Unequivocal Synapomorphies Research Articles

Comprehensive phenotypic phylogenetic analysis supports the monophyly of stromateiform fishes (Teleostei: Percomorphacea)

AbstractMore than half the ray-finned fishes and about one-quarter of all living vertebrates belong to Percomorphacea. Among its 30 orders, Stromateiformes encompass 77 species in 16 genera and six families. Stromateiform monophyly has never been tested using morphology, and it has been rejected by molecular analyses. This comprehensive revision of Stromateiformes includes all its valid genera of all percomorph families previously aligned with the order. We sampled 207 phenotypic characters in 66 terminal taxa representing 14 orders and 46 acanthopterygian families. This dataset significantly surpasses all previous phenotype-based phylogenies of Stromateiformes, which analysed only a fraction of these characters. Stromateiformes is recovered as monophyletic, supported by eight unequivocal synapomorphies. Amarsipidae is the sister group of all other Stromateiformes (= Stromateoidei). Centrolophidae is paraphyletic, with three of its genera allocated into an early-diverging clade and the other four appearing as successive sister groups to a lineage containing the remaining stromateiforms. All other stromateoid families are monophyletic, with the following cladistic arrangement: (Nomeidae (Stromateidae (Tetragonuridae, Ariommatidae))). Our analysis convincingly refutes recent molecular phylogenetic interpretations that fail to recover a monophyletic Stromateiformes. These findings call into question large-scale conclusions of percomorph relationships and trait evolution based solely on molecular data.

Phylogenetic relationships among species of Barleria (Acanthaceae, Lamiales): Molecular data reveal complex patterns of morphological evolution and support a revised classification

Barleria is a genus of ~300 species of herbs and shrubs in Africa and Asia, with highest diversity in tropical East Africa and southern Africa. The genus is part of Barlerieae (Acanthaceae), a lineage that is distinguished from other Acanthaceae by quincuncial corolla aestivation. Unequivocal synapomorphies have yet to be identified for Barleria. However, among Barlerieae, species of Barleria can be recognized by the combination of 4‐partite calyces with the anterior and posterior lobes usually larger than the two lateral lobes, pollen with a coarsely reticulate (honeycomb) exine and the corolla limb variously subactinomorphic to strongly zygomorphic but never markedly bilabiate with a hooded upper lip. All Barleria that we have observed also have filaments that twist through 180° and cross just distal to the synstapetal zone. Barleria species have previously been classified into two subgenera and seven sections based on differences in leaf axil spine systems; configuration of the corolla, androecium and stigma; and morphology of the capsule and seed. We tested the subgeneric classification of Barleria by sampling 53 Barleria species and 9 outgroup species for three plastid intergenic spacers (trnS‐G, ndhF‐rpl32‐trnL(UAG)) and the nuclear region nrITS. We found a monophyletic Barleria and support for the two currently recognized subgenera; four of seven currently recognized sections are monophyletic but one of these four, sect. Fissimura, is nested within other sections. Species of sect. Fissimura unexpectedly resolved in subg. Barleria with strong support, although previous classifications placed the section in subg. Prionitis. We propose recognizing two subgenera (i.e., Barleria, Prionitis), the latter comprising three sections (i.e., Prionitis, Somalia, Stellatohirta). Barleria encompasses remarkable morphological diversity; we used an ultrametric tree to examine the evolution of nine morphological traits used to define infrageneric taxa in previous classifications. All characters evolved homoplasiously, but a few states (e.g., woody capsule septa) are supported as synapomorphies, and combinations of characters can be used to delimit subgenera. Members of subg. Barleria have 4‐seeded capsules that lack a prominent beak, with a transition to 2‐seeded capsules in the clade that corresponds to sect. Fissimura. In contrast, members of subg. Prionitis have 2‐seeded capsules (reversed to 4‐seeded in most members of one clade of sect. Somalia) that generally have a prominent beak. Additionally, we surveyed pollen morphology for 15 species sampled from across the classification. Pollen is consistently tricolporate with a coarse honeycomb exine. We provide an infrageneric classification and key to infrageneric taxa of Barleria.

Varestrongylus (Nematoda: Protostrongylidae), lungworms of ungulates: a phylogenetic framework based on comparative morphology.

Varestrongylus Bhalerao, 1932 comprises ten valid lungworm species infecting wild and domestic ungulates from Eurasia and North America. Here, we present a phylogenetic hypothesis for the genus based on morphological characters in a broader context for the family Protostrongylidae and discuss species relationships and aspects of character evolution. Phylogenetic analysis of 25 structural attributes, including binary and multistate characters, among the 10 species of Varestrongylus resulted in one fully resolved most parsimonious tree (61 steps; consistency index = 0.672, retention index = 0.722, and consistency index excluding uninformative characters = 0.667). Varestrongylus forms a monophyletic clade and is the sister of Pneumostrongylus, supporting recognition of the subfamily Varestrongylinae. Monophyly for Varestrongylus is diagnosed by six unequivocal synapomorphies, all associated with structural characters of the copulatory system of males. Varestrongylus pneumonicus is basal, and sister to all other species within the genus, which form two subclades. The subclade I contains V. sagittatus + V. tuvae and V. qinghaiensis + V. longispiculatus. Subclade II contains V. alpenae, V. capricola, V. capreoli, and V. eleguneniensis + V. alces. Both subclades are diagnosed by two unambiguous synapomorphies. Highlighted is the continuing importance of phylogenetic assessments based on comparative morphology as a foundation to explore the structure of the biosphere across space and time.

The oldest record of Alvarezsauridae (Dinosauria: Theropoda) in the Northern Hemisphere.

Procoelous caudal vertebrae, a carpometacarpus with a hypertrophied metacarpal II, and robust proximal and ungual phalanges of manual digit II of a small theropod dinosaur from the Upper Cretaceous (Turonian) Bissekty Formation at Dzharakuduk, Uzbekistan, show unequivocal synapomorphies of the clade Alvarezsauridae and thus are referred to it. The caudal vertebrae have a unique longitudinal canal within the neural arch. The carpometacarpus, with metacarpal III occupying about one third of the width of the carpometacarpus, shows the most plesiomorphic stage of the evolution of the forelimb among known alvarezsaurids. The proximal phalanx of manual digit II differs from the corresponding bone in Parvicursorinae in having a less asymmetrical proximal articular surface without a dorsal process and short ventral ridges. The ungual phalanx of manual digit II has laterally open ventral foramina. The Bissekty alvarezsaurid possibly represents a basal parvicursorine and is the stratigraphically oldest known alvarezsaurid in Asia known to date.

New Leontiniid Notoungulata (Mammalia) from Chile and Argentina: Comparative Anatomy, Character Analysis, and Phylogenetic Hypotheses

Herein we describe and name two new species of leontiniid notoungulates, one being the first known from Chile, the other from the Deseadan South American Land Mammal Age (SALMA) of Patagonia, Argentina. The Chilean leontiniid is from the lower horizons of the Cura-Mallín Formation (Tcm1) at Laguna del Laja in the Andean Main Range of central Chile. This new species, Colpodon antucoensis, is distinguishable from Patagonian species of Colpodon by way of its smaller I2; larger I3 and P1; sharper, V-shaped snout; and squarer upper premolars. The holotype came from a horizon that is constrained below and above by 40Ar/39Ar ages of 19.53 ± 0.60 and 19.25 ± 1.22, respectively, suggesting an age of roughly 19.5 Ma, or a little older (∼19.8 Ma) when corrected for a revised age of the Fish Canyon Tuff standard. Either age is slightly younger than ages reported for the Colhuehuapian SALMA fauna at the Gran Barranca. Taxa from the locality of the holotype of C. antucoensis are few, but they (e.g., the mylodontid sloth, Nematherium, and a lagostomine chinchillid) also suggest a post-Colhuehuapian faunal age. The second leontiniid named in this paper has been known in the literature for over 75 years as Leontinia sp. Several specimens referable to this species were discovered at Pico Truncado (Deseadan SALMA) during the Field Museums first Marshall Field Expedition, led by Elmer Riggs in 1924. This “new” taxon, Elmerriggsia fieldia, is a small-bodied leontiniid, possessing grooved premolar protocones that lack intermediate lingual cingulae, but have well-developed labial cingulids on their lower molars. This new taxon is fairly common at Pico Truncado, in Santa Cruz, Argentina, but we have not encountered it at other localities.The character-taxon matrix that we constructed for this analysis differs from those previously developed for notoungulates by the substantially greater number of postcranial characters used (41). Colbertia magellanica was used as the outgroup in all analyses. Our initial phylogenetic analysis was limited to only taxa traditionally assigned to the Toxodontia. These included a dozen taxa traditionally considered to be leontiniids, two toxodontids, four notohippids, a homalodotheriid, and two isotemnids. The taxa traditionally classified as leontiniids formed a monophyletic group, in which V-shaped muzzle, caniniform i3, femur with medial suprapatellar ridge, and large wedge-shaped fibular facet of the calcaneum were unequivocal synapomorphies. Colpodon spp. nested within a clade that includes the “tropical” leontiniids, Taubatherium and Huilatherium. Toxodontids and notohippids formed a monophyletic group sister to the leontiniids, with these two clades forming a more inclusive clade that previously had been called the “advanced Toxodontia.” However, when five species of typotheres from three “families” were added to the analysis, the “notohippid” Eurygenium was identified as the nearest outgroup of leontiniids and an “advanced notohippid” plus toxodontid clade (nodes C F). Unequivocal synapomorphies uniting these two nodes were robust calcanonavicular articulation (“reverse alternating tarsus” as evidenced by a distinct navicular facet on the calcaneum) and a distal radius with a styloid process. The presence of an entolophid fossettid in the lower molars and the downturned olecranon process of the ulna were equivocal synapomorphies for this clade. Though lacking the character states that diagnose a more exclusive “notohippid-toxodontid-leontiniid” clade, Eurygenium shared several unequivocal synapomorphies that unite it with these taxa. These include a well-formed fossette of upper molars formed by the posterior cingulum, absence of an entepicondylar foramen of the humerus, lack of a neck on the astragalus, a transversely elongated astragalar head, and absence of the “astragalar buttress” of the navicular.Unconventionally, the interatheriids used in the analysis (Federicoanaya and Protypotherium, both interatheriin

The systematics of Late Jurassic tyrannosauroids (Dinosauria: Theropoda) from Europe and North America

Recent discoveries of more than ten new species of tyrannosauroid theropods are helping to understand the origin and evolution of colossal body size and other characteristic features of Tyrannosaurus rex and its terminal Cretaceous relatives. Particularly important has been the discovery and reinterpretation of Late Jurassic tyrannosauroids from Europe and North America, which are intermediate in size and phylogenetic position between small basal tyrannosauroids and the largest Late Cretaceous species. The fragmentary nature of these Jurassic specimens, however, has frustrated attempts to understand their systematics and phylogeny. A new specimen from the Late Jurassic of England was recently named as a new species (Stokesosaurus langhami) of the genus Stokesosaurus, which is known from several fragmentary fossils from North America. We review the systematics and phylogeny of these European and North American specimens and show that there are no unequivocal synapomorphies uniting them. Furthermore, a revised phylogenetic analysis does not recover them as sister taxa. This necessitates a taxonomic revision of this material, and we name a new genus (Juratyrant) for the British specimen.

Testing the evolutionary and biogeographical history of Glypthelmins (Digenea: Plagiorchiida), a parasite of anurans, through a simultaneous analysis of molecular and morphological data

The genus Glypthelmins includes some of the most common digeneans inhabiting the intestine of anurans in the Americas. Phylogenetic analyses of eight species of Glypthelmins and five outgroups, using 26 morphological characters and sequences of cox1, 18S, 5.8S, 28S genes and ITS2 were performed. Additionally, 2 species for which no molecular data have been obtained were included in the analyses. Following a simultaneous analysis approach and using different methods of phylogenetic inference we obtained a phylogenetic tree where the eight studied species conform a monophyletic clade which is well supported by Bremer support, bootstrap, and posterior probabilities. The mapping of morphological characters showed that traits such as serrate scale-like spines, bipartite seminal vesicle, metraterm running dorsal to the cirrus pouch, and ovary sinistral are unequivocal synapomorphies that support the monophyly of Glypthelmins. Phylogenetic hypothesis based on combined data sets was used to re-evaluate the evolutionary and biogeographical history of this group of digeneans. New information provided in this study, in the context of a more robust analytical method allowed us to corroborate that members of the “ Rana pipiens” group were the plesiomorphic group of hosts for Glypthelmins, with two host switching events occurring from the “ Rana pipiens” group to the “ Rana palmipes” group and to Hylidae during the evolutionary history of this group of parasites, and the origin of the group is proposed in Nearctic frogs, with a colonization of Neotropical hosts represented by a monophyletic clade constituted by G. brownorumae, G. facioi, and G. tuxtlasensis.

An articulated embolomere skeleton (Amphibia: Anthracosauria) from the Lower Pennsylvanian (Bashkirian) of Nova Scotia

Recently discovered skeletal material greatly expands our knowledge of the embolomeres from the Early Pennsylvanian locality of Joggins, Nova Scotia. These specimens are probably attributable to Calligenethlon watsoni Steen that has been described previously from this locality, but despite their articulated condition and relative completeness, this assignment is equivocal. Inclusion of the most complete specimen, NSM 994 GF 1.1, in a previous phylogenetic analysis of the Embolomeri results in a sistergroup relationship between NSM 994 GF 1.1 and Anthracosaurus . However, none of the 16 synapomorphies supporting this relationship are unique to these two taxa, but rather all occur in one or more of the other taxa in the analysis. This indicates extensive homoplasy within embolomeres and emphasizes the difficulties inherent in resolving embolomere interrelationships. The dirth of unequivocal synapomorphies is probably also reflects the conservative nature and basal status of embolomeres within the initial Palaeozoic tetrapod radiation.

Like father, like son? Not amongst the eurypterids (Chelicerata) from Beartooth Butte, Wyoming

The eurypteridStrobilopterus princetoniifrom the Lower Devonian Beartooth Butte Formation of Wyoming is redescribed, and previously unknown morphological features, including shape and position of eyes and ocelli are identified, and the prosomal appendages are described in more detail. The monotypicErieopterus latus, based on a much smaller specimen from the same locality, shares a large number of characters withS. princetonii, and must be interpreted as belonging to the genusStrobilopterus.It is here interpreted as a juvenileS. princetonii, but exhibits extreme ontogenetic variation in the morphology of the swimming leg. The other monotypic eurypterid from the locality,Dorfopterus angusticollis, remains mysterious. It might be aS. princetoniitelson, but evidence is inconclusive. The name of the Devonian eurypterid genusSyntomopterusis preoccupied for a beetle (Coleoptera: Insecta) and the replacement nameSyntomopterellais proposed. The phylogenetic position ofS. princetoniiis problematic since it lacks unequivocal synapomorphies with other eurypterids, but the genus is showing more similarities toSyntomopterella, ErieopterusandBuffalopterusthan it does toDolichopterus, contrary to earlier suggestions.

PHYLOGENY FOR SPECIES OF HAEMONCHUS (NEMATODA: TRICHOSTRONGYLOIDEA): CONSIDERATIONS OF THEIR EVOLUTIONARY HISTORY AND GLOBAL BIOGEOGRAPHY AMONG CAMELIDAE AND PECORA (ARTIODACTYLA)

Phylogenetic analysis of 25 morphological characters among the 12 species of Haemonchus resulted in 1 most parsimonious tree (60 steps; consistency index = 0.67, retention index = 0.80). Monophyly for Haemonchus was diagnosed by 3 unequivocal synapomorphies, including the asymmetric origin of the dorsal ray, relative size of the ventral rays, and the presence of a barb on each spicule tip. Species of Haemonchus have complex histories with respect to host and geographic associations: (1) origins in Africa with basal diversification in antelopes (H. krugeri, H. lawrencei, H. dinniki, H. horaki), (2) independent events of colonization for those species in Caprini and Bovinae (H. contortus, H. placei, H. bedfordi, H. similis), (3) colonization and development of core host associations within Camelidae (H. longistipes) and among Antilopinae, Tragelaphini, and Giraffidae (H. mitchelli, H. okapiae, H. vegliai), and (4) geographically widespread species that are represented only by those that have been translocated with domestic stock. The North American fauna is characterized by 3 introduced and exotic species, H. placei, H. contortus, H. similis, which emphasizes the importance of continued documentation of faunal diversity in the context of predictive foundations derived from phylogenetic studies. Satellite associations for species of Haemonchus, particularly among Cervidae and Camelidae in the Neotropics and Cervidae, Antilocapridae, and possibly wild Caprinae in the Nearctic, have been a consequence of introductions and exchange of parasites at historical interfaces for managed and natural ecosystems. Such distributions are emblematic of the overriding significance of anthropogenic factors as determinants of the global distributions for pathogenic parasites in domestic and wild ruminants.

Phylogenetic Analysis of the Genus Gobionellus (Teleostei: Gobiidae)

Abstract A cladistic analysis of the gobiid fish genus Gobionellus primarily using characters of the postcranial axial skeleton and the cephalic lateralis system gave evidence that the genus as historically conceived is polyphyletic. Its present recognition relies upon characters common to many species of gobionelline gobies. One group of six species is most closely related to the genus Gobioides. This group includes Gobionellus oceanicus and retains the name Gobionellus. Gobionellus is diagnosed by an extensive oculoscapular canal running from the snout to above the rear margin of the operculum with a unique A‘BCDFHKL’ pore pattern, a distally flared fourth neural spine that is spatulate in five of the six species, a vertical row of neuromasts on the rear field of the operculum, and elongate gill rakers on the anterior surface and lobes on the posterior surface of the epibranchial of the first gill arch. No unequivocal synapomorphies are offered for the genus excluding Gobioides. Fifteen species previous...

A phylogenetic and biogeographic study of Euniphysa (Eunicidae, Polychaeta)

Fourteen species have either been described in, or referred to, the genus Euniphysa. Seven of these are here re-described based on type material and two new species, E. quadridentata and E. filibranchia, are described. Euniphysa oculata is found to be a subjective synonym of E. spinea, and E. unicusa is a subjective synonym of E. aculeata. Euniphysa taiwanensis and E. megalodus are correctly assigned to the genus, but cannot be described due to lack of material. Euniphysa misakiensis, E. tubicola and E. tubifex are transferred to Eunice. A key is given to the nine identifiable species retained in Euniphysa. Coding strategies for polymorphic and inapplicable characters, as well as problems associated with shared absences, are discussed. A phylogenetic analysis of Euniphysa based on 24 morphological characters yielded two most parsimonious trees (CI = 0.902, RI = 0.905). The tree topology separates Euniphysa into two distinct groups. Group I includes E. filibranchia n. sp., E. italica, E. jeffreysii, E. quadridentata n. sp. and E. spinea, it is supported by five equivocal similarities. Group II is supported by five unequivocal synapomorphies and two equivocal similarities, it includes E. aculeata, E. auriculata, E. falciseta and E. tridontesa. Based on the phylogenetic topology, Paraeuniphysa and Heterophysa are considered as junior synonyms of Euniphysa. The recognition of a separate family for Euniphysa is not warranted. All species of Euniphysa are fragile, shallow, warm water species. They have been collected mainly from sandy sediments of the Northern Hemisphere. The greatest diversity is from the South China Sea area; other species are found throughout the Indian Ocean, the Mediterranean Sea and the East Atlantic Ocean coasts suggesting the genus may have originated in the Tethys Sea. A few species have also been found in the Gulf of Mexico and the West Atlantic Ocean coast again suggesting a Tethyan origin associated with the westward drift of the North American continent.

A phylogenetic hypothesis for species of the genus Taenia (Eucestoda : Taeniidae).

Cladistic analysis of a numerical data matrix describing 27 characters for species of Taenia resulted in 4 most parsimonious phylogenetic trees (174 steps; consistency index = 0.28; homoplasy index = 0.72; retention index = 0.48). Monophyly for Taenia is diagnosed by the metacestode that is either a cysticercus or a form derived from a bladder-like larva; no other unequivocal synapomorphies are evident. Tree structure provides no support for recognition of a diversity of tribes or genera within the Taeniinae: Fimbriotaeniini and Taeniini have no phylogenetic basis. Hydatigera, Fimbriotaenia, Fossor, Monordotaenia, Multiceps, Taeniarhynchus, Tetratirotaenia must be subsumed within Taenia as synonyms. Taenia saginata and Taenia asiatica are sister species and distantly related to Taenia solium. Cospeciation with respect to carnivorous definitive hosts and Taenia appears to be limited. Although felids are putative ancestral hosts, contemporary associations appear to have resulted from extensive host-switching among felids, canids, hyaenids, and others. In contrast, relationships with herbivorous intermediate hosts are indicative of more pervasive coevolution; rodents as intermediate hosts are postulated as ancestral for the Taeniidae, Taenia + Echinococcus. Patterns appear consistent with rapid shifts between phylogenetically unrelated carnivores but among those that historically exploited a common prey resource within communities in specific biogeographic regions.

The Phylogeny of the Myrmecophagidae (Mammalia, Xenarthra, Vermilingua) and the Relationship of Eurotamandua to the Vermilingua

A cladistic investigation of the phylogenetic relationships among the three extant anteater genera and the three undoubted extinct myrmecophagid genera is performed based upon osteological characteristics of the skull and postcranial skeleton. One hundred seven discrete morphological characters are analyzed using the computer program PAUP. Characters are polarized via comparison to the successive xenarthran outgroups Tardigrada (represented by the living sloth Bradypus) and Cingulata (represented by the recent armadillos Dasypus and Euphractus). The analysis results in a single most-parsimonious tree (TL = 190, CI = 0.699, RI = 0.713). The tree corroborates the monophyly of the subfamilies Cyclopinae and Myrmecophaginae, the former including the extant Cyclopes and the Pliocene genus Palaeomyrmidon. Within the Myrmecophaginae the Miocene genus Protamandua is the sister taxon to a clade including the remaining three genera. The recent Tamandua is in turn the sister taxon to the extant Myrmecophaga plus the Pliocene genus Neotamandua. Contrary to the suggestions of recent authors, weak support is provided for the taxonomic distinctiveness of the latter genus from the recent Myrmecophaga. The monophyly of the Myrmecophagidae is supported by 15 unequivocal synapomorphies. The monophyly of the Cyclopinae and Myrmecophaginae is supported by 3 and 13 unambiguous synapomorphies, respectively. The enigmatic Eocene genus Eurotamandua, from the Messel fauna of Germany, is coded for the 107 morphological characters above and included in two subsequent PAUP analyses. The palaeanodont Metacheiromys is also added to these two analyses as a nonxenarthran outgroup to test for the possibility that Eurotamandua lies outside the Xenarthra. In the first analysis, Eurotamandua is constrained a priori to membership in the Vermilingua. The single most-parsimonious tree (TL = 224, CI = 0.618) that results places Eurotamandua as the sister group to the remaining anteater genera, contra Storch and Habersetzer's (1991) assignment of Eurotamandua to the vermilinguan subfamily Myrmecophaginae. Eurotamandua shares six unequivocal synapomorphies with other anteaters, including the absence of teeth and the presence of a lateral tuberosity on the fifth metatarsal. The remaining vermilinguans are united by 11 unequivocal synapomorphies, plus an additional 10 ambiguous synapomorphies. In the second analysis, the position of Eurotamandua is unconstrained. The resulting single most-parsimonious tree (TL = 219, CI = 0.632) places Eurotamandua outside Vermilingua as the sister group to the Pilosa (Vermilingua plus Bradypus). The monophyly of this node is supported by four unambiguous synapomorphies in the unconstrained analysis. Further manipulation of this second analysis shows that placement of Eurotamandua as the sister group to the Xenarthra or to the Palaeanodonta adds three steps to the shortest tree but is more parsimonious than its placement as a sister group to the Vermilingua is the previous analysis. The addition of pangolins to the analysis does little to alter the major phylogenetic conclusions of the study. The allocation of Eurotamandua to the Xenarthra, but as a sister group to the Pilosa, is a novel arrangement which leaves open the biogeographic question of how a xenarthran reached Western Europe during the Eocene.

A new ‘bone-cracking’ dasyurid (marsupialia), from the Miocene of Riversleigh, northwestern Queensland

Ganbulanyi djadjinguli gen. et sp. nov. is described on the basis of an upper molar and premolar from an early-late Miocene site in Riversleigh, northwestern Queensland. The paucity of material constrains certainty in the determination of it's phylogenetic position. But, among dasyuromorphians, and dependent on the interpretation of tooth homology, this species shows unequivocal synapomorphies only with the derived dasyurine Sarcophilus, and/or Barinya wangala, a possible sister taxon to the modern dasyurid radiation (i.e., Sminthopsinae, Phascogalinae, Dasyurinae). Other apomorphies, evident in G. djadjinguli, are common to both carnivorous thylacinids and dasyurids within the order. Some dental features of Ganbulanyi djadjinguli are treated as adaptations to a ‘bone cracking’ habitus. If this interpretation is correct, then this species represents the only pre-Pliocene Australian taxon known to occupy such a niche and perhaps the smallest specialist ‘bone-cracker’ within Mammalia.

Progress and pitfalls in systematics: cladistics, DNA and morphology*

SUMMARY The ‘natural system’ of organisms reflects their phylogenetic relationship. It is the result of an historical process and has to be inferred from the available evidence. In the morphological phenotype, historical traces are intermeshed with functional adaptations. Overall similarity, even if quantified, can be a misleading indicator of relatedness. Cladistics uses shared derived character states (synapomorphies) to identify groups of common ancestry. Synapomorphies are mostly inferred from their taxonomic context. If apparently equally valid characters suggest mutually exclusive groups, parsimony is invoked: a phylogenetic reconstruction requiring a minimum of evolutionary steps to describe the present character distribution is accepted as the most likely one. Cladistics sets very stringent requirements for informative characters, and a rigorous analysis of morphology is likely to yield very few reliable characters. The direct analysis of DNA sequences provides theoretically the optimal evidence for phylogenetic reconstruction. In practice, very little of this information is readily accessible. Occasionally major sequence rearrangements can be unequivocal synapomorphies. Many phylogenetic problems can be solved by comparative sequencing of an appropriate segment of DNA. Comparative sequencing of the chloroplast gene rbcL has become the model for such studies. Molecular data have confirmed much traditional taxonomy, elucidated doubtful cases and corrected misinterpretations. Molecular data also have clearly shown the limits of the cladistic approach by revealing both known and previously unsuspected modes of reticulate evolution. Molecular approaches separate phylogenetic reconstruction from biological evaluation and will never replace morphological analysis in Systematics. However, molecular methods also facilitate the direct investigation of morphological evolution by revealing the genetic basis of morphogenesis in model systems or by permitting the genetic analysis of diagnostic character changes by genetic mapping.