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Variation, sexual dimorphism, and social structure in the early Eocene horse Hyracotherium (Mammalia, Perissodactyla)

Published online by Cambridge University Press:  08 February 2016

Philip D. Gingerich
Philip D. Gingerich*
Affiliation:
Museum of Paleontology, The University of Michigan, Ann Arbor, Michigan 48109
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Abstract

Patterns of dental and cranial variation are analyzed in a unique sample of early Eocene equid Hyracotherium from one fossil quarry of late Wasatchian age in the Huerfano Basin of southern Colorado. The sample includes remains of two species differing principally in size: H. vasacciense and H. tapirinum. The larger species, H. tapirinum, is represented by 24 individual specimens that show marked bimodality in cranial size and robustness and in upper and lower canine size. These differences are attributed to sexual dimorphism. Males tend to be about 15% larger than females in cranial dimensions and 40% larger than females in canine dimensions suggesting, by comparison with modern ungulates, that early Eocene horses were probably polygynous. The appearance of Hyracotherium in North America and its rise to dominance in early Eocene mammalian communities coincides with development of an environmental mosaic including open park woodland and savanna habitats. The evolutionary success of Hyracotherium may reflect, in part, the adaptive superiority of a social structure in which females in open habitats are grouped for mutual protection from predators, for optimal foraging in patchy environments, or both.

Type
Articles
Information
Paleobiology , Volume 7 , Issue 4 , Fall 1981 , pp. 443 - 455
Copyright
Copyright © The Paleontological Society 

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References

Literature Cited

Alexander, R. D., Hoogland, J. L., Howard, R. D., Noonan, K. M., and Sherman, P. W. 1979. Sexual dimorphisms and breeding systems in pinnipeds, ungulates, primates, and humans. Pp. 402–435. In: Chagnon, N. A. and Irons, W., eds. Evolutionary Biology and Human Social Behavior: An Anthropological Perspective. Duxbury Press; North Scituate, Massachusetts.Google Scholar
Berger, J. 1977. Organizational systems and dominance in feral horses in the Grand Canyon. Behav. Ecol. Sociobiol. 2:131–146.CrossRefGoogle Scholar
Bown, T. M. 1980. Summary of latest Cretaceous and Cenozoic sedimentary tectonic, and erosional events, Bighorn Basin, Wyoming. In: Gingerich, P. D., ed. Early Cenozoic Paleontology and Stratigraphy of the Bighorn Basin, Wyoming. Univ. Mich. Pap. Paleontol. 24:25–32.Google Scholar
Clutton-Brock, T. H., Harvey, P. H., and Rudder, B. 1977. Sexual dimorphism, socionomic sex ration, and body weight in primates. Nature. 269:797–800.CrossRefGoogle Scholar
Coombs, M. C. 1975. Sexual dimorphism in chalicotheres (Mammalia, Perissodactyla). Syst. Zool. 24:55–62.CrossRefGoogle Scholar
Cope, E. D. 1872. On a new genus of Pleurodira from the Eocene of Wyoming. Proc. Am. Phil. Soc. 12:472–477.Google Scholar
Cope, E. D. 1875. Systematic catalogue of the Vertebrata of the Eocene of New Mexico, collected in 1974. Pp. 5–37. In: Geographical Surveys West of the Hundredth Meridian (G. M. Wheeler in charge). U.S. Army Engineer Department; Washington, D.C.Google Scholar
Cope, E. D. 1881. On the Vertebrata of the Wind River Eocene beds of Wyoming. Bull. U.S. Geog. Surv. Terr. 6:183–202.Google Scholar
Crook, J. H. 1972. Sexual selection, dimorphism, and social organization in the primates. Pp. 231–281. In: Campbell, B., ed. Sexual Selection and the Descent of Man. Aldine; Chicago, Illinois.Google Scholar
Dorr, J. A. 1958. Prouintatherium, new uintathere genus, earliest Eocene, Hoback Formation, Wyoming, and the phylogeny of Dinocerata. J. Paleontol. 32:506–516.Google Scholar
Erz, W. 1964. Tooth eruption and replacement in Burchell's zebra, Equus burchelli Gray 1825. Arnoldia (Rhodesia). 1(22):1–8.Google Scholar
Feist, J. D. and McCullough, D. R. 1976. Behavior patterns and communication in feral horses. Zeit. Tierpsychol. 41:337–371.CrossRefGoogle ScholarPubMed
Fleagle, J. G., Kay, R. F., and Simons, E. L. 1980. Sexual dimorphism in early anthropoids. Nature. 287:328–330.CrossRefGoogle ScholarPubMed
Gautier-Hion, A. 1975. Dimorphisme sexuel et organisation sociale chez les cercopithécinés forestiers africains. Mammalia. 39:365–374.CrossRefGoogle Scholar
Geist, V. 1974. On the relationship of social evolution and ecology in ungulates. Am. Zool. 14:205–220.CrossRefGoogle Scholar
Gingerich, P. D. 1974. Size variability of the teeth in living mammals and the diagnosis of closely related sympatric fossil species. J. Paleontol. 48:895–903.Google Scholar
Gingerich, P. D. 1979. Sexual dimorphism in Eocene Adapidae: implications for primate phylogeny and evolution (Abstract). Am. J. Phys. Anthropol. 50:442.Google Scholar
Gingerich, P. D. 1980. Evolutionary patterns in early Cenozoic mammals. Annu. Rev. Earth Planet. Sci. 8:407–424.CrossRefGoogle Scholar
Gingerich, P. D. 1981. Cranial morphology and adaptations in Eocene Adapidae. I. Sexual dimorphism in Adapis magnus and Adapis parisiensis. Am. J. Phys. Anthropol. 56:107–125.Google Scholar
Gingerich, P. D. and Schoeninger, M. J. 1979. Patterns of tooth size variability in the dentition of primates. Am. J. Phys. Anthropol. 51:457–466.CrossRefGoogle ScholarPubMed
Gingerich, P. D. and Simons, E. L. 1977. Systematics, phylogeny, and evolution of early Eocene Adapidae (Mammalia, Primates) in North America. Contrib. Mus. Paleontol. Univ. Mich. 24:245–279.Google Scholar
Gingerich, P. D. and Winkler, D. A. 1979. Patterns of variation and correlation in the dentition of the red fox, Vulpes vulpes. J. Mammal. 60:691–704.CrossRefGoogle Scholar
Godinot, M. 1981. Les mammifères de Rians (Éocène inférieur, Provence). Palaeovertebrata. 10:43–126.Google Scholar
Hamilton, W. D. 1971. Geometry for the selfish herd. J. Theor. Biol. 31:295–311.CrossRefGoogle ScholarPubMed
Hickey, L. J. 1980. Paleocene stratigraphy and flora of the Clark's Fork Basin. In: Gingerich, P. D., ed. Early Cenozoic Paleontology and Stratigraphy of the Bighorn Basin, Wyoming. Univ. Mich. Pap. Paleontol. 24:33–49.Google Scholar
Hutchison, J. H. 1980. Turtle stratigraphy of the Will wood Formation, Wyoming: preliminary results. In: Gingerich, P. D., ed. Early Cenozoic Paleontology and Stratigraphy of the Bighorn Basin, Wyoming. Univ. Mich. Pap. Paleontol. 24:115–118.Google Scholar
Jarman, P. J. 1974. The social organisation of antelope in relation to their ecology. Behaviour. 48:215–267.CrossRefGoogle Scholar
Kitts, D. B. 1956. American Hyracotherium (Perissodactyla, Equidae). Bull. Am. Mus. Nat. Hist. 110:1–60.Google Scholar
Kleiman, D. G. 1977. Monogamy in mammals. Q. Rev. Biol. 52:39–69.CrossRefGoogle ScholarPubMed
Klingel, H. 1975. Social organization and reproduction in equids. J. Reprod. Fert., Suppl. 23:7–11.Google Scholar
Kurtén, B. 1969. Sexual dimorphism in fossil mammals. Pp. 226–233. In: Westermann, G. E. G., ed. Sexual Dimorphism in Fossil Metazoa and Taxonomic Implications. Int. Union Geol. Sci. Series A—Schweizerbart'sche Verlagsbuchhandlung; Stuttgart, West Germany.Google Scholar
Leutenegger, W. 1978. Scaling of sexual dimorphism in body size and breeding system in primates. Nature. 272:610–611.CrossRefGoogle ScholarPubMed
Leutenegger, W. and Kelly, J. T. 1977. Relationship of sexual dimorphism in canine size and body size to social, behavioral, and ecological correlates in anthropoid primates. Primates. 18:117–136.CrossRefGoogle Scholar
Lewontin, R. C. 1966. On the measurement of relative variability. Syst. Zool. 15:141–142.CrossRefGoogle Scholar
Osborn, H. F. 1918. Equidae of the Oligocene, Miocene, and Pliocene of North America, iconographic type revision. Mem. Am. Mus. Nat. Hist. 2:1–217.Google Scholar
Owen, R. 1858. Description of a small lophiodont mammal (Pliolophus vulpiceps Owen) from the London Clay near Harwich. Q. J. Geol. Soc. Lond. 14:54–71.CrossRefGoogle Scholar
Pilbeam, D. R. and Zwell, M. 1972. The single species hypothesis, sexual dimorphism, and variability in early hominids. Yearb. Phys. Anthropol. 16:69–79.Google Scholar
Pirlot, P.-L. 1952. Les canines chez Hipparion et l'apparition d'un charactère sexuel secondaire des mammifères. Bull. Mus. Nat. d'Hist. Natur., Sér. 2. 24:419–422.Google Scholar
Radinsky, L. 1963. Origin and early evolution of North American Tapiroidea. Bull. Peabody Mus. Nat. Hist., Yale Univ. 17:1–106.Google Scholar
Radinsky, L. 1966. The adaptive radiation of the phenacodontid condylarths and the origin of the Perissodactyla. Evolution. 20:408–417.CrossRefGoogle ScholarPubMed
Radinsky, L. 1976. Oldest horse brains: more advanced than previously realized. Science. 194:626–627.CrossRefGoogle ScholarPubMed
Radinsky, L. 1978. Evolution of brain size in carnivores and ungulates. Am. Nat. 112:815–831.CrossRefGoogle Scholar
Ralls, K. 1976. Mammals in which females are larger than males. Q. Rev. Biol. 51:245–276.CrossRefGoogle ScholarPubMed
Ralls, K. 1977. Sexual dimorphism in mammals: avian models and unanswered questions. Am. Nat. 111:917–938.CrossRefGoogle Scholar
Robinson, P. 1966. Fossil Mammalia of the Huerfano Formation, Eocene of Colorado. Bull. Peabody Mus. Nat. Hist., Yale Univ. 21:1–95.Google Scholar
Sachs, R. 1967. Liveweights and body measurements of Serengeti game animals. E. Afr. Wildl. J. 5:24–36.CrossRefGoogle Scholar
Schankler, D. M. 1980. Faunal zonation of the Will wood Formation in the central Bighorn Basin, Wyoming. In: Gingerich, P. D., ed. Early Cenozoic Paleontology and Stratigraphy of the Bighorn Basin, Wyoming. Univ. Mich. Pap. Paleontol. 24:99–114.Google Scholar
Simpson, G. G. 1951. Horses. 247 pp. Oxford Univ. Press; New York, New York.Google Scholar
Simpson, G. G., Roe, A., and Lewontin, R. C. 1960. Quantitative Zoology. 440 pp. Harcourt, Brace, and World; New York, New York.Google Scholar
Skinner, M. F. and Mac Fadden, B. J. 1977. Cormohipparion n. gen. (Mammalia, Equidae) from the North American Miocene (Barstovian-Clarendonian). J. Paleontol. 51:912–926.Google Scholar
St. Clair, L. E. 1975. Teeth. Pp. 460–470. In: Getty, R., ed. Sisson and Grossman's The Anatomy of the Domestic Animals. W. B. Saunders Co.; Philadelphia, Pennsylvania.Google Scholar
Van Houten, F. B. 1945a. Early Cenozoic facies in the Rocky Mountain region. Science. 101:430–431.CrossRefGoogle ScholarPubMed
Van Houten, F. B. 1945b. Review of latest Paleocene and early Eocene mammalian faunas. J. Paleontol. 19:421–461.Google Scholar
Wing, S. L. 1980. Fossil floras and plant-bearing beds of the central Bighorn Basin. In: Gingerich, P. D., ed. Early Cenozoic Paleontology and Stratigraphy of the Bighorn Basin, Wyoming. Univ. Mich. Pap. Paleontol. 24:119–125.Google Scholar
Wittenberger, J. F. and Tilson, R. L. 1980. The evolution of monogamy: hypotheses and evidence. Annu. Rev. Ecol. Syst. 11:197–232.CrossRefGoogle Scholar
Wrangham, R. W. 1980. An ecological model of female-bonded primate groups. Behaviour. 75:262–300.CrossRefGoogle Scholar