Origins,Diversity and Relationships of Lemurs

I review new evidence on origins and adaptive radiation of Malagasy lemurs, a remarkably diverse group containing 13% of living primate species. The number of recognized lemur species has increased significantly, partly due to research revealing specific subdivisions within known populations but mainly because of discovery of new populations through fieldwork. Some species feared to be extinct have also been rediscovered. Specific numbers have increased particularly in small-bodied, cryptic genera for which continued research will surely reveal even more species.Adaptative radiation of lemurs has been essentially confined to Madagascar. The high density of lemur species on that island, associated with very small geographical ranges, has major implications both for their evolutionary divergence and for conservation. Reconstructions of phylogenetic relationships among primates have been considerably enhanced by DNA sequence data. Sufficient data are now available from both nuclear and mitochondrial sequences to examine relationships among and within the major groups of living primates. Most studies have confirmed that lemurs constitute a monophyletic sister-group of the lorisiform clade and all exclude a specific relationship between cheirogaleids and lorisiforms repeatedly inferred from morphological evidence. However, some analyses indicate that the aye-aye may have branched away before the divergence between other lemurs and lorisiforms. DNA sequence analyses have also yielded a broad consensus for relationships between Eulemur, Hapalemur, Lemur and Varecia: Varecia branched away first, while Lemur is more closely related to Hapalemur than to Eulemur. As debate about phylogenetic relationships among lemurs and other primates seems to have been settled in favor of lemur monophyly (possibly excluding the aye-aye), only a single invasion of Madagascar is required; but it must still be explained how ancestral lemurs could have migrated there at an appropriate time. Separation between Madagascar and Africa was apparently complete by about 120 Ma, too far in the past for direct overland migration. A recent hypothesis suggested that uplifted land in the Mozambique Channel assisted colonization of Madagascar 26-45 Ma, seemingly agreeing with an estimated date of about 40 Ma for divergence of lemurs from other primates. However, mounting evidence suggests that divergence occurred significantly earlier. Because the earliest known fossil representatives of several modern orders of placental mammals (including primates) are dated no earlier than the early Tertiary, it is widely accepted that their divergence took place after the Cretaceous/Tertiary mass extinction. Yet the known fossil record can only yield minimum divergence times; if sampling is poor and/or biased there may be a considerable discrepancy between minimum and actual dates. There is, for example, virtually no known fossil record for lemurs in Madagascar and the earliest known representatives are subfossil lemurs, so in this case a direct reading of the fossil record would indicate that the lemurs first originated just a few thousand years ago! Examination of underestimation of times of origin because of poor sampling in the fossil record has confirmed previous suggestions that primates originated considerably earlier than generally believed. Several recent phylogenetic reconstructions based on DNA sequence data and using calibration dates derived from groups other than primates provide independent support for this inference. Overall, it now seems that primates originated at around 90 Ma rather than the 55 Ma indicated by direct reading of the known fossil record. Hence, colonization of Madagascar by lemurs would have taken place at about 80 Ma, double the date usually accepted, and should be interpreted in terms of contemporary continental relationships.     

<Emphasis Type="Italic">Protungulatum</Emphasis>, Confirmed Cretaceous Occurrence of an Otherwise Paleocene Eutherian (Placental?) Mammal

Neither pre-Cenozoic crown eutherian mammals (placentals) nor archaic ungulates (“condylarths”) are known with certainty based on the fossil record. Herein we report a new species of the Paleocene archaic ungulate (“condylarth”) Protungulatum from undisputed Late Cretaceous aged rocks in Montana USA based on an isolated last upper premolar, indicating rare representatives of these common early Tertiary mammals appeared in North America a minimum of 300 k  years before the extinction of non-avian dinosaurs. The other 1200 mammal specimens from the locality are characteristic Late Cretaceous taxa. This discovery overturns the current hypothesis that archaic ungulates did not appear in North America until after the Cretaceous/Tertiary (K/T) boundary and also suggests that other reports of North American Late Cretaceous archaic ungulates may be correct. Recent studies, including ours, cannot determine whether Protungulatum does or does not belong to the crown clade Placentalia.     

Dinosaurs and fluctuating sea levels during the mesozoic

The very different frequency of dinosaurs during the Mesozoic can be allied to the correlation between global sea level cyclicity and fossilization. This is based upon the sedimentary situation in the inner shelf, the area of predominant fossil record of dinosaurs, and sea level fluctuations. A rich fossil record is found in times of high sea level, and vice versa. Due to natural laws acting on sea level stands, the fossil record of dinosaurs and other terrestrial tetrapods is incomplete. This is causally explainable in the sequence stratigraphy. Among causes of global sea level fluctuations, the change from warm to cold times has been accorded greatest probability even in the Mesozoic. Consequently, the problem of dinosaur evolution and distribution should not be confused with the pattern of their fossil record. The latter, however, is so far nearly always used for all interpretations. The context presented here results in basic modifications.

During the phases of reduced to missing fossil record (low sea level, cold times), dinosaurs existed at least in circumequatorial regions in high diversity. Highly diverse faunas recorded exceptionally in the Upper Jurassic, Middle and Late Cretaceous, were each time the result of a long previous evolution and not the result of short term radiations at these times. Phases of sea level highstand and warm times caused an increased fossil record and poleward distribution. Cretaceous dinosaurs in paleolatitudes of 70° to 80° N and S are no proof for endothermy, but are only the effect of favorable climatic conditions at limited times. Any endothermy of the dinosaurs is not coincident with the supposedly uniformly warm equable climate of the Mesozoic, but with the opposite. Cold times did not hamper the existence of dinosaurs, but led in extreme cases (Aalenian and Valanginian) to the global lack of their fossil record. The situation at the Cretaceous‐Tertiary boundary is also explainable in this context. According to the sea level cyclicity, no extreme sea level fall and no globablly cold time were present in the critical time segment. The regression in the late Maastrichtian is found to belong to a sequence of third‐order cycles beginning in the Campanian. Every one of the cycle boundaries with regression and transgression produced apparent extinction effects which in reality are only gaps in the fossil record. After the late Maastrichtian regression the dinosaurs persisted with six lineages. The so far youngest dinosaur fauna in the Puercan (basal Paleocene) lies in a phase of sea level highstand of minor amplitude and duration with comparatively minor chances for a fossil record. The occurrences in the Puercan are governed by natural law, and, thus, dinosaurs are untied from the short term problems of the Cretaceous‐Tertiary boundary. Why dinosaurs are then missing at the next highstand, remains an open question. Anyhow, mechanisms which control fossil record, diversification and distribution, including global cold periods, do not belong to the direct causes of extinction, because identical occurrences happened many times during the Mesozoic without inducing extinction.     

Avian evolution, Gondwana biogeography and the Cretaceous-Tertiary mass extinction event

The fossil record has been used to support the origin and radiation of modern birds (Neornithes) in Laurasia after the Cretaceous-Tertiary mass extinction event, whereas molecular clocks have suggested a Cretaceous origin for most avian orders. These alternative views of neornithine evolution are examined using an independent set of evidence, namely phylogenetic relationships and historical biogeography. Pylogenetic relationships of basal lineages of neornithines, including ratite birds and their allies (Palaleocognathae), galliforms and anseriforms (Galloanserae), as well as lineages of the more advanced Neoves (Gruiformes, (Capimulgiformes, Passeriformes and others) demonstrate pervasive trans-Antarctic distribution patterns. The temporal history of the neornithines can be inferred from fossil taxa and the ages of vicariance events, and along with their biogeographical patterns, leads to the conclusion that neornithines arose in Gondwana prior to the Cretaceous Tertiary extinction event.     

Early penguin fossils, plus mitochondrial genomes, calibrate avian evolution

Testing models of macroevolution, and especially the sufficiency of microevolutionary processes, requires good collaboration between molecular biologists and paleontologists. We report such a test for events around the Late Cretaceous by describing the earliest penguin fossils, analyzing complete mitochondrial genomes from an albatross, a petrel, and a loon, and describe the gradual decline of pterosaurs at the same time modern birds radiate. The penguin fossils comprise four naturally associated skeletons from the New Zealand Waipara Greensand, a Paleocene (early Tertiary) formation just above a well-known Cretaceous/Tertiary boundary site. The fossils, in a new genus (Waimanu), provide a lower estimate of 61-62 Ma for the divergence between penguins and other birds and thus establish a reliable calibration point for avian evolution. Combining fossil calibration points, DNA sequences, maximum likelihood, and Bayesian analysis, the penguin calibrations imply a radiation of modern (crown group) birds in the Late Cretaceous. This includes a conservative estimate that modern sea and shorebird lineages diverged at least by the Late Cretaceous about 74 +/- 3 Ma (Campanian). It is clear that modern birds from at least the latest Cretaceous lived at the same time as archaic birds including Hesperornis, Ichthyornis, and the diverse Enantiornithiformes. Pterosaurs, which also coexisted with early crown birds, show notable changes through the Late Cretaceous. There was a decrease in taxonomic diversity, and small- to medium-sized species disappeared well before the end of the Cretaceous. A simple reading of the fossil record might suggest competitive interactions with birds, but much more needs to be understood about pterosaur life histories. Additional fossils and molecular data are still required to help understand the role of biotic interactions in the evolution of Late Cretaceous birds and thus to test that the mechanisms of microevolution are sufficient to explain macroevolution.     

Molecular and Paleontological Evidence for a Post-Cretaceous Origin of Rodents

The timing of the origin and diversification of rodents remains controversial, due to conflicting results from molecular clocks and paleontological data. The fossil record tends to support an early Cenozoic origin of crown-group rodents. In contrast, most molecular studies place the origin and initial diversification of crown-Rodentia deep in the Cretaceous, although some molecular analyses have recovered estimated divergence times that are more compatible with the fossil record. Here we attempt to resolve this conflict by carrying out a molecular clock investigation based on a nine-gene sequence dataset and a novel set of seven fossil constraints, including two new rodent records (the earliest known representatives of Cardiocraniinae and Dipodinae). Our results indicate that rodents originated around 61.7–62.4 Ma, shortly after the Cretaceous/Paleogene (K/Pg) boundary, and diversified at the intraordinal level around 57.7–58.9 Ma. These estimates are broadly consistent with the paleontological record, but challenge previous molecular studies that place the origin and early diversification of rodents in the Cretaceous. This study demonstrates that, with reliable fossil constraints, the incompatibility between paleontological and molecular estimates of rodent divergence times can be eliminated using currently available tools and genetic markers. Similar conflicts between molecular and paleontological evidence bedevil attempts to establish the origination times of other placental groups. The example of the present study suggests that more reliable fossil calibration points may represent the key to resolving these controversies.     

Faunal change in the Turkana Basin during the late Oligocene and Miocene

Faunal evolution over the last 65 million years of earth's history was dominated by mammalian radiations, but much of this era is poorly represented in Africa. Mammals first appeared early in the Mesozoic, living alongside dinosaurs for millions of years, but it was not until the extinction of dinosaurs 65 myr ago that the first major explosion of mammalian taxa took place. The Cenozoic (65 Ma to Recent) witnessed repeated and dynamic events involving the radiation, evolution, and extinction of mammalian faunas. Two of these events, each marking the extinction of one diverse fauna and subsequent establishment of another equally diverse fauna, both involving advanced catarrhine primates, are recorded in sites in the Turkana Basin, despite the poorly represented record of Cenozoic faunas elsewhere in sub-Saharan Africa. The first of these events occurred at the Oligocene-Miocene transition and the other at the Miocene-Pliocene transition.     

Explosive radiation of Malpighiales supports a mid-cretaceous origin of modern tropical rain forests

Fossil data have been interpreted as indicating that Late Cretaceous tropical forests were open and dry adapted and that modern closed-canopy rain forest did not originate until after the Cretaceous-Tertiary (K/T) boundary. However, some mid-Cretaceous leaf floras have been interpreted as rain forest. Molecular divergence-time estimates within the clade Malpighiales, which constitute a large percentage of species in the shaded, shrub, and small tree layer in tropical rain forests worldwide, provide new tests of these hypotheses. We estimate that all 28 major lineages (i.e., traditionally recognized families) within this clade originated in tropical rain forest well before the Tertiary, mostly during the Albian and Cenomanian (112-94 Ma). Their rapid rise in the mid-Cretaceous may have resulted from the origin of adaptations to survive and reproduce under a closed forest canopy. This pattern may also be paralleled by other similarly diverse lineages and supports fossil indications that closed-canopy tropical rain forests existed well before the K/T boundary. This case illustrates that dated phylogenies can provide an important new source of evidence bearing on the timing of major environmental changes, which may be especially useful when fossil evidence is limited or controversial.     

Diversification of Neoaves: integration of molecular sequence data and fossils

Patterns of diversification and timing of evolution within Neoaves, which includes almost 95% of all bird species, are virtually unknown. On the other hand, molecular data consistently indicate a Cretaceous origin of many neoavian lineages and the fossil record seems to support an Early Tertiary diversification. Here, we present the first well-resolved molecular phylogeny for Neoaves, together with divergence time estimates calibrated with a large number of stratigraphically and phylogenetically well-documented fossils. Our study defines several well-supported clades within Neoaves. The calibration results suggest that Neoaves, after an initial split from Galloanseres in Mid-Cretaceous, diversified around or soon after the K/T boundary. Our results thus do not contradict palaeontological data and show that there is no solid molecular evidence for an extensive pre-Tertiary radiation of Neoaves.     

The rise of birds and mammals: are microevolutionary processes sufficient for macroevolution?

It is a basis of darwinian evolution that the microevolutionary mechanisms that can be studied in the present are sufficient to account for macroevolution. However, this idea needs to be tested explicitly, as highlighted here by the example of the superceding of dinosaurs and pterosaurs by birds and placental mammals that occurred near the Cretaceous/Tertiary boundary approximately 65 million years ago. A major problem for testing the sufficiency of microevolutionary processes is that independent ideas (such as the existence of an extraterrestrial impact, and the extinction of dinosaurs) were linked without the evidence for each idea being evaluated separately. Here, we suggest and discuss five testable models for the times and divergences of modern mammals and birds. Determination of the model that best represents these events will enable the role of microevolutionary mechanisms to be evaluated. The question of the sufficiency of microevolutionary processes for macroevolution is solvable, and available evidence supports an important role for biological processes in the initial decline of dinosaurs and pterosaurs.     

Quantitative Analysis of the Timing of the Origin and Diversification of Extant Placental Orders

Fossil evidence is consistent with origination and diversification of extant placental orders in the early Tertiary (Explosive Model), and with the possibility of some orders having stem taxa extending into the Cretaceous (Long Fuse Model). Fossil evidence that 15 of 18 extant placental orders appeared and began diversification in the first 16 m.y. of the Cenozoic is, however, at odds with molecular studies arguing some orders diversified up to 40 m.y. earlier in the Early Cretaceous (Short Fuse Model). The quality of the fossil record was assessed by tabulating localities of all mammals in the last 105 m.y. Global locality data (except Africa) for 105 m.y. of eutherian evolution indicate discernible biogeographic patterns by the last 15 m.y. of the Cretaceous. Eutherian genera increase from 11 in latest Cretaceous to 139 in earliest Tertiary, although both are represented by about 50 localities. Yet even in the Late Cretaceous of North America and Asia where eutherians are abundant, none of the 18 extant orders are definitely known. A series of Monte Carlo simulations test whether the rapid appearance of most mammalian orders is statistically significant, and if so, whether it is a radiation event or an artifact of a limited fossil record. Monte Carlo tests affirm that the clustering of appearances in the early Cenozoic is statistically significant. Quantitative analysis of the locality data suggests that the number of genera described is a function of the number of localities sampled. In contrast, the number of orders is not a simple function of localities and thus does not appear to be limited by localities. A second set of Monte Carlo simulations confirms that the increase in orders cannot be explained by the limited number of localities sampled. Even for best-fit simulations, the observed pattern of ordinal appearances is steeper than expected under a variety of null models. These quantitative analyses of the fossil record demonstrate that the rapid ordinal appearances cannot be ascribed to limited Late Cretaceous sample sizes; thus, early Tertiary ordinal diversification is real. Although the fossil record is incomplete, it appears adequate to reject the hypothesis that orders of placentals began to diversify before the K/T boundary.     

Polar dinosaurs and the question of dinosaur extinction: a brief review

Although the physiology of dinosaurs is still a matter of controversy, there is no doubt that some of them were able to live in environments that were too cold for ectothermic reptiles, as shown by discoveries of Jurassic and Cretaceous polar vertebrate assemblages which contain dinosaurs but lack turtles and crocodiles. This adaptation of dinosaurs to cool climates invalidates hypotheses according to which dinosaur extinction at the end of the Cretaceous was a result of long-term climatic cooling. The pattern seen at the K/T boundary, with the disappearance of dinosaurs and the survival of ectothermic reptiles, is completely different from that seen in Arctic regions during the Late Cretaceous, where ectotherms disappeared, while dinosaurs subsisted, during cooler periods. The idea of an intense and enduring cold spell at the K/T boundary, caused by the Chicxulub impact, is extremely unlikely in view of the pattern of vertebrate extinction (survival of endotherms, extinction of dinosaurs). Models of environmental events following the impact must take this palaeontological constraint into consideration.     

Did dinosaurs invent flowers? Dinosaur—angiosperm coevolution revisited

Angiosperms first appeared in northern Gondwana during the Early Cretaceous, approximately 135 million years ago. Several authors have hypothesised that the origin of angiosperms, and the tempo and pattern of their subsequent radiation, was mediated by changes in the browsing behaviour of large herbivorous dinosaurs (sauropods and ornithischians). Moreover, the taxonomic and ecological radiation of angiosperms has been associated with the evolution of complex jaw mechanisms among ornithischian dinosaurs. Here, we review critically the evidence for dinosaur-angiosperm interactions during the Cretaceous Period, providing explicit spatiotemporal comparisons between evolutionary and palaeoecological events in both the dinosaur and angiosperm fossil records and an assessment of the direct and indirect evidence for dinosaur diets. We conclude that there are no strong spatiotemporal correlations in support of the hypothesis that dinosaurs were causative agents in the origin of angiosperms; however, dinosaur-angiosperm interactions in the Late Cretaceous may have resulted in some coevolutionary interactions, although direct evidence of such interactions is scanty at present. It is likely that other animal groups (insects, arboreal mammals) had a greater impact on angiosperm diversity during the Cretaceous than herbivorous dinosaurs. Elevated levels of atmospheric CO2 might have played a critical role in the initial stages of the angiosperm radiation.     

Macroevolutionary Dynamics and Historical Biogeography of Primate Diversification Inferred from a Species Supermatrix

Phylogenetic relationships, divergence times, and patterns of biogeographic descent among primate species are both complex and contentious. Here, we generate a robust molecular phylogeny for 70 primate genera and 367 primate species based on a concatenation of 69 nuclear gene segments and ten mitochondrial gene sequences, most of which were extracted from GenBank. Relaxed clock analyses of divergence times with 14 fossil-calibrated nodes suggest that living Primates last shared a common ancestor 71–63 Ma, and that divergences within both Strepsirrhini and Haplorhini are entirely post-Cretaceous. These results are consistent with the hypothesis that the Cretaceous-Paleogene mass extinction of non-avian dinosaurs played an important role in the diversification of placental mammals. Previous queries into primate historical biogeography have suggested Africa, Asia, Europe, or North America as the ancestral area of crown primates, but were based on methods that were coopted from phylogeny reconstruction. By contrast, we analyzed our molecular phylogeny with two methods that were developed explicitly for ancestral area reconstruction, and find support for the hypothesis that the most recent common ancestor of living Primates resided in Asia. Analyses of primate macroevolutionary dynamics provide support for a diversification rate increase in the late Miocene, possibly in response to elevated global mean temperatures, and are consistent with the fossil record. By contrast, diversification analyses failed to detect evidence for rate-shift changes near the Eocene-Oligocene boundary even though the fossil record provides clear evidence for a major turnover event (“Grande Coupure”) at this time. Our results highlight the power and limitations of inferring diversification dynamics from molecular phylogenies, as well as the sensitivity of diversification analyses to different species concepts.     

Primate phylogeny: molecular evidence for a pongid clade excluding humans and a prosimian clade containing tarsiers

Unbiased readings of fossils are well known to contradict some of the popular molecular groupings among primates,particularly with regard to great apes and tarsiers.The molecular methodologies today are however flawed as they are based on a mistaken theoretical interpretation of the genetic equidistance phenomenon that originally started the field.An improved molecular method the ’slow clock’ was here developed based on the Maximum Genetic Diversity hypothesis,a more complete account of the unified changes in genotypes and phenotypes.The method makes use of only slow evolving sequences and requires no uncertain assumptions or mathematical corrections and hence is able to give definitive results.The findings indicate that humans are genetically more distant to orangutans than African apes are and separated from the pongid clade ～17.6 million years ago.Also,tarsiers are genetically closer to lorises than simian primates are.Finally,the fossil times for the radiation of mammals at the K/T boundary and for the Eutheria-Metatheria split in the Early Cretaceous were independently confirmed from molecular dating calibrated using the fossil split times of gorilla-orangutan,mouse-rat,and opossum-kangaroo.Therefore,the re-established primate phylogeny indicates a remarkable unity between molecules and fossils.     

Early Cenozoic increases in mammal diversity cannot be explained solely by expansion into larger body sizes

A prominent hypothesis in the diversification of placental mammals after the Cretaceous–Palaeogene (K/Pg) boundary suggests that the extinction of non-avian dinosaurs resulted in the ecological release of mammals, which were previously constrained to small body sizes and limited species richness. This ‘dinosaur incumbency hypothesis’ may therefore explain increases in mammalian diversity via expansion into larger body size niches, that were previously occupied by dinosaurs, but does not directly predict increases in other body size classes. To evaluate this, we estimate sampling-standardized diversity patterns of terrestrial North American fossil mammals within body size classes, during the Cretaceous and Palaeogene. We find strong evidence for post-extinction diversity increases in all size classes. Increases in the diversity of small-bodied species (less than 100 g, the common body size class of Cretaceous mammals, and much smaller than the smallest non-avialan dinosaurs (c. 400 g)) were similar to those of larger species. We propose that small-bodied mammals had access to greater energetic resources or were able to partition resources more finely after the K/Pg mass extinction. This is likely to be the result of a combination of widespread niche clearing due to the K/Pg mass extinctions, alongside a suite of biotic and abiotic changes that occurred during the Late Cretaceous and across the K/Pg boundary, such as shifting floral composition, and novel key innovations among eutherian mammals.     

Two waves of colonization straddling the K–Pg boundary formed the modern reef fish fauna

Living reef fishes are one of the most diverse vertebrate assemblages on Earth. Despite its prominence and ecological importance, the origins and assembly of the reef fish fauna is poorly described. A patchy fossil record suggests that the major colonization of reef habitats must have occurred in the Late Cretaceous and early Palaeogene, with the earliest known modern fossil coral reef fish assemblage dated to 50 Ma. Using a phylogenetic approach, we analysed the early evolutionary dynamics of modern reef fishes. We find that reef lineages successively colonized reef habitats throughout the Late Cretaceous and early Palaeogene. Two waves of invasion were accompanied by increasing morphological convergence: one in the Late Cretaceous from 90 to 72 Ma and the other immediately following the end-Cretaceous mass extinction. The surge in reef invasions after the Cretaceous–Palaeogene boundary continued for 10 Myr, after which the pace of transitions to reef habitats slowed. Combined, these patterns match a classic niche-filling scenario: early transitions to reefs were made rapidly by morphologically distinct lineages and were followed by a decrease in the rate of invasions and eventual saturation of morphospace. Major alterations in reef composition, distribution and abundance, along with shifts in climate and oceanic currents, occurred during the Late Cretaceous and early Palaeogene interval. A causal mechanism between these changes and concurrent episodes of reef invasion remains obscure, but what is clear is that the broad framework of the modern reef fish fauna was in place within 10 Myr of the end-Cretaceous extinction.     

'First' appearances in the Cenozoic land-mammal record of the Greater Antilles: significance and comparison with South American and Antarctic records

Aim Through analysis of fossil records, the aim of this paper is to show that fossil representatives of at least three land‐mammal clades (pitheciine atelid primates, heteropsomyine echimyid rodents, and megalonychid phyllophagan xenarthrans) that once lived in the Greater Antilles are as old as, if not older than, ‘first’ occurrences of these same groups on the South American mainland. Location Greater Antilles, South America, Antarctic Peninsula. Methods Analysis of Cenozoic land‐mammal fossil records for the three areas. Results Comparison reveals an interesting similarity to the Tertiary vertebrate palaeontological record for the Antarctic Peninsula (Seymour Island), in the sense that the latter also includes early (Eocene) representatives of some typical ‘South American’ groups (e.g. meridiungulates, sloths, certain marsupial groups). Conclusions Given how limited the Antillean and Antarctic records are in quantity and quality, it seems unlikely that these ‘first’ appearances have much bearing on real origins (basal divergences). Rather, it suggests that the fossil basis for interpreting the origin and earliest diversification of ‘South American’ clades during the latest Cretaceous/early Cenozoic is probably even scantier than generally realized. In particular, the Antillean record strengthens arguments that some crown‐group continental lineages are considerably older than fossil evidence currently allows – a point increasingly (if unevenly) supported by molecular studies of many of the same clades.     

Evolution and biogeography of primates: a new model based on molecular phylogenetics,vicariance and plate tectonics

Heads, M. Evolution and biogeography of primates: a new model based on molecular phylogenetics, vicariance and plate tectonics. —Zoologica Scripta, 39, 107–127. The ages of the oldest fossils suggest an origin for primates in the Paleocene (～56 Ma). Fossil‐calibrated molecular clock dates give Cretaceous dates (～80–116 Ma). Both these estimates are minimum dates although they are often ‘transmogrified’ and treated as maximum or absolute dates. Oldest fossils can underestimate ages by tens of millions of years and instead of calibrating the time‐course of evolution with a scanty fossil record, the geographical boundaries of the main molecular clades of primates are calibrated here with radiometrically dated tectonic events. This indicates that primates originated when a globally widespread ancestor (early Archonta) differentiated into a northern group (Plesiadapiformes, extinct), a southern group (Primates), and two south‐east Asian groups (Dermoptera and Scandentia). The division occurred with the breakup of Pangea in the Early Jurassic and the opening of the central Atlantic (～185 Ma). Within primates, the strepsirrhines and haplorhines diverged with volcanism and buckling on the Lebombo Monocline, a volcanic rifted margin in south‐east Africa (Early Jurassic, ～180 Ma). Within strepsirrhines, lorises and galagos (Africa and Asia) and lemurs (Madagascar) diverged with the formation of the Mozambique Channel (Middle Jurassic, ～160 Ma). Within haplorhines, Old World monkeys and New World monkeys diverged with the opening of the Atlantic (Early Cretaceous, ～130 Ma). The main aspects of primate distribution are interpreted as the result of plate tectonics, phylogeny and vicariance, with some subsequent range expansion leading to secondary overlap. Long‐distance, trans‐oceanic dispersal events are not necessary. The primate ancestral complex was already widespread globally when sea‐floor spreading, strike‐slip rifting and orogeny fractured and deformed distributions through the Jurassic and Cretaceous, leading to the origin of the modern clades. The model suggests that the topology of the phylogenetic tree reflects a sequence of differentiation in a widespread ancestor rather than a series of dispersal events.     

The fossil record of North American mammals: evidence for a Paleocene evolutionary radiation

Paleontologists long have argued that the most important evolutionary radiation of mammals occurred during the early Cenozoic, if not that all eutherians originated from a single common post-Cretaceous ancestor. Nonetheless, several recent molecular analyses claim to show that because several interordinal splits occurred during the Cretaceous, a major therian radiation was then underway. This claim conflicts with statistical evidence from the well-sampled latest Cretaceous and Cenozoic North American fossil record. Paleofaunal data confirm that there were fewer mammalian species during the latest Cretaceous than during any interval of the Cenozoic, and that a massive diversification took place during the early Paleocene, immediately after a mass extinction. Measurement data show that Cretaceous mammals were on average small and occupied a narrow range of body sizes; after the Cretaceous-Tertiary mass extinction, there was a rapid and permanent shift in the mean. The fact that there was an early Cenozoic mammalian radiation is entirely compatible with the existence of a few Cretaceous splits among modern mammal lineages.