Elements of the axial skeleton recovered from the Hadar formation 1974Ц1977 collections.код для вставкиСкачать
AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 57531-635 11982) Elements of the Axial Skeleton Recovered From the Hadar Formation: 1974-1 977 Collections C. OWEN LOVEJOY, DONALD C. JOHANSON, AND W E S COPPENS Departments of Anthropology and Bwlogy, Kent State University, Kent, Ohio 44242 fC.OL.1;Department of Orthopaedic Surgery, Case Western Reserve University, Cleveland, Ohio 44106fC.OL.);Cleveland Museum of Natural History, Cleveland, Ohio 44106 fC.OL,D.C.J.);Znstitute of Human Origins, 2700 Bancroff Way, Berkeley, California, 94704 (D.CJ.); Department of Human Anatomy, Northeast Ohio Universities College of Medicine, Rootstown, Ohio 44272 fC.OL.1,and Laboratoire d'Anthropologie, Musde de l'Homme, Paris 75016, France (Y.C.) KEY WORDS Hadar, Vertebrae, Ribs, Hominid, Australopithecus ABSTRACT Anatomical descriptions are presented for the rib and vertebral elements recovered from the Hadar Formation during the 1974-1977 field seasons, inclusive. The following are anatomical descriptions of the elements of the axial skeleton recovered by the International Afar Research Expedition during the field seasons of 1974-1977, inclusive (Johanson et al., this volume). Anatomical nomenclature follows general usage and Trotter and Peterson (1966). Mensuration is included appropriate to the completeness and condition of each specimen. Metrics employed are either those in general use or are specifically described. The vertebral specimens have been given individual description. Rib specimens are presented without further comment in Table 1. While extensive radiography and computed automated tomography were performed on many of the specimens described below, the density of the Hadar fossils makes interpretation difficult and these results are not included at this time. Morphometric, biomechanical, and kinematic studies are currently in progress and results will be reported subsequently. Vertebral and rib elements of the A.L. 288-1 partial skeleton are described in Johanson et al. (this volume). DESCRIPTIONS A.L. 333-51: Thoracic Vertebra (no figure) The specimen is an adult centrum from a midthoracic vertebra. It is in excellent preservation, although the arch was truncated from the body cleanly a t its base. Both superior and inferior surfaces bear demifacets, so it may be restricted in number between two and nine. 0002-948318215704-0631$02.00G 1982 ALAN R. LISS. INC. The superior surface is heart-shaped, with the anterior portion distinctly triangular. The more compact cortical bone formed by the adhesion and fusion of the ring apophysis is unusually broad, with a n average transverse dimension of 6.8 mm. The inferior surface appears more typical of modern human vertebrae, although its surface is less clearly interpreted because of adhering matrix that cannot be safely removed. Both the superior and inferior demifacets are quite large. There appears to be very mild osteophytosis in its earliest stage of development. The specimen is probably from a young adult. The vertical thickness of the centrum taken anteriorly is 16.8 mm. Taken posteriorly it is 18.4 mm. The transverse breadth of the superior surface is 24.8 mm, and that of the inferior is 31.4 mm. The anteroposterior length along the midline of the superior surface is 20.8 mm; that of the inferior 21.8 mm. A.L. 333-73: Lumbar Vertebra (Fig. 1D,F) The specimen is a lumbar vertebral body with no associated arch. The base of the right pedicle is preserved. The entire surface of the specimen has been badly abraded, but it has retained its original shape. Only the lateral and posterior surfaces of the body have original surface intact. All other areas of the specimen have lost a thin layer of surface bone, although this has had only minimal metrical affect. The inferior central rim is broken away on the right Received March 17, 1981; accepted December 10,1981. 632 LOVEJOY, JOHANSON, AND COPPENS TABLE I . Costal skeleton metrics frnm.) Suecimen A.L. 333-118 333w-17 333w-18 333w-19 333w-30 333~-41 333w-44 333w-45 333w-47 Portion Dreserved Side Head Proximal Proximal Middle Distal Left Head Middle Right Robable number Maximum dimension S1 height AP breadth SI height Costochondr. jct. ML breadth Costochondr. jct. 1 1-3 2-3 31.0 25.0 42.5 65.0 63.7 11.2 12.2 7.5 8.3 15.7 10.9 24.4 52.8 11.9 5.9 3-10 3 A.L. 333-83: Altas (Fig. lG,H) The specimen is a fragment from the left side of an atlas vertebra. It includes the superior and inferior articular surfaces and a portion of the posterior arch. The superior articular pit is well preserved although there are two fossilization cracks near its anterior extremity. These have been naturally retained in perfect apposition. The groove for the vertebral artery just posterior to the pit is well preserved and is deep and broad. The transverse process has been truncated cleanly from the articular process a t both points of attachment. A portion of the posterior arch is preserved but is truncated before midline. The area in which the tubercles for the transverse ligament should be represented has suffered mild damage, which has obscured observation of this feature. The articular pits are deep medially and high latA.L. 333-81: Immature Thoracic Centrum erally, resulting in a very steep articular wall, (Fig. 1 A B ) considerably steeper than in modern human The specimen is the body of an immature specimens. The maximum overall dimension is 34.0 thoracic vertebra. This assignation is based on the condition of the superior and inferior sur- mm. The inferior facet has a breadth of 11.3 faces of the centrum, which indicate no fusion and a length of 16.1 mm. The superior facet of the ring apophyses. The arch has been trun- has a breadth of 10.8mm. cated from the body through the right pedicle A.L. 333-101: Axis Vertebra (no &we) and the left lamina, removing approximately one-third of the articular facet on the left side. The specimen is a complete axis vertebra. The specimen has a very small body, but bears Unfortunately, it is so badly abraded that esboth upper and lower demifacets, so it is prob- sentially no surface was left intact, such that ably either a second or third thoracic. The su- only the outline core of the specimen is preperior surface is gently convex, whereas the served. No further description is warranted at inferior surface is moderately concave. There this time. is a central vascular pit in the posterior side A.L. 333-106: Cervical Vertebra (Fig.1CJ) of the centrum for the basivertebral vein. The specimen is an essentially complete The anterior height (superoinferior) of the specimen is 11.8mm; posteriorly it is 12.0mm. lower cervical vertebra. The specimen is adult The anteroposterior centrum diameter supe- and in excellent condition. Both transverse processes have suffered breakage of their distal riorly is 14.2mm; inferiorly it is 15.5 mm. side and is composed of three major apposed fragments on the left. There has been slight distortion as a consequence of imperfect apposition. A sufficient amount of pedicle base is preserved on the left side to indicate that no rib facet was present (hence the lumbar status of the specimen). The most notable features of the specimen are the great height of the body (relative to its other dimensions), and general size. The ring apophyses are fused and the specimen is fully adult. The superoinferior height of the centrum taken anteriorly is 25.0 mm; taken posteriorly it is 24.5 mm. The mediolateral breadth of the inferior surface is 37 .Omm; the anteroposterior length, 24.1 mm. The same measures for the superior surface are 34.0 and 22.7 mm, respectively. HADAR AXIAL SKELETON tips; the spinous process has a minor fossilization crack a t its base of no consequence. The right lamina is traversed by a small crack; the left pedicle is also traversed by a small crack with slight bone loss. Otherwise the specimen is essentially complete and undistorted. The foramina1 area for the basivertebral vein is bifid and bisected by a large bony ridge running superoinferiorly. The foramina for the vertebral arteries are both single and are of approximately equal size. The spinous process is not bifid. The vertebral foramen is large and ovoid, showing relative anteroposterior elongation. The centrum is unusually small relative to the remainder of the specimen. The superior articular surface of the body is typically concave, with marked angulation of the posterolateral lips. The anterior and posterior tubercles of the transverse process are thin and ridge-like, and in general quite gracile. The superior surface of the costotransverse bar bears a deep mediolateral groove (between the anterior and posterior processes). The spinous process is very long, and shows almost no angulation with respect to the plane of the inferior central surface. It is probably a C-6 or c-7. The superior centrum breadth (mediolateral) is 20.5 mm. The length of the spinous process from posterior tip to the vertebral canal is 28.2 mm. The maximum transverse breadth along an axis over both articular facets is 42.5 mm. The internal transverse and anterosuperior dimensions of the spinal canal are 18.0 and 12.6 mm, respectively. A.L. 333w-8:Vertebral Fragment (no figure) The specimen is a fragment of an adult vertebral body. Only the anterior one-third is preserved. Both superior and inferior surfaces are badly eroded. The anterior surface is coated with matrix that cannot be safely removed. No significant morphology is preserved. A.L. 333w-14:Vertebral Spine (no figure) The specimen is the spine of an adult cervical vertebra. No portion of the remainder of the neural arch is preserved. Its apex is not bifid. Its base is large and triangular, and the specimen as a whole is considerably robust. A.L. 333x-12:Thoracic Vertebra (Fig. 2) This is a complete midthoracic or lower thoracic vertebra. While the specimen has good surface morphology and is virtually complete, it has suffered considerable distortion of a cryptic type (mostly as the result of plastic de- 633 formation). This distortion lies in the juncture between the body and neural arch. The most direct way of viewing this change is in lateral view. In this view the inferior vertebral notch can be seen to be unusually V-shaped and not U-shaped. This condition has resulted from some downward compression and superiorward shear of the pedicles, i.e., the specimen has been anteroposteriorly shortened and the neural arch moved superiorly in this process. The external aspects of both pedicles display bony evidence of this process. On the right side there is a prominent ridge of extruded bone along the lateral aspect of the pedicle near the shear crack. On the left, the area is dissected and slightly fragmented. While the body is otherwise undistorted, the neural arch bears several large and many minor fossilization cracks. A large matrix-filled crack traverses the left lamina from the superior articular facet to the inferior articular facet, resulting in some expansion. On the right side, the midpoint of the transverse process is traversed by a crack, which is matrix-filled. The process appears otherwise undisturbed at first glance, but the cryptic nature of the distortion of this specimen is brought out well in this location. The right transverse process is considerably shorter than the left, and its terminal process expanded, with marked rotation of the rib facet. A second fossilization crack runs longitudinally along its centroidal axis. The plastic deformation and crushing of the specimen have produced these changes, which at first sight appear only as minor defects because of the compaction of the bone. The distal half of the spinous process has been fractured and rejoined with some posterior deviation of the distal segment. The laminae are traversed by numerous fossilization cracks of no great consequence, although the bone surface has been largely disrupted by this process. In general, in addition t o the changes described for the transverse process on the right side, the entire neural arch has been translated superiorly and anteriorly, which has also altered the angle of the rib facets and the spinous process. The latter should be more angulated to the plane of the centrum, and the rib facets should face more laterally. The inferior vertebral notch should be more U-shaped and more open than is presently the case. The specimen is subadult. There is no evidence of any ring fusion and the characteristic subapophyseal morphology of the centrum surface is evident. The tip of the spinous process does not bear a fused epiphysis. The specimen is probably a T-7, T-8,or T-9; it is most likely Fig. 1. A, A.L. 333-81, inferior; B, A.L. 333-81, superior; C, A.L. 333-106, inferior; D, A.L. 333-73, inferior; E, A.L. 333106, 333-106. superior, F,A.L. 333-73, superior; G, A.L. 333-83, superior; H, A.L. 333-83, inferior. 635 HADAR AXIAL SKELETON a T-7. There is a very large expanded crack through the inferior articular facet. The right superior facet has had its superior tip broken away. The articular facets are otherwise in good condition* Save for cracks that have no metric significance. There has been abrasion of several areas of the lateral walls of the body. Once corrected for distortion, the specimen bears a remarkable similarity to modern human vertebrae. LITERATURE CITED Trotter. M, and Peterson, R (1966) Osteology. In ELJ Anson (ed): Morris' Human Anatomy. New York: Saunders, pp, 133-315. A B Fig. 2. A, A.L. 333X-12, posterior (specimen inverted); B, A.L. 333X-12, inferior.