Malawisaurus dixeyi: The braincase and inner ear of a Southern African Titanosaur.

Titanosaurs were a group if exceptionally large Sauropod Dinosaurs that dominated many faunas in the Southern Hemisphere during the Cretaceous. The group includes the largest known Dinosaurs, with species such as Argentinosaurus and Puertasaurus thought to have weighed close to 90 tonnes. However the group was quite diverse, and also contained many smaller species, as well as both long and short-necked forms, suggesting a wide range of ecological specialisations.

Titanosaur remains from Malawi, Southern Africa, were first described under the name Gigantosaurus dixeyi in 1928. These fossils underwent several name-changes as our understanding of Dinosaur taxonomy changed and grew during the twentieth century, eventually gaining the current name, Malawisaurus dixeyi, in 1993. The beds which produced these fossils are of Cretaceous age, though a more precise date has eluded geologists to date; biostratigraphic studies using Ostracods (small Crustaceans with distinctive shells and high species turnover), and the beds are closely related to carbonates that have been dated to between 123 and 111 million years old, based upon potassium-argon geochronology (argon is a noble gas, and cannot be incorporated into rocks, but unstable isotopes of potassium, which decay into argon can, and will then remain in the rock; since this happens steadily at a known rate, geochemists can date rocks by establishing the ratio of radioactive potassium to argon within them), but studies of the Vertebrate fauna preserved within these rocks has suggested a Late Cretaceous origin.

In a paper published in the journal PLoS One on 13 February 2019, Kate Andrzejewski, Michael Polcyn and Dale Winkler of the Roy M. Huffington Department of Earth Sciences at Southern Methodist University, Elizabeth Gomani Chindebvu of Culture and Community Development at the Ministry of Civic Education in Malawi, and Louis Jacobs, also of the Roy M. Huffington Department of Earth Sciences at Southern Methodist University, describe new Malawisaurus dixeyi material from Malawi, including a reconstruction of the inner ear and endocast (cast of the inside of the braincase, this is not the same as the brain, but can give information about it), and draw conclusions from this.

The described specimen, Mal-202-1, comprises a nearly complete basicranium and associated parietals, ectopterygoid, quadrate, cervical vertebrae, and post cranial elements, all assigned to Malawisaurus dixeyi, recovered from near Mwakasyunguti in Karonga District, northern Malawi, by the Malawi Dinosaur Project in the 1980s and 90s.

The specimen was scanned at the University of Texas High Resolution X-ray CT facility, enabling Andrzejewski et al. to construct a three dimensional computer model of the brain endocast and inner ear. The bones of the braincase are well preserved, and all show fully ossified sutures, suggesting that the specimen was a mature adult at time of death. An estimate of its size based upon the circumference of the humerus, suggests a living weight of 4.73 tonnes.

Braincase of Malawisaurus dixeyi. (A) lateral view; (B) lateral view with endocast; (C) posterior view. Abbreviations: BO, basioccipital; BP, basipterygoid process; BT, basal tuber; CAR, canal for cerebral carotid artery; FO, fenestra ovalis; LABYR, labyrinth; LS, laterosphenoid; OC, occipital condyle; PFO, pituitary fossa; PP, paroccipital process; SO, supraoccipital; SPHA, canal for sphenopalatine artery; III, oculomotor nerve; IV, trochlear nerve; V, trigeminal nerve; VI, abducens nerve; VII, facial nerve; IX-XI, shared canal for glossopharyngeal, vagus, and spinal accessory nerves; XII, hypoglossal nerve. Scale bar equals 10cm. Andrzejewski et al. (2019).

Andrzejewski et al.’s reconstruction lacks the olfactory and cerebral regions, or caudal dural expansion, a prominent venous feature of Sauropods. Like most Sauropod endocasts it shows a lack of distinction of gross regions of the brain, presumably obscured by the presence of overlying thick meninges and extensive venous sinuses in life, but does show typical Sauropod features such as a large pituitary fossa. The reconstruction does show the connections of the veinous canals (canals through which the veins pass) and cranial nerves, the general pattern of which are consistent with the interpretation of Malawisaurus as a Titanosaur.

Cranial endocast and vestibular labyrinth of Malawisaurus dixeyi. (A) left lateral view; (B) caudal view; (C) ventral view; (D) dorsal view; dashed line represents reconstruction of full endocast based on the endocast of Sarmientosaurus. Endocast represented by purple colouring; cranial nerves by yellow colouring; vestibular labyrinth by pink colouring; carotid artery by red colouring. Scale bar equals 5cm. Andrzejewski et al. (2019).

The inner ears of several Sauropods have been described previously, with a general pattern observed of larger vestibular labyrinths in early members of the group, and smaller in more derived Titanosaurs; that of Malawisaurus dixeyi appears to be intermediate in size, which is roughly what would be expected based upon current interpretations of its phylogenetic position as a Titanosaur that split from the group early in their history. It also shows uneven size of the semicircular canals, something which is found in earlier Sauropods, but not more derived Titanosaurs, again consistent with the current interpretations of the phylogenetic position of the species.

Left vestibular labyrinth of Malawisaurus dixeyi. (A) lateral view; (B) posterior view; (C) dorsal view. Abbreviations: C, cochlea; CRC, crus commune; CSC caudal (posterior) semicircular canal; FP, fenestra perilymphatica; FV fenestra vestibuli; LSC, lateral semicircular canal; RSC, rostral (anterior) semicircular canal; VE, vestibule of inner ear. Scale bar equals 2cm. Andrzejewski et al. (2019).

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Lavocatisaurus agrioensis: A new species of Rebbachisaurid Sauropod Dinosaur from the Early Cretaceous of Argentina.

The Rebbachisaurids are a group of Diplodocimorph Sauropod Dinosaurs known from the Cretaceous of South America, Africa and Europe. They are considered to be the sister group to the other two Diplodocimorph clades, the Diplodocids and the Dicraeosaurid, which along with their presence on both sides of the Atlantic (implying they must have appeared before this ocean opened) suggests that they first appeared in the Middle Jurassic, though the earliest fossils confidently assigned to the group date from the middle of the Early Cretaceous, with the group persisting till the middle of the Late Cretaceous, making them the last surviving Diplodocimorph group.

In a paper published in the journal Acta Palaeontologica Polonica on 29 October 2018, José Canudo of the Facultad de Ciencias at the Universidad de Zaragoza, José Carballido of the Museo ‘Egidio Feruglio’, Alberto Garrido of the Museo Provincial de Ciencias Naturales ‘Prof. Dr. Juan Olsacher’ and the Departamento Geología y Petróleo at the Universidad Nacional del Comahue, and Leonardo Salgado of the Instituto de Investigación en Paleobiología y Geología at the Universidad Nacional de Río Negro, describe a new species of Rebbachisaurid from the Early Cretaceous Rayoso Formation at Agrio del Medio in Neuquén Province in Patagonia.

The new species is named Lavocatisaurus agrioensis, where ‘Lavocatisaurus’ honours the French palaeontologist René Lavocat (1909-2007), who described Rebbachisaurus, the first known Rebbachisaurid and the genus from which the group takes its name, and ‘agrioensis’ means ‘from Agrio’. The species is described from a fragmentary yet still partly articulated skeleton comprising both dentaries, the left surangular, premaxillae and maxillae, the left jugal, the right squamosal, the quadrates, 23 isolated teeth and two series of 8 and 9 maxillary teeth, thehyoid bone, 11 cervical vertebrae (including the atlas and axis), 28 caudal vertebrae, cervical ribs, 2 dorsal ribs, a humerus, and a fragment of what is probably the radius, plus 24 other bone fragments thought to have come from juvenile specimens of the same species.

Rebbachisaurid Sauropod Lavocatisaurus agrioensis from Agrio del Medio (Argentina), Aptian–lower Albian. (A) Axis in lateral view (A₁) photograph, (A₂) drawing; eight cervical vertebrae in lateral view view (A₃) photograph, (A₄) drawing; anterior caudal vertebra in lateral view (A₅); middle caudal vertebra in lateral view (A₆); posterior caudal vertebra in lateral view (A₇); posteriormost caudal vertebra in lateral view (A₈); left tibia in lateral view (A₉). (B) Left scapula from a juvenile specimen, in lateral view. (C) Skeletal reconstruction based on the holotype and paratype specimens. Scale bars are 10 cm. Canudo et al. (2018). 

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Maraapunisaurus fragillimus: Edward Drinker Cope’s giant Sauropod revisited, reclassified, and downsized (a bit).

In 1878 Oramel and Ira Lucas of Garden Park, Colorado, excavated a gigantic neural spine (projection on the top of a vertebra) from the Cope’s Nipple location of the Late Jurassic Morrison Formation, and shipped it to Edward Drinker Cope at the Academy of Natural Sciences of Philadelphia. Cope carefully examined, measured and illustrated this specimen, concluding that it came from a Diplodocid Sauropod Dinosaur, and reconstructed it as having come from a Vertebra over six feet (220 cm) high, which he named Amphicoelis fragillimus. Sadly, the specimen was lost some time between this description being made and Cope’s collection being curated at the American Museum of Natural History after his death, leaving modern scientists only Cope’s illustrations to go on. This is unfortunate, since it has been estimated that if the measurements of the specimen are correct, and it did come from a Diplodocid, then the animal that produced it would have been 58 m in length, by far the largest Dinosaur known, and dwarfing even modern Baleen Whales, which has led to some scientists making the opposite conclusion, that Cope’s measurements were inaccurate or even wildly exaggerated.

In a paper published in the journal Geology of the Intermountain West on 19 October 2018, Kenneth Carpenter of the Prehistoric Museum at Utah State University Eastern, and the University of Colorado Museum of Natural History re-examines Cope’s illustrations of the giant neural spine, and draws new conclusions about the affinities of the specimen, and the nature of the animal that produced it.

The controversial vertebra and Edward D. Cope who described the specimen in 1878. Carpenter 2018. 

When Cope was examining the specimen, very few Sauropods were known, and less than a year had passed since the first description of a North American species. This meant that there were very few Sauropod specimens to compare the neural spine to. Of the available specimens, one struck Cope as being particularly likely, Amphicoelias altus, one of the first described Diplodocids (though this term was not coined until the 1920s), with the similarity apparently so great that Cope described the specimen as a new species within the same genus, Amphicoelias fragillimus.

Illustrations of different sauropod dorsals made by Cope to show why he thought that the neural spine of "Amphicoelias" fragillimus (A) was most similar to that of Amphicoelias altus (B) than to Camarasaurus supremus (C) mid-dorsal and (D) more posterior mid-dorsal. Scale bar is 1 m. Carpenter 2018.

Diplodocids were large animals, among the largest Sauropods and therefore Dinosaurs of any kind, but their vertebrae had relatively small centra (disks) with a large neural spine located above. Interpreted as the neural spine of a Diplodocid, Cope's specimen calculated to have come from a vertebra six foot four inches (1.93 m) high, which in turn has been used to suggest an animal 58 m in length. 

This is excepionally large, even for a Sauropod Dinosaur, and has provoked some extreme scepticism among palaeontologists, some of whom have gone as far as to sugest that Cope's measurements were inaccurate. Carpenter, however, notes that Cope's measurements and illustrations were generally considered to be excellent, and that, where they can be checked against still extant specimens, appear to be highly reliable. Instead he puts forward an alternative theory, that Cope's specimen comes not from a Diplodocid, but instead from a Rebbachisaurid, a group of Dinosaurs entirely unknown in Cope's day, and which had rather different proportions. To this end he proposes that the name Amphicoelias fragillimus is wrong for the neural arch, since Amphicoelias refers to a genus of Diplodocid Dinosaurs, which was described prior to the specimen, and therefore suggests a new genus name, Maraapunisaurus, meaning 'Huge Reptile'.

Comparison of the neural spine of Maraapunisaurus fargillimus restored as a Rebbachisaurid (A), and the dorsal vertebrae of Rebbachisaurus garasbae (B), and Histriasaurus boscarollii (C). Increments on scale bars are 10 cm. Carpenter 2018.

Like Diplodocids, Rebbachisaurids were big animals, but their proportions were somewhat different, with their vertebrae typically composing a large, wide centra surmounted by a large neural arch, with the whole structure being far larger compared to the overall size of the animal; interpreted as a neural arch from a Rebbachisaurid, Carpenter estimates that Cope's specimen would have come from a vertebra 2.4 m in height, but that this would have come from an animal only 30.3 m in length (big, but not absurd - and it has never been doubted that the vertebra came from a big animal).

Body comparisons of Maraapunisaurus as a 30.3-m-long Rebbachisaurid (green) compared with previous version as a 58-m-long Diplodocid (black). Lines within the silhouettes approximate the distal end of the diapophyses (i.e., top of the ribcage). Carpenter 2018.

The Rebbachisaurids as a group are currently known only from South America, Africa and Europe, and only from the Cretaceous, which at first sight seems a problem for the assignment of the specimen to this group. However, the Rebbachisaurids are considered to be the sister group to the Diplodocids (hence having neural spines similar enough to be mistaken), and therefore the two groups must have had a common ancestor living in one place, so finding an ancestral Rebbachisaurid living in an area known to have been home to early Diplodocids is not especially surprising, particularly as North America was probably still attached to Europe in the Late Jurassic, and Europe subsequently came into contact with North Africa, while West Africa was still attached to South America, creating a pathway known to have been used by other groups.

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Lingwulong shenqi: A new species of Diplodocoid Sauropod Dinosaur from the Middle Jurassic of the Ningxia Hui Autonomous Region of northwest China.

Sauropod dinosaurs were massive, long-necked, long-tailed creatures that have long been regarded as the largest land animals ever to have lived. They reached their most diverse in the Late Jurassic, when the break-up of the supercontinent of Pangea facilitated the splitting of the group into several regional subgroups, each of which underwent an evolutionary radiation in their local environment.

In a paper published in the journal Nature Communications on 24 July 2018, Xing Xu of the Institute of Vertebrate Paleontology & Paleoanthropology of the Chinese Academy of Sciences, Paul Upchurch of the Department of Earth Sciences at University College London, Philip Mannion of the Department of Earth Science and Engineering at Imperial College London, Paul Barrett of the Department of Earth Sciences at the Natural History Museum, Omar Regalado-Fernandez, also of the Department of Earth Sciences at University College London, Jinyou Mo of the Natural History Museum of Guangxi, Jinfu Ma of the Lingwu National Geopark Administration, and Hongan Liu of the Lingwu Historic Relic Administration, describe a new species of Diplodocoid Sauropod Dinosaur from the Middle Jurassic of the Ningxia Hui Autonomous Region of northwest China.

The new species is named Lingwulong shenqi, where 'Lingwulong' means 'Drangon of Lingwu', in reference to the Lingwu National Geopark, where the specimen from which it is described was found, and 'shenqi' means 'amazing'. Lingwulong shenqi is described from a partial skull and partial skeleton from the Middle Jurassic Yanan Formation; these were recovered from the same location, and probably come from the same individual, though this cannot be stated with absolute confidence. A number of other partial skeletons from the same location also thought to belong to the same species. 

Skeletal reconstruction and exemplar skeletal remains of Lingwulong shenqi. Silhouette showing preserved elements (a); middle cervical vertebra in left lateral (b) and anterior (c) views; anterior dorsal vertebra in left lateral (d) and anterior (e) views; posterior dorsal vertebra in lateral view (f); sacrum and ilium in left lateral view (g); anterior caudal vertebra in left lateral (h) and anterior (i) views; right scapulocoracoid in lateral view (j); right humerus in anterior view (k); left pubis in lateral view (l); right ischium in lateral (m) views; right femur in posterior view (n); and right tibia in lateral view (o). Abbreviations: ap, ambiens process; ar, acromial ridge; ip, iliac peduncle; naf, notch anterior to glenoid; np, neural spine; podl, postzygodiapophyseal lamina; ppr, prezygapophyseal process ridge; prp, prezygapophysis; pvf, posteroventral fossa; slf, shallow lateral fossa; spol, spinopostzygapophyseal lamina; sprl, spinoprezygapophyseal lamina; wls, wing-like structure. Scale bars are100 cm for (a) and 5 cm for (b)–(o). Xu et al. (2018).

Lingwulong shenqi has a number of features which lead Xu et al. to conclude that it should unequivocally be placed within the Diplodocoidea, a group previously thought to have been excluded from East Asia by the break-up of Pangea. The presence of a Diplodocoid  in this area implies that (1) either the supercontinent did not break up as soon as is currently thought, a timeline based upon numerous lines of evidence and considered to be highly robust, or that Diplodocoids, and by extension Neosuaropods (the group that includes Diplodocoids and Titanosaurs) first appeared at least 15 million years earlier than previously supposed.

Paleogeographic maps showing the formation and disappearance of an epicontinental seaway between Europe and Central Asia during the Middle Jurassic through Early Cretaceous. (a) Middle Jurassic, 170 million years ago; (b) Late Jurassic, 160 million years ago; (c) Early Cretaceous, 138 million years ago. Green indicates land, light blue shallow sea, and deep blue ocean. Abbreviations: R, Russian Platform Sea; T, Turgai Sea. Xu et al. (2018).

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Dinosaur phylogenetics, a radical new proposal.

Phylogenetics is the study of the relationships between organisms, as determined by examining similarities between species and reconstructing family trees. The early origins of the science relied very much on informed guesswork, but modern phylogenetics is a highly mathematical discipline, in which practitioners attempt to measure mathematically differences between the morphologies, or better still DNA, of different species, and allow computer models to estimate the most likely relationships between them. The phylogeny of the Dinosaurs, although it has changed a great deal in detail with the discovery of numerous new species, has remained essentially the same since 1887, with the earliest Dinosaurs appearing in the Middle-to-Late Triassic and rapidly diverging into two distinct groups the ‘Lizard-hipped’ Saurischians and the ‘Bird-hipped’ Ornithischians, and the Saurischians splitting shortly afterwards into the Sauropods and Theropods.

In a paper published in the journal Nature on 23 March 2017, Matthew Baron of the Department of Earth Sciences at the University of Cambridge and the Department of Earth Sciences at the Natural History Museum, David Norman also of the Department of Earth Sciences at the University of Cambridge and Paul Barrett also of the Department of Earth Sciences at the Natural History Museum describe a radically different phylogeny for the Dinosaurs, based upon a new study which incorporated data on 457 morphological characteristics of 74 taxa of Dinosaurs and Dinosauromorph Archosaurs (i.e. Archosaurs thought to be closely related to Dinosaurs). 

Remarkably Baron et al. did not recover the two ‘Saurischian’ Dinosaur groups as being one-another’s closest relatives to the exclusion of the Ornithischians; rather they produced a model in which the Dinosaurs split early into two groups, one comprising the Sauropods plus the Herrerasauridae (a group of early Dinosaurs generally thought to be primitive Theropods) and the other comprising the Ornithischians plus all other Theropods.

Phylogenetic relationships of early dinosaurs. Time-calibrated strict consensus of 94 trees from an analysis with 73 taxa and 457 characters. (A) the least inclusive clade that includes Passer domesticus, Triceratops horridus and Diplodocus carnegii — Dinosauria, as newly defined. (B) the least inclusive clade that includes Passer domesticus and Triceratops horridus — Ornithoscelida, as defined. (C) the most inclusive clade that contains Diplodocus carnegii, but not Triceratops horridus —Saurischia, as newly defined. All subdivisions of the time periods (white and grey bands) are scaled according to their relative lengths with the exception of the Olenekian (Early Triassic), which has been expanded relative to the other subdivisions to better show the resolution within Silesauridae and among other non-Dinosaurian Dinosauromorphs. Baron et al. (2017).

If this is correct, then it presents a number of serious challenges for our understanding of Dinosaur phylogeny. Firstly there is the definition of the term 'Dinosaur' itself. The current definition of Dinosaur is 'Passer domesticus, Triceratops horridus, their most recent common ancestor and everything descended from it'. This made sense because Passer domesticus, the modern House Sparrow, is a highly derived Theropod and Triceratops horridus, is a highly derived Ornithischian, so that a clade comprising all the descendants of their most recent common ancestor and everything descended from it, would, if Theropods and Ornithischians are the most distantly related Dinosaur groups, include everything we would consider to be a Dinosaur. However, if Ornithischians and Theropods are more closely related to one-another than either group is related to the Sauropods, then Sauropods can no longer be considered to be Dinosaurs. Since this goes completely against the common understanding of the term Dinosaur, Baron et al. suggest that rather than exclude the Sauropods from the Dinosaurs, the definition of the group should be amended to 'Passer domesticus, Triceratops horridus and Diplodocus carnegii, their most recent common ancestor and everything descended from it', thereby retaining everything that we would think of as being a Dinosaur within the group.

Then there is the problem of how to split the Dinosaurs into subgroups. The taxon Saurischia, which comprises the Theropods plus the Suaropods, and which has for over a hundred years been seen as one of the major Dinosaur divisions, is no longer valid under this hypothesis. Baron et al. suggest that instead the term Ornithoscelida, first proposed by Thomas Huxley in 1870 to describe a group comprising the Compsognatha (Theropods), Iguanodontidae (Ornithischians), Megalosauridae (Theropods) and Scelidosauridae (Ornithischians), i.e. a group of Dinosaur clades thought to be unrelated since the Ornithischian/Saurischian split was proposed in 1887, but which now appears valid. They retain the term Saurischia to describe the clade that includes the Sauropods and Herreosaurs, as these groups were both fall within the original definition of that group.

This hypothesis also has implications for the origins of the Dinosaurs, and the nature of the earliest members of the group. Since the earliest Therapods (the Herrerasauridae) and the earliest Ornithischians (the Heterodontosaurids) were both thought to have been carnivores, and the earliest members of the most closely related non-Dinosaurian group, the Silesauridae, were also thought to have been carnivores, it was presumed that the earliest Dinosaurs were probably carnovores, but it was unclear what they would have been like. However if the Herrerasauridae are outside the Theropods, then this balance changes. The earliest member of the Theropods become Eoraptor, a small omnivorous Dinosaur with heterodont dentition (i.e. different shaped teeth in different parts of the mouth) and grasping hands, while the earliest Ornithischians, the Heterodontosaurids, were also small with heterodont dentition and grasping hands, as were the Prosuaropods (earliest Suaropods). Only the Herrerosaurs differe from this pattern, being small with grasping hands but having serrated, recurved teeth reminiscent of later Theropods and indicatinve of a hypercarnivorous diet (diet in which little or no vegetable food is ingested), however, this group is not well known, and it is possible that early member of the group did have a different form of dentition. This points to a model where the earliest Dinosaur would have been a small, omnivorous animal with grasping hands and heterodont dentition, a versatile generalist lifestyle and anatomy that could explain how the Dinosaurs were able to diversify rapidly into so many different niches.

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Savannasaurus elliottorum & Diamantinasaurus matildae: Sauropod Dinosaurs from the Late Cretaceous of Queensland.

The breakup of the Gondwanan Supercontintent into its constituent parts (South America, Antarctica, Africa, Madagascar, India, Australia, New Zealand and some smaller landmasses) during the Cretaceous played an important role in the distribution of terrestrial animals and plants in the Southern Hemisphere that can still be seen today. How this would have affected the distribution of large animals such as Dinosaurs is particularly interesting, but is hard to assess as of these continents only South America has a good terrestrial fossil record extending all the way through the Cretaceous. Northern and Southeast Africa, and eastern Australia have strata which produce numerous terrestrial fossils including Dinosaurs, but almost no such fossils are known from the Late Cretaceous here, while the reverse is true in India, Madagascar and Antarctica, with numerous Late Cretaceous Dinosaurs but very few Middle Cretaceous specimens.

In a paper published in the journal Scientific Reports on 20 October 2016, Stephen Poropat of the Department of Earth Sciences at Uppsala University and the Australian Age of Dinosaurs Museum of NaturalHistory, Philip Mannion of the Department of Earth Science and Engineering at Imperial College London, Paul Upchurch of the Department of Earth Sciences at University College London, ScottHocknull of Geosciences at the Queensland Museum, Benjamin Kear, also of the Department of Earth Sciences at Uppsala University and of the Museum of Evolution, also at Uppsala University, Martin Kundrát of the Department of Ecology at Comenius University and the Center for Interdisciplinary Biosciences at the University of Pavol Jozef Šafárik, and Travis Tischler, Trish Sloan, George Sinapius, Judy Elliott and David Elliott, all of the Australian Age of Dinosaurs Museum of Natural History, describe two new Sauropod Dinosaur specimens from the early Late Cretaceous Winton Formation of Queensland.

The Winton Formation is an iron rich sandstone laid down in a shallow inland sea (the Etomanga Sea) and associated river systems that covered parts of Queensland and central Australia during the early Late Cretaceous (98-95 million years ago). which extends from Hungerford on the New South Wakes border northwest to the area around Kynuna, a distance of over 1000 kilometres. This formation is famous for its Dinosaurs, but also produces Crocodylians, Turtles, Fish and a wide range of Invertebrates. It is also noted for the production of opals, which are typically found in cracks in ironstone concretions (themselves formed by precipitation from water that has accumulated iron as it peculated through the feruginous sandstone), and is commonly called 'boulder opal'.

 Map of Queensland, northeast Australia, showing the distribution of Cretaceous outcrop. Porapat et al. (2016).

The first specimen described is assigned to a new species and genus and named Savannasaurus elliottorum, where 'Savannasaurus' refers to the Savanah Grasslands where the specimen was found and 'elliottorum' honours the Elliott family for their contributions to Australian palaeontology. The specimen comprises a series of vertebrae and ribs plus a fragmentary scapula, a left coracoid, the left and right sternal plates, incomplete left and right humeri, a shattered ulna, the left radius a number of metacarpals and phalanges, fragments of the left and right ilias, the left and right pubes and ischia, fused together, the left astragalus the right third metatarsal and some other fragmentary remains.

Savannasaurus elliottorum. (a–e) Dorsal vertebrae (left lateral view). (f) Sacrum (ventral view). (g,h) Caudal vertebrae (left lateral view). (i) Left coracoid (lateral view). (j) Right sternal plate (ventral view). (k) Left radius (posterior view). (l) Right metacarpal III (anterior view). (m) Left astragalus (anterior view). (n) Co-ossified right and left pubes (anterior view). A number of ribs were preserved but have been omitted for clarity. Scale bar is 500 mm. Porapat et al. (2016).

The second of specimen is referred to the species Diamantinasaurus matildae, which has previously been described from the Winton Formation. This specimen comprises a left squamosal, a nearly complete braincase, a right surangular, several skull fragments, the atlas-axis, five post-axial cervical vertebrae, three dorsal vertebrae, a partial sacrum, some dorsal ribs, a right scapula, both iliac preacetabular processes, a paired pubes and ischia and some other fragmentary material. The preservation of skull material in this specimen is particularly noteworthy, as this is the first such material known not only for this species but for any Australian Sauropod.

 Diamantinasaurus matildae, new specimen. (a,b) Braincase (left lateral and caudal views). (c,d) endocranium (left lateral oblique and ventral views). (e) Axis (left lateral view). (f) Cervical vertebra III (left lateral view). Abbreviations: bt, basal tuber; cca, internal carotid artery; coch, cochlea; crb, cerebral hemisphere; crbl, cerebellum; dds, dorsal dural sinus; fm, foramen magnum; hfp, hypophyseal fossa placement; ioa, internal ophthalmic artery; jug, jugular vein; lbr, endosseous labyrinth; mf, metotic foramen; midb, midbrain; mo, medulla oblongata; nc, nuchal crest; occ, occipital condyle; ofb, olfactory bulb; oft, olfactory tract; pp, paroccipital process; II, optic tract; III, oculomotor nerve; IV, trochlear nerve; V, trigeminal nerve; V1, ophthalmic branch of the trigeminal nerve; V2+3, maxillo-mandibular branch of the trigeminal nerve; VI, abducens nerve; VII, facial nerve; IX, glossopharyngeal nerve; X, vagus nerve; XI, accessory nerve; XII, hypoglossal nerve? structure of unknown or disputable identity/placement. Scale bar is 100 mm. Porapat et al. (2016).

Both of these specimens are adjudged to be Titanosaurs, a group of (often extremely large) Sauropod Dinosaurs that originated in South America and spread across much of the globe during the Cretaceous, which has interesting biogeographical implications for the Australian fauna of the Cretaceous. The extremely large size of Titanosaurs means that they are highly unlikely to have been dispersed across oceans by rafting or any similar mechanism, suggesting that they must have walked from South America to Australia overland. This was certainly possible during the Cretaceous, as the continents of Gondwana were still largely attached at the beginning of this period, and even at the end Australia was still attached to South America via a land-bridge across Antarctica. Titanosaurs, and Sauropods in general, appear to have favoured warmer climates, being absent from latitudes higher than 66° in either hemisphere, and much less diverse in higher latitudes than they were within the tropics. Antarctica was attached to both South America and Australia throughout the Cretaceous, but is known to have had a much cooler climate, with a distinct flora and fauna of its own that were apparently adapted to much cooler conditions during the Middle Cretaceous. This would appear to make a dispersal from South America across Africa, Madagascar and India during the Early Cretaceous (reaching Australia before 119 million years ago, when the connection between Indo-Madagascar and Australia was finally broken) the most likely method for these animals to reach Australia.

Palaeogeographic map of the mid-Cretaceous world. Showing the possible high latitude dispersal routes that might have been utilised by titanosaurs and other sauropods during the late Albian–Turonian. Porapat et al. (2016).

However, Australia has a reasonably good fossil record for part of the Middle Cretaceous (in this case roughly the period from 115-105 million years ago, which has produced a wide variety of Dinosaur specimens, but not yet to date any Sauropods. Neither have Titanosaurs thought to be closely related to the Australian species been recovered from the Middle Cretaceous deposits of Africa or the Late Cretaceous deposits of India or Madagascar, something which might be expected if the ancestors of these Sauropods had walked across Africa, India and Madagascar into Australia.

As an alternative route Porapat et al. suggest that the arrival of Titanosaurs in Australia may have occurred via Antarctica in the much warmer climate of the Late Cretaceous, after about 105 million years ago, when rapidly rising global temperatures brought a much warmer climate to Antarctica, possibly allowing rapid dispersal of warmth-loving Titanosaurs across the Antarctic land bridge.

See also...

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