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Thoracic Vertebral Morphology and Locomotor Adaptation in Anthropoid Primates
Author(s) -
Sarrazin Blake D,
Middleton Emily R,
Ward Carol V
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1037.5
Subject(s) - anatomy , rib cage , biology , vertebral column , transverse plane , thoracic vertebrae , orientation (vector space) , dorsum , lumbar vertebrae , geometry , lumbar , mathematics
Thoracic shape is related to locomotor adaptation in anthropoid primates. Pronograde quadrupeds tend to have narrow, deep rib cages, whereas those of hominoids tend to be broader mediolaterally. Further, hominoids, especially humans, have the thoracic vertebral column invaginated into the rib cage to support orthograde posture. Humans, and to a lesser extent apes, also exhibit declination of the sternal ends of the ribs. Although the ribs may be the best indicator of overall thoracic shape, they are not well preserved as fossils and are not found in articulation with the vertebral column. However, thoracic form and vertebral invagination should be reflected in orientation of the transverse processes of the thoracic vertebrae, as they articulate with the ribs. To test this hypothesis, we examined the fifth and ninth thoracic (T5, T9) vertebrae from 168 anthropoids. Landmark data were collected using a Microscribe G2X digitizer and analyzed using Polyworks software (Innovmetric, Inc.). Using this program, planes were fit to the superior surface of the vertebral body and to the median plane. A vector was fit between costovertebral and costotransverse articular facets, and used to measure the angles of dorsal and inferior inclination of the transverse process orientation. Statistical analysis of the data was performed using the R statistical software package. As predicted, hominoids, in particular humans, have more dorsally inclined transverse processes than monkeys. However, the semisuspensory atelines are similar to hominoids in regards to this feature, suggesting a relationship between suspension and invagination of the thoracic column into the rib cage. Differences are greater in T9 than at T5. Hominoids, including humans, were found to have more horizontally projecting T5 transverse processes than monkeys. At T9, humans are even more horizontal than apes, and all hominoids have more horizontally projecting transverse processes than do monkeys. These patterns reflect variation in rib declination among taxa and show that a relatively more superior position of the costotransverse joints contributes to declination of the sternal end of the ribs. Comparing these relationships using in silico models of thoracic shape will further refine our understanding of the geometry of all of these elements together. Overall, our results support our hypothesis that the thoracic transverse processes are able to reflect ventral invagination of the vertebral column into the rib cage and variation in rib declination, and so are a useful indicator of thoracic form in fossil anthropoids.