The Pliocene fossil ‘Lucy’ (Australopithecus afarensis) was discovered in the Afar region of Ethiopia in 1974 and is among the oldest and most complete fossil hominin skeletons discovered. Here we propose, on the basis of close study of her skeleton, that her cause of death was a vertical deceleration event or impact following a fall from considerable height that produced compressive and hinge (greenstick) fractures in multiple skeletal elements. Impacts that are so severe as to cause concomitant fractures usually also damage internal organs; together, these injuries are hypothesized to have caused her death. Lucy has been at the centre of a vigorous debate about the role, if any, of arboreal locomotion in early human evolution. It is therefore ironic that her death can be attributed to injuries resulting from a fall, probably out of a tall tree, thus offering unusual evidence for the presence of arborealism in this species.
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Extended data figures and tables
Extended Data Figures
- Extended Data Figure 1: Right humerus (A.L. 288-1m) CT segmentation compared with photographs of fossil. (161 KB)
Right proximal humerus (A.L. 288-1m) illustrating the fractured fragments segmented from the CT scans compared with photographs of fossil. Nearly 30 fractured bone and articular head fragments and slivers were isolated by segmentation. Some small fragments remain embedded within the sediment on the posterior aspect of the head. One large fragment was avulsed off of the posteroinferior aspect of the articular head and not recovered. Scale bar, 10 mm. See Methods, Extended Data Fig. 2 and Supplementary Note 1 for a full description; also see Supplementary Video 1.
- Extended Data Figure 2: Right humerus (A.L. 288-1m) CT segmentation with ‘before’ reconstruction and ‘after’ discovery state. (386 KB)
Right proximal humerus (A.L. 288-1m) illustrating the head and diaphyseal shaft fragments segmented from the CT scans. The before image presents a reconstruction of the crushed proximal portion of the head that also straightens the spiral fracture at the diaphysis, and the after image shows the condition of the fossil in its discovery state. The impact compressed the proximal humerus against the glenoid of the scapula, with the glenoid acting as an anvil, which in turn fractured and shattered the components of the proximal humerus including the articular head, greater and lesser tuberosities, and shaft. Each pair of before and after images depicts the distal portion of the shaft in the same position and illustrates how the proximal portion of the head and shaft were angled in a posteromedial direction by the fracture. In some pairs of images the proximal end of the humerus is angled slightly towards the viewer to show a greater percentage of the head. Scale bar, 10 mm (approximate because of the differences in perspective). See Methods, Fig. 1, Extended Data Fig. 1 and Supplementary Note 1 for a full description; also see Supplementary Video 1.
- Extended Data Figure 3: Mandible (A.L. 288-1i, -1j and -1k) photographs and CT scan. (443 KB)
A comparison of photographs with CT scan of mandible (A.L. 288-1i, -1j and -1k) illustrating in red the major fractures across the parasymphyseal region, left body, and left (A.L. 288-1j) and right (A.L. 288-1k) subcondylar regions; and in green the fractures across the edges of the coronoid processes. The condyles were discovered and catalogued as separate specimens, and there is a set of closed fractures through the right condyle. Binding materials used in the reconstruction of the mandible are seen in yellow in the photographs, and as smooth dark brown in the CT scans. Note the generally tight contacts between adjacent bone fragments. Right p3–m3 teeth are complete whereas the anterior dentition and the teeth on the left side are fractured along the base of their crowns or are missing. This fracture pattern is typical of a tripartite guardsman fracture with fractures at parasymphysis and bilateral fractures in the subcondylar region. a, b, Left anterolateral view; c, d, right anterolateral view; e, f, superior view. Scale bars, approximately 10 mm because of angled views. See Supplementary Note 1 for a full description; also see Supplementary Videos 2, 3.
- Extended Data Figure 4: Mandible (A.L. 288-1i, -1j and -1k) CT scan. (215 KB)
CT scan of mandible (A.L. 288-1i, -1j and -1k) illustrating in red the major fractures across the parasymphyseal region, left body, and left (A.L. 288-1j) and right (A.L. 288-1k) subcondylar regions. The coronoid processes are missing and their fractured edges outlined in green. This fracture pattern is typical of a tripartite guardsman fracture with fractures at parasymphysis and bilateral fractures in the subcondylar region. a, Anterior view; b, posterior view; c, superior view; d, inferior view. e–g, Anterior views of coronal slices: e, slice through the centre of canine alveolae that shows the major parasymphyseal fractures; f, slice at mesial edge of m3; and g, slice through mesial edge of coronoid process that shows the position of the right and left subcondylar fractures. Scale bar, 10 mm. See Supplementary Note 1 for a full description; also see Supplementary Videos 2, 3.
Extended Data Tables
- Video 1: Right humerus (A.L. 288-1m) and scapula (A.L. 288-1l) compressive fracture reconstruction (30.46 MB, Download)
- Video of hypothetical impact scenario for the right humerus and scapula that illustrates the progression of the fracture. The "before" reconstruction of the humerus is seen in the first full rotation. Next, the fragments are colorized and the humerus is impacted into the anvil of the glenoid of the scapula, fracturing and shattering the components of the proximal humerus including the articular head, greater and lesser tuberosities, and shaft. Finally, the "after" condition is shown in the last rotation. See Methods, Extended Data Figures 1 & 2, Supplementary Note 2 for a description of the reconstruction, and Supplementary Video 4.
- Video 2: CT scan coronal slices of mandible (A.L. 288-1i, -1j & -1k) (19.35 MB, Download)
- Video of CT scan (see Methods) of the original reconstruction of the mandible illustrates the fractures across the mandible and especially those in the parasymphyseal region, left body, and subcondylar regions. Slices are in the coronal plane. The smooth dark brown regions are binding materials used in the reconstruction. This fracture pattern is typical of a tripartite guardsman fracture. See Extended Data Figures 3 & 4 for the location of the fractures, and Supplementary Note 1 for a full description.
- Video 3: CT scan sagittal slices of mandible (A.L. 288-1i, -1j & -1k) (16.22 MB, Download)
- Caption as in Supplementary Video 2. Slices are in the sagittal plane.
- Video 4: Lucy’s fall and vertical deceleration event (20.09 MB, Download)
- Stop motion video depicts a hypothetical scenario for Lucy’s fall out of a tall tree and the subsequent vertical deceleration event based on the patterning of the fractures. The first segment depicts about the last half of the fall from 7.4 m with a real time duration of 0.45 seconds, and the second segment shows a close-up of the last 2.2 m of the fall. The third segment shows a slow-motion (about 1/5 speed) close-up of the last 1.7 m of the fall. The last frame illustrates the fractures. See Figure 2 for a full description.