XYZ coordinates of middle lumbar vertebrae - 3D GM analysis for: A nearly complete lower back of Australopithecus sediba
Data files
Sep 30, 2021 version files 222.65 KB
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Raw_landmark_coordinates.zip
Abstract
Adaptations of the lower back to bipedalism are frequently discussed but infrequently demonstrated in early fossil hominins. Newly discovered lumbar vertebrae contribute to a near-complete lower back of Malapa Hominin 2 (MH2), offering additional insights into posture and locomotion in Australopithecus sediba. We show that MH2 demonstrates a lower back consistent with lumbar lordosis and other adaptations to bipedalism, including an increase in the width of intervertebral articular facets from the upper to lower lumbar column (“pyramidal configuration”). These results contrast with some recent work on lordosis in fossil hominins, where MH2 was argued to demonstrate no appreciable lordosis (“hypolordosis”) similar to Neandertals. Our three-dimensional geometric morphometric (3D GM) analyses show that MH2’s nearly complete middle lumbar vertebra is human-like in overall shape but its vertebral body is somewhat intermediate in shape between modern humans and great apes. Additionally, it bears long, cranially and ventrally oriented costal (transverse) processes, implying powerful trunk musculature. We interpret this combination of features to indicate that A. sediba used its lower back in both bipedal and ape-like arboreal positional behaviors, as previously suggested based on multiple lines of evidence from other parts of the skeleton and reconstructed paleobiology of A. sediba.
Methods
Data were collected on 3D models using AMIRA and analyzed in R Studio.
Usage notes
The 3D landmarks are as follows:
- Superior vertebral body – ventral transverse midline
- Superior vertebral body – central transverse midline
- Superior vertebral body – dorsal transverse midline
- Superior vertebral body – lateral sagittal midline
- Superior vertebral body – ventro-lateral point
- Superior vertebral body – dorso-lateral point (at ventral pedicle base)
- Pedicle – superior midpoint
- Pedicle – superior dorsal point (at ventral base of prezygapophysis)
- Pedicle – medial midpoint
- Pedicle – lateral midpoint
- Pedicle – inferior midpoint
- Pars interarticularis – dorsal midpoint
- Pars interarticularis – ventral midpoint
- Inferior vertebral body – ventral transverse midline
- Inferior vertebral body – central transverse midline
- Inferior vertebral body – dorsal transverse midline
- Inferior vertebral body – lateral sagittal midline
- Inferior vertebral body - ventro-lateral point
- Inferior vertebral body – dorso-lateral point
- Lumbar transverse process (LTP) – superior medial point (based of LTP at pedicle)
- Lumbar transverse process – inferior medial point (based of LTP at pedicle)
- Lumbar transverse process – superior mediolateral midpoint
- Lumbar transverse process – inferior mediolateral midpoint
- Lumbar transverse process – superior lateral point
- Lumbar transverse process – inferior lateral point
- Superior articular facet – cranial-most point
- Mammillary process – dorsal-most extension
- Superior articular facet – midpoint
- Superior articular facet – caudal-most point
- Spinous process – superior ventral point (at spinous process base)
- Spinous process – superior sagittal midpoint
- Spinous process – superior dorsal point (tip of spinous process)
- Spinous process – inferior dorsal point (tip of spinous process)
- Spinous process – inferior sagittal midpoint
- Spinous process – inferior ventral point (at spinous process base)
- Lamina – inferior midpoint
- Inferior articular facet – cranial-most point
- Inferior articular facet – midpoint
- Inferior articular facet – caudal-most point
- Inferior articular facet – medial-most point
- Inferior articular facet – lateral-most point
- Superior articular facet – medial-most point
- Superior articular facet – lateral-most point
- Vertebral body – ventral midpoint
- Vertebral body – lateral midpoint
- Lumbar transverse process – ventral extension of base at its midpoint
- Spinous process – lateral-most extension of the spinous process tip
- Lamina – superior midpoint