The joint at the base of the thumb, specifically the one between the trapezium and the first metacarpal (MC 1), has been the focus of many studies aiming at testing whether it bears signals that correlate to the different locomotor behaviors and/or to functional capabilities of the hand of extant hominids ([1-5]). is study quantifies the proximal articular surface of MC 1 using three-dimensional morphometrics in extant hominids (Homo, n = 18; Pan, n = 15; Gorilla, n = 15; and Pongo, n = 9) and fossil hominins (SK 84, cf. Paranthropus robustus and Stw 418, cf. Australopithecus aicanus) to test the following hypotheses: 1) different modes of locomotion in nonhuman hominids will show different signals in joint surface morphology; 2) humans and nonhuman hominids will have a significantly different articular surface that represents skeletal correlates to greater stability of the human trapeziometacarpal joint and greater mobility of the joint in nonhuman hominids; 3) the fossil specimen SK 84 will most closely resemble Homo; and 4) the fossil specimen Stw 418 will most closely resemble nonhuman hominids. A principal components (PC) analysis was used to compare MC 1 proximal surface shape. An ANOVA and Tukey’s HSD post-hoc test were conducted to determine whether group principal component scores are significantly different. ere is a significant result for PC 1 and an insignificant result for all other PC axes. Homo is significantly different from all nonhuman hominids for PC 1, but none of the nonhuman hominids groups are significantly different from one another. Hypothesis 1 is therefore falsified. e shape on the PC 1 axis represents a highly curved joint surface in the radioulnar and dorsovolar aspects in nonhuman hominids, and a relatively flatter surface in both aspects for Homo. In addition, Homo has a laterally extended surface that is not present in nonhuman hominids. Hypothesis 2 cannot be falsified. Both fossil specimens most closely resemble the nonhuman hominids, and do not overlap Homo on the PC 1 axis. Hypothesis 3 is therefore falsified, and hypothesis 4 cannot be falsified. Neither of the fossils demonstrates shape associated with a more stable trapeziometacarpal joint. e specimen Stw 418 occupies a location for PC 1 and PC 2 that shows a relatively shallower surface in the radioulnar and dorsovolar aspects, and lacks lateral extension of the surface associated with Homo. SK 84 occupies a similar location to Stw 418 on PC 1, but it is on the opposite side of the axis for PC 2. Its location shows a surface that is shorter in the dorsovolar aspect, and more highly curved in the radioulnar aspect. SK 84 also lacks the lateral extension associated with Homo. Overall the three-dimensional characterization of the proximal MC1 articular surface is in agreement with previous studies ([2, 4]) that used different methods to quantify articular curvature; moreover, this study highlights the presence of a trait (a laterally extended surface) present in Homo that could be related to human manipulation activities. Both fossils analyzed here shows a primitive MC 1 proximal articular surface shape probably indicating lack of the distinctive human morphology that facilitates forceful precision and power gripping.
Proximal metacarpal 1 articular surface shape in human and nonhuman hominids: its relationship with locomotion and hand functional capabilities
MARCHI, DAMIANO;
2015-01-01
Abstract
The joint at the base of the thumb, specifically the one between the trapezium and the first metacarpal (MC 1), has been the focus of many studies aiming at testing whether it bears signals that correlate to the different locomotor behaviors and/or to functional capabilities of the hand of extant hominids ([1-5]). is study quantifies the proximal articular surface of MC 1 using three-dimensional morphometrics in extant hominids (Homo, n = 18; Pan, n = 15; Gorilla, n = 15; and Pongo, n = 9) and fossil hominins (SK 84, cf. Paranthropus robustus and Stw 418, cf. Australopithecus aicanus) to test the following hypotheses: 1) different modes of locomotion in nonhuman hominids will show different signals in joint surface morphology; 2) humans and nonhuman hominids will have a significantly different articular surface that represents skeletal correlates to greater stability of the human trapeziometacarpal joint and greater mobility of the joint in nonhuman hominids; 3) the fossil specimen SK 84 will most closely resemble Homo; and 4) the fossil specimen Stw 418 will most closely resemble nonhuman hominids. A principal components (PC) analysis was used to compare MC 1 proximal surface shape. An ANOVA and Tukey’s HSD post-hoc test were conducted to determine whether group principal component scores are significantly different. ere is a significant result for PC 1 and an insignificant result for all other PC axes. Homo is significantly different from all nonhuman hominids for PC 1, but none of the nonhuman hominids groups are significantly different from one another. Hypothesis 1 is therefore falsified. e shape on the PC 1 axis represents a highly curved joint surface in the radioulnar and dorsovolar aspects in nonhuman hominids, and a relatively flatter surface in both aspects for Homo. In addition, Homo has a laterally extended surface that is not present in nonhuman hominids. Hypothesis 2 cannot be falsified. Both fossil specimens most closely resemble the nonhuman hominids, and do not overlap Homo on the PC 1 axis. Hypothesis 3 is therefore falsified, and hypothesis 4 cannot be falsified. Neither of the fossils demonstrates shape associated with a more stable trapeziometacarpal joint. e specimen Stw 418 occupies a location for PC 1 and PC 2 that shows a relatively shallower surface in the radioulnar and dorsovolar aspects, and lacks lateral extension of the surface associated with Homo. SK 84 occupies a similar location to Stw 418 on PC 1, but it is on the opposite side of the axis for PC 2. Its location shows a surface that is shorter in the dorsovolar aspect, and more highly curved in the radioulnar aspect. SK 84 also lacks the lateral extension associated with Homo. Overall the three-dimensional characterization of the proximal MC1 articular surface is in agreement with previous studies ([2, 4]) that used different methods to quantify articular curvature; moreover, this study highlights the presence of a trait (a laterally extended surface) present in Homo that could be related to human manipulation activities. Both fossils analyzed here shows a primitive MC 1 proximal articular surface shape probably indicating lack of the distinctive human morphology that facilitates forceful precision and power gripping.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
