The Dragon's Tales

Cranial anatomy of Paleogene Micromomyidae and implications for early primate evolution

Authors:

Bloch et al

Abstract:

Paleogene micromomyids are small (∼10–40 g) euarchontan mammals with primate-like molars and postcrania suggestive of committed claw-climbing positional behaviors, similar to those of the extant arboreal treeshrew, Ptilocercus. Based primarily on evidence derived from dental and postcranial morphology, micromomyids have alternately been allied with plesiadapiforms, Dermoptera (colugos), or Primatomorpha (Primates + Dermoptera) within Euarchonta. Partial crania described here of Paleocene Dryomomys szalayi and Eocene Tinimomys graybulliensis from the Clarks Fork Basin of Wyoming are the first known for the family Micromomyidae. The cranium of D. szalayi exhibits a distinct, small groove near the lateral extreme of the promontorium, just medial to the fenestra vestibuli, the size of which suggests that the internal carotid artery was non-functional, as has been inferred for paromomyid and plesiadapid plesiadapiforms, but not for Eocene euprimates, carpolestids, and microsyopids. On the other hand, D. szalayi is similar to fossil euprimates and plesiadapoids in having a bullar morphology consistent with an origin that is at least partially petrosal, unlike that of paromomyids and microsyopids, although this interpretation will always be tentative in fossils that lack exhaustive ontogenetic data. Micromomyids differ from all other known plesiadapiforms in having an inflated cochlear part of the bony labyrinth and a highly pneumatized squamosal and mastoid region with associated septa. Cladistic analyses that include new cranial data, regardless of how bullar composition is coded in plesiadapiforms, fail to support either Primatomorpha or a close relationship between micromomyids and dermopterans, instead suggesting that micromomyids are among the most primitive known primates.

When a groove is not a groove: Clarification of the appearance of the dentary groove in tyrannosauroid theropods and the distinction between Nanotyrannus and Tyrannosaurus. Reply to Comment on: “Distribution of the dentary groove of theropod dinosaurs: implications for theropod phylogeny and the validity of the genus Nanotyrannus Bakker et al., 1988”

Authors:

Schmerge et al

Abstract:

The occurrence of a lateral groove in the dentary of theropod dinosaurs was argued to be a key diagnostic character for establishing the validity of Nanotyrannus lancensis as a unique taxon separate from Tyrannosaurus rex by Schmerge and Rothschild (2016). The validity of this distinction has been challenged in a comment paper by Brusatte et al. (2016). The main criticisms raised in this comment address the methodology of the original study, the distribution of the dentary groove in theropods, the possibility of ontogenetic variability in the occurrence of the dentary groove, and the application of phylogenetic analysis to studying character distributions. In this reply, we clarify the definition of the theropod dentary groove, elucidate the difference between a true dentary groove and the appearance of a false “pseudo-groove”, justify our original methodology with a discussion of the errors involved in identifying grooves by Brusatte et al. (in press), and support our original findings with descriptions of additional specimens. Investigation of additional specimens of Nanotyrannus, as well as critical examination of Tyrannosaurus specimens presented by Brusatte et al. (2016), reaffirm the result of our original study that Nanotyrannus can be differentiated from Tyrannosaurus based on the depth of its dentary groove, independent of ontogenetic stage. Despite any possible ontogenetic variation in the appearance of the dentary groove that can be interpreted, all specimens of Nanotyrannus possess distinct grooves whereas Tyrannosaurus lacks a groove. The most parsimonious explanation for the different appearance of these grooves is that Nanotyrannus does not represent a juvenile Tyrannosaurus.

Dentary groove morphology does not distinguish ‘Nanotyrannus’ as a valid taxon of tyrannosauroid dinosaur. Comment on: “Distribution of the dentary groove of theropod dinosaurs: Implications for theropod phylogeny and the validity of the genus Nanotyrannus Bakker et al., 1988”

Authors:

Brusatte et al

Abstract:

There has been considerable debate about whether the controversial tyrannosauroid dinosaur ‘Nanotyrannus lancensis’ from the uppermost Cretaceous of North America is a valid taxon or a juvenile of the contemporaneous Tyrannosaurus rex. In a recent Cretaceous Research article, Schmerge and Rothschild (2016) brought a new piece of evidence to this discussion: the morphology of the dentary groove, a depression on the lateral surface of the dentary that houses neurovascular foramina. They argued that an alleged ‘Nanotyrannus’ specimen, which possesses a groove, cannot be referable to Tyrannosaurus rex, which they considered as lacking the groove, and they hypothesized that ‘Nanotyrannus’ is closely related to albertosaurine tyrannosauroids, which also are said to possess the groove. However, we show that the groove is a widespread feature of tyrannosauroids that is present in T. rex and many other specimens, and that it is an ontogenetically variable feature that changes from a sharp, deeply-impressed groove to a shallower sulcus as an individual matures. As a result, the presence or absence of a dentary groove does not clarify the validity of ‘Nanotyrannus’ or its phylogenetic position among tyrannosauroids. We consider it most parsimonious that ‘Nanotyrannus’ specimens belong to juvenile T. rex.

In this second article on maniraptorans, we look at the main groups that constitute this clade: you’ll need to remember the main group names if the trends and tendencies discussed in later parts of this series are to make any sense. The previous article – part 1 – looked briefly at maniraptoran origins and at the fact that maniraptorans are nested within coelurosaurian theropods. Ok, onwards…

Reappraisal of the Early Cretaceous sauropod dinosaur Amargatitanis macni (Apesteguía, 2007), from northwestern Patagonia, Argentina

Authors:

Gallina et al

Abstract:

Amargatitanis macni Apesteguía, 2007 was described as a purported titanosaur sauropod. That referral is significant because Amargatitanis would represent one of the oldest known members of Titanosauria. However, this referral and even the systematic validity of the taxon were questioned. Here, all the available remains of the taxon are evaluated including a description of unpublished elements. The identity of the type material is discussed based on a first-hand examination of the specimens and evaluation of the original field notes as reliable evidence for bone association. The original holotype of Amargatitanis is a chimaera, as pointed out by previous authors. Herein a new, modified holotype for Amargatitanis is proposed. This analysis presents a revised diagnosis for Amargatitanis macni as a valid taxon, and description of unpublished material clarifies the anatomy of this sauropod dinosaur. The inclusion of Amargatitanis macni in an updated phylogenetic analysis revealed the presence of a second species of the family Dicraeosauridae in the La Amarga Formation, suggesting that, at present, there is no record of titanosaur body fossils in Patagonia prior to Cenomanian times.

The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms

Author:

Ezcurra

Abstract:

The early evolution of archosauromorphs during the Permo-Triassic constitutes an excellent empirical case study to shed light on evolutionary radiations in deep time and the timing and processes of recovery of terrestrial faunas after a mass extinction. However, macroevolutionary studies of early archosauromorphs are currently limited by poor knowledge of their phylogenetic relationships. In particular, one of the main early archosauromorph groups that need an exhaustive phylogenetic study is “Proterosuchia,” which as historically conceived includes members of both Proterosuchidae and Erythrosuchidae. A new data matrix composed of 96 separate taxa (several of them not included in a quantitative phylogenetic analysis before) and 600 osteological characters was assembled and analysed to generate a comprehensive higher-level phylogenetic hypothesis of basal archosauromorphs and shed light on the species-level interrelationships of taxa historically identified as proterosuchian archosauriforms. The results of the analysis using maximum parsimony include a polyphyletic “Prolacertiformes” and “Protorosauria,” in which the Permian Aenigmastropheus and Protorosaurus are the most basal archosauromorphs. The enigmatic choristoderans are either found as the sister-taxa of all other lepidosauromorphs or archosauromorphs, but consistently placed within Sauria. Prolacertids, rhynchosaurs, allokotosaurians and tanystropheids are the major successive sister clades of Archosauriformes. The Early Triassic Tasmaniosaurus is recovered as the sister-taxon of Archosauriformes. Proterosuchidae is unambiguosly restricted to five species that occur immediately after and before the Permo-Triassic boundary, thus implying that they are a short-lived “disaster” clade. Erythrosuchidae is composed of eight nominal species that occur during the Early and Middle Triassic. “Proterosuchia” is polyphyletic, in which erythrosuchids are more closely related to Euparkeria and more crownward archosauriforms than to proterosuchids, and several species are found widespread along the archosauromorph tree, some being nested within Archosauria (e.g., “Chasmatosaurus ultimus,” Youngosuchus). Doswelliids and proterochampsids are recovered as more closely related to each other than to other archosauromorphs, forming a large clade (Proterochampsia) of semi-aquatic to aquatic forms that includes the bizarre genus Vancleavea. Euparkeria is one of the sister-taxa of the clade composed of proterochampsians and archosaurs. The putative Indian archosaur Yarasuchus is recovered in a polytomy with Euparkeria and more crownward archosauriforms, and as more closely related to the Russian Dongusuchus than to other species. Phytosaurs are recovered as the sister-taxa of all other pseudosuchians, thus being nested within Archosauria.

The phylogenetic affinities of the extinct glyptodonts

Authors:

Delsuccor et al

Abstract:

Among the fossils of hitherto unknown mammals that Darwin collected in South America between 1832 and 1833 during the Beagle expedition [1] were examples of the large, heavily armored herbivores later known as glyptodonts. Ever since, glyptodonts have fascinated evolutionary biologists because of their remarkable skeletal adaptations and seemingly isolated phylogenetic position even within their natural group, the cingulate xenarthrans (armadillos and their allies [2] ). In possessing a carapace comprised of fused osteoderms, the glyptodonts were clearly related to other cingulates, but their precise phylogenetic position as suggested by morphology remains unresolved [3,4] . To provide a molecular perspective on this issue, we designed sequence-capture baits using in silico reconstructed ancestral sequences and successfully assembled the complete mitochondrial genome of Doedicurus sp., one of the largest glyptodonts. Our phylogenetic reconstructions establish that glyptodonts are in fact deeply nested within the armadillo crown-group, representing a distinct subfamily (Glyptodontinae) within family Chlamyphoridae [5] . Molecular dating suggests that glyptodonts diverged no earlier than around 35 million years ago, in good agreement with their fossil record. Our results highlight the derived nature of the glyptodont morphotype, one aspect of which is a spectacular increase in body size until their extinction at the end of the last ice age.

The Chinese pareiasaurs

Author:

Benton

Abstract:

Pareiasaurs were important medium- to large-sized herbivores in the Middle and Late Permian, some 268–252 Ma. They are best known from abundant remains of several taxa found in South Africa and Russia, with isolated finds from other parts of the world. Six genera and species of pareiasaurs have been described from China, and yet they have not been reviewed. Of these six, Tsiyuania may be a synonym of Honania, but this taxon is not further considered here. The other four, which were named for separate finds from the Sunjiagou Formation (Changhsingian, 254–252 Ma), show considerable similarities. Despite earlier suggestions, there are no convincing anatomical characters to distinguish Shihtienfenia, Shansisaurus, and Huanghesaurus, and these three genera are synonymized as Shihtienfenia permica Young & Yeh, 1963. The fourth taxon, Sanchuansaurus pygmaeus Gao, 1989, shows distinctly different teeth from those of Huanghesaurus (= Shihtienfenia), and was about one-third of the size, so it is retained as a second valid pareiasaur from the Chinese latest Permian. Phylogenetic analysis confirms the validity of these two taxa, with Sanchuansaurus belonging among the derived forms, close to Elginiidae, and with Shihtienfenia associated with Pumiliopareiasauria and Pareiasuchus.

Placental mammals consist of three main groups that diverged rapidly, evolving in wildly different directions: Afrotheria (for example, elephants and tenrecs), Xenarthra (such as armadillos and sloths) and Boreoeutheria (all other placental mammals). The relationships between them have been a subject of fierce controversy with multiple studies coming to incompatible conclusions over the last decade leading some researchers to suggest that these relationships might be impossible to resolve.

There are thus many outstanding questions such as which is the oldest sibling of the three? Did the mammals go their separate ways due to South America and Africa breaking apart? And if not, when did placentals split up?

"This has been one of the areas of greatest debate in evolutionary biology, with many researchers considering it impossible to resolve," said lead author Dr Tarver of Bristol's School of Earth Sciences. "Now we've proven these problems can be solved - you just need to analyse genome-scale datasets using models that accurately reflect genomic evolution."

A reevaluation of Brachyprosopus broomi and Chelydontops altidentalis, dicynodonts (Therapsida, Anomodontia) from the middle Permian Tapinocephalus Assemblage Zone of the Karoo Basin, South Africa

Authors:

Angielczyk et al

Abstract:

Brachyprosopus broomi was described in 1937 based on a specimen from the Tapinocephalus Assemblage Zone (Karoo Basin, South Africa), but it was largely overlooked by subsequent workers. We have identified several new specimens that show that Brachyprosopus is a valid taxon. An autapomorphy for the taxon is a curled lateral edge of the squamosal that forms a lateral wall of the external adductor fossa. Other important characters are absence of anterior median palatal ridges; maxillary tooth rows bounded laterally by a shelf; unfused vomers; raised margins of the interpterygoid vacuity; broad intertemporal region; pineal boss; dentary tables; and a long, wide posterior dentary sulcus that extends posterior to the dentary teeth. Chelydontops altidentalis is a junior synonym of B. broomi. A phylogenetic analysis places Brachyprosopus among basal dicynodonts, not as a close relative of Endothiodon. It is noteworthy that some characters, such as well-developed medial maxillary tooth rows and the shape of the palatines, are shared by Brachyprosopus, Pristerodon, Endothiodon, and Niassodon, hinting that a final resolution of relationships among toothed dicynodonts remains to be achieved. Most Brachyprosopus specimens are from the upper Abrahamskraal Formation (Moordenaars and Karelskraal members). One specimen is from low in the Koonap Formation, just above the lowermost maroon mudrocks of the Beaufort Group, and an exact correlation between this level and the strata of the Abrahamskraal Formation is uncertain. Therefore, it is likely that the stratigraphic range of Brachyprosopus extends throughout the Tapinocephalus zone and possibly down into the Eodicynodon Assemblage Zone.

Reevaluation of the largest published morphological data matrix for phylogenetic analysis of Paleozoic limbed vertebrates 

Authors:

Marjanović​ et al

Abstract:

The largest data matrix for phylogeny of early limbed vertebrates (Ruta M, Coates MI. 2007. J. Syst. Palaeont. 5:69–122) has supported controversial hypotheses; e.g., it has recovered Seymouriamorpha, Diadectomorpha and (in some trees) Caudata as paraphyletic and found the “temnospondyl hypothesis” on the origin of Lissamphibia (TH) to be one step more parsimonious than the “lepospondyl hypothesis” (LH). Scrutiny of the matrix reveals thousands of suboptimal scores (many clearly due to typographic and similar errors) as well as logically linked (redundant) characters, characters with only one described state, and even cases where taxa were scored after presumed relatives. Moreover, all characters – even obviously continuous ones – were unordered, effects of ontogeny were not sufficiently taken into account, and the authors mostly excluded data published after 2001, even their own. Our revised version – we document and justify all changes – yields much longer trees with a different topology, e.g. monophyletic Caudata, Diadectomorpha and (sometimes) Seymouriamorpha, Ichthyostega more rootward than Acanthostega, Anthracosauria more rootward than Temnospondyli, and the LH, which is 10 steps more parsimonious than the TH and 15 more than the “polyphyly hypothesis” (PH). Bootstrap values, though, are low, and few of the topologies are statistically distinguishable. For another set of analyses, we added 48 OTUs to the original 102. This destabilizes parts of the tree, e.g. the relationships of Anthracosauria and Temnospondyli. However, many of the added taxa have a fully resolved position or nearly so; this concerns the well-known Chroniosaurus (sister to a clade containing Solenodonsaurus, Seymouriamorpha, Diadectomorpha, Amniota and Amphibia), but also isolated lower-jaw material from the Devonian and Carboniferous. Despite the addition of Gerobatrachus, Micropholis and Tungussogyrinus and the extremely peramorphic salamander Chelotriton, the difference between LH and TH only shrinks to 9 steps, that between LH and PH to 13 steps. The “lepospondyl” Brachydectes is neither found as sister to Lissamphibia nor in the “microsaur” grade. Bootstrap values plummet, though, and all three hypotheses become statistically indistinguishable at p = 0.05. We then duplicated all analyses after coding all losses of bones as irreversible. Anthracosauria is then consistently placed more rootward than Temnospondyli; given the original taxon sample, the LH is 12 steps shorter than the “temnospondyl hypothesis” and 17 steps shorter than the PH, while the expanded taxon sample makes the LH 10 steps shorter than the TH and only 12 steps shorter than the PH. More robust results could likely be obtained by adding the many characters used in other analyses or discussed in the literature. We discuss phylogeny, approaches to coding, and certain character complexes, in particular the supposed middle ear of temnospondyls.

The systematic relationships and biogeographic history of ornithischian dinosaurs

Author:

Boyd

Abstract:

The systematic relationships of taxa traditionally referred to as ‘basal ornithopods’ or ‘hypsilophodontids’ remain poorly resolved since it was discovered that these taxa are not a monophyletic group, but rather a paraphyletic set of neornithischian taxa. Thus, even as the known diversity of these taxa has dramatically increased over the past two decades, our knowledge of their placement relative to each other and the major ornithischian subclades remained incomplete. This study employs the largest phylogenetic dataset yet compiled to assess basal ornithischian relationships (255 characters for 65 species level terminal taxa). The resulting strict consensus tree is the most well-resolved, stratigraphically consistent hypothesis of basal ornithischian relationships yet hypothesized. The only non-iguanodontian ornithopod (=basal ornithopod) recovered in this analysis is Hypsilophodon foxii. The majority of former ‘hypsilophodontid’ taxa are recovered within a single clade (Parksosauridae) that is situated as the sister-taxon to Cerapoda. The Parksosauridae is divided between two subclades, the Orodrominae and the Thescelosaurinae. This study does not recover a clade consisting of the Asian taxa Changchunsaurus, Haya, and Jeholosaurus (=Jeholosauridae). Rather, the former two taxa are recovered as basal members of Thescelosaurinae, while the latter taxon is recovered in a clade with Yueosaurus near the base of Neornithischia.The endemic South American clade Elasmaria is recovered within the Thescelosaurinae as the sister taxon to Thescelosaurus. This study supports the origination of Dinosauria and the early diversification of Ornithischia within Gondwana. Neornithischia first arose in Africa by the Early Jurassic before dispersing to Asia before the late Middle Jurassic, where much of the diversification among non-cerapodan neornithischians occurred. Under the simplest scenario the Parksosauridae originated in North America, with at least two later dispersals to Asia and one to South America. However, when ghost lineages are considered, an alternate dispersal hypothesis has thescelosaurines dispersing from Asia into South America (via North America) during the Early Cretaceous, then back into North America in the latest Cretaceous. The latter hypothesis may explain the dominance of orodromine taxa prior to the Maastrichtian in North America and the sudden appearance and wide distribution of thescelosaurines in North America beginning in the early Maastrichtian. While the diversity of parksosaurids has greatly increased over the last fifteen years, a ghost lineage of over 40 myr is present between the base of Parksosauridae and Cerapoda, indicating that much of the early history and diversity of this clade is yet to be discovered. This new phylogenetic hypothesis provides a comprehensive framework for testing further hypotheses regarding evolutionary patterns and processes within Ornithischia.

Mandibular and dental characteristics of Late Triassic mammaliaform Haramiyavia and their ramifications for basal mammal evolution

Authors:

Luo et al

Abstract:

As one of the earliest-known mammaliaforms, Haramiyavia clemmenseni from the Rhaetic (Late Triassic) of East Greenland has held an important place in understanding the timing of the earliest radiation of the group. Reanalysis of the type specimen using high-resolution computed tomography (CT) has revealed new details, such as the presence of the dentary condyle of the mammalian jaw hinge and the postdentary trough for mandibular attachment of the middle ear—a transitional condition of the predecessors to crown Mammalia. Our tests of competing phylogenetic hypotheses with these new data show that Late Triassic haramiyids are a separate clade from multituberculate mammals and are excluded from the Mammalia. Consequently, hypotheses of a Late Triassic diversification of the Mammalia that depend on multituberculate affinities of haramiyidans are rejected. Scanning electron microscopy study of tooth-wear facets and kinematic functional simulation of occlusion with virtual 3D models from CT scans confirm that Haramiyavia had a major orthal occlusion with the tallest lingual cusp of the lower molars occluding into the lingual embrasure of the upper molars, followed by a short palinal movement along the cusp rows alternating between upper and lower molars. This movement differs from the minimal orthal but extensive palinal occlusal movement of multituberculate mammals, which previously were regarded as relatives of haramiyidans. The disparity of tooth morphology and the diversity of dental functions of haramiyids and their contemporary mammaliaforms suggest that dietary diversification is a major factor in the earliest mammaliaform evolution.

Phylogeny of the Ichthyopterygia incorporating recent discoveries from South China

Authors:

Ji et al

Abstract:

During the last decade, abundant ichthyopterygian material has been found from the Triassic of South China as well as the Upper Jurassic and Lower Cretaceous of Europe and South America, significantly expanding our knowledge of ichthyopterygian diversity through the Mesozoic. Previous phylogenetic hypotheses of the group no longer account for these extensive additions, necessitating a new phylogenetic framework for the entire Ichthyopterygia to enable evolutionary studies of the group. We present here a comprehensive phylogenetic hypothesis for Ichthyopterygia based on cladistic analysis of 163 characters coded for 59 ingroup and five outgroup taxa. The monophyly of Ichthyopterygia is strongly supported by a Bremer index value of 7. Five major groups of Ichthyopterygia during the Triassic, viz., Grippioidea, Cymbospondylidae, Mixosauridae, Shastasauridae, and Toretocnemidae, are well supported by Bremer index values between 3 and 5. Major clades that evolved in the Triassic, including Merriamosauria, Euichthyosauria, and Parvipelvia, are also robustly supported, whereas most post-Triassic clades are very weakly supported with a Bremer index value of 1, with a few exceptions, such as Thunnosauria and Ophthalmosauridae. The traditional Shastasauridae is expanded to comprise six genera but excludes Callawayia, which is more closely related to Parvipelvia than to Shastasauridae. ‘C.’ wolonggangensis is a shastasaurid but does not form a monophyletic clade with Callawayia neoscapularis or Guizhouichthyosaurus tangae as previously asserted. The new phylogenetic hypothesis is generally consistent with the stratigraphic occurrences of each taxon especially for the Triassic taxa.

Cladistic analysis of Caseidae (Caseasauria, Synapsida): using the gap-weighting method to include taxa based on incomplete specimens

Authors:

Romano et al

Abstract:

Occupying the role of primary consumer and having an early–middle Permian age range, caseids (Caseasauria, Synapsida) are fundamental to the interpretation of the early history of terrestrial vertebrate ecosystems. Despite this importance, no comprehensive, species-level phylogenetic study of Caseidae has yet been performed. Herein, we present a phylogenetic analysis of the group, using gap weighting to include poorly known taxa. Besides the description and comments on the resultant topologies, some more general issues concerning cladistic methodologies are briefly addressed. This study highlights the importance of a total-evidence approach, including as many within-group taxa and characters as possible. Continuously varying characters, in the form of indices derived from measurement of individual skeletal elements, proved to be highly important, adding significantly to the resolution of, and support for, recovered trees. The utility of the postcranial skeleton in understanding relationships among basal synapsids is highlighted.

Jurassic Pork: What Could a Jewish Time Traveler Eat?

Authors:

Plotnick et al

Abstract:

Paleontologists use multiple methods to reconstruct the anatomy and behavior of extinct animals, including direct observations from well-preserved fossils and inferences from the phylogeny of modern and extinct relatives. We illustrate these techniques by reference to the biblical definitions of kosher and non-kosher animals; that is, how can we apply these approaches to the hypothetical question of whether an extinct form would have been kosher. The biblical categories do not readily map to modern understandings of systematics, but are heavily based on life mode. When given, distinguishing characteristics, such as the presence of fins and scales in aquatic animals, can be readily seen directly in fossils. In other cases, such as cud chewing, they need to be inferred from the phylogenetic relationships of the fossil forms. Dinosaurs (other than birds), unfortunately, are not kosher. A kosher “paleo diet” would be increasingly difficult further in the past. The use of biblical content as a way of introducing concepts from paleontology and evolutionary biology, such as crown groups and stem groups, should be of broad interest.

A new Ordovician arthropod from the Winneshiek Lagerstätte of Iowa (USA) reveals the ground plan of eurypterids and chasmataspidids

Authors:

Lamsdell et al

Abstract:

Euchelicerates were a major component of Palaeozoic faunas, but their basal relationships are uncertain: it has been suggested that Xiphosura—xiphosurids (horseshoe crabs) and similar Palaeozoic forms, the synziphosurines—may not represent a natural group. Basal euchelicerates are rare in the fossil record, however, particularly during the initial Ordovician radiation of the group. Here, we describe Winneshiekia youngae gen. et sp. nov., a euchelicerate from the Middle Ordovician (Darriwilian) Winneshiek Lagerstätte of Iowa, USA. Winneshiekia shares features with both xiphosurans (a large, semicircular carapace and ophthalmic ridges) and dekatriatan euchelicerates such as chasmataspidids and eurypterids (an opisthosoma of 13 tergites). Phylogenetic analysis resolves Winneshiekia at the base of Dekatriata, as sister taxon to a clade comprising chasmataspidids, eurypterids, arachnids, and Houia. Winneshiekia provides further support for the polyphyly of synziphosurines, traditionally considered the stem lineage to xiphosurid horseshoe crabs, and by extension the paraphyly of Xiphosura. The new taxon reveals the ground pattern of Dekatriata and provides evidence of character polarity in chasmataspidids and eurypterids. The Winneshiek Lagerstätte thus represents an important palaeontological window into early chelicerate evolution.

Taxonomic revision of tribosphenic mammals from the Lower Cretaceous Antlers Formation of Texas and Oklahoma, USA.

Author:

Averianov

Abstract:

There are five taxa of tribosphenic mammals in the Early Cretaceous Antlers Formation of Texas and Oklahoma, USA: a basal stem therian (Kermackia texana), stem therians near the eutherian-metatherian dichotomy (Holoclemensia texana and Pappotherium pattersoni), and stem marsupials (Atokatheridium boreni and Oklatheridium szalayi). K. texana has a primitive therian postcanine formula with three molars, replacement of p5, M3 with low protocone and no conules, lower molars with a large trigonid angle, oblique protocristid, paraconid smaller than metaconid (except m3), strong distal metacristid, narrow talonid, small talonid basin, and small entoconid (absent on m3). H. texana also has replacement in the fifth premolar locus and three molars. It is more derived in having a larger protoconal region with higher protocone and conules present, lack of distal metacristid, smaller trigonid angle, transverse protocristid, and wide talonid with larger talonid basin. It is similar to Eutheria by having M1 with reduced ectoflexus, semimolariform p5, and low trigonid angle with transverse protocristid. Holoclemensia cannot be referred to Eutheria because of the lack of the second rank postvallum/prevallid shear and unwinged conules. P. pattersoni (=Slaughteria eruptens) has replacement in the fifth premolar position, premolariform p5, and three molars (symplesiomorphies for Theria). It is more derived than Holoclemensia in having a wider and shorter talonid. Pappotherium is similar to Eutheria in having a low trigonid angle, transverse protocristid, and the cristid obliqua labial to the protocristid notch. It cannot be attributed to the Eutheria because of the narrow protoconal region, low protocone, small conules lacking internal cristae, postprotocrista not extending labially past the metacone base, and a small talonid basin. Atokatheridium boreni and Oklatheridium szalayi (=O. minax, syn. nov.) have four molars and emphasis on the postvallum/prevallid shear (large metacone on M2, strong postmetacrista, paraconid higher than metaconid). These taxa cannot be attributed to the Deltatheroida because of large protoconal region with winged conules. Oklatheridium is further different from the Deltatheroida in having a wider talonid and better developed entoconid.

Evidence for a Mid-Jurassic Adaptive Radiation in Mammals

Authors:

Close et al

Abstract:

A series of spectacular discoveries have transformed our understanding of Mesozoic mammals in recent years. These finds reveal hitherto-unsuspected ecomorphological diversity that suggests that mammals experienced a major adaptive radiation during the Middle to Late Jurassic [ 1 ]. Patterns of mammalian macroevolution must be reinterpreted in light of these new discoveries [ 1–3 ], but only taxonomic diversity and limited aspects of morphological disparity have been quantified [ 4, 5 ]. We assess rates of morphological evolution and temporal patterns of disparity using large datasets of discrete characters. Rates of morphological evolution were significantly elevated prior to the Late Jurassic, with a pronounced peak occurring during the Early to Middle Jurassic. This intense burst of phenotypic innovation coincided with a stepwise increase in apparent long-term standing diversity [ 4 ] and the attainment of maximum disparity, supporting a “short-fuse” model of early mammalian diversification [ 2, 3 ]. Rates then declined sharply, and remained significantly low until the end of the Mesozoic, even among therians. This supports the “long-fuse” model of diversification in Mesozoic therians. Our findings demonstrate that sustained morphological innovation in Triassic stem-group mammals culminated in a global adaptive radiation of crown-group members during the Early to Middle Jurassic.

Bayesian analysis of a morphological supermatrix sheds light on controversial fossil hominin relationships

Authors:

Dembo et al

Abstract:

The phylogenetic relationships of several hominin species remain controversial. Two methodological issues contribute to the uncertainty—use of partial, inconsistent datasets and reliance on phylogenetic methods that are ill-suited to testing competing hypotheses. Here, we report a study designed to overcome these issues. We first compiled a supermatrix of craniodental characters for all widely accepted hominin species. We then took advantage of recently developed Bayesian methods for building trees of serially sampled tips to test among hypotheses that have been put forward in three of the most important current debates in hominin phylogenetics—the relationship between Australopithecus sediba and Homo, the taxonomic status of the Dmanisi hominins, and the place of the so-called hobbit fossils from Flores, Indonesia, in the hominin tree. Based on our results, several published hypotheses can be statistically rejected. For example, the data do not support the claim that Dmanisi hominins and all other early Homo specimens represent a single species, nor that the hobbit fossils are the remains of small-bodied modern humans, one of whom had Down syndrome. More broadly, our study provides a new baseline dataset for future work on hominin phylogeny and illustrates the promise of Bayesian approaches for understanding hominin phylogenetic relationships.

The original snake ancestor was a nocturnal, stealth-hunting predator that had tiny hindlimbs with ankles and toes, according to research published in the open access journal BMC Evolutionary Biology.

The study, led by Yale University, USA, analyzed fossils, genes, and anatomy from 73 snake and lizard species, and suggests that snakes first evolved on land, not in the sea, which contributes to a longstanding debate. They most likely originated in the warm, forested ecosystems of the Southern Hemisphere around 128 million years ago.

Snakes show incredible diversity, with over 3,400 living species found in a wide range of habitats, such as land, water and in trees. But little is known about where and when they evolved, and how their original ancestor looked and behaved.

Lead author Allison Hsiang said: "While snake origins have been debated for a long time, this is the first time these hypotheses have been tested thoroughly using cutting-edge methods. By analyzing the genes, fossils and anatomy of 73 different snake and lizard species, both living and extinct, we've managed to generate the first comprehensive reconstruction of what the ancestral snake was like."

By identifying similarities and differences between species, the team constructed a large family tree and illustrated the major characteristics that have played out throughout snake evolutionary history.

Their results suggest that snakes originated on land, rather than in water, during the middle Early Cretaceous period (around 128.5 million years ago), and most likely came from the ancient supercontinent of Laurasia. This period coincides with the rapid appearance of many species of mammals and birds on Earth.

The ancestral snake likely possessed a pair of tiny hindlimbs, and targeted soft-bodied vertebrate and invertebrate prey that were relatively large in size compared to prey targeted by lizards at the time. While the snake was not limited to eating very small animals, it had not yet developed the ability to manipulate prey much larger than itself by using constriction as a form of attack, as seen in modern Boa constrictors.

While many ancestral reptiles were most active during the daytime (diurnal), the ancestral snake is thought to have been nocturnal. Diurnal habits later returned around 50-45 million years ago with the appearance of Colubroidea - the family of snakes that now make up over 85% of living snake species. As colder night time temperatures may have limited nocturnal activity, the researchers say that the success of Colubroidea may have been facilitated by the return of these diurnal habits.