Acknowledgments
The author would like to thank Miguel Pereira Lopes, Pedro Correia and Traute Meyer for helpful discussions and Arjun Bedi, Catarina Grilo, Tiago Mata, and the editor for detailed comments. Sara Grilo provided excellent research assistance. Cristina Borra, John Marcis, Peter Sloane, Richard Freeman and Timothy Hinks kindly provided information to complete the dataset.