William Alvin Clemens Jr. (May 15, 1932 — November 17, 2020) was a

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

at the

University of California at Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant univ ...

. He was faculty of the Department of Paleontology from 1967, then the Department of Integrative Biology from 1994 to his retirement and curator of the UC Museum of Paleontology. Clemens was also director of the museum (1987–1989) and chair of the Department of Paleontology (1987–1989). He was awarded a

Guggenheim Fellowship Guggenheim Fellowships are grants that have been awarded annually since by the John Simon Guggenheim Memorial Foundation to those "who have demonstrated exceptional capacity for productive scholarship or exceptional creative ability in the ar ...

(1974–75), a U.S. Senior Scientist Award by the Alexander von Humboldt Foundation, the

Romer-Simpson Medal The Romer-Simpson Medal is the highest award issued by the Society of Vertebrate Paleontology for "sustained and outstanding scholarly excellence and service to the discipline of vertebrate paleontology". The award is named in honor of Alfred S. Ro ...

(2006), and was made a Fellow of the

California Academy of Sciences The California Academy of Sciences is a research institute and natural history museum in San Francisco, California, that is among the largest museums of natural history in the world, housing over 46 million specimens. The Academy began in 1853 ...

Early life and education

Clemens was born in

Berkeley, California Berkeley ( ) is a city on the eastern shore of San Francisco Bay in northern Alameda County, California, United States. It is named after the 18th-century Irish bishop and philosopher George Berkeley. It borders the cities of Oakland and Emer ...

. After graduating from Berkeley High School, he attended the

University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant u ...

, earning a B.A. in paleontology in 1954 and a Ph.D. in 1960. From 1961 to 1967, he served as faculty in the Zoology Department at the

University of Kansas The University of Kansas (KU) is a public research university with its main campus in Lawrence, Kansas, United States, and several satellite campuses, research and educational centers, medical centers, and classes across the state of Kansas. Tw ...

and as the curator of higher

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

s in their Museum of Natural History.

Research

Clemens' research focussed on the

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

s in the

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...

Era, both their origin and diversification as well as the microstructure of the early mammalian jaw and

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

. He was also noted for his research into the

extinction Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

of the

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s at the

Cretaceous–Paleogene boundary The Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K–T) boundary, is a geological signature, usually a thin band of rock containing much more iridium than other bands. The K–Pg boundary marks the end of ...

(K–Pg or K-T boundary). Clemens supported a view contrary to the more familiar

Alvarez hypothesis The Alvarez hypothesis posits that the Extinction event, mass extinction of the non-avian dinosaurs and many other living things during the Cretaceous–Paleogene extinction event was caused by the Impact event, impact of a large asteroid on the ...

model of sudden catastrophic extinction precipitated by an asteroid, which was proposed in part by

Walter Alvarez Walter Alvarez (born October 3, 1940) is a professor in the Earth and Planetary Science department at the University of California, Berkeley. He is most widely known for the theory that dinosaurs were killed by an asteroid impact, developed in c ...

, also at the University of California, Berkeley, at the time. Clemens' research in western

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

suggests that the dinosaurs were already undergoing gradual extinction prior to the end of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

and that other groups of vertebrates were not severely impacted by the event.

Selected publications

* Clemens, William A. (1997). "Characterization of enamel microstructure and application of the origins of prismatic structures in systematic analyses", pages 85–112 ''in'' W. V. Koenigswald (ed.) ''Tooth enamel microstructure''. Rotterdam: A. A. Balkema. * Clemens, William A. (2001). "Patterns of mammalian evolution across the Cretaceous-Tertiary boundary". ''Mitteilungen aus dem Museum für Naturkunde in Berlin, Zoologische Reihe'' 77:175–191. * Clemens, William A. (2002). "Evolution of the mammalian fauna across the Cretaceous-Tertiary boundary in northeastern Montana and other areas of the Western Interior." ''Geological Society of America'', Special Paper 361: 217–245. * Clemens, William A. (2006). ''Ecological diversification of mammals during the Mesozoic, the Age of Dinosaurs''. McGraw-Hill.

References

{{DEFAULTSORT:Clemens, William A. Jr. 1932 births 2020 deaths People associated with the California Academy of Sciences Berkeley High School (Berkeley, California) alumni Writers from Berkeley, California University of California, Berkeley College of Letters and Science faculty American paleontologists Presidents of the Society of Vertebrate Paleontology