Tracing the origin of the panda’s thumb


We investigate the relative development of the carnivoran radial sesamoids to untangle the evolution of this iconic structure. In the pandas (both giant and red), this ‘false thumb’ is known to perform a grasping role during bamboo feeding in both the red and giant pandas. An original locomotor role has been inferred for ailurids, but this remains to be ascertained for ursids. A large sample of radial sesamoids of Indarctos arctoides from the Miocene of Batallones-3 (Spain) indicates that this early ailuropodine bear displayed a relatively hypertrophied radial sesamoid, with a configuration more similar to that of the red panda and other carnivorans than to that of giant pandas. This false thumb is the first evidence of this feature in the Ursidae, which can be linked to a more herbivorous diet. Moreover, in the two extant pandas, the false thumb should not be interpreted as an anatomical convergence, but as an exaptive convergence regarding its use during the bamboo feeding, which changes the evolutionary view of this singular structure.

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This study was supported by the Spanish Ministerio de Economía y Competitividad (CGL2011-25754, CGL2011-28681 and RYC–2009–04533 to D.M.A.), the Universidad Complutense de Madrid (BSCH-UCM910607) and the Generalitat de Catalunya (2009 SGR 754 GRC and 2014 SGR 416 GRC). J.A. thanks the ‘Proyecto Prometeo’ of the ‘Secretaria de Educación Superior, Ciencia Tecnología e Innovación’, Republic of Ecuador. A.V. is a researcher in formation in the CSIC program JAE-PRE_CP2011 (CSIC program ‘Junta para la ampliación de estudios’), co-funded by the European Social Fund and has received funding from the European Union’s Seventh Framework Programme (FP7/2007–2013) under grant agreement no. 226506 (SYNTHESYS; SE-TAF-3637), the USC School of Medicine (Columbia, South Carolina, USA) and the AMNH (Collection Study Grant Programme 2014). M.D.E. thanks the MACN for a PhD student grant. We are indebted to S. Roussiakis for photographs of the radial sesamoid of I. punjabiensis from Pikermi; to S. Wallace, M.A. Nieto Cambra, R. Portela Miguez, E. Westwig, D. Lunde, E. López Errasquin, D. Kalthoff, P. Moreno, F. Pastor, D. Flores and S. Lucero and D. Verzi and I. Olivares for the access to comparative material under their care; to M. Bastir (Paleoanthropology Group, MNCN, Spain) for the scans of the radius and ulna of I. arctoides; to Louis de Bonis for his recommendations on the manuscript; to Ó. Sanisidro for Fig. 1; and to the editors and the many reviewers who helped us to improve this manuscript.

Authors’ contribution

J.A., P.M. and J.M. conceived and designed the experiments. J.A., A.P.R. and A.V. performed the experiments. J.A., M.D.E. and A.V. analysed the data. J.A., A.V., A.P.R. and D.H. contributed reagents/materials/analysis tools. J.A., D.M.A. and J.M. wrote the paper.

Author information

Correspondence to Juan Abella.

Additional information

Communicated by: Sven Thatje

Electronic supplementary material

Below is the link to the electronic supplementary material.

Video showing the grasping action of the right forepaw, based on the fossil remains of Indarctos arctoides from Batallones 3. This video only shows the last phase of the movement, since supination of the forepaw and flexion of carpals and metacarpals occur prior to the digit flexion shown here. (AVI 2443 kb)

Supporting Information Table 1 (SIT 1)

List of taxa included in the comparative sample, which includes skeletons of extant and extinct carnivorans, showing sample size (N), species name, housing institution and catalogue number. (DOCX 153 kb)

Supporting information Video 1 (SIV1)

Video showing the grasping action of the right forepaw, based on the fossil remains of Indarctos arctoides from Batallones 3. This video only shows the last phase of the movement, since supination of the forepaw and flexion of carpals and metacarpals occur prior to the digit flexion shown here. (AVI 2443 kb)

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Abella, J., Pérez-Ramos, A., Valenciano, A. et al. Tracing the origin of the panda’s thumb. Sci Nat 102, 35 (2015).

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  • Cerro de los Batallones
  • Late Miocene
  • Radial sesamoid
  • Carnivora
  • Ursidae