Forelimb myology of the pygmy hippopotamus (Choeropsis liberiensis)
Open accessAbstract
Based on morphological analyses, hippos have traditionally been classified as Suiformes, along with pigs and peccaries. However, molecular data indicate hippos and cetaceans are sister taxa (see review in Uhen, , this issue). This study analyzes soft tissue characters of the pygmy hippo forelimb to elucidate the functional anatomy and evolutionary relationships of hippos within Artiodactyla. Two specimens from the National Zoological Park in Washington, D.C. were dissected, revealing several adaptations to an aquatic lifestyle. However, these adaptations differ functionally from most aquatic mammals as hippos walk along river or lake bottoms, rather than swim. Several findings highlight a robust mechanism for propelling the trunk forward through the water. For example, mm. pectoralis superficialis and profundus demonstrate broad sites of origin, while the long flexor tendons serve each of the digits, reflecting the fact that all toes are weight‐bearing. Pygmy hippos also have eight mm. interossei and a well‐developed m. lumbricalis IV. Retention of intrinsic adductors functions to prevent splaying of the toes, an advantageous arrangement in an animal walking on muddy substrates. Published descriptions indicate common hippos share all of these features. Hippo and ruminant forelimbs share several traits; however, hippos are unique among artiodactyls in retaining several primitive muscles (e.g., mm. palmaris longus and flexor digitorum brevis). These findings are consistent with the hypothesis that hippos diverged from other Artiodactyla early in the history of this group. Additional analyses of hindlimb and axial muscles may help determine whether this trajectory was closely allied to that of Cetacea. Anat Rec, 290:673–693, 2007. © 2007 Wiley‐Liss, Inc.
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Recent molecular phylogenetic studies and comparative morphological analyses support Hippopotamidae and Cetacea as forming a monophyletic group.
“Recent molecular phylogenetic studies and comparative morphological analyses have supported Hippopotamidae and Cetacea as forming a monophyletic group (Shimamura et al. 1997;Nomura et al. 1998;Ursing and Arnason 1998;Nomura and Yasue 1999;Geisler and Uhen 2003;Boisserie 2005;Boisserie et al. 2005;Fisher et al. 2007);”
From Choeropsis liberiensis (Artiodactyla: Hippopotamidae) (2019) · cites this paper as Fisher et al. 2007
The Abstract says molecular studies indicate that hippos and cetaceans are sister taxa. In “Functional and Phylogenetic Considerations,” the authors say their forelimb comparisons support the molecular data, but they call for further study to determine whether hippos were closely allied to Cetacea. The paper therefore supports the molecular part of the claim, but does not establish that its comparative morphological analysis supports the hippo–cetacean clade. (LLM, conf=0.87)
Experimental — accuracy not yet measuredC. liberiensis has retained several features more adapted to a terrestrial lifestyle compared to the common hippopotamus, including proportionally longer limbs and only moderately webbed toes that spread more widely under its own weight.
“Choeropsis liberiensis has retained several features more adapted to a terrestrial lifestyle compared to the common hippopotamus, including proportionally longer limbs and only moderately webbed toes that spread more widely under its own weight (Johnston 1906 ;Pocock 1923;Fisher et al. 2007).”
From Choeropsis liberiensis (Artiodactyla: Hippopotamidae) (2019) · cites this paper as Fisher et al. 2007
The Functional and Phylogenetic Considerations section says hippos retain terrestrial locomotor patterns and have tendons that control toe splay on soft ground. It does not establish that pygmy hippos have proportionally longer limbs, moderately webbed toes, or greater terrestrial adaptation than common hippos; the Abstract says common hippos share the described toe-control features. (LLM, conf=0.85)
Experimental — accuracy not yet measuredRetention of intrinsic adductor muscles in the feet functions to prevent splaying of the toes, an adaptation to walking on muddy substrates.
“Retention of intrinsic adductor muscles in the feet functions to prevent splaying of the toes, an adaptation to walking on muddy substrates (Fisher et al. 2007).”
From Choeropsis liberiensis (Artiodactyla: Hippopotamidae) (2019) · cites this paper as Fisher et al. 2007
The rhomboid muscle group can either originate in the neck or from the occipital bone in C. liberiensis.
“For example, the rhomboid muscle group can either originate in the neck (Campbell 1936;Fisher et al. 2007) or from the occipital bone (Macalister 1873).”
From Choeropsis liberiensis (Artiodactyla: Hippopotamidae) (2019) · cites this paper as Fisher et al. 2007
The insertion site of the brachialis muscle can be on the radius only or on both the radius and ulna in C. liberiensis.
“The insertion site of the brachialis muscle can be on the radius only (Macalister 1873;Fisher et al. 2007) or on both the radius and ulna (Campbell 1936); the radius and ulna are functionally or actually fused in artiodactyls.”
From Choeropsis liberiensis (Artiodactyla: Hippopotamidae) (2019) · cites this paper as Fisher et al. 2007
The trapezius muscle can variably originate from the last two cervical vertebrae or the occipital bone in C. liberiensis, whereas the common hippopotamus lacks an occipital origin.
“Similarly, the trapezius muscle can variably originate from the last two cervical vertebrae (Campbell 1936) or the occipital bone (Macalister 1873;Fisher et al. 2007) in C. liberiensis, whereas the common hippopotamus lacks an occipital origin.”
From Choeropsis liberiensis (Artiodactyla: Hippopotamidae) (2019) · cites this paper as Fisher et al. 2007
Overall, the myology of C. liberiensis resembles ruminants more closely than suids, and both extant hippo species are unique in retaining several primitive features in the forelimb, consistent with the hypothesis that hippopotamids diverged from other Artiodactyla early in the history of this group.
“Overall, the myology of the C. liberiensis resembles ruminants more closely than suids, and both extant hippo species are unique in retaining several primitive features in the forelimb, consistent with the hypothesis that hippopotamids diverged from other Artiodactyla early in the history of this group (Fisher et al. 2007).”
From Choeropsis liberiensis (Artiodactyla: Hippopotamidae) (2019) · cites this paper as Fisher et al. 2007
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References 21 · Cited by 70
Research works printed but not linked: 6
- Campbell B. 1935. The comparative myology of the hippopotamus, pig, and tapir. Ph.D. Dissertation, Johns Hopkins University.
- Cuvier G. 1850. Anatomie compare ´e. Recueil de planches de myolo- gie dessine ´es par Georges Cuvier ou exe ´cute ´es sous ses yeux par M. Laurillard. Paris: Imprimerie d 0 E. Duverger. Dalzell BB. 1970. Descriptive and functional morphology of the ex- trinsic shoulder musculature in Artiodactyls. Masters Thesis, University of California, Berkeley.
- Getty R. 1975. Ruminant Myology. In: Getty R, editor. Sisson and Grossman's; The anatomy of the domestic animals. 5th ed. Phila- delphia: WB Saunders Company. p 791-860.
- Sisson S. 1975a. Porcine myology. In: Getty R, editor. Sisson and Grossman's; The anatomy of the domestic animals. 5th ed. Phila- delphia: WB Saunders Company. p 1256-1267.
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- Authors
- Fisher, R. E., Scott, K. M., & Naples, V. L.
- Affiliations
- University of Arizona College of Medicine- Phoenix (US)
- Rutgers, The State University of New Jersey (US)
- Northern Illinois University (US)
- Corresponding author
- Fisher, Rebecca E.
- Venue
- The Anatomical Record
- Publisher
- Wiley
- Published
- 2007-05-21
- Volume
- 290
- Issue
- 6
- Pages
- 673-693
- ISSN
- 1932-8486 (ISSN-L)
- 1932-8494
- OpenAlex
- W2018095290
- Cited by
- 70
- References
- 21
- Citations by year
- 2026: 4 · 2025: 3 · 2024: 2 · 2023: 6 · 2022: 2 · 2021: 9 · 2020: 3 · 2019: 16 · 2018: 3 · 2017: 2 · 2016: 1 · 2015: 3 · 2014: 4 · 2013: 2 · 2012: 1
- FWCI
- 3.32
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Locations
- The Anatomical Record (publishedVersion)
- PubMed (publishedVersion)
- Funders
- Smithsonian Institution
- Yale University
- Johns Hopkins University
- National Museum of Natural History
- Topics
- Health Sciences › Medicine › Urology › Comparative Animal Anatomy Studies
- Physical Sciences › Earth and Planetary Sciences › Paleontology › Evolution and Paleontology Studies
- Physical Sciences › Earth and Planetary Sciences › Paleontology › Paleontology and Evolutionary Biology
- Keywords
- pygmy hippopotamus, Choeropsis liberiensis, Artiodactyla, aquatic adaptation, pectoralis muscle, flexor tendons, palmaris longus, flexor digitorum brevis, soft tissue anatomy
- MeSH terms
- Adaptation, Physiological, Animals, Artiodactyla, Dissection, Female, Forelimb, Water, Muscle, Skeletal
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