Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence

This study is undertaken in order to evaluate specific hypotheses of relationship among extant and extinct sloths (Mammalia, Xenarthra, Tardigrada). Questions of particular interest include the relationship among the three traditional family groupings of extinct ground sloths and the monophyletic or diphyletic origin of the two genera of extant tree sloths. A computer‐based cladistic investigation of the phylogenetic relationships among 33 sloth genera is performed based upon 286 osteological characteristics of the skull, lower jaw, dentition and hyoid arch. Characters are polarized via comparisons with the following successive outgroups, all members of the supraordinal grouping Edentata: the Vermilingua, or anteaters; the Cingulata, or armadillos and glyptodonts; the Palaeanodonta; and the Pholidota, or pangolins. The results of the analysis strongly corroborate the diphyly of living tree sloths, with the three‐toed sloth Bradypus positioned as the sister‐taxon to all other sloths, and the two‐toed sloth Choloepus allied with extinct members of the family Megalonychidae. These results imply that the split between the two extant sloth genera is ancient, dating back perhaps as much as 40 Myr, and that the similarities between the two taxa, including their suspensory locomotor habits, present one of the most dramatic examples of convergent evolution known among mammals. The monophyly of the three traditional ground sloth families Megatheriidae, Megalonychidae and Mylodontidae is confirmed in the present study, and the late Miocene–Pleistocene nothrotheres are shown to form a clade. It is suggested that this latter clade merits recognition as a distinct family‐level grouping, the family Nothrotheriidae. The monophyly of the Megatherioidea, a clade including members of the families Megatheriidae, Megalonychidae and Nothrotheriidae, is also supported. Within Megatherioidea, the families Nothrotheriidae and Megatheriidae form a monophyletic group called the Megatheria. The relationships within the families Megatheriidae and Mylodontidae are fully and consistently resolved, although the hypothesized scheme of relationships among the late Miocene to Pleistocene members of the mylodontid subfamily Mylodontinae differ strongly from any proposed by previous authors. Within the family Megalonychidae, Choloepus is allied to a monophyletic grouping of West Indian sloths, although the relationships within this clade are not fully resolved. © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society, 2004, 140 , 255–305.     

A Paleogeographic Overview of Tropical Fossil Sloths: Towards an Understanding of the Origin of Extant Suspensory Sloths?

Modern sloths are among the more characteristic mammals of South and Central American faunas. Recent discovery in four Paleogene, 22 Neogene, and dozens of Pleistocene fossiliferous localities in the tropics has revealed an unexpected paleobioversity constituted by some 81 fossil sloth species. Probably originating in southern South America near the Eocene/Oligocene transition, sloths were represented in the tropics during the late Oligocene by Pseudoglyptodon, Mylodontidae, and Megalonychidae. The latter occupied the West Indies between at least the late early Miocene and late Pleistocene, and two mylodontid clades, Octodontobradyinae and Urumacotheriinae, were characteristic of Amazonian localities from the Colhuehuapian and the Laventan periods, respectively, until the end of the Miocene. Megatheriinae and Nothrotheriidae appeared during the middle Miocene, colonizing the tropics and then North America, where Mylodontidae and Megalonychidae had already been present since the early late Miocene. Nothrotheriids are more abundant and diversified during the late Miocene in the tropics than in southern South America. Remains closely related to either of the modern sloths are absent from the fossil record, including those in the tropics. The characteristic suspensory posture of Bradypus and Choloepus appeared independently and likely after the Miocene epoch, and thus well after the hypothesized split suggested by molecular studies of the respective clades of these genera. Given their current widespread distribution in and reliance on the tropics, prospecting efforts for the direct fossil kin of suspensory sloths should concentrate on deposits in the Amazonian region, as this area has shown promise in producing fossil sloths.     

Grazing in a New Late Oligocene Mylodontid Sloth and a Mylodontid Radiation as a Component of the Eocene-Oligocene Faunal Turnover and the Early Spread of Grasslands/Savannas in South America

We describe a new taxon of mylodontid sloth from the late Oligocene (Deseadan South American Land Mammal “age”), Salla Beds of Bolivia. This taxon, Paroctodontotherium calleorum, new genus and species, is one of the oldest known sloths, but it is surprisingly derived. It is referable to the Mylodontidae and, with just a little doubt, to the Mylodontinae. It shares a number of derived characteristics with other mylodontids and even mylodontines. These include: a relatively low temporomandibular joint; a relatively short zygomatic process of the squamosal; an elongated, narrow braincase; anteriorly diverging toothrows; broad muzzle; and greatly enlarged external nares. The relative width of the muzzle of Paroctodontotherium is as great as any Pleistocene mylodontid except the giant grazer, Lestodon. We review and critique methods of estimating diets of extinct sloths and propose a hypothesis in regard to the feeding ecology of Paroctodontotherium. Based upon its broad muzzle, the degree of tooth wear, and its presence in a habitat dominated by hypsodont herbivores, we propose that Paroctodontotherium was a bulk feeder that foraged near ground level. Grasses were likely a major component of its diet. The addition of this new taxon, along with other recently discovered taxa, illustrates that late Oligocene sloths had much greater diversity than recognized just a decade ago. This diversity is evident in species richness, variations in body sizes, dental morphologies, and means of locomotion. We regard this relatively sudden sloth radiation as a significant component of the Eocene-Oligocene faunal turnover and was related to the development of more open habitats of post-Eocene South America.     

The South American Gomphotheres (Mammalia, Proboscidea, Gomphotheriidae): Taxonomy, Phylogeny, and Biogeography

The taxonomic history of South American Gomphotheriidae is very complex and controversial. Three species are currently recognized: Amahuacatherium peruvium, Cuvieronius hyodon, and Notiomastodon platensis. The former is a late Miocene gomphothere whose validity has been questioned by several authors. The other two, C. hyodon and N. platensis, are Quaternary taxa in South America, and they have distinct biogeographic patterns: Andean and lowland distributions, respectively. South American gomphotheres became extinct at the end of the Pleistocene. We conducted a phylogenetic analysis of Proboscidea including the South American Quaternary gomphotheres, which resulted in two most parsimonious trees. Our results support a paraphyletic Gomphotheriidae and a monophyletic South American gomphothere lineage: C. hyodon and N. platensis. The late Miocene gomphothere record in Peru, Amahuacatherium peruvium, seems to be a crucial part of the biogeography and evolution of the South American gomphotheres.     

The New World oil‐collecting bees Centris and Epicharis (Hymenoptera,Apidae): molecular phylogeny and biogeographic history

We present a first comprehensive time‐calibrated phylogeny for two Neotropical genera of bees, Centris and Epicharis, whose females collect floral oil together with pollen for larval provisioning, and that traditionally have been grouped in the tribe Centridini. Our analyses rely on a matrix of 167 taxa and 4228 aligned nucleotides for the subfamily Apinae, with denser sample of Centris and Epicharis. Centris and Epicharis are strongly supported monophyletic groups, but Centridini is paraphyletic in relation to the corbiculate bees. The inner phylogenetic relationships of Epicharis agree with the current taxonomic classification. In Centris, three main clades were recovered, namely the Centris, Trachina and Melacentris groups. Inner relationships in Centris suggest the reinstatement of some subgenera and proposition of new ones. Early diversification of Centris and Epicharis took place at the tropical regions of South America. Epicharis and the Melacentris group in Centris mostly diversified in that region, expanding over Central America and tropical North America only recently in the last 3 My. The groups Trachina and Centris present a complex biogeographic history, with expansions to the Nearctic region, the Antilles, and temperate regions of South America in the late Oligocene and Miocene.     

Tertiary climate change and the diversification of the Amazonian gecko genus Gonatodes (Sphaerodactylidae, Squamata)

The genus Gonatodes is a monophyletic group of small-bodied, diurnal geckos distributed across northern South America, Central America, and the Caribbean. We used fragments of three nuclear genes (RAG2, ACM4, and c-mos) and one mitochondrial gene (16S) to estimate phylogenetic relationships among Amazonian species of Gonatodes. We used Penalized Likelihood to estimate timing of diversification in the genus. Most cladogenesis occurred in the Oligocene and early Miocene and coincided with a burst of diversification in other South American animal groups including mollusks, birds, and mammals. The Oligocene and early Miocene were periods dominated by dramatic climate change and Andean orogeny and we suggest that these factors drove the burst of cladogenesis in Gonatodes geckos as well as other taxa. A common pattern in Amazonian taxa is a biogeographic split between the eastern and western Amazon basin. We observed two clades with this spatial distribution, although large differences in timing of divergence between the east-west taxon pairs indicate that these divergences were not the result of a common vicariant event.     

Neogene sloth assemblages (Mammalia,Pilosa) of the Cocinetas Basin (La Guajira,Colombia): implications for the Great American Biotic Interchange

We describe sloth assemblages from the Cocinetas Basin (La Guajira peninsula, Colombia), found in the Neogene Castilletes and Ware formations, located in northernmost South America, documenting otherwise poorly known biotas. The tentative referral of a specimen to a small megatherioid sloth, Hyperleptus?, from the early–middle Miocene Castilletes Formation, suggests affinities of this fauna with the distant Santa Cruz Formation and documents a large latitudinal distribution for this taxon. The late Pliocene Ware Formation is much more diverse, with five distinct taxa representing every family of ‘ground sloths’. This diversity is also remarkable at the ecological level, with sloths spanning over two orders of magnitude of body mass and probably having different feeding strategies. Being only a few hundred kilometres away from the Isthmus of Panama, and a few hundred thousand years older than the classically recognized first main pulse of the Great American Biotic interchange (GABI 1), the Ware Formation furthermore documents an important fauna for the understanding of this major event in Neogene palaeobiogeography. The sloths for which unambiguous affinities were recovered are not closely related to the early immigrants found in North America before GABI 1.     

The evolution of the diatoms (Bacillariophyta). I. Origin of the group and assessment of the monophyly of its major divisions

The diatoms are one of the best characterised algal groups. Despite this, little is known of the evolution of the group from the earliest cell to the myriad of taxa known today. Relationships among taxa at the family or generic level have been recognised in some diatoms. However, relationships at higher taxonomic levels are poorly understood and have often been strongly influenced by the first appearances of key taxa in the fossil record. An independent assessment of relationships among the diatoms at these higher taxonomic levels has been made using rRNA sequence data to infer phylogenetic relationships. In this paper we present an analysis of 18S rRNA data from several chosen centric, araphid and raphid pennate taxa. The phylogenetic inferences from these 18S rRNA sequences are supported by evidence from the fossil record and evidence from ontogenetic data. Ribosomal RNA data indicate that both the centric and araphid pennate lineages may not be monophyletic.     

Phylogenetic and biogeographic complexity of Magnoliaceae in the Northern Hemisphere inferred from three nuclear data sets

This study employs three nuclear genes (PHYA, LFY, and GAI1) to reconstruct the phylogenetic and biogeographic history of Magnoliaceae. A total of 104 samples representing 86 taxa from all sections and most subsections were sequenced. Twelve major groups are well supported to be monophyletic within Magnoliaceae and these groups are largely consistent with the recent taxonomic revision at the sectional and subsectional levels. However, relationships at deeper nodes of the subfamily Magnolioideae remain not well resolved. A relaxed clock relying on uncorrelated rates suggests that the complicated divergent evolution of Magnolioideae began around the early Eocene (54.57mya), concordant with paleoclimatic and fossil evidence. Intercontinental disjunctions of Magnoliaceae in the Northern Hemisphere appear to have originated during at least two geologic periods. Some occurred after the middle Miocene, represented by two well-recognized temperate lineages disjunct between eastern Asia and eastern North America. The others may have occurred no later than the Oligocene, with ancient separations between or within tropical and temperate lineages.     

Recent Advances on Variability, Morpho-Functional Adaptations, Dental Terminology, and Evolution of Sloths

The occasion of the Xenarthra Symposium during the ICVM 9 meeting allowed us to reflect on the considerable advances in the knowledge of sloths made by the “X-community” over the past two decades, particularly in such aspects as locomotion, mastication, diet, dental terminology, intraspecific variation, sexual dimorphism, and phylogenetic relationships. These advancements have largely been made possible by the application of cladistic methodology (including DNA analyses) and the discovery of peculiar forms such as Diabolotherium, Thalassocnus, and Pseudoglyptodon in traditionally neglected areas such as the Chilean Andes and the Peruvian Pacific desert coast. Modern tree sloths exhibit an upside-down posture and suspensory locomotion, but the habits of fossil sloths are considerably more diverse and include locomotory modes such as inferred bipedality, quadrupedality, arboreality or semiarboreality, climbing, and an aquatic or semi-aquatic lifestyle in saltwater. Modern tree sloths are generalist browsers, but fossil sloths had browsing, grazing, or mixed feeding dietary habits. Discovery of two important sloth faunas in Brazil (Jacobina) and southern North America (Daytona Beach and Rancho La Brea) have permitted evaluation of the ontogenetic variation in Eremotherium laurillardi and the existence of possible sexual dimorphism in this sloth and in Paramylodon harlani. A new dental terminology applicable to a majority of clades has been developed, facilitating comparisons among taxa. An analysis wherein functional traits were plotted onto a phylogeny of sloths was used to determine patterns of evolutionary change across the clade. These analyses suggest that megatherioid sloths were primitively semiarboreal or possessed climbing adaptations, a feature retained in some members of the family Megalonychidae. Pedolateral stance in the hindfoot is shown to be convergently acquired in Mylodontidae and Megatheria (Nothrotheriidae + Megatheriidae), this feature serving as a synapomorphy of the latter clade. Digging adaptations can only be securely ascribed to scelidotheriine and mylodontine sloths, and the latter are also the only group of grazing sloths, the remainder being general browsers.     

Phylogenetic relationships and evolution in Chrysosplenium (Saxifragaceae) based on matK sequence data

Chrysosplenium (Saxifragaceae) consists of 57 species widely distributed in temperate and arctic regions of the Northern Hemisphere, with two species restricted to the southern part of South America. Species relationships within the genus are highly problematic. The genus has traditionally been divided into two groups, sometimes recognized as sections (Oppositifolia and Alternifolia), based on leaf arrangement, or, alternatively, into 17 series. Based on morphological features, Hara suggested that the genus originated in South America and then subsequently migrated to the Northern Hemisphere. We conducted phylogenetic analyses of DNA sequences of the chloroplast gene matK for species of Chrysosplenium to elucidate relationships, test Hara's biogeographic hypothesis for the genus, and examine chromosomal and gynoecial diversification. These analyses revealed that both sections Oppositifolia and Alternifolia are monophyletic and form two large sister clades. Hence, leaf arrangement is a good indicator of relationships within this genus. Hara's series Pilosa and Macrostemon are each also monophyletic; however, series Oppositifolia, Alternifolia, and Nepalensia are clearly not monophyletic. MacClade reconstructions suggest that the genus arose in Eastern Asia, rather than in South America, with several independent migration events from Asia to the New World. In one well-defined subclade, species from eastern and western North America form a discrete clade, with Old World species as their sister group, suggesting that the eastern and western North American taxa diverged following migration to that continent. The South American species forms a clade with species from eastern Asia; this disjunction may be the result of ancient long-distance dispersal. Character mapping demonstrated that gynoecial diversification is dynamic, with reversals from inferior to half-inferior ovaries, as well as to ovaries that appear superior. Chromosomal evolution also appears to be labile with several independent origins of n = 12 (from an original number of n = 11) and multiple episodes of aneuploidy.     

Revisiting the Great American Biotic Interchange through analyses of amphitropical bees

The Great American Biotic Interchange (GABI) is zoogeographic event characterized by the exchange of taxa between North and South America, typically associated with the rise of the Isthmus of Panama in the late Pliocene. Recent geologic evidence suggests the connections between North and South America may be much older, and that the interchange of organisms between the two continents could have therefore happened much earlier than 3 Ma. Most of the research investigating the GABI has come from tropical vertebrate taxa; little work has been done on invertebrates or on non‐tropical species. To investigate how the GABI shaped the distribution of arid‐adapted species, particularly those with amphitropical distributions (i.e. taxa found in South and North American xeric regions yet absent from the tropics), we examine the historical biogeography of the bee genus Diadasia using a hypothesis of Diadasia phylogenetic relationships. Nuclear and mitochondrial genetic loci are used to reconstruct a phylogeny of Diadasia, which is then used to estimate divergence dates and reconstruct ancestral area relationships. Our analyses suggest the divergence between North and South American Diadasia species occurred between 20.5 and 15 Ma, long before the formation of the Isthmus of Panama. This study is the first to show a Miocene connection for an amphitropically‐distributed insect group. It suggests that the biotic connection between continents is more complicated than previously thought and may have initiated long before the late Pliocene.     

Collagen Sequence Analysis of the Extinct Giant Ground Sloths Lestodon and Megatherium

For over 200 years, fossils of bizarre extinct creatures have been described from the Americas that have ranged from giant ground sloths to the ‘native’ South American ungulates, groups of mammals that evolved in relative isolation on South America. Ground sloths belong to the South American xenarthrans, a group with modern although morphologically and ecologically very different representatives (anteaters, armadillos and sloths), which has been proposed to be one of the four main eutherian clades. Recently, proteomics analyses of bone collagen have recently been used to yield a molecular phylogeny for a range of mammals including the unusual ‘Malagasy aardvark’ shown to be most closely related to the afrotherian tenrecs, and the south American ungulates supporting their morphological association with condylarths. However, proteomics results generate partial sequence information that could impact upon the phylogenetic placement that has not been appropriately tested. For comparison, this paper examines the phylogenetic potential of proteomics-based sequencing through the analysis of collagen extracted from two extinct giant ground sloths, Lestodon and Megatherium. The ground sloths were placed as sister taxa to extant sloths, but with a closer relationship between Lestodon and the extant sloths than the basal Megatherium. These results highlight that proteomics methods could yield plausible phylogenies that share similarities with other methods, but have the potential to be more useful in fossils beyond the limits of ancient DNA survival.     

Life in proto‐Amazonia: Middle Miocene mammals from the Fitzcarrald Arch (Peruvian Amazonia)

The Middle Miocene has been identified as a time of great diversification in modern lineages now distributed in tropical South America, and when basic archetypal traits defining Amazonia appear, including climatic humid conditions, basic floral physiognomy and phylogenetic composition of modern rainforests. Nonetheless, Middle Miocene localities in South America are poorly known, especially at low latitudes where only one species‐rich locality, La Venta in Colombia, has been extensively studied. The present contribution describes the mammal fauna of Fitzcarrald, a new Middle Miocene local fauna from western Amazonia in Peru. Fitzcarrald is correlated with the Laventan South American Land Mammal Age based on the presence of taxa defining the ‘Miocochilius assemblage zone’ in La Venta. The mammalian fauna of Fitzcarrald comprises 24 taxa among cingulates, folivores, astrapotheres, notoungulates, litopterns, rodents, odontocetes and a possible marsupial. At this time, tropical South America was characterized by the presence of the Pebas megawetland, a huge lacustrine complex that provided unique ecological and environmental conditions most likely isolating northern South America from southern South America. These isolating conditions might have come to an end with its disappearance in the Late Miocene and the establishment of the subsequent Acre system, the predecessor fluvial system of modern Amazonia. Results of faunistic similarity between Fitzcarrald and other Miocene faunas throughout South America support these scenarios. The Fitzcarrald mammal fauna exhibits first appearance datums and last appearance datums of various taxa, showing that tropical South America has played a crucial role in the evolutionary history and biogeography of major clades, and revealing a more complex biological history than previously proposed, based on the record from the southern cone of the continent.     

Phylogeny of North American amblemines (Bivalvia, Unionoida): prodigious polyphyly proves pervasive across genera

Abstract. The subfamily Ambleminae is the most diverse subfamily of fresh‐water mussels (order Unionoida), a globally diverse and ecologically prominent group of bivalves. About 250 amblemine species occur in North America; however, this diversity is highly imperiled, with the majority of species at risk. Assessing and protecting this diversity has been hampered by the uncertain systematics of this group. This study sought to provide an improved phylogenetic framework for the Ambleminae. Currently, 37 North American genera are recognized in Ambleminae. Previous phylogenetic studies of amblemines highlighted the need for more extensive sampling due to the uncertainties arising from polyphyly of many currently recognized taxa. The present study incorporated all amblemine genera occurring in North America north of the Rio Grande, with multiple species of most genera, including the type species for all but seven genera. A total of 192 new DNA sequences were obtained for three mitochondrial gene regions: COI, 16S, and ND1. In combination with published data, this produced a data matrix incorporating 357 gene sequences for 143 operational taxonomic units, representing 107 currently recognized species. Inclusion of published data provides additional taxa and a summary of present molecular evidence on amblemine phylogeny, if at the cost of increasing the amount of missing data. Parsimony and Bayesian analyses suggest that most amblemine genera, as currently defined, are polyphyletic. At higher taxonomic levels, the tribes Quadrulini, Lampsilini, and Pleurobemini were supported; the extent of Amblemini and the relationships of some genera previously assigned to that tribe remain unclear. The eastern North American amblemines appear monophyletic. Gonidea and some Eurasian taxa place as probable sister taxa for the eastern North American Ambleminae. The results also highlight problematic taxa of particular interest for further work.     

A molecular phylogeny of two extinct sloths

Xenarthra (Edentata) is an extremely diverse mammalian order whose modern representatives are the armadillos, anteaters, and sloths. The phylogeny of these groups is poorly resolved. This is particularly true for the sloths (phyllophagans), originally a large and diverse group now reduced to two genera in two different families. Both morphological analyses and molecular analyses of rDNA genes of living and extinct sloths have been used with limited success to elucidate their phylogeny. In an attempt to clarify relationships among the sloths, DNA was extracted and mitochondrial cytochrome b gene sequences were determined from representatives of two extinct groups of sloths (Mylodontidae and Megatheriidae), their two living relatives (two-toed sloths [Megalonychidae], three-toed sloths [Bradypodidae]), anteaters and armadillos. A consistent feature of the latter two species was the nuclear copies of cytochrome b gene sequences. Several methods of phylogenetic reconstruction were applied to the sequences determined, and the results were compared with 12S rDNA sequences obtained in previous studies. The cytochrome b gene exhibited a phylogenetic resolving power similar to that of the 12S rDNA sequences. When both data sets were combined, they tended to support the grouping of two-toed sloths with mylodontids and three-toed sloths with megatheriids. The results strengthen the view that the two families of living sloths adapted independently to an arboreal life-style.     

Evolution of the Madrean–Tethyan disjunctions and the North and South American amphitropical disjunctions in plants

Abstract The present paper reviews advances in the study of two major intercontinental disjunct biogeographic patterns: (i) between Eurasian and western North American deserts with the Mediterranean climate (the Madrean–Tethyan disjunctions); and (ii) between the temperate regions of North and South America (the amphitropical disjunctions). Both disjunct patterns have multiple times of origin. The amphitropical disjunctions have largely resulted from long‐distance dispersal, primarily from the Miocene to the Holocene, with available data indicating that most lineages dispersed from North to South America. Results of recent studies on the Mediterranean disjuncts between the deserts of Eurasia and western North America support the multiple modes of origin and are mostly consistent with hypotheses of long‐distance dispersal and the North Atlantic migration. Axelrod's Madrean–Tethyan hypothesis, which implies vicariance between the two regions in the early Tertiary, has been favored by a few studies. The Beringian migration corridor for semiarid taxa is also supported in some cases.     

Phylogeny and origins of Enchytraeidae

Phylogenetic analyses of Achaetinae (Enchytraeidae: Oligochaeta) and other bisetate enchytraeids indicate that the achaetines include the earliest species of Enchytraeidae but that Achaetinae is not monophyletic. The earliest species of bisetate enchytraeid now extant are restricted to South America, Africa, and India. As this part of the enchytraeid lineage is ancestral to other enchytraeid taxa, it is suggested that Enchytraeidae may have arisen in South America or a contiguous Southern land mass.Less than 50% of the 11 genera of Enchytraeidae considered are supported by the results of these analyses as evolutionary or phylogenetic groups. Five are substantiated as monophyletic: Achaeta, Lumbricillus, Fridericia, Randidrilus, and Enchytronia. In addition to most of the achaetine genera, Marionina is shown to be in great need of revision. Its recognition is a continuing source of confusion to taxonomic resolution of Enchytraeidae.     

Relationships within tribe Lycieae (Solanaceae): paraphyly of Lycium and multiple origins of gender dimorphism

We infer phylogenetic relationships among Lycium, Grabowskia, and the monotypic Phrodus microphyllus, using DNA sequence data from the nuclear granule-bound starch synthase gene (GBSSI, waxy) and the chloroplast region trnT-trnF. This is the first comprehensive molecular phylogenetic study of tribe Lycieae (Solanaceae). In addition to providing an understanding of evolutionary relationships, we use the phylogenetic hypotheses to frame our studies of breeding system transitions, floral and fruit evolution, and biogeographical patterns within Lycieae. Whereas Lycium is distributed worldwide, Phrodus and the majority of Grabowskia species are restricted to South America. Tribe Lycieae is strongly supported as monophyletic, but Lycium likely includes both Grabowskia and Phrodus. Results also suggest a single dispersal event from the Americas to the Old World, and frequent dispersal between North and South America. The diversity of fruit types in Lycieae is discussed in light of dispersal patterns and recent work on fruit evolution across Solanaceae. Dimorphic gender expression has been studied previously within Lycium, and results indicate that transitions in sexual expression are convergent, occurring multiple times in North America (a revised estimate from previous studies) and southern Africa.     

Integration of morphological data sets for phylogenetic analysis of Amniota: the importance of integumentary characters and increased taxonomic sampling

Several mutually exclusive hypotheses have been advanced to explain the phylogenetic position of turtles among amniotes. Traditional morphology-based analyses place turtles among extinct anapsids (reptiles with a solid skull roof), whereas more recent studies of both morphological and molecular data support an origin of turtles from within Diapsida (reptiles with a doubly fenestrated skull roof). Evaluation of these conflicting hypotheses has been hampered by nonoverlapping taxonomic samples and the exclusion of significant taxa from published analyses. Furthermore, although data from soft tissues and anatomical systems such as the integument may be particularly relevant to this problem, they are often excluded from large-scale analyses of morphological systematics. Here, conflicting hypotheses of turtle relationships are tested by (1) combining published data into a supermatrix of morphological characters to address issues of character conflict and missing data; (2) increasing taxonomic sampling by more than doubling the number of operational taxonomic units to test internal relationships within suprageneric ingroup taxa; and (3) increasing character sampling by approximately 25% by adding new data on the osteology and histology of the integument, an anatomical system that has been historically underrepresented in morphological systematics. The morphological data set assembled here represents the largest yet compiled for Amniota. Reevaluation of character data from prior studies of amniote phylogeny favors the hypothesis that turtles indeed have diapsid affinities. Addition of new ingroup taxa alone leads to a decrease in overall phylogenetic resolution, indicating that existing characters used for amniote phylogeny are insufficient to explain the evolution of more highly nested taxa. Incorporation of new data from the soft and osseous components of the integument, however, helps resolve relationships among both basal and highly nested amniote taxa. Analysis of a data set compiled from published sources and data original to this study supports monophyly of Amniota, Synapsida, Reptilia, Parareptilia, Eureptilia, Eosuchia, Diapsida, Neodiapsida, Sauria, Lepidosauria, and Archosauriformes, as well as several more highly nested divisions within the latter two clades. Turtles are here resolved as the sister taxon to a monophyletic Lepidosauria (squamates + Sphenodon), a novel phylogenetic position that nevertheless is consistent with recent molecular and morphological studies that have hypothesized diapsid affinities for this clade.