Return of a lost structure in the evolution of felid dentition revisited: A DevoEvo perspective on the irreversibility of evolution

There is a longstanding interest in whether the loss of complex characters is reversible (so-called “Dollo’s law”). Reevolution has been suggested for numerous traits but among the first was Kurtén (1963), who proposed that the presence of the second lower molar (M 2 ) of the Eurasian lynx ( Lynx lynx ) was a violation of Dollo’s law because all other Felids lack M 2 . While an early and often cited example for the reevolution of a complex trait, Kurtén (1963) and Werdelin (1987) used an ad hoc parsimony argument to support their proposition that M 2 reevolved in Eurasian lynx. Here I revisit the evidence that M 2 reevolved in Eurasian lynx using explicit parsimony and maximum likelihood models of character evolution and find strong evidence that Kurtén (1963) and Werdelin (1987) were correct – M 2 reevolved in Eurasian lynx. Next, I explore the developmental mechanisms which may explain this violation of Dollo’s law and suggest that the reevolution of lost complex traits may arise from the reevolution of cis-regulatory elements and protein-protein interactions, which have a longer half-life after silencing that protein coding genes. Finally, I present a model developmental model to explain the reevolution M 2 in Eurasian lynx.