Platyrrhines, PAUP, parallelism, and the Long Lineage Hypothesis: A reply to Kay et al. (2008)

Kayet al. (2008) presented aparsimony (PAUP) analysis of platyrrhines involving a craniodental database of 268 characters, several targeted Patagonian fossils, Tarsius, and 29 anthropoid genera. Their core conclusion challenges a central idea about platyrrhine evolution, but it is flawed by interlocking problems concerning research design, data quality, and methodology. This conclusion rests on a weakly supported cladistic artifact, a purported monophyletic group of southern platyrrhines involving four poorly known, unevenly preserved, barely comparable sets of fossils that emerged by default, juxtaposed against a grouping of essentially modern platyrrhine genera, 94% of which are living forms represented by effectively complete datasets. To rationalize these results, Kay et al. (2008) oddly misconstrue the nature of phylogenetic, functional, and adaptive evidence in historical evolutionary reconstruction, using false analogies. And, their argument ignores the body of evidence supporting the evolutionarymodel they seek to refute, the Long Lineage Hypothesis (LLH). The LLH proposes that modern NewWorld monkeys (NWM) are characterized by a relatively large number of long lived genera and subclades (e.g., Rosenberger, 1979, 1992, 2002; Delson and Rosenberger, 1984; Rosenberger et al., 2009). Predicated on an ecophylogenetic study of all platyrrhines known up until 1979 and a major reorganization of NWM systematics, its central hypotheses sought to establish: 1) direct fossil evidence that three of the 16 modern platyrrhine genera, Saimiri, Alouatta, and later Aotus could have arisen within or earlier than the approximately 11e20 Ma time bracket while a fourth, Cebus, the living sister-taxon of Saimiri, was inferred to be equally as old; 2) generic distinctions between the La Venta fossils Stirtonia and Alouatta and the modern Neosaimiri and Saimiri, respectively, were questionable; 3) withinlineage morphological continuity between these sets was evidence for stasis; and, 4) modern NWM differentiation has deeper temporal roots than comparable catarrhine splits. Two Patagonian fossils, Tremacebus and Dolichocebus, at about 20 Ma, were identified as the oldest affiliates of the modern taxa, related to Aotus and Saimiri, respectively; the broader affinities of Dolichocebus as a cebine (hence the Cebus-Saimiri clade) were also explicitly discussed (e.g., Rosenberger et al., 1990). Kay et al. (2008) argued instead that Tremacebus andDolichocebuswere part of a four-genus, southern “stem platyrrhine” group, proving that NWM evolution unfolded in a more “layered” fashion. A fifth Argentine genus, Homunculus, was held to be part of this group but it was not analyzed (see below), while the older Bolivian fossil, Branisella, fell outside it. Although Kay et al. (2008) make no mention that the LLH has been corroborated independently by distinctly different types of data and varied methods of analysis since it was proposed, numerous molecular studies (e.g., references in Opazo et al., 2006) have confirmed the majority of the underlying cladistic hypotheses (e.g., Schneider and Rosenberger, 1997; Schneider et al., 2001; Rosenberger, 2002) and uniformly support the early differentiation model. The median ages (in millions of years) of the divergence of critical genera and subclades calculated from Schrago’s (2007) summary of six projects gives the following: Aotus, 17.6; Callicebus, 15.4; Alouatta, 13.7; Callimico, 9.7; Cebus and Saimiri, 16.5; cebines vs. callitrichines, 19.9; cebids vs. atelids, 20.1. A separate study (Opazo et al., 2006), for reference, yields even older divergence dates: Aotus, 22; Callicebus, 19.3; Alouatta, 16.8; Callimico, 12.1; Cebus vs. Saimiri, 19.5; cebines vs. callitrichines, 22.8; cebids vs. atelids, 24.4. Another recent molecular study (Hodgson et al., 2009) inveighed against the LLH, saying “The MRCA [most recent common ancestor] of the living platyrrhines is estimated to have lived 19.5 Ma (95% credibility interval 16.8e23.4 Ma).” and specifying that Dolichocebus and Tremacebus thus cannot be E-mail address: alfredr@brooklyn.cuny.edu