The Interpretation of Caribbean Paleogeography: Reply to Hedges

La hipòtesi de GMRlàndia (Iturralde-Vinent & MacPhee, 1999) especifica que una llengua de terra, capaç d'actuar com a via de dispersió per a organismes terrestres, va connectar les futures Antilles Majors amb la vorera del nord-oest de Sud Amèrica durant un període curt cap a la transició Eocè/Oligocè. Hedges (2001) ha criticat aquesta hipòtesi sota diferents prismes, i a aquest treball tractam de replicar algunes de les seves objeccions, tenint en compte l'evidència més recent que tenim sobre les següents tres qüestions: (1) Quant ha durat la presència dels ambients terrestres actuals de la conca del Carib? (2) Quines han estat les dates d'emergència més probables per a les illes que tenen aquests ambients? (3) Quin efecte tenen les corrents de superfície marines sobre la distribució dels objectes que suren a l'àrea del Carib? Primer, en contra del que diu Hedges, encara no hi ha evidència geològica per a donar suport a una continuïtat als ambients terrestres del Carib abans de fa 37 Ma. A llavors, la pretensió d'Hedges que com a mínim algunes entitats biòtiques haurien persistit in situ per períodes de més de 37 Ma (la data més primerenca suportada per tal evidència), com a minim a algunes de les illes actuals, encara no es pot mantenir sobre bases geològiques. Segon, l'esdeveniment d'importància decisiva en l'emergència de GMRlàndia no fou la baixada del nivell eustàtic de la mar, sinó l'aixecament d'lm arc insular tot seguint el final de la seva fase magmàtica. A llavors, notar, com Hedges fa, que l'emergència de GAARIàndia no va estar correlacionada amb una baixada identificable principal-encara que fos correcte- no és pertinent al problema plantejat. Ni ho són les incerteses de les datacions, tant de les baixades com de l' esdeveniment d'aixecament. Finalment, encara que el moviment de les corrents de superfície marines està afectat per la força de Coriolis, el vent és molt més important per al moviment dels objectes sobre la superfície. Experiments reals revelen que aquests moviments són significativament caòtics, cosa que condueix a que el transport passiu virtualment mai esdevindrà en línia recta. Com a resultat, encara que els objectes transportats pels rius de Sud Amèrica eventualment poden embarrancar a les costes del Carib, els temps de trànsit són probablement llargs. Aquest fet, tal volta més que qualsevol altre, condueix a que les llargues estades a la mar siguin un mètode improbable de dispersió exitosa per a moltes castes d'organismes. Òbviament, les investigacions geològiques i paleontològiques no poden falsar escenaris històrics, però poden subministrar termini ad qu.em per precisament el tipus d'esdeveniments en que els biogeògrafs insulars haurien d'estar interessats, tals com quan apareixen per primera vegada a una àrea ambients desitjables per organismes terrestres, i quins organismes (representats per les seves restes) eren els primers en disposar de l'avantatge d'aquestes noves terres.La hipòtesi de GMRlàndia (Iturralde-Vinent & MacPhee, 1999) especifica que una llengua de terra, capaç d'actuar com a via de dispersió per a organismes terrestres, va connectar les futures Antilles Majors amb la vorera del nord-oest de Sud Amèrica durant un període curt cap a la transició Eocè/Oligocè. Hedges (2001) ha criticat aquesta hipòtesi sota diferents prismes, i a aquest treball tractam de replicar algunes de les seves objeccions, tenint en compte l'evidència més recent que tenim sobre les següents tres qüestions: (1) Quant ha durat la presència dels ambients terrestres actuals de la conca del Carib? (2) Quines han estat les dates d' emergència més probables per a les illes que tenen aquests ambients? (3) Quin efecte tenen les corrents de superfície marines sobre la distribució dels objectes que suren a l'àrea del Carib? Primer, en contra del que diu Hedges, encara no hi ha evidència geològica per a donar suport a una continuïtat als ambients terrestres del Carib abans de fa 37 Ma. A llavors, la pretensió d'Hedges que com a mínim algunes entitats biòtiques haurien persistit in situ per períodes de més de 37 Ma (la data més primerenca suportada per tal evidència), com a minim a algunes de les illes actuals, encara no es pot mantenir sobre bases geològiques. Segon, l'esdeveniment d'importància decisiva en l'emergència de GMRlàndia no fou la baixada del nivell eustàtic de la mar, sinó l'aixecament d'lm arc insular tot seguint el final de la seva fase magmàtica. A llavors, notar, com Hedges fa, que l'emergència de GAARIàndia no va estar correlacionada amb una baixada identificable principal-encara que fos correcte- no és pertinent al problema plantejat. Ni ho són les incerteses de les datacions, tant de les baixades com de l' esdeveniment d'aixecament. Finalment, encara que el moviment de les corrents de superfície marines està afectat per la força de Coriolis, el vent és molt més important per al moviment dels objectes sobre la superfície. Experiments reals revelen que aquests moviments són significativament caòtics, cosa que condueix a que el transport passiu virtualment mai esdevindrà en línia recta. Com a resultat, encara que els objectes transportats pels rius de Sud Amèrica eventualment poden embarrancar a les costes del Carib, els temps de trànsit són probablement llargs. Aquest fet, tal volta més que qualsevol altre, condueix a que les llargues estades a la mar siguin un mètode improbable de dispersió exitosa per a moltes castes d'organismes. Òbviament, les investigacions geològiques i paleontològiques no poden falsar escenaris històrics, però poden subministrar termini ad quem per precisament el tipus d'esdeveniments en que els biogeògrafs insulars haurien d'estar interessats, tals com quan apareixen per primera vegada a una àrea ambients desitjables per organismes terrestres, i quins organismes (representats per les seves restes) eren els primers en disposar de l'avantatge d'aquestes noves terres.The GMRlandia hypothesis (Iturralde-Vinent & MacPhee, 1999) specifies that a landspan, capable of acting as a dispersal conduit for terrestrial organisms, connected the future Greater Antilles with the margin of northwestern South America for a short period around the time of the Eocene/Oligocene transition. Hedges (2001) has criticized this hypothesis on various grounds, and in this paper we seek to reply to several of his objections by considering the most recent evidence bearing on these three questions: (1) How long have the present land environments of the Caribbean basin been in existence? (2) What are the likeliest emergence dates for the islands supporting those environments? (3) What effect do sea-surface currents have on the distribution of flotsam in the Caribbean area? First, contra Hedges, there is still no geological evidence for continuity in Caribbean land envirorunents earlier than 37 Ma. Therefore, Hedges' claim that biotic entities on at least some of the present islands have persisted in situ for periods longer than 37 Ma (the earliest date supported by such evidence) still GUillot be sustained on geological grounds. Secondly, the event of overriding importance in the emergence of GMRlandia was not drawdown in eustatic sea level, but uplíft in the island arc following the termination of its magmatic phase. Therefore, noticing as Hedges does that the emergence of GMRlandia was not correlated with an identifiable major drawdown-even if correct-has no pertinence to the issue at hand. Neither do uncertainties in the dating of either drawdowns or the uplift event. Finally, although the movement of sea-surface currents is affected by the Coriolis force, wind is much more important for the motion of objects on the surface (flotsam). Actual experiments reveal that such motions are significantly chaotic, which means that passive transport will virtually never occur in a straight line. As a result, although objects carried by South American rivers may eventually wash up on Caribbean shores, transit times are likely to be long. This fact, perhaps more than any other, makes long seas journeys an improbable method of successful dispersal for many kinds of organisms. Among such organisms we count most land mammals, for a host of autecological and physiological reasons. For other kinds of organisms, including herps, different considerations may apply. Obviously, paleontological and geological investigations cannot falsify historical scenarios, but they can provide termini ad quem for precisely the kinds of events that island biogeographers should be interested in, such as when environments suitable for land organisms first appeared in an area, and what organisms (as represented by their remains) were the first to take advantage of these new lands.The GMRlandia hypothesis (Iturralde-Vinent & MacPhee, 1999) specifies that a landspan, capable of acting as a dispersal conduit for terrestrial organisms, connected the future Greater Antilles with the margin of northwestern South America for a short period around the time of the Eocene/Oligocene transition. Hedges (2001) has criticized this hypothesis on various grounds, and in this paper we seek to reply to several of his objections by considering the most recent evidence bearing on these three questions: (1) How long have the present land environments of the Caribbean basin been in existence? (2) What are the likeliest emergence dates for the islands supporting those environments? (3) What effect do sea-surface currents have on the distribution of flotsam in the Caribbean area? First, contra Hedges, there is still no geological evidence for continuity in Caribbean land envirorunents earlier than 37 Ma. Therefore, Hedges' claim that biotic entities on at least some of the present islands have persisted in situ for periods longer than 37 Ma (the earliest date supported by such evidence) still GUillot be sustained on geological grounds. Secondly, the event of overriding importance in the emergence of GMRlandia was not drawdown in eustatic sea level, but uplíft in the island arc following the termination of its magmatic phase. Therefore, noticing as Hedges does that the emergence of GMRlandia was not correlated with an identifiable major drawdown-even if correct-has no pertinence to the issue at hand. Neither do uncertainties in the dating of either drawdowns or the uplift event. Finally, although the movement of sea-surface currents is affected by the Coriolis force, wind is much more important for the motion of objects on the surface (flotsam). Actual experiments reveal that such motions are significantly chaotic, which means that passive transport will virtually never occur in a straight line. As a result, although objects carried by South American rivers may eventually wash up on Caribbean shores, transit times are likely to be long. This fact, perhaps more than any other, makes long seas journeys an improbable method of successful dispersal for many kinds of organisms. Among such organisms we count most land mammals, for a host of autecological and physiological reasons. For other kinds of organisms, including herps, different considerations may apply. Obviously, paleontological and geological investigations cannot falsify historical scenarios, but they can provide termini ad quem for precisely the kinds of events that island biogeographers should be interested in, such as when environments suitable for land organisms first appeared in an area, and what organisms (as represented by their remains) were the first to take advantage of these new lands

Radiocarbon Chronologies and Extinction Dynamics of the Late Quaternary Mammalian Megafauna of the Taimyr Peninsula, Russian Federation

This paper presents 75 new radiocarbon dates based on late Quaternary mammal remains recovered from eastern Taimyr Peninsula and adjacent parts of the northern Siberian lowlands, Russian Federation, including specimens of woolly mammoth (Mammuthus primigenius), steppe bison (Bison priscus), muskox (Ovibos moschatus), moose (Alces alces), reindeer (Rangifer tarandus), horse (Equus caballus) and wolf (Canis lupus). New evidence permits reanalysis of megafaunal extinction dynamics in the Asian high Arctic periphery. Increasingly, radiometric records of individual species show evidence of a gap at or near the Pleistocene/Holocene boundary (PHB). In the past, the PHB gap was regarded as significant only when actually terminal, i.e., when it marked the apparent ‘‘last’’ occurrence of a species (e.g., current ‘‘last’’ occurrence date for woolly mammoth in mainland Eurasia is 9600 yr BP). However, for high Arctic populations of horses and muskoxen the gap marks an interruption rather than extinction, because their radiocarbon records resume, nearly simultaneously, much later in the Holocene. Taphonomic effects, ΔC14 flux, and biased sampling are unlikely explanations for these hiatuses. A possible explanation is that the gap is the signature of an event, of unknown nature, that prompted the nearly simultaneous crash of many megafaunal populations in the high Arctic and possibly elsewhere in Eurasia.

PoLAR-FIT: Pliocene Landscapes and Arctic Remains—Frozen in Time

This short summary presents selected results of an ongoing investigation into the feedbacks that contribute to amplified Arctic warming. The consequences of warming for Arctic biodiversity and landscape response to global warmth are currently being interpreted. Arctic North American records of large-scale landscape and paleoenvironmental change during the Pliocene are exquisitely preserved and locked in permafrost, providing an opportunity for paleoenvironmental and faunal reconstruction with unprecedented quality and resolution. During a period of mean global temperatures only ~2.5°C above modern, the Pliocene molecular, isotopic, tree-ring, paleofaunal, and paleofloral records indicate that the high Arctic mean annual temperature was 11°C–19°C above modern values, pointing to a much shallower latitudinal temperature gradient than exists today. It appears that the intense Neogene warming caused thawing and weathering to liberate sediment and create a continuous and thick (>2.5 km in places) clastic wedge from at least Banks Island to Meighen Island to form a coastal plain that provided a highway for camels and other mammals to migrate and evolve in the high Arctic. In this summary we highlight the opportunities that exist for research on these and related topics with the PoLAR-FIT community.RÉSUMÉCe bref résumé présente les résultats choisis d'une enquête en cours sur les déclencheurs qui contribuent à l’amplification du réchauffement de l'Arctique. Les conséquences du réchauffement sur la biodiversité arctique et de la réponse du paysage au réchauffement climatique sont en cours d’être interprété. Des dossiers nord-américains de paysage à grande échelle et le changement paléoenvironnementales durant le Pliocène sont exceptionnellement préservés et scellées dans un état de congélation qui fournissant une occasion pour la reconstruction paléoenvironnementale et faunistique avec une qualité et une résolution sans précédent. Pendent une période de réchauffement global seulement ~2,5°C au-dessus de moderne les dossiers, moléculaire, isotopique, annaux de croissance, paléofaunistique et paléovégétation indiquent que l'Arctique a connu une augmentation de la température annuelle moyenne de 11°C–19°C au-dessus de moderne, en montrant un inferieur gradient de température latitudinal qu'aujourd'hui. Il semble que le réchauffement intense pendent le Néogène a provoqué la décongélation et erosion pour libérer les sédiments et créer une plaine côtière continuel et épaisse (> 2,5 km dans lieux) qui a fourni une route pour les chameaux et autres mammifères pour migrer et évoluer dans l’Haut-Arctique. Dans ce résumé, nous soulignons les opportunités qui existent pour la recherche sur ces sujets et les sujets connexes avec la communauté PoLAR-FIT

The phylogenetic affinities of the extinct glyptodonts

Among the fossils of hitherto unknown mammals that Darwin collected in South America between 1832 and 1833 during the Beagle expedition [1] were examples of the large, heavily armored herbivores later known as glyptodonts. Ever since, glyptodonts have fascinated evolutionary biologists because of their remarkable skeletal adaptations and seemingly isolated phylogenetic position even within their natural group, the cingulate xenarthrans (armadillos and their allies [2]). In possessing a carapace comprised of fused osteoderms, the glyptodonts were clearly related to other cingulates, but their precise phylogenetic position as suggested by morphology remains unresolved [3,4]. To provide a molecular perspective on this issue, we designed sequence-capture baits using in silico reconstructed ancestral sequences and successfully assembled the complete mitochondrial genome of Doedicurus sp., one of the largest glyptodonts. Our phylogenetic reconstructions establish that glyptodonts are in fact deeply nested within the armadillo crown-group, representing a distinct subfamily (Glyptodontinae) within family Chlamyphoridae [5]. Molecular dating suggests that glyptodonts diverged no earlier than around 35 million years ago, in good agreement with their fossil record. Our results highlight the derived nature of the glyptodont morphotype, one aspect of which is a spectacular increase in body size until their extinction at the end of the last ice age.Facultad de Ciencias Naturales y Muse

A new mammal from the Turonian–Campanian (Upper Cretaceous) Galula Formation, southwestern Tanzania

We here establish a new mammaliaform genus and species, Galulatherium jenkinsi (Mammalia), from the Upper Cretaceous Galula Formation in the Rukwa Rift Basin of southwestern Tanzania. This represents the first named taxon of a mammaliaform from the entire Late Cretaceous of continental Afro-Arabia, an interval of 34 million years. Preliminary study of the holotypic and only known specimen (a partial dentary) resulted in tentative assignation to the Gondwanatheria, a poorly known, enigmatic clade of Late Cretaceous–Paleogene Gondwanan mammals (Krause et al. 2003). The application of advanced imaging (μCT) and visualization techniques permits a more detailed understanding of key anatomical features of the new taxon. It reveals that the lower dentition consisted of a large, procumbent lower incisor and four cheek teeth, all of which were evergrowing (hypselodont). Importantly, all of the teeth appear devoid of enamel. Comparisons conducted with a range of Mesozoic and selected Cenozoic mammaliaform groups document a number of features (e.g., columnar, enamel-less and evergrowing teeth, with relatively simple occlusal morphology) expressed in Galulatherium that are reminiscent of several distantly related groups, making taxonomic assignment difficult at this time. Herein we retain the provisional referral of Galulatherium (RRBP 02067) to Gondwanatheria; it is most similar to sudamericids such as Lavanify and Bharratherium from the Late Cretaceous of Madagascar and India, respectively, in exhibiting relatively simple, high-crowned, columnar cheek teeth. Other features (e.g., enamel-less dentition) are shared with disparate forms such as the Late Jurassic Fruitafossor and toothed xenarthrans (e.g., sloths), here attributed to convergence. Revised analyses of the depositional context for the holotype place it as having lived sometime between the late Turonian and latest Campanian (roughly 91–72 million years ago). This enhanced geochronological context helps to refine the palaeobiogeographical significance of Galulatherium among Cretaceous mammals in general and those from Gondwanan landmasses specifically

The phylogenetic affinities of the extinct glyptodonts

Among the fossils of hitherto unknown mammals that Darwin collected in South America between 1832 and 1833 during the Beagle expedition [1] were examples of the large, heavily armored herbivores later known as glyptodonts. Ever since, glyptodonts have fascinated evolutionary biologists because of their remarkable skeletal adaptations and seemingly isolated phylogenetic position even within their natural group, the cingulate xenarthrans (armadillos and their allies [2]). In possessing a carapace comprised of fused osteoderms, the glyptodonts were clearly related to other cingulates, but their precise phylogenetic position as suggested by morphology remains unresolved [3,4]. To provide a molecular perspective on this issue, we designed sequence-capture baits using in silico reconstructed ancestral sequences and successfully assembled the complete mitochondrial genome of Doedicurus sp., one of the largest glyptodonts. Our phylogenetic reconstructions establish that glyptodonts are in fact deeply nested within the armadillo crown-group, representing a distinct subfamily (Glyptodontinae) within family Chlamyphoridae [5]. Molecular dating suggests that glyptodonts diverged no earlier than around 35 million years ago, in good agreement with their fossil record. Our results highlight the derived nature of the glyptodont morphotype, one aspect of which is a spectacular increase in body size until their extinction at the end of the last ice age.Facultad de Ciencias Naturales y Muse

American Mastodon Mitochondrial Genomes Suggest Multiple Dispersal Events in Response to Pleistocene Climate Oscillations

Pleistocene glacial-interglacial cycles are correlated with dramatic temperature oscillations. Examining how species responded to these natural fluctuations can provide valuable insights into the impacts of present-day anthropogenic climate change. Here we present a phylogeographic study of the extinct American mastodon (Mammut americanum), based on 35 complete mitochondrial genomes. These data reveal the presence of multiple lineages within this species, including two distinct clades from eastern Beringia. Our molecular date estimates suggest that these clades arose at different times, supporting a pattern of repeated northern expansion and local extirpation in response to glacial cycling. Consistent with this hypothesis, we also note lower levels of genetic diversity among northern mastodons than in endemic clades south of the continental ice sheets. The results of our study highlight the complex relationships between population dispersals and climate change, and can provide testable hypotheses for extant species expected to experience substantial biogeographic impacts from rising temperatures

The Evolutionary and Phylogeographic History of Woolly Mammoths: A Comprehensive Mitogenomic Analysis

Near the end of the Pleistocene epoch, populations of the woolly mammoth (Mammuthus primigenius) were distributed across parts of three continents, from western Europe and northern Asia through Beringia to the Atlantic seaboard of North America. Nonetheless, questions about the connectivity and temporal continuity of mammoth populations and species remain unanswered. We use a combination of targeted enrichment and high-throughput sequencing to assemble and interpret a data set of 143 mammoth mitochondrial genomes, sampled from fossils recovered from across their Holarctic range. Our dataset includes 54 previously unpublished mitochondrial genomes and significantly increases the coverage of the Eurasian range of the species. The resulting global phylogeny confirms that the Late Pleistocene mammoth population comprised three distinct mitochondrial lineages that began to diverge ∼1.0-2.0 million years ago (Ma). We also find that mammoth mitochondrial lineages were strongly geographically partitioned throughout the Pleistocene. In combination, our genetic results and the pattern of morphological variation in time and space suggest that male-mediated gene flow, rather than large-scale dispersals, was important in the Pleistocene evolutionary history of mammoths

New evidence for late Eocene-early Oligocene uplift of Aves Ridge and paleogeography of GAARlandia

The GAARlandia hypothesis has produced vigorous debate among biologists regarding whether now-submerged landforms that existed in the Caribbean region during the late Paleogene might have acted as a barrier for marine organisms and as a bridge for terrestrial biotas migrating from South America into the Greater Antilles. This concept derived from the hypothesized emergence history of the Aves Ridge. In the quarter century since GAARlandia was first proposed, new paleontological, geological and geophysical information has greatly extended the database available. Here we reaffirm that GAARlandia was a positive topographic feature from middle Eocene, and was exposed above sea level between late Eocene and early Oligocene when it facilitated biotic colonization of the northern Greater Antilles and their satellite islands, whether as a series of closely spaced islands or as a continuous peninsula projecting from northeastern South America along the crown of the rise

Reevaluación de los circuitos craneanos de la arteria carótida interna en Notoungulata (Mammalia, Panperissodactyla)

On the basis of selected osteological markers, Patterson (1936) identified two pathways (here designated A and B) along which the internal carotid artery in notoungulates was said to travel in order to enter the skull and supply the brain. The existence of these pathways, at least as Patterson defined them, has been disputed but no substantive alternatives have been proposed. Using comparative embryological and morphological evidence based on conditions in extant mammals, we find that pathway A (intratympanic) is not supported. Pathway B (enclosed extratympanic) is supportable, but as far as is now known applies only to a small number of notoungulate taxa. On the basis of new evidence, we propose another route, pathway C, briefly mentioned by Scott (1912) but subsequently ignored, that may apply to the majority of notoungulates. In pathway C (unenclosed extratympanic) the internal carotid passed directly into the endocranium via a naturally unossified area of the basicranium, the piriform fenestra, rather than coursing through or alongside the middle ear in a canal. The absence of a separate, bony carotid foramen on the basicranium's ventral surface may explain the hesitancy of previous workers to consider this routing. There is no evidence that the function of the internal carotid artery was supplanted by another vessel (e.g., external carotid artery) in any notoungulate. Conditions in other major clades of South American native ungulates are poorly investigated, but some clearly differed from notoungulates in carotid patterning, pointing to the existence of substantial intertaxon disparities.Sobre la base de indicadores osteológicos, Patterson (1936) reconoció dos circuitos (aquí designados A y B) del supuesto recorrido de la arteria carótida interna en los notoungulados para ingresar al cráneo e irrigar el cerebro. La existencia de estos circuitos, al menos como fueron definidos por Patterson, ha sido cuestionada, aunque no existen en la literatura alternativas viables. Utilizando la embriología comparativa y la evidencia morfológica de los mamíferos vivientes, entendemos que el circuito A (intratimpánico) no está sustentado. El circuito B (extratimpánico confinado) es plausible, pero de acuerdo a nuestra revisión, se aplica únicamente a un número reducido de taxa de notoungulados. Sobre la base de la nueva evidencia, proponemos otro circuito (C), brevemente mencionado por Scott (1912), pero luego ignorado, que podría aplicarse a la mayoría de los notoungulados. En el circuito C (extratimpánico no-confinado), la carótida interna ingresa al endocráneo a través de un espacio sin osificación, la fenestra piriforme, en vez de atravesar el oído medio o pasar por un canal próximo a este. La ausencia de un foramen carotídeo delimitado por osificación en la superficie ventral del basicráneo podría explicar la vacilación de los investigadores previos de considerar esta ruta. No hay evidencia de que la función de la arteria carótida interna fuera reemplazada por otro vaso sanguíneo (e.g., arteria carótida externa) en ningún notoungulado. La condición de otros clados mayores de ungulados nativos sudamericanos está menos explorada, aunque algunos difieren claramente de los notoungulados en su patrón carotídeo, sugiriendo la existencia de una disparidad morfológica importante.Fil: MacPhee, Ross D.E.. American Museum of Natural History; Estados UnidosFil: Forasiepi, Analia Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin