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

 

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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

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

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

Molecular signatures of fossil leaves

Leaves of Ptilophyllum mueller, from Emmaville, New South Wales. Scale bars=10 mm (From McLoughlin et al., 2011)

The first plants colonized land approximately 450 million years ago. The transition from an exclusively aquatic to a terrestrial life style implied the evolution of a new set of morphological and physiological features. The most critical adaptive trait for survival during terrestrialization was the ability to retain water in increasingly dehydrating habitats. Consequently, the capacity to maintain a hydrophobic surface layer, or cuticle, over the surfaces of aerial organs was arguably one of the most important innovations in the history of plant evolution.

Spores, pollen and leaf cuticles, are among the most resilient organic structures in the geological record. These components may retain some phylogenetically unique signals, not only in well-preserved fossils, but also in remains with a high level of diagenetic maturity.

Ginkgo biloba, Eocene fossil leaf from the Tranquille Shale of MacAbee, British Columbia, Canada (From Wikipedia Commons)

Generally, the cuticle is divided into two major structural constituents: cutin and cutan. The fatty acid polyesters which constitute cutin, gives the cuticle considerable resistance to biodegradation. Cutan is a non-ester and non-hydrolyzable matrix of aliphatic compounds linked by ether bonds, which remain after cutin hydrolysis. Additionally, the surface of the cuticle may be covered by various long-chain hydrophobic waxes. All these components  favours the survival of the cuticle in many fossil plants, and can be used to resolve the stratigraphic ranges and relationships of extinct plants.

Data from infrared spectroscopy of modern plant cuticles, have been used successfully to support and clarify the species-level taxonomy of extant plants, for example, in Camellia and angiosperm pollen. Using infrared spectroscopy and statistical analysis, researchers at Lund University, the Swedish Museum of Natural History in Stockholm, and Vilnius University, analysed a selection of fossil Cycadales, Ginkgoales and conifers. The team obtained two major groups in the dendrogram of infrared spectra. One branch unites podocarpacean and araucariacean conifers (excluding the Jurassic Allocladus). A relationship consistent with all modern phylogenetic analyses of gymnosperm. The second branch unites a broad range of gymnosperms. Within this branch, Bennettitales (Otozamites and Pterophyllum) form a well-defined group in association with Ptilozamites and Nilssoniales. This cluster is linked to a group incorporating Cycadales on one sub-branch, and Leptostrobales, Ginkgoales and the putative araucariacean Jurassic conifer Allocladus on a second sub-branch.

 

Dendrogram based on HCA of infrared absorption spectra of an expanded group of 13 fossil gymnosperm taxa (From Vajda et al., 2017)

Early palaeobotanical studies generally linked Bennettitales to Cycadales, but more recent anatomical studies and cladistic analyses have indicated that Bennettitales are not closely related to Cycadales. By contrast, Bennettitales, Nilssoniales and Ptilozamites are grouped closely. Additionally,  the systematic position of Allocladus within Araucariaceae should be reassessed based on its close association with Ginkgo in the cluster analysis of infrared spectra.

References:

Vivi Vajda, Milda Pucetaite, Stephen McLoughlin, Anders Engdahl, Jimmy Heimdal, Per Uvdal. Molecular signatures of fossil leaves provide unexpected new evidence for extinct plant relationships. Nature Ecology & Evolution, 2017; DOI: 10.1038/s41559-017-0224-5

Stephen McLoughlinRaymond J. Carpenter, and Christian Pott, Ptilophyllum muelleri (Ettingsh.) comb. nov. from the Oligocene of Australia: Last of the Bennettitales?, International Journal of Plant Sciences 2011 172:4574-585, DOI: 10.1086/658920

Forelimb posture in Chilesaurus diegosuarezi.

 

Chilesaurus holotype cast (MACN. From Wikipedia Commons. Author: Evelyn D’Esposito)

Chilesaurus diegosuarezi is a bizarre tetanuran 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. For a basal tetanuran, Chilesaurus possesses a number of surprisingly plesiomorphic traits on the hindlimbs, especially in the ankle and foot, which resemble basal sauropodomorphs.

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. However, the hindlimbs of Chilesaurus are posteriorly extended, rather than ventrally flexed. So it seems that individuals of Chilesaurus were buried quickly and fossilized almost in life position during passive activity (e.g. feeding, resting).

Cast of SNGM-1937 specimen of Chilesaurus diegosuarezi in dorsal (1), 471 lateral (2), and anterolateral view (3).

Cast of SNGM-1937 specimen of Chilesaurus diegosuarezi in dorsal (1), 471 lateral (2), and anterolateral view (3). Scale: 20 mm.

The specimen SNGM-1937 shows an angular relation in the wrist that resembles that in Deinonychus. In fact, several coelurosaurs have the same resting position as the forelimbs of Chilesaurus, with the humerus and radius-ulna in perpendicular relation or elbow flexed in an acute angle, hands under the radius-ulna, and palmar surface posterodorsal and dorsomedial oriented with respect to the main body axis. The resting posture of the forelimbs has been studied in theropod species, in relation to the acquisition of flight. It was suggested that the presence of the forelimb folded structure in advanced theropods are related with soft structures, as patagial skin and muscles, present in several maniraptoran dinosaurs.

The cojoined flexion of wrist and elbow in living birds is mainly conducted by the action of a large number of tendons located within the propatagium. Although the existence of propatagium was considered as unique to modern birds, it have also been described for coelurosaurs and Pterosauria. The preserve of a flexed forearm in Chilesaurus, may be also regarded as an indirect indicative of the presence of propatagium in this taxon.

 

References:

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 (advance online publication) 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

 

A mid-Cretaceous enantiornithine frozen in time

Overview of HPG-15-1 in right lateral view. (From Xing et al., 2017)

Overview of HPG-15-1 in right lateral view. (From Xing et al., 2017)

Amber from the Hukawng Valley in northern Myanmar, called Burmese amber, has been commercially exploited for millennia. Of the seven major deposits of amber from the Cretaceous Period, Burmese amber has probably the most diverse paleobiota, including the tail of a non-avian coelurosaurian theropod, and three juvenile enantiornithine birds. The third specimen, HPG-15-1, is the most complete fossil bird discovered in Burmese amber. It comes from the Angbamo site, and measures approximately 86 mm x 30 mm x 57 mm, and weighs 78 g. It  was encapsulated during the earliest stages of its feather production, and  plumage preserves an unusual combination of precocial and altricial features unlike any living hatchling bird.

 Details of the head in HPG-15-1. A, x-ray µCT reconstruction in left lateral view

Details of the head in HPG-15-1. A, x-ray µCT reconstruction in left lateral view (From Xing et al., 2017)

The skull was split when the amber was cut. The rostrum is preserved in one section and the neck and most of the braincase in the other. The skull is mesorostrine. A  single tooth is visible in the left premaxilla. As in Early Cretaceous enantiornithines, the premaxillary corpus is short, forming approximately one-third of the rostrum. The exoccipitals contributed to the dorsal portion of the condyle and were unfused at the time of death. The frontals articulate for most of their length with a small gap between their rostral ends as in Archaeopteryx.  The inner ear and its semicircular canals are preserved. There are at least six articulated cervical vertebrae, including the atlas and axis, preserved in articulation with the skull. The post-axial vertebrae are rectangular with large neural canals, low and caudally displaced neural spines, and a ventral keel as in many enantiornithines. The articulated skull and series of cervical vertebrae bear plumage in dense fields. The individual feathers  are dark brown in color, and appear to consist of tufts of four or more barbs. Skin is preserved as a translucent film in unfeathered regions of both the head and neck.

Microstructure and pigmentation of feathers on wing and body of HPG-15-1. Scale bars equal 1 mm in (A, C); 0.5 mm in (B, D). From Xing et al., 2017

The new specimen also preserves a partial distal wing, the distal right tibiotarsus and complete right foot as well as part of the left pes. Both skeletal material and integumentary structures from the wing’s apex are well-preserved. The plumage consists of fragments of some of the primaries, and alula feathers, some of the secondaries and coverts, and traces of contours from the wing base. The hind limbs preserve feathers and traces of skin. The absence of fusion between the tarsals indicates that the specimen is ontogenetically immature. The proportions of the pedal digits suggest an arboreal lifestyle. Plumage within the femoral and crural tracts consists of neoptile feathers with a short or absent rachis. These feathers are nearly transparent, suggesting that they were pale or white. The skin beneath the crural tract is thin and smooth. The tip of the tail clearly preserves the remains of a single large sheathed rectrix.

The slow post-natal growth results in a protracted period of vulnerability, which is reflected in the Enantiornithes by the large number of juveniles found in the fossil record, whereas young juveniles of other Cretaceous bird lineages are unknown.

 

References:

Lida Xing, Jingmai K. O’Connor, Ryan C. McKellar, Luis M. Chiappe, Kuowei Tseng, Gang Li, Ming Bai , A mid-Cretaceous enantiornithine (Aves) hatchling preserved in Burmese amber with unusual plumage, (2017), doi: 10.1016/j.gr.2017.06.001