Top fossils discoveries of 2018.

Ingentia prima outcropping from the soil.

Paraphrasing Dickens, 2018 was the best of years, and it was the worst of years. Marked by extreme weather, earthquakes, and an intense volcanic activity, 2018 is also noted by amazing fossil discoveries. My top list include:

  • The oldest Archaeopteryx

Articulated dorsal vertebral column of the new Archaeopteryx, including dorsal ribs and gastralia. Scale bar is 10 mm. (From Rauhut et al., 2018)

The Archaeopteryx story began in  the summer of 1861, two years after the publication of the first edition of Darwin’s Origin of Species, when workers in a limestone quarry in Germany discovered the impression of a single 145-million-year-old feather. Over the years, eleven Archaeopteryx specimens has being recovered. The new specimen from the village of Schamhaupten, east-central Bavaria is the oldest representative of the genus (earliest Tithonian). The shoulder girdles and arms, as well as the skull have been slightly dislocated from their original positions, but the forelimbs remain in articulation. The skull is triangular in lateral outline and has approximately 56 mm long. The orbit is the largest cranial opening (approximately 16 mm long), and the lateral temporal fenestra is collapsed. There are probably four tooth positions in the premaxilla, nine in the maxilla and 13 in the dentary. The postcranial skeleton was affected by breakage and loss of elements prior to or at the time of discovery.

  • Tratayenia rosalesi

Fossilized vertebrae and right hip bone of Tratayenia rosalesi. From Porfiri et al., 2018

Patagonia has yielded the most comprehensive fossil record of Cretaceous theropods from Gondwana, including Megaraptora, a clade of medium-sized and highly pneumatized theropods represented by Fukuiraptor, Aerosteon, Australovenator, Megaraptor, Murusraptor, and Orkoraptor, and characterized by the formidable development of their manual claws on digits I and II and the transversely compressed and ventrally sharp ungual of the first manual digit. Tratayenia rosalesi is the first megaraptoran theropod described from the Santonian Bajo de la Carpa Formation of the Neuquén Group. The genus name is for Tratayén, the locality where the holotype was collected. The specific name honors Diego Rosales, who discovered the specimen in 2006. Tratayenia is also the largest carnivorous taxon known from Bajo de la Carpa Formation, reinforcing the hypothesis that megaraptorids were apex predators in South America from the Turonian through the Santonian or early Campanian, following the extinction of carcharodontosaurids.

  • Lingwulong shenqi

Skeletal reconstruction and exemplar skeletal remains of Lingwulong shenqi. Scale bars = 100 cm for a and 5 cm for b–o. From Xi et al., 2018

Sauropods were the largest terrestrial vertebrates. Their morphology is easy recognizable: a long, slender neck and a tail at the end of a large body supported by four columnar limbs. Sauropods dominated many Jurassic and Cretaceous terrestrial faunas. Although they were globally distributed, the absence of Diplodocoidea from East Asia has been interpreted as a biogeographic pattern caused by the Mesozoic fragmentation of Pangea. Lingwulong shenqi — literally the “amazing dragon from Lingwu” — is the first well-preserved confirmed diplodocoid from East Asia (23 synapomorphies support the placement of Lingwulong within Diplodocoidea with 10 of these being unequivocal). The holotype, (LM) V001a, is a partial skull comprising the braincase, skull roof, and occiput, and an associated set of dentary teeth. The paratype, (LGP) V001b, comprises a semi-articulated partial skeleton including a series of posterior dorsal vertebrae, complete sacrum, the first caudal vertebra, partial pelvis, and incomplete right hind limb. The Lingwulong specimens were found in the Yanan Formation at Ciyaopu, in northwest China. The presence of a conchostracans assemblage (including Palaeoleptoestheria, Triglypta, and Euestheria) is indicative of a Middle Jurassic age. The discovery of Lingwulong undermines the EAIH (East Asian Isolation Hypothesis), forcing a significant revision of hypotheses concerning the origins and early radiation of Neosauropoda.

  • Ingentia prima

Skeletal anatomy of Ingentia prima (From Apaldetti et al., 2018)

Ingentia prima — literally the “first giant” in Latin — from the Late Triassic of Argentina shed new lights on the origin of gigantism in this group. The holotype, PVSJ 1086, composed of six articulated posterior cervical vertebrae, glenoid region of right scapula and right forelimb lacking all phalanges, has been recovered from the southern outcrops of the Quebrada del Barro Formation, northwestern Argentina. Discovered in 2015 by Diego Abelín and a team led by Cecilia Apaldetti of CONICET-Universidad Nacional de San Juan, Argentina, this new fossil weighed up to 11 tons and measured up to 32 feet (10 meters) long. Ingentia was unearthed with three new specimens of Lessemsaurus sauropoides. The four dinosaurs belongs to the clade Lessemsauridae, that differs from all other Sauropodomorpha dinosaurs in possessing robust scapulae with dorsal and ventral ends equally expanded; slit-shaped neural canal of posterior dorsal vertebrae; anterior dorsal neural spines transversely expanded towards the dorsal end; a minimum transverse shaft width of the first metacarpal greater than twice the minimum transverse shaft of the second metacarpal; and bone growth characterized by the presence of thick zones of highly vascularized fibrolamellar bone, within a cyclical growth pattern.

  • Caelestiventus hanseni

A 3D printed model of the C. hanseni skull discovered in Utah

Caelestiventus hanseni, from the Upper Triassic of North America, is the oldest pterosaur ever discovered, and it predates all known desert pterosaurs by more than65 million years. The holotype, BYU 20707, includes the left maxilla fused with the jugal, the right maxilla, the right nasal, the fused frontoparietals, the right and left mandibular rami, the right terminal wing phalanx and three fragments of indeterminate bones. The maxilla, jugal, frontoparietal, and mandibular rami of the specimen are pneumatic. The unfused skull and mandibular elements suggest that BYU 20707 was skeletally immature or had indeterminate growth. Based on the relationship between the length of the terminal wing phalanges and wing span in other non-pterodactyloid pterosaurs the new taxon would have a wing span greater than 1.5 m. The significance of C. hanseni lies in its exceptional state of preservation, and its close phylogenetic relationship with Dimorphodon macronyx, indicating that dimorphodontids originated by the Late Triassic and survived the end-Triassic extinction event.

  • Macrocollum itaquii

Skull of Macrocollum itaquii (From Müller et al 2018)

Macrocollum itaquii is the oldest long-necked dinosaur known. Discovered in 2012, from rocks belonging to the upper part of the Candelaria Sequence constrained as about 225 Ma, the three individuals described as M. itaquii are relatively well preserved. The holotype specimen (CAPPA/UFSM 0001a) consists of an almost complete and articulated skeleton. The two paratype specimens (CAPPA/UFSM 0001b and CAPPA/UFSM 0001c) are both articulated skeletons with one missing a skull and its cervical series. The clustered preservation of the three skeletons also represents the oldest evidence of gregarious behaviour in sauropodomorphs, a pattern seen in other Triassic associations, such as the ‘Plateosaurus bonebed’ from Central Europe, and the Mussaurus remains from the Laguna Colorada Formation, Argentina. M. itaquii was only 3.5 meters long and weighed about 101.6 kilograms. In contrast to most Carnian members of the group, the teeth of M. itaquii and other Norian taxa are fully adapted to an omnivore/herbivore diet. The neck elongation may also have provided a competitive advantage for gathering food resources, allowing members of the group to reach higher vegetation. The modifications of the hindlimb of M. itaquii could be related to the progressive loss of cursorial habits.

  • Soft-tissue evidence in a Jurassic ichthyosaur.

Stenopterygius specimen from the Holzmaden quarry. Credit: Johan Lindgren

During the Norian, the evolution of ichthyosaurs took a major turn, with the appearance of the clade Parvipelvia (ichthyosaurs with a small pelvic girdle). They were notably similar in appearance to extant pelagic cruisers such as odontocete whales. An exquisitely fossilized parvipelvian Stenopterygius from the Early Jurassic (Toarcian) of the Holzmaden quarry in southern Germany, indicates that their resemblance with dolphin and whales is more than skin deep. The specimen (MH 432; Urweltmuseum Hauff, Holzmaden, Germany) reveals endogenous cellular, sub-cellular and biomolecular constituents within relict skin and subcutaneous tissue. The external surface of the body is smooth, and was presumably comparable in life to the skin of extant cetaceans. The histological and microscopic examination of the fossil, evinced a multi-layered subsurface architecture. The approximately 100-μm-thick epidermis retains cell-like structures that are likely to represent preserved melanophores. The subcutaneous layer is over 500 μm thick, and comprises a glossy black material superimposed over a fibrous mat. The anatomical localization, chemical composition and fabric of the subcutaneous material is interpreted as fossilized blubber, a hallmark of warm-blooded marine amniotes.

  • Pterosaurs and feathers

 

Type 3 filaments (arrows) and similar structures (triangles). Scale bars: 10 mm in a, c and d; 1 mm in b. From Yang et al., 2018

Feathers were once considered to be unique avialan structures. Recent studies indicated that non avian dinosaurs, as part of Archosauria, possessed the entirety of the known non keratin protein-coding toolkit for making feathers. Primitive theropods, such as Sinosauropteryx and the tyrannosaurs Dilong and Yutyrannus, and some plant-eating ornithischian dinosaurs, such as Tianyulong and Kulindadromeus, are known from their spectacularly preserved fossils covered in simple, hair-like filaments called ‘protofeathers’. Other integumentary filaments, termed pycnofibres, has been reported in several pterosaur specimens, but there is still a substantial disagreement regarding their interpretation. J. Yang and colleagues described two specimens of short-tailed pterosaurs (NJU–57003 and CAGS–Z070) from the Middle-Late Jurassic Yanliao Biota, in northeast China (around 165-160 million years ago) with preserved structural fibres (actinofibrils) and four different types of pycnofibres. The specimens resemble Jeholopterus and Dendrorhynchoides, but they are relatively small. Pterosaurs were winged cousins of the dinosaurs and lived from around 200 million years ago to 66 million years ago. In the early 1800’s, a fuzzy integument was first reported from the holotype of Scaphognathus crassirostris. A recent study on this specimen shows a subset of pycnofibers and actinofibrils. The discovery of integumentary structures in other pterosaurs, such as Pterorhynchus wellnhoferi(another rhamphorhynchoid pterosaur), and these exquisitely preserved pterosaurs from China, suggest that all Avemetatarsalia (the wide clade that includes dinosaurs, pterosaurs and close relatives) were ancestrally feathered.

References:

Rauhut OWM, Foth C, Tischlinger H. (2018The oldest Archaeopteryx (Theropoda: Avialiae): a new specimen from the Kimmeridgian/Tithonian boundary of Schamhaupten, BavariaPeerJ 6:e4191 https://doi.org/10.7717/peerj.4191

Porfiri, J.D., Juárez Valieri, Rubé.D., Santos, D.D.D., Lamanna, M.C., A new megaraptoran theropod dinosaur from the Upper Cretaceous Bajo de la Carpa Formation of northwestern Patagonia, Cretaceous Research (2018), doi: 10.1016/j.cretres.2018.03.014.

Xing Xu, Paul Upchurch, Philip D. Mannion, Paul M. Barrett, Omar R. Regalado-Fernandez, Jinyou Mo, Jinfu Ma and Hongan Liu. 2018. A New Middle Jurassic Diplodocoid Suggests An Earlier Dispersal and Diversification of Sauropod Dinosaurs. Nature Communications.9, 2700.  DOI:  10.1038/s41467-018-05128-1 

Cecilia Apaldetti, Ricardo N. Martínez, Ignacio A. Cerda, Diego Pol and Oscar Alcober (2018). An early trend towards gigantism in Triassic sauropodomorph dinosaurs. Nature Ecology & Evolution. https://doi.org/10.1038/s41559-018-0599-y

Brooks B. Britt et al. Caelestiventus hanseni gen. et sp. nov. extends the desert-dwelling pterosaur record back 65 million years, Nature Ecology & Evolution (2018). DOI: 10.1038/s41559-018-0627-y

Müller RT, Langer MC, Dias-da-Silva S. 2018, An exceptionally preserved association of complete dinosaur skeletons reveals the oldest long-necked sauropodomorphs. Biol. Lett. 14: 20180633. http://dx.doi.org/10.1098/rsbl.2018.0633

Lindgren, J., Sjövall, P., Thiel, V., Zheng, W., Ito, S., Wakamatsu, K., … Schweitzer, M. H. (2018). Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur. Nature. doi:10.1038/s41586-018-0775-x

Yang Z. et al., 2018. Pterosaur integumentary structure with complex feather-like branching. Nature Ecology and Evolution https://doi.org/10.1038/s41559-018-0728-7

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Introducing Macrocollum itaquii.

M. itaquii, the oldest long-necked dino ever found, dating back 225 million years. (Credit: Müller et al 2018)

Sauropodomorphs were the largest land animals ever recorded in the history of life. Additionally to their colossal size, the sauropodomorph bauplan is also characterised by a small head, long neck, barrel-shaped body and columnar limbs. The group was successful and diverse, achieving a worldwide geographical distribution. Nevertheless, the rise of sauropodomorphs is still poorly understood due to the scarcity of well-preserved fossils in early Norian rocks. The Wachholz site (Caturrita Formation), in southern Brazil, is an important window to early Norian land ecosystems. This unit has yielded several sauropodomorphs, including Unaysaurus tolentinoi and the recently described Macrocollum itaquii, the oldest long-necked dinosaur known, that shed light on the rise of the group.

Discovered in 2012, from rocks belonging to the upper part of the Candelaria Sequence constrained as about 225 Ma, the three individuals described as M. itaquii are relatively well preserved. The holotype specimen (CAPPA/UFSM 0001a) consists of an almost complete and articulated skeleton. The two paratype specimens (CAPPA/UFSM 0001b and CAPPA/UFSM 0001c) are both articulated skeletons with one missing a skull and its cervical series. The clustered preservation of the three skeletons also represents the oldest evidence of gregarious behaviour in sauropodomorphs, a pattern seen in other Triassic associations, such as the ‘Plateosaurus bonebed’ from Central Europe, and the Mussaurus remains from the Laguna Colorada Formation, Argentina.

 

Skull of Macrocollum itaquii (From Müller et al 2018)

The generic name combines the Greek word macro (long) and the Latin word collum (neck), referring to the animal’s elongated neck. The specific epithet honours José Jerundino Machado Itaqui, one of the main actors behind the creation of CAPPA/UFSM (Centro de Apoio à Pesquisa Paleontológica da Quarta Colônia/Universidade Federal de Santa Maria).

M. itaquii was only 3.5 meters long and weighed about 101.6 kilograms, and differs from all other known sauropodomorphs in possessing the following characters: antorbital fossa perforated by a promaxillary fenestra; medial margin of the supratemporal fossa with a simple smooth curve at the frontal/parietal suture; proximal articular surface of metacarpal I transversely narrow; acetabulum not fully open; ischiadic longitudinal groove not reaching the caudal half of the ischium; absence of trochanteric shelf on the femur; medial condyle of distal femoral articulation subrectangular in distal view; proximal end of metatarsal II with a straight medial margin.

An artist’s impression of M. itaquii.

In contrast to most Carnian members of the group, the teeth of M. itaquii and other Norian taxa are fully adapted to an omnivore/herbivore diet. The neck elongation may also have provided a competitive advantage for gathering food resources, allowing members of the group to reach higher vegetation. The modifications of the hindlimb of M. itaquii could be related to the progressive loss of cursorial habits.

 

References:

Müller RT, Langer MC, Dias-da-Silva S. 2018, An exceptionally preserved association of complete dinosaur skeletons reveals the oldest long-necked sauropodomorphs. Biol. Lett. 14: 20180633. http://dx.doi.org/10.1098/rsbl.2018.0633

 

 

Triassic World: Rise of the Kingdom

Eoraptor lunensis, outcropping from the soil. Valle de la Luna (Moon Valley), Parque Provincial Ischigualasto, Provincia de San Juan, Argentina.

“Jurassic World: Fallen Kingdom” has finally been released, but don’t worry, this post is spoiler free. I just use the hype to the tell the story of the rise of dinosaurs to ecological dominance.

There have been many opinions about the origin of the dinosaurs. In the competitive model the success of dinosaurs was explained in terms of their upright posture, predatory skills, or warm-bloodedness. In the opportunistic model, dinosaurs emerged in the late Carnian or early Norian, and then diversified explosively. The current view contains some aspects of both the classic competition model and the opportunistic model. In this model, the crurotarsan-dominated faunas were replaced by a gradual process probably accelerated by the ecological perturbation of the CPE (Carnian Pluvial Episode).

Early-late Carnian (Late Triassic) palaeogeographic reconstruction showing some of the main vertebrate-bearing units (From Bernardi et al. 2018)

The CPE is often described as a shift from arid to more humid conditions (global warming, ocean acidification, mega-monsoonal conditions, and a generalised increase in rainfall). The widespread extinction caused by the CPE was followed by the first substantial diversification of dinosaurs. That diversification can in fact be
divided into three phases: (1) the possible origin in the Olenekian-Anisian (248–245 Ma) related to the turmoil of recovering life in the aftermath of the devastating Permian-Triassic mass extinction (PTME), (2) a rapid diversification of saurischians, primarily sauropodomorphs and possible theropods, termed the dinosaur diversification event (DDE), at 232 Ma, and (3) a further diversification of theropods and especially ornithischians after the end-Triassic mass extinction, 201 Ma.

In Tanzania, the Manda Beds yielded the remains of the possible oldest dinosaur, Nyasasaurus parringtoni, and Asilisaurus, a silesaurid (the immediate sister-group to Dinosauria). However the oldest well-dated identified dinosaurs are from the late Carnian of the lower Ischigualasto Formation in northwestern Argentina, dated from 231.4 Ma to 225.9 Ma. Similarly, the Santa Maria and Caturrita formations in southern Brazil preserve basal dinosauromorphs, basal saurischians, and early sauropodomorphs. In North America, the oldest dated occurrences of vertebrate assemblages with dinosaurs are from the Chinle Formation. Two further early dinosaur-bearing formations, are the lower (and upper) Maleri Formation of India and the Pebbly Arkose Formation of Zimbabwe. These skeletal records of early dinosaurs document a time when they were not numerically abundant, and they were still of modest body size (Eoraptor had a slender body with an estimated weight of about 10 kilograms).

 

Mounted skeleton of Plateosaurus engelhardti (almost complete specimen AMNH FARB 6810 from Trossingen, Germany)

The CPE is one of the most severe biotic crises in the history of life. On land, palaeobotanical evidence shows a shift of floral associations of towards elements more adapted to humid conditions (the palynological record across the CPE suggest at least 3–4 discrete humid pulses). Several families and orders make their first appearance during the Carnian: bennettitaleans, modern ferns, and conifer families (Pinaceae, Araucariaceae, Cheirolepidaceae). The oldest biological inclusions found preserved in amber also come from the Carnian; and key herbivorous groups such as dicynodonts and rhynchosaurs, which had represented 50% or more of faunas, disappeared.

The DDE likely occurred in steps. Followed the extinction of rhynchosaurs in most, or all, parts of the world, there was a burst of dinosaurian diversity in the late Carnian, represented by the upper Ischigualasto Formation and coeval units, with mostly carnivorous small- to medium-sized dinosaurs. Then, the long span of the early Norian, from 228.5–218 Ma, during which dicynodonts and sauropodomorph dinosaurs were the major herbivores. Finally, with the disappearance of dicynodonts, sauropodomorph dinosaurs became truly large in the middle and late Norian, from 218 Ma. This was followed by the extinction of basal archosaur groups during the end-Triassic mass extinction, 201 Ma, and the diversification of sauropods, larger theropods, ornithopods, and armoured dinosaurs subsequently, in the Jurassic.

 

References:

Michael J. Benton et al. The Carnian Pluvial Episode and the origin of dinosaurs, Journal of the Geological Society (2018). DOI: 10.1144/jgs2018-049

Massimo Bernardi et al. Dinosaur diversification linked with the Carnian Pluvial Episode, Nature Communications (2018). DOI: 10.1038/s41467-018-03996-1

Jessica H. Whiteside, Sofie Lindström, Randall B. Irmis, Ian J. Glasspool, Morgan F. Schaller, Maria Dunlavey, Sterling J. Nesbitt, Nathan D. Smith, and Alan H. Turner. 2015. Extreme ecosystem instability suppressed tropical dinosaur dominance for 30 million years. PNAS: doi:10.1073/pnas.1505252112

On the rise of the archosauromorphs

Proterosaurus speneri at Teyler’s Museum.

In the aftermath of the devastating Permo-Triassic mass extinction (~252 Ma), synapsid groups such as anomodonts and gorgonopsians and parareptiles such as pareiasaurs, were decimated and largely displaced by the archosauromorphs. The group, which include the ‘ruling reptiles’ (crocodylians, pterosaurs, dinosaurs, and their descendants, birds), originated during the middle–late Permian. The most basal archosauromorphs are Aenigmastropheus and Protorosaurus.

During the Triassic, the archosauromorphs achieved high morphological diversity, including aquatic or semi aquatic forms, highly specialized herbivores, massive predators, armoured crocodile-like forms, and gracile dinosaur precursors. The group constitutes an excellent empirical case to shed light on the recovery of terrestrial faunas after a mass extinction.

The Permian-Triassic boundary at Meishan, China (Photo: Shuzhong Shen)

The massive volcanic eruptions in Siberia at the end of the Permian, covered more than 2 millions of km 2 with lava flows, releasing more carbon in the atmosphere. High amounts of fluorine and chlorine increased the climatic instability, which means that the Mesozoic began under extreme hothouse conditions. Isotope studies and fossil record, indicates that temperatures in Pangaea interiors during the Early Triassic oscillated between 30 and 40 degrees Celsius, with heat peaks in the Induan and during the Early and Late Olenekian. It was suggested that during that time there was a moderate oxygen depletion that caused the low body size of the amphibian and reptilian life-forms found in those rocks.

After the mass extinction event, a distributed archosauromorph ‘disaster fauna’ dominated by proterosuchids, established for a short time. In South Africa, Proterosuchus occurs only between 5 and 14 m above the PT boundary and a similar pattern has been documented for the synapsid Lystrosaurus. During the Olenekian (1–5 million years after the extinction), archosauromorphs underwent a major phylogenetic diversification with the origins or initial diversification of major clades such as rhynchosaurs, archosaurs, erythrosuchids and tanystropheids.

Stenaulorhynchus stockleyi, a rhynchosaur from the Middle Triassic (From Wikimedia Commons)

The Mid Triassic is marked by the return of conifer-dominated forests, and the end of an interval of intense carbon perturbations, suggesting the recovery and stabilization of global ecosystems. The Anisian (5–10 Myr after the extinction) is characterized by a high diversity among the archosauromorphs with the appearance of large hypercarnivores, bizarre and highly specialized herbivores, long-necked marine predators, and gracile and agile dinosauromorphs. This phylogenetic diversity of archosauromorphs by the Middle Triassic paved the way for the ongoing diversification of the group (including the origins of dinosaurs, crocodylomorphs, and pterosaurs) in the Late Triassic, and their dominance of terrestrial ecosystems for the next 170 million years.

 

 

References:

Ezcurra MD, Butler RJ. 2018 The rise of the ruling reptiles and ecosystem recovery from the Permo-Triassic mass
extinction. Proc. R. Soc. B 285: 20180361. http://dx.doi.org/10.1098/rspb.2018.0361

Ezcurra MD. (2016) The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms. PeerJ 4:e1778 https://doi.org/10.7717/peerj.1778

Holz, M., Mesozoic paleogeography and paleoclimates – a discussion of the diverse greenhouse and hothouse conditions of an alien world, Journal of South American Earth Sciences (2015), doi: 10.1016/j.jsames.2015.01.001

Introducing Shringasaurus indicus

Cranial anatomy of Shringasaurus indicus (From Sengupta et al., 2017)

In the aftermath of the Permo-Triassic mass extinction (~252 Ma), well diversified archosauromorph groups appear for the first time in the fossil record, including aquatic or semi aquatic forms, highly specialized herbivores, and massive predators. Allokotosaurians, meaning “strange reptiles” in Greek, comprise a bizarre suite of herbivorous archosauromorphs with a high disparity of craniodental features.

Shringasaurus indicus, from the early Middle Triassic of India, is a new representative of the Allokotosauria. The generic name is derived from ‘Śṛṅga’ (Shringa), horn (ancient Sanskrit), and ‘sauros’ (σαῦρος), lizard (ancient Greek), referring to the horned skull.  The species name ‘indicus’, refers to the country where it was discovered. The holotype ISIR (Indian Statistical Institute, Reptile, India) 780, consist of a partial skull roof (prefrontal, frontal, postfrontal, and parietal) with a pair of large supraorbital horns. The fossil bones have been collected from the Denwa Formation of the Satpura Gondwana Basin. At least seven individuals of different ontogenetic stages were excavated in the same area. Most of them were disarticulated, with exception of a partially articulated skeleton.

Skeletal anatomy of Shringasaurus indicus (From Sengupta et al., 2017)

Shringasaurus reached a relatively large size (3–4 m of total length) that distinctly exceeds the size range of other Early-Middle Triassic archosauromorphs. This new species shows convergences with sauropodomorph dinosaurs, including the shape of marginal teeth, and a relative long neck.  

Shringasaurus has a proportionally small skull with a short, rounded snout and confluent external nares. The premaxilla lacks a prenarial process and has four tooth positions. The prefrontal, nasal, frontal, and postfrontal of each side of the skull are fused to each other in large individuals. But the most striking feature of Shringasaurus indicus is the presence of a pair of large supraorbital horns, ornamented by tangential rugosities and grooves. Individuals of Shringasaurus of different ontogenetic stages indicate the size and robustness of the horns were exacerbated towards the adulthood, with a distinct variability in their orientation and anterior curvature in large individuals. Several amniotes have horns very similar to those of Shringasaurus (e.g. bovid mammals, chamaeleonid lepidosaurs). The independent evolution of similar horn shapes and robustness among different groups can be explained as the result of sexual selection.

References:

Saradee Sengupta, Martín D. Ezcurra and Saswati Bandyopadhyay. 2017. A New Horned and Long-necked Herbivorous Stem-Archosaur from the Middle Triassic of India. Scientific Reports. 7, Article number: 8366. DOI: s41598-017-08658-8

Ezcurra MD. (2016The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriformsPeerJ 4:e1778 https://doi.org/10.7717/peerj.1778

 

A Unique Late Triassic Dinosauromorph Assemblage from Brazil

The skull of Buriolestes shultzi. (Image credit: Cabreira et al., 2016)

The skull of Buriolestes shultzi. (Image credit: Cabreira et al., 2016)

The Santa Maria Formation in southern Brazil, comprises a succession of Middle to Late Triassic sedimentary rocks that have been long renowned for their rich tetrapod fossils including one of the oldest (and the best preserved) associations of dinosaur and dinosaur precursor, respectively represented by new species of Lagerpetidae and Sauropodomorph.

The lagerpetids, a family of basal dinosauromorphs, are represented by a semi-articulated skeleton and a pair of fragmentary femora. As for the dinosaurs, a large articulated individual was preserved, together with smaller and non-duplicated bone elements that indicate the presence of another individual The two articulated specimens are named  Ixalerpeton polesinensis and Buriolestes shultzi.

Ixalerpeton polesinensis helps to define traits of anatomical parts previously unknown for lagerpetids. For example, a skull roof broader than that of most early dinosaurs, an anterior tympanic recess in the braincase, as is typical of Dinosauriforme, although retains traits unknown to that group, such as a large post-temporal fenestra, a postfrontal bone, and a frontal not excavated by the supratemporal fossa.

A: Skeletal reconstruction of Ixalerpeton polesinensis. B: Skull roof. C: Braincase. (Adapted from Cabreira et al., 2016)

A: Skeletal reconstruction of Ixalerpeton polesinensis. B: Skull roof. C: Braincase. Abbreviations: f, frontal; fm, foramen magnum; p, parietal; pof, postfrontal; pp, paroccipital process; so, supraoccipital. (Adapted from Cabreira et al., 2016)

 

Buriolestes shultzi is the earliest member of Sauropodomorpha, although lacks usual sauropodomorph traits such as a reduced skull and an enlarged external naris, and as in all early dinosaurs, the frontal is excavated by the supratemporal fossa. As typical of sauropodomorphs, the humerus is longer than 60% the length of the femur, and the deltopectoral crest extends for more than 40% of its length. The dentary traits are compatible with a faunivorous diet suggesting that early members of the Sauropodomorpha were likely predators.

The fossils, found by a team from the Lutheran University of Brazil, confirms that the co-occurrence between non-dinosaurian Dinosauromorpha and dinosaurs was not restricted to later stages of the Triassic and to the northern parts of Pangaea, suggesting that a rapid replacement was a very unlikely scenario for the initial radiation of dinosaurs.

References:

Cabreira et al., A Unique Late Triassic Dinosauromorph Assemblage Reveals Dinosaur Ancestral Anatomy and Diet, Current Biology (2016), http://dx.doi.org/10.1016/j.cub.2016.09.040

Langer, M.C., Nesbitt, S.J., Bittencourt, J.S., and Irmis, R.B. (2013). Non-dinosaurian Dinosauromorpha. Geol. Soc. Spec. Publ. 379, 157–186.

The Chañares Formation and the origin of dinosaurs.

The Chañares Formation (© 2012 Idean)

The Chañares Formation (© 2012 Idean)

The Chañares Formation crops out in the Ischigualasto-Villa Unión Basin, formed along the western margin of South America  during the  breakup  of  Gondwana. It represents one of the most continuous continental Triassic succesions in South America. These beds were explored by Alfred Romer and Jensen (1966) in their report on the geology of the Rio Chañares and Rio Gualo region.

Located in Talampaya National Park (La Rioja Province), the Chañares Formation is characterized at its base by a sandstone–siltstone fluvial facies with distinct lower and upper levels. The lower levels are composed of light olive grey fine-grained sandstones with abundant small brown carbonate concretions. The upper levels include fine-grained sandstones and siltstones that preserve vertebrate remains (Mancuso et al., 2014).

Geological map of the Chañares–Gualo area in Talampaya National Park (From Marsicano et al., 2015)

Geological map of the Chañares–Gualo area in Talampaya National Park (From Marsicano et al., 2015)

Volcanism played an important role in the generation and preservation of the Chañares Formation’s exceptional tetrapod fossil record. The diverse and well-preserved tetrapod assemblage includes proterochampsids, pseudosuchians, ornithodirans, large dicynodonts and smaller cynodonts. Almost all dinosauromorphs are preserved in diagenetic concretions that erode out of a thick siltstone interval 15–20 m above the base of the formation, and include Lagosuchus talampayensis, Marasuchus lilloensis Lewisuchus admixtus and Pseudolagosuchus major.

Analysing the ratio of U–Pb inside the zircon crystals found in the rocks assigns the Chañares Formation to the Late Triassic, specifically the early Carnian (236–234 Ma), between 5 to 10 million years younger than previous estimate. This also suggests a similarly age for the lower Santa Maria Formation in southern Brazil, because it shares with the Chañares assemblage a variety of tetrapod genera and species unknown from anywhere else. The new results provide the basis to construct a robust framework for calibrating the timing of macro-evolutionary patterns related to the origin and early diversification of dinosaurs in Gondwana (Marsicano et al., 2015). It also suggests there was little compositional difference between the Chañares assemblage and the earliest dinosaur assemblage from the lower part of the Ischigualasto succession, where dinosauromorphs (including dinosaurs) are a minority, with synapsids still dominant. Only 15 million years later dinosaurs begin to dominate the ecosystem.

Artist’s reconstruction of the Chanares environment during the Middle Triassic. (From Mancusso et al., 2014. Art by Jorge Fernando Herrman.)

Artist’s reconstruction of the Chanares environment during the Middle Triassic. (From Mancusso et al., 2014. Art by Jorge Fernando Herrman.)

 

References:

Marsicano, C. A., Irmis, R. B., Mancuso, A. C., Mundil, R. & Chemale, F., The precise temporal calibration of dinosaur origins, Proc. Natl Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1512541112 (2015).

Brusatte SL, et al. (2010) The origin and early radiation of dinosaurs. Earth Sci Rev 101:68100.

Mancuso AC, Gaetano LC, Leardi JM, Abdala F, Arcucci AB (2014) The ChañaresFormation: A window to a Middle Triassic tetrapod community. Lethaia 47:244265.

Romer AS, Jensen J (1966) The Chañares (Argentina) Triassic reptile fauna. II. Sketch of the geology of the Rio Chañares, Rio Gualo region. Breviora 252:1–20.