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(American Journal of Botany. 1999;86:32-38.)
© 1999 Botanical Society of America, Inc.

The Tertiary history of the northern temperate element in the northern Latin American biota1

Alan Grahama

a Department of Biological Sciences, Kent State University, Kent, Ohio 44242


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 THE EARLY DATABASE
 THE PRESENT DATABASE
 DISCUSSION
 REFERENCES
 
The time of origin of cool-to-cold-temperate plants of northern affinities in the Latin American biota is unsettled. Two models have been proposed—a Paleogene origin from a once widespread temperate rain forest, and a Neogene origin by introductions from the north which is best supported by new evidence. Fourteen palynofloras of Tertiary age are now available from Mexico and Central America, in addition to numerous others from the southeastern United States and northern South America. Pollen of cool-temperate plants occurs in the Eocene of southeastern United States, but not in northern Mexico, central Panama, or northern South America. In the Miocene this pollen is sparse in deposits from Mexico and Guatemala, rare in Panama, and absent from northern South America. In the Pliocene pollen representing a diverse northern temperate element of ten genera is present in the Pliocene of southeastern Veracruz, Mexico, five in northeastern Guatemala, and two (Myrica, Salix) first appear in northern South America; Alnus and Quercus are added in the Pleistocene. This north-to-south and early-to-late pattern is consistent with the appearance of highlands in southern Central America and northern South America in the Neogene, closure of the isthmian marine portal between 3.5 and 2.5 Ma (million years ago), and the late Cenozoic cooling trend evident in the O/O-based paleotemperature curve.

Key Words: Cenozoic • Latin America • temperate vegetation


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
THE EARLY DATABASE
 THE PRESENT DATABASE
 DISCUSSION
 REFERENCES
 
The vegetation of a region is composed of a complex of elements that arrived at different times, from different places, and that followed different routes of immigration. The tropical component of the northern neotropics includes mostly taxa that came from South America (Cronquist, 1988, p. 153) after closure of the Panama land bridge between 3.5 and 2.5 Ma (Coates et al., 1992; Graham, 1992; Hooghiemstra, 1994; Jackson, Budd, and Coates, 1996; Webb and Rancy, 1996). However, there is also an assemblage that likely came from Gondwana via the North Atlantic land bridge, a Laurasian component that crossed that bridge and through Beringia, and a South American contingency that arrived prior to connections with North America (Wendt, 1993).

The vegetation of northern Latin America also presently includes temperate plants and animals related to those in eastern United States. Their range is disrupted by the Chihuahuan Desert of southern Texas and northeastern Mexico. Along the eastern escarpment of the Sierra Madre Oriental of Mexico in an elevational zone between ~1000 and 2000 m, there are more than 50 species of plants that illustrate this pattern, including Abies, Picea, Pinus, Acer, Alnus, Carpinus, Celtis, Cercis, Cornus, Diospyros, Fagus, Fraxinus, Ilex, Juglans, Liquidambar, Magnolia, Myrica, Nyssa, Ostrya, Platanus, Populus, Prunus, Quercus, Rhus, Salix, Smilax, Tilia, and Ulmus (Fernald, 1931; Miranda and Sharp, 1950; McVaugh, 1952; Gómez-Pompa, 1973). The biotic similarity between the two regions also includes vertebrates (Martin and Harrell, 1957) and amphibians and reptiles (Martin, 1958). The diversity and abundance of the plants decline southward into Chiapas (Breedlove, 1973), Guatemala (Lundell, 1937; Standley and Steyermark, 1945; Steyermark, 1950; Berendsohn, 1991), and Costa Rica (Islebe and Kappelle, 1994). In South America they are represented by Alnus, Ilex, Myrica, Populus, Quercus, and Salix.

An early observation was that these elements appeared earliest in the north and in diminishing diversity and abundance toward the south (Graham, 1973). This suggested that introductions were from the north and that they arrived into Latin America with late Cenozoic cooling, the availability of more extensive highlands, and closure of the isthmian land bridge. This would place the origin of biotic affinities between eastern United States and eastern Mexico primarily in the Neogene (Miocene and Pliocene). However, the number of fossil floras upon which this model was based was meager (Fig. 1), and Axelrod (1975, pp. 318–319) suggested an alternative explanation. According to this view, the Appalachian elements in the uplands of Mexico and Central America were part of an ancient widespread temperate rain forest that has persisted there from at least the early and middle Eocene. Since the 1970s a considerable amount of new information has become available, and it is worthwhile to examine this expanded database for the Cenozoic record of cool-temperate plants in Latin America.



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  		Fig. 1. The 1973 database for tracing Tertiary history of northern temperate elements in the northern Latin American and adjacent regions.

 

   THE EARLY DATABASE
TOP
 ABSTRACT
 INTRODUCTION
 THE EARLY DATABASE
THE PRESENT DATABASE
 DISCUSSION
 REFERENCES
 
A number of cool- to cold-temperate trees and shrubs were known from Eocene and older strata of southeastern United States. In the Claiborne Formation of southwestern Alabama (Fig. 2) these include Abies, Pinus, Alnus, Betula?, Carya, Castanea, Celtis, Fagus, Ilex, Juglans, Liquidambar, Liriodendron, Myrica, Nyssa, Ostrya-Carpinus, Quercus, Tilia, and Ulmus (Gray, 1960). The only Eocene flora known from northern Latin America was the late Eocene Gatuncillo palynoflora of Central Panama and, although it had not been studied completely (Graham, 1985), it was known to contain no pollen of northern temperate elements. In northern South America, plant microfossils had been described from the Eocene Los Cuervos and Mirador formations of Colombia (González Guzmán, 1967), and pollen of northern temperate elements was not recovered.



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  		Fig. 2. Age and distribution of pollen of north-temperate trees and shrubs reported from the Gulf/Caribbean region as of 1973 (modified from Graham [1973 ]).

 
No floras of Oligocene age were known from Mexico or Central America [the Oligo-Miocene Simojovel flora described by Langenheim, Hackner, and Bartlett (1967) from Chiapas, Mexico is now considered early Miocene in age; Graham, 1999]. The original study was concerned primarily with establishing the depositional environment for inclusions of amber. Pinus? was the only northern temperate element mentioned (`a few poorly preserved grains probably of Pinus'; Langenheim, Hackner, and Bartlett, 1967, p. 319). Farther south in Panama, the early Miocene Culebra, Cucaracha, and La Boca floras had not been fully studied (Graham, 1988a, b, 1989a), but temperate elements were not present, and they were not found in the Miocene San Mateo flora of Venezuela (unpublished data of Lina Balseiro) or in other Tertiary palynofloras from northern South America (e.g., van der Hammen and Wymstra, 1964; Wymstra, 1971). Thus, the only northern temperate pollen known from fossil deposits in Latin America was Pinus? from the early Miocene of Chiapas, Mexico.

Pollen of these plants were first known in significant diversity and abundance from the middle Pliocene Paraje Solo Formation of Veracruz, Mexico (Graham, 1976; preliminary study and considered at that time to be Miocene in age). The flora includes Abies, Picea, Alnus, Celtis, Fagus, Juglans, Liquidambar, Myrica, Populus, and Ulmus. Farther south in Panama pollen of cool-temperate plants were not found in the Mio-Pliocene Gatun Formation [then considered Miocene in age; tentative identifications of Alnus, Juglans, and Myrica were not confirmed; Quercus (rare) is now reported; Graham, 1991a, b, c]. Alnus, Ilex, and Myrica occur in early Holocene deposits in Gatun Lake, Panama (~12 ka, thousand years ago; Bartlett and Barghoorn, 1973). None were then known from northern South America (Salix is now reported from the late Pliocene (rare, <1% in the early Pliocene) and Myrica from the late Pliocene of the High Plain of Bogotá, Colombia; Wijninga, 1996). Pollen of Alnus first appears in the highlands of Colombia at ~1 Ma, and Quercus is not found until 330 ka (Hooghiemstra, 1984, 1989, 1994; Hooghiemstra and Sarmiento, 1991; Hooghiemstra and Ran, 1994).

Collectively, these records showed earliest appearance and greatest diversity in southeastern United States, and only later appearance and in decreasing numbers and kinds toward the south in Latin America. As noted, however, there were few paleofloras available, and only preliminary identifications had been made from those in Mexico and Central America, or they had been studied for other purposes (viz., amber deposition).


   THE PRESENT DATABASE
TOP
 ABSTRACT
 INTRODUCTION
 THE EARLY DATABASE
 THE PRESENT DATABASE
DISCUSSION
 REFERENCES
 
In the southeastern United States pollen similar to Alnus, Betula, and Carya has been reported from the Paleocene (Frederiksen, 1991), and Platanus is added to the list of cool- to cold-temperate elements of the Eocene provided by Gray (1960; Frederiksen, 1981, 1988). At the Texas-Mexico border a small assemblage of palynomorphs has been reported from the Laredo Formation of middle Eocene age (Casa Blanca flora, Claiborne Group). Only a single, poorly preserved grain of Pinus representing temperate vegetation was recovered, and it is interpreted as growing well beyond the local depositional basin (Westgate and Gee, 1990, p. 172)

In 1973 information on the Tertiary vegetational history of Mexico and Central America was based on preliminary studies of two palynofloras in Mexico and five in Panama (Fig. 1). Now the early Miocene Simojovel flora from the La Quinta Formation of Chiapas, Mexico (Langenheim, Hackner, and Bartlett, 1967) has been reexamined (Graham and Palacios Chávez, 1996; Graham, 1999). Study of five other assemblages from Panama has been completed—the late Eocene Gatuncillo (Graham, 1985); early Miocene Culebra (Graham, 1988a), Cucaracha (Graham, 1988b), and La Boca (Graham, 1989a); and the Mio-Pliocene Gatun flora (Graham, 1991a, b, c). In addition, seven new paleofloras have been added. These are Eocene deposits of the Claiborne/Jackson Group in the Burgos Basin of Nuevo Leon and Tamaulipas, Mexico (Martínez-Hernández, Hernández-Campos, and Sánchez-López, 1980), the early-to-middle Miocene Méndez flora of Chiapas, Mexico (Palacios Chávez and Rzedowski, 1993), the middle to late Miocene Ixtapa flora of Chiapas, Mexico (Martínez-Hernández, 1992), the early Miocene Uscari flora of Costa Rica (Graham, 1987), the Mio-Pliocene Padre Miguel flora of Guatemala (Graham, 1998), the Pliocene Herrería flora of Guatemala (Graham, 1998), and the Pliocene Rio Banano flora of Costa Rica (Graham and Dilcher, 1998). The new database (Figs. 3, 4) consists of 14 palynofloras ranging in age from Eocene to middle Pliocene and distributed from Mexico (5) to Guatemala (2), Costa Rica (2), and Panama (5). In addition, several recently investigated assemblages of Neogene (Wijninga, 1996) and Quaternary age (Hooghiemstra, 1984, 1989, 1994; Hooghiemstra and Sarmiento, 1991; Hooghiemstra and van der Hammen, 1993; Hooghiemstra and Ran, 1994) continue to document the late Neogene arrival of northern temperate elements in South America.



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  		Fig. 3. The present database for interpreting the Tertiary history of northern temperate elements in the Gulf/Caribbean region.

 


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  		Fig. 4. Age and distribution of pollen of north-temperate trees and shrubs presently known from the Gulf/Caribbean region.

 
In the re-examination of the Simojovel material, pollen of Pinus was not encountered and it can only be listed as rare (if present) in the vicinity during the early Miocene. However, a few grains of the cool- to cold-temperate Picea with distinct northern affinities were recovered (Graham, 1999). Picea is also known from the middle Pliocene Paraje Solo Formation of Veracruz, Mexico (Graham, 1976), and from the Mio-Pliocene Padre Miguel Group of adjacent Guatemala (Graham, 1998). It was not recovered from Neogene assemblages farther south in Costa Rica or Panama, and the Guatemalan occurrence is the southernmost extent of Picea presently known. In the modern vegetation, the closest stands of Picea are found in the mountains of northern Mexico (P. mexicana in the states of Coahuila and Nuevo Leon; P. chihuahuana in Chihuahua and Durango).

Among the seven new paleofloras studied since the 1973 summary, the palynomorphs of the Eocene Burgos Basin flora of Nuevo Leon/Tamaulipas are named by an artificial system of nomenclature and the biological affinities are not known. From the illustrations, only Ilex appears to represent a possible temperate element.

The early-to-middle Miocene Méndez flora of northern Chiapas is reported to contain a surprising mixture of plants with temperate eastern Asian, tropical southeastern Asian, African, and South American affinities (Cedrus, Keteleeria, Baikiaea, cf. Berula, Codiaeum, Engelhardia, Kleinhovia, Nypa, Platycarya, Nothofagus; Palacios Chávez and Rzedowski, 1993). There is a considerable array of ecotypes represented, including Ephedra and Taxodium. Also identified are Abies, Larix, Picea, Pseudotsuga, Tsuga, Sequoia, Alnus, Liriodendron, Magnolia, Liquidambar, Platanus, Celtis, Ulmus-Chaetoptelea, Castanea, Fagus, Quercus, Corylus, Carpinus, Myrica, Carya, Juglans, Populus, Salix, Tilia, Crataegus, Prunus, Rosa, Rubus, Acer, Cornus, Nyssa, Ilex, Vitis, Fraxinus, Lonicera, and Viburnum. Pollen of Nypa is reported from the Eocene of southwestern Texas (Westgate and Gee, 1990), while elsewhere in the Caribbean region it is not known after the late Eocene (e.g., Germeraad, Hopping, and Muller, 1968). Some confirmation of these intriguing identifications is necessary to assess this enigmatic flora.

The middle-to-late Miocene Ixtapa flora from Chiapas, Mexico, contained only Pinus representing northern temperate vegetation, and none of the African, Asian, or Southern Hemisphere taxa reported for the Méndez Formation were recovered. In Guatemala several pollen types representing north-temperate trees are present in the Mio-Pliocene Padre Miguel Group (Picea, Pinus, Quercus, Juglans, and Ulmus), and in the Pliocene Herrería Formation (Pinus, Ulmus). Farther south in Costa Rica, these pollen types were not found in the early Miocene Uscari Sequence, and only Ilex is known from the Pliocene Rio Banano Formation.

Study of the five Tertiary palynofloras from Panama noted earlier has been completed. No northern temperate elements were found in the late Eocene Gatuncillo flora, or in the early Miocene Cucaracha, Culebra, and La Boca assemblages. Rare grains of Quercus first appear in the late Miocene (to possibly earliest Pliocene) Gatun flora.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 THE EARLY DATABASE
 THE PRESENT DATABASE
 DISCUSSION
REFERENCES
 
In assessing the record of northern temperate elements in the Latin American paleovegetation, it is necessary to note that factors of time (early to late) and direction (north to south) are involved. In the Paleogene only Ilex has been reported from northern Latin America, and only from the northernmost locality in the Burgos Basin at the Texas-Mexico border (Fig. 4). This is the least temperate of the relevant genera, and in both the modern and paleovegetation it is frequently associated with warm-temperate to subtropical communities. In northern South America Ilex is reported from the Miocene of Colombia (Wijninga, 1996), and as Ilexpollenites from the Maestrichtian (Late Cretaceous) to the Recent in other parts of the region (Muller, Di Giacomo, and van Erve, 1987). This is considerably older than any strictly northern temperate element in South America. Northern temperate elements are essentially absent from the four Eocene assemblages studied from the region (Burgos Basin, Gatuncillo, Los Cuervos, and Mirador floras).

In the Miocene, a few northern temperate trees appear in the northernmost localities at Simojovel (La Quinta Formation; Picea, Pinus?) and Ixtapa (Pinus). To the south there are none in the Uscari flora of Costa Rica; the Cucaracha, Culebra, or La Boca formations of Panama; or in the San Mateo flora of Venezuela (and other paleofloras of similar age from the region; Germeraad, Hopping, and Muller, 1968; Muller, de Di Giacomo, and van Erve, 1987).

In the Pliocene there is good representation in the northern paleofloras (Paraje Solo flora of southeastern Veracruz, ten genera; Padre Miguel and Herrería floras of northeastern Guatemala, five genera), and fewer to the south (Rio Banano of Costa Rica, Ilex; Gatun of Panama, Quercus; Salix and Myrica in northern South America; Fig. 4).

These data are most consistent with the earlier interpretation of an introduction of cool- to cold-temperate trees and shrubs from the north, with later arrival in progressively decreasing numbers toward the south. This model would be strengthened, however, if there were evidence from an independent source of physical and climatic trends facilitating the late arrival of these elements in Latin America.

The latest reviews of plate tectonic models for the isthmian region place the early emergence of essentially continuous land surfaces at ~3.5 Ma (Coates et al., 1992; Graham, 1992; Jackson, Budd, and Coates, 1996) with a greater diversity of upland habitats appearing at ~2.5 Ma (Webb and Rancy, 1996). Moderate and scattered uplands also appeared in southern Central America at about this time (Graham, 1989b), and the northern Andean highlands developed later (Miocene) than the southern Andes. These events correlate temporally with the earliest appearance of cool- to cold-temperate plants in southern Central America and in northern South America.

Each of the 14 palynofloras from northern Latin America are plotted on the global paleotemperature curve based on O/O ratios in the shells of marine invertebrates (Miller, Fairbanks, and Mountain, 1987; Fig. 5). This curve shows major declines in temperature at the end of the early Eocene, corresponding to the early appearance of glaciations on Antarctica; at the end of the middle Miocene, marking the initial appearance of Arctic glaciations; and in the late Pliocene, which eventually culminated in the ice ages of the Pleistocene. Of particular interest is the temperature decline in the middle Miocene. All Tertiary palynofloras from northern Latin America older than this decline contain few or no northern temperate elements; those in the transition interval of early-to-late Miocene contain a few representatives in the northern floras; and those of Pliocene age contain a good representation in the north with diminishing representation toward the south. If these wind-pollinated trees and shrubs were present in the region in Paleogene times, they left no record among the fossil floras studied to date, and there are no existing data to document their presence. Although the database is still meager, considering the time interval involved and the extent of region, the most parsimonious interpretation is that the history of the cool- to cold-temperate component of northern affinities in the northern Latin American vegetation involved introductions from the north with the temperature decline of the late Cenozoic.



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  		Fig. 5. The paleotemperature curve (after Miller, Fairbanks, and Mountain [1987 ]), and Tertiary palynofloras from northern Latin America plotted with reference to the occurrence of northern temperate elements. Note the decline in paleotemperature in the middle Miocene that divides the floras into those in which these elements are absent or rare (predecline), and those in which they are present to abundant (postdecline).

 


   FOOTNOTES
 
1 The author thanks Henry Hooghiemstra for information on northern temperate elements in South America and Shirley A. Graham for reading the manuscript. Research supported by NSF grants, including NSF DEB-9206743. Back


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TOP
 ABSTRACT
 INTRODUCTION
 THE EARLY DATABASE
 THE PRESENT DATABASE
 DISCUSSION
 REFERENCES
 
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