr. Abigail Tucker who researches the way that our skin grows features such as teeth, glands, and hair; a meeting with actor Michael Berryman, known for his portrayal of “monsters and aliens”, who is stricken with a rare disorder in his EDA gene; and the work of Dr. Karen Sears, who traces the evolution of our inner ear bones by studying the embryonic development of marsupial mammals like the gray opossum. Dr. Sears is able to demonstrate the conversion of reptile jaw hinge bones in opossum embryos into the fully developed three-bone mammalian hearing structure.
The video documents the adaptations that amphibians and early reptiles used to live away from water. One striking adaptation, the solid egg, enabled early reptiles to colonize the land. Reptile skin also developed as a barrier to keep water from leaving the body, and skin also resulted in the development of diverse “skin organs” such as teeth, hair, and glands, even including the mammary gland, the signature feature of mammalian life. Driven underground by the presence of early predators and dinosaurs, early mammals spent the day in burrows and led a nocturnal lifestyle requiring the development of large brains to process the sensory data used in tunnel navigation and nighttime food gathering. The video ends with the realization that the extinction of the dinosaurs paved the way for our mammalian ancestors to thrive and take over the earth, leading to the advent of modern humans as the most recent expression of this history. In summary, we learn that our skin, teeth, glands, hair, inner ear bones, and large brains likely derived from the evolutionary change of earlier reptiles and mammals.
The PDF contains a two-sided video worksheet consisting of 47 multiple choice and true-or-false questions, along with an answer key, an MS Word download link, and an original drawing by R. McNeely. You will need to obtain a DVD of the video, use the PBS Internet site, or YouTube
The entire video series, Your Inner Fish, Your Inner Reptile, and Your Inner Monkey is available on the Howard Hughes Medical Institute (HHMI) Biointeractive
Neil Shubin's wonderful book Your Inner Fish
was the inspiration for this video series.
Note: The video contains some stomach-churning scenes of skeletons being stripped of flesh by beetle larvae, a technique used to prepare specimens in museums and laboratories world-wide.