Jennifer Alice Clack, FRS, FLS (née Agnew; 3 November 1947 – 26 March 2020) was an English palaeontologist and evolutionary biologist.

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 layperson in mind.

Clack was curator at the Museum of Zoology and Professor of Vertebrate Palaeontology at the University of Cambridge, where she devoted her career to studying the early development of tetrapods, the "four-legged" animals said to have evolved from Devonian lobe-finned fishes and colonised the freshwater swamps of the Carboniferous period.

[1] On 1 October 2006, Clack was awarded a personal chair by Cambridge, taking the title Professor of Vertebrate Palaeontology.

Clack also undertook extensive fieldwork expeditions in order to search for further remains of early tetrapods.

[13] Most recently, she led a major consortium project (TW:eed[14]) investigating some exciting new fossils from Northumberland and the Borders Region of Scotland which date from the Tournaisian stage of the earliest Carboniferous period; this project has produced numerous publications furthering the understanding of early tetrapod evolution.

[5] In April 2012 she was featured in an episode[41] of the BBC television series Beautiful Minds, a set of documentaries about scientists who have made important discoveries.

[57] In 2008, Clack was awarded the Daniel Giraud Elliot Medal from the U.S. National Academy of Sciences, the first woman to achieve the honor.

The university described her as "an internationally preeminent palaeontologist whose research has profoundly changed the understanding of the origin of terrestrial vertebrate life.