The Great American Biotic Interchange: Dispersals, Tectonics, Climate, Sea Level and Holding Pens

Michael O. Woodburne 0 ) Department of Geology , Museum of Northern Arizona, Flagstaff, AZ 86001, USA The biotic and geologic dynamics of the Great American Biotic Interchange are reviewed and revised. Information on the Marine Isotope Stage chronology, sea level changes as well as Pliocene and Pleistocene vegetation changes in Central and northern South America add to a discussion of the role of climate in facilitating trans-isthmian exchanges. Trans-isthmian land mammal exchanges during the Pleistocene glacial intervals appear to have been promoted by the development of diverse non-tropical ecologies. - The Great American Biotic Interchange (Stehli and Webb 1985) refers to the exchange of land mammals that represents the strongest biogeographic link between North and South America ever achieved (Simpson 1950, 1953; Webb 1976, 1985; Marshall et al. 1982; Woodburne et al. 2006; Morgan 2008). Woodburne et al. (2006) summarized aspects of Central American and Mexican faunas in this context. In addition to contributing to the mammalian range extensions of which the Great American Biotic Interchange (GABI) is comprised, these regions also served as a source of cladogenesis on one Central American Seaway; Bartoli et al. (2005). The region encompassed between the southern border of Panama and the Isthmus of Tehuantepec, Mexico (Fig. 1). GABI GP GPTS holding pen a taxon that either phyletically originates in, or is introduced to, but in any case subsequently remains restricted to, the area indicated. Great American Biotic Interchange. GABI began about 2.6 Ma (see text). Glacial pulse corresponding to a MIS in Fig. 7 that represents a strong departure from the general pattern during a time of stable or lowering of mean sea level as indicated by the heavy black line thereupon. This is noted as GP in Fig. 4 opposite MIS stages numbered in italic boldface in both Figs. 4 and 7. Geomagnetic Polarity Time Scale (after Lourens et al. 2004). this refers to situations in which a taxon occurs earlier in a given location, only to be found later on in an adjacent area. As discussed below and by Flynn et al. (2005), a number of taxa have an earlier record in deposits of the Guanajuato region of central Mexico (G; Fig. 1) relative to their first occurrence in the United States. In that case, the Mexican record is considered as having been a holding pen with respect to the later occurrence. All references in the text to Flynn et al. (2005) refer to this record in Guanajuato. Ice-rafted debris, in the context of indicating episodes of Northern Hemisphere Glaciation (NHG) (Bartoli et al. 2005) and other significant glacial events (Lawrence et al. 2009). Kiloyear, a segment of geologic time 1,000 years in duration or the age of an event (e.g., 200,000 years ago) without reference to a point or a set of points on the radioisotopic time scale. This (also abbreviated L.F.) is an aggregate of fossil vertebrates that have a limited distribution in time and space, derived from a number of closely grouped localities in a limited geographic area. See Tedford (1970). A local fauna could be based on taxa from as single locality. Megannum. One million years in the radioisotopic time scale (e.g., 10 Ma refers to the 10 million year point on that time scale). SALMA South America Marine isotope scale, astronomically calibrated (Lisecki and Raymo 2005). Segment of geologic time 1 million years in duration or the age of an event (e.g., 10 million years ago) without reference to a point or a set of points on the radioisotopic time scale. North American Land Mammal Age (Woodburne 2004). The content of the Neogene System/ Period and the base of the Pleistocene Series/Epoch at 1.81 Ma follows Lourens et al. (2004), contra Gibbaard et al. (2010). Northern Hemisphere glaciation, which began at about 3.6 Ma, but exhibited its first glacial event at about 3.3 Ma (Mudelsee and Raymo 2005). The North American continent north of Central America (Fig. 1). Pliocene climatic optimum (Dowsett et al. 1994), where temperatures rose about 60C (Lawrence et al. 2009) during an interval from 3.253.05 Ma. (Mudelsee and Raymo 2005). South American Land Mammal Age (see text). The South American continent from the northern border of Colombia with Panama (Fig. 1). The traditional viewpoint has been that GABI signaled the development of an overland corridor across the Panamanian region, and that this transpired about 3.0 Ma (e.g., Marshall et al. 1979, 1982 and references cited therein). It also was recognized that there had been a limited exchange of taxa in both directions prior to this time, and presumably prior to the development of a well-defined land bridge, with the precursors being designated variably as heralds (Webb 1976, 1985, 2006) or New Island Hoppers, with the latter appellation indicating the method of dispersal (Simpson 1950). The geologic and tectonic reconstructions of Coates et al. (2004) indicate that the Panamanian region contained a series of islands as early as 6 Ma (Fig. 2), with the formerly through-going Central American Seaway (CAS) being largely interrupted by an evolving volcanic arc as early as about 12 Ma, as the southwestern margin of the Caribbean Plate collided with the South American continent. Fig. 1 Map of Florida, Mexico, and Central America showing fossil localities and other areas discussed in the text. EG=El Golfo, Mexico; ES=El Salvador; G=Guanajuato, Mexico; Gu=Guatemala; H=Honduras; IT=Isthmus of Tehuantepec; L=Leisey Bone Bed, Florida; Ni =Nicaragua; P=Panama; TMVB=Transmexican Volcanic Belt. Tectonic highlights include a widespread unconformity at about 8.67.1 Ma that reflects complete docking and widespread uplift of the Central American Isthmus (including Panama). This apparently fostered the 7.3 Ma entry of the Procyonidae to South America (Fig. 3). From Costa Rica to Colombia (Fig. 2), marine deposits reflect shallow marine (neritic) conditions adjacent to emergent lands between about 7.14.0 Ma (and 4.8 Ma in Colombia; 4.0 Ma in Costa Rica) subsequent to which the region was further strongly uplifted, including the final emergence of the Panamanian district. In this context (including a brief increase of marine flooding about 6 Ma; Coates et al. 2004), overall conditions reflected increased shallowing of the CAS until about 2.8 Ma (Bartoli et al. 2005), after which time the isthmian region apparently was dry land. From the evidence in Fig. 3 and the following discussion of the dispersal pattern (Fig. 4) it appears that land mammals began to extend their ranges across Central America soon after the initial tectonic closure from about 12 Ma. Whereas the first sloths arrived in North America at about 9 Ma, that is only a minimum age regarding their actual crossing of the isthmian region, and whether they were present in Central America prior to their occurrence in continental North America remains to be determined. In fact, the degree to which Central Americ (...truncated)