# The Earliest Known Radiation of Pitheciine Primates

## TL;DR

This paper shows that two ancient Patagonian primates, Soriacebus and Mazzonicebus, are early members of the pitheciine lineage, not distant relatives, based on dental and phylogenetic analysis.

## Contribution

The study provides the first strong evidence that Soriacebus and Mazzonicebus are deeply nested within the pitheciine clade, supporting the Long Lineage Hypothesis.

## Key findings

- Soriacebus and Mazzonicebus are sister-taxa within the pitheciid clade, not stem platyrrhines.
- Differences between these fossils and younger pitheciines are explained by more primitive character states.
- Shared dental adaptations confirm their status as early pitheciines.

## Abstract

Two of the more interesting and controversial platyrrhine primate taxa from the Miocene of Patagonia are Soriacebus and Mazzonicebus. Although they are known basically from isolated teeth and partial mandibles and maxillae, their morphology is highly distinctive. Opinions about their phylogenetic relationships differ widely. We interpret these fossils as belonging to the lineage of the anatomically derived, living pitheciine seed‐predators; others hold the view that they are stem platyrrhines with convergent adaptations with pitheciines (with the single exception of Proteropithecia among the Patagonian forms), somewhat distant relatives converging coincidently with pitheciines. Here we tested these hypotheses in two ways: (1) by summarizing a character analysis of taxonomically informative traits; (2) we implemented “blind” parsimony analyses using the software package TNT, including a combined matrix of both morphological and molecular data, and replication studies of other matrices. We make some criticisms on the applied methodology of Parsimony in our analysis. Soriacebus and Mazzonicebus resulted sister‐taxa nested deeply within the pitheciid clade; thus, and according to our inferences, they are not stem platyrrhines. Most of the differences separating them from the younger and uniformly recognized pitheciine fossils Proteropithecia, Nuciruptor and Cebupithecia are explained as being of more primitive character states; the vast majority of resemblances and their broader functional patterns are definitively pitheciine, as typified by the living pitheciines (sakis and uakaris). We therefore found that none of the Miocene Patagonian genera treated here can be reliably interpreted as stem platyrrhines. Rather, they tend to ratify the Long Lineage Hypothesis.

Right mandible and dentition of the holotype of Soriacebus ameghinorum (MACN Pv SC2), from the Early Miocene of Patagonia, compared with the living Cacajao calvus (FMNH 88813, cast), both representing extinct and extant morphologies of the Pitheciinae: Procumbent and styliform incisors and projecting canines represent a morphological complex for sclerocarpic harvesting, a key dietary adaptation of pitheciines. As summarized in the present work, the morphology of the anterior dentition shows a remarkable adaptation shared by both species, being Soriacebus, as well as Mazzonicebus and Proteropithecia, early representatives of the subfamily.

The pitheciine primates include the living sakis and uakaris, as well as their fossil relatives since the Early Miocene.Morphology and molecules support the view that Patagonian pitheciines are part of the crown Platyrrini.

The pitheciine primates include the living sakis and uakaris, as well as their fossil relatives since the Early Miocene.

Morphology and molecules support the view that Patagonian pitheciines are part of the crown Platyrrini.