Double invasion of Tertiary island South America by ancestral New World monkeys?

Abstract

Comparative Determinant Analysis was used to characterize antigenic determinants from 69 functionally diverse serum proteins for the phylogenetic study of anthropoid cladogenesis, of which 32 homologues with 66 antigenic determinants were compared betweenLagothrix lagotrichaandCebus albifrons. Nine epitopes (one each of complement factors Cls, C3, C6, C7, C9, factor B, retinol-binding protein, β2-glycoprotein III, and histidine rich α2-glycoprotein) defined a robust clade unitingLagothrix lagotrichawith the Old World primatesMacaca, PapioandHomoto the exclusion ofCebus albifrons. This tree indicates platyrrhine paraphyly or demonstrates an accelerated antigen substitution rate ofCebuswhen compared withLagothrix. Narrow phylogenetic sampling does not permit the final resolution of this problem but strongly different evolutionary rates are considered unlikely because ancestral serum protein determinants, which are plesiomorphic for Primates as an order, are equally conserved in bothCebusandLagothrix. If platyrrhine paraphyly is correct, our molecular-immunological clock estimates a divergence date ofCebusof 52·5 × 106years before present, i.e. 6·5 × 106years before the ateline clade diverged (possibly at 46·0 × 106years BP) from catarrhine ancestors. A scenario of platyrrhine paraphyly implies the necessity for double invasion of the isolated Tertiary South American island continent by primates across open ocean, and suggests a considerably earlier phylogenetic emergence of platyrrhines than is proposed by the oldest simian fossils from the Neotropics.