The female reproductive unit of Ephedra (Gnetales): comparative morphology and evolutionary perspectives

Morphological variation in Ephedra (Gnetales) is limited and confusing from an evolutionary perspective, with parallelisms and intraspecific variation. However, recent analyses of molecular data provide a phylogenetic framework for investigations of morphological traits, albeit with few informative characters in the investigated gene regions. We document morphological, anatomical and histological variation patterns in the female reproductive unit and test the hypothesis that some Early Cretaceous fossils, which share synapomorphies with Ephedra, are members of the extant clade. Results indicate that some morphological features are evolutionarily informative although intraspecific variation is evident. Histology and anatomy of cone bracts and seed envelopes show clade‐specific variation patterns. There is little evidence for an inclusion of the Cretaceous fossils in the extant clade. Rather, a hypothesized general pattern of reduction of the vasculature in the ephedran seed envelope, probably from four vascular bundles in the fossils, to ancestrally three in the living clade, and later to two, is consistent with phylogenetic and temporal analyses, which indicate that extant diversity evolved after the Cretaceous–Tertiary boundary. Notwithstanding striking similarities between living and Cretaceous Ephedra, available data indicate that the Mesozoic diversity went almost entirely extinct in the late Cretaceous causing a bottleneck effect in Ephedra, still reflected today by an extraordinarily low level of genetic and structural diversity. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 163 , 387–430.     

Global phylogeny of Hadrosauridae (Dinosauria: Ornithopoda) using parsimony and Bayesian methods

The late Cretaceous hadrosaurids were the most specialized and diverse clade of ornithopod dinosaurs. Parsimony and Bayesian methods were implemented to elucidate the phylogenetic relationships of all hadrosaurid species. Traditional and geometric morphometrics were applied to discover patterns of variation containing phylogenetic information. In total, 286 phylogenetically informative characters (196 cranial and 90 postcranial) were defined and documented: the most extensive character data set ever constructed for hadrosaurid dinosaurs. Of these, 136 characters were used for the first time in phylogenetic analysis of these ornithopods, and 93 were modified from those of other authors. Parsimony and the Bayesian analysis (using the Mk model without the gamma parameter) confirmed the split of hadrosaurids into Saurolophinae and Lambeosaurinae. Saurolophines included a major clade composed of the Prosaurolophus–Saurolophus and the Kritosaurus–Gryposaurus–Secernosaurus subclades. Edmontosaurus and Shantungosaurus were recovered outside the major clade of saurolophines. The Brachylophosaurus clade was recovered as the most basal clade of saurolophines in the parsimony analysis, whereas following the Bayesian analysis it was recovered as the sister clade to the Kritosaurus–Gryposaurus–Secernosaurus clade. These two analyses resulted in a Lambeosaurinae composed of a succession of Eurasian sister taxa to two major clades: the Parasaurolophus clade and the Hypacrosaurs altispinus–Corythosaurus clade. In contrast, the Bayesian analysis using the Mk model with the gamma parameter included, resulted in an unbalanced hadrosauroid tree, with a paraphyletic Saurolophinae, and with the Prosaurolophus clade, Edmontosaurus, and Shantungosaurus as successively closer sister taxa to Lambeosaurinae. Based on the strict reduced consensus tree derived from the parsimony analysis, Hadrosauridae was redefined as the clade stemming from the most recent common ancestor of Hadrosaurus foulkii and Parasaurolophus walkeri. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159 , 435–502.     

Faunal turnover of marine tetrapods during the Jurassic–Cretaceous transition

Marine and terrestrial animals show a mosaic of lineage extinctions and diversifications during the Jurassic–Cretaceous transition. However, despite its potential importance in shaping animal evolution, few palaeontological studies have focussed on this interval and the possible climate and biotic drivers of its faunal turnover. In consequence evolutionary patterns in most groups are poorly understood. We use a new, large morphological dataset to examine patterns of lineage diversity and disparity (variety of form) in the marine tetrapod clade Plesiosauria, and compare these patterns with those of other organisms. Although seven plesiosaurian lineages have been hypothesised as crossing the Jurassic–Cretaceous boundary, our most parsimonious topology suggests the number was only three. The robust recovery of a novel group including most Cretaceous plesiosauroids (Xenopsaria, new clade) is instrumental in this result. Substantial plesiosaurian turnover occurred during the Jurassic–Cretaceous boundary interval, including the loss of substantial pliosaurid, and cryptoclidid diversity and disparity, followed by the radiation of Xenopsaria during the Early Cretaceous. Possible physical drivers of this turnover include climatic fluctuations that influenced oceanic productivity and diversity: Late Jurassic climates were characterised by widespread global monsoonal conditions and increased nutrient flux into the opening Atlantic‐Tethys, resulting in eutrophication and a highly productive, but taxonomically depauperate, plankton. Latest Jurassic and Early Cretaceous climates were more arid, resulting in oligotrophic ocean conditions and high taxonomic diversity of radiolarians, calcareous nannoplankton and possibly ammonoids. However, the observation of discordant extinction patterns in other marine tetrapod groups such as ichthyosaurs and marine crocodylomorphs suggests that clade‐specific factors may have been more important than overarching extrinsic drivers of faunal turnover during the Jurassic–Cretaceous boundary interval.     

Do different disparity proxies converge on a common signal? Insights from the cranial morphometrics and evolutionary history of Pterosauria (Diapsida: Archosauria)

Disparity, or morphological diversity, is often quantified by evolutionary biologists investigating the macroevolutionary history of clades over geological timescales. Disparity is typically quantified using proxies for morphology, such as measurements, discrete anatomical characters, or geometric morphometrics. If different proxies produce differing results, then the accurate quantification of disparity in deep time may be problematic. However, despite this, few studies have attempted to examine disparity of a single clade using multiple morphological proxies. Here, as a case study for this question, we examine the disparity of the volant Mesozoic fossil reptile clade Pterosauria, an intensively studied group that achieved substantial morphological, ecological and taxonomic diversity during their 145+ million-year evolutionary history. We characterize broadscale patterns of cranial morphological disparity for pterosaurs for the first time using landmark-based geometric morphometrics and make comparisons to calculations of pterosaur disparity based on alternative metrics. Landmark-based disparity calculations suggest that monofenestratan pterosaurs were more diverse cranially than basal non-monofenestratan pterosaurs (at least when the aberrant anurognathids are excluded), and that peak cranial disparity may have occurred in the Early Cretaceous, relatively late in pterosaur evolution. Significantly, our cranial disparity results are broadly congruent with those based on whole skeleton discrete character and limb proportion data sets, indicating that these divergent approaches document a consistent pattern of pterosaur morphological evolution. Therefore, pterosaurs provide an exemplar case demonstrating that different proxies for morphological form can converge on the same disparity signal, which is encouraging because often only one such proxy is available for extinct clades represented by fossils. Furthermore, mapping phylogeny into cranial morphospace demonstrates that pterosaur cranial morphology is significantly correlated with, and potentially constrained by, phylogenetic relationships.     

The early evolution of titanosauriform sauropod dinosaurs

Titanosauriformes was a globally distributed, long‐lived clade of dinosaurs that contains both the largest and smallest known sauropods. These common and diverse megaherbivores evolved a suite of cranial and locomotory specializations perhaps related to their near‐ubiquity in Mesozoic ecosystems. In an effort to understand the phylogenetic relationships of their early (Late Jurassic–Early Cretaceous) members, this paper presents a lower‐level cladistic analysis of basal titanosauriforms in which 25 ingroup and three outgroup taxa were scored for 119 characters. Analysis of these characters resulted in the recovery of three main clades: Brachiosauridae, a cosmopolitan mix of Late Jurassic and Early Cretaceous sauropods, Euhelopodidae, a clade of mid‐Cretaceous East Asian sauropods, and Titanosauria, a large Cretaceous clade made up of mostly Gondwanan genera. Several putative brachiosaurids were instead found to represent non‐titanosauriforms or more derived taxa, and no support for a Laurasia‐wide clade of titanosauriforms was found. This analysis establishes robust synapomorphies for many titanosauriform subclades. A re‐evaluation of the phylogenetic affinities of fragmentary taxa based on these synapomorphies found no body fossil evidence for titanosaurs before the middle Cretaceous (Aptian), in contrast to previous reports of Middle and Late Jurassic forms. Purported titanosaur track‐ways from the Middle Jurassic either indicate a substantial ghost lineage for the group or – more likely – represent non‐titanosaurs. Titanosauriform palaeobiogeographical history is the result of several factors including differential extinction and dispersal. This study provides a foundation for future study of basal titanosauriform phylogeny and the origins of Titanosauria. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166 , 624–671.     

Mode of miniaturisation influences body shape evolution in New World anchovies (Engraulidae)

We explored the macroevolutionary dynamics of miniaturisation in New World anchovies by integrating a time-calibrated phylogeny, geometric morphometrics and phylogenetic comparative methods. We found that the paedomorphic species Amazonsprattus scintilla occupies a novel region of shape space, while the dwarf species Anchoviella manamensis has an overall shape consistent with other anchovies. We found that miniaturisation did not increase overall clade disparity in size or shape beyond the expectations of Brownian motion, nor were there differences in rates of size or shape evolution among clades. Overall, our study shows that while the mode of miniaturisation influences shape evolution, the phenotypic novelty produced by the evolution of miniaturisation did not seem to alter macroevolutionary dynamics.     

The anatomy of the basal ornithischian dinosaur Eocursor parvus from the lower Elliot Formation (Late Triassic) of South Africa

Ornithischia is a morphologically and taxonomically diverse clade of dinosaurs that originated during the Late Triassic and were the dominant large‐bodied herbivores in many Cretaceous ecosystems. The early evolution of ornithischian dinosaurs is poorly understood, as a result in part of a paucity of fossil specimens, particularly during the Triassic. The most complete Triassic ornithischian dinosaur yet discovered is Eocursor parvus from the lower Elliot Formation (Late Triassic: Norian–Rhaetian) of Free State, South Africa, represented by a partial skull and relatively complete postcranial skeleton. Here, the anatomy of Eocursor is described in detail for the first time, and detailed comparisons are provided to other basal ornithischian taxa. Eocursor is a small‐bodied taxon (approximately 1 m in length) that possesses a plesiomorphic dentition consisting of unworn leaf‐shaped crowns, a proportionally large manus with similarities to heterodontosaurids, a pelvis that contains an intriguing mix of plesiomorphic and derived character states, and elongate distal hindlimbs suggesting well‐developed cursorial ability. The ontogenetic status of the holotype material is uncertain. Eocursor may represent the sister taxon to Genasauria, the clade that includes most of ornithischian diversity, although this phylogenetic position is partially dependent upon the uncertain phylogenetic position of the enigmatic and controversial clade Heterodontosauridae. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 160 , 648–684.     

What is Geosaurus? Redescription of Geosaurus giganteus (Thalattosuchia: Metriorhynchidae) from the Upper Jurassic of Bayern,Germany

The holotype and referred specimens of Geosaurus giganteus, a metriorhynchid crocodile from the Tithonian (Upper Jurassic) of Germany, is redescribed, along with a historical overview of the genus and species. This taxon is unique among metriorhynchids as its serrated, strongly lateromedially compressed dentition is arranged as opposing blades, suggesting it was adapted to efficiently slice through fleshy prey. A new phylogenetic analysis of Crocodylomorpha is presented, which finds G. giganteus to be nested within what is currently considered Dakosaurus, whereas the other species currently assigned to Geosaurus form a clade with Enaliosuchus and the holotype of Cricosaurus. The phyletic relationship of G. giganteus with other metriorhynchids indicates that the current definition of the genus Geosaurus is polyphyletic, and that the inclusion of subsequent longirostrine species to this genus is in error. The re‐analysis presented herein demonstrates Geosaurus to be composed of three species sensu stricto. The appropriate taxonomic amendments to the Metriorhynchidae are also provided. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 157 , 551–585.     

A new phylogenetic hypothesis of turtles with implications for the timing and number of evolutionary transitions to marine lifestyles in the group

Evolutionary transitions to marine habitats occurred frequently among Mesozoic reptiles. Only one such clade survives to the present: sea turtles (Chelonioidea). Other marine turtles originated during the Mesozoic, but uncertain affinities of key fossils have obscured the number of transitions to marine life, and the timing of the origin of marine adaptation in chelonioids. Phylogenetic studies support either a highly‐inclusive chelonioid total‐group including fossil marine clades from the Jurassic and Cretaceous (e.g. protostegids, thalassochelydians, sandownids) or a less inclusive chelonioid total‐group excluding those clades. Under this paradigm, these clades belong outside Cryptodira, and represent at least one additional evolutionary transition to marine life in turtles. We present a new phylogenetic hypothesis informed by high resolution computed tomographic data of living and fossil taxa. Besides a well‐supported Chelonioidea, which includes protostegids, we recover a previously unknown clade of stem‐group turtles, Angolachelonia, which includes the Late Jurassic thalassochelydians, and the Cretaceous–Palaeogene sandownids. Accounting for the Triassic Odontochelys, our results indicate three independent evolutionary transitions to marine life in non‐pleurodiran turtles (plus an additional two‐three in pleurodires). Among all independent origins of marine habits, a pelagic ecology only evolved once, among chelonioids. All turtle groups that independently invaded marine habitats in the Jurassic–Cretaceous (chelonioids, angolachelonians, bothremydid pleurodires) survived the Cretaceous–Palaeogene mass extinction event. This highlights extensive survival of marine turtles compared to other marine reptiles. Furthermore, deeply‐nested clades such as chelonioids are found by the middle Early Cretaceous, suggesting a rapid diversification of crown‐group turtles during the Early Cretaceous.     

Biogeography of the grasses (Poaceae): a phylogenetic approach to reveal evolutionary history in geographical space and geological time

The grasses (Poaceae) are the fifth most diverse family of angiosperms, including 800 genera and more than 10 000 species. Few phylogenetic studies have tried to investigate palaeo‐biogeographical and palaeo‐ecological scenarios that may have led to present‐day distribution and diversity of grasses at the family level. We produced a dated phylogenetic tree based on combined plastid DNA sequences and a comprehensive sample of Poaceae. Furthermore, we produced an additional tree using a supermatrix of morphological and molecular data that included all 800 grass genera so that ancestral biogeography and ecological habitats could be inferred. We used a likelihood‐based method, which allows the estimation of ancestral polymorphism in both biogeographical and ecological analyses for large data sets. The origin of Poaceae was retrieved as African and shade adapted. The crown node of the BEP + PACCMAD clade was dated at 57 Mya, in the early Eocene. Grasses dispersed to all continents by approximately 60 million years after their Gondwanan origin in the late Cretaceous. PACCMAD taxa adapted to open habitats as early as the late Eocene, a date consistent with recent phytolith fossil data for North America. C₄ photosynthesis first originated in Africa, at least for Chloridoideae in the Eocene at c. 30 Mya. The BEP clade members adapted to open habitats later than PACCMAD members; this was inferred to occur in Eurasia in the Oligocene. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162 , 543–557.     

Ecological and phylogenetic dimensions of cranial shape diversification in South American caviomorph rodents (Rodentia: Hystricomorpha)

Caviomorph rodents represent an excellent model to explore morphological diversification on a macroevolutionary scale, as they are ecologically and morphologically diverse. We analysed cranial shape variation using geometric morphometrics and phylogenetic comparative methods. Most variation involved the shape of the rostrum, basicranium, and cranial vault, and clearly matched the phylogenetic structure. At the same time, a strong allometric pattern was associated with the length of the rostrum and cranial vault, size of the auditory bulla, and depth of the zygomatic arch. After accounting for size influence, and taking phylogenetic structure into account, shape variation was significantly associated with habitat. Our results highlight the presence of complex relationships between morphological, phylogenetic, and ecological dimensions in the diversification of the caviomorph cranium. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 898–913.     

A new Patagonian species of Cricosaurus (Crocodyliformes,Thalattosuchia): first evidence of Cricosaurus in Middle–Upper Tithonian lithographic limestone from Gondwana

Abstract:  Upper Jurassic (Tithonian) deposits in north‐western Patagonia, Argentina, have yielded rich and taxonomically diverse assemblages of marine reptiles. These assemblages are also remarkable by their quality of preservation and are represented by ichthyosaurs, plesiosaurs, turtles and crocodyliforms. Despite the abundant crocodyliform record, only two metriorhynchid taxa have been identified: Cricosaurus araucanensis and Dakosaurus andiniensis. Here we described a new species of Cricosaurus, which represents the second species of Cricosaurus in the Tithonian of the Neuquén Basin, and the first metriorhynchid found in lithographic limestone from Gondwana. Furthermore, this specimen has the most complete postcranial remains of any metriorhynchid from South America. The new species is characterized by a short distance between the premaxilla and the nasal, a relatively narrow interorbital width, 23–25 mandibular teeth, bicarinated teeth with fine apicobasally aligned ridges, interalveolar spaces between the first seven teeth approximately 1.5 times longer than the anteroposterior diameter of the respective alveoli. To test the assignment of the new species to Cricosaurus, we carried out two phylogenetic analyses. In both analyses, Cricosaurus lithographicus sp. nov. is nested with other species referred to this genus. This new species has peculiar enamel ornamentation, characterized by numerous, fine apicobasally aligned ridges, when compared to other species of the genus.     

Tooth and cranial disparity in the fossil relatives of Sphenodon (Rhynchocephalia) dispute the persistent ‘living fossil’ label

The tuatara (Sphenodon punctatus) is the only living representative of Rhynchocephalia, a group of small vertebrates that originated about 250 million years ago. The tuatara has been referred to as a living fossil; however, the group to which it belongs included a much greater diversity of forms in the Mesozoic. We explore the morphological diversity of Rhynchocephalia and stem lepidosaur relatives (Sphenodon plus 13 fossil relatives) by employing a combination of geometric morphometrics and comparative methods. Geometric morphometrics is used to explore cranium size and shape at interspecific scale, while comparative methods are employed to test association between skull shape and size and tooth number after taking phylogeny into account. Two phylogenetic topologies have been considered to generate a phylomorphospace and quantify the phylogenetic signal in skull shape data, the ancestral state reconstruction as well as morphological disparity using disparity through time plots (DTT). Rhynchocephalia exhibit a significant phylogenetic signal in skull shape that compares well with that computed for other extinct vertebrate groups. A consistent form of allometry has little impact on skull shape evolution while the number of teeth significantly correlates with skull shape also after taking phylogeny into account. The ancestral state reconstruction demonstrates a dramatic shape difference between the skull of Sphenodon and its much larger Cretaceous relative Priosphenodon. Additionally, DTT demonstrates that skull shape disparity is higher between rather than within clades while the opposite applies to skull size and number of teeth. These results were not altered by the use of competing phylogenic hypotheses. Rhynchocephalia evolved as a morphologically diverse group with a dramatic radiation in the Late Triassic and Early Jurassic about 200 million years ago. Differences in size are not marked between species whereas changes in number of teeth are associated with co‐ordinated shape changes in the skull to accommodate larger masticatory muscles. These results show that the tuatara is not the product of evolutionary stasis but that it represents the only survivor of a diverse Mesozoic radiation whose subsequent decline remains to be explained.     

Phylogenetics and biogeography of the parasitic genus Thesium L. (Santalaceae), with an emphasis on the Cape of South Africa

Thesium is a large genus of parasitic shrubs belonging to tribe Thesieae of Santalaceae. It has a principally Old World distribution, with the greatest diversity being found in southern Africa. Little is known about the relationships within Thesium or its relationships with its closest relatives. In this article, we present a first estimate of species‐level phylogenetic relationships in Thesium based on internal transcribed spacer (ITS) and trnL–trnF sequence data, and use this to explore the biogeographical history of the group. One hundred and four samples representing 72 Thesium spp. were included in a phylogenetic analysis. Plastid and combined data resolve Thesium as paraphyletic relative to Thesidium and Austroamericium with high posterior probability and bootstrap support. ITS sequence data place Thesidium as sister to a large Thesium clade, but with weak support. Ancestral range reconstruction and dating analysis suggest a southern African origin for the group, with a crown age of 39.1 ± 11.9 Mya, followed by dispersal into Europe and South America. A large clade of Cape species split in the Miocene from a clade comprising tropical species (25.5 ± 7.3 Mya) with the diversification of extant species beginning at 16.7 ± 6.3 Mya. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162 , 435–452.     

Cretaceous and Eocene fossils of the rare extant genus Synneuron Lundstrom (Diptera: Canthyloscledidae): evidence of a true Pangean clade

The first two fossil species of the canthyloscelid genus Synneuron are described based on compression wings. Synneuron eomontana sp. nov. is described from the Middle Eocene Coal Creek Member of the Kishenehn Formation, in the USA, and Synneuron jelli sp. nov. is described from the Lower Cretaceous Koonwarra Fossil Bed of the Korumburra Group, in Australia. The wings are illustrated and compared to the extant species of the genus, to species of the three other recent genera of Canthyloscelidae and to an anisopodid. A phylogenetic analysis of the relationships between the species of Synneuron was performed. The Eocene fossil S. eomontana appears as sister of the pair of recent Holarctic species of the genus, while the Australian Cretaceous species S. jelli is sister of the clade with the species of Synneuron of the northern hemisphere. The sister group of Synneuron is the canthyloscelid clade (Hyperoscelis + Canthyloscelis), for which a middle Jurassic fossil is known. At the early Cretaceous, Gondwana was already separated from Laurasia and the disjunction between the species of Synneuron in Australia and the northern hemisphere clade of the genus suggest a true pangeic origin for the genus. The biology of the canthyloscelid larvae is shaped by its trophic specialization—xylosaprophagous. This suggests that the transition from the Pangean Jurassic gymnosperm-dominated forests to the late Cretaceous angiosperm-dominated forests may be related to the low recent diversity of Synneuron or of the canthyloscelids in the world—and maybe to the extinction of the genus in the southern hemisphere. This major turnover of the vegetation type along the Cretaceous may be also somehow related to the complete extinction of other groups of flies strictly associated with gymnosperms, as may be the case of the lower brachyceran family Zhangsolvidae. This speculation needs additional corroboration from other groups, that will become available with the combination of systematics, paleontology and biogeographical information of different early Cretaceous clades.     

Steneosaurus edwardsi (Thalattosuchia: Teleosauridae), the largest known crocodylomorph of the Middle Jurassic

Teleosaurids were a clade of marine crocodylomorphs that were globally distributed during the Jurassic Period. They evolved a wide range of body sizes, from small (～2–3 m) to very large (> 9 m). Until now, the largest known Middle Jurassic teleosaurid was ‘Steneosaurus’ obtusidens, from the Oxford Clay Formation of the UK. Here, we re‐examine a very large Oxford Clay specimen (ilium, ischium, and femur) that had been tentatively attributed to ‘S.’ obtusidens. Based on comparative anatomical study with the ‘S.’ obtusidens holotype and referred specimens of Steneosaurus edwardsi and Steneosaurus leedsi, we conclude that this very large individual actually pertains to S. edwardsi. Based on comparisons with the Machimosaurus mosae neotype (which has a complete femur and skeleton), we estimate a total length in excess of 7 m for this large S. edwardsi individual, making it the largest known Middle Jurassic teleosaurid. Therefore, along with the closely related genus Machimosaurus, this clade of large‐bodied Middle–Late Jurassic teleosaurids were the largest species during the first 100 million years of crocodylomorph evolution. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, ●● , ●●–●●.