Litorosuchus somnii: A new Armored and Aquatic Archosauriform From Ladinian Triassic China

A new armored archosauriform (Diapsida: Archosauromorpha) from the marine Middle Triassic of China, with implications for the diverse life styles of archosauriforms prior to the diversification of Archosauria

Authors:

Li et al

Abstract:

Reptiles have a long history of transitioning from terrestrial to semi-aquatic or aquatic environments that stretches back at least 250 million years. Within Archosauria, both living crocodylians and birds have semi-aquatic members. Closer to the root of Archosauria and within the closest relatives of the clade, there is a growing body of evidence that early members of those clades had a semi-aquatic lifestyle. However, the morphological adaptations to a semi-aquatic environment remain equivocal in most cases. Here, we introduce a new Middle Triassic (245–235 Ma) archosauriform, Litorosuchus somnii, gen. et sp. nov., based on a nearly complete skeleton from the Zhuganpo Member (Ladinian [241–235 Ma]) of the Falang Formation, Yunnan, China. Our phylogenetic analyses suggest that Litorosuchus is a stem archosaur closely related to the aberrant Vancleavea just outside of Archosauria. The well-preserved skeleton of L. somnii bears a number of morphological characters consistent with other aquatic-adapted tetrapods including: a dorsally directed external naris, tall neural spines and elongate chevrons in an elongated tail, a short and broad scapula, webbed feet, long cervical vertebrae with long slender ribs, and an elongated rostrum with long and pointed teeth. Together these features represent one of the best-supported cases of a semi-aquatic mode of life for a stem archosaur. Together with Vancleavea campi, the discovery of L. somnii demonstrates a growing body of evidence that there was much more diversity in mode of life outside Archosauria. Furthermore, L. somnii helps interpret other possible character states consistent with a semi-aquatic mode of life for archosauriforms, including archosaurs.

Dagasuchus santacruzensis: A New Rauisuchian Archosaur From Ladinian Triassic Brazil

First 'Rauisuchian' archosaur (Pseudosuchia, Loricata) for the Middle Triassic Santacruzodon Assemblage Zone (Santa Maria Supersequence), Rio Grande do Sul State, Brazil

Authors:

Lacerda et al

Abstract:

The ‘Rauisuchia’ are a group of Triassic pseudosuchian archosaurs that displayed a near worldwide distribution. In Brazil, their fossils are found only in the Santa Maria Formation (Paraná Basin) of the Rio Grande do Sul State, specifically in the Middle Triassic Dinodontosaurus assemblage zone (AZ) and the Late Triassic Hyperodapedon AZ (Rauisuchus tiradentes). Between these two cenozones is the Santacruzodon AZ (Middle Triassic), whose record was, until now, restricted to non-mammalian cynodonts and the proterochampsian Chanaresuchus bonapartei. Here we present the first occurrence of a rauisuchian archosaur for this cenozone, from the Schoenstatt outcrop, located near the city of Santa Cruz do Sul and propose a new species, based on biostratigraphical evidence and a comparative osteological analysis.

Wangosaurus brevirostris: a new Ladinian Triassic Pistosauroid From China

A new pistosauroid (Reptilia, Sauropterygia) from the late Ladinian Xingyi marine reptile level, southwestern China

Authors:

Ma et al

Abstract:

Sauropterygia is a diverse group of Mesozoic marine reptiles that includes the Plesiosauria, one of the most successful clades from the Jurassic to the Cretaceous. The body plan of the Plesiosauria differs from that of basal sauropterygians by adaptations for life in the open ocean, as expressed by the propulsive, paddle-like limbs (Storrs, 1993; Sato et al., 2010; Benson et al., 2012). Triassic pistosauroids are believed to be important in the search for the origin of Plesiosauria (Rieppel et al., 2002; Sato et al., 2010). Until recently, the sister-group relationship between them was mainly based on cranial information, because of the generally poor preservation of Triassic pistosauroid specimens. Eight genera have been reported so far (Meyer, 1839; Yang, 1959, 1965; Storrs, 1991; Rieppel, 1997, 1998, 1999; Sander et al., 1997; Cheng et al., 2006; Dalla Vecchia, 2006), but some of these are known only from relatively complete cranial material (Augustasaurus Sander et al., 1997; Corosaurus Case, 1936; Cymatosaurus Fritsch, 1894; Pistosaurus Meyer, 1839; Yunguisaurus Cheng et al., 2006), whereas Yunguisaurus remains to date the only taxon represented by a complete skeleton.

Three genera of pistosauroids have been reported from the Triassic marine reptile faunas of southwestern China. Chinchenia sungi Young, 1965, from the upper Middle Triassic of Qingzhen, Guizhou Province, and Kwangsisaurus orientalis Young, 1959, from the upper Lower or lower Middle Triassic of Wuming, Guangxi Province, are both extremely fragmentary and listed as Pistosauroidea incertae sedis (Yang, 1959, 1965; Rieppel, 1999, 2000). Yunguisaurus liae Cheng, Sato, Wu, and Li, 2006, from the late Middle Triassic of Chajiang, Guizhou Province, and Fuyuan, Yunnan Province, is the only one represented by a complete skeleton, which is suggestive of early stages of adaptation towards the plesiosaurian functional style (Cheng et al., 2006; Zhao et al., 2008; Sato et al., 2010, 2014). Thus, more complete material should be described to provide new information that would better resolve the origin of Plesiosauria.

Here, we report a new pistosauroid, Wangosaurus brevirostris, gen. et sp. nov., from the late Middle Triassic of Xingyi, Guizhou Province, which shows a combination of plesiomorphic and derived characters (Fig. 1). Due to the rarity of complete and articulated skeletons of pistosauroids, and the presence of enough unique characters gleaned from the dorsal view of this specimen to establish a new genus, we here provide a preliminary description and phylogenetic analysis.

Horaffia kugleri: a new Ladinian Triassic Marine Reptile With Unknown Affinities

Humerus morphology and histology of a new marine reptile (Diapsida) from the Muschelkalk-Keuper-Grenzbonebed (Middle Triassic, Ladinian)

Authors:

Klein et al

Abstract:

A survey in the collection of the Muschelkalkmuseum Ingelfingen revealed a growth series of five humeri from the Grenzbonebed collected from localities in northeastern Baden-Württemberg (Southwest Germany). The Grenzbonebed is a tempestitic condensation horizon at the base of the Keuper that contains prefossilized vertebrate fossils reworked during a 100 ka minor sedimentary cycle. The humeri share a unique but simplified morphology due to adaptation to aquatic life. They are very robust and pachyostotic and have a dorsopreaxially elongated margin, a massive and ventrally protruding triangular proximal head as well as a preaxially slanted asymmetrical distal end. A detailed morphological comparison with humeri of other Triassic marine reptiles showed that they differ from humeri of all known taxa, including those of placodonts such as Paraplacodus, Placodus, Cyamodus, and Henodus. However, an analysis of the bone microstructure and histology revealed a close relationship with the humeri of Cyamodus, despite of distinct morphological differences. The five humeri and humeri of Cyamodus share a plexiform radiating fibro-lamellar bone tissue with moderate to high vascular density in the middle and outer cortex and a poorly developed medullary region, indicating osteosclerosis. Contrary to the pachyostotic humeri from the Grenzbonebed, Cyamodus humeri are not pachyostotic, thus suggesting different modes of locomotion in a similar shallow marine environment. The histological features of the pachyostotic humeri from the Grenzbonebed, which could point to placodont or pistosauroid affinities, respectively, are no reliable phylogenetic markers because convergent evolution of bone tissue is common among aquatic vertebrates sharing a similar environment and life style. Due to the unique humerus morphology the establishment of a new taxon, Horaffia kugleri gen. et sp. nov., is justified, although the remains are too poor to include them into a phylogenetic analysis or to assign them to a certain group.

Parasite Egg Found in Ladinian Triassic Cynodont Coprolite

Discovery of a 240 million year old nematode parasite egg in a cynodont coprolite sheds light on the early origin of pinworms in vertebrates


Authors:

Hugot et al

Abstract:


Background

We report the discovery of a nematode parasite egg (Nemata: Oxyurida) from a coprolite closely associated with the remains of several species of Cynodontia, dated to 240 million years old. This finding is particularly significant because this is the oldest record of an oxyurid nematode yet discovered, and because the cynodonts are considered a stem-group of the mammals.

Methods

We extracted material from a fully mineralized coprolite by both scraping the surface, and removing fragments from its interior with clean dental instruments used a single time. A single drop of glycerol from a new vial was added as a clearing reagent. Each slide was sealed with wax and examined with an optical microscope at 100× to 400× magnification.

Results

From one coprolite, 550 slides were examined; from 275 of these slides, sediment was examined that was scraped from the surface of the coprolite, and from the other 275 slides, material was examined that was extracted from the interior of the coprolite. All microscopic structures encountered were photographed, measured, and identified when possible.

Conclusions

From the coprolite examined, we discovered an egg representing a new species of pinworm that, based on the egg structure, clearly places it in the family Heteroxynematidae. Nematodes of the order Oxyurida have very constrained life-histories, occurring only in animals that are not strictly carnivorous and also ingest large amounts of plant material. This fact enabled us to determine which species of cynodont, from several collected at the site in Brazil, are most likely the depositors of the coprolite, and therefore were the putative host of the parasite.

Revised Chronostratigraphy of Chinle Formation has Implications for Late Triassic Dinosaur Evolution

Revised chronostratigraphy of the Lower Chinle Formation strata in Arizona and New Mexico (USA): High-precision U-Pb geochronological constraints on the Late Triassic evolution of dinosaurs

Authors:

Ramezani et al

Abstract:

The early history of dinosaurs in North America is obscured by an incomplete fossil record, taxonomic uncertainties and speculative correlations of tetrapod-bearing rocks, as well as poor calibration of the Late Triassic time scale. High-precision U-Pb geochronology provides a reliable means of correlating terrestrial rock formations independent of equivocal lithostratigraphy or vertebrate biostratigraphy, and hence the possibility of properly evaluating models for the early radiation and diversification of Dinosauria. Here we present new, high-precision, U-Pb ID-TIMS zircon geochronology from the presumed lowermost strata of the Upper Triassic Chinle Formation of the Colorado Plateau in Southwest United States, including a mean 206Pb/238U date of 219.39 ± 0.16 Ma from the renowned Placerias Quarry Bone Bed in eastern Arizona. The new results prompt revisions to the chronostratigraphy of the lower Chinle and provide a new temporal context for its rich tetrapod fauna.

The oldest documented dinosaurs of North America coexisted with their non-dinosaurian near-relatives for a minimum of 12 m.y., from ca. 223 Ma to ca. 211 Ma, in the Norian. This early dinosauromorph record follows a ca. 6 m.y. period from which no tetrapod fossils have been documented and which was itself preceded by a ca. 10 m.y. depositional hiatus spanning nearly the entire Ladinian and Carnian stages of the terrestrial North America. The supposed late appearance of dinosauromorphs in North America compared to those in South America thus appears to be an artifact of incomplete preservation, as well as unsubstantiated age interpretations. This, together with the conspicuous biogeographic distinctions among the Triassic dinosauromorph assemblages, invalidates a simple diachronous model for the transcontinental radiation of early dinosaurs.

Gracilisuchids: A new Clade Erected for Anisian to Carnian Triassic Chinese and Argentinian Pseudosuchians

New clade of enigmatic early archosaurs yields insights into early pseudosuchian phylogeny and the biogeography of the archosaur radiation

Authors:

Butler et al

Abstract:

Background

The origin and early radiation of archosaurs and closely related taxa (Archosauriformes) during the Triassic was a critical event in the evolutionary history of tetrapods. This radiation led to the dinosaur-dominated ecosystems of the Jurassic and Cretaceous, and the high present-day archosaur diversity that includes around 10,000 bird and crocodylian species. The timing and dynamics of this evolutionary radiation are currently obscured by the poorly constrained phylogenetic positions of several key early archosauriform taxa, including several species from the Middle Triassic of Argentina (Gracilisuchus stipanicicorum) and China (Turfanosuchus dabanensis, Yonghesuchus sangbiensis). These species act as unstable 'wildcards' in morphological phylogenetic analyses, reducing phylogenetic resolution.

Results

We present new anatomical data for the type specimens of G. stipanicicorum, T. dabanensis, and Y. sangbiensis, and carry out a new morphological phylogenetic analysis of early archosaur relationships. Our results indicate that these three previously enigmatic taxa form a well-supported clade of Middle Triassic archosaurs that we refer to as Gracilisuchidae. Gracilisuchidae is placed basally within Suchia, among the pseudosuchian (crocodile-line) archosaurs. The approximately contemporaneous and morphologically similar G. stipanicicorum and Y. sangbiensis may be sister taxa within Gracilisuchidae.

Conclusions

Our results provide increased resolution of the previously poorly constrained relationships of early archosaurs, with increased levels of phylogenetic support for several key early pseudosuchian clades. Moreover, they falsify previous hypotheses suggesting that T. dabanensis and Y. sangbiensis are not members of the archosaur crown group. The recognition of Gracilisuchidae provides further support for a rapid phylogenetic diversification of crown archosaurs by the Middle Triassic. The disjunct distribution of the gracilisuchid clade in China and Argentina demonstrates that early archosaurs were distributed over much or all of Pangaea although they may have initially been relatively rare members of faunal assemblages.

Not Below 15%: Evidence of Wild Fires in Anisian & Ladinian Triassic Dolomites, Italy

Wildfires in the late Palaeozoic and Mesozoic of the Southern Alps—the Anisian and Ladinian (Mid Triassic) of the Dolomites (Northern Italy)

Authors:

Uhl et al

Abstract:

Based on anatomical studies of fossil charcoal fragments the first evidence for palaeo-wildfires is presented for the Anisian and Ladinian of the Dolomites (Northern Italy). These charcoals are from the localities Kühwiesenkopf/Monte Prà della Vacca (middle-upper Pelsonian, upper Anisian) and Ritberg/Ju Rit (Longobardian, upper Ladinian), and they help to fill a gap in our current scientific knowledge on the fossil record of Triassic wildfires worldwide. Charcoal reflectance values from Kühwiesenkopf are surprisingly high, indicating a palaeo-wildfire temperature of approximately 650 °C.

Chañares Formation is a SnapShot of a Ladinian Triassic Ecology

The Chañares Formation: a window to a Middle Triassic tetrapod community

Authors:

Mancuso et al

Abstract:

The Chañares Formation is known worldwide for its diverse and well-preserved Ladinian non-marine tetrapod assemblage, including a wide variety of archosauriform reptiles (proterochampsids, early offshoots of the crocodilian line and dinosaurian precursors) and synapsids represented by dicynodonts and cynodonts. This tetrapod record offers an opportunity to evaluate, within a taphonomic context, the palaeoecology of this Middle Triassic fauna. The taphonomic analysis of the Chañares assemblage, under precise stratigraphical control, indicates that it is a good representation of the original faunal composition allowing us to address the palaeoecological interactions between its components. Mass estimations and morphology-based palaeobiological inferences of Chañares tetrapods are used to reconstruct the trophic structure of the community. Chañares tetrapod fauna was numerically dominated by middle-sized herbivorous and small faunivorous cynodonts, whereas middle-sized faunivorous cynodonts and large dicynodonts were less common. In contrast to the therapsids, which show a low species-richness and high abundance, the archosauriforms are less abundant, but are the most taxonomically diverse group. The large paracrocodylomorphs (estimated body masses between 350 and 500 kg) are identified as the top predators of the community, and the traversodontid cynodonts and dicynodonts (estimated body masses reaching approximately 43 and 360 kg, respectively) are indentified as the base herbivores of the trophic pyramid. We conclude that the worldwide faunal composition in the Ladinian reveals two continental assemblages: an eastern Laurasian assemblage dominated by temnospondyl amphibians; and a western Gondwanan assemblage dominated by therapsids but including a wide diversity of archosauriforms.

New Exquisite Ladinian Triassic Nothosaurus youngi From Guizhou, China

A new specimen of Nothosaurus youngi from the Middle Triassic of Guizhou, China

Authors:

Ji et al

Abstract:

The Xingyi Fauna has been known widely for yielding abundant specimens of the pachypleurosaur sauropterygian Keichousaurus hui, the first Triassic marine reptile described from China (Young, 1958). Later stratigraphic studies placed it within the Zhuganpo Member of the Falang Formation (latest Ladinian, Middle Triassic) that is exposed across a wide area ranging from Dingxiao and Wusha (Xingyi, Guizhou Province) to Luoping and Fuyuan (Yunnan Province) (Li and Jin, 2003). Despite the extensive exposure of this unit, K. hui remained the only tetrapod from this fauna until the end of the last century, when limited progress was made in both taxonomic and stratigraphic studies. The situation changed during the last decade when a significant quantity of K. hui material was described in detail, in addition to eight new taxa of Triassic marine reptiles, i.e., Lariosaurus xingyiensis, Nothosaurus youngi, Tanystropheus sp., Yunguisaurus liae, Anshunsaurus wushaensis, Macrocnemus fuyuanensis, Glyphoderma kangi, and Qianxisaurus chajiangensis (Li et al., 2002, 2007; Li and Rieppel, 2004; Cheng et al., 2006, 2012; Rieppel et al., 2006, 2008; Zhao et al., 2008a, 2008b). However, precise stratigraphic and locality information still remained unknown for these new taxa, as well as the Xingyi Fauna at large.

Nothosaurus youngi was named by Li and Rieppel (2004) based on an incomplete skeleton from the Xingyi Fauna. It was characterized by the combination of the following features: pineal foramen located in a trough near the posterior end of the parietal, and the longitudinal diameter of the upper temporal fenestra nearly twice of that of the orbit. The postcranial osteology was only briefly described from the incompletely preserved skeleton, including the vertebrae and ribs, parts of the pelvic girdle, and a forelimb. Most of the pectoral girdle was overlapped by the gastralia, and no information was available for the hind limb.

Here, we describe a new specimen of Nothosaurus youngi that we recovered during an excavation of the fossiliferous levels of the Zhuganpo Member at Nimaigu village in the Wusha Town, Xingyi, Guizhou Province, South China, in 2011. The excavation provided us with precise knowledge of the locality and stratigraphic level of Xingyi Fauna for the first time (see below). The specimen is more complete than the holotype and provides new information on the postcranial osteology of N. youngi, which was not known when the species was erected.

Megalophthalma ockerti : A New Ladinian Triassic Plagiosaurid Temnospondyl From Germany

Skull morphology and phylogenetic relationships of a new Middle Triassic plagiosaurid temnospondyl from Germany, and the evolution of plagiosaurid eyes

Authors:

Schoch et al

Abstract:

A partial skull from the Lower Keuper (Middle Triassic) of Germany is recognized as belonging to a new genus and species of plagiosaurid temnospondyl. It is readily identified by the following autapomorphies: (1) extremely large orbits medially extended to give very thin interorbital region and cheek; (2) posterior skull table abbreviated, with splint-like supratemporals, postparietals and parietals; (3) supraorbital lateral line sulcus absent on frontal, with blind ending on parietal, and continued at the anterior margin of the postorbital; (4) occiput sloping posteriorly, with subtympanic fossa exposed in ventral view; (5) cultriform process and basicranial suture extremely narrow; (6) mandibular and maxillary teeth very long with crowns markedly curved inwards. The new taxon shares the following derived character states with Plagiosternum: (1) the pentagonal shape of orbits; (2) the slender interorbital region and cultriform process; (3) the small-scale, polygonal pit-and-ridge ornament on posterior skull table, with single prominent tubercles rising from ridges. Phylogenetic analysis finds plagiosaurids to be monophyletic within a broad range of temnospondyls, nesting within a clade of short-skulled stereospondyls. Plagio-suchus is the most basal plagiosaurid, and Plagiosternum forms the sister group to the new taxon. The biological significance of the large orbits of plagiosaurids and their relationships to the eyeballs is discussed. The only type of eyeball that would be feasible for all known plagiosaurids would be a small spherical structure possibly situated near the anterior edge of the orbit. For those plagiosaurs with extremely large shallow orbits like Plagiosternum and Megalophthalma, a possible adaptation would be a lens-less eye comprising a flat retinal plate across the entire orbit.

Italian Ladinian-Carnian Triassic Reefs Document Transition from Paleozoic- to Modern-type Reefs

Biogeochemical and redox record of mid-late Triassic reef evolution in the Italian Dolomites

Authors:

Tosti et al

Abstract:

Geochemical signatures and carbonate microfacies highlight contrasts between two distinctive mid-late Triassic reef communities in the Dolomite Alps, Italy. In the first community, sponges, bryozoans, calcified cyanobacteria and problematic organisms (Archaeolithoporella, Shamovella), together with a variety of micritic fabrics, formed compact reefs in high energy shallow-water at the margins of high-rise Ladinian-Carnian carbonate platforms. Debris from these margins created steep foreslopes, and some large blocks of the allochthonous material (Wengen-Cassian formations, Cipit Boulders) were buried in basinal shales that protected them from subsequent alteration and regional dolomitization. In the second and slightly younger community, small Carnian patch reefs (Heiligkreuz Formation, Alpe di Specie) developed in quieter shallow water, where they too were protected against alteration by enclosing shales. They were constructed mainly by scleractinian corals, sponges and red algae, and contain relatively large framework cavities with clotted-peloidal micrite. These early examples of coralgal reefs have broad similarities to present-day examples, whereas the community represented by the Cipit Boulders has more in common with Late Permian reefs.

Both bioconstructions preserve primary microfabrics and biomarkers. The Cipit Boulder samples contain bacterial, mainly cyanobacterial biomarkers, lack specific molecules typical of sulfate-reducing bacteria (SRB), and have Rare Earth Element (REE) values indicative of oxic conditions. These signatures are consistent with their original high-energy platform margin location, compact structure, and presence of calcified cyanobacteria such as Cladogirvanella and Girvanella. In contrast, the coralgal patch reefs contain SRB biomarkers, lack specific molecules typical of cyanobacteria, and have REE values indicative of sub-oxic conditions. These signatures are consistent with their lower energy depositional conditions and well-developed skeletal framework that created protected low-oxygen micro-habitats. The SRB biomarkers can be linked to the associated clotted-peloidal fabrics which resemble those commonly present in younger coral-reef frameworks. These details of redox conditions and bacterial processes underscore the important biotic, structural and environmental changes that affected shallow marine reefs during the Triassic.

Continental Collision Between Western/Eastern Qiangtang not Completed until Ladinian Triassic.

Late Triassic granitic magmatism in the Eastern Qiangtang, Eastern Tibetan Plateau: Geochronology, petrogenesis and implications for the tectonic evolution of the Paleo-Tethys

Authors:

Peng et al

Abstract:

Triassic granites are widely exposed in the central Qiangtang, northern Tibetan Plateau. They, therefore, made an important contribution to the growth of the Tibetan Plateau. In this paper, we present zircon U–Pb dating and Hf isotopic results, and whole-rock elemental and Sr–Nd isotopic analyses of the Dongdashan (DDS) batholith in the central Qiangtang in order to understand their petrogenesis and tectonic setting. LA-MC-ICP-MS zircon U–Pb results show that the DDS batholith was emplaced at 220.3 ± 0.7 Ma. All the granites in the DDS possess high A/CNK values (greater than 1.0) and display peraluminous characteristics, similar to S-type granite. Their strongly fractionated REE patterns ((La/Yb)N = 6.98–13.9) with conspicuous negative Eu anomalies (Eu*/Eu = 0.51–0.67), together with negative εNd(t) and εNd(t) values, and depleted Nd and Hf model ages, suggest that the DDS granitic magma had a dominantly crustal source, likely the Paleoproterozoic basement (i.e., the Ningduo and Caoqu group metasediments) in the area.

In combination with regional studies, our new geochemical data and geochronological results demonstrate that the Late Triassic magmatism was generated in a post-collisional tectonic setting. The spatial distribution pattern of the Mesozoic igneous rocks, coupled with the exhumation of high-pressure metamorphic rocks in the central Qiangtang, favors a slab breakoff model, which resulted in post-collisional extension and asthenospheric upwelling that induced large-scale partial melting of the middle-lower crust to produce voluminous amounts of felsic magma. Therefore, the occurrence of the Late Triassic post-collisional magmatism, and particularly the exhumation of high-pressure eclogites and blueschists as well as their presence in the lowermost portion of the Late Triassic volcanoclastics in the Qiangtang basin, clearly indicate that the final closure of the of Paleo-Tethys Ocean and associated continent-continent collision between the Gondwana-derived Western Qiangtang and Eastern Qiangtang terranes had not been completed until the early mid-Triassic.

Ladinian Through Rhaetian Triassic Carbon and Oxygen Isotope Record From the Tethyan Ocean

A Middle–Late Triassic (Ladinian–Rhaetian) Carbon and Oxygen isotope record from the Tethyan Ocean

Authors:

Muttoni et al

Abstract:

We obtained bulk-sediment δ18O and δ13C data from biostratigraphically-constrained Tethyan marine sections at Aghia Marina (Greece), Guri Zi (Albania), Brumano and Italcementi Quarry (Italy), and revise the published chemostratigraphy of the Pizzo Mondello section (Italy). We migrated these records from the depth to the time domain using available chronostratigraphic tie points, generating Ladinian–Rhaetian δ13C and δ18O records spanning from ~ 242 to ~ 201 Ma. The δ18O record seems to be affected by diagenesis, whereas the δ13C record appears to preserve a primary signal and shows values increasing by ~ 1‰ in the Ladinian followed by a ~ 0.6‰ decrease across the Ladinian–Carnian boundary, followed by relatively constant (but oscillatory) Carnian values punctuated by a negative excursion at ~ 233 Ma in the early Carnian, a second negative excursion at ~ 229.5 Ma across the early–late Carnian boundary, and a positive excursion at ~ 227 Ma across the Carnian–Norian boundary. The Norian record is characterized by a long-term decreasing trend and a negative excursion at ~ 216 Ma. Rapid increases and decreases in δ13C have been observed in the Rhaetian, but these may be at least in part due to mixing of different sources of carbonate carbon with different δ13C values. Our Triassic δ13C record has been compared to data from the literature, and a composite δ13C record spanning the last ~ 242 Myr of Earth’s history has been generated. This composite record shows a sequence of dated δ13C trends and events that can be used for stratigraphic correlation as well as for a better understanding of the global carbon cycle in the Mesozoic–Cenozoic.

Yunguisaurus: a new Specimen of the Ladinian Triassic Pistosauroid With Implications for Pleisosaur Origins

A new specimen of the Triassic pistosauroid Yunguisaurus, with implications for the origin of Plesiosauria (Reptilia, Sauropterygia)

Authors:

Sato et al

Abstract:

An adult skeleton of the pistosauroid sauropterygian Yunguisaurus liae reveals a number of morphological features not observed in the holotype, such as the complete morphology of the skull roof, stapes, atlas and axis, ventral view of the postcranium, and nearly complete limbs and tail. Size and morphological differences between the two specimens are mostly regarded as ontogenetic variation, and newly added data did not affect the phylogenetic relationships with other pistosauroids significantly. The number of mesopodia (11 carpals and 8 tarsals) exceeds that known in any other Triassic marine reptiles and does not serve as a precursor of the plesiosaurian pattern with fewer mesopodia of different topology; it demonstrates variability of the limb morphology among the Triassic pistosauroids. The pectoral girdles of Corosaurus, Augustasaurus and Yunguisaurus may indicate early stages of the adaptation towards the plesiosaurian style of paraxial limb movements with ventroposterior power stroke.

Wrangellian Volcanism in the Late Ladinian Caused the Biotic Crisis in the Carnian Triassic?

Cause of Upper Triassic climate crisis revealed by Re-Os geochemistry of Boreal black shales

Authors:

Xu et al

Abstract:

The Triassic Period is bracketed by two of the ‘big five’ Phanerozoic mass extinctions. Though long viewed as a period of climatic stability, emerging data suggest multiple climatic swings and at least one severe ecological crisis. Linking these climatic instabilities with probable causes is hampered by poor age control within the Triassic time scale. Here we present new Re-Os ages for shale sections straddling Middle-Upper Triassic stage boundaries. Nominal Re-Os isochron ages of 236.6 and 239.3 Ma for the top and base of the Ladinian (upper Middle Triassic) bring absolute time into the contentious Triassic time scale, and place the beginning of the Late Triassic about 12 m.y. earlier than previously assigned. A marked decrease in initial 187Os/188Os in Upper Ladinian shale records input from Wrangellian flood basalts – an instigator in the Carnian (Late Triassic) Pluvial Event and accompanying radiation of key fossil groups (e.g., dinosaurs and calcareous nanoplankton). An absolute time scale is proposed for the Anisian – Ladinian – Carnian boundaries based on Re-Os geochronology.

Ladinian/Carnian Triassic Dicynodont (Dinodontosaurus?) Communal Latrine Found in Argentina

The oldest known communal latrines provide evidence of gregarism in Triassic megaherbivores

Authors:

Fiorelli et al

Abstract:

Defecation in communal latrines is a common behaviour of extant mammals widely distributed among megaherbivores. This behaviour has key social functions with important biological and ecological implications. Herbivore communal latrines are only documented among mammals and their fossil record is exceptionally restricted to the late Cenozoic. Here we report the discovery of several massive coprolite associations in the Middle-Late Triassic of the Chañares Formation, Argentina, which represent fossil communal latrines based on a high areal density, small areal extension and taphonomic attributes. Several lines of evidence (size, morphology, abundance and coprofabrics) and their association with kannemeyeriiform dicynodonts indicate that these large synapsids produced the communal latrines and had a gregarious behaviour comparable to that of extant megaherbivores. This is the first evidence of megaherbivore communal latrines in non-mammal vertebrates, indicating that this mammal-type behaviour was present in distant relatives of mammals, and predates its previous oldest record by 220 Mya.

 

Euparkeria Grew Like a Warm Blooded Animal

Evidence for high bone growth rate in Euparkeria obtained using a new paleohistological inference model for the humerus

Authors:

Lucas J. Legendre, Loic Segalen & Jorge Cubo

Abstract:

The study of bone growth rate and metabolic rate evolution in archosaurs (crocodiles, dinosaurs including birds, and pterosaurs) and close outgroups has become a subject of major interest among paleontologists in recent years. In this paper, we estimate the bone growth rate of Euparkeria using a new statistical inference model for the humerus. We modified the taxonomic range of extant species used in previous studies, on which we performed quantitative measurements of histological features and bone growth rates. Bone growth rate values estimated for Euparkeria are crucial in understanding the ancestral condition for archosaurs because this taxon is considered the closest relative to the archosaur crown group. We obtained an instantaneous growth rate of 6.12 μm/day, suggesting that Euparkeria shared with other non-archosaurian archosauromorphs (Prolacerta, Proterosuchus, and Erythrosuchus) a condition of high growth rate compatible with endothermy. This derived state may have been inherited by some Triassic crurotarsans, as suggested by the high instantaneous bone growth rate (14.52 μm/day) estimated in this study for Postosuchus. Jurassic crurotarsans may have lost endothermy during the transition from terrestrial habitats and active predation to aquatic habitats and sit-and-wait predation behaviors, so that Cretaceous crocodiles may be secondarily ectothermic, as suggested by δ18O values. In conclusion, we provide new evidence for the hypothesis of an ancestral endothermic state for the last common ancestor of archosaurs, and show that non-archosaurian archosauromorphs and Triassic crurotarsans may have been characterized by a thermometabolism more similar to that of dinosaurs than to that of lepidosaurs and turtles.

A New Specimen of Shansisuchus shansisuchus From Ladinian Triassic China

A New Specimen of Shansisuchus shansisuchus Young, 1964 (Diapsida: Archosauriformes) from the Triassic of Shanxi, China

Authors:

WANG Runfu, XU Shichao, WU Xiaochun, LI Chun, WANG Suozhu

Abstract:

Shansisuchus shansisuchus Young, 1964 was restudied on the basis of a new specimen. Some anatomical features that were either briefly or not described at all in the original study were detailed. The new specimen not only provides further information on the skull anatomy and the vertebral column but also expands the range of the geographical distribution of the taxon. With new information, the diagnosis of S. shansisuchus was emended and its phylogenetic relationships were further analyzed. S. shansisuchus differs from other archosauriforms primarily in the presence of a large subnarial fenestra anterior to the antorbital fenestra, tongue-in-groove articulations between the ascending process of the premaxilla and nasal and between the premaxilla and maxilla, a tall and posterodorsally directed ascending process of the maxilla, a knee-shaped process of the postorbital projecting into the orbit, a broad descending process of squamosal distally well forked and a large, deeply bow-shaped intercentrum tightly anchoring/capping the sharp ventral edges of two neighboring centra together in cervical and at least first eight dorsal vertebrae. With additional information derived from the new specimen, the phylogenetic relationships of S. shansisuchus were reanalyzed; it is closely related to Erythrosuchus-Vjushkovia clade.

Saurichthys curionii : A Ladinian Triassic Fish With Unique Body Elongation Strategy

Snake and eel bodies are elongated, slender and flexible in all three dimensions. This striking body plan has evolved many times independently in the more than 500 million years of vertebrate animals history. Based on the current state of knowledge, the extreme elongation of the body axis occurred in one of two ways: either through the elongation of the individual vertebrae of the vertebral column, which thus became longer, or through the development of additional vertebrae and associated muscle segments.

A team of paleontologists from the University of Zurich headed by Professor Marcelo Sánchez-Villagra now reveal that a third, previously unknown mechanism of axial skeleton elongation characterized the early evolution of fishes, as shown by an exceptionally preserved form. Unlike other known fish with elongate bodies, the vertebral column of Saurichthys curionii does not have one vertebral arch per myomeric segment, but two, which is unique. This resulted in an elongation of the body and gave it an overall elongate appearance. "This evolutionary pattern for body elongation is new," explains Erin Maxwell, a postdoc from Sánchez-Villagra's group. "Previously, we only knew about an increase in the number of vertebrae and muscle segments or the elongation of the individual vertebrae."

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