Vegaviidae, a new clade of southern diving birds

Vegavis iaai by Gabriel Lio. / Photo: CONICET

The fossil record of Late Cretaceous–Paleogene modern birds in the Southern Hemisphere is fragmentary.  It includes Neogaeornis wetzeli from Maastrichtian beds of Chile, Polarornis gregorii and Vegavis iaai from the Maastrichtian of Antarctica, and Australornis lovei from the Paleogene of New Zealand. The phylogenetic relationships of these taxa have been variously interpreted by different authors. In a more recent analysis, Polarornis, Vegavis, Neogaeornis, and Australornis, are including in a new clade: Vegaviidae.

Vegaviids share a combination of characters related to diving adaptations, including compact and thickened cortex of hindlimb bones, femur with anteroposteriorly compressed and bowed shaft, deep and wide popliteal fossa delimited by a medial ridge, tibiotarsus showing notably proximally expanded cnemial crests, expanded fibular crest, anteroposterior compression of the tibial shaft, and a tarsometatarsus with a strong transverse compression of the shaft.

Histological sections of Vegavis iaai (MACN-PV 19.748) humerus (a), femur (b), polarized detail of humerus (c). Scale bar equals 10 mm for (a), (b) and 5 mm for (c). From Agnolín et al., 2017

The recognition of Polarornis, Vegavis, Neogaeornis, Australornis, and a wide array of isolated specimens as belonging to the new clade Vegaviidae reinforces the hypothesis that southern landmasses constituted a center for neornithine diversification, and emphasizes the role of Gondwana for the evolutionary history of Anseriformes and Neornithes.

The most informative source for anatomical comparison among Australornis, Polarornis, Vegavis as well as other southern avian is a recently published Vegavis skeleton (MACN-PV 19.748). Vegavis overlaps with Australornis in the proximal portion of the humerus, proximal part of the coracoid, scapula, and ulna; with Polarornis in the humerus, femur, and proximal end of the tibia; and with Neogaeornis in the tarsometatarsus.

Phylogeny with geographical distribution of Vegaviidae. From Agnolín et al., 2017.

The humerus is probably the most diagnostic element among anseriforms. In Vegavis and Australornis the humerus is notably narrow and medially tilted on its proximal half, and the deltopectoral crest extends for more than one third of the humeral length. The femur is well known both in Vegavis and Polarornis, and share a combination of characters absent in other Mesozoic or Paleogene birds, including strongly anteriorly bowed and anteroposteriorly compressed shaft (especially near its distal end)

Osteohistological analysis of the femur and humerus of V. iaai. shows a highly vascularized fibrolamellar matrix lacking lines of arrested growths, features widespread among modern birds. The femur has some secondary osteons, and shows several porosities, one especially large, posterior to the medullar cavity. The humerus exhibits a predominant fibrolamellar matrix, but in a portion of the anterior and medial sides of the shaft there are a few secondary osteons, some of them connected with Volkman’s canals, and near to these canals, there are a compact coarse cancellous bone (CCCB) with trabeculae. This tissue disposition and morphology suggests that Vegavis had remarkably high growth rates, a physiological adaptation that may be critical for surviving in seasonal climates at high latitudes, and  may also constitute the key adaptation that allowed vegaviids to survive the K/T mass extinction event.

 

References:

Agnolín, F.L., Egli, F.B., Chatterjee, S. et al. Sci Nat (2017) 104: 87. https://doi.org/10.1007/s00114-017-1508-y

Jordi Alexis Garcia Marsà, Federico L. Agnolín & Fernando Novas (2017): Bone microstructure of Vegavis iaai (Aves, Anseriformes) from the Upper Cretaceous of Vega Island, Antarctic Peninsula, Historical Biology, DOI: 10.1080/08912963.2017.1348503

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Junornis houi and the evolution of flight

Holotype of Junornis houi. (From Liu et. al; 2017)

Birds originated from a theropod lineage more than 150 million years ago. By the Early Cretaceous, they diversified, evolving into a number of groups of varying anatomy and ecology. The Enantiornithes are the most successful clade of Mesozoic birds. In the last decades, exceptionally well preserved avian fossils han been recovered from China. The most recent, 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. The name Jun is derived from a Chinese character meaning beautiful; and ornis is Greek for bird. The species name, houi honors Dr. Hou Lianhai.

Photograph and interpretative drawing of the forelimb of Junornis houi (From Liu et. al; 2017)

Junornis exhibits the following combination of characters: rounded craniolateral corner of sternum; distinct trough excavating ventral surface of mediocranial portion of sternum; triangular process at base of sternal lateral trabecula; sternal lateral trabecula broad and laterally deflected; sternal intermediate trabecula nearly level with mid-shaft of lateral trabecula; sternal xiphoid process level with lateral trabeculae; costal processes of last two penultimate synsacral vertebrae three times wider than same process of last synsacral vertebra; and very broad pelvis. Non-pennaceous, contour feathers cover much of the skeleton except the wings and feet.

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 and to other small-sized birds that fly using intermittent bounds. The low aspect ratio (AR = 5.5) wings of BMNHC-PH 919 suggest that it may have been adapted to rapid take-offs, given that modern birds with proportionally short, broad wings tend to maximize thrust during slow flight. The low wing loading (WL = 0.18 g/cm2) of this fossil indicates that this bird would have been able to generate a large magnitude of lift at low speeds because for a given speed and angle of attack, birds with greater wing area (and therefore lower WL) generate more lift than those with small wing areas. This value also suggest that this bird would have been highly maneuverable and able to perform tight turns.

References:

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

Forgotten women of Paleontology: Margaret Benson

Margaret Jane Benson. Portrait in the Archives of Royal Holloway, University of London (RHC PH/282/13) From Fraser & Cleal, 2007

It is a truth universally acknowledged, that women has always work harder than men to gain some recognition. It was true in the 16th, and it’s true now. In “A Room of One’s Own”, Virginia Woolf explores the conflicts that a gifted woman must have felt during the Renaissance through the fictional character of Judith Shakespeare, the sister of William Shakespeare, and cites as obstacles the indifference of most of the world, the profusion of distractions, and the heaping up of various forms of discouragement. But not only in the Elizabethan times. In the Victorian times there was the common assumption that the female brain was too fragile to cope with mathematics, or science in general. In a letter from March 1860, Thomas Henry Huxley wrote to great geologist Charles Lyell FRS: “Five-sixths of women will stop in the doll stage of evolution, to be the stronghold of parsonism, the drag on civilisation, the degradation of every important pursuit in which they mix themselves – intrigues in politics and friponnes in science.”

Margaret Crosfield on a Geologists’ Association fieldtrip to Leith Hill with Professor Lapworth (From Burek and Malpas, 2007).

Women have played  various and extensive roles in the history of geology. Unfortunately, their contribution has not been widely recognised by the public or academic researchers. In the 18th and 19th centuries women’s access to science was limited, and science was usually a ‘hobby’ for intelligent wealthy women. Early female scientists were often born into influential families, like Grace Milne, the eldest child of Louis Falconer and sister of the eminent botanist and palaeontologist, Hugh Falconer; or Mary Lyell, the daughter of the geologist Leonard Horner. They collected fossils and mineral specimens, and were allowed to attend scientific lectures, but they were barred from membership in scientific societies. But by the first half of the 20th century, a third of British palaeobotanists working on Carboniferous plants were women. The most notable were  Margaret Benson, Emily Dix, and Marie Stopes.

Newnham began as a house for five students in Regent Street in Cambridge in 1871

Margaret Benson was born on the 20th October 1859 in London. Between 1878 and 1879, she studied at Newnham College Cambridge. After obtaining her BSc at University College London (UCL) in 1891, she started research on plant embryology.  In 1893, Benson was appointed head of the new Department of Botany at Royal Holloway College, the first woman in the United Kingdom to hold such a senior position in the field of botany. Her palaeobotanical research centred on the anatomy of reproductive structures, especially of Carboniferous pteridosperms and lycophytes. In 1904, she was among the first group of women to be elected as Fellows of the Linnean Society, and in 1912 she was appointed Professor of Botany at the University of London. Her major study on lycophyte fructifications was on the cones of the Sigillaria plant. She also speculated on the relationship between the Palaeozoic arborescent lycophytes and the Recent Isoetes, with the Triassic Pleuromeia as a possible intermediate form. She worked with ferns and cordaites and described a new species, Cordaites felicis. Benson’s work is characterized by careful description. One of her most important theoretical works concerns the phylogenetic significance of the sporangiophore in lycophytes, sphenophytes and ferns. After her retirement in 1922, she was encouraged by D. H. Scott to write up some of her earlier unpublished work on the root anatomy of the early Carboniferous pteridosperm Heterangium. She even continued with fieldwork when she was in her 70s. There is an unpublished manuscript in which she described a new fertile Rhacopteris that she collected from Teilia Quarry in North Wales in 1933. She died on 20th June 1936 at Highgate, Middlesex.

References:

H. E. Fraser and C. J. Cleal, The contribution of British women to Carboniferous palaeobotany during the first half of the 20th century, Geological Society, London, Special Publications, 281, 51-82, 1 January 2007, https://doi.org/10.1144/SP281.4

C. V. Burek (2007). The role of women in geological higher education – Bedford College, London (Catherine Raisin) and Newnham College, Cambridge, UK, Geological Society, London, Special Publications, eds Burek C. V., Higgs B. 281, pp 9–38

 

A brief history of the Spinosaurus.

One of the photographs donate by W. Stromer. Image from the Washington University in St. Louis

Despite its low fossil record, Spinosaurus is one of the most famous dinosaur of all time. This gigantic theropod possessed highly derived cranial and vertebral features sufficiently distinct for it to be designated as the nominal genus of the clade Spinosauridae. In 1910, E. Stromer went to his third paleontological expedition to Egypt. He arrived to Alexandria on November 7. He was initially looking for early mammals and planned visit the area of Bahariya, in the Western Desert, which has sediments from the Cretaceous era. But an expedition to the Western Desert needed the permission by the English and French colonial authorities and of course the Egyptian authorities. Although diplomatic relations with Germany were rapidly deteriorating, Stromer managed to get the permissions. He arrived to the Bahariya Oasis on January 11, 1911. After facing some difficulties during the journey, on January 17 he began to explore the area of Gebel el Dist, and at the bottom of the Bahariya Depression, Stromer found  the remains of four immense and entirely new dinosaurs (Aegyptosaurus, Bahariasaurus, Carcharodontosaurus and Spinosaurus aegyptiacus), along with dozens of other unique specimens. Stromer and Markgraf recovered the right and left dentaries and splenials from the lower jaw; a straight piece of the left maxilla that was described but not drawn; 20 teeth; 2 cervical vertebrae; 7 dorsal (trunk) vertebrae; 3 sacral vertebrae; 1 caudal vertebra; 4 thoracic ribs; and gastralia. This gigantic predator is estimated to have been about 14 m, with unusually long spines on its back that probably formed a large, sail-like structure.

1) Photograph of the right mandibular ramus of the holotype of Spinosaurus aegyptiacus Stromer, 1915 (BSP 1912 VIII 19), in lateral view. 2) Reproduction of Stromer’s (1915, pl. I, fig. 12a) illustration of the right mandibular ramus.

Due to political tensions before and after World War I, many of this fossils were damaged after being inspected by colonial authorities and not arrived to Munich until 1922. The shipping from El Cairo was paid by the Swiss paleontologist Bernhard Peyer (1885-1963), a former student and friend of Stromer. During the World War II, E. Stromer tried to convince Karl Beurlen -a young nazi paleontologist who was in charge of the collection- that he had to move the fossils to a safer place, but Beurlen refused to do it. Unfortunately, on April 24, 1944, a British Royal Air Force raid bombed the museum and incinerated its collections. Only two photographs of the holotype of Spinosaurus aegyptiacus were recovered in in the archives of the Paläontologische Museum in June 2000, after they were donated to the museum by Ernst Stromer’s son, Wolfgang Stromer, in 1995. These photographs provide additional insight into the anatomy of the holotype specimen of Spinosaurus aegyptiacus.

“Illustrations of the vertebrate “sail” bones of Spinosaurus that appeared in one of Stromer’s monographs. From Wikimedia Commons.

In his original monograph, Stromer emphasized the peculiar character of the teeth of this unusual theropod. Because of their morphological convergence with those of crocodilians and other fish-eating reptiles, isolated spinosaurid teeth have frequently been misinterpreted. It appears that Baryonyx-like teeth were collected by Gideon Mantell in Sussex around 1820. Georges Cuvier was the first to publish an illustration of the four teeth from Tilgate Forest. These teeth, however, were generally considered as belonging to crocodilians, and when Richard Owen erected the taxon Suchosaurus cultridens to designate them he placed it among the crocodiles. Even when Owen realized that these teeth were peculiar in many respects and hinted at possible affinities with dinosaurs, he persistently classified Suchosaurus as a crocodilian, an interpretation that was accepted by most subsequent authors.

Although Stromer’s original description of Spinosaurus aegyptiacus was published in 1915, a more complete detailed picture of its anatomy, evolution, and biogeography only begun to emerge in recent decades.

 

References:

HONE, D. W. E. and HOLTZ, T. R. (2017), A Century of Spinosaurs – A Review and Revision of the Spinosauridae with Comments on Their Ecology. Acta Geologica Sinica, 91: 1120–1132. doi: 10.1111/1755-6724.13328

Smith, et al. “NEW INFORMATION REGARDING THE HOLOTYPE OF SPINOSAURUS AEGYPTIACUS STROMER, 1915.” J. Paleont., 80(2), 2006, pp. 400–406

New tetrapod assemblage from the Chañares Formation

Skeletal anatomy of the erpetosuchid pseudosuchian Tarjadia ruthae. From Ezcurra et al., 2017

In the aftermath of the Permo-Triassic mass extinction (~252 Ma), several typical Palaeozoic synapsids and parareptiles were replaced by stem and crown archosaurs (archosauromorphs) and eucynodonts, and the Late Triassic fossil record of South America has been crucial to shed light on their evolutionary histories.

The Chañares Formation is part of the Ischigualasto-Villa Unión Basin, and represents one of the most continuous continental Triassic succesions in South America. 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 yielded a rich tetrapod assemblage composed of kannemeyeriiform dicynodonts, traversodontid and probainognathian cynodonts, proterochampsid stem-archosaurs, stem-crocodylians, and dinosaur precursors.

Volcanism played an important role in the generation and preservation of the Chañares Formation’s exceptional tetrapod fossil record. Recent radioisotopic datings temporally constrained most of the lower half of this unit to the earliest Carnian (236–231 Ma), showing that this assemblage preceded the oldest members of typical Late Triassic archosaur clades that are found in the Ischigualasto Formation. The new assemblage is called here as the Tarjadia Assemblage Zone, while the upper, historically known assemblage is called the Massetognathus–Chanaresuchus Assemblage Zone. This new assemblage sheds light on the link between the Early–Middle Triassic tetrapod assemblages of Africa (for example, Karoo, Ruhuhu and Otiwarongo basins) and those from the Middle–Late Triassic of South America.

The Chañares Formation (© 2012 Idean)

Tarjadia ruthae is characterized by a dorsoventrally thick skull roof ornamented by deep pits and grooves of random arrangement; Y-shaped tuberosity on the dorsal surface of the anterior end of the parietals; marginal dentition with serrations; spine table of the presacral and anterior caudal vertebrae with a transversely concave dorsal surface; a femur with a poorly developed fourth trochanter and a hook-shaped tibial condyle; and thick dorsal osteoderms with a coarse pitted ornamentation. The abundance of the erpetosuchid Tarjadia in the lowermost levels of the Chañares Formation indicates that this pseudosuchian was an important secondary consumer in its ecosystem

The Tarjadia and Massetognathus–Chanaresuchusassemblage zones currently do not share species or low level taxa, indicating a profound faunal replacement involving both primary and secondary consumers. Therefore, the rise of dinosaurs and other archosauromorph clades that diversified worldwide in the Late Triassic was preceded by a phase of relatively rapid changing ecosystems in southwestern Pangaea, including two (Tarjadia and Massetognathus–Chanaresuchus assemblage zones) profound faunal replacements in a time span shorter than 6 Myr (around 236–231 Ma).

References:

Martín D. Ezcurra, Lucas E. Fiorelli, Agustín G. Martinelli, Sebastián Rocher, M. Belén von Baczko, Miguel Ezpeleta, Jeremías R. A. Taborda, E. Martín Hechenleitner, M. Jimena Trotteyn & Julia B. Desojo; Deep faunistic turnovers preceded the rise of dinosaurs in southwestern Pangaea, Nature Ecology & Evolution (2017) doi:10.1038/s41559-017-0305-5

Benton, M. J., Tverdokhlebov, V. P. & Surkov, M. V. Ecosystem remodelling among vertebrates at the Permian–Triassic boundary in Russia. Nature 432, 97–100 (2004).

A Brief Introduction to the Osteology of Viavenator exxoni

Viavenator exxoni, Museo Municipal Argentino Urquiza

The Abelisauridae is the best-known carnivorous dinosaur group from Gondwana. Their fossil remains have been recovered in Argentina, Brazil, Morocco, Niger, Libya, Madagascar, India, and France. These theropods exhibit spectacular cranial ornamentation in the form of horns and spikes and strongly reduced forelimbs and hands. The group was erected by Jose Bonaparte with the description of  Abelisaurus comahuensis, and includes: Carnotaurus sastrei, Aucasaurus garridoi, Ekrixinatosaurus novasi, Skorpiovenator bustingorryi, Eoabelisaurus and Viavenator exxoni

The holotype of Viavenator exxoni (MAU-Pv-LI-530) was found in the outcrops of the Bajo de la Carpa Formation (Santonian, Upper Cretaceous), northwestern Patagonia, Argentina. Viavenator series of autapomorphies are: transversely compressed parietal depressions on both sides of the supraoccipital crest; ventral edges of the paraoccipital processes located above the level of the dorsal edge of the occipital condyle; basioccipital-opisthotic complex about two and a half times the width and almost twice the height of the occipital condyle, in posterior view; well-developed crest below the occipital condyle; deeply excavated and sub-circular basisphenoidal recess; basipterygoid processes horizontally placed with respect to the cranial roof and located slightly dorsally to the basal tubera; mid and posterior cervical centra with slightly convex lateral and ventral surfaces; presence of an interspinous accessory articular system in middle and posterior dorsal vertebrae; presence of a pair of pneumatic foramina within the prespinal fossa in anterior caudal vertebrae; distal end of the scapular blade posteriorly curved.

Figure 1. Rendering of the type braincase of Viavenator exxoni (MAU-Pv-LI-530) in dorsal (A,B), and right lateral (C,D) view. Adapted from Carabajal y Filippi, 2017.

Viavenator presents highly-derived postcranial characters, and a relatively plesiomorphic skull in comparison with Carnotaurus and Aucasaurus. Cranial elements of this specimen include the complete neurocranium: frontals, parietals, sphenethmoids, orbitosphenoids, laterosphenoids, prootics, opisthotics, supraoccipital, exoccipitals, basioccipital, parasphenoids and basisphenoids. The plesiomorphic traits of the skull of Viavenator are mainly related with the anatomy of frontals, wich lack osseous prominences such as domes or horns. The dorsal surface of the frontals exhibits an ornamentation that consists of pits and sinuous furrows and ridges, although it is not well-preserved. The  exoccipitals form the lateral and possibly the laterodorsal margins of the foramen magnum, as apparently occurs in Carnotaurus. 

Vertebrae of Viavenator exxoni. Scale bar: 5 cm. From Filippi et al., 2017),

The postcranial skeleton of Viavenator is represented by eight cervical vertebrae (the atlas; seven dorsal vertebrate, four of them articulated; twelve caudal vertebrae); ribs; gastralias; one chevron; scapulocoracoid; ischium foot; and fibulae. The atlas is similar to that of Carnotaurus, though less robust and anteroposteriorly shorter; and there  are not observed prezygapophyseal facets in the neurapophyses, so it is inferred that the proatlas was absent, as also occurs in Carnotaurus and Majungasaurus. The shape of the epipophyses of the cervical region, which are
characterized by anterior and posterior projections, is shared by Viavenator and Carnotaurus, but it is not present in pre-Santonian forms such as Ilokelesia and Skorpiovenator. The derived vertebral characters of Viavenator are linked with an increase in the structural rigidity of the vertebral column, and with an increase in the cursorial abilities of these abelisaurids. This combination of plesiomorphic and derived traits suggests that Viavenator is a transitional form.

 

References:

Filippi, L.S., Méndez, A.H., Gianechini, F.A., Juárez Valieri, Rubé.D., Garrido, A.C., Osteology of Viavenator exxoni (Abelisauridae; Furileusauria) from the Bajo de la Carpa Formation, NW Patagonia, Argentina, Cretaceous Research (2017), doi: 10.1016/j.cretres.2017.07.019.

Leonardo S. Filippi, Ariel H. Méndez, Rubén D. Juárez Valieri and Alberto C. Garrido (2016). «A new brachyrostran with hypertrophied axial structures reveals an unexpected radiation of latest Cretaceous abelisaurids». Cretaceous Research 61: 209-219. doi:10.1016/j.cretres.2015.12.018

Paulina-Carabajal, A., Filippi, L., Neuroanatomy of the abelisaurid theropod Viavenator: The most complete reconstruction of a cranial endocast and inner ear for a South American representative of the clade, Cretaceous Research (2017), doi: 10.1016/j.cretres.2017.06.013

 

Geomythology: On Cyclops and Lestrigons

Pellegrino Tibaldi, The Blinding of Polyphemus, c. 1550-1

In Greek mythology giants are connected to the origin of the cosmos and represent the primordial chaos which contrasts with the rationality of the Gods. They were the sons of the earth (Gea) fertilized by the blood of the castrated Uranus (Heaven). In that chaotic, primal era, strange creatures proliferated, such as the Cyclopes, and the Centaurs. Lestrigons, a tribe of man-eating giants, appears in Homer’s Odyssey. Polyphemus, is one of the Cyclopes also described in Homer’s Odyssey. Greeks believed that the Laestrygonians, as well as the Cyclopes, had once inhabited Sicily.

But the ancient myth of giants is a common element in almost all cosmogonies. In Scandinavians legends, the blood of the giant Ymo formed the seas of th Earth, and his bones formed the mountains. In Peru, Brazil, and Mexico, the giants are part of the folk tradition. Judaism, more precisely, the Talmud and the Torah, converges with Genesis on the origin of the giants.

Laestrygonians Hurling Rocks at the Fleet of Odysseus

The discovery of huge fossil bones has always stimulated the imagination of local people, giving rise to legends. We found direct reference in the works of Herodotus which mentions the large bones of the giant Orestes recovered in Acadia, or even Virgil in his Georgics speaks of gigantic bones. In the sixteenth century, Italian historians, such as the Sicilian Tommaso Fazello, used the sacred texts to demonstrate that the first populations of many islands of the Mediterranean (among them Sicily and Sardinia), were of giants. At the same time, the first notices of South American fossils were reported by early Spanish explorers. These fossils were interpreted as the remains of an ancestral race of giant humans erased from the face of the Earth by a divine intervention. Fray Reginaldo de Lizarraga (1540-1609) also wrote about those “graves of giants” found in Córdoba, Argentina.

The case of Filippo Bonanni, an Italian Jesuit scholar, is very curious. He used the topic of the giants as an element in support of his theory of the inorganic origin of fossils. He properly rejects the myth of giants, but wrongly identify the nature of fossils. The most strong supporter for the organic origin of fossils was the italian painter Agostino Scilla. He published only one scientific treatise: La vana speculazione disingannata dal senso, lettera risponsiva Circa i Corpi Marini, che Petrificati si trouano in vari luoghi terrestri (The vain speculation disillusioned by the sense, response letter concerning the marine remains, which are found petrified in various terrestrial places). The aim of the work was the demonstration that fossils, which are found embedded in sediments on mountains and hills, represent the remains of lithified organisms, which at one time lived in the marine environment. The text was later translated to Latin and it was written as a response to a letter sent to him by Giovanni Francesco Buonamico, a doctor from Malta.

Femur of Mammuth interpreted as a bone of a giant and preserved as a relic in St. Stephen’s Cathedral in Vienna.

Madrisio (1718) is one of the first authors in Italy to suggest that much of this giant bones may be referred, without problem, to elephants from the past. But te real interpretative turning point takes place with the influential work of the Hans Sloane, who stressed the importance of a comparative study of the bones in various vertebrates. Applying this method, he demonstrated how the big bones and teeth found in sediments or in caves are nothing more than remains of cetaceans and large quadrupeds, remarking on the major anatomical differences between humans and other known vertebrates. Among the few precursors of Sloan, the Italian naturalist Giovanni Ciampini in 1688, using direct comparisons with the famous elephant exhibited in Florence in the Medicean Museum, was able to correctly interpret the bones found at Vitorchiano near Viterbo, initially attributed to gigantic men.

References:

Marco Romano & Marco Avanzini (2017): The skeletons of Cyclops and Lestrigons: misinterpretation of Quaternary vertebrates as remains of the mythological giants, Historical Biology, DOI: 10.1080/08912963.2017.1342640

Dark skies at the end of the Cretaceous

A time-lapse animation showing severe cooling due to sulfate aerosols from the Chicxulub asteroid impact 66 million years ago (Credit: PKI)

Thirty years ago, the discovery of anomalously high abundance of iridium and other platinum group elements in the Cretaceous/Palaeogene (K-Pg) boundary led to the hypothesis that an asteroid collided with the Earth and caused one of the most devastating events in the history of life. The impact created the 180-kilometre wide Chicxulub crater causing widespread tsunamis along the coastal zones of the surrounding oceans and released an estimated energy equivalent of 100 teratons of TNT and produced high concentrations of dust, soot, and sulfate aerosols in the atmosphere. Three-quarters of the plant and animal species on Earth disappeared. Marine ecosystems lost about half of their species while freshwater environments shows low extinction rates, about 10% to 22% of genera.

Recent studies suggest that the amount of sunlight that reached Earth’s surface was reduced by approximately 20%. Photosynthesis stopped and the food chain collapsed. The decrease of sunlight caused a drastic short-term global reduction in temperature (15 °C on a global average, 11 °C over the ocean, and 28 °C over land). While the surface and lower atmosphere cooled, the tropopause became much warmer, eliminate the tropical cold trap and allow water vapor mixing ratios to increase to well over 1,000 ppmv in the stratosphere. Those events accelerated the destruction of the ozone layer. During this period, UV light was able to reach the surface at highly elevated and harmful levels.

Gravity anomaly map of the Chicxulub impact structure (From Wikimedia Commons)

In 1980, Walter Alvarez and his father, Luis Alvarez ignited a huge controversy when they concluded that the anomalous iridium concentration at the K-Pg boundary is best interpreted as the result of an asteroid impact. They even calculated the size of the asteroid (about 7 km in diameter) and the crater that this body might have caused (about 100–200 km across). In 1981, Pemex (a Mexican oil company) identified Chicxulub as the site of a this massive asteroid impact. The crater is more than 180 km (110 miles) in diameter and 20 km (10 miles) in depth, making the feature one of the largest confirmed impact structures on Earth.

 

References:

Charles G. Bardeen, Rolando R. Garcia, Owen B. Toon, and Andrew J. Conley, On transient climate change at the Cretaceous−Paleogene boundary due to atmospheric soot injections, PNAS 2017 ; published ahead of print August 21, 2017 DOI: 10.1073/pnas.1708980114

Brugger J.G. Feulner, and S. Petri (2016), Baby, it’s cold outside: Climate model simulations of the effects of the asteroid impact at the end of the CretaceousGeophys. Res. Lett.43,  doi:10.1002/2016GL072241.

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

 

The Enigmatic Chilesaurus and the evolution of ornithischian dinosaurs

Chilesaurus diegosuarezi (MACN)

Chilesaurus diegosuarezi is a bizarre dinosaur from the Upper Jurassic of southern Chile. Holotype specimen (SNGM-1935) consists of a nearly complete, articulated skeleton, approximately 1.6 m long. Four other partial skeletons (specimens SNGM-1936, SNGM-1937, SNGM-1938, SNGM-1888) were collected in the lower beds of Toqui Formation. All the preserved specimens of Chilesaurus show ventrally flexed arms with the hands oriented backwards, an arrangement that closely resembles the resting posture similar described in Mei long, Sinornithoides youngi, and Albinykus baatar. 

Chilesaurus possesses a number of surprisingly plesiomorphic traits on the hindlimbs, especially in the ankle and foot, which resemble basal sauropodomorphs; but the pubis closely resembles that of basal ornithischians. The bizarre anatomy of Chilesaurus raises interesting questions about its phylogenetic relationships. The features supporting the basal position of Chilesaurus within Tetanurae are: scapular blade elongate and strap-like; distal carpal semilunate; and manual digit III reduced.

Chilesaurus holotype cast (MACN)

But the position of Chilesaurus within within Tetanurae conflicts with the presence of several highly derived coelurosaurian features (e.g., opisthopubic pelvis, large supratrochanteric process on ilium, reduced supracetabular crest) which are present in combination with a number of surprisingly plesiomorphic traits present in basal sauropodomorphs.

Ornithischian features of Chilesaurus (From Baron and Barret, 2017)

Chilesaurus also 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. For instance, Chilesaurus lacks a predentary bone, one of the features previously regarded as a fundamental ornithischian feature, although it possesses a retroverted pubis, suggesting that opisthopuby preceded the evolution of some craniodental modifications. Opisthopuby has also been related to herbivory, as it has been suggested that pubic retroversion might be related to the evolution of a more complex, longer digestive tract (Baron and Barret, 2017).

References:

Baron MG, Barrett PM. 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

Nicolás R. Chimento, Federico L. Agnolin, Fernando E. Novas, Martín D. Ezcurra, Leonardo Salgado, Marcelo P. Isasi, Manuel Suárez, Rita De La Cruz, David Rubilar-Rogers & Alexander O. Vargas (2017) Forelimb posture in Chilesaurus diegosuarezi (Dinosauria, Theropoda) and its behavioral and phylogenetic implications. Ameghiniana doi: 10.5710/AMGH.11.06.2017.3088

Novas, F.E., Salgado, L., Suarez, M., Agnolín, F.L., Ezcurra, M.D., Chimento, N.R., de la Cruz, R., Isasi, M.P., Vargas, A.O., and Rubilar-Rogers, D. 2015. An enigmatic plant-eating theropod from the Late Jurassic period of Chile. Nature 522: 331-334. doi:10.1038/nature14307