Top fossils discoveries of 2017

 

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

On April 22, 2017, the March for Science reunited more than a million persons worldwide to protest against the attack on science, budget cuts and censorship. A fight that doesn’t over yet. But despite all that, 2017 was also an extraordinary year for palaeontological discoveries. My top list includes:

• Borealopelta

Holotype of Borealopelta markmitchelli

Borealopelta markmitchelli, from the Early Cretaceous of Alberta, is a three-dimensionally preserved ankylosaurian,  discovered in the Suncor Millennium Mine in Canada. The generic name Borealopelta is derived from “borealis” (Latin, “northern”) and “pelta” (Greek, “shield”). The holotype (TMP 2011.033.0001), with an estimated living mass of 1,300 kg, is an articulated specimen preserving the head, neck, most of the trunk and sacrum, a complete right and a partial left forelimb and manus, and partial pes. The skull is covered in dermal plates, which are overlain by their associated epidermal scales. Cervical and thoracic osteoderms form continuous transverse rows completely separated by transverse rows of polygonal basement scale. Osteoderms are covered by a thick, dark gray to black organic layer, representing the original, diagenetically altered, keratinous epidermal scales. The distribution of the film correlates well to the expected distribution of melanin, a pigment present in some vertebrate integumentary structures. The keratinized tissues in this nodosaur are heavily pigmented. The possible presence of eumelanin and pheomelanin, suggested it had reddish-brown camouflage. The evidence of countershading in a large, heavily armored herbivorous dinosaur also provides a unique insight into the predator-prey dynamic of the Cretaceous Period.

• Isaberrysaura

 

Isaberrysaura skull in lateral view and maxillary teeth (Adapted from Salgado et al., 2017)

 

Isaberrysaura mollensis gen. et sp. nov. is the first dinosaur recovered in the marine-deltaic deposits of the Los Molles Formation (Neuquén Province, Argentina), and the first neornithischian dinosaur known from the Jurassic of South America. The holotype of Isaberrysaura is an incomplete articulated skeleton with an almost complete skull, and a partial postcranium consisting of 6 cervical vertebrae, 15 dorsal vertebrae, a sacrum with a partial ilium and an apparently complete pubis, 9 caudal vertebrae, part of a scapula, ribs, and unidentifiable fragments. One of the most notable features of the discovery is the presence of permineralized seeds in the middle-posterior part of the thoracic cavity. The seeds were assigned to the Cycadales (Zamiineae) on the basis of a well-defined coronula in the micropylar region. The findings suggest the hypothesis of interactions (endozoochory) between cycads and dinosaurs, especially in the dispersion of seeds.

•  Junornis 

 

Holotype of Junornis houi. From Chiappe et. al; 2017)

Junornis houi, from the Yixian Formation of eastern Inner Mongolia, represents a new addition to the enantiornithine diversity of the Jehol Biota. The holotype (BMNHC-PH 919; Beijing Museum of Natural History), from the Early Cretaceous (~ 126±4 mya) of Yixian Formation,  is a nearly complete and articulated skeleton contained in two slabs, and surrounded by feather impressions defining the surface of its wings and body outline. Based on the well-preserved skeleton and exquisite plumage of Junornis, it was possible  make some estimation of its flight capacity. The body and wings of this bird were similar to those of modern passeriforms such as Alauda arvensis. 

• Shringasaurus

Cranial anatomy of Shringasaurus indicus

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.

• Patagotitan 

Patagotitan reconstruction (Image: Diego Pol)

Patagotitan mayorum, originally discovered in 2010 by the rural farmer Aurelio Hernandez  is the largest and the most complete titanosaur taxa recovered to date. The generic name Patagotitan is derived from Patago (in reference to the geographic origin of the fossils, Patagonia), and titan (symbolic of its large size). The species name honours the Mayo family (owner of La Flecha Farm, the place where the fossils were found). The holotype (MPEF-PV 3400), includes an anterior and two middle cervical vertebrae, three anterior, two middle and two posterior dorsal vertebrae, six anterior caudal vertebrae, three chevrons, dorsal ribs, both sternal plates, right scapulocoracoid, both pubes and both femora. Six individuals were found in the same quarry, distributed in three distinct but closely spaced horizons, corresponding to  three different burial events. The first estimations of Patagotitan body mass suggest that it would weigh around 70 tons. The dorsal vertebrae preserved in Patagotitan, Argentinosaurus and Puertasaurus allows distinguishing the new taxon from previously known giant titanosaurs from the ‘mid-Cretaceous’ of Patagonia.

 

References:

Brown, C.M.; Henderson, D.M.; Vinther, J.; Fletcher, I.; Sistiaga, A.; Herrera, J.; Summons, R.E. “An Exceptionally Preserved Three-Dimensional Armored Dinosaur Reveals Insights into Coloration and Cretaceous Predator-Prey Dynamics”. Current Biology. doi:10.1016/j.cub.2017.06.071

Salgado, L. et al. A new primitive Neornithischian dinosaur from the Jurassic of Patagonia with gut contents. Sci. Rep. 7, 42778; doi: 10.1038/srep42778 (2017)

Liu D, Chiappe LM, Serrano F, Habib M, Zhang Y, Meng Q (2017) Flight aerodynamics in enantiornithines: Information from a new Chinese Early Cretaceous bird. PLoS ONE12(10): e0184637. https://doi.org/10.1371/journal.pone.0184637

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

Carballido JL, Pol D, Otero A, Cerda IA, Salgado L, Garrido AC, Ramezani J, Cúneo NR, Krause JM. 2017 A new giant titanosaur sheds light on body mass evolution among sauropod dinosaurs. Proc. R. Soc. B 284: 20171219.
DOI: 10.1098/rspb.2017.1219

Pisanosaurus and the Triassic ornithischian crisis

Pisanosaurus mertii holotype. Dorsal vertebrae in left lateral (A) and right lateral (B) views. Scale bar: 5 cm. From Agnolín and Rozadilla, 2017.

In 1887, Harry Govier Seeley was the first to subdivide dinosaurs into Saurischians and the Ornithischians based on the nature of their pelvic bones and joints. While the clade Saurischia is well represented in the Late Triassic, the record of the Ornithischia is certainly more problematic. Only a single Triassic ornithischian taxon was generally considered to still be valid: Pisanosaurus mertii, originally described by Argentinian paleontologist Rodolfo Casamiquela in 1967, based on a poorly preserved but articulated skeleton from the upper levels of the Ischigualasto Formation (Late Triassic).

The holotype and only known specimen (PVL 2577) is a fragmentary skeleton including partial upper and lower jaws, seven articulated dorsal vertebrae, four fragmentary vertebrae of uncertain position in the column; the impression of the central portion of the pelvis and sacrum; an articulated partial hind limb including the right tibia; fibula; proximal tarsals and pedal digits III and IV; the distal ends of the right and left femora; a left scapular blade (currently lost); a probable metacarpal III;  and the impressions of some metacarpals (currently lost).

Reconstructed skeleton reflecting the traditional interpretation of Pisanosaurus (Royal Ontario Museum)

But Pisanosaurus shows some derived traits that resulted as unambiguous synapomorphies of the Silesauridae clade, and include: reduced to absent denticles on maxillary and dentary teeth; sacral ribs shared between two sacral vertebrae; lateral side of proximal tibia with a fibular flange; dorsoventrally flattened ungual phalanges; and ankylothecodonty, teeth partially fused to maxilla and dentary bone. The inclusion of Pisanosaurus within Silesauridae implies that this taxon does not constitute the oldest ornithischian. This is consistent with previous interpretations proposing that ornithischian radiation occurred after the Triassic–Jurassic boundary.

To explain the relatively low diversity exhibited by Ornithischia in the Late Triassic-Early Jurassic, several hypotheses have been proposed. One, suggests that Ornithischia is the sister-taxon of Neotheropoda (the least inclusive clade that includes Coelophysis and modern birds) within the clade of ‘traditional theropod taxa’. In this model, a ‘transitional’ ornithischian may possess some anatomical features of theropods that appear to be more like those in more derived than Eodromaeus murphi and Tawa hallae.

Hypothesis 4, in which Ornithischia forms the sister-taxon of Averostra (From Baron 2017)

In a second hypothesis, Ornithischia is positioned as the sister-taxon to the coelophysids. In this model, Neotheropoda and Ornithoscelida would encompass the same set of taxa, but Ornithoscelida would, theoretically, take priority of Neotheropoda as it is the older name. In a third hypothesis, Ornithischia is positioned as the sister-taxon to the ‘other neotheropods’ not contained in the coelophysid clade.

Another hypothesis proposes that Ornithischia forms the sister-taxon of Averostra. Like Ornithischia, Averostra is only known from the Jurassic and Cretaceous Periods, and both share a number of anatomical features, such as fusion of the sacral neural. Another anatomical traits that could unite such a group include the possession of six or more sacral vertebrae; and the fusion of the sacral neural spines into a broad and continuous sheet, as in early ornithischians like Lesothosaurus diagnosticus and tetanuran theropods like Megalosaurus bucklandii. It’s worth mentioning the fact the earliest known unambiguous members of both Ornithischia and Averostra, are found in the same formation in South America: Laquintasaura venezuelae and Tachiraptor admirabilis.

Laquintasaura venezuelae gen. et sp. nov (From Barret et al., 2014)

 

It was suggested (Baron and Barrett 2017) that Chilesaurus diegosaurezi from the Late Jurassic, might represent the earliest diverging member of Ornithischia. Chilesaurus shows several characters typical of ornithischians. The features include a premaxilla with an edentulous anterior region;  loss of recurvature in maxillary and dentary teeth; a postacetabular process that is 25–35% of the total anteroposterior length of the ilium; possession of a retroverted pubis; a pubis with a rod-like pubic shaft; a pubic symphysis that is restricted to the distal end of the pubis; and a femur that is straightened in anterior view. The unique combination of ‘primitive’ and ‘derived’ characters for Chilesaurus has the potential to illuminate the order in which traditional ornithischian synapomorphies were acquired.

The Phytodinosauria hypothesis suggest that Ornithischia is nested among the taxa traditionally termed as sauropodomorphs could also offer a solution to the problem of the lack of unambiguous ornithischians in the Carnian and Late Triassic in general.

 

References:

Baron, M. G. (2017): Pisanosaurus mertii and the Triassic ornithischian crisis: could phylogeny offer a solution?, Historical Biology, DOI: 10.1080/08912963.2017.1410705

Agnolín FL, Rozadilla S. (2017): Phylogenetic reassessment of Pisanosaurus mertii Casamiquela, 1967, a basal dinosauriform from the Late Triassic of Argentina, Journal of Systematic Palaeontology DOI: 10.1080/14772019.2017.1352623

Baron M. G, Barrett P. M. 2017, A dinosaur missing-link? Chilesaurus and the early evolution of ornithischian dinosaurs. Biol. Lett. 13: 20170220. http://dx.doi.org/10.1098/rsbl.2017.0220

Baron, M. G., Norman, D. B. & Barrett, P. M. A new hypothesis of dinosaur relationships and early dinosaur evolution.  Nature 543, 501–506  (2017).  doi:10.1038/nature21700

Barrett, Paul M.; Butler, Richard J.; Mundil, Roland; Scheyer, Torsten M.; Irmis, Randall B.; Sánchez-Villagra, Marcelo R. (2014). A palaeoequatorial ornithischian and new constraints on early dinosaur diversification, Proceedings of the Royal Society B, DOI: 10.1098/rspb.2014.1147

Max C. Langer, Martín D. Ezcurra, Oliver W. M. Rauhut, Michael J. Benton, Fabien Knoll, Blair W. McPhee, Fernando E. Novas, Diego Pol & Stephen L. Brusatte, Untangling the dinosaur family tree, Nature 551 (2017) doi; oi:10.1038/nature24012

Padian K. Dividing the dinosaurs. Nature 543, 494–495 (2017) doi:10.1038/543494a

 

The bizarre Halszkaraptor escuilliei

H. escuilliei MPC D-102/109. From Cau et al., 2017.

Maniraptoran lineages evolved novel ecomorphologies during the Cretaceous period, including active flight, gigantism, cursoriality and herbivory. This group share the following characteristics: large brain but a reduced skull in comparison to their body size, beaks, and smaller teeth. Now, a well-preserved maniraptoran from Mongolia, revealed a mosaic of features, most of them absent among non-avian maniraptorans but shared by reptilian and avian groups with aquatic or semiaquatic ecologies. This new theropod, Halszkaraptor escuilliei gen. et sp. nov., adds an amphibious ecomorphology to those evolved by maniraptorans.

The holotype, MPC (Institute of Paleontology and Geology, Mongolian Academy of Sciences, Ulaanbaatar, Mongolia) D-102/109, is an articulated and almost complete skeleton preserved three-dimensionally. The generic name, honours Halszka Osmólska (1930–2008) for her contributions to theropod palaeontology. The species name, ‘escuilliei’ refers to François Escuillié, who returned the holotype to Mongolia.

Reconstruction of Halszkaraptor escuilliei. Photograph: Lukas Panzarin/Andrea Cau

Halszkaraptor is related to other enigmatic Late Cretaceous maniraptorans from Mongolia in a novel clade at the root of Dromaeosauridae. It was the size of a mallard. Originally poached from Ukhaa Tolgod, Mongolia, the fossil was in private collections in Japan and England for an unknown amount of time, and later it  was transferred to the Royal Belgian Institute of Natural Sciences (RBINS). Thanks to a cooperation agreement between the Ministry of Education, Culture and Science of Mongolia, the Belgian Science Policy Office and the RBINS, the specimen returned to the Institute of Paleontology and Geology, Mongolian Academy of Science.

The skeleton is almost complete. The skull is lightly built, and is still articulated with the first cervical vertebra. The preorbital region forms 60% of basicranial length, and each premaxilla is elongate, bearing eleven teeth, the highest number among dinosaurs. The presacral vertebrae include 10 cervicals and 12 dorsals. The neck forms 50% of snout–sacrum length.

Skull of H. escuilliei. From Cau et al., 2017

The forelimb is relatively shorter than in most dromaeosaurids. The ulna is flattened and possesses an acute posterior margin. The hand has a morphology that is unique among theropods, with a progressive elongation of the lateral fingers, with the third being the longest and most robust. The 76 mm long femur has a robust greater trochanter. The metatarsus lacks cursorial adaptations and measures 80% of femoral length. The feet are complete and articulated, although some elements are poorly visible.

Based on the neck hyperelongation for food procurement, the forelimb proportions that may support a swimming function, and postural adaptations convergent with short-tailed birds, Halszkaraptor may represent the first case among non-avian dinosaurs of a double locomotory module.

References:

Cau, A.; Beyrand, V.; Voeten, D.; Fernandez, V.; Tafforeau, P.; Stein, K.; Barsbold, R.; Tsogtbaatar, K.; Currie, P.; Godrfroit, P.; “Synchrotron scanning reveals amphibious ecomorphology in a new clade of bird-like dinosaurs”. Nature. doi:10.1038/nature2467