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.

 

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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

The sixth mass extinction

Painting of the Dodo by Roelandt Savery executed in ca. 1626 and held at the NHMUK, London.

Mass extinctions had shaped the global diversity of our planet several times during the geological ages. The fossil record indicates that more than 95% of all species that ever lived are now extinct. During times of normal background extinction, the taxa that suffer extinction most frequently are characterized by small geographic ranges and low population abundance. Occasionally extinction events reach a global scale, with many species of all ecological types dying out in a near geological instant. In a conservative palaeontological sense, a mass extinction occurs when extinction rates accelerate relative to origination rates such that over 75% of species disappear within a geologically short interval (typically less than 2 million years).

Over the past 500 years, humans have triggered a wave of extinction, threat, and local population declines that may be comparable with the five previous mass extinctions of Earth’s history. Although anthropogenic climate change is playing a growing role, the primary drivers of modern extinctions seem to be habitat loss, human predation, and introduced species. The term defaunation was created to designate the declining of top predators and herbivores triggered by human activity, that results in a lack of agents that control the components of the ecosystems vegetation.

The percentage of species of land mammals from five major continents/
subcontinents in the period ∼1900–2015 (From Ceballos et al., 2017)

The most recent Living Planet Index (LPI) has estimated that wildlife abundance on the planet decreased by as much as 58% between 1970 and 2012. Several species of mammals that were relatively safe one or two decades ago are now endangered. The highest percentage of decreasing species is concentrated in tropical regions, mostly in the Neotropics and Southeast Asia. In 2016, there were only 7,000 cheetahs in existence, and less than 5,000 Borneo and Sumatran orangutans. Populations of African lion has dropped 43% since 1993, and populations of giraffes dropped from around 115,000 individuals in 1985 to around 97,000 representing what is now recognized to be four species (Giraffa giraffa, G. tippelskirchi, G. reticulata, and G. camelopardalis) in 2015.

Amphibians offer an important signal to the health of biodiversity; when they are stressed and struggling, biodiversity may be under pressure. Decreasing amphibians are prominent in Mexico, Central America, the northern Andes, Brazil, West Africa, Madagascar, India, Indonesia and Philippine. In the case of reptiles, the proportional decline concentrates almost exclusively in Madagascar; and decreasing species of birds are found over large regions of all continents. Other studies document that invertebrates and plants are suffering massive losses of populations and species. Long-term distribution data on moths and four other insect orders in the UK show that a substantial proportion of species have experienced severe range declines in the past several decades. Therefore, the acceleration of extinctions over the past decades, in which humans have played an increasingly important role, has left a number of hard questions about how the Anthropocene should be defined and whether or not extinctions should contribute to this definition.

 

References:

Gerardo CeballosPaul R. Ehrlichand Rodolfo Dirzo; Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines, Proceedings of the National Academy of Sciences (2017) doi: 10.1073/pnas.1704949114 

Rodolfo Dirzo et al., Defaunation in the Anthropocene, Science 345, 401 (2014); DOI: 10.1126/science.1251817

 

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

Solving a Darwinian mystery

Macrauchenia patachonica by Robert Bruce Horsfall.

During the first two years of his voyage aboard HMS Beagle, Charles Darwin collected a considerable number of fossil mammals from various South American localities. Darwin sent all the specimens to the Reverend Professor John Stevens Henslow, his mentor and a close friend. The samples were deposited in the Royal College of Surgeons where Richard Owen began its study. Between 1837 and 1845, Owen described eleven taxa, including: Toxodon platensis, Macrauchenia patachonica, Equus curvidens, Scelidotherium leptocephalum, Mylodon darwinii, and Glossotherium sp.

Macrauchenia, meaning “big neck,” was named by Richard Owen based on limb bones and vertebrae collected by Charles Darwin on January 1834 at Puerto San Julian, in Santa Cruz Province, Argentina. The bizarre animal had a camel-like body, with sturdy legs, a long neck and a relatively small head. Owen described as “A large extinct Mammiferous Animal, referrible to the Order Pachydermata; but with affinities to the Ruminantia, and especially to the Camelidae”Macrauchenia is now considered among the more derived native South American litopterns, an endemic order whose fossil record extends from the Paleocene to the end of the Pleistocene and includes some 50 described genera. Darwin also made inferences about the environment which Macrauchenia lived: “Mr. Owen… considers that they form part of an animal allied to the guanaco or llama, but fully as large as the true camel. As all the existing members of the family of Camelidae are inhabitants of the most sterile countries, so we may suppose was this extinct kind… It is impossible to reflect without the deepest astonishment, on the changed state of this continent. Formerly it must have swarmed with great monsters, like the southern parts of Africa, but now we find only the tapir, guanaco, armadillo, capybara; mere pigmies compared to antecedents races… Since their loss, no very great physical changes can have taken place in the nature of the Country. What then has exterminated so many living creatures?…We are so profoundly ignorant concerning the physiological relations, on which the life, and even health (as shown by epidemics) of any existing species depends, that we argue with still less safety about either the life or death of any extinct kind” (Voyage of the Beagle, Chapter IX, Jan. 1834).

Dated mitogenomic phylogenetic tree. (From Westbury, M. et al)

The unusual morphological traits displayed by extinct South American native ungulates defied both Charles Darwin and Richard Owen, who tried to resolve their relationships. Two recently published molecular studies, using protein (collagen) sequence information, found that litopterns as well as notoungulates formed a monophyletic unit that shared more recent common ancestry with Perissodactyla than with any other extant placental group.

A valuable tool for uncovering phylogenetic relationships of extinct animals is ancient DNA (aDNA), although, attempts to use standard aDNA methodologies to collect genetic material from specimens from low-latitude localities have been largely unsuccessful. However, a new study recovered a nearly complete mitochondrial genome for Macrauchenia from a cave in southern Chile. The small size of the mitochondrial genome simplifies the assembly of fossil sequences using de novo methods.

In theory, reconstructing an ancient genome de novo can be undertaken without relying on a close relative’s DNA for guidance, but due to contaminant DNA and low average fragment lengths, de novo assembly is generally considered not computationally feasible. A promising new approach is using  the genetic codes of numerous living species as reference points, allowing them to reliably predict the fossil’s likeliest genetic sequences. Using the new approach, the phylogenetic analyses place Macrauchenia as a sister taxon to all living Perissodactyla, with the origin of Panperissodactlya at 66 Ma.

 

References:

Westbury, M. et al. A mitogenomic timetree for Darwin’s enigmatic South American mammal Macrauchenia patachonicaNat. Commun. 8, 15951 doi: 10.1038/ncomms15951 (2017).

Welker, F. et al. Ancient proteins resolve the evolutionary history of Darwin’s South American ungulates. Nature 522, 81–84 (2015). doi:10.1038/nature14249

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Neuroanatomy of the abelisaurid theropod Viavenator exxoni

Viavenator exxoni, Museo Municipal Argentino Urquiza

The Abelisauridae represents the best-known carnivorous dinosaur group from Gondwana. Their fossil remains have been recovered in Argentina, Brazil, Morocco, Niger, Libya, Madagascar, India, and France. The group was erected by Jose Bonaparte with the description of  Abelisaurus Comahuensis. These theropods exhibit spectacular cranial ornamentation in the form of horns and spikes and strongly reduced forelimbs and hands. In South America, braincase remains are known for Carnotaurus sastrei, Abelisaurus comahuensis, 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. Cranial elements of this specimen include the complete neurocranium: frontals, parietals, sphenethmoids, orbitosphenoids, laterosphenoids, prootics, opisthotics, supraoccipital, exoccipitals, basioccipital, parasphenoids and basisphenoids. The cranial endocast of Viavenator measures 157.7 mm from the olfactory bulbs to the foramen magnum, with a volume of approximately 141.6 cm3. The general shape of cranial endocast is elongate and narrow, similar to Aucasaurus and Majungasaurus. The widest part of the cranial endocast of Viavenator is at the level of the cerebral hemispheres. Four blood vessel foramina are recognized in the braincase: the caudal middle cerebral vein, the rostral middle cerebral vein, the cerebral internal carotid artery and the sphenoid artery.

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.

The forebrain of Viavenator include the olfactory tracts and olfactory bulbs, the cerebral hemispheres, optic nerves, the infundibular stalk, and the pituitary body. The CT scans show that the olfatory tracts are undivided. The olfactory bulbs are oval and are separated by a median septum at the anterior region of the sphenethmoids. The optic lobes are not clearly defined. The visible features of the hindbrain in the cranial endocast include the cerebellum, medulla oblongata, and cranial nerves V–XII. The cerebellum is not clearly expanded in the endocast; however, the floccular process of the cerebellum is well defined. The general morphology of both, brain and inner ear of Viavenator is markedly similar to that of Aucasaurus.
Neurosensorial capabilities of extinct animals can be inferred in part based on the relative development of certain regions of the brain. The flocculus of the cerebellum plays a role in coordinate eye movements, and tends to be enlarged in taxa that rely on quick movements of the head and the body. The flocculus of Viavenator is particularly large compared with Majungasaurus, suggesting that Viavenator relied more on quick movements of the head and sophisticated gaze stabilization mechanisms than the African form. The dimensions of the auditory sensory epithelium of Viavenator is similar to Majungasaurus, suggesting that they had similar hearing capabilities. In large dinosaurs, hearing was restricted to low frequencies with high frequency limit below 3 kHz.

References:

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

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