Evolutionary transformations of chorioallantoic placental characters in rodentia with special reference to hystricognath species

The aim of this paper is to reconstruct the evolution of chorioallantoic placental characters in Rodentia. The analysis is based on pre-existing hypotheses of rodent relationships and the tracing of character evolution. Data on 64 rodent species of 49 genera are derived from the literature. New results refer to the hystricognath species Petromus typicus A. Smith, 1831 and Octodon degus (Molina, 1782). This comprehensive analysis confirms that the stem species pattern of Rodentia is characterised by a haemochorial placenta which is divided horizontally. Inside the placental labyrinth, fetal vessels and their trophoblastic external border build up a network through which the maternal blood flows. The trophoblastic tissue is one-layered, syncytial and possess a considerable surface extension. Within Rodentia, evolutionary transformations occurred on the macroscopic as well as the fine structural level. The results suggest that the stem species of Hystricognathi underwent transformations only on the macroscopic level, i.e., forming a ring-shaped arrangement of placental regions with centrally situated maternal arteries and the acquisition of a subplacenta. By contrast, in Muridae the chorioallantoic placenta shows derived features only in regard to the fine structure of the labyrinth, i.e. the interhaemal membrane is modified in composition, and the fetal capillary endothelium is fenestrated. Geomyoidea underwent transformations on both levels. Macroscopically, their placenta is modified into a hillock shape. Microscopically, the interhaemal membrane is formed by the cytotrophoblast. In addition to the mentioned transformations, some aspects of other fetal membrane differentiation in Rodentia are briefly discussed.     

Chromosome painting among Proboscidea, Hyracoidea and Sirenia: support for Paenungulata (Afrotheria, Mammalia) but not Tethytheria

Despite marked improvements in the interpretation of systematic relationships within Eutheria, particular nodes, including Paenungulata (Hyracoidea, Sirenia and Proboscidea), remain ambiguous. The combination of a rapid radiation, a deep divergence and an extensive morphological diversification has resulted in a limited phylogenetic signal confounding resolution within this clade both at the morphological and nucleotide levels. Cross-species chromosome painting was used to delineate regions of homology between Loxodonta africana (2n=56), Procavia capensis (2n=54), Trichechus manatus latirostris (2n=48) and an outgroup taxon, the aardvark (Orycteropus afer, 2n=20). Changes specific to each lineage were identified and although the presence of a minimum of 11 synapomorphies confirmed the monophyly of Paenungulata, no change characterizing intrapaenungulate relationships was evident. The reconstruction of an ancestral paenungulate karyotype and the estimation of rates of chromosomal evolution indicate a reduced rate of genomic repatterning following the paenungulate radiation. In comparison to data available for other mammalian taxa, the paenungulate rate of chromosomal evolution is slow to moderate. As a consequence, the absence of a chromosomal character uniting two paenungulates (at the level of resolution characterized in this study) may be due to a reduced rate of chromosomal change relative to the length of time separating successive divergence events.     

The historical biogeography of Mammalia

Palaeobiogeographic reconstructions are underpinned by phylogenies, divergence times and ancestral area reconstructions, which together yield ancestral area chronograms that provide a basis for proposing and testing hypotheses of dispersal and vicariance. Methods for area coding include multi-state coding with a single character, binary coding with multiple characters and string coding. Ancestral reconstruction methods are divided into parsimony versus Bayesian/likelihood approaches. We compared nine methods for reconstructing ancestral areas for placental mammals. Ambiguous reconstructions were a problem for all methods. Important differences resulted from coding areas based on the geographical ranges of extant species versus the geographical provenance of the oldest fossil for each lineage. Africa and South America were reconstructed as the ancestral areas for Afrotheria and Xenarthra, respectively. Most methods reconstructed Eurasia as the ancestral area for Boreoeutheria, Euarchontoglires and Laurasiatheria. The coincidence of molecular dates for the separation of Afrotheria and Xenarthra at approximately 100 Ma with the plate tectonic sundering of Africa and South America hints at the importance of vicariance in the early history of Placentalia. Dispersal has also been important including the origins of Madagascar's endemic mammal fauna. Further studies will benefit from increased taxon sampling and the application of new ancestral area reconstruction methods.     

Evolution of the placenta and associated reproductive characters in bats

Recent advances in molecular phylogenetics indicate that the order Chiroptera is monophyletic and that one of four lineages of microbats (Rhinolophoidea) shares a common origin with megabats. Against this background we undertook a comprehensive analysis of placental evolution in bats. We defined a range of characters and character states associated with female reproduction, early development, placentation and the neonate. These were then mapped on a pre-existing hypothesis of bat relationships that represents the current view from molecular studies. Our purpose was threefold. First, on the assumption of bat monophyly, we wished to establish the stem species pattern of extant chiropterans. Secondly, we asked whether there are derived character conditions in support of a common origin for Rhinolophoidea and the megabats. Thirdly, we looked for evolutionary character transformations that characterize higher-level clades within Chiroptera, i.e. the megabats and the four lineages of microbats. The character condition occurring in the last common ancestor of Chiroptera was unequivocal for 21 of the 25 characters included in the analysis. The data did not offer support for a megabat-rhinolophoid clade or the implication that microbats are paraphyletic. However, analysis of early development, placentation and other reproductive parameters resulted in derived character conditions for the megabats as well as for each of the four major lineages of microbats.     

Phylogenetic analysis of pelecaniformes (aves) based on osteological data: implications for waterbird phylogeny and fossil calibration studies

Background

Debate regarding the monophyly and relationships of the avian order Pelecaniformes represents a classic example of discord between morphological and molecular estimates of phylogeny. This lack of consensus hampers interpretation of the group''s fossil record, which has major implications for understanding patterns of character evolution (e.g., the evolution of wing-propelled diving) and temporal diversification (e.g., the origins of modern families). Relationships of the Pelecaniformes were inferred through parsimony analyses of an osteological dataset encompassing 59 taxa and 464 characters. The relationships of the Plotopteridae, an extinct family of wing-propelled divers, and several other fossil pelecaniforms (Limnofregata, Prophaethon, Lithoptila, ?Borvocarbo stoeffelensis) were also assessed. The antiquity of these taxa and their purported status as stem members of extant families makes them valuable for studies of higher-level avian diversification.

Methodology/Principal Findings

Pelecaniform monophyly is not recovered, with Phaethontidae recovered as distantly related to all other pelecaniforms, which are supported as a monophyletic Steganopodes. Some anatomical partitions of the dataset possess different phylogenetic signals, and partitioned analyses reveal that these discrepancies are localized outside of Steganopodes, and primarily due to a few labile taxa. The Plotopteridae are recovered as the sister taxon to Phalacrocoracoidea, and the relationships of other fossil pelecaniforms representing key calibration points are well supported, including Limnofregata (sister taxon to Fregatidae), Prophaethon and Lithoptila (successive sister taxa to Phaethontidae), and ?Borvocarbo stoeffelensis (sister taxon to Phalacrocoracidae). These relationships are invariant when ‘backbone’ constraints based on recent avian phylogenies are imposed.

Conclusions/Significance

Relationships of extant pelecaniforms inferred from morphology are more congruent with molecular phylogenies than previously assumed, though notable conflicts remain. The phylogenetic position of the Plotopteridae implies that wing-propelled diving evolved independently in plotopterids and penguins, representing a remarkable case of convergent evolution. Despite robust support for the placement of fossil taxa representing key calibration points, the successive outgroup relationships of several “stem fossil + crown family” clades are variable and poorly supported across recent studies of avian phylogeny. Thus, the impact these fossils have on inferred patterns of temporal diversification depends heavily on the resolution of deep nodes in avian phylogeny.     

Convergence and parallelism: is a new life ahead of old concepts?

In comparative biology, character observations initially separate similar and dissimilar characters. Only similar characters are considered for phylogeny reconstruction; their homology is attested in a two‐step process, firstly a priori of phylogeny reconstruction by accurate similarity statements, and secondly a posteriori of phylogeny analysis by congruence with other characters. Any pattern of non‐homology is then a homoplasy, commonly, but vaguely, associated with “convergence”. In this logical scheme, there is no way to analyze characters which look similar, but cannot meet usual criteria for homology statements, i.e., false similarity detected a priori of phylogenetic analysis, even though such characters may represent evolutionarily significant patterns of character transformations. Because phylogenies are not only patterns of taxa relationships but also references for evolutionary studies, we propose to redefine the traditional concepts of parallelism and convergence to associate patterns of non‐homology with explicit theoretical contexts: homoplasy is restricted to non‐similarity detected a posteriori of phylogeny analysis and related to parallelism; non‐similarity detected a priori of phylogenetic analysis and necessarily described by different characters would then correspond to a convergence event s. str. We propose to characterize these characters as heterologous (heterology). Heterology and homoplasy correspond to different non‐similarity patterns and processes; they are also associated with different patterns of taxa relationships: homoplasy can occur only in non‐sister group taxa; no such limit exists for heterology. The usefulness of these terms and concepts is illustrated with patterns of acoustic evolution in ensiferan insects. © The Willi Hennig Society 2005.     

Evolutionary advances in the higher fungi

In this report the phrase evolutionary advances; is used in three ways: 1. to describe monophyletic changes perceived within a lineage; 2. to describe evolutionary sequences that appear to have become parallel/convergent; 3. to describe major transitions inferred between primary taxa. In monophyletic evolution the changes occur within a specific lineage that arises from a common ancestor, e.g., modern Man, horses, rusts. In parallel/convergent evolution different lineages respond similarly over time to environmental challenges and opportunities and come to acquire a great deal of comparability (e.g., Webster, 1987). Such lineages may be designated as separate taxa, e.g., similarities in marsupial and placental carnivores, or, if the polyphyleticism is cryptic, as a collective taxon, e.g., Aves, the class of birds, the obsolete Amentiferae for catkin bearing plants, the Gasteromycetes, and lichens. In major transitions there are significant paradigm shifts in which evolutionary changes from one predominant life style pattern to another are accompanied by increases in complexity (see Smith & Szatháry, 1995), e.g., symbiosis, the water to land transition, the changes between the phyla of land fungi. Three particular terms are used in evaluating evolutionary relationships (Moore, 1996a): homology, paramology, and analogy. Homology, from Darwin';s theory of common descent, is the phenomenon of having a common historical origin but not necessarily the same final structure or function (e.g., vertebrate forelimbs). Paramology (Moore, 1971) applies to inferred relationships in evolutionary schemes based on contemporary forms that lack fossil antecedents, e.g., the various phylogenetic interpretations of prokaryotes, algae, and fungi; Boekhout et al. (1993) have evaluated the taxonomic resolution of a variety of morphologic, biochemical, physiological, and molecular characters (Table 1). Analogy is generally applied to similar forms that are unrelated, e.g., insect/vertebrate wings; prokaryote/eukaryote flagella. It should also be borne in mind that, in a given taxon, biotrophism (Coffey, 1975) is an advanced character (Heath, 1987) over, respectively, weaker parasitism, symbiotism, commensalism, and freeliving and that seemingly simple or less differentiated forms can be, and more than likely than not are, reduced, polyphyletic, and specialized rather than ancient and rudimentary, e.g., yeasts (Hoog et al., 1988; Kurtzman & Fell, 1996; Moore, 1988b; 1996a).     

THE NATURE OF CLADISTIC DATA

Abstract— Cladistic data are the characters of organisms. Character is defined as a feature that can be evaluated as a variable with two or more mutually exclusive and ordered states. Cladistic characters must be treated as multistate variables, and coded as sequential numbers or in additive binary fashion. Any other interpretation and handling of cladistic data will introduce error into analysis. Character states cannot be treated independently as present or absent, i.e., as nominal variables, because redundancy is introduced into the data and information content is sacrificed. Non-additive binary coding demonstrates that treating cladistic variables as nominal data will lead to multiple, equally parsimonious solutions. Defining characters found universally in a group of organisms, but unknown outside those organisms have no alternative state that can be designated as absent. Absence, however, is valid as a character state if it can be shown to be apomorphic. When two or more character states occur within a taxon, that taxon must be coded as having an unknown state for that character, or the taxon must be split in two or more taxa. Continuously varying quantitative data are not suitable for cladistic analysis because there is no justifiable basis for recognizing discrete states among them. Quantitative data are questionable even when they exhibit mutually exclusive states because the states can be interpreted only in reference to an archetype, i.e., as implied homologies not subject to test.     

A comparison of numerical and biosystematic studies in Haplopappus

Numerical phenetics, based on indiscriminate choice of characters and equal weighting, does not directly reflect cladistic or lineage relationships in some taxa ofHaplopappus. However, the degree to which the lineage and phenetic relationships diverge may be used as an assay of the amount of parallel evolution that has occurred. Several numerical taxonomic methods were employed. For each method a change in the number of characters from 31 to 29, by deletion of two karyotypic characters, yielded a significant change in the results. Uses of numerical techniques for the study of character dines and adaptive character complexes are discussed.     

Primates: cladistic diagnosis and relationships

The morphological evidence for the phylogenetic relationships of euprimates, archaic primates, and related eutherian orders is reviewed following the methods of Hennigian phylogenetic systematics. Euprimates, the group including living primates and their closest common ancestor, is diagnosed by a suite of shared derived characters of the cranium and posteranium exhibiting relatively unique distributions among Eutheria. Plesiadapiformes, the group of archaic primates generally held to be the sister group to Euprimates, is not demonstrably monophyletic (with or without Microsyopidae). The Superorder Archonta (primates, tree shrews, bats, and colugos) is the only higher-level grouping including Euprimates that is based on uniquely derived morphological characters. Hypotheses of relationships within Archonta ally Euprimates with either tree shrews or some plesiadapiforms (paromomyids and plesiadapids), but the eurprimate-tree shrew clade receives more support from the distribution of derived characters among the taxa studied. Because the higher-level affinities of Euprimates are not well resolved, we advocate equating the Order Primates with the taxon Euprimates.     

Phylogeny of Dicranophoridae (Rotifera: Monogononta) – a maximum parsimony analysis based on morphological characters

This study presents the first phylogenetic analysis of Dicranophoridae (Rotifera: Monogononta), a species rich rotifer family of about 230 species currently recognized. It is based on a maximum parsimony analysis including 77 selected ingroup and three outgroup taxa and a total of 59 phylogenetically informative morphological characters. Character coding is based on personal investigation of material collected by the authors and an extensive survey of the literature. Apart from covering general body organization, character coding primarily relies on scanning electron microscopic preparations of the mastax jaw elements. Our study suggests monophyly of Dicranophoridae with a clade of Dicranophorus and Dorria as the sister taxon of all other dicranophorid species. Monophyly of Encentrum , the most species rich genus within Dicranophoridae, cannot be demonstrated. Within Dicranophoridae our study identifies the monophyletic taxa Caudosubbasifenestrata, Intramalleata, Praeuncinata and Proventriculata, each based on unambiguous character transformations evolved in their stem lineages. However, resolution within Praeuncinata and Proventriculata is very limited. Although some terminal clades within Praeuncinata and Proventriculata are recognized, basal splits remain obscure. Probably, other characters such as DNA sequence data are needed to further our understanding of phylogenetic relationships within these poorly resolved taxa.     

Recapitulating the evolution of Afrotheria: 57 genes and rare genomic changes (RGCs) consolidate their history

The decipherment of higher level relationships among the orders of Afrotheria – an extraordinary assumption in mammalian evolution – constitutes one of the major disputes in the evolutionary history of mammals. Recent comprehensive studies of various genomic data, including mitochondrial and nuclear DNA sequences, chromosomal syntenic associations and retroposon insertions support strongly the monophyly of Afrotheria. However, the relationships within Afrotheria have remained ambiguous and there is a necessity for a more sophisticated analysis (i.e. combination of gene phylogeny and Rare Genomic Changes (RGCs)), which could aid in the comprehension of the evolutionary history of this old group of mammals. The present study investigated the phylogenetic relationships within Afrotheria by analysing a data set of coding and non-coding sequences (～32 000 bp) comprising 57 orthologous genes and 31 RGCs, such as chromosomal associations and retroposon insertions, and re-evaluated a molecular timescale for afrotherian mammals using a Bayesian relaxed clock approach. The interordinal afrotherians phylogeny presented here contributed to the elucidation of the evolutionary history of this ancient clade of mammals, which is one of the most unorthodox proposals in mammalian biology. This is critical not only for understanding how Afrotheria evolved in Africa, but also to comprehend the early biogeographical history of placental mammals.     

Cladistic relationships of extant and fossil hominoids

There is general agreement that the hominoid primates form a monophyletic group, that the extant great apes and humans form a second clade within that group with the gibbons as the sister group, and that the African apes and humans form a third clade. Although it has recently been proposed that humans and orang utans are sister taxa and also that the great apes form a clade to the exclusion of humans, our analysis, particularly of the molecular evidence, supports the existence of an African ape and human clade. The major problem in hominoid phylogeny at present is the relationships of the species within this clade: morphological data generally support the existence of an African ape clade which is the sister group to humans; some molecular data also support this conclusion, but most molecular evidence indicates the existence of a chimpanzee/human clade. We have cladistically re-analysed the DNA and protein sequence data for which apomorphic character states can be assessed. It is clear that there is a high degree of homoplasy whichever branching pattern is produced, with some characters supporting the existence of a chimpanzee/human clade and others supporting an African ape clade. When the cladistic analyses of morphological and molecular data are combined we believe that the most parsimonious interpretation of the data is that the African apes form a clade which is the sister taxon of the human (i.e., Australopithecus, Homo and Paranthropus) clade.This paper is not intended as a survey of all hominoid fossils but as a study of branching points in hominoid evolution and fossils are included which are relevant to this branching pattern. The analysis of fossil taxa in this study leads us to conclude that Proconsul is the sister taxon to the later Hominoidea. A number of middle Miocene forms such as Dryopithecus, Kenyapithecus, Heliopithecus and Afropithecus are shown to share derived characters with great apes and humans and provide evidence for the divergence of that clade from the gibbon lineage prior to 18 Ma. The position that Sivapithecus represents the sister group of the orang utan clade is supported here and shows that the orang utan lineage had diverged from the African ape and human lineage prior to 11·5 Ma. There is unfortunately no definitive fossil cvidence on branching sequences within the African ape and human clade, although a new specimen from Samburu, Kenya may be related to the gorilla.     

Heterochrony of the ostracod hingement and its significance for taxonomy

The hingement of cytheracean ostracods is a very significant character for taxonomy. In some taxa, adult hinge characters develop abruptly at the last moult, whilst in others no significant change of hingement is observed throughout ontogeny. These two types of hinge development are regarded to as 'leap type' and 'gradual type', respectively. In the five major cytheracean families examined, heterochronic relationships were detected in 11 pairs, i.e. in each family, the adult hinge character of the gradual-type taxon corresponds to the A-1 hingement of the leap-type taxon. Furthermore, these 11 heterochronic pairs can be classified into two categories. The first are 'complete pairs', in which the adult hinge character of gradual-type taxa can be almost completely identified in the A-1 of the counterpart leap-type taxa. The second group are 'incomplete pairs', in which the relationship is not so complete. Palaeontological evidence indicates that in most cases the heterochronic evolution is characterized by paedomorphosis, because the leap type always has the older fossil record than the gradual type in each pair. Most of the gradual-type species of complete pairs originated in the Miocene, while all the gradual-type species of incomplete pairs appeared in and after the Pleistocene. Heterochronic changes must occur universally in the cytheracean ostracods, but the degree of completeness of the heterochronic pair seems to be related to the age of speciation.     

Astragalar morphology of late Eocene anthropoids from the Fayum Depression (Egypt) and the origin of catarrhine primates

The phylogenetic relationships of the late Eocene anthropoids Catopithecus browni and Proteopithecus sylviae are currently a matter of debate, with opinion divided as to whether these taxa are stem or crown anthropoids. The phylogenetic position of Catopithecus is of particular interest, for, unlike the highly generalized genus Proteopithecus, this taxon shares apomorphic dental and postcranial features with more derived undoubted catarrhines that appear in the same region 1-2 Ma later. If these apomorphies are homologous and Catopithecus is a stem catarrhine, the unique combination of plesiomorphic and apomorphic features preserved in this anthropoid would have important implications for our understanding of the crown anthropoid morphotype and the pattern of morphological character transformations that occurred during the early phases of stem catarrhine evolution.Well-preserved astragali referrable to Proteopithecus, Catopithecus, and the undoubted early Oligocene stem catarrhine Aegyptopithecus have provided additional morphological evidence that allows us to further evaluate competing hypotheses of interrelationships among Eocene-Oligocene Afro-Arabian anthropoids. Qualitative observations and multivariate morphometric analyses reveal that the astragalar morphology of Proteopithecus is very similar to that of early Oligocene parapithecids and living and extinct small-bodied platyrrhines, and strengthens the hypothesis that the morphological pattern shared by these taxa is primitive within crown Anthropoidea. In contrast, Catopithecus departs markedly from the predicted crown anthropoid astragalar morphotype and shares a number of apomorphic features (e.g., deep cotylar fossa, laterally projecting fibular facet, trochlear asymmetry, mediolaterally wide astragalar head) with Aegyptopithecus and Miocene-Recent catarrhines. The evidence from the astragalus complements other independent data from the dentition, humerus and femur of Catopithecus that support this taxon's stem catarrhine status, and we continue to maintain that oligopithecines are stem catarrhines that constitute the sister group of a clade containing propliopithecines and Miocene-Recent catarrhines.     

Phylogeny of the great cats (Felidae: Pantherinae), and the influence of fossil taxa and missing characters

Molecular phylogenetic studies of the extant Pantherinae have resulted in a variety of different hypotheses of relationships. This study presents the results of a cladistic study encompassing 45 osteological and dental characters in the skull and mandible, as well as 13 soft‐tissue and behavioural characters. Analyzing extant pantherines with osteological data only resulted in two equally parsimonious trees, which differed only with respects to the jaguar, a taxon which shows morphological affinity to the tiger as well as the lion + leopard. Addition of soft‐tissue characters resolved this ambiguity, and led to markedly improved bootstrap values. The inclusion of fossil taxa did not have an impact on topology, but was important for a correct understanding of character evolution, due to the fossils having a combination of characters unlike those of any extant taxon. The clouded leopard is the most basal pantherine, followed by the snow leopard. The large pantherines are a well supported group, to which the snow leopard does not belong, contrary to some molecular studies. Panthera palaeosinensis is no tiger, but may be close to the stem group from which the tiger evolved. P. atrox and P. spelaea are not on the lion lineage, as traditionally assumed, but are successive outgroups to the lion + leopard, although the position of P. spelaea is tentative, but is supported by other lines of evidence such as brain anatomy. © The Willi Hennig Society 2008.     

The evolution of insect sperm − an unusual character system in a megadiverse group

Spermatozoa provide an unusual character system, with a limited number of components organized in a single cell. Similar spermatozoa occur in groups widely separated in the phylogenetic tree of Metazoa. Nevertheless, the character system contains phylogenetic information. Hexapoda have acquired spermatophores along with the switch from aquatic to terrestrial habitats, and related to this, a multitude of different sperm types. The aim of this study is a formal evaluation of the phylogenetic information content of spermatozoa. For the first time, sperm characters are coded for formal phylogenetic analyses. Different approaches are used and compared. Mainly due to a high level of homoplasy, the evaluation of sperm characters alone is insufficient for a reconstruction of the phylogeny of the group. Yet, a reliable reconstruction of the evolution of insect sperm is possible when character transformations are assessed using a phylogeny based on extensive molecular data. Important changes took place in the early evolution of Hexapoda. Sperm characters support some major clades (e.g. Hexapoda, Dicondylia, Polyneoptera, Psocodea), but important steps in the evolution are not reflected by transformations of spermatozoa, notably the rise of Pterygota or Holometabola. Important innovations are the formation of mitochondrial derivatives and the acquisition of accessory microtubules. Some features are conservative, whereas others evolved rapidly (e.g. presence or absence of the acrosome vesicle). Some groups are conservative in their sperm features (e.g. Odonata, Heteroptera), whereas the evolution of spermatozoa was distinctly accelerated in others (e.g. Ephemeroptera). The rate of evolution can change drastically in closely related groups. Profound changes in the morphologically uniform Zoraptera underline that sperm evolution can follow a pattern very different from the general somatic morphology. The mode of character reconstruction preferred here will be useful for the evaluation of specialized morphological character systems and strengthen the concept of evolutionary morphology.     

Inference of higher-order relationships in the cycads from a large chloroplast data set

Theria includes Eutheria and its sister taxon Metatheria. Placentalia includes extant eutherians plus their most recent common ancestor. The oldest eutherian is from 125mya (million years ago). Molecular studies place this origin at about 130-185mya. Older dates cannot be refuted based on fossil evidence as earliest eutherian remains are scarce. Earliest superordinal clades (hence Placentalia) range from 64-104mya (median 84mya) based on molecules, similar to 85-90mya based on fossils. Superordinal clades Archonta, Ferungulata, Glires, and Paenungulata based on fossils are similar to molecularly based clades, except Afrotheria was not predicted by fossils. Both fossils and molecules recognize 16 of 18 extant placental orders. Fossils place the origins of orders around 65mya as do some molecular studies, but others suggest ordinal diversification as old as 100mya. Fossil evidence supports a Laurasian origin for Eutheria (and Metatheria) and Placentalia, although some molecular studies suggest a Gondwanan origin for both taxa.