Saturday, April 23, 2016

[PaleoMammalogy • 2016] Panamacebus transitus • First North American Fossil Monkey and early Miocene Tropical Biotic Interchange

Panamacebus transitus 
Bloch, Woodruff, Wood, Rincon, Harrington, Morgan, Foster, Montes, Jaramillo, Jud, Jones & MacFadden, 2016 DOI: 10.1038/nature17415

New World monkeys (platyrrhines) are a diverse part of modern tropical ecosystems in North and South America, yet their early evolutionary history in the tropics is largely unknown. Molecular divergence estimates suggest that primates arrived in tropical Central America, the southern-most extent of the North American landmass, with several dispersals from South America starting with the emergence of the Isthmus of Panama 3-4 million years ago (Ma). The complete absence of primate fossils from Central America has, however, limited our understanding of their history in the New World. Here we present the first description of a fossil monkey recovered from the North American landmass, the oldest known crown platyrrhine, from a precisely dated 20.9-Ma layer in the Las Cascadas Formation in the Panama Canal Basin, Panama. This discovery suggests that family-level diversification of extant New World monkeys occurred in the tropics, with new divergence estimates for Cebidae between 22 and 25 Ma, and provides the oldest fossil evidence for mammalian interchange between South and North America. The timing is consistent with recent tectonic reconstructions of a relatively narrow Central American Seaway in the early Miocene epoch, coincident with over-water dispersals inferred for many other groups of animals and plants. Discovery of an early Miocene primate in Panama provides evidence for a circum-Caribbean tropical distribution of New World monkeys by this time, with ocean barriers not wholly restricting their northward movements, requiring a complex set of ecological factors to explain their absence in well-sampled similarly aged localities at higher latitudes of North America.

Figure 2: Comparison of Panamacebus with middle Miocene cebid Neosaimiri fieldsi from La Venta, Colombia.

Primates Linnaeus, 1758
Anthropoidea Mivart, 1864

Platyrrhini Geoffroy, 1812
Cebidae Bonaparte, 1831

Panamacebus transitus gen. et sp. nov.

Etymology. Generic name combines ‘Panama’ with ‘Cebus’, root taxon for Cebidae. Specific name ‘transit’ (Latin, crossing) refers to its implied early Miocene dispersal between South and North America.

Holotype. UF 280128, left upper first molar (M1; Fig. 2a, b).

Referred material. Left upper second molar (M2; UF 281001; Fig. 2a, b), partial left lower first incisor (I1; UF 280130), right lower second incisor (I2; UF 267048), right lower canine (C1; UF 280131), possibly associated left lower second (P2; UF 280127) and fourth (P4; UF 280129) premolars (Fig. 2e–g).

Locality. Lirio Norte (site key YPA-024 in the Florida Museum of Natural History Vertebrate Paleontology Collection), Panama Canal area, Panama, Central America (Extended Data Fig. 1).

Figure 4: Palaeogeographic reconstruction showing hypothetical dispersal route of Panamacebus across the CAS in the early Miocene.
Yellow and ochre colours indicate subaerial environments, blue colours indicate marine environments (dark, coastal and platform; light, abyssal). Criteria used to arrive at this reconstruction include regional tectonic reconstructions, local and regional palaeomagnetic data, and regional strain markers and piercing points (see Extended Data Fig. 8, Methods, and Supplementary Methods). Fm., formation; Fms, formations.
DOI: 10.1038/nature17415

Jonathan I. Bloch, Emily D. Woodruff, Aaron R. Wood, Aldo F. Rincon, Arianna R. Harrington, Gary S. Morgan, David A. Foster, Camilo Montes, Carlos A. Jaramillo, Nathan A. Jud, Douglas S. Jones and Bruce J. MacFadden. 2016. First North American Fossil Monkey and early Miocene Tropical Biotic Interchange. Nature. (2016) DOI: 10.1038/nature17415

Seven tiny teeth tell the story of an ancient monkey that made a 100-mile ocean crossing between North and South America into modern-day Panama – the first fossil evidence for the existence of monkeys in North America.