Bipedalism in Glyptodon Clavipes (Mammalia, Xenarthra): the results of a biomechanical model

Glyptodont clavipes (Cingulata, Glyptodontidae) was a massive mammal with a rigid carapace for which bipedalism has been proposed. In this work, bipedal posture is explored by way of a biomechanical model that has been previously tested in extant
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  Elissamburu Andrea-ms 2015 1 Bipedalism in Glyptodon Clavipes  (Mammalia, Xenarthra): the results of a biomechanical model.  The manuscript is accepted with minimal corrections by the 50% of the reviewers, and it is rejected by the other 50% of the reviewers, so it is not published. I disagree with the opinion about the work is not a valuable contribution to the knowledge, so I pass the work to which can be interested in it. It work can be an interesting contribution to some study areas and it can promote the knowledge. The work gives a postural analysis of the bipedal stance of Glyptodon clavipes  (here is proposed that G. clavipes  could adopt a bipedal posture with the body trunk in a horizontal position, similar to living armadillos), but besides this, the biomechanical model presented can predict the body trunk posture needed to adopt a bipedal stance; and I think it can be of interest to study some hominids, among other possibilities. Additionally, body proportions that supporting a bipedal posture are given. I hope It work be of interest and can give you some contribution. I am very grateful by possible comments about the work or by future references to this manuscript. Sincerely, Dr. Andrea Elissamburu Bipedalism in Glyptodon Clavipes  (Mammalia, Xenarthra): the results of a biomechanical model.  Es un manuscrito que, en resumen, el 50% de los revisores lo aceptan con modificaciones mínimas y alientan su publicación, mientras que el otro 50% lo rechaza diciendo que creen que no sirve o no es un aporte al conocimiento, por lo que el trabajo no ha salido publicado. Estoy en desacuerdo con que no sirva o no sea un aporte valorable, por lo que lo dejo al alcance del que le interese leerlo. Puede ser una aporte interesante para algunas áreas de estudio y puede promover el conocimiento mismo. Más allá del análisis postural de Gliptodon clavipes  (para el que se propone podría pararse bípedamente manteniendo una posición casi horizontal de la columna vertebral, similar a lo que sucede en algunos armadillo vivientes) el modelo biomecánico presentado predice la postura que el cuerpo tiene que adoptar para mantener una postura bípeda, que creo puede ser de interés para la aplicación en estudio de homínidos, entre otros casos. Además se dan proporciones del cuerpo que respaldan la posibilidad de pararse o no en las patas traseras. Espero que este trabajo sea de vuestro interés y pueda servir en algún punto como contribución. Agradezco desde ya los posibles comentarios sobre el trabajo y futuras referencias a este manuscrito. Sinceramente Dr. Andrea Elissamburu  Elissamburu Andrea-ms 2015 2 Bipedalism in Glyptodon Clavipes  (Mammalia, Xenarthra): the results of a biomechanical model 1 Elissamburu Andrea. CONICET. Cátedra de Anatomía Comparada, Facultad de Ciencias Naturales 2 y Museo de La Plata, Calle 64 s/n entre calle 120 y diagonal 113, laboratorio 13, 1900 La Plata, 3 Argentina.   4 5 Corresponding author:   Elissamburu Andrea, Cátedra de Anatomía Comparada, Facultad de 6 Ciencias Naturales y Museo de La Plata, Calle 64 s/n entre calle 120 y diagonal 113, laboratorio 7 13, 1900 La Plata, Argentina. E-mail: 8 9 10 11 12 13 14  Elissamburu Andrea-ms 2015 3 ABSTRACT 15 Glyptodont clavipes  (Cingulata, Glyptodontidae) was a massive mammal with a rigid carapace for 16 which bipedalism has been proposed. In this work, bipedal posture is explored by way of a 17 biomechanical model that has been previously tested in extant mammals, and the predictions are 18 supported with biomechanical and morphofunctional approaches. I show that G. clavipes  could 19 adopt a bipedal posture rest its mass on the hind limbs while maintaining its trunk in a horizontal 20 position, leaving forelimb free of its body support function. This work clarifies the bipedalism of G. 21 clavipes  and discusses its biological importance for locomotion and other biological functions. 22 Additionally, limb and body proportions needed to adopt bipedal stance in quadruped mammals, 23 and a model that may be used to interpret bipedal postures in extant and fossil mammals is given, 24 thus offering a new means to study bipedalism. 25 26 Keywords: Biomechanics, bipedal posture, bipedal locomotion, Glyptodon clavipes , paleoecology. 27 28 29 30 31 32  Elissamburu Andrea-ms 2015 4 1.Introduction 33 Glyptodon   clavipes  Owen 1839 (Xenarthra, Cingulata) is a member of the Glyptodontidae, 34 which lived in South America and southern North America during the Pleistocene (Bonaerense and 35 Lujanense (Carlini and Scillato-Yané, 1999). It   was a massive herbivorous mammal of 2,000 kg 36 (Fariña, 1995) with a rigid carapace lacking mobile bands (Rose and Gaudin, 2010). 37 Glyptodonts are related to living armadillos. Traditionally the cingulates have been split into 38 two groups of superfamily or family-level status; the Dasypodoidea/Dasypodidae included the 39 living and extinct armadillos and the pampatheres, and the Glyptodontoidea/Glyptodontidae 40 typically included only the glyptodonts, although some authors suggest a shared common ancestry 41 between glyptodonts and pampatheres (Engelmann, 1985). 42 Although paleobiological reconstructions historically have show to Glyptodon  in 43 quadrupedal posture, a possible erect bipedal posture was proposed twenty years ago, hypothesizing 44 bipedal locomotion, or as a posture needed to copulation, to display behavior, or to fighting routines 45 (Fariña, 1995). This hypothesis had not a solid morphological and functional support (e.g., 46 morphology of the carapace and pelvis do not permit a erect bipedal posture, see discussion) and the 47 erect bipedal posture was not tested in dept. Some other works suggest that bipedal posture in 48 glyptodonts would had favored the use of the tail in intraspecific fighting (Alexander et al., 1999; 49 Vizcaíno et al., 2011), or in defense, feeding or observation; these supported by a center of mass 50 displaced backwards and with greater proportion of body mass resting on hind limbs than on 51 forelimbs (Vizcaíno et al., 2011). Additionally, it was proposed that as consequence of bipedalism, 52 forelimbs were liberated from their function of body support and could be able to act on the 53 substrate for digging (Vizcaíno et al., 2011; Milne et al., 2009), although there are doubts about it 54 because the structure of forelimbs could be related to body mass support and not to dig (Vizcaíno et 55 al., 2011, Milne et al., 2009). Some of these behavioral hypothesis lacked rigorous biomechanical 56 explanations (e.g., the use of the tail in intraspecies fighting and the digging capacity, see 57  Elissamburu Andrea-ms 2015 5 discussion). However, bipedal posture could have favored different behaviors and locomotion 58 functions, as to improve locomotion for get along better at displacements in counteraction to 59 rigidity of movements imposed by the carapace. 60 The erect bipedal posture of G . clavipes  was proposed based on the differences in values of 61 the index of athletic capacity (IAC) found between the humerus and the femur in a quadrupedal 62 stance (Fariña, 1995). The value of the humerus (11 GPa -1 ) is lower than the value of the femur (22 63 GPa -1 ). Additionally, the humeral shaft diameter is lower than expected for a mammal of its size (it 64 is 0.7 of the expected value, while the femoral diameter is accord to expected), thus bipedal posture 65 could have lowered the risk of bone limb failure (Fariña, 1995; Fariña, 2001). 66 Bipedalism is defined as to go or to stand on the hind limbs (Real Academia Española, 67 2001). Generally bipedalism is approach from the different forms of bipedal locomotion 68 (Alexander, 2004). In the present work I do reference to static bipedal stance (stand on the hind 69 limbs without that it meaning possibility of going by hind limbs), to bipedal walk, bipedal run, or 70 bipedal jump (to walk, run or jump on the hind limbs, respectively). Static bipedal stance requires 71 the body to be in an equilibrium position on the hind limbs, with the center of mass projected above 72 the feet. In accord with the Support Polygon Model for static stability in bipedal forms (Gray, 73 1944), during bipedal stance the center of mass is projected to a point on the feet where the heel and 74 toes act as the points of the area of support maintaining the body. Additionally, bipedal locomotion 75 requires the center of mass to move about a point above the hind limbs, rather than within regions 76 between the fore and hind limbs. If we trace a line between the feet during the bipedal equilibrium 77 stance, the center of mass will be projected on the line. A small displacement of the center of mass 78 forward or behind the line will be balanced with limb muscular action and torque from the body and 79 the tail using balance and counterbalance between body parts respect to the area of support. While a 80 displacement of the center of mass forward the line will be related to the displacement in 81 locomotion. Taking this into account, the hind limb design (i.e., segment proportions and angles 82
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