The Yucatan peninsula: biogeographical history 65 million years in the making

Zoogeographical studies on Tardigrada are limited by the extent of our knowledge on tardigrade taxonomy and faunistics. In this paper we analyse the relationships between the tardigrade fauna of North, Central and South America (Nearctic and Neotropical regions) and provide the first test of whether the tardigrade fauna of the Americas has undergone the great American interchange. Our analyses were based on 384 tardigrade species records obtained for 1702 localities in North, South and Central America. We found that (1) some tardigrade species are distributed, as predicted by the Great American Biotic Interchange (GABI) hypothesis, on both sides of the Panama Isthmus; (2) the Central American tardigrade fauna is specific and different from both the South and the North American faunas, although it is closer to the tropical areas of South America; (3) either the tardigrade fauna of South and North America appear to be more similar to each other than to that of Central America, or there is a Nearctic–Neotropic division of the faunas; and (4) endemism in Central America suggests a more complex biogeographical process than predicted by the connection of two continents.

North America-Eurasia and South America-Africa were certainly joined in the classic reconstruction of Pangaea by Middle Triassic time. The line of collision and suture included the Appalachian Quachita-Marathon orogenic trend in the United States extending southwestward into what is now northeastern and southeastern Mexico and into Guatemala. Widespread continentality prevailed and there was no Gulf of Mexico or Caribbean Sea. In Late Triassic time and continuing into Early Jurassic time this construct began to founder by initial rifting between South America-Africa and North America. No oceanic crust was formed, however, thus Africa-South America were still completely connected by land or shallow sea to North America until mid-Jurassic time. During this same uppermost Triassic to Middle Jurassic period a largely continental magmatic arc was draped across the Pacific margin of southwestern North America and apparently continued unbroken into northwestern South America. Sometime in the Middle Jurassic oceanic crust began to form by seafloor spreading in the central Atlantic and Gulf of Mexico as separation of South America-Africa from North America accelerated. Once this dense crust began to form the trailing margins of the continents subsided below sea-level and construction of the Atlantic and Gulf coast continental shelves began. Evidence is quite conclusive that this ocean floor spreading did not reach the Pacific Ocean, but was transformed from the southwestern corner of the newly opened Gulf of Mexico northwestward across Mexico via a complex left-slip transform fault system that reached the Pacific margin near Los Angeles. In Early Cretaceous time spreading continued in the central Atlantic but extended southward into the southern Atlantic. As the main axis of spreading extended into the south Atlantic, spreading ceased in the Gulf of Mexico. The south Atlantic spreading initiated separation of South America from Africa, but they probably remained in partial contact via ridge-ridge transform faults until Late Cretaceous time. South America must have finally completely separated from North America in Early Cretaceous time, probably via a rift along the eastern edge of Yucatan and the Nicaraguan rise. By Late Jurassic time the Pacific continental margin arc had waned and was replaced by a complex, largely oceanic, magmatic arc whose position relative to southwestern North America and northwestern South America is not known. What we do know is that by Late Cretaceous-Early Tertiary time it had accreted against the Pacific margins of both. Connections between the continents are also not known but could have included a largely submarine magmatic arc, parts of which may have subsequently dispersed eastward as the Greater Antilles. Much of what is now Middle America is apparently underlain by oceanic crust at least as young as Late Cretaceous in age. By Late Cretaceous time the Greater Antilles magmatic arc seems to have fully formed and subsequently moved northeastward as a northeast-facing subduction system during Late CretaceousEarly Tertiary Laramide time. The Greater Antilles arc-trench system ceased activity in Late Eocene time as it collided with Florida and the Bahama platform and as Laramide orogeny waned throughout western North America. This was followed by a major plate reorganization in the Caribbean-Middle America region nearly 40 m.y. B.P. which established the Caribbean plate more or less as we know it today. The principal change was initiation of the Lesser Antilles magmatic arc as an east-facing subduction system that began to consume Atlantic ocean floor. Also, a west-facing subduction system may have formed about this time along a proto-Central American western margin of the Caribbean plate. However, much of what is now Central America may have initially been off southern Mexico. The northern and southern margins of the Caribbean plate evolved into complex transform and transpressive systems as North and South America moved westward past a nearly stationary Caribbean plate. These motions significantly fragmented the Greater Antilles into their present array. There is no evidence for any complete land connection between North and South America via the Greater and/or Lesser Antilles throughout later Mesozoic or Tertiary time. Nor is there any evidence for complete land connection via Central America and the Isthmus of Panama before Neogene time.

The Glyptodontidae is one of the most conspicuous groups in the Pleistocene megafauna of the Americas. The Glyptodontinae were involved in the Great American Biotic Interchange (GABI) and their earliest records in North America are about 3.9 Ma, suggesting an earlier formation of the Panamanian landbridge. Taxonomically it is possible to recognize two Pleistocene genera of Glyptodontinae:Glyptodon (ca. 1.8 – 0.008 Ma), restricted to South America, andGlyptotherium (ca. 2.6 – 0.009 Ma), including records in both North and Central America. Here we present the first report of the genusGlyptotherium in South America, from the Late Pleistocene of several fossil localities in Falcon State, northwestern Venezuela. A comparative analysis of the material, represented by cranial and postcranial parts, including the dorsal carapace and caudal rings, suggests a close affinity withGlyptotherium cylindricum (Late Pleistocene of Central Mexico). This occurrence in the latest Pleistocene of the northernmost region of South America Supports the bidirectional faunal migration during the GABI and the repeated re-immigration from North America of South American clades, as has been reported in other members of the Cingulata (e.g., Pampatheriidae).

The fourth volume in the series Topics in Geobiology, The Great American Biotic Interchange is an up-to-date, authoritative work on a fascinating but complex subject. Twenty-six experts summarize recent advances in the causes, timing, nature, and biotic results of isolation followed by interchange between North and South America. The book is divided into five parts: an overview of the subject, Cretaceous-Paleogene events, Tertiary isolation, the great interchange, and results of the interchange. A strength of the book is the examination of geobiological events from different perspectives. The book is fittingly dedicated to the late George Gaylord Simpson who devoted 50 years of his long and productive life to the study of South American mammals. The thorough work of Larry Marshall and his colleagues on the geobiochronology of South America has increased knowledge and dating of South American faunas and has permitted the timing of interchange events and the correlation with North American faunas. To them we are indebted. Only with the emergence of the land bridge was interamerican immigration a factor. Before then, as Webb and other authors point out, faunal exchanges were between North America and the Old World. After the breakup of Gondwanaland, South America was isolated for about 80 million years, with occasional dispersals taking place via a filter bridge. The time of the closure between Central and South America ranges between 10 and 3 Ma (megaannums or millions of years before present). In their comprehensive reviews of the plate tectonics and paleomagnetism of the Caribbean region, Smith, Donnelly, and Gose estimate that the closure occurred sometime between 10 and 5 Ma. Savin and Douglas place the isolation of marine invertebrate faunas at 3.5 Ma and suggest that a change in sea levels probably caused the emergence then, with ephemeral emergences in earlier times. Jones and Hassan point out that a land bridge is a sea barrier, and, between 3.5 and 3.0 Ma, marine invertebrate faunas were isolated on both sides of the isthmus. Biochronological studies indicate that land vertebrates were using the bridge by 3.0 Ma.

BackgroundThe Middle Miocene fauna of La Venta, Colombia, offers a grand opportunity to understand low-latitude South American ecosystems prior to the late Cenozoic Great American Biotic Interchange (GABI). We present new material of two proterotheriid litopterns, Villarroelia totoyoi and Mesolicaphrium sanalfonense, and a macraucheniid litoptern, Theosodon, from La Venta. During the GABI, North and South American faunas intermixed, after which some lineages proliferated and others died out. We conducted an ecomorphological analysis of 11 North and South American faunas pre-dating and post-dating the GABI by scoring all mid- to large-sized mammalian herbivores on their body size, tooth morphology, and feeding height.ResultsThe fossils studied here offer new information on the deciduous dentition of M. sanalfonense and mandible of the La Venta Theosodon. Pre-GABI South American faunas were more ecomorphologically diverse than their North American counterparts. The post-GABI Pleistocene fauna exhibited similar ecomorphological diversity to pre-GABI South American faunas, but modern faunas show this diversity was mostly lost in the end-Pleistocene extinctions.ConclusionsThe new litoptern fossils provide previously unknown information on these species’ morphology, but they do not resolve outstanding systematic and phylogenetic questions. Discrepancies in ecomorphological diversity between pre-GABI North and South American faunas is attributable to the presence of small, high-feeding (arboreal) taxa and hypselodont (ever-growing cheek teeth) taxa in South America, which North America lacked. Arboreal herbivores (porcupines and primates) experienced some success in North America after dispersing during the GABI. Although hypselodont xenarthrans were successful in post-GABI North America, the fact that most other hypselodont lineages went extinct during and after the GABI suggests that dental morphology may not fully capture the ecomorphological diversity in diet of North American herbivores. Future studies could examine faunas immediately before and after the GABI to uncover the precise dynamics of the interchange and why certain lineages succeeded while others failed.Supplementary informationThe online version contains supplementary material available at 10.1186/s40850-025-00232-4.

Understanding how the assemblage of present and recently extinct non-volant terrestrial vertebrates on the Greater Antilles (Cuba, Hispaniola, Jamaica and Puerto Rico; Fig. 1) came to be is one of the most intriguing challenges in biogeography. Until the introduction of plate tectonic theory in the 1960s, explanations were dominated by over-water dispersal (e.g. Darlington, 1938). Critical evidence included the observation that the fauna was conspicuous for its limited high-order taxonomic composition; in a number of cases, those forms that crossed to the islands underwent large adaptive radiations as a consequence of filling an array of vacant niches; South America appears to be their principal source, which is consistent with Caribbean sea-surface flow. Maps of the Caribbean and adjacent regions showing (a) simplified bathymetry and (b) schematic development of the Caribbean plate during the Late Cretaceous and Cenozoic. Abbreviations: Cu., Cuba; Ja., Jamaica, Hisp., Hispaniola; P.R., Puerto Rico; Yuc., Yucatan Peninsula. Panel (b) depicts the Caribbean plate's eastward migration relative to North and South America (based on Escalona & Mann, 2011). Solid red lines represent the inferred leading edge of the Caribbean plate during: 1, mid–Late Cretaceous, c. 80 Ma; 2, Middle Palaeocene, c. 60 Ma; 3, Middle Eocene, c. 44 Ma; 4, mid-Oligocene, c. 30 Ma; 5, Middle Miocene, c. 14 Ma; 6, Early Pliocene, c. 5 Ma; and 7, Present. In the 1970s and 1980s, and riding on the back of plate tectonics, vicariance models rose to prominence (e.g. Rosen, 1975). It was argued that during the Late Cretaceous, New World animals were 'trapped' on the Greater Antilles as the proto-Caribbean plate migrated eastwards from a location corresponding to today's southern Central America (Fig. 1b; Rosen, 1975). In the early 1990s, over-water dispersal re-emerged as a result of the then newly developed molecular dating techniques being applied to the Greater Antillean faunas. Key was the discovery that the ancestors of the non-flying vertebrates, particularly the reptiles and amphibians, had arrived at ostensibly random times in the Cenozoic (e.g. Hedges et al., 1992). Furthermore that the endemics were relatively young circumvented the need for these lineages to have survived the direct blast and indirect effects (tsunamis, debris clouds) of the massive Cretaceous–Tertiary boundary-age bolide impact on the nearby Yucatan Peninsula (Fig. 1a). In 1999, the debate took another twist. Armed with a deep understanding of the Caribbean's geotectonic development, and sceptical of the efficacy of sweepstake colonization, Iturralde-Vinent & MacPhee (1999) introduced a radical explanation: the mid-Cenozoic GAARlandia (GAAR = Greater Antilles + Aves Ridge) land bridge. They proposed that many of the Greater Antilles' non-volant terrestrial vertebrates were descended from animals that had walked to the archipelago from South America. Colonization was via a quasi-continuous causeway atop the Aves Ridge during a 1–2 Myr interval close to the Eo-Oligocene boundary, c. 34 Ma. The proposal has since spurred a passionate discourse (e.g. Graham, 2003; MacPhee & Iturralde-Vinent, 2005; Hedges, 2006; and references therein). A new paper by Alonso et al. (2011) firmly favours GAARlandia. Their phylogenetic investigation of 10 species of the toad genus Peltophryne on Cuba, Hispaniola and Puerto Rico indicates that a common ancestor reached the islands c. 33 Ma, exactly when the purported land bridge is thought to have existed. On the basis that amphibians are largely (but not exclusively) salt-water intolerant, Alonso et al. (2011) argued that they could not have swum/rafted to the Great Antilles, arriving instead via the land bridge. With the hypothesis receiving a fillip, it is timely to re-appraise GAARlandia. The first step in such a process inevitably involves evaluating the elements underpinning Iturralde-Vinent & MacPhee's (1999) model. From their knowledge of the regional geology, they argued that the Greater Antilles and the broader area experienced a 1–2 Myr period of tectonic uplift around the Eo-Oligocene boundary. Critically, the Aves Ridge (Fig. 1a) is thought to have been involved; the bathymetric high then formed the volcanic arc to the east-advancing Caribbean plate (today the ridge sits c. 200 km 'behind' and to the west of the active Lesser Antilles arc, which in turn, relative to North America, South America and the Greater Antilles, is c. 1000 km east of its Late Eocene location, see Fig. 1b). Furthermore, the up-forcing coincided with a dramatic sea-level fall due to rapid ice-sheet growth on Antarctica. Thus the combination of tectonic compression and a lowered global ocean exposed large portions of Aves. A second aspect that Iturralde-Vinent & MacPhee dwelt upon was the assumed surface-water circulation of the western Atlantic–Caribbean Sea–eastern Pacific during the Late Eocene–Early Oligocene and the Early to Middle Miocene. At both instants, and effectively up until the Late Miocene, they inferred that the regional flows were unsuited for over-water dispersal between South America and the Greater Antilles. Curiously, the one feature we would anticipate from GAARlandia, namely a spike in terrestrial vertebrate arrivals at the Eo-Oligocene boundary, was never demonstrated by Iturralde-Vinent & MacPhee (1999). Alonso et al. (2011) have attempted to rectify this, listing various studies apparently supportive of the land-bridge model. These include investigations of non-volant terrestrial mammals, specifically megalonychid sloths, hystricognath rodents and primates, plus certain frogs, fishes, spiders and plants. However, the significance of some of the data is probably overplayed. For instance, of the listed mammals, the oldest are Early Miocene (c. 20 Ma) palaeontological finds, and are thus much younger than GAARlandia. Furthermore, only the rodents exist today, but they have not yet been subjected to molecular-clock dating. Whilst the Peltophryne toad study (Alonso et al., 2011) adds support for GAARlandia, I remain unconvinced about the causeway's role in shaping Greater Antillean biogeography. With a geology–geophysics background, my prime concern is the lack of ocean-floor drilling data demonstrating the extent to which Aves was sub-aerial in the mid-Cenozoic. Insights can, however, be gleaned from active island arcs around the globe, e.g. Marianas–Bonin (Western Pacific), Scotia (South Atlantic), Kermadec–Tonga (south-west Pacific), Sangihe (Molucca Sea), Luzon (western Philippine Sea), as well as the Lesser Antilles. Cursory inspection of these archipelagos renders it highly improbable that the Aves volcano chain ever formed an unbroken land bridge between South America and the Greater Antilles. None forms anything close to a continuous area of emergent land; even a major sea-level drop associated with a glacial maximum (say c. 130 m) would change the patterns only slightly. Indeed, if the system with the closest-spaced islands is used as a guide (curiously, the Lesser Antilles), then the largest gaps were c. 60 km, with many others of a similar magnitude. Such an arrangement must have acted as a strong impediment to gene flow along Aves; investigation of the frog Leptodactylus validus on northern South America, Trinidad, Tobago and the southern Lesser Antilles provides a pertinent example (Camargo et al., 2009), as does Henderson's (2004) wider-ranging snake survey. Furthermore, and like Hedges (2006), I am sceptical about Iturralde-Vinent & MacPhee's (1999) inferences regarding Caribbean surface-water currents being incorrectly configured to permit South America–Greater Antilles over-water dispersal. Their assertions concerning land–sea distributions, bathymetry and atmosphere–ocean interactions seem overly simplistic. Moreover, their analysis failed to incorporate computer-based palaeoceanographical simulations. Thus their original and re-stated view (Iturralde-Vinent & MacPhee, 1999; MacPhee & Iturralde-Vinent, 2005) that sweepstake colonization was highly unlikely is questionable. In fact, ocean–atmosphere modelling for various points in the Cenozoic invariably shows currents flowing from northern South America to the Greater Antilles (e.g. Huber & Caballero, 2003). Whilst GAARlandia might explain some of the biological data, I contend that the overwhelming majority of terrestrial vertebrates on the Greater Antilles have ancestors that arrived as over-water dispersalists; possibly a small number of forms are relictual (Cuban night lizard, solenodonid mammals: Hedges, 2006). As many others have recognized (e.g. Darlington, 1938; Hedges, 2006), the key question is, why do we not observe in both extant taxa and the fossil record a broad range of orders and families? Instead we see a restricted high-order taxonomic composition, plus at the lower levels several broad adaptive radiations due to species exploiting a wide range of unoccupied niches (e.g. ground sloths, capromyid rodents, eleutherodactyline frogs, and anoline and sphaerodactyline lizards). A second critical point concerns the estimated arrival times not clustering at c. 34 Ma (e.g. fig. 6 in Hedges, 2006). To provide perspective, since South America connected with Central and North America c. 3 Ma, there has been a massive biotic exchange between the two continents; based on GAARlandia, a not too dissimilar pattern, or at least influx, must be anticipated for the Great Antilles back in the mid-Cenozoic. In conclusion, GAARlandia is a thought-provoking hypothesis, but appreciably more data (geological, biological and to a lesser extent palaeoceanographical) are required before I will be persuaded of its importance in explaining Caribbean biogeography. I thank R.J. Whittaker for inviting me to write this commentary, M. Huber for sharing information, J.C. Aitchison and P. Cunich for reviewing various drafts, and A. de Queiroz and an anonymous referee for their constructive critiques. Editor: John Lambshead

The Maya civilization developed in Mesoamerica persisted approximately 3,000 years and was one of the most advanced of its time. Mayas had the only known full writing system, as well as highly developed mathematical and astronomical systems. They also developed sophisticated architecture and arts. The Maya area of settlement ranged from the Yucatan Peninsula through Guatemala, Belize, and part of the Mexican states of Tabasco and Chiapas, as well as parts of Honduras and El Salvador. The Maya civilization reached its peak of power and influence in the Preclassic period, from 2000 BCE to 250 CE. Despite the profound impact of the Mayan civilization on Mesoamerica and neighboring populations, studies of genetic variation of ancient Maya populations in pre-European times are scarce. Therefore, this work examines evidence in ancient DNA from archaeological sites in the states of Yucatan, Chiapas, Quintana Roo, and Tabasco. We report data analysis from sequences of the mtDNA hypervariable region I (HV1) from bone remains found in excavations of archaeological sites of the Maya region and their relationship with ancient and contemporary communities in this region, including Central and South America, as well as with Asia and Beringia. We discuss the results in the light of the influence of climate change in the area and relate them to evidence from language change. Gene flow within the Maya area occurred with a directional flow to South America in the Preclassic and Classic eras of the Mesoamerican chronology. This is supported by historical documentation, that has shown that the ancestors of the Maya civilization entered the Yucatan Peninsula after the first movement of people from Northern Asia into the Americas, with later migrations of the Maya ancestors to Mesoamerica, through Central America and the Caribbean, and toward the northern portions of South America.

Comments on Steadman, D.W., Martin, P.S., MacPhee, R.D.E., Jull, A.J.T., McDonald, H.G., Woods, C.A., Iturralde-Vinent, M. & Hodgins, G.W.L. (2005) Asynchronous extinction of late Quaternary sloths on continents and islands. Proceedings of the National Academy of Sciences USA, 102, 11763–11768. The debate over the causes of the Pleistocene megafaunal extinction dates back to the early 19th century (Grayson, 1984), and continues to generate considerable controversy (e.g. Grayson & Meltzer, 2003; Araujo et al., 2004; De Vivo & Carmignotto, 2004; Fiedel & Haynes, 2004; Burney & Flannery, 2005; Wroe et al., 2006). Typically, protagonists in this debate can be classified into two groups. One group argues that Late Pleistocene megafaunal extinctions were primarily caused by direct and indirect human action through hunting, habitat modification or introduction of new predators (Burney & Flannery, 2005, 2006; Barnosky et al., 2004; Fiedel & Haynes, 2004). The other interpretation is that humans had at most a minor role in the megafaunal extinction, and that the loss was attributable principally to a climatic cause (Ficcarelli et al., 2003; Grayson & Meltzer, 2003, 2004; Barnosky et al., 2004; De Vivo & Carmignotto, 2004; Boeskorov, 2006; Guthrie, 2006; Wroe et al., 2006; Wroe & Field, 2006). Here we contest the position of Steadman et al. (2005), who favour the overkill hypothesis to explain the ground sloth extinction in the Americas. Although making an important contribution to the debate on extinction of the New World megafauna, Steadman et al. (2005) make some important assumptions in their analysis. Steadman et al. (2005) argue that the extinction of ground sloths in the New World was concomitant with, and a consequence of, the human occupation of the Americas. Their argument is two-fold. First, the radiocarbon dates (14C) accepted by them for the last appearance dates (LADs) of these animals roughly correspond to megafaunal extinction dates in South and North America and the West Indies. These dates coincide with the human colonization of these regions and they argue that this supports the thesis that human arrival caused extinction of the ground sloth. Second, according to Steadman et al., extinctions caused by climatic fluctuation would result in concomitant LADs across the entire continent and associated islands, as they viewed these fluctuations as being widespread and uniform, whilst they found that the LADs for the West Indies, around 4400 14C yr bp [c. 4800–5050 calibrated years before present (cal. bp); dates calibrated with calib 5.0, Stuiver et al., 2005], are much younger than those found in the continent (c. 11,000 14C yr bp; c. 12,880–12,950 cal. bp for North America and c. 10,500 14C yr bp; c. 12,390–12,640 cal. bp for South America). We contend that the chronological data presented by Steadman et al. (2005) are incomplete, especially when considering South America. While Steadman et al. (2005) suggest that there are no acceptable Holocene LADs for ground sloths, a large number of Holocene dates generated through direct dating of bone and dung remains are indeed available in the literature. Barnosky et al. (2004; supporting material) revised the radiocarbon dates available for megafaunal remains throughout the world. In South America, they listed four articles with remains of megafauna dated within the Holocene, based both on direct and indirect dates. Even when considering only the results based on direct dates of bone remains, sufficient evidence still supports Holocene LADs for subequatorial ground sloths. For instance, from Argentina, Borrero et al. (1998) presented a total of seven 14C dates consistent with a Holocene survival of megafauna, albeit two of these ages are potentially unreliable, and four were obtained from one single specimen (indeed, one of the unreliable dates comes from this specimen; Table 1). Other reports not included in Barnosky et al. (2004) provide two direct radiocarbon ages of megafaunal bone remains from central Brazil at the Pleistocene/Holocene boundary (Table 1; Neves & Piló, 2003; Araujo et al., 2004). Politis et al. (2004; also not included in Barnosky et al., 2004) presented two additional Holocene direct radiocarbon ages of Megatherium americanum (Blumenbach) specimens (Table 1) and a third one from the Holocene/Pleistocene boundary (10,190 ± 120 14C yr bp; c. 11,820–12,020 cal. bp; Table 1), all in Argentina; and Marshall et al. (1984; also not included in Barnosky et al., 2004) reported a single Holocene age of 8910 ± 200 14C yr bp (c. 9780–10,150 cal. bp; GIF-4116) of a Scelidodon chiliensis (Lydekker) in Peru (Marshall et al., 1984;Pujos & Salas, 2004). Four of the sites where these dates were obtained are located in Argentina, while two are located in central Brazil and the last in Peru (Fig. 1). All the Argentinean sites (Arroyo Seco 2, La Moderna, Campo Laborde and Paso Otero 5) are open-air archaeological sites, i.e. the megafaunal remains are associated with prehistoric human occupations (see Borrero et al., 1998; Politis et al., 2004 for detailed descriptions). Arroyo Seco 2 is interpreted as a base camp where a large variety of activities were undertaken (Politis et al., 2004), including the exploitation of ground sloths and other megafauna by humans. However, Borrero et al. (1998) and Politis et al. (2004) do not state clearly if the two specimens (M. americanum and Equus neogeus Lund) that dated to the Holocene (Table 1) showed marks of human manipulation. The remaining open-air sites are believed to be sites used for specific activities (Politis et al., 2004): La Moderna is interpreted as an occasional megafaunal processing site, where the remains of a single glyptodont (Doedicurus clavicaudatus Owen) dated to the Holocene (Table 1) were recovered; Campo Laborde presents evidence that it was used as a hunting and processing site for ground sloths (M. americanum; Table 1); and Paso Otero 5, was also identified as a hunting and processing site for local megafauna. Archaeological and palaeontological sites in South America presenting direct Late Pleistocene/Early Holocene radiocarbon (14C) dates for megafaunal remains. Circles represent sites with no evidence of human exploitation of the megafaunal remains, whereas triangles represent sites with evidence of human exploitation of megafauna. 1, Gruta Cuvieri; 2, Escrivânia 5; 3, Gruta del Indio; 4, La Moderna; 5, Campo Laborde; 6, Arroyo Seco 2; 7, Paso Otero 5; 8, Pampa de los Fósiles. The two Brazilian sites, in contrast, are exclusively palaeontological, i.e. they are not associated with human occupations, and are located in limestone caves in the karstic region of Lagoa Santa. Gruta Cuvieri is a cave where three vertical chambers functioned as natural traps for the now extinct megafauna and other animals. The only megafauna species found so far is Catonyx cuvieri (Lund), a medium-sized ground sloth. The Holocene date presented in Table 1 was obtained from one of these ground sloths, found at the surface of one of the chambers. The other Brazilian site, Escrivânia 5, is part of a complex of caves, generically referred to as Escrivânia, representing one of the richest palaeontological limestone outcrops known at Lagoa Santa. Together with tons of animal fossil bones, in one of the chambers (Escrivânia 3) an almost complete human skeleton was also recently recovered, dated to 7650 ± 80 14C yr bp (c. 8370–8420 cal. bp; Beta 174734). The Peruvian site, Pampa de los Fósiles, is also a palaeontological site located in the Cupisnique Desert. Several archaeological sites in the region have revealed no evidence of human interaction with the megafauna in the region (Pujos & Salas, 2004). In addition to these reported dates, Steadman et al. (2005; supporting material) disqualified two other Holocene dates as unreliable (they also rejected a third date, but it has a very large margin of error). These were the only Holocene dates found in their bibliographical revision and they ‘have means that are up to 1000 years younger than means of any [of the accepted LADs] [Supplementary online material]’. As 10 reliable Holocene direct radiocarbon dates for megafauna are described here, there is no further reason to reject the dates of 8990 ± 90 14C yr bp (c. 9920–10,190 cal. bp; LP-925; Garcia, 2003) and 9560 ± 90 14C yr bp (c. 10,680–10,860 cal. bp; GrN-5772; Long et al., 1998) as unacceptable outliers. These two dates are from an Argentinean site, Gruta del Indio (Fig. 1; see Long et al., 1998; Garcia, 2003 for detailed descriptions). This site is a rockshelter, and although it presents chronological information placing humans together with megafauna in time, there is no evidence of humans exploiting the local megafauna (Long et al., 1998; Garcia, 2003). As presented in Table 1, from the 14 existing Holocene dates we found for megafaunal remains in South America eight are derived from ground sloths, which severely weakens the position of Steadman et al. (2005), that there are no acceptable Holocene LADs for ground sloths in the Americas. Assuming that human groups already inhabited South America around 12,500 14C yr bp (c. 14,300–14,950 cal. bp; Dillehay, 2000), the argument that the ground sloth LADs were concomitant with the human arrival in the New World can no longer be accepted, at least not as an immediate phenomenon. The second argument presented by Steadman et al. (2005) is that the apparent delay observed in the LADs of Central America islands, when compared with the continental ones, favours the overkill hypothesis. Delayed LADs in insular regions have been found in other parts of the world, independent of human presence (Guthrie, 2004; Boeskorov, 2006). Boeskorov (2006) showed that in northern Eurasian islands, megafauna survived into the Holocene, e.g. the mammoths of Wrangel Island. Nonetheless, the extinction of megafauna in Eurasia as a whole is believed to be primarily due to climatic changes (Barnosky et al., 2004; Boeskorov, 2006), particularly because no human presence is found in the Wrangel Islands until well after the extinction of the megafauna (Boeskorov, 2006). Although these data do not peremptorily disqualify Steadman’s argument, they do bring into question whether the overkill hypothesis is the most parsimonious explanation for megafaunal extinctions. Finally, it must be emphasized that there is a general lack of evidence of sloth remains in archaeological contexts in the Americas as a whole (but see Politis et al., 2004 for an exception), which also speaks against the overkill hypothesis. Specifically, in Lagoa Santa, despite the excavation of dozens of archaeological sites dated to the Pleistocene/Holocene transition (showing human evidence as old as 11,000–11,500 14C yr bp; c. 12,880–13,400 cal. bp; Neves et al., 1999), evidence is lacking of megafaunal use by humans, either as a source of food or raw material (Kipnis, 1998; Prous & Fogaça, 1999). In North America, a similar situation is observed. According to Grayson & Meltzer (2003), there are only two genera of megafauna (Mammuthus Burnett, 1830 and Mammut Blumenbach, 1799) known to have been hunted by humans during the Clovis period (Grayson & Meltzer, 2003). This scenario is accepted even by Fiedel & Haynes (2004), strong defenders of the overkill hypothesis. Thus, at least in South America (and most probably in North and Central America as well), the idea that ground sloths went extinct due to overkill lacks archaeological support. In conclusion, the ground sloth overkill hypothesis, as defended by Steadman et al. (2005), is not sufficiently supported in the empirical world. As we have briefly pointed out: (1) a considerable number of reliable Holocene dates for megafaunal specimens in South America already exist, including for ground sloths; (2) the existence of late megafaunal LADs in Central America islands can be equally well explained through overkilling or environmental changes; and (3) the general lack of megafaunal killing sites and megafaunal remains in archaeological contexts is inconsistent with the overkill hypothesis. Nonetheless, it is important to emphasize that the amount of information regarding the presence of megafauna in archaeological sites is still too small to be considered as strong evidence against human predation of megafauna, and thus this piece of information must be interpreted as complementary to the others. Collectively, the data presented here are more consistent with a model explaining megafaunal extinction through climatic fluctuations, although in South America the poor chronological contextualization of the megafaunal decline does not yet allow for a percentage estimate of megafaunal genera that survived until human arrival. In North America (Grayson & Meltzer, 2002, 2003) and in Australia (Wroe et al., 2006; Wroe & Field, 2006), this percentage seems to have been small, suggesting that the megafaunal extinction was a protracted process, beginning much earlier than the human settlement of these continents. Such a decline may have been the case in South America, as only a few megafaunal genera apparently survived until the Holocene. While a human presence could have accelerated the process of extinction of the remaining megafaunal genera, climatic fluctuations could also have been responsible. Araujo et al. (2005) suggested a period of drought during the mid-Holocene in central Brazil, based on a general abandonment of the region by humans and also on palaeoenvironmental data. At least for central Brazil, megafaunal extinction could thus be also explained by the dry period that started between 8500 and 7500 14C yr bp (c. 9520–8190 cal. bp). Furthermore, according to Araujo et al. (2005) several authors recognize the existence of dry climatic periods during the early and mid-Holocene in South America. Bush et al. (2005) also found evidence suggesting the existence of this drier period in the Andes region (between 0° and 24°), although in this case it was not a single or synchronous event. Even if asynchronous, the important point here is that this dry period seems to have been a widespread phenomenon in South America. Thus, we concur with Borrero et al. (1998, p. 197) who propose that ‘people played at most a secondary role in the mega mammal extinctions, perhaps accelerating a process already underway before human arrival in South America’. We would like to thanks Rodolfo Salas for his kindness in assisting us in determining the Holocene date in Peru. Our long-term research in Lagoa Santa is funded by FAPESP (grant 04/01321-6) and by scholarships given to AH (FAPESP 04/11485-6), MH (FAPESP 04/01253-0) and to WAN (CNPQ 305918/85-0). Alex Hubbe is a graduate student at the Laboratory for Human Evolutionary Studies, Instituto de Biociências, Universidade de São Paulo. His main interests are the palaeoecology and extinction of the South America megafauna. Mark Hubbe is an investigator at the Instituto de Investigaciones Arqueológicas y Museo, Universidad Católica del Norte, Chile. His main research interest is the origin and dispersion of the First Americans. Walter Neves is the coordinator of the Laboratory for Human Evolutionary Studies, Instituto de Biociências, Universidade de São Paulo. His main research interest is the origins and adaptations of the First Americans. Editor: Mark Bush

Megafauna: giant beasts of Pleistocene South America

The deglaciation of the Americas during the Last Glacial Termination

Apologetics and Antiquity: Book of Mormon Reception, 1830–1844

Several hypotheses have been advanced for the origin and diversification of the bat fauna of the New World. Traditional models considered one of the families (Vespertilionidae) to have had a North American origin, whilst the diversification of other seven families was thought to have occurred in South America. Present‐day patterns of diversity are the result, according to these hypotheses, of the mixing of faunas, mostly coinciding with the Great American Biotic Interchange (GABI) of the Americas. Recent research has challenged the traditional model and has posited the possibility of dual centres of diversification (in South and North America) for families traditionally considered of strict South American origin. Here we examine the latitudinal patterns of bat diversity and endemism at the genus level and show that present‐day patterns are more consistent with this dual‐diversification hypothesis than with the traditional models. We document an asymmetrical latitudinal gradient of genus richness with a plateau near the equator, but with a decline in Central America and Mexico; however, in this area the relative number of genera, considering the species richness, is higher than expected by chance, as shown by a proper null model. The distribution and identity of endemic genera are consistent with models considering a North American origin for two of the families (Vespertilionidae and Natalidae), an early arrival to South America for another family (Molossidae), and a complex diversification process, involving two centres of diversification, for at least two of the families of the Noctilionoidea (Mormoopidae and Phyllostomidae) and possibly for the Emballonuridae. The recently identified Panamanian Realm (including southern Mexico and Central America) seems to have played a significant role in the diversification of New World bats.

AimOne of the most widely cited natural experiments in biogeography is the Great American Biotic Interchange (GABI). Here, we re‐assess the famous asymmetry in the exchange for mammals, with North American clades being much more successful in South America than vice versa. We investigate if this directionality could reflect higher susceptibility to predation in South American mammals rather than low competitive ability, as is usually believed.LocationNorth and South America.MethodsPrior to the GABI, South America lacked effective mammalian predators. Since its fauna did not co‐evolve with such predators, colonization of North America may only have been possible for species whose natural history makes them less susceptible to mammalian predation. To investigate this we used phylogenetic regressions to investigate species traits associated with the ability of clades originally from South America to colonize North America, and vice versa, during the GABI. Analyses were conducted both with and without species that went extinct in the late Quaternary.ResultsWhen extinct species were included, traits associated with lower predation risk (large body size, arboreality) were associated with greater success in colonizing North America for South American clades. This pattern was not visible in analyses based on the current fauna, since most of the mammals that invaded North America went extinct at the end of the Pleistocene, probably due to human predation. The pattern for northern colonizers of South America was similar whether or not extinct species were included and was not linked to predation risk.ConclusionsOur findings are consistent with the asymmetric GABI in mammals being explained by predation and not with expectations from competition. The GABI therefore illustrates that trophic interactions can be a powerful driver of long‐term dynamics of biotic interchange, as seen in many human‐driven invasions of formerly isolated regions.

Roles of land bridges in global biogeography and ecosystems

The Great American Biotic Interchange is considered to be a punctuated process, primarily occurring during four major pulses that began approximately 2.5 Ma. Central America and southeastern Mexico have a poor fossil record of this dynamic faunal history due to tropical climates. Exploration of submerged caves in the Yucatán, particularly the natural trap Hoyo Negro, is exposing a rich and remarkably well-preserved late Pleistocene fauna. Radiometric dates on megafauna range from approximately 38 400-12 850 cal BP, and extinct species include the ursid Arctotherium wingei and canid Protocyon troglodytes. Both genera were previously thought to be indigenous to and confined to South America and appear to represent an instance of large placental mammals, descended from North American progenitors, migrating back north across the Panama Isthmus. This discovery expands the distribution of these carnivorans greater than 2000 km outside South America. Their presence along with a diverse sloth assemblage suggests a more complex history of these organisms in Middle America. We suggest that landscape and ecological changes caused by latest Pleistocene glaciation supported an interchange pulse that included A. wingei, P. troglodytes and Homo sapiens.