Intermembral index

The intermembral index is a ratio used to compare limb proportions, expressed as a percentage.[1] It is equal to the length of forelimbs (humerus plus radius) divided by the length of the hind limbs (femur plus tibia) multiplied by 100,[2] otherwise written mathematically as:

The intermembral index is used frequently in primatology, since it helps predict primate locomotor patterns. For scores lower than 100, the forelimbs are shorter than the hind limbs, which is common in leaping primates and bipedal hominids. Quadrupedal primates tend to have scores around 100, while brachiating primates have scores significantly higher than 100. This information can also be used to predict locomotion patterns for extinct primates in cases where forelimb and hind limb fossils have been found.[1]

Primate species

Intermembral Index of Extant Primate Species[3]
Species Intermembral Index
Cheirogaleus major 72
Microcebus murinus 72
Phaner furcifer 68
Lemur catta 70
Hapalemur griseus 64
Eulemur fulvus 72
Lepilemur edwardsi 60
Avahi laniger 58
Indri indri 64
Daubentonia madagascariensis 71
Galagoides demidovii 71
Galago senegalensis 52
Otolemur crassicaudatus 70
Perodicticus potto 88
Arctocebus calabarensis 89
Loris tardigradus 90
Nycticebus coucang 88
Carlito syrichta 58
Cephalopachus bancanus 52
Callicebus moloch 74
Pithecia pithecia 75
Chiropotes sagulatus 83
Cacajao calvus 83
Alouatta seniculus 97
Lagothrix lagotricha 98
Brachyteles arachnoides 104
Ateles paniscus 105
Cebus capucinus 81
Sapajus apella 81
Saimiri sciurius 80
Aotus lemurinus 74
Callimico goeldii 69
Callithrix jacchus 76
Cebuella pygmaea 83
Saguinus geoffroyi 76
Leontopithecus rosalia 89
Macaca fascicularis 93
Macaca nemestrina 98
Cercocebus agilis 84
Mandrillus sphinx 95
Lophocebus albigena 78
Papio anubis 97
Theropithecus gelada 100
Mioithecus talapoin 83
Chlorocebus aethiops 83
Erythrocebus patas 92
Allochrocebus lhoesti 80
Cercopithecus mitis 82
Colobus guereza 79
Piliocolobus badius 87
Procolobus verus 80
Presbytis siamensis 78
Trachypithecus obscurus 83
Semnopithecus entellus 83
Nasalis larvatus 94
Pygathrix nemaeus 94
Hylobates lar 130
Symphalangus syndactylus 147
Nomascus concolor 140
Hoolock hoolock 129
Pongo pygmaeus 139
Pan troglodytes 106
Pan paniscus 102
Gorilla gorilla 116
Homo sapiens 72

Variation

In a diverse ethnic sample of 314 modern human skeletons covering African Pygmies, Andaman Islanders, Khoesan, Zulu, African Americans, Sami and Inuit the intermembral index was found to vary between 64 and 74.[4] An study published in 1937 found a range of variation between 64.5 and 79.2. This study found no link with humans of different groups with individuals from different ethnic groups showing similar scatter of variation.[5] Variation has also beem found in chimapanzees (100.1 - 113.7), gorillas (110.3 - 125.0), orangutan (135.0 -150.9), siamang (145.0 - 155.2), gibbon (120.5 - 137.1), and macque monkeys (83.0 - 91.0).[5]

References

  1. ^ a b Ankel-Simons, F. (2007). Primate Anatomy (3rd ed.). Academic Press. pp. 49–53. ISBN 0-12-372576-3.
  2. ^ Conroy, G.C. (1990). Primate Evolution (1st ed.). New York: W.W. Norton and Co. ISBN 978-0-393-95649-8.
  3. ^ Fleagle, John G. (2017-04-16), Intermembral Index, Wiley, p. 1–3, doi:10.1002/9781119179313.wbprim0189, ISBN 978-0-470-67337-9
  4. ^ Jungers, William L. (2009). "Interlimb Proportions in Humans and Fossil Hominins: Variability and Scaling". Vertebrate Paleobiology and Paleoanthropology. Dordrecht: Springer Netherlands. p. 93–98. doi:10.1007/978-1-4020-9980-9_9. ISBN 978-1-4020-9979-3. ISSN 1877-9077.
  5. ^ a b Schultz, Adolph H. (1937). "PROPORTIONS, VARIABILITY AND ASYMMETRIES OF THE LONG BONES OF THE LIMBS AND THE CLAVICLES IN MAN AND APES". Human Biology. 9 (3): 281–328. ISSN 0018-7143. JSTOR 41447326.


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