Boid snake fossils from the Neogene of Southern Costa Rica

We report the first record of Megatheriidae-Megatheriinae fossil record in Central and North America, which also represents the earliest record of a Megatheriidae-Megatheriinae outside of South America at 5.8 Ma, and before the closure of the Isthmus of Panama. The fossil record of the Megatheriidae record comes the from Curre Formation, Late Hemphillian (Hh3) (Late Miocene), San Gerardo de Limoncito locality, Canton of Coto Brus, Puntarenas Province, Costa Rica, and shows a combination of plesiomorphic and advance characters whose combination is unique among the Megatheriinae. These Megatheriidae remains are scarce and fragmentary, however, they have enough morphological information and key morphological characters to allow us to propose a new genus and species of Megatheriinae, Sibotherium ka gen. et sp. nov. Based on the morphology preserved in these remains, Sibotherium ka is more closely related to Megathericulus, Pyramiodontheroium or Anisodontherium than to the more advanced Megatheriinae genera Urumaquia, Megatherium or Eremotherium. We explain the early record of this xenarthran in Costa Rica by the presence of a land corridor established for short periods of time as a result of tectonic uplift or by a drop in sea level or a mixture of both at approximately 5.8 Ma in Southern Central America.

news and update ISSN 1948-6596 commentary The less-splendid isolation of the South American continent Only few biogeographic scenarios capture the im- agination as much as the closure of the Isthmus of Panama. The establishment of this connection ended the “splendid isolation” of the South Amer- ican continent (Simpson 1980), a continent that had been unconnected to any other land mass for over 50 million years. When the Isthmus rose out of the water some 3 million years ago (mya) the Great American Biotic Interchange started. Since terrestrial biotic interchange was no longer blocked by the Central American Seaway, (asymmetrical) invasion of taxa across this new land bridge transformed biodiversity in North as well as South America (Leigh et al. 2014). Or so the story goes. A recent paper by Montes et al. (2015) casts further serious doubt on this scenario from a geo- logical perspective. They show that a river system existed, originating in the volcanic arc of Panama and flowing into northern Colombia, about 15 to 13 mya. They base this hypothesis on geological mapping in conjunction with geochronological analyses of river deposits found in northern Co- lombia. With this they built on previous work (Farris et al. 2011, Montes et al. 2012a,b) in which the hypothesis of a fairly recent closure of the Isthmus was also questioned. Montes et al. (2015) reason that when a river system existed in the Panama-Colombia area, a terrestrial connection needed to be present. Any connection between the Caribbean Sea and Pacific Ocean could only have existed to the west of the current day Pana- ma Canal area, where they postulate the origin of this river system. So, how do these data fit in with what biolo- gists know about migrations between North and South America? Leigh et al. (2014) provide a com- prehensive overview of the historical biogeogra- phy of the Isthmus and review for instance that ground sloths had reached North from South America around 10 million years ago and Panama was well populated with all kinds of animals in the Early Miocene (18-19 mya), that fresh water fishes already dispersed in the late Miocene between lower Central America (Costa Rica) and South America (northern Colombia), and that some snapping shrimp populations were already split long before the Isthmus had finally closed (most between 7–10 mya but some >15 mya). Next to this, several papers showed that plants also mi- grated between North and South America prior to the closure of the Isthmus (e.g., Erkens et al. 2007, Bacon et al. 2013), although for plants it is difficult to rule out that this happened via long-distance dispersal. Thus, the new findings of Montes and colleagues fit much better with a wealth of evi- dence from the biological realm that has been amassed over the last years, than the old model of a relatively rapid rise of the Isthmus. If the land-bridge was available much earli- er to many terrestrial organisms, the question that remains, of course, is why they only began to mi- grate in large numbers between North and South America around 3 mya? The generally accepted scenario that a wide seaway blocked their path is, given the above mentioned studies, not support- ed. The answer can probably be found in two di- rections. First of all, the sudden onset at 3 mya is just a remnant from past analyses. As discussed above, earlier migrations indeed have been found and the onset itself of the interchange is placed much earlier than previously accepted (Carrillo et al. 2015), starting already around 10 mya. Alt- hough the bulk of migrations might have hap- pened more recently, the onset is more gradual than was postulated. Second, another type of ex- planation can be found in the type of vegetation present (Leigh et al. 2014), accepting that species ranges can be limited by more than geographic barriers alone (Feeley et al. 2014). Due to climatic cooling around 3 mya a corridor of grassland and savannah allowed open-country animals and some plants to move between North and South America (Molnar 2008, Bacon 2013). Before and after cooling such migration was not possible since tropical forests formed effective obstacles to any migration of these open-country animals. Sup- port for such a scenario is, for instance, provided frontiers of biogeography 7.3, 2015 — © 2015 the authors; journal compilation © 2015 The International Biogeography Society

Sloths, like other xenarthrans, are an extremely interesting group of mammals that, after a long history of evolution and diversification in South America, became established on islands in the Caribbean and later reached North America during the Great American Biotic Interchange. In all three regions, they were part of the impressive Pleistocene megafauna. Most taxa became extinct and only two small, distantly related tree-dwelling genera survived. Here, we incorporate several recently described genera of sloths into an assembled morphological data supermatrix and apply Bayesian inference, using phylogenetic and morphological clock methods, to 64 sloth genera. Thus, we investigate the evolution of the group in terms of the timing of divergence of different lineages and their diversity, morphological disparity and biogeographical history. The phylogeny obtained supports the existence of the commonly recognized clades for the group. Our results provide divergence time estimates for the major clades within Folivora that could not be dated with molecular methods. Lineage diversity shows an early increase, reaching a peak in the Early Miocene followed by a major drop at the end of the Santacrucian (Early Miocene). A second peak in the Late Miocene was also followed by a major drop at the end of the Huayquerian (Late Miocene). Both events show differential impact at the family level. After that, a slight Plio-Pleistocene decline was observed before the marked drop with the extinction at the end of the Pleistocene. Phenotypic evolutionary rates were high during the early history of the clade, mainly associated with Mylodontidae, but rapidly decreased to lower values around 25 Ma, whereas Megalonychidae had lower rates at the beginning followed by a steady increase, peaking during the Late Miocene and the Pliocene. Morphological disparity showed a similar trend, with an early increase, followed by a slowly increasing phase through the Late Oligocene and Early Miocene, and ending with another increase beginning at the middle of the Miocene. Biogeographic analysis showed southern South America as the most probable area of origin of the clade and the main region in which the early diversification events took place. Both Megatheriinae and Nothrotheriinae basal nodes were strongly correlated with Andean uplift events, whereas the early history of Mylodontidae is closely associated with southern South America and also shows an early occupation of the northern regions. Within Megalonychidae, our results show Choloepus as a descendant of an island dispersing ancestor and a probable re-ingression to South America by a clade that originated in Central or North America.

Newly described marsupial specimens of Judithian (late Campanian) and Lancian (Maastrichtian) age in the western interior of North America (Wyoming to Alberta) have dental morphologies consistent with those expected in comparably aged sediments in South America (yet to be found). Three new Lancian species are referable to the didelphimorphian Herpetotheriidae, which suggests that the ameridelphian radiation was well under way by this time. The presence of a polydolopimorphian from Lancian deposits with a relatively plesiomorphic dental morphology and an additional polydolopimorphian taxon from Judithian deposits with a more derived molar form indicate that this lineage of typically South American marsupials was diversifying in the Late Cretaceous of North America. This study indicates that typical South American lineages (e.g. didelphimorphians and polydolopimorphians) are not the result of North American peradectian progenitors dispersing into South America at the end of the Cretaceous (Lancian), or at the beginning of the Paleocene (Puercan), and giving rise to the ameridelphian marsupials. Instead, these lineages, and predictably others as well, had their origins in North America (probably in more southerly latitudes) and then dispersed into South America by the end of the Cretaceous. Geophysical evidence concerning the connections between North and South America in the Late Cretaceous is summarized as to the potential for overland mammalian dispersal between these places at those times. Paleoclimatic reconstructions are considered, as is the dispersal history of hadrosaurine dinosaurs and boid snakes, as to their contribution to an appraisal of mammalian dispersals in the Late Cretaceous. In addition, we present a revision of the South American component of the Marsupialia. One major outcome of this process is that the Polydolopimorphia is placed as Supercohort Marsupialia incertae sedis because no characteristics currently known from this clade securely place it within one of the three named marsupial cohorts.

Colonizing the Caribbean: is the GAARlandia land‐bridge hypothesis gaining a foothold?

In this contribution seven forms of digenetic trematodes, some parasitic on cattle and some in wild animals, are described. Excepting Fasciola hepatica Linnaeus, 1758, whose presence in cattle and horses in Costa Rica has been cited by Chavarria in 1940, all the species considered are new to the helminthologic fauna of Costa Rica. Specimens of a paramphistomid found in Costa Rica catt1e have been classified as Paramphistomum cervi (Zeder, 1790) Fischoeder, 1901, in view of the presence of a genital sucker, the configuration of the digestive apparatus, and the structure and disposition of the reproductive organs and vitelline glands. Fasciola hepatica Linnaeus, 1758 is also a frequent parasite in Costa Rica, the precise life cycle of this parasite is unknown in the Republic but studies have been undertaken to determine its intermediate mollusean host. Choledocystus intermedius Caballero, Bravo and Cerecero, 1944 has been found for the first time in Costa Rica, in toads Bufo marinus marinus Linnaeus, 1758 thus allowing its range to be defined from southern Mexico to Panama. Gorgoderina megalorchis Bravo, 1948 is another species of trematode parasite of the amphibian host cited above; our specimens differ from those studied by M. Bravo Hollis only in size, the specimens from Costa Rica being larger than those from Mexican toads; the new locality record extends its geo­graphical distribution to Central America. Urotrema scabridum Braun, 1900 has been collected in Costa Rica for the first time, from the bat Eptesicus propinquus Peters which is also considered to be a new host record. Two species of the genus Rhapalias: R. coronatus (Rudolphi 1819) Stiles and Hassall, 1898 and R. horridus (Diesing, 1850) Stiles and Hassall, 1898 are registered from the Costa Rican opossum, Didelphis marsupialis etensi Allen; both species are known to parasitize various South American and Mexican marsupials and the Costa Rican specimens do not differ from these in structural or measurable details. Finally, the trematode Heronimus chelydrae Mac Callum, 1902 has been collected from the lungs of freshwater turtles of the genus Kinosternon. According to the studies of E. Caballero y C. 1940, it is believed that this is the only species in the genus; it has also been reported from turtles of Panama, Mexico and the United States in North America. It has been noted that an early regression of the testes occurs in this species, since these were persistent in only a few of the specimens described.

The fourth biennial meeting of the International Biogeography Society (IBS) in Merida, Yucatan in January 2009 represented a double opportunity for Mexican biologists. First, it fostered the integration of the large community of Mexican biogeographers with the activities of the IBS. Second, the meeting allowed us to welcome a large number of delegates from distant parts of the world who were able to visit what has been considered an obligate destination for nature lovers and cultural tourists alike: the Yucatan peninsula. As Edward O. Wilson pointed out, besides economic power every country has two additional and important types of wealth: cultural and natural. Cultural richness is a naturally embedded component of the Mexican way of life.

A phytogeographic analysis of the distributions of 454 species of trees native to the Osa Peninsula in 22 families revealed that 4.8% of the species are endemic to the Osa Peninsula and the adjacent mainland of Costa Rica. However, nearly one-fourth of the species might be regionally endemic to Central-South Mesoamerica (Costa Rica, Nicaragua, and Panama). Our sample suggests that 53.6% of the species occur in some part of Mesoamerica and sometimes range into northwestern South America, and that 44.5% of the species have wide distributions throughout tropical America. There is a strong affinity with the flora of northwestern South America, with 46.2% of the species on the Osa also found there. In addition, 50.6% of the tree species on the Osa occur on both the Atlantic and Pacific slopes of Central America or, if they reach South America, are sometimes found on both sides of the Andes. Major contributions to the tree flora of the Osa have been made by species arriving in the Osa by 1) dispersal from South and North America to islands in proto Central America before the formation of a dry-land connection between the two continents, and 2) migration from South America and North America after the closure of the Panamanian isthmus was made. This analysis demonstrates the importance of the Osa as a regional refuge for protecting species with distributions limited to the Osa and parts of Panama, Costa Rica, or Nicaragua. The Osa is also important because it harbors the last expanse of tropical wet forest on the Pacific slope of Central America large enough to ensure the survival of the Central American populations of widely distributed plants and animals.

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 Neogene of North American represents a time of climatic change from an initially warm, non-arid climate to one with the development of increasing aridity, with warming temperatures through the early part and fluctuating (but basically cooler) temperatures through the later part. This reflects the classic story of a vegetational change from woodland to savanna and eventually to prairie. Note that the transition to true savanna in the Late Miocene was considerably earlier than the first savannas in the Pliocene of the Old World. The evolutionary trends in mammals reflect these climactic and vegetational changes.Some general broad trends are as follows: the replacement of terrestrial and subfossorial moles and geomyid rodents with more specialized fossorial ones; a decrease in the diversity of brachydont rodents and an increase in the diversity of hypsodont ones (including saltatorial forms), and a late Neogene diversification of microtines and deer mice; a decline in the diversity of tree squirrels and terrestrial beavers, and an increase in diversity of ground squirrels and aquatic beavers; the replacement of carnivores belong to more archaic families by more modern types; taxa and an increase in body size, leg length, and hypsodonty in most ungulate taxa, including oreodonts, protoceratids, camelids, antilocaprids, rhinos and equine horses although a couple of taxa show an apparent reversal of these trends: dromomerycids (cervoids) and some anchitherine horses show other morphological changes that suggest progressively more woodland-adapted (rather than savanna-adapted) forms. Tapirs and (to a lesser extent) peccaries seem little affected by the Neogene changes, and persist until the Recent.The Neogene was also punctuated by immigration events (primarily from Asia) and extinctions. The start of the Neogene shows surprisingly little change, with many Paleogene “holdovers”: some new forms appear as either the result of evolution in situ (e.g. equine horses and osteoborine dogs) or as immigrants (e.g. chalicotheres and hemicyonine “dog bears”). The initial major immigrations are during the late Early Miocene, marked by the Asian appearances of true felids (replacing the “false saber-tooths” or nimravids), pecoran ruminants (replacing the hypertragulids), more derived rhinos (replacing the diceratherine rhinos), neomustelids and procyonids. Archaic suoids such as anthracotheres and entelodonts become extinct at this time, and only the more derived ticholeptine oreodonts survive this period. The start of the Middle Miocene is notable for the appearance of proboscideans and deer mice. The Late Miocene sees the decline and eventual disappearance of hedgehogs, archaic carnivores (hemicyonine bears and amphicyonids), most browsing ungulates (oreodonts, protoceratids, many camelids, anchitherine horses, dromomerycids, merycodontine antilocaprids, hornless ruminants, chalicotheres, bunodont gomphotheres), and rhinos. New taxa appearing including ursine bears (immigrants), oversized camels and more derived gomphotheres (in situ evolution). The Pliocene marks a new wave of immigration: microtines, hyenas, true saber-tooths, and cervids come in from Asia; ground sloths (two families appearing in the Late Miocene), glyptodonts, armadillos and capybaras come in from South America. Most mammals that survived the end Miocene extinctions persist, but for many of them (such as horses, camels and antilocaprids) the generic diversity is greatly reduced.

Neogene stratigraphy, paleoceanography and paleobiogeography in northwest South America and the evolution of the Panama seaway

Early Holocene survival of megafauna in South America

New Campylopus Records from South and Central America

New Campylopus Records from South and Central America. II

The Pleurotus ostreatus species complex is saprotrophic and of significant economic and ecological importance. However, species delimitation has long been problematic because of phenotypic plasticity and morphological stasis. In addition, the evolutionary history is poorly understood due to limited sampling and insufficient gene fragments employed for phylogenetic analyses. Comprehensive sampling from Asia, Europe, North and South America and Africa was used to run phylogenetic analyses of the P. ostreatus species complex based on 40 nuclear single-copy orthologous genes using maximum likelihood and Bayesian inference analyses. Here, we present a robust phylogeny of the P. ostreatus species complex, fully resolved from the deepest nodes to species level. The P. ostreatus species complex was strongly supported as monophyletic, and 20 phylogenetic species were recognized, with seven putatively new species. Data from our molecular clock analyses suggested that divergence of the genus Pleurotus probably occurred in the late Jurassic, while the most recent common ancestor of the P. ostreatus species complex diversified about 39 Ma in East Asia. Species of the P. ostreatus complex might migrate from the East Asia into North America across the North Atlantic Land Bridge or the Bering Land Bridge at different times during the late Oligocene, late Miocene and late Pliocene, and then diversified in the Old and New Worlds simultaneously through multiple dispersal and vicariance events. The dispersal from East Asia to South America in the middle Oligocene was probably achieved by a long-distance dispersal event. Intensification of aridity and climate cooling events in the late Miocene and Quaternary glacial cycling probably had a significant influence on diversification patterns of the complex. The disjunctions among East Asia, Europe, North America and Africa within Clade IIc are hypothesized to be a result of allopatric speciation. Substrate transitions to Apiaceae probably occurred no earlier than 6 Ma. Biogeographic analyses suggested that the global cooling of the late Eocene, intensification of aridity caused by rapid uplift of the QTP and retreat of the Tethys Sea in the late Miocene, climate cooling events in Quaternary glacial cycling, and substrate transitions have contributed jointly to diversification of the species complex.