A group of researchers, including a professor from the Johns Hopkins University School of Medicine, has made significant discoveries regarding the anatomy and ecology of an extinct primate that roamed Hispaniola, the Caribbean island shared by Haiti and the Dominican Republic, by examining rare fossils of jaws and skull fragments.
These fossils were discovered in submerged caves in the Dominican Republic. The findings include seven skulls, five jawbones, and numerous other skeletal remains, making Cueva Macho the richest fossil site for primates in Hispaniola, according to the researchers.
The research findings were published on September 30 in the Journal of Human Evolution.
Evidence suggests that the monkey species, Antillothrix bernensis, went extinct sometime in the last 10,000 years, as stated by senior author Siobhán Cooke, Ph.D., who is an associate professor of functional anatomy and evolution at the Johns Hopkins University School of Medicine.
“These fossils enhance our understanding of Antillothrix‘ anatomy, helping us identify ecological factors that may have led to its extinction,” Cooke explains. “This information can ultimately inform policies aimed at conserving the remaining mammalian diversity on Caribbean islands and beyond.”
In 2009, Cooke was part of the team that discovered the first juvenile Hispaniolan monkey skull from a flooded cave in the Dominican Republic. Following this, divers from the Dominican Republic Speleological Society, in partnership with Juan Almonte-Milán, curator at the Museo Nacional de Historia Natural “Prof. Eugenio de Jesús Marcano,” continued to explore similar wet caves nearby, leading to the unearthing of the latest fossils in 2018.
According to Cooke, the opportunity to investigate multiple fossils of monkeys from South America and the Caribbean is rare. There is only one other extinct South American monkey species, Homunculus patagonicus, known from a comparably extensive fossil record.
“The quantity and quality of the Antillothrix skulls discussed in this paper allow us to fully describe the skull and gain insights into the variations among individuals,” Cooke remarks. “This can inform us about their diet and social structures.”
Using three-dimensional virtual models created from the fossils, which are housed in the National Museum of Natural History in Santo Domingo, Dominican Republic, researchers determined that male and female Hispaniolan monkeys were monomorphic, with similar sizes, weighing up to five pounds.
“This suggests minimal competition for mates among males,” Cooke notes. “They likely lived in small family units consisting of a female, a male, and dependent young.”
Examining their rounded teeth and relatively small canine teeth, the researchers concluded that the extinct monkeys primarily fed on fruit.
Antillothrix could have a modern descendant. At just over two pounds, the South American Titi monkey, with its shorter canine teeth, provides a glimpse into what the Hispaniolan monkey might have looked like in its natural habitat.
However, what could have led to seven or eight Hispaniolan monkeys being found at the bottom of a cave roughly 10,000 years ago?
Cooke suggests it may have been bad luck, although it seems unlikely for several tree-dwelling primates to fall into a cave randomly.
Injuries observed in the jaw fossils offered another possible explanation: predation by owls.
One Antillothrix skull has only the front teeth remaining, missing the ramus, which is the back part of the jaw. Other skulls are lacking small sections or significant parts of their jaws.
“Owls tend to preferentially eat the masseter, a significant muscle connected to the jaw, and the injuries align with that behavior,” Cooke explains. “It’s plausible that a now-extinct, large owl captured these monkeys and took them into the cave where it lived, instead of them just falling in by accident. Owl feeding deposits are commonly found in Hispaniolan caves.”
The researchers plan to further investigate other Antillothrix bones, such as limb bones, ribs, and vertebrae.
Cooke emphasizes that gaining knowledge about these animals offers insight into the past and enhances our understanding of biological diversity in the Dominican Republic and Haiti, both of which once hosted not only monkeys and giant owls but also massive sloths, large rodents, various insect-eating shrews, crocodiles, and tortoises.
In addition to Cooke and Milán, the research team includes first author Lauren Halenar-Price from Farmingdale State College, Zachary Klukkert from Oklahoma State University, Phillip Lehman from the Dominican Republic Speleological Society, and Zana Sims, a postdoctoral fellow at the University of Southern California who worked on this study while pursuing her Ph.D. at Johns Hopkins.
