Panamacebus transitus: a Monkey in North America During the Miocene Neogene

Seven tiny teeth tell the story of an ancient monkey that made a 100-mile ocean crossing between North and South America into modern-day Panama - the first fossil evidence for the existence of monkeys in North America.

The find provides the oldest fossil evidence for the interchange of mammals between South and North America and challenges long-held views of South America as an island continent that evolved in isolation before the Isthmus of Panama was formed and animals began crossing between the continents about 3.5 million years ago, said Jonathan Bloch, curator of vertebrate paleontology at the Florida Museum of Natural History on the University of Florida campus. Study findings are detailed online today in the journal Nature.

Scientists uncovered the teeth belonging to the 21-million-year-old forest-dwelling primate during recent excavations related to the expansion of the Panama Canal. The new genus and species, dubbed Panamacebus transitus, received its name from the Latin word transit, meaning crossing.

link.

Only 22% of men in Panama Have Y Chromosomes From the Indigenous Population

The Spanish conquest of the Americas was devastating for native peoples. Many native men died in conflicts with the invaders. Male Spanish colonists often came without their wives and took native women as partners. A new genetic analysis of Panamanian men by a team including a Smithsonian scientist shows this historical legacy: only 22 percent had Y-chromosomes of native origin, even though most Panamanians are of female indigenous ancestry.

Everyone has a pair of sex chromosomes that determine their gender. Females have two X-chromosomes, while males have one X and one Y, the latter inherited from their father. These chromosomes are found in each cell's nucleus. Another genetic component called mitochondrial DNA (mtDNA) is found in cells outside the nucleus. Both males and females inherit their mtDNA from their mother alone. Over time, small mutations accumulate in both mtDNA and Y-chromosomes, allowing scientists to trace their history.

A team of geneticists from the University of Pavia including Antonio Torroni found that among the 408 Panamanian men whose genetics were analyzed, 60 percent had Y-chromosomes that originated in West Eurasia and North Africa (probably mostly from Europe). About 22 percent were of Native American origin, 6 percent from sub-Saharan Africa and 2 percent from South Asia (probably China or the Indian sub-continent). In contrast, a large majority of this group--including nearly all those with Native American, African and Asian Y-chromosomes--had mtDNA of indigenous origin. Among men with Eurasian Y-chromosomes, 13 percent had mtDNA from sub-Saharan Africa and only a very few had European mtDNA.

link.

Academic Bun Fight: Panama Isthmus Closed Earlier Than Currently Thought (or did it)

Biological evidence supports an early and complex emergence of the Isthmus of Panama
Authors:

Bacon et al

Abstract:

The linking of North and South America by the Isthmus of Panama had major impacts on global climate, oceanic and atmospheric currents, and biodiversity, yet the timing of this critical event remains contentious. The Isthmus is traditionally understood to have fully closed by ca. 3.5 million years ago (Ma), and this date has been used as a benchmark for oceanographic, climatic, and evolutionary research, but recent evidence suggests a more complex geological formation. Here, we analyze both molecular and fossil data to evaluate the tempo of biotic exchange across the Americas in light of geological evidence. We demonstrate significant waves of dispersal of terrestrial organisms at approximately ca. 20 and 6 Ma and corresponding events separating marine organisms in the Atlantic and Pacific oceans at ca. 23 and 7 Ma. The direction of dispersal and their rates were symmetrical until the last ca. 6 Ma, when northern migration of South American lineages increased significantly. Variability among taxa in their timing of dispersal or vicariance across the Isthmus is not explained by the ecological factors tested in these analyses, including biome type, dispersal ability, and elevation preference. Migration was therefore not generally regulated by intrinsic traits but more likely reflects the presence of emergent terrain several millions of years earlier than commonly assumed. These results indicate that the dramatic biotic turnover associated with the Great American Biotic Interchange was a long and complex process that began as early as the Oligocene–Miocene transition.

That was a bad analysis!!!

Appearance of an early closure of the Isthmus of Panama is the product of biased inclusion of data in the metaanalysis

Author:

Lessios

Extract:

In their PNAS article “Biological evidence supports an early and complex emergence of the Isthmus of Panama,” Bacon et al. (1) use data from molecular comparisons of terrestrial and marine organisms taken from the literature to estimate dates of rate shifts in migration. One of their conclusions is that “events separating marine organisms in the Atlantic and Pacific oceans [occurred] at ca. 23 and 7 Ma” (1). The authors base this conclusion on two kinds of molecular dating: (i) 31 dates from phylogenies with evolutionary rates calibrated from fossils at one or more nodes, and (ii) 52 dates from mitochondrial divergence between sister species on either side of the Isthmus taken from the review by Lessios (2) (note: complete data are available from the Dryad Digital Repository). For the latter, divergence was converted to time by assuming a mitochondrial DNA divergence rate of 2% per million years. Unfortunately, Bacon et al.’s (1) metaanalysis of separations of marine organisms contains unexplained omissions of data and mistakes. Nine of the fossil calibrated divergence values are wrong, and three are omitted (though present in publications used to derive other dates). Thirty-eight comparisons from Lessios (2) are excluded. Criteria for inclusion of data are not stated but, judging from the estimated dates, only data from Cytochrome c oxidase subunit 1 were taken into account, even though Lessios (2) presents data for multiple mitochondrial genes. This selectivity in the marine dataset of Bacon et al. (1) is hard to explain, because the terrestrial data come from various genes, and because eight comparisons of Cytochrome c oxidase subunit 1 of marine species are among those excluded.

no!  it wasn't, damnit!

Reply to Lessios and Marko et al.: Early and progressive migration across the Isthmus of Panama is robust to missing data and biases

Authors:

Bacon et al

Extract:

The emergence of the Isthmus of Panama left a major imprint on the biodiversity of the Americas. The connection between South and North America facilitated dispersal of terrestrial and freshwater organisms, while separating marine species between the eastern Pacific and Caribbean seas. Recent geological data have questioned the long-standing view of a Pliocene emergence of the Isthmus (1) and show that the Central American Seaway, defined as the deep oceanic seaway along the tectonic boundary of the South American plate and Panama arc, was already closed by 15–13 Ma (2). Caribbean–Pacific shallow water exchange probably continued, albeit intermittently, until a full closure at 3.5 Ma (1–3). Recently Bacon et al. (3) used molecular and fossil data to evaluate the timing, tempo, and directionality of biotic exchange and vicariance across the Isthmus, and tested whether biological data are congruent with recent geological evidence. Significant increases in terrestrial dispersals were found at ca. 20 and 6 Ma, and increases in marine vicariance at ca. 23 and 7 Ma. Similar patterns prevailed despite intrinsic differences among the taxonomic groups surveyed. This led Bacon et al. (3) to reject the assumption of a single closure of the Isthmus at ca. 3.5 Ma in favor of an older, more complex model of land emergence and biotic interchange.

Central America Connected to South America Much Earlier During the Middle Miocene Neogene

Middle Miocene closure of the Central American Seaway

Authors:

Montes et al

Abstract:

Uranium-lead geochronology in detrital zircons and provenance analyses in eight boreholes and two surface stratigraphic sections in the northern Andes provide insight into the time of closure of the Central American Seaway. The timing of this closure has been correlated with Plio-Pleistocene global oceanographic, atmospheric, and biotic events. We found that a uniquely Panamanian Eocene detrital zircon fingerprint is pronounced in middle Miocene fluvial and shallow marine strata cropping out in the northern Andes but is absent in underlying lower Miocene and Oligocene strata. We contend that this fingerprint demonstrates a fluvial connection, and therefore the absence of an intervening seaway, between the Panama arc and South America in middle Miocene times; the Central American Seaway had vanished by that time.

Two New Miocene Crocodilian and Hippolike Anthracothere Found in Panama

University of Florida paleontologists have discovered remarkably well-preserved fossils of two crocodilians and a mammal previously unknown to science during recent Panama Canal excavations that began in 2009.

The two new ancient extinct alligator-like animals and an extinct hippo-like species inhabited Central America during the Miocene about 20 million years ago. The research expands the range of ancient animals in the subtropics — some of the most diverse areas today about which little is known historically because lush vegetation prevents paleontological excavations — and may be used to better understand how climate change affects species dispersal today. The two studies appear online today in the same issue of the Journal of Vertebrate Paleontology.

The fossils shed new light on scientists' understanding of species distribution because they represent a time before the formation of the Isthmus of Panama, when the continents of North and South America were separated by oceanic waters.

"In part we are trying to understand how ecosystems have responded to animals moving long distances and across geographic barriers in the past," said study co-author Jonathan Bloch, associate curator of vertebrate paleontology at the Florida Museum of Natural History on the UF campus. "It's a testing ground for things like invasive species – if you have things that migrated from one place into another in the past, then potentially you have the ability to look at what impact a new species might have on an ecosystem in the future."

The research was funded by the National Science Foundation Panama Canal Partnerships in International Research and Education project, which supports paleontological excavation of the canal during construction expected to continue through 2014.

"We're very fortunate we could get the funding for PIRE to take advantage of this opportunity — we're getting to sample these areas that are completely unsampled," said Alex Hastings, lead author of the crocodilian study and a visiting instructor at Georgia Southern University who conducted the research for the project as a UF graduate student.

Researchers analyzed all known crocodilian fossils from the Panama Canal, including the oldest records of Central American caimans, which are cousins of alligators. The more primitive species, named Culebrasuchus mesoamericanus, may represent an evolutionary transition between caimans and alligators, Hastings said.

"You mix an alligator and one of the more primitive caimans and you end up with this caiman that has a much flatter snout, making it more like an alligator," Hastings said. "Before this, there were no fossil crocodilian skulls known from Central America."

Christopher Brochu, an assistant professor of vertebrate paleontology in the department of geoscience at the University of Iowa, said "the caiman fossil record is tantalizing," and the new data shows there is still a long way to go before researchers understand the group.

"The fossils that are in this paper are from a later time period, but some of them appear to be earlier-branching groups, which could be very important," said Brochu, who was not involved with the study. "The problem is, because we know so little about early caiman history, it's very difficult to tell where these later forms actually go on the family tree."

The new mammal species researchers described is an anthracothere, Arretotherium meridionale, an even-toed hooved mammal previously thought to be related to living hippos and intensively studied on the basis of its hypothetical relationship with whales. About the size of a cow, the mammal would have lived in a semi-aquatic environment in Central America, said lead author and UF graduate student Aldo Rincon.

"With the evolution of new terrestrial corridors like this peninsula connecting North America with Central America, this is one of the most amazing examples of the different kind of paths land animals can take," Rincon said. "Somehow this anthracothere is similar to anthracotheres from other continents like northern Africa and northeastern Asia."

Researchers also name a second crocodilian species, Centenariosuchus gilmorei, after Charles Gilmore, who first reported evidence of crocodilian fossils collected during construction of the canal 100 years ago. The genus is named in honor of the canal's centennial in 2014.

Crocodilians Dispersed Differently Than Mammals in the Americas

The uplift of the Isthmus of Panama 2.6 million years ago formed a land-bridge that has long thought to be the crucial step in the interchange of animals between the Americas, including armadillos and giant sloths moving up into North America and relatives of modern horses, rabbits, foxes, pigs, cats, dogs, and elephants down into South America.

However, in the March 2013 issue of the Journal of Vertebrate Paleontology, researchers from the University of Florida and the Smithsonian Tropical Research institute describe fossil crocodilians that shed a surprising new light on the history of interchange and animal distributions between the Americas.

The fossils are partial skulls of two new species of caiman, relatives of alligators, who live exclusively in South America today. They were discovered in rocks dated from 19.83 and 19.12 million years old and that were exposed by excavations associated with the expansion of the Panama Canal.

"These are the first fossil crocodilian skulls recovered from all of Central America. They fill a gap in evolution between the alligators of North America and the caimans of South America. It's quite incredible." states lead author Alex Hastings, a fossil crocodilian specialist at Georgia Southern University.

The presence of the fossils in Panama indicates that caimans dispersed North from South America by the early Miocene, which is over ten million years earlier than the spread of mammals. This discovery is additionally important because caimans lack the ability to excrete excess salt from their bodies and are restricted to freshwater environments. As a result, they could have only dispersed a short distance across sea water, which supports a recent hypothesis that Central and South America were much closer to each other 19 million years ago than previously thought, and paints a new picture of the past histories of American animals.

Says co-author Jonathan Bloch, a vertebrate paleontologist at the Florida Museum of Natural History, "We are starting to understand that while the mammals in Panama 19-21 million years ago were very similar to those found in Mexico, Texas, and Florida at that time, the reptiles tell a different story. Somehow, they were able to cross over from South America when it was completely isolated by seaways—this is one of the mysteries that will drive future inquiry and research in this region."

Browsing Horse Found in Panama Canal Zone

Rushing to salvage fossils from the Panama Canal earthworks, Aldo Rincon, paleontology intern at the Smithsonian Tropical Research Institute, unearthed a set of fossil teeth. Bruce J. MacFadden, curator of vertebrate paleontology at the Florida Museum of Natural History, University of Florida in Gainesville, describes the fossil as Anchitherium clarencei, a three-toed browsing horse, in the May 2009 issue of the Journal of Paleontology.

By far the most complete fossil of a horse collected at the site in excavations spanning the last century, characteristics such as the shape of the teeth confirm the identity of two earlier finds and indicate that this horse was primarily a forest-dwelling browser living in the area between 15 and 18 million years ago. This evidence supports MacFadden's earlier proposal that the habitat was probably a mosaic of relatively dense forest and open woodlands. The presence of this browsing horse in Panama significantly extends the southern tip of its range from previous finds from roughly the same period in Florida, Nebraska and South Dakota.

No time to comment.