Six New Papers from the Forthcoming Volume 'Anatomy, Phylogeny, and Palaeobiology of Early Archosaurs and their Kin.

You can access the abstracts electronically here.

Mastrantonio, B. M., Schultz, C. L., Desojo, J. B., and J.  Bittencourt Garcia. 2013. The braincase of Prestosuchus chiniquensis (Archosauria: Suchia)From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, doi:10.1144/SP379.10

Abstract - The osteology of an almost complete braincase of the rauisuchian archosaurs Prestosuchus chiniquensis from the Middle Triassic of Brazil is described for first time, based on two specimens (UFRGS-PV-0629-T and UFRGS-PV-0156-T). A comparative description with other taxa of rauisuchians is presented that forms the basis of a phylogenetic analysis. To perform the phylogenetic analysis, we describe and discuss each character codification for a modified version of the recent matrices of Gower (2002), Gower & Nesbitt (2006) and Brusatte et al.(2010). The analysis resulted in two most parsimonious trees that differ from the topologies recovered by Gower (2002) in a few aspects within Rauisuchia, and Prestosuchus chiniquensis was unequivocally depicted as deeply nested within Pseudosuchia, as the sister taxon of Batrachotomus kuperferzellensis in both topologies, supported by a single synapomorphy: the reduced to small fissure of the post-temporal fenestra between parietal, supraoccipital and exoccipital-opisthotic.


Sues, H.-D., Desojo, J. B., and M. D. Ezcurra. 2013. Doswelliidae: a clade of unusual armoured archosauriforms from the Middle and Late Triassic. From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, first published on April 23, 2013, doi:10.1144/SP379.13

Abstract - Doswelliidae is a clade of armoured non-archosaurian archosauriform reptiles more closely related to Archosauria than are Proterosuchidae, Erythrosuchidae and possibly Euparkeria capensis. It is currently known from the late Middle Triassic (Ladinian) of Germany, the late Middle to early Late Triassic (Ladinian–Carnian) of Argentina and Brazil, and the Late Triassic (Carnian–Norian) of the USA. To date, two unambiguous synapomorphies diagnose Doswelliidae: (i) osteoderm ornamentation coarse, incised, and composed of central regular pits of subequal size and shape, and (ii) osteoderms with anterior articular lamina. Five taxa are currently recognized: Archeopelta arborensis, Doswellia kaltenbachi, Doswellia sixmilensis, Tarjadia ruthae and a new taxon from Germany. Based on skeletal features and occurrence, doswelliid archosauriforms may have had a semi-aquatic mode of life.


Langer, M. C., and J. Ferigolo. 2013. The Late Triassic dinosauromorph Sacisaurus agudoensis (Caturrita Formation; Rio Grande do Sul, Brazil): anatomy and affinities. From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin.  Geological Society, London, Special Publications, 379, first published on April 23, 2013, doi:10.1144/SP379.16

Abstract - Silesauridae is an exclusively Triassic group of dinosauromorphs, knowledge on the diversity of which has increased dramatically in the last few years. Silesaurid relationships are still contentious, as a result in part of different homology statements, particularly regarding the typical edentulous mandible tip of these animals. One of the most complete silesaurids yet discovered is Sacisaurus agudoensis from the Caturrita Formation (Late Triassic: Norian) of Rio Grande do Sul, Brazil, represented by numerous isolated bones recovered from a single site. The anatomy of S. agudoensis is fully described for the first time here, and comparisons are provided to other basal dinosauromorphs. S. agudoensis is a small-bodied animal (less than 1 m in length) that possesses a dentition consisting of leaf-shaped crowns with large denticles in the carinae, a plesiomorphic propubic pelvis with an almost fully closed acetabulum, elongate distal hindlimbs suggesting well-developed cursorial ability, and a laterally projected outer malleolus in the tibia. All previous numerical phylogenies supported a non-dinosaur dinosauromorph affinity for Silesauridae, but the reanalysis of one of those studies suggests that a position within Dinosauria is not unlikely, with silesaurids forming the basal branch of the ornithischian lineage.


Turner, A. H., and S. J. Nesbitt. 2013. Body size evolution during the Triassic archosauriform radiation. From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin.  Geological Society, London, Special Publications, 379, first published on April 23, 2013, doi:10.1144/SP379.15

Abstract - The first large (>1 m) diapsids appeared near the Permian–Triassic extinction and a subset of diapsids, the archosauriforms, expanded their body size range soon after in the Early–Middle Triassic. Here, we examine body size at key evolutionary events within Archosauriformes during the Triassic and through the end-Triassic extinction. Using femoral length as a body size proxy and a temporally calibrated phylogeny of Archosauriformes, we estimate ancestral body sizes using a maximum likelihood approach and test for the presence of an adapative radiation by comparing the fit of competing evolutionary models. Archosauriform body size is characterized by punctuated change with more change occurring early in the Triassic. Archosaurs crossing the Triassic–Jurassic boundary show a wide range in ancestral size, and dinosaurs (sauropodomorphs and theropods) are considerably larger in the Jurassic. Crocodylomorph origins are characterized by a drop in body size; however, both the relative amount of change and the rate of change are matched among other archosaur clades. Archosauriforms increase in absolute body size through the Triassic and evidence suggests that a directional trend in size increase occurred in the early Mesozoic. The morphological signature of adaptive radiation is rare in comparative data from extant animals but is present at the origination of Archosauriformes.


Niedźwiedzki, G., Brusatte, S. L., and R. J. Butler. 2013. Prorotodactylus and Rotodactylus tracks: an ichnological record of dinosauromorphs from the Early–Middle Triassic of Poland. From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, first published on April 23, 2013, doi:10.1144/SP379.12

Abstract - We present the first comprehensive description of Prorotodactylus and Rotodactylus  dinosauromorph tracks from the Early and Middle Triassic of the Holy Cross Mountains, Poland. We describe and comprehensively figure tracks that have been mentioned briefly in previous accounts as well as new, recently discovered material, and analyse the variation and stratigraphic distribution of these specimens. Tracks have been recorded from four sites – Koszary, Stryczowice, Wióry and Baranów – which span the early Olenekian – early Anisian (c.250–246 Ma). These tracks therefore represent an ichnological record of the evolutionary succession of early dinosauromorphs during the earliest part of their evolutionary history. Recognized track types include cf. Prorotodactylus isp., Prorotodactylus isp., Prorotodactylus mirus, Rotodactylus cursorius, Rotodactylus isp. and cf. Rotodactylus isp. At least three distinct Early and early Middle Triassic early dinosauromorph ichnofaunas can be recognized. The oldest, which is early Olenekian in age, is characterized by the presence of Prorotodactylus isp., cf.Prorotodactylus isp. and non-archosaurian archosauromorph or archosaur tracks (e.g. Synaptichnium isp., Protochirotherium isp.), recorded at the Stryczowice and Koszary sites. The following assemblage, recorded at the late Olenekian Wióry site, displays the highest ichnodiversity of dinosauromorphs, with four track types present (Prorotodactylus isp., Prorotodactylus mirus, Rotodactylus cursorius and cf. Rotodactylus isp.). The youngest site, Baranów, includes Rotodactylus isp., as well as other larger dinosauromorph tracks. The first body fossil evidence of dinosauromorphs is a few million years younger than the youngest Polish tracks, so Prorotodactylus and Rotodactylus tracks currently provide the oldest record of dinosauromorph morphology, biology and evolution.


Ezcurra, M. D., Butler, R. J., and D. J. Gower. 2013. ‘Proterosuchia’: the origin and early history of Archosauriformes.. From: Nesbitt, S. J., Desojo, J. B. & Irmis, R. B. (eds) 2013. Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and their Kin. Geological Society, London, Special Publications, 379, first published on April 23, 2013, doi:10.1144/SP379.11

Abstract - The earliest history of Archosauriformes is mainly represented by members of Proterosuchidae and Erythrosuchidae, which are known worldwide from latest Permian to Middle Triassic beds. These two groups were historically combined within ‘Proterosuchia’, with approximately 30 nominal species. Two morphotypes have been recognized among proterosuchians: proterosuchids with a generally more sprawling gait and elongated and low skulls with an overhanging premaxilla, and the more heavily built erythrosuchids, with a probably less sprawling gait and large, presumably hypercarnivorous, skulls. The systematics of ‘Proterosuchia’ was relatively chaotic throughout most of the twentieth century, but currently there exists consensus regarding the non-monophyly of proterosuchians and their phylogenetic position outside all other archosauriforms. In contrast, the delimitation and taxonomic content of Proterosuchidae and Erythrosuchidae remain unstable. Few studies of proterosuchian palaeobiology have been carried out. Current lines of evidence favour a predominantly terrestrial lifestyle for proterosuchians. Limb bone histology indicates rapid continuous growth rates in Proterosuchus and Erythrosuchus before reaching sexual maturity. A better knowledge of proterosuchian anatomy, systematics, evolution and ecology is important for advancing understanding of the origin and early radiation of Archosauriformes and the patterns of biotic recovery following the Permo-Triassic mass extinction event. There remains much research to be carried out in proterosuchian palaeobiology.

Postcranial Skeletal Pneumaticity in Triassic Archosaurs

Butler, R. J., Barrett, P. M., and D. J. Gower. 2012. Reassessment of the evidence for postcranial skeletal pneumaticity in Triassic archosaurs, and the early evolution of the avian respiratory system. PLoS ONE 7(3): e34094. doi:10.1371/journal.pone.0034094


Abstract - Uniquely among extant vertebrates, birds possess complex respiratory systems characterised by the combination of small, rigid lungs, extensive pulmonary air sacs that possess diverticula that invade (pneumatise) the postcranial skeleton, unidirectional ventilation of the lungs, and efficient crosscurrent gas exchange. Crocodilians, the only other living archosaurs, also possess unidirectional lung ventilation, but lack true air sacs and postcranial skeletal pneumaticity (PSP). PSP can be used to infer the presence of avian-like pulmonary air sacs in several extinct archosaur clades (non-avian theropod dinosaurs, sauropod dinosaurs and pterosaurs). However, the evolution of respiratory systems in other archosaurs, especially in the lineage leading to crocodilians, is poorly documented. Here, we use mCT-scanning to investigate the vertebral anatomy of Triassic archosaur taxa, from both the avian and crocodilian lineages as well as non-archosaurian diapsid outgroups. Our results confirm previous suggestions that unambiguous evidence of PSP (presence of internal pneumatic cavities linked to the exterior by foramina) is found only in bird-line (ornithodiran) archosaurs. We propose that pulmonary air sacs were present in the common ancestor of Ornithodira and may have been subsequently lost or reduced in some members of the clade (notably in ornithischian dinosaurs). The development of these avian-like respiratory features might have been linked to inferred increases in activity levels among ornithodirans. By contrast, no crocodile-line archosaur (pseudosuchian) exhibits evidence for unambiguous PSP, but many of these taxa possess the complex array of vertebral laminae and fossae that always accompany the presence of air sacs in ornithodirans. These laminae and fossae are likely homologous with those in ornithodirans, which suggests the need for further investigation of the hypothesis that a reduced, or non-invasive, system of pulmonary air sacs may be have been present in these taxa (and secondarily lost in extant crocodilians) and was potentially primitive for Archosauria as a whole.

Early Evolution of Postcranial Skeletal Pneumaticity in Sauropodomorph Dinosaurs

I don't think I've posted this paper previously, but it has been in press for a year...

Yates, A. M., Wedel, M. J., and M. F. Bonnan. 2012. The early evolution of postcranial skeletal pneumaticity in sauropodomorph dinosaurs. Acta Palaeontologica Polonica 57:85-100.  

doi: http://dx.doi.org/10.4202/app.2010.0075

Abstract - Postcranial skeletal pneumaticity (PSP) is present in a range of basal sauropodomorphs spanning the basal sauropodomorph—sauropod transition. We describe the PSP of five taxa, Plateosaurus engelhardti, Eucnemesaurus fortis, Aardonyx celestae, Antetonitrus ingenipes, and an unnamed basal sauropod from Spion Kop, South Africa (hereafter referred to as the Spion Kop sauropod). The PSP of Plateosaurus is apparently sporadic in its occurrence and has only been observed in very few specimens, in which it is of very limited extent, affecting only the posterior cervical vertebrae and possibly the mid dorsals in one specimen. The PSP of Eucnemesaurus, Aardonyx, Antetonitrus, and the Spion Kop sauropod consists of subfossae (fossa within-fossa structures) that excavate the vertices of the posterior infradiapophyseal fossae of the posterior dorsal vertebrae. These subfossae range from simple shallow depressions (Eucnemesaurus) to deep, steepsided, internally subdivided and asymmetrically developed chambers (Antetonitrus). The middle and anterior dorsal vertebrae of these taxa lack PSP, demonstrating that abdominal air sacs were the source of the invasive diverticula. The presence of pneumatic features within the infradiapophyseal fossae suggest that the homologous fossae of more basal saurischians and dinosauriforms were receptacles that housed pneumatic diverticula. We suggest that it is probable that rigid non-compliant lungs ventilated by compliant posterior air sacs evolved prior to the origination of Dinosauria.

Guest Post - Roland Sookias Discusses His New Study Examining How Dinosaurs Came to Fill Most Ecological Niches During the Mesozoic

Why were dinosaurs, and other archosauromorphs (the group of animals including crocodiles, dinosaurs, pterosaurs and several other extinct groups), so big? Was natural selection for increasing size responsible for archosauromorphs’ dramatic rise to larger sizes and did selection for decreasing size drive therapsids’ (‘mammal-like reptiles’, which were the dominant land vertebrates before archosauromorphs) reduction in size during the Triassic (see picture)? These are the questions which my, Richard Butler’s and Roger Benson’s recent publication in Proceedings of the Royal Society B – “Rise of dinosaurs reveals major body size transitions are driven by passive processes of trait evolution” – attempts to answer.
Most of the work in the paper was done as part of my MSc thesis project, which Richard, Roger and Andrew Smith supervised. To carry out the project I spent a good deal of last summer collecting femur and skull length measurements (which we used as proxies for body mass) in the Natural History Museum Library, London. Though barely seeing daylight for a month or two, I managed to collect measurements for ~200 species, which, in combination with data from Benson et al. 2011 got us to >400 species in total. To answer the questions above we focused on getting data for archosauromorphs and therapsids from the Late Permian to Middle Jurassic. This allowed comparison between the two groups, and the interval brackets the rise of archosauromorphs to become the dominant terrestrial vertebrates, replacing therapsids. Thus it allowed us to look at body size evolutionary dynamics during a major faunal transition.

Archosauromorphs (dinosaurs, crocodiles, pterosaurs and their relatives) increased greatly in maximum size (black line, black triangles) from the Permian to Jurassic, and therapsids (‘mammal-like reptiles’) decreased. However in both this was due to expansion in the size variance (i.e. both size increase and decrease), but with subsequent extinction of larger therapsid species. Figure from Sookias et al. 2012, Proc Roy Soc B.

Once we’d got the data together we analysed them using maximum likelihood model fitting approaches. We tried both phylogenetic – i.e. incorporating evolutionary relationships – and time series (ignoring within-group evolutionary relationships and simply averaging size within time ‘bins’) models. Time series models confirmed that on average archosauromorphs tended to increase across the time interval, and that therapsids got smaller. However when we included phylogeny (evolutionary relationships) we found that there was no directional trend in either group along individual lineages. Thus the apparent trends through time were in fact due to ‘passive expansion’ in size, but as the original size was nearer the bottom than the top of the eventual size range the average size tended to increase (see picture). We thus can say that the long-repeated idea of “Cope’s rule” – that taxa in a clade tend to get larger over time due to within-lineage natural selection for larger body sizes – is not found in either archosauromorphs or therapsids during this time interval.

Our work excludes larger size in archosauromorphs as an explanation for their success, as if larger size was especially beneficial one would expect a directional evolutionary trend towards larger sizes. Instead, archosauromorphs probably replaced therapsids opportunistically, as many have hypothesized before. However, the exceptionally high growth, and thus reproductive, rates of archosauromorphs may have allowed them to re-fill empty ecological niches especially easily and rapidly after they went empty due to extinction of therapsids. Thus, while size and growth rate probably did not allow archosauromorphs to outcompete therapsids, it did allow them to fill up free niches quickly.

We also found that archosauromorph predators exceeded the size of the largest herbivores – anomodont therapsids – during the Middle-early Late Triassic. This finding – that the largest carnivores are larger than herbivores - is extremely rare in ecosystems throughout time. It demonstrates that extinct archosauromorphs really were exceptionally large, and that they were able to grow to larger sizes than therapsids given the same resources.

Well, there’s not much more to say about that paper except hope you enjoy it! However, we should be publishing some more work based on my MSc thesis in the near future, so stay tuned, and I’ve just started a PhD with Richard Butler on the early archosauromorph radiation, so hopefully I’ll be involved in answering a few more interesting questions in the coming years. Finally, a very big thank you to Bill Parker for giving us a guest slot here on the esteemed Chinleana.

The paper’s full citation is:


Sookias, R. B., Butler, R. J., Benson, R. B. J. (2012). Rise of dinosaurs reveals major body size transitions are driven by passive processes of trait evolution. Proceedings of the Royal Society B.
doi: 10.1098/rspb.2011.2441 



Abstract- A major macroevolutionary question concerns how long-term patterns of body-size evolution are underpinned by smaller scale processes along lineages. One outstanding long-term transition is the replacement of basal therapsids (stem-group mammals) by archosauromorphs, including dinosaurs, as the dominant large-bodied terrestrial fauna during the Triassic (approx. 252–201 million years ago). This landmark event preceded more than 150 million years of archosauromorph dominance. We analyse a new body-size dataset of more than 400 therapsid and archosauromorph species spanning the Late Permian–Middle Jurassic. Maximum-likelihood analyses indicate that Cope’s rule (an active within-lineage trend of body-size increase) is extremely rare, despite conspicuous patterns of body-size turnover, and contrary to proposals that Cope’s rule is central to vertebrate evolution. Instead, passive processes predominate in taxonomically and ecomorphologically more inclusive clades, with stasis common in less inclusive clades. Body-size limits are clade-dependent, suggesting intrinsic, biological factors are more important than the external environment. This clade-dependence is exemplified by maximum size of Middle–early Late Triassic archosauromorph predators exceeding that of contemporary herbivores, breaking a widely accepted ‘rule’ that herbivore maximum size greatly exceeds carnivore maximum size. Archosauromorph and dinosaur dominance occurred via opportunistic replacement of therapsids following extinction, but were facilitated by higher archosauromorph growth rates.



Popular press coverage:

http://news.discovery.com/animals/how-dinosaurs-got-so-big-120131.html

http://news.sciencemag.org/sciencenow/2012/01/the-secret-of-dinos-success.html?ref=hp

MicroRNAs Show that Turtles are Lepidosauromorph Diapsids

Last spring when I was in Austin, Kevin Peterson came and gave a talk on the promise of microRNA's in determining phylogenetic relationships of organisms. In a follow-up question Sterling Nesbitt and I asked him if this could be used to solve the debate regarding the relationships of turtles. Peterson replied that they were already working on the problem and that preliminary data suggested that turtles were close to lepidosaurs. You can read more details from the final study below. Fascinating stuff.

http://www.nature.com/news/2011/110719/full/news.2011.425.html

http://www.ecnmag.com/News/Feeds/2011/07/blogs-the-cutting-edge-discovery-places-turtles-next-to-lizards-on-family/

Update: Here is the abstract

Lyson, T. R., Sperling, E. A., Heimberg, A. M., Gauthier, J. A., King, B. L., and K. J. Peterson. 2011. MicroRNAs support a turtle + lizard clade. Biology Letters. doi: 10.1098/rsbl.2011.0477

Abstract - Despite much interest in amniote systematics, the origin of turtles remains elusive. Traditional morphological phylogenetic analyses place turtles outside Diapsida—amniotes whose ancestor had two fenestrae in the temporal region of the skull (among the living forms the tuatara, lizards, birds and crocodilians)—and allied with some unfenestrate-skulled (anapsid) taxa. Nonetheless, some morphological analyses place turtles within Diapsida, allied with Lepidosauria (tuatara and lizards). Most molecular studies agree that turtles are diapsids, but rather than allying them with lepidosaurs, instead place turtles near or within Archosauria (crocodilians and birds). Thus, three basic phylogenetic positions for turtles with respect to extant Diapsida are currently debated: (i) sister to Diapsida, (ii) sister to Lepidosauria, or (iii) sister to, or within, Archosauria. Interestingly, although these three alternatives are consistent with a single unrooted four-taxon tree for extant reptiles, they differ with respect to the position of the root. Here, we apply a novel molecular dataset, the presence versus absence of specific microRNAs, to the problem of the phylogenetic position of turtles and the root of the reptilian tree, and find that this dataset unambiguously supports a turtle + lepidosaur group. We find that turtles and lizards share four unique miRNA gene families that are not found in any other organisms' genome or small RNA library, and no miRNAs are found in all diapsids but not turtles, or in turtles and archosaurs but not in lizards. The concordance between our result and some morphological analyses suggests that there have been numerous morphological convergences and reversals in reptile phylogeny, including the loss of temporal fenestrae.

Transitional Mammalian Middle Ear from a new Cretaceous Eutriconodont

Non Triassic per se but still relevent and extremely cool and important...

Meng, J., Wang, Y., and C. Li. 2011. Transitional mammalian middle ear from a new Cretaceous Jehol eutriconodont. Nature 472:181-185. doi:10.1038/nature09921

Abstract - The transference of post-dentary jaw elements to the cranium of mammals as auditory ossicles is one of the central topics in evolutionary biology of vertebrates. Homologies of these bones among jawed vertebrates have long been demonstrated by developmental studies; but fossils illuminating this critical transference are sparse and often ambiguous. Here we report the first unambiguous ectotympanic (angular), malleus (articular and prearticular) and incus (quadrate) of an Early Cretaceous eutriconodont mammal from the Jehol Biota, Liaoning, China. The ectotympanic and malleus have lost their direct contact with the dentary bone but still connect the ossified Meckel’s cartilage (OMC); we hypothesize that the OMC serves as a stabilizing mechanism bridging the dentary and the detached ossicles during mammalian evolution. This transitional mammalian middle ear narrows the morphological gap between the mandibular middle ear in basal mammaliaforms and the definitive mammalian middle ear (DMME) of extant mammals; it reveals complex changes contributing to the detachment of ear ossicles during mammalian evolution.

Leonerasaurus taquetrensis, a New Derived Sauropodomorph from the Early Jurassic (or Late Triassic?) of Argentina

I'm not even going to attempt to delve into this new paper here because Adam Yates is back and has the detailed write-up at Dracovenator!

All of these recent sauropodomorph finds have me totally fired up to find one in the Chinle Formation this summer!  (but I'll settle for the skull of Chindesaurus).


Pol, D., Garrido, A., and I. A. Cerda. 2011. A New Sauropodomorph Dinosaur from the Early Jurassic of Patagonia and the Origin and Evolution of the Sauropod-type Sacrum. PLoS ONE 6(1): e14572. doi:10.1371/journal.pone.0014572

ABSTRACT
Background
The origin of sauropod dinosaurs is one of the major landmarks of dinosaur evolution but is still poorly understood. This drastic transformation involved major skeletal modifications, including a shift from the small and gracile condition of primitive sauropodomorphs to the gigantic and quadrupedal condition of sauropods. Recent findings in the Late Triassic–Early Jurassic of Gondwana provide critical evidence to understand the origin and early evolution of sauropods.

Methodology/Principal Findings
A new sauropodomorph dinosaur, Leonerasaurus taquetrensis gen. et sp. nov., is described from the Las Leoneras Formation of Central Patagonia (Argentina). The new taxon is diagnosed by the presence of anterior unserrated teeth with a low spoon-shaped crown, amphicoelous and acamerate vertebral centra, four sacral vertebrae, and humeral deltopectoral crest low and medially deflected along its distal half. The phylogenetic analysis depicts Leonerasaurus as one of the closest outgroups of Sauropoda, being the sister taxon of a clade of large bodied taxa composed of Melanorosaurus and Sauropoda.

Conclusions/Significance
The dental and postcranial anatomy of Leonerasaurus supports its close affinities with basal sauropods. Despite the small size and plesiomorphic skeletal anatomy of Leonerasaurus, the four vertebrae that compose its sacrum resemble that of the large-bodied primitive sauropods. This shows that the appearance of the sauropod-type of sacrum predated the marked increase in body size that characterizes the origins of sauropods, rejecting a causal explanation and evolutionary linkage between this sacral configuration and body size. Alternative phylogenetic placements of Leonerasaurus as a basal anchisaurian imply a convergent acquisition of the sauropod-type sacrum in the new small-bodied taxon, also rejecting an evolutionary dependence of sacral configuration and body size in sauropodomorphs. This and other recent discoveries are showing that the characteristic sauropod body plan evolved gradually, with a step-wise pattern of character appearance.

Rainforest Collapse Triggered Carboniferous Tetrapod Diversification in Euramerica

A new paper that argues that ecosystem devestation in the Carboniferous provided conditions that led to increased diversity in amniotes and basically set the stage for the rise of archosaurs in the Mesozoic.

From Science Daily article: "Global warming devastated tropical rainforests 300 million years ago. Now scientists report the unexpected discovery that this event triggered an evolutionary burst among reptiles -- and inadvertently paved the way for the rise of dinosaurs, 100 million years later".  Read more here.


Sahney, S., Benton, M. J., and H. J. Falcon-Lang. 2010. Rainforest collapse triggered Carboniferous tetrapod diversification in Euramerica. Geology 38: 1079-1082. DOI: 10.1130/G31182.1



Abstract - Abrupt collapse of the tropical rainforest biome (Coal Forests) drove rapid diversification of Carboniferous tetrapods (amphibians and reptiles) in Euramerica. This finding is based on analysis of global and alpha diversity databases in a precise geologic context. From Visean to Moscovian time, both diversity measures steadily increased, but following rainforest collapse in earliest Kasimovian time (ca. 305 Ma), tetrapod extinction rate peaked, alpha diversity imploded, and endemism developed for the first time. Analysis of ecological diversity shows that rainforest collapse was also accompanied by acquisition of new feeding strategies (predators, herbivores), consistent with tetrapod adaptation to the effects of habitat fragmentation and resource restriction. Effects on amphibians were particularly devastating, while amniotes (‘reptiles’) fared better, being ecologically adapted to the drier conditions that followed. Our results demonstrate, for the first time, that Coal Forest fragmentation influenced profoundly the ecology and evolution of terrestrial fauna in tropical Euramerica, and illustrate the tight coupling that existed between vegetation, climate, and trophic webs.

Special Issue on Transitional Fossils in the Journal Evolution: Education and Outreach

This was already announced on the Vertebrate Paleontology Listserver; however, for those of you who do not subscribe:

The new issue of the open access journal "Evolution: Education and Outreach" is now available online here. This is a special issue on transitional fossils an contains articles from a number of specialists on a the origins of variety of animal groups as well as articles on evolution and systematics.

And of course as open access it is all freely available.

Enjoy