(Elhuyar Fundazioa) The Ikerbasque researcher Raúl Pérez-Jiménez of nanoGUNE's Nanobiomechanics group has led a piece of research in which, starting from the sequences of the titin protein of a selection of modern day animals, they inferred the phylogenetic tree of tetrapods (all animals with four limbs including mammals, birds, reptiles and amphibians), and reconstructed the sequence that this protein would have had in the common ancestors of these animal groups.