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. 2009 Nov 22;276(1675):3971-8.
doi: 10.1098/rspb.2009.1144. Epub 2009 Aug 26.

The sweet spot of a biological hammer: the centre of percussion of glyptodont (Mammalia: Xenarthra) tail clubs

Affiliations

The sweet spot of a biological hammer: the centre of percussion of glyptodont (Mammalia: Xenarthra) tail clubs

R Ernesto Blanco et al. Proc Biol Sci. .

Abstract

The importance of the centre of percussion (CP) of some hand-held sporting equipment (such as tennis rackets and baseball bats) for athletic performance is well known. In order to avoid injuries it is important that powerful blows are located close to the CP. Several species of glyptodont (giant armoured mammals) had tail clubs that can be modelled as rigid beams (like baseball bats) and it is generally assumed that these were useful for agonistic behaviour. However, the variation in tail club morphology among known genera suggests that a biomechanical and functional analysis of these structures could be useful. Here, we outline a novel method to determine the CP of the glyptodont tail clubs. We find that the largest species had the CP very close to the possible location of horny spikes. This is consistent with the inference that they were adapted to delivering powerful blows at that point. Our new analysis reinforces the case for agonistic use of tail clubs in several glyptodont species.

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Figures

Figure 1.
Figure 1.
Artistic reconstruction of Doedicurus clavicaudatus, with a human for scale. The distal rigid caudal sheath and the mobile free rings are shown. Adapted from Ubilla et al. (2008) (fig. 13.3, with permission of Perea, D. ed. 2008).
Figure 2.
Figure 2.
Lateral (above) and dorsal (below) views of caudal bony sheaths: Neosclerocalyptus spp. (a), Pseudoplohophorus absolutus (b), Panochthus tuberculatus (c), Castellanosia spp. (d), Doedicurus clavicaudatus (e). The solid circles indicate the positions of the centre of mass (xcm) and CP using 1400 kg m−3 for internal density. The error range for xcm and CP based on variations of internal density are shown. Scale bar, 15 cm.

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