Pygmy Hippo


Ansell, W. F. H. (1971). Order Artiodactyla. In J. Meester & H. W. Setzer (Eds.), The mammals of Africa: An identification manual: Smithsonian Institution Press.

Burton, M. (1962). Systematic dictionary of mammals of the world. London: Museum Press.

Dean, K. S. (2013). Mammals of Africa, vol 6, Pigs, Hippopotamuses, Chevrontain, Giraffe, Deer and Bovids. Library Journal, 138(10), 136-+.

Eltringham, S. K. (1999). The hippos. London: Academic Press.

Flacke, G. L., Decher, J., Rose, R. K., & Hamilton, M. J. (2019). Choeropsis liberiensis (Artiodactyla: Hippopotamidae). Mammalian Species, 51(982), 100-118. doi: 10.1093/mspecies/sez017

Oliver, W. L. R. (1993). Pig, peccaries, and hippos: status survey and conservation Action Plan. Gland: IUCN.

Robinson, P. T., Flacke, G. L., & Hentschel, K. M. (2017). The pygmy hippo story. New York: Oxfrod University Press.

Anatomy & Morphology

Fisher, R. E., Scott, K. M., & Naples, V. L. (2005). The comparative anatomy of the pygmy hippopotamus (Choeropsis liberiensis): appendicular myology. Faseb Journal, 19(5), A1361-A1361.

Fisher, R. E., Scott, K. M., & Naples, V. L. (2007). Forelimb myology of the pygmy hippopotamus (Choeropsis liberiensis). Anatomical Record-Advances in Integrative Anatomy and Evolutionary Biology, 290(6), 673-693. doi: 10.1002/ar.20531

Hegner, B., & Pilleri, G. (1968). Note zur Morphologie des Auges von Hippopotamus amphibius und Choeropsis liberiensis (Mammalia, Artiodactyla, Hippopotamidae) mit besonderer Berücksichtigung des Tapetum lucidum fibrosum und des Schlemmschen Kanals. Cells Tissues Organs, 69(3), 458-461.

Kleckowska-Nawrot, J., Gozdziewska-Harlajczuk, K., & Paszta, W. (2020). The histological and histochemical analysis of the superficial gland of the third eyelid and lacrimal gland in the neonate pygmy hippopotamus (Choeropsis liberiensis, Morton 1849). Journal of Anatomy, 236, 281-281.

Krahnert, R. (1942). Zur anatomie des flußpferdeherzens: (Hippopotamus amphibius L. u. Choeropotamus liberiensis Mort). Zeitschrift für wissenschaftliche Zoologie, CLV(4), 317-342.

Langer, P. (1975). Macroscopic anatomy of the stomach of the Hippopotamidae Gray, 1821. Anatomia, Histologia, Embryologia, 4(4), 334-359.

Pandolfi, L., Martino, R., Rook, L., & Piras, P. (2020). Investigating ecological and phylogenetic constrains in Hippopotamidae skull shape. Rivista Italiana Di Paleontologia E Stratigrafia, 126(1), 37-49.

Pocock, R. I. (1923). The external characters of the pygmy hippopotamus (Choeropsis liberiensis) and of the Suidae and Cainelidae. Proceedings of the Zoological Society of London, 1923, 531-549.

R., M. N. S. (1994). Renal anatomy of the pigmy hippopotamus (Choeropsis liberiensis): An overview. Anatomia, Histologia, Embryologia, 23(3), 189-206.

Schwarm, A., Ortmann, S., Fritz, J., Flach, E., Rietschel, W., & Clauss, M. (2013). No distinct stratification of ingesta particles and no distinct moisture gradient in the fore-stomach of non-ruminants: The wallaby, peccary, hippopotamus, and sloth. Mammalian Biology, 78(6), 412-421. doi: 10.1016/j.mambio.2013.04.001


Fradrich, H. (1967). Das verhalten der Schweine und Flusspferde. Handbuch der Zoologie, 8(10), 1-44.

Jones, M. L. (1993). Longevity of ungulates in captivity. International Zoo Yearbook, 32, 159-169.

Orliac, M. J., Pezzino, P., Bourien, J., Casrouge, E., Lebrun, R., Glotin, H., & Celerier, A. (2019). Acoustic communication and olfaction in the pygmy hippopotamus Choeropsis liberiensis. Journal of Morphology, 280, S194-S194.

Pluháček, J., & Steck, B. L. (2015). Different sex allocations in two related species: the case of the extant hippopotamus. Ethology, 121(5), 462-471. doi: 10.1111/eth.12357

Pucora, E., Schiffmann, C., & Clauss, M. (2019). Resting postures in terrestrial mammalian herbivores. Journal of Mammalogy, 100(2), 552-563. doi: 10.1093/jmammal/gyz044

Ralls, K., Kranz, K., & Lundrigan, B. (1986). Mother-young relationships in captive ungulates:variability and clustering. Animal Behaviour, 34(1), 134-145.

Ralls, K., Lundrigen, B., & Kranz, K. (1987). Mother-young relationships in captive ungulates: behavioral changes over time. Ethology, 75(1), 1-14. 


Collen, B., Howard, R., Konie, J., Daniel, O., & Rist, J. (2011). Field surveys for the endangered pygmy hippopotamus Choeropsis liberiensis in Sapo National Park, Liberia. Oryx, 45(1), 35-37. doi: 10.1017/s0030605310001444

Conway, A. L., deMaar, T. W., Hernandez, S. M., & Carroll, J. P. (2015). Evaluation of radio-transmitter attachments for the pygmy hippopotamus (Choeropsis liberiensis). African Journal of Ecology, 53(4), 606-608. doi: 10.1111/aje.12226

Conway, A. L., Hernandez, S. M., Carroll, J., Green, G. T., & Larson, L. (2015). Local awareness of and attitudes towards the pygmy hippopotamus Choeropsis liberiensis in the Moa River Island Complex, Sierra Leone. Oryx, 49(3), 550-558. doi: 10.1017/s003060531300077x

Eltringham, S. K. (1993). Review of priorities for conservation action and future research on Hippopotamuses. In R. L. Oliver (Ed.), Pigs, Peccaries and Hippos Status Survey Action Plan (1993) (Vol. Chapter 3.4, pp. 1-7). Cambridge: IUCN.

Freeman, B., Roehrdanz, P. R., & Peterson, A. T. (2019). Modeling endangered mammal species distributions and forest connectivity across the humid Upper Guinea lowland rainforest of West Africa. Biodiversity and Conservation, 28(3), 671-685. doi: 10.1007/s10531-018-01684-6

Hillers, A., Buchanan, G. M., Garteh, J. C., Tommy, S. M., Fofana, M. L., & Lindsell, J. A. (2017). A mix of community-based conservation and protected forests is needed for the survival of the Endangered pygmy hippopotamus Choeropsis liberiensis. Oryx, 51(2), 230-239. doi: 10.1017/s003060531600020x

Kablan, Y. A., Diarrassouba, A., Mundry, R., Campbell, G., Normand, E., Kuhl, H. S., . . . Boesch, C. (2019). Effects of anti-poaching patrols on the distribution of large mammals in Tai National Park, Cote d'Ivoire. Oryx, 53(3), 469-478. doi: 10.1017/s0030605317001272

Laurie, A., & Olivier, R. (1977). Pachyderms in peril. New Scientist, 75(1069), 658-660.

Lindsell, J. A., Klop, E., & Siaka, A. M. (2011). The impact of civil war on forest wildlife in West Africa: mammals in Gola Forest, Sierra Leone. Oryx, 45(1), 69-77. doi: 10.1017/s0030605310000347

Luiselli, L., Amori, G., Akani, G. C., & Eniang, E. A. (2015). Ecological diversity, community structure and conservation of Niger Delta mammals. Biodiversity and Conservation, 24(11), 2809-2830. doi: 10.1007/s10531-015-0975-8

Roth, H. H., Hoppe-Dominik, B., Mühleneberg, M., Steinhauer-Burkart, B., & Fischer, F. (2004). Distribution and status of hippopotamids in the Ivory Coast. African Zoology, 39(2), 211-224. 

Distribution & Status

Anstey, S. (1991). Large mammal distribution in Liberia. WWF-International, Gland.

Dorst, J., & Dandelot, P. (1972). A field guide to the large mammals of Africa. London. : Collins

Ritchie, J. (1930). Distribution of the pygmy hippopotamus. Nature, 126, 204-205. 


Robinson, P. T. (1981). The reported use of denning structures by the pygmy hippopotamus Choeropsis liberiensis. Mammalia, 45(4), 506-508.

Evolution & Paleontology & Taxonomy

Agnarsson, I., & May-Collado, L. J. (2008). The phylogeny of Cetartiodactyla: The importance of dense taxon sampling, missing data, and the remarkable promise of cytochrome b to provide reliable species-level phylogenies. [Review]. Molecular Phylogenetics and Evolution, 48(3), 964-985. doi: 10.1016/j.ympev.2008.05.046

Boisserie, J. R. (2005). The phylogeny and taxonomy of Hippopotamidae (Mammalia : Artiodactyla): a review based on morphology and cladistic analysis. Zoological Journal of the Linnean Society, 143(1), 1-26.

Boisserie, J. R., & Lihoreau, F. (2006). Emergence of Hippopotamidae: New scenarios. Comptes Rendus Palevol, 5(5), 749-756. doi: 10.1016/j.crpv.2005.11.004

Coryndon, S. C. (1977). The taxonomy and nomenclature of the Hippopotamidae (Mammalia, Artiodactyla) and a description of two new fossil species. Proc. Kon. Ned. Akad. Wetensch Series B, 80, 61-88.

Grubb, P. (1993). The afro-tropical hippopotamuses - Hippopotamidae Hippopotamus and Hexaprotodon. Taxonomy and Description. In R. L. Oliver (Ed.), Pigs, Peccaries and Hippos Status Survey Action Plan (1993) (Vol. Chapter 3.1, pp. 1-3). Cambridge: IUCN.

Kulemzina, A. I., Trifonov, V. A., Perelman, P. L., Rubtsova, N. V., Volobuev, V., Ferguson-Smith, M. A., . . . Graphodatsky, A. S. (2009). Cross-species chromosome painting in Cetartiodactyla: reconstructing the karyotype evolution in key phylogenetic lineages. Chromosome Research, 17(3), 419-436.

McGowen, M. R., Tsagkogeorga, G., Alvarez-Carretero, S., dos Reis, M., Struebig, M., Deaville, R., . . . Rossiter, S. J. (2020). Phylogenomic resolution of the Cetacean tree of life using target sequence capture. Systematic Biology, 69(3), 479-501. doi: 10.1093/sysbio/syz068

Morton, S. G. (1944). On a supposed new species of hippopotamus. Proceedings of the Academy of Natural Sciences of Philadelphia, 2, 14-17.

Morton, S. G. (1949). Additional observations on a new living species of hippopotamus. Journal of the Academy of Natural Sciences of Philadelphia, 2(1), 231-239. 

Husbandry & Captivity

Da Re, F., Graczyk, M., Cwiertnia, P., Cassandro, M., Szwaczkowski, T., & Sell-Kubiak, E. (2018). Explorative statistical analysis to identify factors affecting the survival of pygmy hippopotamus (Choeropsis liberiensis) kept in zoological gardens. Belgian Journal of Zoology, 148(1), 1-12. doi: 10.26496/bjz.2018.15

Flacke, G. L., Tkalcic, S., Steck, B., Warren, K., & Martin, G. B. (2016). A retrospective analysis of mortality in captive pygmy hippopotamus (Choeropsis liberiensis) From 1912 to 2014. Zoo Biology, 35(6), 556-569. doi: 10.1002/zoo.21336

Jacobi, E. F. (1969). Hippopotamus, tapir and manatee house at Amsterdam Zoo. International Zoo Yearbook, 9, 63-65.

Jones, M. L. (1993). Longevity of ungulates in captivity. International Zoo Yearbook, 32, 159-169.

Turner, E. (1960). The large mammal building at Dallas zoo. International Zoo Yearbook, 2, 1-2.

Zschokke, S. (2002). Distorted sex ratio at birth in the captive pygmy hippopotamus, Hexaprotodon liberiensis. Journal of Mammalogy, 83(3), 674-681. 

Molecular Biology

Butti, C., Fordyce, R. E., Raghanti, M. A., Gu, X. S., Bonar, C. J., Wicinski, B. A., . . . Hof, P. R. (2014). The cerebral cortex of the pygmy hippopotamus, Hexaprotodon liberiensis (Cetartiodactyla, Hippopotamidae): MRI, cytoarchitecture, and neuronal morphology. Anatomical Record-Advances in Integrative Anatomy and Evolutionary Biology, 297(4), 670-700. doi: 10.1002/ar.22875

Frohlich, J., Kubickova, S., Musilova, P., Cernohorska, H., Muskova, H., & Rubes, J. (2017). A comparative study of pygmy hippopotamus (Choeropsis liberiensis) karyotype by cross-species chromosome painting. Journal of Mammalian Evolution, 24(4), 465-474. doi: 10.1007/s10914-016-9358-5

Kulemzina, A. I., Trifonov, V. A., Perelman, P. L., Rubtsova, N. V., Volobuev, V., Ferguson-Smith, M. A., . . . Graphodatsky, A. S. (2009). Cross-species chromosome painting in Cetartiodactyla: reconstructing the karyotype evolution in key phylogenetic lineages. Chromosome Research, 17(3), 419-436.

Senn, H., O'Donoghue, P., McEwing, R., & Ogden, R. (2014). Hundreds of SNPs for the Endangered pygmy hippopotamus (Choeropsis liberiensis). Conservation Genetics Resources, 6(3), 535-538. doi: 10.1007/s12686-014-0178-8


Butti, C., & Hof, P. R. (2010). The insular cortex: a comparative perspective. Brain Structure & Function, 214(5-6), 477-493. doi: 10.1007/s00429-010-0264-y

Olivier, R. C. D. (1975). Aspects of skin physiology in pygmy hippopotamus Choeropsis liberiensis. Journal of Zoology 176(211-213).

Paris, M., Millar, R., Colenbrander, B., & Schwarzenberger, F. (2008). Non-invasive assessment of female reproductive physiology in the pygmy hippopotamus (Choeropsis liberiensis). Reproduction in Domestic Animals, 43, 21.

Schwarm, A., Ortmann, S., Hofer, H., Streich, W. J., Flach, E. J., Kühne, R., . . . Clauss, M. (2006). Digestion studies in captive Hippopotamidae: A group of large ungulates with an unusually low metabolic rate. Journal of Animal Physiology and Animal Nutrition, 90(7‐8), 300-308.

Schwarm, A., Ortmann, S., Wolf, C., Streich, W. J., & Clauss, M. (2009). More efficient mastication allows increasing intake without compromising digestibility or necessitating a larger gut: comparative feeding trials in banteng (Bos javanicus) and pygmy hippopotamus (Hexaprotodon liberiensis). Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 152(4), 504-512.

Vendl, C., Frei, S., Dittmann, M. T., Furrer, S., Ortmann, S., Lawrenz, A., . . . Clauss, M. (2016). Methane production by two non-ruminant foregut-fermenting herbivores: The collared peccary (Pecan tajacu) and the pygmy hippopotamus (Hexaprotodon liberiensis). Comparative Biochemistry and Physiology a-Molecular & Integrative Physiology, 191, 107-114. doi: 10.1016/j.cbpa.2015.09.021


Flacke, G. L., Schwarzenberger, F., Penfold, L. M., Walker, S. L., Martin, G. B., Millar, R. P., & Paris, M. C. J. (2017). Characterizing the reproductive biology of the female pygmy hippopotamus (Choeropsis liberiensis) through non-invasive endocrine monitoring. Theriogenology, 102, 126-138. doi: 10.1016/j.theriogenology.2017.07.017

Porton, I., & Hornbeck, B. (1993). A North American contraceptive database for ungulates. International Zoo Yearbook, 32, 155-159.

Saragusty, J., Hermes, R., Hofer, H., Bouts, T., Goritz, F., & Hildebrandt, T. B. (2012). Male pygmy hippopotamus influence offspring sex ratio. Nature Communications, 3. doi: 10.1038/ncomms1700

Saragusty, J., Hildebrandt, T. B., Bouts, T., Goritz, F., & Hermes, R. (2010). Collection and preservation of pygmy hippopotamus (Choeropsis liberiensis) semen. Theriogenology, 74(4), 652-657. doi: 10.1016/j.theriogenology.2010.03.002

Saunders, R. A., Killick, R. S., Barrows, M. G., Bowlt, K. A., & Denk, D. (2017). Diagnosis and treatment of concurrent dermal malignant melanoma and melanocytomas in a pygmy hippopotamus (Choeropsis liberiensis). Veterinary Dermatology, 28(5), 520-+. doi: 10.1111/vde.12460


Boothe, M., Kottwitz, J., Harmon, R., Citino, S. B., Zuba, J. R., & Boothe, D. M. (2016). Results of the megavertebrate analgesia survey: giraffe and hippopotamus. Journal of Zoo and Wildlife Medicine, 47(4), 1049-1056. doi: 10.1638/2015-0268.1

Bouts, T., Hermes, R., Gasthuys, F., Saragusty, J., Taylor, P., Routh, A., & Hildebrandt, T. B. (2012). Medetomidine-ketamine-isoflurane anaesthesia in pygmy hippopotami (Choeropsis liberiensis) - a case series. Veterinary Anaesthesia and Analgesia, 39(1), 111-118. doi: 10.1111/j.1467-2995.2011.00671.x

Bouts, T., Vordermeier, M., Flach, E., & Routh, A. (2009). Positive skin and serologic test results of diagnostic assays for bovine tuberculosis and subsequent isolation of mycobacterium interjectum in a pygmy hippopotamus (Hexaprotodon liberiensis). Journal of Zoo and Wildlife Medicine, 40(3), 536-542. doi: 10.1638/2008-0001.1

Flacke, G. L., Tomkins, J. L., Black, R., & Steck, B. (2017). Demographics of polycystic kidney disease and captive population viability in pygmy hippopotamus (Choeropsis liberiensis). Zoo Biology, 36(2), 136-151. doi: 10.1002/zoo.21351

Flach, E. J., Furrokh, I. K., Thornton, S. M., Smith, J., Parkyn, J. P., & Campbell, E. J. (1998). Caesarean section in a pygmy hippopotamus (Choeropsis liberiensis) and the management of the wound. Veterinary Record, 143(22), 611-613. doi: 10.1136/vr.143.22.611

Franklinos, L. H. V., Masters, N., Feltrer, Y., Pocknell, A., Bolt, D. M., Dakin, S., . . . Molenaar, F. M. (2017). The management of an oral anaplastic sarcoma in a pygmy hippopotamus (Choeropsis liberiensis) using intralesional chemotherapy. Journal of Zoo and Wildlife Medicine, 48(1), 260-264. doi: 10.1638/2016-0015.1

McCurdy, P., Sangster, C., Lindsay, S., & Vogelnest, L. (2014). Acute lymphoblastic leukemia in a pygmy hippopotamus (Hexaprotodon liberiensis). Journal of Zoo and Wildlife Medicine, 45(4), 906-910. doi: 10.1638/2014-0005.1

Ness, S., Schade, B., Clauss, M., Steinmetz, H. W., Ehrensperger, F., Steck, B., & Hatt, J. M. (2009). Polycystic kidney disease in the pygmy hippopotamus (Hexaprotodon liberiensis). Journal of Zoo and Wildlife Medicine, 40(3), 529-535.

Pearce, P. C., Gustavo, C., Gulland, F., & Knight, J. (1985). Immobilization of a pygmy hippopotamus (Choeropsis liberiensis). Journal of Zoo Animal Medicine, 16(3), 104-106. 


Pycraft, W. P. (1938). Pygmies and giants: Two species of hippopotamus. The Illustrated London News, 193(5182), 273.