Jennifer Alice Clack, FRS (née Agnew; born 3 November 1947) is an English paleontologist, an expert in the field of evolutionary biology. She studies the "fish to tetrapod" transition— the origin, evolutionary development and radiation of early tetrapods and their relatives among the lobe-finned fishes. She is best known for her book Gaining Ground: the Origin and Early Evolution of Tetrapods, published in 2002 (second edition, 2012) and written with the layman in mind.
Clack is curator at the Museum of Zoology and Professor of Vertebrate Palaeontology at Cambridge University, where she has devoted her career to studying the early development of tetrapods, the "four-legged" animals said to have evolved from Devonian lobe-finned fishes and colonized the freshwater swamps of the Carboniferous period.
Clack attended Bolton School Girls' Division before receiving a B.Sc. in Zoology from the University of Newcastle upon Tyne in 1970, and a Ph.D. from the University in 1984. She also holds a Graduate Certificate in Museum Studies from the University of Leicester and an M.A. and D.Sc. from the University of Cambridge.
In 2006, Clack was awarded a personal chair by the University of Cambridge, taking the title Professor of Vertebrate Palaeontology. In 2008 she was awarded the Daniel Giraud Elliot Medal from the U.S. National Academy of Sciences. She was elected a Fellow of the Royal Society in 2009  and Foreign Honorary Member of the American Academy of Arts and Sciences. In 2013 she was awarded an Honorary Doctorate by the University of Chicago and the T Neville George Medal by the Geological Society of Glasgow. In 2014 she was made an Honorary Foreign Member of the Royal Swedish Academy of Sciences.
She is currently leading a major consortium project investigating some exciting new fossils from Northumberland and the Borders Region of Scotland which date from the Tournaisian stage of the earliest Carboniferous period. Collaborating with experts from the Universities of Southampton and Leicester, the British Geological Survey and the National Museums of Scotland, the team is studying the plants, fish, tetrapods and invertebrates which survived the end Devonian extinction and existed within the (until now) fossil-poor period known as Romer's Gap, as well as the environment and depositional conditions in which they lived. More information can be found on the Project website .
Clack has published the following books:
- Gaining Ground: The Origin and Early Evolution of Tetrapods (Life of the Past), Indiana University Press, 2002, ISBN 978-0253340542.
- Fossils of the Castillo Formation, Venezuela: Contributions in Neotropical Palaeontology (Special Papers in Palaeontology), with Marcelo R. Sánchez-Villagra, Wiley-Blackwell, 2004, ISBN 978-0901702821.
- Localities, Distribution and Stratigraphical Context of the Late Devonian Tetrapods of East Greenland (Meddelelser om Grønland), with Henning Blom and Per Erik Ahlberg, Danish Polar Center, 2005, ISBN 978-8790369767.
- An article in Nature in 2008, "Ventastega curonica and the origin of tetrapod morphology" (co-author)
- A letter to Nature in 2001 about a new tetrapod with at least five digits, Pederpes, from within Romer's gap: An early tetrapod from ‘Romer's Gap’.
- "Daniel Giraud Elliot Medal". National Academy of Sciences. Retrieved 15 February 2011.
- "Fellows". Royal Society. Retrieved 22 December 2010.
- "Professor Jenny Clack" at BBC Programmes
- "Jennifer A. Clack". Amazon UK. Retrieved 12 April 2012.
- "Getting a Leg Up on Land". Scientific American. 21 November 2005. Retrieved 12 April 2012.
- Ahlberg, Per E.; Jennifer A. Clack, Ervins Luksevics, Henning Blom and Ivars Zupins (26 June 2008). "Ventastega curonica and the origin of tetrapod morphology". Nature 453 (7199): 1199–1204. doi:10.1038/nature06991. PMID 18580942.
- Clack, J.A. (2002-07-04). "An early tetrapod from ‘Romer's Gap’". Nature 418 (6893): 72–76. doi:10.1038/nature00824. PMID 12097908.
- Jenny Clack on the Cambridge University website
- Home page - Jennifer "Jenny" Clack
- Profile on PBS website
- Interview on PBS website