A Triassic stem turtle with an edentulous beak.

The early evolution of turtles continues to be a contentious issue in vertebrate palaeontology. Recent reports have suggested that they are diapsids1-6, but the position of turtles within Diapsida is controversial7-12 and the sequence of acquisition of turtle synapomorphies remains unclear1-3. Here we describe a Triassic turtle from China that has a mixture of derived characters and plesiomorphic features. To our knowledge, it represents the earliest known stem turtle with an edentulous beak and a rigid puboischiadic plate. The discovery of this new form reveals a complex early history of turtles.

A basal ichthyosauriform with a short snout from the Lower Triassic of China.

The incompleteness of the fossil record obscures the origin of many of the more derived clades of vertebrates. One such group is the Ichthyopterygia, a clade of obligatory marine reptiles that appeared in the Early Triassic epoch, without any known intermediates. Here we describe a basal ichthyosauriform from the upper Lower Triassic (about 248 million years ago) of China, whose primitive skeleton indicates possible amphibious habits. It is smaller than ichthyopterygians and had unusually large flippers that probably allowed limited terrestrial locomotion. It also retained characteristics of terrestrial diapsid reptiles, including a short snout and body trunk. Unlike more-derived ichthyosauriforms, it was probably a suction feeder. The new species supports the sister-group relationships between ichthyosauriforms and Hupehsuchia, the two forming the Ichthyosauromorpha. Basal ichthyosauromorphs are known exclusively from south China, suggesting that the clade originated in the region, which formed a warm and humid tropical archipelago in the Early Triassic. The oldest unequivocal record of a sauropterygian is also from the same stratigraphic unit of the region.

Morphology and Phylogeny.

The concept that renders morphology a tool for phylogeny reconstruction is homology. The concept of homology is rooted in pre-evolutionary idealistic morphology. The claim that the goal of idealistic morphology was the seriability of form may sound paradoxical given that this discipline proceeded within a framework of strictly delimited types. But the types only demarcate where seriability starts and where it comes to an end. Carl Gegenbaur's (Grundzüge der vergleichenden Anatomie, Wilhelm Engelmann, Leipzig, 1859) was recognized as a milestone in idealistic morphology. A comparison with the second edition of 1870 illustrates Gegenbaur's turn to evolutionary morphology. The methodology remained the same-seriability of form-but the series was no longer merely descriptive or conceptual but now a historical, evolutionary one. Gegenbaur emphasized that seriability of form was possible not only between species of the same type, but also between parts (organs) of organisms of the same type. Pursuing this project, he found that different parts of organisms evolve at different rates, resulting in an incongruence between the series of parts (organs) relative to the series of species under comparison. This incongrence was called chevauchement des spécialisations by Louis Dollo, Spezialisationskreuzungen by Othenio Abel, and heterobathmy of characters by Armen Takhtajan. Willi Hennig, the founder of modern methods in phylogenetic systematics, discovered that the heterobathmy of characters was a precondition for the establishment of the phylogenetic relationships based on shared derived characters. The result was a replacement of the search for ancestors by a search for relative degrees of phylogenetic relationships (sister-group relationships).

Macropredatory ichthyosaur from the Middle Triassic and the origin of modern trophic networks.

The biotic recovery from Earth's most severe extinction event at the Permian-Triassic boundary largely reestablished the preextinction structure of marine trophic networks, with marine reptiles assuming the predator roles. However, the highest trophic level of today's marine ecosystems, i.e., macropredatory tetrapods that forage on prey of similar size to their own, was thus far lacking in the Paleozoic and early Mesozoic. Here we report a top-tier tetrapod predator, a very large (>8.6 m) ichthyosaur from the early Middle Triassic (244 Ma), of Nevada. This ichthyosaur had a massive skull and large labiolingually flattened teeth with two cutting edges indicative of a macropredatory feeding style. Its presence documents the rapid evolution of modern marine ecosystems in the Triassic where the same level of complexity as observed in today's marine ecosystems is reached within 8 My after the Permian-Triassic mass extinction and within 4 My of the time reptiles first invaded the sea. This find also indicates that the biotic recovery in the marine realm may have occurred faster compared with terrestrial ecosystems, where the first apex predators may not have evolved before the Carnian.

Adult sex ratio, sexual dimorphism and sexual selection in a Mesozoic reptile.

The evolutionary history of sexual selection in the geologic past is poorly documented based on quantification, largely because of difficulty in sexing fossil specimens. Even such essential ecological parameters as adult sex ratio (ASR) and sexual size dimorphism (SSD) are rarely quantified, despite their implications for sexual selection. To enable their estimation, we propose a method for unbiased sex identification based on sexual shape dimorphism, using size-independent principal components of phenotypic data. We applied the method to test sexual selection in Keichousaurus hui, a Middle Triassic (about 237 Ma) sauropterygian with an unusually large sample size for a fossil reptile. Keichousaurus hui exhibited SSD biased towards males, as in the majority of extant reptiles, to a minor degree (sexual dimorphism index -0.087). The ASR is about 60% females, suggesting higher mortality of males over females. Both values support sexual selection of males in this species. The method may be applied to other fossil species. We also used the Gompertz allometric equation to study the sexual shape dimorphism of K. hui and found that two sexes had largely homogeneous phenotypes at birth except in the humeral width, contrary to previous suggestions derived from the standard allometric equation.

The semaphorontic view of homology.

The relation of homology is generally characterized as an identity relation, or alternatively as a correspondence relation, both of which are transitive. We use the example of the ontogenetic development and evolutionary origin of the gnathostome jaw to discuss identity and transitivity of the homology relation under the transformationist and emergentist paradigms respectively. Token identity and consequent transitivity of homology relations are shown to be requirements that are too strong to allow the origin of genuine evolutionary novelties. We consequently introduce the concept of compositional identity that is grounded in relations prevailing between parts (organs and organ systems) of a whole (organism). We recognize an ontogenetic identity of parts within a whole throughout the sequence of successive developmental stages of those parts: this is an intra-organismal character identity maintained throughout developmental trajectory. Correspondingly, we recognize a phylogenetic identity of homologous parts within two or more organisms of different species: this is an inter-species character identity maintained throughout evolutionary trajectory. These different dimensions of character identity--ontogenetic (through development) and phylogenetic (via shared evolutionary history)--break the transitivity of homology relations. Under the transformationist paradigm, the relation of homology reigns over the entire character (-state) transformation series, and thus encompasses the plesiomorphic as well as the apomorphic condition of form. In contrast, genuine evolutionary novelties originate not through transformation of ancestral characters (-states), but instead through deviating developmental trajectories that result in alternate characters. Under the emergentist paradigm, homology is thus synonymous with synapomorphy.

Unique method of tooth replacement in durophagous placodont marine reptiles, with new data on the dentition of Chinese taxa.

The placodonts of the Triassic period (~252-201 mya) represent one of the earliest and most extreme specialisations to a durophagous diet of any known reptile group. Exceptionally enlarged crushing tooth plates on the maxilla, dentary and palatine cooperated to form functional crushing areas in the buccal cavity. However, the extreme size of these teeth, combined with the unusual way they occluded, constrained how replacement occurred. Using an extensive micro-computed tomographic dataset of 11 specimens that span all geographic regions and placodont morphotypes, tooth replacement patterns were investigated. In addition, the previously undescribed dental morphologies and formulae of Chinese taxa are described for the first time and incorporated into the analysis. Placodonts have a unique tooth replacement pattern and results follow a phylogenetic trend. The plesiomorphic Placodus species show many replacement teeth at various stages of growth, with little or no discernible pattern. On the other hand, the more derived cyamodontoids tend to have fewer replacement teeth growing at any one time, replacing teeth unilaterally and/or in functional units, thus maintaining at least one functional crushing area at all times. The highly derived placochelyids have fewer teeth and, as a result, only have one or two replacement teeth in the upper jaw. This supports previous suggestions that these taxa had an alternative diet to other placodonts. Importantly, all specimens show at least one replacement tooth growing at the most posterior palatine tooth plates, indicating increased wear at this point and thus the most efficient functional crushing area.

Does counting species count as taxonomy? On misrepresenting systematics, yet again.

Recent commentary by Costello and collaborators on the current state of the global taxonomic enterprise attempts to demonstrate that taxonomy is not in decline as feared by taxonomists, but rather is increasing by virtue of the rate at which new species are formally named. Having supported their views with data that clearly indicate as much, Costello et al. make recommendations to increase the rate of new species descriptions even more. However, their views appear to rely on the perception of species as static and numerically if not historically equivalent entities whose value lie in their roles as "metrics". As such, their one-dimensional portrayal of the discipline, as concerned solely with the creation of new species names, fails to take into account both the conceptual and epistemological foundations of systematics. We refute the end-user view that taxonomy is on the rise simply because more new species are being described compared with earlier decades, and that, by implication, taxonomic practice is a formality whose pace can be streamlined without considerable resources, intellectual or otherwise. Rather, we defend the opposite viewpoint that professional taxonomy is in decline relative to the immediacy of the extinction crisis, and that this decline threatens not just the empirical science of phylogenetic systematics, but also the foundations of comparative biology on which other fields rely. The allocation of space in top-ranked journals to propagate views such as those of Costello et al. lends superficial credence to the unsupportive mindset of many of those in charge of the institutional fate of taxonomy. We emphasize that taxonomy and the description of new species are dependent upon, and only make sense in light of, empirically based classifications that reflect evolutionary history; homology assessments are at the centre of these endeavours, such that the biological sciences cannot afford to have professional taxonomists sacrifice the comparative and historical depth of their hypotheses in order to accelerate new species descriptions.

An ancestral turtle from the Late Triassic of southwestern China.

The origin of the turtle body plan remains one of the great mysteries of reptile evolution. The anatomy of turtles is highly derived, which renders it difficult to establish the relationships of turtles with other groups of reptiles. The oldest known turtle, Proganochelys from the Late Triassic period of Germany, has a fully formed shell and offers no clue as to its origin. Here we describe a new 220-million-year-old turtle from China, somewhat older than Proganochelys, that documents an intermediate step in the evolution of the shell and associated structures. A ventral plastron is fully developed, but the dorsal carapace consists of neural plates only. The dorsal ribs are expanded, and osteoderms are absent. The new species shows that the plastron evolved before the carapace and that the first step of carapace formation is the ossification of the neural plates coupled with a broadening of the ribs. This corresponds to early embryonic stages of carapace formation in extant turtles, and shows that the turtle shell is not derived from a fusion of osteoderms. Phylogenetic analysis places the new species basal to all known turtles, fossil and extant. The marine deposits that yielded the fossils indicate that this primitive turtle inhabited marginal areas of the sea or river deltas.

Othenio Abel (1875-1946) and "the phylogeny of the parts"1.

The reconstruction of the evolutionary history of animal phyla was an integral part of Othenio Abel's paleobiology (paleozoology). Abel took issue with those phylogeneticists who, following the lead of Haeckel, would draw up phylogenetic trees on the basis of transformation series of singular characters considered to be of particular importance. Abel highlighted Louis Dollo's principle of the chevauchement des spécialisations (crossing of specializations), which transformed phylogenetics from a search for ancestor-descendant sequences to research into relative degrees of relationships. This replacement resolved the conflict, much discussed at the time, between the continuity of ancestor-descendant lineages and the discontinuity inherent in the natural (phylogenetic) system. Walter Zimmermann refined Abel's methodology, which he called character-phylogenetics (Merkmalsphylogenie), an approach that was eventually adopted by Willi Hennig.

A new long-necked archosauromorph from the Guanling Formation (Anisian, Middle Triassic) of southwestern China and its implications for neck evolution in tanystropheids.

A long neck is an evolutionary innovation convergently appearing in multiple tetrapod lineages, including groups of plesiosaurs, non-archosauriform archosauromorphs, turtles, sauropodomorphs, birds, and mammals. Among all tetrapods both extant and extinct, two Triassic archosauromorphs, Tanystropheus and Dinocephalosaurus, have necks that are particularly elongated relative to the lengths of their trunks. However, the evolutionary history of such hyper-elongated necks in these two archosauromorph clades remains unknown, partially because known close relatives such as Macrocnemus and Pectodens possess only moderately elongated necks. Here, we describe a newly discovered early diverging archosauromorph, Gracilicollum latens gen. et sp. nov., based on a specimen comprising a partial neck and an incompletely preserved skull. The long neck is composed of at least 18 cervical vertebrae. The dentition suggests that this new taxon most likely represents an aquatic piscivore, similar to Dinocephalosaurus and Tanystropheus hydroides. Despite possessing a high number of cervical vertebrae, Gracilicollum gen. nov. is recovered as a tanystropheid in an evolutionary grade between Macrocnemus and Tanystropheus rather than as a close relative of Dinocephalosaurus, a result that is primarily attributable to the presence of palatal teeth and the anatomy of the cervical vertebrae in Gracilicollum gen. nov. Considering the information provided by the new specimen, we provide a detailed discussion of the cervical evolution in dinocephalosaurids and tanystropheids, which is shown to be highly complex and mosaic in nature.

Species are individuals-the German tradition.

The German tradition of considering species, and higher taxonomic entities, as individuals begins with the temporalization of natural history, thus pre-dating Darwin's 'Origin' of 1859. In the tradition of German Naturphilosophie as developed by Friedrich Schelling, species came to be seen as parts of a complex whole that encompasses all (living) nature. Species were comprehended as dynamic entities that earn individuality by virtue of their irreversible passage through time. Species individuality was conceived in terms of species taxa forming a spatiotemporally located relational system (complex whole), a conception of species that was easily assimilated to an evolutionary world view. However, the dynamics of an evolutionary process driven by variation and natural selection created a tension between continuity in nature as opposed to the discreteness and relative stasis of species. As a consequence, some authors such as Ernst Haeckel and Karl August Möbius denied the reality of species, while others explicitly linked the reality and individuality of species to their temporal duration. The mature conception of species as individuals, as formulated by Ludwig von Bertalanffy and adopted by Willi Hennig, is one of an historically conditioned, spatiotemporally located, causally integrated, dynamic yet transiently homeostatically stabilized relational system.

Willi Hennig's dichotomization of nature.

Two formal assumptions implied in Willi Hennig's "phylogenetic systematics" were repeatedly criticized for not being biologically grounded. The first is that speciation is always dichotomous; the second is that the stem-species always goes extinct when its lineage splits into two daughter species. This paper traces the theoretical roots of Hennig's "principle of dichotomy". While often considered merely a methodological principle, Hennig's realist perspective required him to ground the "principle of dichotomy" ontologically in speciation. As a methodological principle, the adherence to a strictly dichotomously structured phylogenetic system allowed Hennig to be unequivocal in character analysis and precise in the rendition of phylogenetic relationships. The ontological grounding of the "principle of dichotomy" in speciation remains controversial, however. This has implications for the application of techniques of phylogeny reconstruction to populations of bisexually reproducing organisms (phylogeography). Beyond that, the "principle of dichotomy" has triggered an intensive debate with respect to phylogeny reconstruction at the prokaryote level. © The Willi Hennig Society 2010.

Are monophyly and synapomorphy the same or different? Revisiting the role of morphology in phylogenetics.

Species are groups of organisms, marked out by reproductive (replicative) properties. Monophyletic taxa are groups of species, marked out by synapomorphies. In Nelson's analysis, monophyly and synapomorphy are identical relations. Monophyly and synapomorphy, however, are not equivalent relations. Monophyly is epistemically not accessible, whereas synapomorphy is epistemically accessible through character analysis. Monophyly originates with speciation, the two sister-species that come into being through the splitting of the ancestral species lineage forming a monophyletic taxon at the lowest level of inclusiveness. Synapomorphy provides the empirical evidence for monophyly, inferred from character analysis in the context of a three-taxon statement. If synapomorphy and monophyly were equivalent, phylogenetic systematists should find a single tree, instead of multiple equally parsimonious trees. Understanding synapomorphy as the relevant evidence for phylogenetic inference reveals a category mistake in contemporary phylogenetics: the treatment of morphological characters mapped onto molecular trees as synapomorphies and homoplasies. The mapping of morphological characters onto nodes of a molecular tree results in an empirically empty procedure for synapomorphy discovery. Morphological synapomorphies and homoplasies can only be discovered by morphological and combined analyses. The use of morphology in phylogenetic inference in general is defended by examples from Laurales and Squamata in particular. To make empirical evidence scientifically relevant in order to search for concordance, or dis-concordance, of phylogenetic signal, is certainly more fruitful for phylogenetics than the uncritical mapping of morphological traits on a molecular scaffold. © The Willi Hennig Society 2010.

Sinai Tschulok (1875-1945)-a pioneer of Cladistics.

Sinai Tschulok emigrated from the Ukraine to Switzerland, where he studied natural sciences, in particular biology. He founded and managed his own high school, which prepared students for entry to university-level education. This left him little time for research, which may explain why his work largely fell into oblivion. He did publish two influential books, however (Tschulok, S., 1910, Das System der Biologie in Forschung und Lehre, Gustav Fischer, Jena and Tschulok, S., 1922, Deszendenzlehre, Gustav Fischer, Jena), which were cited and commented upon favourably by both Walter Zimmermann and Willi Hennig. The most important point, in their opinion, was how Tschulok's explication of biological systematics had turned the "natural system" into a proof for the "Theory of Descent". The influence of Walter Zimmermann on Willi Hennig and the development of phylogenetic systematics is well known. Here some parts of Tschulok's writings are discussed that render him a pioneer in Cladistics. © The Willi Hennig Society 2009.

Evidence Supporting Predation of 4-m Marine Reptile by Triassic Megapredator.

Air-breathing marine predators have been essential components of the marine ecosystem since the Triassic. Many of them are considered the apex predators but without direct evidence-dietary inferences are usually based on circumstantial evidence, such as tooth shape. Here we report a fossil that likely represents the oldest evidence for predation on megafauna, i.e., animals equal to or larger than humans, by marine tetrapods-a thalattosaur (∼4 m in total length) in the stomach of a Middle Triassic ichthyosaur (∼5 m). The predator has grasping teeth yet swallowed the body trunk of the prey in one to several pieces. There were many more Mesozoic marine reptiles with similar grasping teeth, so megafaunal predation was likely more widespread than presently conceived. Megafaunal predation probably started nearly simultaneously in multiple lineages of marine reptiles in the Illyrian (about 242-243 million years ago).

Aquatic Habits and Niche Partitioning in the Extraordinarily Long-Necked Triassic Reptile Tanystropheus.

Tanystropheus longobardicus is one of the most remarkable and iconic Triassic reptiles. Mainly known from the Middle Triassic conservation Lagerstätte of Monte San Giorgio on the Swiss-Italian border, it is characterized by an extraordinarily long and stiffened neck that is almost three times the length of the trunk, despite being composed of only 13 hyper-elongate cervical vertebrae [1-8]. Its paleobiology remains contentious, with both aquatic and terrestrial lifestyles having been proposed [1, 9-12]. Among the Tanystropheus specimens, a small morphotype bearing tricuspid teeth and a large morphotype bearing single-cusped teeth can be recognized, historically considered as juveniles and adults of the same species [4]. Using high-resolution synchrotron radiation microtomography (SRµCT), we three-dimensionally reconstruct a virtually complete but disarticulated skull of the large morphotype, including its endocast and inner ear, to reveal its morphology for the first time. The skull is specialized toward hunting in an aquatic environment, indicated by the placement of the nares on the top of the snout and a "fish-trap"-type dentition. The SRµCT data and limb bone paleohistology reveal that the large morphotype represents a separate species (Tanystropheus hydroides sp. nov.). Skeletochronology of the small morphotype specimens indicates that they are skeletally mature despite their small size, thus representing adult individuals of Tanystropheus longobardicus. The co-occurrence of these two species of disparate size ranges and dentitions provides strong evidence for niche partitioning, highlighting the surprising versatility of the Tanystropheus bauplan and the complexity of Middle Triassic nearshore ecosystems.

The cranial morphology of Tanystropheus hydroides (Tanystropheidae, Archosauromorpha) as revealed by synchrotron microtomography.

The postcranial morphology of the extremely long-necked Tanystropheus hydroides is well-known, but observations of skull morphology were previously limited due to compression of the known specimens. Here we provide a detailed description of the skull of PIMUZ T 2790, including a partial endocast and endosseous labyrinth, based on synchrotron microtomographic data, and compare its morphology to that of other early Archosauromorpha. In many features, such as the wide and flattened snout and the configuration of the temporal and palatal regions, Tanystropheus hydroides differs strongly from other early archosauromorphs. The braincase possesses a combination of derived archosaur traits, such as the presence of a laterosphenoid and the ossification of the lateral wall of the braincase, but also differs from archosauriforms in the morphology of the ventral ramus of the opisthotic, the horizontal orientation of the parabasisphenoid, and the absence of a clearly defined crista prootica. Tanystropheus hydroides was a ram-feeder that likely caught its prey through a laterally directed snapping bite. Although the cranial morphology of other archosauromorph lineages is relatively well-represented, the skulls of most tanystropheid taxa remain poorly understood due to compressed and often fragmentary specimens. The recent descriptions of the skulls of Macrocnemus bassanii and now Tanystropheus hydroides reveal a large cranial disparity in the clade, reflecting wide ecological diversity, and highlighting the importance of non-archosauriform Archosauromorpha to both terrestrial and aquatic ecosystems during the Triassic.