Callilllico goeldii. Callithrix jace/lIIs ...... Callimico, with Calli trichinae here used only for marmosets and tamarins ... Callimico or any living marmoset or tamarin.
30 Paleogeography and Paleoecology Richard F. Kay and Richard H. Madden
RESUMEN El resumen de todas las evidencias disponibles acerca del entorno geografico regional y ambienta] durante el Mioceno medio en el area de La Venta conduce a las
siguientes conclusiones generales. El area de La Venta se ubico durante el Mioceno medio sobre una peninsula aislada del resto del continente por un brazo del mar que se extenrua desde la cuenca del Maracaibo basta la Amazonia occidental. Comparaciones entre faunas mamfferas en base a indices de semejanza sugieren que el aislamiento geogratico parcial, distancia, y / 0 diferencias climaticas entre la zona ecuatorial y Patagonia podian haber sido responsables del alto grade de endemismo registrado para
la fauna de La Venta. El area de La Venta correspondia a un medio ecuatorial de bajas alturas, con poco relieve local. Fuentes de sedimento ubicadas al oeste contribuyeron sedimentos que fueron transportados por rios que bajaban hacia el sureste. Inundaciones peri6dicas estan indicadas POt los sedimentos de llanura de inundaci6n del Grupo Honda y sugeridas por los diversos peces adaptados a aguas temporales y que se alimentan dentro de selvas inundadas. Estas inundaciones pudieron haber sido provocadas POt fluctuaciones en lluvias. Sin embargo, estas ITlismas evidencias no permiten conduir que el ambiente sufrio un deficit de agua estacional prolongado. La actual distribucion de peces pulmonados, POt ejemplo, no esta restringida a ambientes con estaciones marcadas de sequfa.
520
Los ambientes de deposici6n en el Grupo Honda no induyen caracterfsticas generalmente asociadas a deficits estacionales prolongados de lluvias. Los vertebrados fosiles demuestran evidencias mas fehacientes de presencia de bosques, y son uniformes en indicar la presencia de biotopos terrestres de bosque dentro del area de La Venta durante el intervalo de deposid6n del Grupo Honda. La diversidad de adaptaciones presentada por la fauna de mamiferos de la Capa de Los Monos demuestra una alta propotd6n de especies de habitos arboricolas, semejante a faunas Neotropicales actuates, como, por ejemplo, las de Cocha Cashu en el Parque Nadonal del Manu y del alto RIo Maranon, Peru. EI alto porcentaje de especies ramoneadoras en comparaci6n con espedes pastoreadores es semejante a faunas tropicales actuales de ambientes con precipitaciones de mas de 2.000 mmporaiio. La unica especie de planta Cosil del Grupo Honda es afin aI genero Goupia, taxon que se encuentra en la actualidad restringida a ambientes riberenos en zonas de mas de 2.000 mm de precipitacfon anual. La formacion vegetal sugerida para el Mioceno medio quizas experimento una estacion seca, pero esta hubiera sido menos de tres meses de duracion. La reconstrucci6n del ambiente de La Venta apoyada por estas evidencias se distingue del panorama de llanos extendidos entre bosques angostos de galerfa presentado por Stirton.
RICHARD F. KAY AN D RI C HARD H . MADDEN
T
he preceding chapters of this book have presented detailed information and interpretation about the pa-
leobiology of La Venra animals. In this chapter we summarize information about the paleogeography and sedimentary environments at La Vema and the evidence used by many contributors to infer the paleobiology of La Venta animals. Finally, the composition ofehe fauna as a w hole is compared w ith selected tropical faunas in South America today in an effort to portray the paleoenvironment of La Venta in the middle Miocene. First efforts to understand the paleoecology of La Venra were made more than thirty years ago by R . A. Stirton in his 1953 monograph on Miocochilius (Imeratheriidae, Notoungulata). Stinon was impressed by this animal's ce mentum-covered, ever-gr,owing cheek teeth and possible cursoriallocomotion, features he took to be signs of opencountry grazing habits. At the same time he sought to balance this interpretation against the apparently conflicting evidence of monkey fossils that implied forests at La
521
level. Nor is there any question that broad flood plains and oxbow lakes existed within a meander belt characterized by periods of flooding. The important unresolved questions revolve around the severity and length of the dry season, total annual rainfall, and whether both forested and more open-country environments were present and, if so, in what proportions. Upon review of all the available evidence and comparisons with modern Neo tropical faunas, we are led to the conclusion that the vertebrate fauna does not present a picture of extensive, interfluvial savanna grasslands with narrow, semideciduous gallery forests as Stircon and Fields claimed. We contend that moist evergreen forests were far more extensive and the open areas probably much less so. Support for our conclusion is seen in the La Venta vertebrate fauna, especially (1) the large number of nonvolant mammalian species; (2) the hlgh proportion of browsing species and relatively few grazing species; (3) the large number of frugivorous raxa; (4) the large number of arboreal
Vema:
species, especially primates: and (5) the presence of stillextant species of forest-dwelling marsupials, bats, lizards,
Our evidence will not permit, at this time, an accurate restoration of the environment throughout the area, since it probably varied in different places or even in the same place at different times. Neverth eless, there must have been wide stretches of savanna in the La Venta, Rio Tatacoa and Cerro Gordo areas with heavy forests near the streams. Oxbows, developed and isolated by meandering streams, became mud traps for terrestrial animals as water evaporated during the dry seasons.... The only obviously arboreal animals were monkeys, though some of the smaller sloths may have climbed the trees. (Stirton 1953a, 268)
and birds. All these indicate that moist forests were exten-
Fields (1957, 1959) reached similar conclusions, noting that La Venta sediment depositio n had occurred on a broad flood plain th rough which large rivers meandered. He suggested that the climate was seasonal and that stream borders were heavily forested while there were broad expanses of op en lands on the slightly hlgher ground stretchlng back from the mud flats. H e identified primates, opossums, and small sloths as denizens of the forest and interatheres, toxodoms, and a rodent Prodolicllotis (whose closest living relative is Dolicllotis, the " Patagonian mara") as living in nearby
sive and open areas less so. From comparisons with Recent Neotropical faunas and their environments, it appears that rainfall must have been 1,500- 2,000 mm /year. If the area experienced a seasonal water deficit, the dry season would not have exceeded about three to four months. We propose a vege tational setting similar to the riparian succession described at Cocha Cashu, eastern Peru (Terborgh 1983; Foster 1986; Salo et aI. 1986; Foster 1990; Janson and Emmons 1990). This would have been a vege tation mosaic characterized by successional stages initiated by changes in the courses of the rivers, and possibly modified by large herbivores.
Paleogeography and Geology CO LOMBIA I N THE MIDDLE MIOCENE
In the middle Miocene the area of northern Ecuador, central and western Colombia, and western Venezuela
savannas.
formed a peninsula (fig. 30. 1). To the north and west the
No one has questioned, nor do we, that the La Venta fa una was situated in a trop ical region oflow relief near sea
peninsula was bordered by the Pacific and Caribbean oceans. No land connection existed with Ce ntral America,
RICHARD F. KAY AND RICHARD H. MADDEN
523
and these two oceans were joined across what is now the
the Maracaibo / upper Amazon seaway. There is no evi-
Isthmus of Panama (Whitmore and Stewart 1965; Duque-
dence from the fossil vertebrates or invertebrates to suggest
Caro 1979, 1980). A seaway also exte nded southward from
marine or coastal influences. None of the La Vema freshwa-
the Caribbean through the Maracaibo basin into the upper
ter fish have affinities with brackish or marine taxa (chap. 5),
Amazon basin, separating the peninsula from the Guyana
and the sirenian is most closely related to freshwater forms
shield (Nutall 1990). Domning (1982) and othetS have
rather than marine taxa (chap. 23). Likewise, th e fossil crab
speculated that Colombia may also have been cut off to the
in the La Vema fauna, Si/viocarcinus piriformis, belongs co the
south by the Maranon or Guayaquil Portal, a marine or
living freshwater family Trichodactylidae (c hap. 4).
continental lowland connection between the upper Amazon and the Pacific. In the middle Miocene the South American continent
LOCAL TOPOGRAPHY
occupied a latitudinal position roughly similar to or a few
We infer that this area was lowland because of the prese nce
degrees 50uch of where it is today. Thus, the La Venta fauna,
of animals wi th narrow elevation or temperature tolerances
located today at approximately 3°N, during the middle
and limited dispetSai abilities. Among freshwater fish there
Miocene fell squarely within the equatorial tropics, within
are many very large species and species that today inhabit
5° north or so uth of the geographic equator.
slow-moving, lowland rivers. Included among the large
The middle Miocene peninsula had a mountainous
turtles is Podocnemis, found today only below 100 m eleva-
backbone, and the La Vema area was situated on the eastern
tion (Hoogmoed 1979; Lynch 1979; Rivero-Blanco and
lowland region. Sediments shed by the Central Cordillera
Dixon 1979). Likewise, limbless amphibians of th e family
of the Andes (to the west) were deposited continuously
Typhlonectidae are found today only between sea level and
across the area (Campbell and BurgI 1965; Lundbetg et al.
40 m. Geologic structures in the area surrounding the Tat-
1986). The freshwater fish and decapods described by
acoa Desert, however, suggest some local relief. Hills in the
Lundberg (c hap. 5) and Rodriguez (chap. 4) include many
La Venta area, such as Cerro Chacar6n and Cerro Gordo,
species congeneric or conspecific with taxa found today in
composed of the Jurassic Payande Group were exposed in
the Amazon, Maracaibo, and Orinoco basins. Between
Miocene times as evidenced by the presence of angular
13.8 and 12.0 Ma these lowland rivers flowed eastward.
clasts of the Payande Group in sediments of the La Victoria
After about 12 Ma drainage in the La Venta area shifted to
Formation (chap. 2).
flow westward, signaling the formation of the eastern Cordillera (chap. 2). Today, the eastern Cordillera channels the rainfall of the La Venta area into the Magdalena River and thence northward into the Caribbean Sea. The La Venta area was several hundred kilometers from
REGIONAL AND LOCAL GEOLOGY
Fossils of Miocene age, described in this volume, come principally from the region informally called the Tatacoa
Figure 30.1. Paleogeography of South America in the middle Miocene. Filled o·rdes, middle Miocene fossil vertebr:ate localities, from north to south: La Venta area of Colombia, Giron basin of southern Ecuador, Quebrada H onda in southern Bolivia, Rio Collon-Cura in Rio Negro and Neuquen Provinces, Argentina, Rio Cisnes in southern Chile, Rio Mayo vicinity ofChubut Province, Argentina. Squam, middle to late Miocene paleofloras: filled squares, tropical floras; 'Iaif:/Uled squares, mixed-temperate and warm-climate floras; optn sqllares, temperate broad-leaved evergreen floras (Berry 1925a, 1925b. 1934, 1936, 1938, 1945; Menendez 1971). Question mark, Maranon Portal. Climate indicators: C, coal deposits; E, evaporite deposits. Sediment facies: diago"al/ralilllTe, areas covered by marine transgression; stippling, areas covered by brackish Wolter facies (Weeks 1947; Harrington 1962; Camacho 1967; Beurlen 1970; Bigarrella 1973; Bigarrella and Ferreira 1985; Duque-Cam 1990). Ocean surface currents: ope" arrow, Warm current; ji/ftd arrows, cold currents (Frakes and Kemp 1972; Berggren and Hollister 1974; H odell and Kenett 1985). Vegetation zones follow Solbrig (1976). Relative precipitation isohyets after Parrish et al. (1982). Base map after H . M. Leppard 1961, Goode Base Map Series, Department of Geography, University of Chicago.
524
PALEOGEOGRAPHY AND PALEOECOL OGY
Desen, or La Venta area, adjacent to the towns of PoIonia, Villavieja, and La Victoria, sou th of the Rio Cabrer.1, along the eastern side of the Rio Magdalena (see fig. 2.9). A few fossils were collected along the eastern side of the river south of the town of Aipe. Today, the area is sparsely vege-
Victoria Formation. Red beds increase in number and thickness up-section in the Villavieja Formation. At the top of the formation occur the Polonia R ed Beds where sandstone is uncommon (c hap. 2). For the purposes of faunal analysis in this chapter, we pay special attention to one unit,
tated by woody cactus, sparse grasses, and thorny acacia and shrubs. Few trees and thickets occur except along river and
the Monkey Beds. This unit, of approximately 14 m, is the lowest part of the Villavieja Formation. Other units men-
stream courses. The Honda Group in this region was de-
tioned in the text may be identified by referring to Guerrero (chap. 2).
posited in a structural depression. The base of the section is exposed at the northern end of the area where the group laps unconformably onto Jurassic andesites of the Saldana Formation at the foot of Cerro Gordo and Cerro Chacaron. Except for some local faulting and minor folding, the Honda Group beds dip gently to the south so that successively younger rocks are exposed as one proceeds southward. The Neiva Formation disconformably Qve!lies the Honda Group (chap. 2). In the La Venta area the Honda Group is subdivided into two constituent formations, the La Victoria Formation and the conformably overlying Villavieja Formation. As noted earlier, the La Victoria Formation begins with a disconformity on Mesozoic rocks. In the type area it is composed of 460-650 m of repeating "fining-upward" sequences of sa ndston es and mudstones. The sandstones are fine grained but contain some pebbly layers. They alternate vertically and laterally with reddish-brown to greenish-gray mudstones. At several levels the sandstones are stacked vertically in thicknesses up to 30 m, representing persistent river channels. These thick sandstone units can be traced for tens of kilometers in the direction of stream £low and are used in the La Venta area as stratigraphic marker horizons. At the top of the La Victoria Formation is a 10- m-thick coarsepebble conglomerate called the Cerbatana Conglomerate Beds. The ViUavieja Formation rests conformably on the Cerbatana Gravel Beds of the La Victoria Formation. T he Villaviej a Formation is composed of 580 m of variegated mudstones with minor layers of sa ndstone. The sandstones are more abundant in the lower part of the Formation (the Baraya Member) and far less so in the overlying Cerro Colorado Member. It is much less common for these sandstones to be stacked vertically. Only four stacked sandstones were encountered that are greater than 10m in thickness; by comparison eleven such units are encountered in the La
The geologic time represented by the H onda Group is tightly constrained by a combination of radiometric and paleomagnetic evidence co a 2.1 million year interval (c haps. 2, 3) . According to this evidence, deposition of the La Victoria Formation began about 13.5 Ma and ended at about 12.9 Ma, The Villavieja Formation spans the time interval from 12.9 Ma to 11.4 Ma. A temporal hiatus of approximately 1.3 million years occurs between the Honda Group and the overlying Neiva Formation. At prese nt, the Eastern Cordillera of the Andes intervenes between the Magdalena River and the Amazon Basin in the vicinity of La Venta. Guerrero (chap. 2) notes that th e time of uplift of this mountain range is reflected in a shift in the direction of river flow at about 11 .8 Ma. Before this shift, sediment shed from the Central Cordillera was transported generally sou theastward into what is now the Amazon Basin. The Pebas Formation in eastern Peru and Colombia represents the temporal equivalent of the Honda Group to the east. The Pebas Formation contains benthic foraminifera and brackish-water molluscs with Caribbean affinities.
The La Venla Fauna In appendix 30.1 we summarize the vertebrate fauna in the Honda Group in the La Venta area. Madden etal. (chap. 29) provide added information abo ut the temporal distribution of these taxa within the stratigraphi c section. In the following accounts emphasis is placed up on w hat the species at La Venta tell us about the ecological setting at that time.
F ISH
The diverse freshwater fis h fauna of thirteen families and twenty-three species is a lowland fluvial assemblage (chap.
RICHARD F. KAY AN D RI C HARD H. MADDEN
525
5) . Among the described taxa are no elements indicative of
forests. In contrast, Dracaetla and CrocodilrmlS are found only
upland environments. The fish indicate that heterogeneous
at elevations below 90 m and both inhabit rain forests al-
aquatic environments were prese nt, including both large, ope n river and in-shore habitats, marginal shallow waters, and relatively still, even anoxic, temporary waters. This
though Dracaena may also be found along forest edges (H oogmoed 1979; Rivero-Blanco and Dixon 1979).
dive rsity of aquatic biotopes is typical of modern lowland meandering stream systems. The fish fauna presents wide dietary diversity (algivores, detritivores, carnivores, etc.)
CROCOD ILES
and includes the frugivorous / granivorous Colossoma macropomul1I (Lundberg et a1. 1986), suggesting the presence of fr uiting plants along the river margins or in the flood plain.
In terms of number of taxa, body size range, and presumed feeding ecology, crocodilian diversity in the La Vema fa una is unparalleled in the Cenozoic record of tropi cal South Ameri ca (c hap. 8). Long-sno uted, presumably piscivorous
AMPHIBIANS, SNAKES, AN D LIZARDS
crocodiles are especially diverse in the La Venta fauna, being represe nted by gavials (GrypoSllch IlS), the unique crocodilid Charactosllclms, and the broad, flat-snouted MOllrasllcllUs.
A toad, Brifo maritms, was reported by Estes and Wassersug (1963) from the Monkey Beds. This living species inhabits Amazonian flood plain forests but also has a broader geograp hic and altitudinal range; Rivero-Blanco and Dixon (1979) recorded it in dry forests and very dry forests. A limbless aquatic caecilian of the family Typhlonectidae is also represented at La Venta (chap. 6). Living typhlonectids are distributed discontinuously in the Caribbean and Amazo nian lowlands and in the Parana Basi n. The three extant ge nera that live in northern South America occur in marshes and rivers oflowland forests. The group has been hypothesized to have originated in lowland rain forests (Lynch 1979). Two genera of aniliid snakes are represented at La Venta, Colombophis and another unnamed ge nus. Found also are boids, including Eunectes (a n anaconda) and represe ntatives of the Colubroidea and Scolecophidia. Of the La Venta snakes three taxa are fossorial or forest-floor leaf-litter inhabitants (chap. 6).
Among the caimans, specimens of PllnlSmmlS tleivel1sis had a body length estimated to be between 7 and 8 m and an estimated body mass of more than 1,000 kg (Langs ton 1965). The ziphodont Sebews is reconstructed to have been a powerful terrestrial carnivore (Colbert 1946; Buffetaut and H offitetter 1977; Buffetaut 1980). Sebecosuchia had a wide distribution in Late Cretaceous and Cenozoic South America, last occurring in the middle and late Miocene tropical lowlands of Colombia and eastern Peru (Gasparini 1984). Buffetaut (1980) speculated that their extinction may have been linked to the arrival of Carnivora (Felidae, Cani dae, Procyonidae) in South America during the Great American Faunal Interchange.
TURTLES
Three families of turtles are represented at La Vema. T he aquatic C helidae (represented by one species of CI"ll1s) and Pelomedusidae (represented by three species of PodoCtlemis) are quite conunon. These aquatic genera have living repre-
Lizards rep orted by Sullivan and Estes (chap. 7) substantially amplify w hat was known hitherto about this group at La Venta. Poorly preserved and indeterminate iguanid material has been repotted. In the entire collection just one specimen is still referable to Tt'pinambis. Most of the mate-
sentatives in the Venez uelan llanos today. Specimens of Tesrudinidae Oand tortoises) are more scarce at La Vema.
rial previously allocated to Tt'pitlambis and also to Dracaetla is now allocated to a new ge nus Paradracaena, which is morphologically intermediate between extan t Dracaena and Crocodilrmls. The reallocation of this material is important
There appear to have been two species, an extremely large species of Geoclzelone and a second smaller one. Geochelone is found today only in the northern fringes of the Venezuelan llanos where it prefers forested areas rather than the exten-
for understanding the paleoenvironment at La Venta because Tt'piflambis occ urs today only in dry and very dry
sive ope n savannas (Rivero-Blanco and Dixon 1979; also chap. 9).
526
PALEOGEOGRAPHY AND PALEOECOLOGY
BIRDS
Fossil birds often provide an unambiguous picture of paleoenvironments because their closely related living ana-
microbiothere PachybiotheriH11I. The living microbiothere, Dromiciops, is a forest-dwelling animal.
logues have well-known and rather specific habitat preferences (Olson and Rasmussen 1986; also chap. 10). Based
XENARTHRANS
upon the habits of their closest living relatives, most of the fossil birds in the La Vema fauna inhabited riparian environ-
The xenarthrans of La Vema are abundant and diverse. In
ments. The extant Allhinga al1hillga (Anhingidae), a riparian piscivore, inhabits freshwater marshes in both the Amazon and Orinoco river systems. The living limpkin (Aramus guarmma) prefers heavily vegetated freshwater marshes, wooded swamps, and other similar fluvial wetlands. The jabiru (Jabiru mycteria) occurs both in wetlands and more open grasslands. Two of the fossil birds suggest the presence of nearby forests. Jacamars (Galbula) occupy the canopy of tall primary forests, mature secondary forests, or forest-edge habitats. Finally, the living hoatzin (Opisthocomus hoazin), similar to the extinct Hoazilloides, is an obligate folivore and not a proficient flier. This species occurs today along the banks of forested streams in both the Orinoco and Amazon river systems where it clambers in low trees and shrubs near the water's edge. MARSUPIALS
Eleven species and ten genera of marsupials are now known for the La Venta fauna (Bown and Fleagle 1993; also chaps. 11,12). Several of these marsupials have recognizable adaptive counterparts in the Neotropical marsupial fau na of today. For example, new species of the extant insectivorous/ frugivorous arboreal opossums Thylamys and Micoureus (Didelphinae) are described (chap. 11). La Vema marsupial diversity includes a hyenalike borhyaenid, Arctodietis (Marshall 1976a, 1978), doglike prothylacynines, Lycopsis lotlgirostrns and Dukecynlls magnus, and a sabre-toothed thylacosmilid, Anaeillysietis (Marshall 1976a, 1978; also chap. 11). Caenolestoids Pithieulites and HOlldatltentes, the first ever described from tropical lowlands, have modern adaptive analogs among frugivorous or nectarivorous Australian phalangeroid marsupials (Pascual and Ortiz Jaureguizar 1990; Strait et al. 1990; also chap. 12) and may have been replaced by immigram arboreal squirrels. Finally, the La Vema marsupials include the shrewlike
this volume the sloths, armadillos, and glyptodonts are described. Compared with living sloths, the sloths of the Miocene La Venta fauna are remarkable for their diversity (Hirschfeld 1985; also chap. 15). Seven sloth species are reported in the La Vema fauna (chap. 15), including representatives of three families-mylodontids, megalonychids, and megatheriids. All but one of these sloth species show postcranial morphology associated with arboreal habits although none shows specializations for suspensory behavior like those of the living tree sloths Bradypus and Choloepus (chap. 16). The body size range of these species is great. Judging from distal femur bicondylar widths, all were larger than the living Myrmecophaga. The mylodontine mylodontid Pseudoprepotherium is the largest, with a skull length of about 0.3 m and an estimated shoulder height in quadrupedal posture of 1.3 m, suggesting it was roughly half the weight of Mylodon, or about 500 kg. Pseudoprepotlteriwn exhibits a suite of features indicative of terrestrial habits, including walking on abducted hindlimbs and inverted hind feet (chap. 16). The cheektooth morphology of this animal suggests a folivorous di~t. The scelidotheriine mylodontid Neonematherium was a smaller sloth with a skull length of approximately 0.150.2 m. Postcranially, it greatly resembled the living anteater Tamandlla, suggesting a mix of arboreal and terrestrial habits. Neonematlieril4m displays a single transverse loph on its cheek teeth, suggesting that food was being sliced, not ground and, thus, that leaves or other fibrous foods may have comprised its diet (chap. 15). Postcranial bones are not known for the somewhat smaller mylodontine Glossotheriopsis. All the remaining sloths were smaller than Neonematheriutn. Among megatheriids, Hapalops and a smaller nothrothere exhibit primarily arboreal or climbing adaptations (chap. 16). The megalonychids are represented by two species, the smaller of which has distal phalanges suggesting
RI C HARD F. KAY AND R I C HAR D H. MADDEN
527
arboreality, whereas th e larger one has a distal femur more nearly resembling that of terrestr ial slmhs.
stated that the diets of the larger cingulates (glyptodonts and
One genus of anteater, Neolamafldua occurred in the La Venta area (Hirschfeld 1976). The similar-sized living Neo-
matter, perhaps including grasses. We view this interpretation with caution. These taxa have neither living close relatives nor plausible modern analogs on which dietary inter-
J
tropical anteater Tamandua is an accomplished arborealist. There is a great diversity of armored xenarthrans in the Honda Gro up (c haps. 13, 14), including two tribes of dasypodid armadillos, Dasypodini (Anadasyplls) and futegotheriini (NaIiMstegotherium) , a tolypeutine (Pedroly-
pelltes), a pampathere (Scirrotheriul1I), and two glyptodonts (Neoglyptatellls and Asterostemma). This taxonomic representation is strikingly different from that observed among armored edentates from the middle Miocene of Patagonia.
pampatheres) were probably dominated by coarse vege table
pretations can be based. In the absence of more convincing evidence from tooth function in living armadillos and microwear or stable isotope studies it is plausible that either or both these taxa could have been low-vegetation browse rs or frugivores.
RODENTS
In the Sancacrucian of Patagonia Euphractinae are dominant and occur along with Peltephilinae and Stegotheriini. Neither Astegotheriini, Dasypodini, nor Tolypeutinae oc-
Substantially increased rodene diversity is now known for
cur in the middle Miocene of Patagonia. No hypothesis has yet been advanced to explain this difference.
some that are within the size range of Neotropical murid rodents. All of the rodent taxa found at La Venta are caviomorphs. Thus, murids, notwithstanding their sub-
Given the lack of published descriptions of dental or skeletal material, the behavior and ecology of these xenarthrans must be inferred from generalizations about the living taxa to which they are most closely related and from the pattern of diversity itself. All of these taxa were almost
the La Vema fauna; Walton (c hap. 24) recognizes five families, thirteen genera, and twenty-eight species, including
stantial diversity in South America today, probably had not arrived in South America by the middle Miocene. As with the cingulates, most ofwhat is now known about the adaptive roles of the La Venta rodents is based on tax-
certainly terrestrial and possibly semifossorial. Judged by comparison with body lengths of living armadillos, body weights for La Vema armadillos and glypcodonts are comparable to those of living armadillos and do not include
onomic affinity rather than detailed morphological assessment. For example, there are at least three species of porcupines (Erethizontidae) (two of ?Steiromys and one Microsteiromys Walton). Because living erethizontids are ca-
giant taxa of a size comparable to those of the Pleistocene pampas. The largest armored xenarthrans in the La Venta
pable climbers and several are restricted to tropical evergreen forests, the presence of erithizontids suggests forested
fauna (Asterostemmagigalltea and Scirrotherium ho"daensis) are comparable in carapace size co the living giant armadillo PriodOlltes which weighs around 30 kg. Interestingly, PriodOlltes is one of the most broadly tolerant of modern tropical mammals, occurring in both wet and dry habitats (see tables
environments. Such an approach leads to valid conclusions only if a fossilized species is identical to its living descendant (in which case it is not a distinct species), or differs mor-
J
30.1,30.2). Carlini et a!. (chap. 13) suggest that the diversity of armored forms could indicate environmental heterogeneity. They state that two tribes of armadillos with living represe ntatives, Dasypodini and Astegotheriini, suggest the pres-
phologically only in ways that are unrelated to habitat preference. Walton (chap. 24) points up an example of th e pitfalls of such an approach. She reports two genera of dolichotine caviids, Prodolicltotis and another unnamed genus. Living dolichotines occur exclusively outside the tropics. They are cursorial open-country forms inhabiting
e nce of humid forests, and that the glyptodontids and pampath ere may have inhabited grasslands. The prese nce of a
the arid Andean / Patagonian steppes. She notes, however, that th e postcraniums of Prodolichotis more closely resemble that of another caviid, Cavia, than th ey do Dolichotis.
tolype utine suggests ecotonal settings such as where Tolypelltes occurs in th e Federal District, Brazil, where rainfall exceeds 1,500 mm /year (tables 30.1, 30.2). It is often
With the above caveats it is possibly significant that the remainder of the rodent fauna of La Venta has taxonomi c affinities with forest-dwelling living species. Three genera
Table 30.1. Characteristics of the modern Neotropical mammal fauna sampling localities discussed in the text
Locality
Area Sampled
State or Province, Country
Latitude
Longitude
Altitude (m)
Annual Rainfall (mm)
250-1,430
1,500
Semideciduous, submontane to montane forest; 6 months
Eisenberg et al. 1979
Vegetation and Length of Dry Season
Source(s)
Guatopo
926km'
Miranda, Venezuela
lOoN
66°W
Masaguaral
30km2
Guarico, Venezuela
8°34'N
67°35'W
75
1,250
Subtropical vegetational mosaic high savanna; 7 months
Eisenberg et al. t 979
Federal District
16km 2
Brasilia. Brazil
15°57'5
47°54'W
1,100
1,586
Seasonal xerophyllo us savanna grasslands and gallery forests; 4 months
Mares et al. 1989
Cayapas
450km'
Esmeraldas, Ecuador
OON
78°W
300-600
>5,000
Evergreen pluvial forest; omonths
Albuja and Orees. manuscript; Madden and Albuja 1989
Low Montane
Regional fa una
Salta, Argentina
22°-24°5
64°-66°W
500-1,500
800- 1,200
Lower montane moist forest
Ojeda and Mares 1989; Mares eta!' 1989
Chaco
R egional fauna
Salta, Argentina
22°-24°5
63°W
Subtropical, droughtresistant, thorn forest; 6 months
Ojeda and Mares 1989; Mares eta!' 1989
Manaus
5,OOOkm2
AnlaZOllaS, Brazil
2030'S
600W
10
2,200
Primary upland terra firme fore st; 3 months
Malcolm 1990
Cocha Cashu
10km 2
Madre de Dios, Peru
12°S
700W
400
2,080
Lowland floodplain rain forest; 4 months
Janson and Emmons 1990
Patagonia
Regional fauna
Chubut, Argentina
42°S
69°W
200
200
Temperate tussock grass steppe / scrubland
Redford and Eisenberg 1992
Pampas
Regional fa una
Buenos Aires, Argentina
34°5
58°W
50
800-1,000
Temperate grasslands
Redford and Eisenberg 1992
Alto Maranon
3 localities of restricted area
Amazonas, Peru
4°47'5
78°17'W
210
2,880
Abandoned fields, secondary regrowth riparian forest, undisturbed humid forest
Patcon et al. 1982
200-500
700
Table 30.2 . Distributions and adaptations of tropical South American mammals. (See fl otes
0 11
page 533.)
Locality Taxon
Gu
Ms
FD
Ca
Ch
Mn
CC
AM
Diet
Substrate
Body Weight Category
M E T A TH E R I A
D IDELPHIMORPHIA
Caillromys derbialllls Caillromys la/laWS Ca/uromys philal/der Caillromysiops imlpta Cllirollecres millimlls D idelphis albivemris Didelphis marmpialis GUrol/ia Veill/Sla Gracilillmllls agilis Mamzosa murif/a Marmosa robillSolli Ma rmosa mbra ?Marmosa sp. Ma rmosopsjilscallls Marmosops impavidlls Ma nl1osops lIocrivagus Marmosops parvide/ls Metachirus l/udicalidaClis lv/ieollfem demerame N/icollrel/s regilla MOl/odelphis adllsta MOllodelphis ameriullla Mouodelphis brevica udala MOI /Odelphis dOlllcstica MO/lodelphis kl/lISi Philauder oposmm Thyla mys elegallS TIlylamys pmilla
• •
• •
+
•
•
•
•
•
• •
+ +
+
+
+
+
•
• •
• •
+
•
+
• •
+
• • • +
• • • •
+
• • • +
• •
+
• •
• •
• •
•
+
• • •
• • • • • • • • • • • • • •
+ +
• • • •
• •
+
+
• •
•
• •
•
• +
• •
• • • • • +
• • • • • • • • •
• • • •
•
•
+
+
+
•
• •
• •
+
+
• • •
+
+
+ +
• • +
• • • •
+
IF IF IF IF IF IF IF IF IF
• • •
+ +
• •
• •
•
•
•
• • •
+
•
My,
• • •
+
•
• •
+
•
+
+
+
• • •
•
•
IF IF IF IF IF IF IF IF
•
+
+
+
+
•
+
• •
+
• •
•
• •
+
•
+
• •
• •
•
+
+
•
• •
•
•
•
•
+
+
+
•
• •
•
• •
• •
• •
II II II II II I II III II
+
• •
• • • •
+
• • • • •
•
•
•
• • • I II II
•
I
II
•
EU TH ER I A
PRI MATES
Alouat/a eamya A IOllalta pa/Jiata Alollatra sCllicu/us AOllls trivirgarus Ateles belzebllth A teles jiISCieeps Ateles pal/iscus Cal/ieeblls lII%eh Callilllico goeldii Callithrix jace/lIIs CebueUa pygmaea CebllS albifrollS Ceblls apella Ceblls cap"cillllS
• •
• •
+
+
•
•
+
•
• • •
• • •
• •
• •
•
• •
• •
• • •
+
• • •
•
+
•
+
• •
• •
• •
• •
•
•
• •
• •
+
•
+
+
+
•
•
+
+
+
• •
• • • •
• • •
•
• • • •
• •
• •
+
•
• • • •
• •
+ + +
•
+ +
• • •
+
•
• •
+
+
+ + +
•
•
•
•
A A A A A A A A A A A A
III III III II III III III II II II II III II I .
A
III
A
COl/til/l/ed Oil /lex! pa~e
Table 30.2. Continued Locality
Taxon Ceblls uigrivittllllls Clliropotes sacallas LAgotllrix lagotllricha Pitlleda lIIotlach/IS Sagl/ill/Is JI/sdcol/is Sagl/illlis imperator SagllimlS midas Saimiri scill reus
Gu
Ms
FD
C.
Ch
+
+
•
• • • •
• • •
• • • • •
• • • • • • • •
• • • • • •
•
• •
• • • •
• •
•
+
•
•
•
• •
Mn
CC
AM
•
• •
•
+
•
•
•
•
+
+
•
• +
•
Substrate A A A A A A A A
•
+ + + +
+
Diet
• • •
•
Body Weight Category
III III III III
II II II II
CARNIVORA
Ate/ocymls microtis Bassaricyotl gabbij Cerdocyotl thol/s CltrySOCYOfI brachYllnis COtlepalllS cll il/ga Cotlepaws semistriatlls Era barbara Galictis wja Galiais vittata Herpailllnis yagl/arolludi Leopardl/s pardalis Leopardlls lViedii Lomra lotlgiealldus NaSI/a uaSlla Q /lcije/is geoffioyi Pattlltera o/tea POlOS jlavlIs Procyol/ cal1crivonls Pselldalopex grisem Pselldalopex gyml/ocerws PterDlwra brasilictlSis P,II/la cOl/color Speotllos vcl/atiCIIs Tremarclos art/alliS
•
•
•
•
• • •
+
+
•
+
+
+ +
+
+
•
•
•
+
• •
•
+
• • •
+ +
+
+
+
+
• • •
• • •
•
•
+
• • •
•
+
• • •
•
•
•
+
•
+
+
+ + + + + +
• + + +
•
• •
+
•
+
• • • •
+ +
• •
• • • • • •
+
+ +
• • • •
• • • •
+
+
+
• • • •
•
•
•
+ +
• +
+ +
+
+
•
•
• • •
•
+
•
• •
+
+
•
•
•
+
•
•
•
+
+
•
•
+
+
• • •
• • •
•
•
• •
+ +
• •
+
• •
+
+
+
+
+
+ + + +
•
+ +
•
+
•
+
+
+
+
•
+
+
• •
• • • •
• • •
+ +
+ +
• •
+ +
+
+
+
• • •
•
• • • •
•
III
F, Ve F, IF IF Ve Ve Ve Ve Ve Ve Ve F, Ve Ve F, IF Ve Ve Ve Ve Ve F,
III
III
IV III III III III III III
IV III
IV III III V III
III III III
IV IV III V
RODENTIA
Agouti paca Akodol/ CIIrsor Akodoll lindberghi Akodo/l molUs Akodoll reil/hardli Akodofl sp. 1 Akodol/ sp. 2 Akodoll urichi Akodoll varius Bolomys lasiunls Calomys callosl/s Calomys lallcha Calomys tefler Carterodoll SIlIcide/Is CalJia aperea
• •
•
+
• • • • •
• •
• •
• • • • • • •
• •
+ +
• •
•
+
+
•
+ +
• • + +
•
+ + +
•
• • • • • • • • •
•
• • •
• • •
+
• •
+
• • •
• • • • •
• •
• • • •
• • • •
•
• •
•
•
• •
• • • •
• •
• • • •
• •
•
T T
IV
•
•
s s s s s s
T T T T T T
s
T
F, F, F, L G
II II
Table 30.2. Continued
Locality Taxon Clyomys fatieeps Coel/doll bieolor Coel/doll prehellSilis CtellolllYs melldociol/s Daetylomys dactylitllls Dasyprocta fliliginosa Dasyprocta leporitla Dasyprocta pllt/etata Dasyprocta sp. Dit/omys bral1iekii Diplomys eanieeps Doliellotis salillieola Eehimys braziliellsis Eellimys semillilloslls EeIJimys sp.
Gu
Ms
FD
•
•
+
• • • • •
•
Mn
CC
AM
Diet
Substrate
•
•
• •
• •
•
•
T
+
+
+
•
• • •
• • • •
•
+
• • •
• • • • • •
+
• •
• •
• • •
Ch
+
+
•
Ca
•
•
+
• •
• • •
+
•
• •
•
+
• •
• • •
+
•
H eteromys atlOma/11S H eteromys allstralis H%ellillis brasilimsis Hoplomys gymtlllnls HydrocJlOeris ltydrocJweris
+
+
• • • •
• • •
+
•
+
+
+
•
lcIJthyomys hydrobates Isothrix pagllnlS
• •
• •
• •
+
JIIseelil/omys cat/dal/go
•
•
Kllt/sia frOf/lO
•
LagOStOl1lllS maxim liS
• •
Melatlomys eaiigil/oslls Mesomys hispidus Mierocallia australis Microscilln/s flallillenter Myocastor coypus Myoprocta acol/chy Neacomys glliatlae Neacomys spillosJls Neacomys (muipes Nectomys sql/amipes Oeeomys bicolor Oecomys cot/color Oeeomys parieola Oeeomys sllperatls Oligoryzomys /Oflgieal/da/lls Oligoryzomys microlis OligoryzolllYs t!(gripes
• • • • •
•
+
• •
+
• • •
• •
•
+
•
•
+
• •
• •
• •
• • • •
+
+
•
•
•
+
•
• •
+
• • • •
• • •
• •
•
+
•
• •
• • • • •
• •
•
•
• • •
• • •
•
•
•
+
+
• • • •
•
•
+
• • • •
+
+
• • •
•
+
•
+
• •
+
Galea /11l1steloides Galea spixii Graomys griseciflalllls
• •
• • • • •
• • • • • • • •
+
• •
+
•
+
• •
• •
+
+
• •
•
• •
• • •
•
II II II
T T
II II I
AT
s S
T T
L
AT
FL
I
II II IV
G
T QT
• •
• •
Ve
QT
+
•
A
•
•
•
•
T
•
•
•
•
•
• •
T
II
+
• •
• •
• • •
T
III
• •
+
•
•
+
• • •
• • •
+
A
•
+
QT T
+
•
•
•
•
T
•
T T T
+
+
• •
+
• •
+
+
+
•
• •
+
+
+
•
• •
+
• •
+
• • • •
•
+
•
AT
•
•
• •
• •
A A
+
•
• • • •
A A A
+
•
• •
• • • • • •
T
II III III III III IV II III
A A
•
II III III II
+
+
•
•
•
•
A
T T T T
•
+
+
+ +
+ +
•
+
•
+
•
+
+
•
• •
• •
• • • •
• • •
+
A A T
Body Weight Category
• •
II II
II II I III III
A A A A
AT T A
Continued at! flext page
Table 30.2. Continued Locality Taxon Oligoryzomys spodil/rlls Oligoryzomys IItiaritellsis Oryzomys albiglllaris Oryzomys alforoi Oryzomys capito OryzolllYs IWlllmolldi OryzolllYs lamia Oryzomys maccOtltlelli Oryzomys tlitidlls Oryzomys SIIbjlalllls Oxymyctems roberti Oxymyctenls sp. Proechimys brevicallda Procc/Jimys caYClltletlSis Proec/Jimys wllieri Proechimys IOtlgicalldatlls Proechimys semispitJoSlls Proechimys simomi Proechimys sp. Proechimys steerei Pselldoryzomys simplex Rhipidomys collesi Rhipidomys latimallllS Rhipidomys lel/codactyills Rhipidomys mastacalis Rhipidomys sp. 1 Rhipidomys sp. 2 Rhipidomys I)enezlleiae ScillniSgi/lligll/aris SciJlnls gmtJatemis &illnJS iglliws Scil/nlS ignivetllris &illnls sallbomi ScillnlS spadiceJIs Sigmodon alstoni Sigmodofl hispidlls SigmodontolllYs alfari TIlrichomys apereoides Tylomys mime Zygodofllomys brellicallda
Gu
Ms
• •
• • • • •
+
•
+
• •
•
• • •
•
• • • •
•
• •
• • • •
• • • • •
+
• • • • • • •
•
• • •
• • •
FD
Ca
•
+
+
• •
+
• +
• • +
+
•
• •
• •
+
+
• +
• • •
•
+
•
+
+
•
•
•
• •
•
•
• •
•
•
•
• • • • • •
•
+
• •
•
• •
+
+
+
• • •
+
• •
•
•
+ + +
• • •
• •
+
•
• • • • • • •
•
•
• • • •
+ +
Cb
Mu
CC
•
• • • •
• • • •
• • •
• • •
•
• • •
•
•
+
•
• •
• •
+ +
•
• • • • • •
•
• •
+
•
+
+
•
•
• •
•
s s s s
+
s
• • • •
S IF IF
+
• • •
+ +
•
•
+
•
T A
• • • •
•
• • • •
•
A A A A
• •
+ +
•
s s s
• •
• • •
•
•
• +
+
•
Substrate
+
•
• • • • • • • •
Diet
+
•
•
AM
•
• • •
•
• • • •
+
• • • +
•
•
• • •
•
+
•
• • • • •
+
• +
• •
•
•
• • • •
+
• • • • •
+ +
• • •
+
+
•
•
• • •
• • •
s
s s s s s s s s
•
Body Weight Category
A A A A
T T
T T
T T T T T
T QT
I! I! I! I! I! I! I! I!
•
A A A A A A A
• •
• •
• • • •
I! I! I! I! I! I!
+
•
+
• •
•
• I!
• • • •
•
T
• •
•
•
s
T
+
+
•
•
G G
T T
I! II!
L L
T T
v
I! I!
LAGOMORPHA
Sylllilaglis brasiliCIIsis SY/llilagm jloridalllls
•
+
+
+
•
+
•
•
•
• •
•
• •
•
+
+
• •
+
+
PERISSODACTYLA
Tapims bairdi; TapinlS terrestris
+
•
•
•
+
•
+
V
533
RICHARD F. KAY AND RICHARD H. MADDEN
Table 30.2. Continued
Locality Taxon
Body Weight
Gu
Ms
FD
Ca
Ch
Mu
CC
AM
Diet
Substrate
• •
• •
•
• •
+ +
• •
• •
•
G
+
L L L
Category
ARTI O DACTYLA
Blast()(ems dichototllus Catagonus wagneri Mazama americana Mazama gOlwzollpira Odocoifells virgilll'allllS Ozotoceros bezoarriClis Pecari IajaCII Tayassli pecan'
•
+
+
• •
•
+
•
• •
•
•
+
+
+
•
•
•
• • • •
+
•
• •
•
+ +
+ +
+
•
• •
•
• •
L L
+
L
T T T T T T T
+
FL
T
•
L L
A
My,
T
+
+ +
+ +
+
•
+ +
• •
• •
•
+
•
+ +
• •
V
IV IV IV IV IV IV IV
X ENARTHRA
Bradyplls fridactyills Bradyplls If(lriegallls Cabassous /I/licinct/ls CllOetopllractus velleroslls ClIlamyphoms refUSIlS Choloeplls didactylus Clloloepus hoffmmllli Cyclopes didactyilis Dasyplls kappleri Dasyplls /lovemcitlctllS Dasyplls septemci/lctlls Ellphracllls SeXcillctlls Myrmecophaga tridactyla Priodomes maximllS Tamalldlla tetradactyla Tolypwtes mataClis Tolypelltes lriciuctlls
+ +
• • • • • •
• • •
• •
+
+
• • •
• • +
•
+ +
+
• •
• •
+
• • • •
• •
• •
• •
+
+
•
+ + + + + +
+
•
• •
+
• •
+
•
+
• •
+
+
• •
• • • •
+ + + + +
•
• • • •
+
•
+ + +
• •
•
+
• •
+ +
+ +
• • •
IF IF L L
+
•
•
My, My,
• •
+
+
+
•
• •
•
+ + +
+ + +
+
• •
• •
• •
+ +
IF IF
My, My, My, My, My' My,
A T
T A A
A
T T T T T T
AT T T
III III III III II III III II III III III III
IV IV III III III
Souref'S: Species lists referenced in u.bIe 30.1 . Behavior and size data from Eisenberg (1989), Mares et aI. (1989), Ojeda and Mares (1989), Enunons and Feer (1990). and R edford and Eisenberg (1992). If behavior or size has not been reported for a particular species, it is extrapolated from a congener.
Noles: Localities: GU, Guatopo, Venezuela; Ms, Masaguaral, Venezuela; FD, Federal District. Brazil; CA, Cayapas, Ecuador; Ch, Chaco, Argentina ; Mn, Manaus, Brazil; ec, Cacha Cashu, Peru; AM, Alto Maranon, Peru, Dietary categories: Ve, vertebrate prey; Myr, termites and ants; IF ' insects and fr uit or nectar; Fl , fruit with invertebrates; S, small seeds of grasses and other plants; FL, fruit with leaves; L, leaves (browse); G, grass stems and leaves (graze). Locomotor or substrate preferences: A, arboreal; A-n arboreal and terrestrial (scansorial); T, terrestrial and fo ssorial; Q-n semiaquatic. Body weight: I, 109 to 100 g; II, 100 g to 1 kg; III , t kg to 10 kg; IV, 10 kg to 100 kg; V, 100 kg to 500 kg; vr. >500 kg. Symbols: . , unknown or not present; +, known presence.
of echimyids are present (Acarechimys, Ricardomys Walton,
3.5 kg, and IIOlenopsis" species from 8 to 20 kg. The 2- to
and an unnamed larger species). Acarechimys, at an estimated
3-kg dasyproctid ((NeoreomysJl is abundant at La Venca. Ad-
weight of 90-150 g. falls within the size range of modern
ditionally, there are two species of a new genus, Microscler-
muri~;
Modern echimyids are mainly forest dwellers and many are
OIllY' Walton, small coden" (100-200 g) with dynomyid 0' dasyproctid affinities. Walton suggests a phylogenetic rela-
arboreal.
tionship between the La Venta dasyproctids and extant
the other two were larger. between 150 and 300 g.
There are at least two genera of dinomyids. each represented by two species. "Scleromys" species range from 1 to
Cuniculus, the paca. a forest-dwelling frugivore that is found in Colombia and Venezuela,
534
PALEOGEOGRAPHY AND PALEOECOLOGY
LITOPTERNS
Litopterns were especially diverse at La Venta. Four species of proterotheriids 500 kg.
'Rank order is in parentheses.
541
R. I CHAR.D F. KAY AND R. I C H A R. D H. MA DDEN
Table 30.5. Comparison of faunas from selected tropical environments in South America today with fauna of the Monkey Beds, Villavieja Formation, middle Miocene
Modern South American Mammal Faunas A number of significam associations are found between the numbers and percentages of species occupying various die-
Browser / Grazer Index·
Locality
Frugivore Arboreality Index b Indexc
tary and substrate categories. Tables 30.4 and 30.5 summarize the specializations of the mammal species occurring in both the modern Neotropical faunas and the Monkey Beds
Cayapas (n = 59) Alto Maranon (0 = 59) Manaus (n = 51) Cacha Cashu (0 = 70) Federal District (n = 68) Guatopo (n=41 ) Masaguaral (n = 29) C haco (n = 36) Monkey Beds (n = 50)
86 75 \00 80 73 83 67 58 71
80 75 77 78 70 73 62 29 46
53 52 58 60 33 49 43 25 41
N ow: n = number ofspedes. Dietary categories: F[, fruit with invertebrates; $, small seeds of grasses and other plants; FL , fruit with leaves; L, leaves (browse); G, grass stems and leaves (graze). Locomotor or substrate preferences: A, arboreal; A-n arboreal and terrestrial (scansorial); T. terrestrial and fossorial; QT' semiaquatic. ' 100 · (L)/(L + G).
enumerated in table 30.6.
We find a significam positive correla-
DIETARY TRENDS
tion (Spearman's rho and Kendall's tau) at the p
= O.OS level
betwee n the number of nonvolant frugivoro us species and rainfall (= habitat). Wetter environments supporting evergreen forests always have more frugivores than drier gallery forest/ savanna or thorn forest environments. At Cayapas there are twenty-eight species of frugivores, w hereas in the Chaco there are just five. This relationship also is significam for frugivorous species that obtain substantial amounts of
blOO· (F[ + FL +S)/(F[ + FL + S + L + G).
