Ohrknorpel und äusseres ohr der Säugetiere; eine vergleichend-anatomische Untersuchung - Boas, J. E. V. (Johan Erik Vesti), 1855 -1935 ([Nielsen & Lydiche (A. Simmelkiær)], 1912)

Old bones : or, Notes for young naturalists - Brooks, Vincent, 1815? -1885 (Robert Hardwicke, 1861)

Old bones : or, Notes for young naturalists, on vertbebrate animals, their fossil predecessors and allies - Symonds, W. S. 1818 -1887 (Robert Hardwicke, 1864)

The Oligocene Hsanda Gol Formation, Mongolia : a revised faunal list - Mellett, James Silvan, 1936 - (American Museum of Natural History, 1968)

On growth and form - Thompson, D'Arcy Wentworth, 1860 -1948 (University press, 1917)

On growth and form - Thompson, D'Arcy Wentworth, 1860 -1948 (University Press, 1945)

On some Mammalia of the Lowest Eocene beds of New Mexico - American Philosophical Society. ([publisher not identified], 1881)

On the anatomy of vertebrates - Owen, Richard, 1804 -1892 (Longmans, Green, 1866)

On the anatomy of vertebrates ... - Owen, Richard, 1804 -1892 (Longmans, Green and Co, 1866)

On the classification and geographical distribution of the Mammalia, being a lecture on Sir Robert Reade's foundation, delivered before the University of Cambridge ... May 10, 1859. To which is added an appendix "On the gorilla," and "On the extinction and transmutation of species." - Owen, Richard, 1804 -1892 (J. W. Parker and son, 1859)

On the flat-clawed carnivora of the eocene of Wyoming - Cope, E. D. (Edward Drinker), 1840 -1897 (American Philosophical Society, 1873)

On the primitive types of the orders of Mammalia Educabilia - Cope, E. D. (Edward Drinker), 1840 -1897 (1873)

On the short footed ungulata of the eocene of Wyoming - Cope, E. D. (Edward Drinker), 1840 -1897 (American Philosophical Society, 1873)

On the supposed presence of Miocene Tayassuidae and Dromomerycinae (Mammalia, Cetartiodactyla) in South America - Croft, Darin A. (American Museum of Natural History, 2021)

On vertebrata from the Tertiary and Cretaceous rocks of the North West Territory - Cope, E. D. (Edward Drinker), 1840 -1897 (W.F. Brown & Co, 1891)

On Vertebrata from the Tertiary and Cretaceous rocks of the North West Territory - Cope, E. D. (Edward Drinker), 1840 -1897 (W.F. Brown & Co, 1891)

Opinions and declarations rendered by the International Commission on Zoological Nomenclature - International Commission on Zoological Nomenclature (Printed by order of the International Trust for Zoological Nomenclature, 1958)

The orders of mammals - Gregory, William K. (William King), 1876 -1970 (The Trustees, 1910)

Organic evolution considered - Fairhurst, Alfred, 1843 -1921 (Christian publishing, 1897)

The origin and affinities of the South American Condylarthra and early Tertiary Litopterna (Mammalia) - Cifelli, Richard (American Museum of Natural History, 1983)

The origin of the fittest : essays on evolution - Cope, E. D. (Edward Drinker), 1840 -1897 (D. Appleton, 1887)

The origin of the fittest : essays on evolution - Cope, E. D. (Edward Drinker), 1840 -1897 (Macmillan and Company, 1887)

The origin of the fittest; essays on evolution - Cope, E. D. (Edward Drinker), 1840 -1897 (D. Appleton, 1887)

Le origini umane; ricerche paleontologiche - Sergi, Giuseppe, 1841 -1936 (Fratelli Bocca, 1913)

Ornithological bibliography - Coues, Elliott, 1842 -1899 (Geological Survey [etc.], 1878)

[Orr's Circle of the sciences. A series of treatises on the principles of science, with their application to practical pursuits. Organic nature ... - Owen, Richard, 1804 -1892 (W.S. Orr, 1854)

Osteology of the Middle Eocene ceratomorph Hyrachyus modestus (Mammalia, Perissodactyla) - Wang, Yuanqing (Paleontologist) (American Museum of Natural History, 2017)

Outlines of comparative anatomy and medical zoology - Allen, Harrison, 1841 -1897 (Lippincott, 1874)

Outlines of comparative anatomy and medical zoology - Allen, Harrison, 1841 -1897 (J.B. Lippincott & co, 1869)

Outlines of economic zoölogy - Reese, A. M. (Albert Moore), 1872 -1965 (P. Blakiston's Son & Co, 1919)

Outlines of evolutionary biology - Dendy, Arthur, 1865 -1925 (Constable, 1912)

Outlines of evolutionary biology - Dendy, Arthur, 1865 -1925 (D. Appleton and company, 1912)

Outlines of evolutionary biology - Dendy, Arthur, 1865 -1925 (D. Appleton and company, 1914)

Outlines of vertebrate palæontology for students of zoology - Woodward, Arthur Smith, 1864 -1944 (University Press, 1898)