TY - JOUR
T1 - Evolution of vertebral numbers in primates, with a focus on hominoids and the last common ancestor of hominins and panins
AU - Spear, Jeffrey K.
AU - Grabowski, Mark
AU - Sekhavati, Yeganeh
AU - Costa, Christina E.
AU - Goldstein, Deanna M.
AU - Petrullo, Lauren A.
AU - Peterson, Amy L.
AU - Lee, Amanda B.
AU - Shattuck, Milena R.
AU - Gómez-Olivencia, Asier
AU - Williams, Scott A.
N1 - Publisher Copyright:
© 2023 Elsevier Ltd
PY - 2023/6
Y1 - 2023/6
N2 - The primate vertebral column has been extensively studied, with a particular focus on hominoid primates and the last common ancestor of humans and chimpanzees. The number of vertebrae in hominoids—up to and including the last common ancestor of humans and chimpanzees—is subject to considerable debate. However, few formal ancestral state reconstructions exist, and none include a broad sample of primates or account for the correlated evolution of the vertebral column. Here, we conduct an ancestral state reconstruction using a model of evolution that accounts for both homeotic (changes of one type of vertebra to another) and meristic (addition or loss of a vertebra) changes. Our results suggest that ancestral primates were characterized by 29 precaudal vertebrae, with the most common formula being seven cervical, 13 thoracic, six lumbar, and three sacral vertebrae. Extant hominoids evolved tail loss and a reduced lumbar column via sacralization (homeotic transition at the last lumbar vertebra). Our results also indicate that the ancestral hylobatid had seven cervical, 13 thoracic, five lumbar, and four sacral vertebrae, and the ancestral hominid had seven cervical, 13 thoracic, four lumbar, and five sacral vertebrae. The last common ancestor of humans and chimpanzees likely either retained this ancestral hominid formula or was characterized by an additional sacral vertebra, possibly acquired through a homeotic shift at the sacrococcygeal border. Our results support the ‘short-back’ model of hominin vertebral evolution, which postulates that hominins evolved from an ancestor with an African ape–like numerical composition of the vertebral column.
AB - The primate vertebral column has been extensively studied, with a particular focus on hominoid primates and the last common ancestor of humans and chimpanzees. The number of vertebrae in hominoids—up to and including the last common ancestor of humans and chimpanzees—is subject to considerable debate. However, few formal ancestral state reconstructions exist, and none include a broad sample of primates or account for the correlated evolution of the vertebral column. Here, we conduct an ancestral state reconstruction using a model of evolution that accounts for both homeotic (changes of one type of vertebra to another) and meristic (addition or loss of a vertebra) changes. Our results suggest that ancestral primates were characterized by 29 precaudal vertebrae, with the most common formula being seven cervical, 13 thoracic, six lumbar, and three sacral vertebrae. Extant hominoids evolved tail loss and a reduced lumbar column via sacralization (homeotic transition at the last lumbar vertebra). Our results also indicate that the ancestral hylobatid had seven cervical, 13 thoracic, five lumbar, and four sacral vertebrae, and the ancestral hominid had seven cervical, 13 thoracic, four lumbar, and five sacral vertebrae. The last common ancestor of humans and chimpanzees likely either retained this ancestral hominid formula or was characterized by an additional sacral vertebra, possibly acquired through a homeotic shift at the sacrococcygeal border. Our results support the ‘short-back’ model of hominin vertebral evolution, which postulates that hominins evolved from an ancestor with an African ape–like numerical composition of the vertebral column.
KW - Ancestral state reconstruction
KW - Bipedalism
KW - Hominin evolution
KW - Last common ancestor
KW - Vertebral column
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U2 - 10.1016/j.jhevol.2023.103359
DO - 10.1016/j.jhevol.2023.103359
M3 - Article
C2 - 37099927
AN - SCOPUS:85153398833
SN - 0047-2484
VL - 179
JO - Journal of Human Evolution
JF - Journal of Human Evolution
M1 - 103359
ER -