Way back in 2006 I included Antillothrix bernensis in my “know your primate” series. At that point there wasn’t much to say;
Skeletal analysis of A. bernensis (primarily of the teeth) indicate a close relationship with Paralouatta varonai. A. bernensis was a midsized primate, and weighed around 2-5 kg. Since the skeletal material for A. bernensis is scanty (consisting mainly of a lower jaw and a tibia) not much else is known about the species. One point of interest. The teeth of A. bernensis are similar to P. varonai and because of that paleoanthropologists were able to determine that the resemblances between P. varonai and Alouatta are due to convergence rather than a close phylogenetic relationship.
However a recent paper in the Proc. R. Soc. B. by a group headed by Alfred Rosenberger has added some more information. The paper reports on a nearly complete cranium (lacking the mandible), a femur, an ulna, one vertebrate, and five ribs. The find was discovered in the Dominican Republic in La Jeringa Cave. At this point a date has not been determined. The find is, at this point, considered to be that of a young male and throws some interesting light on platyrrhine evolution. There is currently a debate concerning how primates, such as Xenothrix and Paralouatta populated the Carribean. One theory is that:
MacPhee and co-workers (e.g. ) proposed that all these primates radiated from a sole ancestral species linked cladistically with the mainland pitheciine atelid Callicebus. Rosenberger  argued instead that at least two clades were present, one embodied by Paralouatta, related to howler monkeys, and another by Xenothrix, possibly related to Aotus—or to Callicebus, according to his earlier view.
Rosenberger et al argue that Antillothrix bernensishas morphology more primitive than modern cebids and resembles Killikaike blackei and Dolichocebus. They also argue that Xenothrix, and Paralouatta represent unique clades related to Aotus and howler monkeys respectively – as you can see from the phylogeny below.
Consequently, Rosenberger et al argue that three species are relicts derived from an early mainland platyrrhine radiation.
Rosenberger et al (2010) First skull of Antillothrix bernensis, an extinct relict monkey from the Dominican Republic. Proc. R. Soc. B.