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

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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

Patagotitan and the problem of body mass estimation

Image: A. Otero.

Since the discovery of dinosaur remains in the Neuquen basin in 1882, Argentina has gained the title of Land of the Giants. The tittle was reinforced by recent discoveries of more remains of giant titanosaurs like Argentinosaurus, Dreadnoughtus, Notocolossus, Puertasaurus.

Titanosaurus were a diverse group of sauropod dinosaurs represented by more than 30 genera, which included all descendants of the more recent common ancestor of Andesaurus and Saltasaurus. The group includes the smallest (e.g. Rinconsaurus, Saltasaurus; with estimated body masses of approximately 6 tonnes) and largest sauropods known to date. They had their major radiation during the middle Early Cretaceous. The evolution of body mass in this clade is key element to understand sauropod evolution.

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.

(a) Middle cervical vertebra in right lateral view; (b) anterior dorsal vertebra in anterior view (From Carballido et al., 2017)

During the last decades Argentinosaurus hiunculensis has been considered the largest dinosaur that ever walked the Earth. But because of the fragmentary nature of the type specimen, quantitative methods for body mass estimation cannot be directly applied. Two previous studies (Mazzetta et al., 2004; Benson et al., 2014) estimated the body mass of Argentinosaurus by applying scaling equations and measurements taken from two isolated femoral shafts found in deposits of the Huincul Formation. Calculations based in one of these fragmentary femora, housed at the Museo de La Plata collection and at the Museo Municipal “Carmen Funes”, estimates a body mass of 73 tons, but for the moment none of the femora can be confidentially referred to Argentinosaurus given the complete absence of femoral remains in the type material.

The team lead by Dr. José Luis Carballido from the Egidio Feruglio Paleontology Museum (Mef), used the anterior dorsal vertebrae (preserved in Argentinosaurus, Puertasaurus, Notocolossus) for a size comparison between Patagotitan and other giant titanosaurs from Patagonia. The direct comparison of these elements indicate that the dorsal vertebrae of Patagotitan are 8%–18% larger than that of Argentinosaurus and Puertasaurus, and even larger when compared to Notocolossus. Unfortunatelly, as the team remarks, this cannot be extrapolate to determine the body mass for Argentinosaurus and Puertasaurus and the only way to obtain a reliable body mass estimation is contingent on finding new associated material that can be referred to these taxa.

 

References:

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

Mazzetta, G. V., Christiansen, P., & Fariña, R. a. (2004). Giants and Bizarres: Body Size of Some Southern South American Cretaceous Dinosaurs. Historical Biology: A Journal of Paleobiology, 16(2–4), 71–83. http://dx.doi.org/10.1080/08912960410001715132

Benson, R. B. J., Campione, N. E., Carrano, M. T., Mannion, P. D., Sullivan, C., Upchurch, P., & Evans, D. C. (2014). Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage. PLoS Biology, 12(5), http://doi.org/10.1371/journal.pbio.1001853.

 

Pisanosaurus revisited

Reconstructed skeleton of Pisanosaurus (Royal Ontario Museum)

Pisanosaurus mertii was 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).

Pisanosaurus mertii holotype. Right lower mandible in medial (A) and lateral (B) views. Scale bar: 5 cm. From Agnolín and Rozadilla, 2017.

In the original description, Casamiquela considered that Pisanosaurus was a very distinct ornithischian, and even proposed a family: Pisanosauridae. The dentition and tooth-bearing bones of Pisanosaurus possess a large number of ornithischian traits, like its barricade-like dentition. But Pisanosaurus shows some features that strongly differ from those of ornithischians. For instance, vertebral centra are very elongated and transversely compressed, differing from the short and stout dorsal vertebrae of known ornithischians, including heterodontosaurids. The pelvis is another portion of the skeleton of Pisanosaurus strongly different from that of ornithischians.

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

On the other hand, 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 (present also in heterodontosaurids and several saurischians); dorsoventrally flattened ungual phalanges; and ankylothecodonty, teeth partially fused to maxilla and dentary bone. The first and last characters are lacking in ornithischians. Of course, the inclusion of Pisanosaurus within Silesauridae implies that this taxon does not constitute the oldest ornithischian. This also suggests a significant gap between Pisanosaurus and the oldest unambiguous records of ornithischians: Laquintasaura and Lesothosaurus, which may be dated as Hettangian in age. This is consistent with previous interpretations proposing that ornithischian radiation occurred after the Triassic–Jurassic boundary.

References:

Federico L. Agnolín & Sebastián Rozadilla (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., 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

Padian K. The problem of dinosaur origins: integrating three approaches to the rise of Dinosauria. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, Available on CJO 2013 doi:10.1017/S1755691013000431 (2013).

Meet Borealopelta markmitchelli

Holotype of Borealopelta markmitchelli (From Brown et al., 2017)

The Ankylosauria is a group of herbivorous, quadrupedal, armoured dinosaurs subdivided in two major clades, the Ankylosauridae and the Nodosauridae. The most derived members of this clade are characterized by shortened skulls, pyramidal squamosal horns, and tail clubs, among other features. Nodosauridae have a kinked ischium and more massive osteoderms, but lack a tail club. Ankylosaurs were present primarily in Asia and North America,  but the early origins of this clade are ambiguous. A three-dimensionally preserved ankylosaurian discovered in the Suncor Millennium Mine in northeastern Alberta, Canada, offers new evidence for understanding the anatomy of this group.

The new specimen, Borealopelta markmitchelli, from the Early Cretaceous of Alberta, preserves integumentary structures as organic layers, including continuous fields of epidermal scales and intact horn sheaths capping the body armor. The generic name Borealopelta is derived from “borealis” (Latin, “northern”) and “pelta” (Greek, “shield”). The specific epithet markmitchelli honors Mark Mitchell for his preparation of the holotype.

Schematic drawing of TMP 2011.033.0001 in dorsal view (From Brown et al., 2017)

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.

 

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

Arbour, V. M.; Currie, P. J. (2015). “Systematics, phylogeny and palaeobiogeography of the ankylosaurid dinosaurs”. Journal of Systematic Palaeontology: 1–60. doi: 10.1080/14772019.2015.1059985

Introducing Corythoraptor jacobsi.

The cranial casque of Corythoraptor jacobsi and recent cassowaries (From Lü et al., 2017)

Oviraptorosaurs are a well-defined group of coelurosaurian dinosaurs, characterized by short, deep skulls with toothless jaws, pneumatized caudal vertebrae, anteriorly concave pubic shafts, and posteriorly curved ischia.  The most basal forms were small, similar to a chicken or a turkey. They have only been found in Asia and North America and include animals like Protarcheoepteryx, Caudipteryx, Microvenator, Avimimus, Anzu, and Citipati. The most famous dinosaur of this group, Oviraptor, was discovered in 1923 by Roy Chapman Andrews in Mongolia, associated with a nest of what was thought to be Protoceratops eggs. The misconception persisted until 1990s when it was revealed that the eggs actually belonged to Oviraptor, not Protoceratops. Since then, more skeletons of Oviraptor and other oviraptorids like Citipati and Nemegtomaia have been found brooding over their eggs.

The Ganzhou area in the Jiangxi Province, in southern China, is one of the most productive oviraptorosaurian regions of the world. Six oviraptorosaurian dinosaurs have been named from Ganzhou: Banji long, Jiangxisaurus ganzhouensis, Nankangia jiangxiensis, Ganzhousaurus nankangensis, Huanansaurus ganzhouensis, and Tongtianlong limosus.  

The holotype of Corythoraptor jacobsi gen. et sp. nov. (From Lü et al., 2017)

The new oviraptorid dinosaur unearthed from the Upper Cretaceous deposits of Ganzhou, was named Corythoraptor jacobsi. The generic name Corythoraptor refers to a raptor bearing a “cassowary-like crest” on its head. The holotype (JPM-2015-001), an almost complete skeleton with the skull and lower jaw, probably corresponds to a young adult that was approaching a stationary stage of development. The anterodorsal part of the crest is missing, but apparently the highest point of the crest would project far above the orbit. The internal structure of the crest is similar to the casque of Casuarius unappendiculatus. The extensive cranial casque was probably composed of the skull roofing bones: nasals, frontals and parietals. The inner structure consists of randomly branching, sparse, trabeculae of variable thickness ranging from 0.3 to 1.2 mm, which implies that the inner core was light, fragile, and not suitable for percussive behavior including intraspecific combat.

Corythoraptor jacobsi forms one clade with Huanansaurus ganzhouensis, but both mainly differs in the skull morphology and the structure of the cervical vertebrae

 

References:

Lü, J., Li, G., Kundrát, M., Lee, Y., Sun, Z., Kobayashi, Y., Shen, C., Teng, F., Liu, H. 2017. High diversity of the Ganzhou oviraptorid fauna increased by a new “cassowary-like” crested species. Scientific Reports. doi: 10.1038/s41598-017-05016-6

 

Sapeornis and the flight modes of birds

Sapeornis chaoyangensis (DNHM-3078) showing well-preserved primary (P) and secondary (S) feathers. From Serrano and Chiappe, 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. Most of these fossils, like Sapeornis chaoyangensis (125 to 120 Ma), are from the Jehol Biota of northeastern China. Sapeornis shows a combination of derived and primitive features, like a short, robust non-strut-like coracoid and a fibula reaching the distal end of the tarsal joint, a pygostyle, reduced manual digits, and a well-fused carpometacarpus. All of these features indicates a mosaic pattern in the early evolution of birds and confirm the basal position of Sapeornis near Archaeopteryx and Jeholornis in the phylogeny of early birds.

The evolution of flight involved a series of adaptive changes at the morphological and molecular levels, that included the fusion and elimination of some bones and the pneumatization of the remaining ones. Archaeopteryx lacked a bony sternum and a compensatory specialized gastral basket for anchoring large flight muscles, while Jelohornis had several derived flight-related features of modern birds like fused sacral vertebrae, an elongated coracoid with a procoracoid process, a complex sternum, a narrow furcula, and curved scapula. In Enantiornithines, their robust pygostyle appears to have been unable to support the muscles that control the flight feathers on the tail in modern birds.

Morphofunctional fitness of the wing shape for soaring as depicted by the relation between the lift surface and the wingspan in modern soaring birds and Sapeornis (From Serrano and Chiappe, 2017)

The flight modes of modern birds are a reflection of their different strategies to reduce the energetic costs of a highly demanding style of locomotion. Among these features are wing shape, and the use of thermals and tail winds. Flapping flight is energetically more costly  than gliding and soaring flight, consequently, large birds have either elongated wingspans that allow them to gain height through air currents and to glide for long distances with much lower transit costs than flapping.

Fossil evidence suggests that S. chaoyangensis was a specialized flier that used continental soaring as its main flight mode. Computational models of S. chaoyangensis are also congruent with other morphological similarities between S. chaoyangensis and modern soaring birds including the shape of the furcula and the proportions of the forelimbs. Modern soaring birds include dynamic soarers that exploit air velocity gradients over sea waves, and thermal soarers that use ascending air currents mainly generated in continental areas. Because, exceptionally well preserved fossils of S. chaoyangensis have revealed seeds and/or fruits in its intestinal tract, this interpretation of the flight capabilities of S. chaoyangensis is consistent with the energetic disadvantages from a herbivorous diet, because soaring is a less demanding flight mode than continuous flapping.

References:

Serrano FJ, Chiappe LM. 2017 Aerodynamic modelling of a Cretaceous bird reveals thermal soaring capabilities during early avian evolution. J. R. Soc. Interface 14: 20170182. http://dx.doi.org/10.1098/rsif.2017.0182

Butler PJ. 2016 The physiological basis of bird flight. Phil. Trans. R. Soc. B 371, 20150384 doi:10. 1098/rstb.2015.0384

Zhou, Zhonghe & Zhang, Fucheng (2003): Anatomy of the primitive bird Sapeornis chaoyangensis from the Early Cretaceous of Liaoning, China. Canadian Journal of Earth Sciences 40(5): 731–747. doi 10.1139/E03-011

Osteohistological analysis of Vegavis iaai

Vegavis iaai by Gabriel Lio. / Photo: CONICET

The earliest diversification of extant birds (Neornithes) occurred during the Cretaceous period. Today, with more than 10500 living species, birds are the most species-rich class of tetrapod vertebrates. Vegavis iaai is the first unquestionable neornithine bird from the Cretaceous and is known by the holotype and specimen MACN-PV 19.748. The holotype specimen MLP 93-I-3-1 (Museo de La Plata, Argentina) from Vega Island, western Antarctica, was discovered in 1992 by a team from the Argentine Antarctic Institute, but was only described as a new species in 2005 (Clarke et al., 2005). Polarornis gregrorii, from the López de Bertodano Formation of Seymour Island, Antarctica, and Vegavis form a monophyletic basal clade of foot-propelled anseriform birds (Agnolín 2016), a group that includes ducks, geese and swans.

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.

Detail of the humerus of Vegavis iaai (MACN-PV 19.748) in polarised light. Scale = 1 mm. (From G. Marsà et al., 2017)

Many studies on avian microanatomy have established a relationship between high bone compactness (i.e., considerable degree of osteosclerosis) and diving behavior. Differences in the degree of osteosclerosis could be tentatively related to variations in diving behaviour. Vegavis was a diver, characterised by a medium level of limb osteosclerosis. Polarornis, with more massive bones, was possibly adapted to deeper and more prolonged diving than Vegavis, as occurs in modern penguins.

The value of Relative Bone Thickness (RBT) in Vegavis is comparable with two genera of extant foot-propelled diving ducks. A high RBT is related with increased stiffening the forelimb, regardless of body mass or depth of diving. Flightless Pan-Alcidae and penguins, have a very rigid, flipper-like wings suggesting that decreased wing flexion and increased cortical thickness of forelimbs are somehow correlated. Based on  the values of RBT present in both Vegavis and Polarornis is possible to infer that these taxa were foot-propelled birds.

References:

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

Agnolín FL. 2016. A brief history of South American birds. Contribuciones del MACN 6:157–172

Clarke, J. A., C. P. Tambussi, J. I. Noriega, G. M. Erickson, and R. A. Ketcham. 2005. Definitive fossil evidence for the extant avian radiation in the Cretaceous. Nature 433:305-308. DOI: 10.1038/nature03150