Terrestrial floras at the Triassic-Jurassic Boundary in Europe.

Proportions of range-through diversities of higher taxonomic categories of microfloral elements over the Middle Triassic–Early Jurassic interval (From Barbacka et al., 2017)

Over the last 3 decades, mass extinction events  have become the subject of increasingly detailed and multidisciplinary investigations. Most of those events are associated with global warming and proximal killers such as marine anoxia. Volcanogenic-atmospheric kill mechanisms include ocean acidification, toxic metal poisoning, acid rain, increased UV-B radiation, volcanic darkness, cooling and photosynthetic shutdown. The mass extinction at the Triassic-Jurassic Boundary (TJB) has been linked to the eruption of the Central Atlantic Magmatic Province (CAMP), a large igneous province emplaced during the initial rifting of Pangea. Another theory is that a huge impact was the trigger of the extinction event. At least two craters impact were reported by the end of the Triassic. The Manicouagan Impact crater in the Côte-Nord region of Québec, Canada was caused by the impact of a 5km diameter asteroid, and it was suggested that could be part of a multiple impact event which also formed the Rochechouart crater in France, Saint Martin crater in Canada, Obolon crater in Ukraine, and the Red Wing crater in USA (Spray et al., 1998).

Photographs of some Rhaetian–Hettangian spores and pollen from the Danish Basin (From Lindström, 2015)

Most mammal-like reptiles and large amphibians disappeared, as well as early dinosaur groups. In the oceans, this event eliminated conodonts and nearly annihilated corals, ammonites, brachiopods and bivalves. In the Southern Hemisphere, the vegetation turnover consisted in the replacement to Alisporites (corystosperm)-dominated assemblage to a Classopollis (cheirolepidiacean)-dominated one. But there was no mass extinction of European terrestrial plants during the TJB. The majority of genera and a high percentage of species still existed in its later stages, and replacement seems to have been local, explainable as a typical reaction to an environmental disturbance. In Greenland, for example, the replacement of Triassic wide-leaved forms with Jurassic narrow-leaved forms was linked to the reaction of plants to increased wildfire. In Sweden, wildfire in the late Rhaetian and early Hettangian caused large-scale burning of conifer forests and ferns, and the appearance of new swampy vegetation. In Austria and the United Kingdom, conifers and seed ferns were replaced by ferns, club mosses and liverworts. In Hungary, there was a high spike of ferns and conifers at the TJB, followed by a sudden decrease in the number of ferns along with an increasing share of swamp-inhabiting conifers.

Although certain taxa/families indeed became extinct by the end of the Triassic (e.g. Peltaspermales), the floral changes across Europe were rather a consequence of local changes in topography.

References:

Maria Barbacka, Grzegorz Pacyna, Ádam T. Kocsis, Agata Jarzynka, Jadwiga Ziaja, Emese Bodor , Changes in terrestrial floras at the TriassicJurassic Boundary in Europe, Palaeogeography, Palaeoclimatology, Palaeoecology (2017), doi: 10.1016/j.palaeo.2017.05.024

S. Lindström, Palynofloral patterns of terrestrial ecosystem change during the end-Triassic event — a review, Geol. Mag., 1–23 (2015) https://doi.org/10.1017/S0016756815000552

Van de Schootbrugge, B., Quan, T.M., Lindström, S., Püttmann, W., Heunisch, C., Pross, J., Fiebig, J., Petschick, R., Röhling, H.-G., Richoz, S., Rosenthal, Y., Falkowski, P. G., 2009. Floral changes across the Triassic/Jurassic boundary linked to flood basalt volcanism. Nat. Geosci. 2, 589–594. doi: 10.1038/NGEO577.

N.R. Bonis, W.M. Kürschner, Vegetation history, diversity patterns, and climate change across the Triassic/Jurassic boundary, Paleobiology, 8 (2) (2012), pp. 240–264 https://doi.org/10.1666/09071.1

Zuul, the Gatekeeper

Skull of Zuul (Photograph: Brian Boyle/Royal Ontario Museum)

The Ankylosauria is a group of herbivorous, quadrupedal, armoured dinosaurs subdivided in two major clades, the Ankylosauridae and the Nodosauridae. Zuul crurivastator, from the Coal Ridge Member of the Judith River Formation of northern Montana, is the most complete ankylosaurid ever found in North America. The generic name refers to Zuul the Gatekeeper of Gozer (from the 1984 film Ghostbusters), and the species epithet combines crus (Latin) for shin or shank, and vastator (Latin) for destroyer, in reference to the sledgehammer-like tail club. The extraordinary preservation of abundant soft tissue in the skeleton, including in situ osteoderms and skin impressions make this specimen an important reference for understanding the evolution of dermal and epidermal structures in this clade. Until the discovery of Zuul, Laramidian ankylosaurin specimens were primarily assigned to three taxa: Euoplocephalus tutus and Ankylosaurus magniventris from northern Laramidia, and Nodocephalosaurus kirtlandensis from southern Laramidia.

The holotype (ROM 75860)  is a partial skeleton consisting of a nearly complete cranium, and a partially articulated postcranium. It is estimated to be over 6 metres long, and it would have weighed approximately 2500 kg. It has been dated to approximately 75 million years ago, and it was discovered accidentally on 16 May 2014 during overburden removal for a scattered tyrannosaurid skeleton, when a skid-steer loader encountered the tail club knob.

Overview of the tail of Zuul crurivastator in dorsal view, with insets of detailed anatomy (From Arbour and Evans, 2017)

The skull is almost complete, missing only the tip of the right quadratojugal horn and the ventral edge of the vomers, and is the largest ankylosaurine skull recovered from Laramidia. The skull is relatively flat dorsally, and had an elaborate ornamentation across the snout. The squamosal horns are robust and pyramid-shaped, and the quadratojugal horns had a sharp, posteriorly offset apex.

The tail club (including the 13 caudal vertebrae in the handle and the knob) is at least 210 cm long. Osteoderms are preserved not only in the anterior, flexible portion of the tail but also along the tail club handle. The first three pairs of caudal osteoderms are covered with a black film, that probably represent preserved keratin, and is similar to the texture observed at the base of bovid horn sheaths.

The discovery of Zuul fills a gap in the ankylosaurine record and further highlights that Laramidian ankylosaurines were undergoing rapid evolutionary rates and stratigraphic turnover as observed for Laramidian ceratopsids, hadrosaurids, pachycephalosaurids and tyrannosaurids.

References:

Arbour V. M., Evans D. C., (2017), A new ankylosaurine dinosaur from the Judith River Formation of Montana, USA, based on an exceptional skeleton with soft tissue preservation , Royal Society Open Science, rsos.royalsocietypublishing.org/lookup/doi/10.1098/rsos.161086

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

Jianianhualong and the evolution of feathers.

Jianianhualong tengi holotype (From Xu, X. et al., 2017)

In recent years, several discovered fossils of theropods and early birds have filled the morphological, functional, and temporal gaps along the line to modern birds. Most of these fossils are from the Jehol Biota of northeastern China, dated between approximately 130.7 and 120 million years ago. Among them are many fossils of troodontids, which are considered as the closest relatives of birds. Previous reported troodontid species include Mei long, Sinovenator changii, Sinusonasus magnodens and Jinfengopteryx elegans. Now a new troodontid, Jianianhualong tengi gen. et sp. nov., has anatomical features that shed light on troodontid character evolution.

The holotype (DLXH 1218) is a nearly complete skeleton with associated feathers, and is inferred to be an adult. It is estimated to be 112 cm in total skeletal body length with a fully reconstructed tail, and its body mass is estimated to be 2.4 kg, similar to most other Jehol troodontids, such as Sinovenator. The skull and mandible are in general well preserved, and  has a relatively short snout and highly expanded skull roof. There are probably 21 maxillary teeth and 25 dentary teeth on each side of the jaw. The vertebral column is nearly completely represented and  the tail is 54 cm long. The furcula is poorly preserved, and the humerus is 70% of femoral length. The manus is typical of maniraptoran theropods, and measures 112 mm in length. The pelvis is in general similar to those of basal troodontids, with a proportionally small ilium, a posteroventrally oriented pubis, and a short ischium. A phylogenetic analysis places Jianianhualong in an intermediate position together with several species between the basalmost and derived troodontids.

Plumage of Jianianhualong tengi (Adapted from Xu, X.  et al, 2017)

The tail frond of Jianianhualong preserves an asymmetrical feather, the first example of feather asymmetry in troodontids. Feathers were once considered to be unique avialan structures. Since the discovery of the feathered Sinosauropteryx in 1996, numerous specimens of most theropod groups and even three ornithischian groups preserving feathers have been recovered from the Jurassic and Cretaceous beds of China, Russia, Germany, and Canada. These feathers fall into several major morphotypes, ranging from monofilamentous feathers to highly complex flight feathers.

Evidence indicates that the earliest feathers evolved in non-flying dinosaurs for display or thermoregulation, and later were co-opted into flight structures with the evolution of asymmetrical pennaceous feathers in Paraves, therefore, the discovery of tail feathers with asymmetrical vanes in a troodontid theropod indicates that feather asymmetry was ancestral to Paraves.

 

 

References:

Xu, X. et al. Mosaic evolution in an asymmetrically feathered troodontid dinosaur with transitional features. Nat. Commun. 8, 14972 doi: 10.1038/ncomms14972 (2017).

Xu, X. et al. An integrative approach to understanding bird origins, Science, Vol. 346 no. 6215 (2014). DOI: 10.1126/science.1253293

Dinosaur Island

 

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Batman #1, New 52

In Batman #1 in the New 52, we see a giant animatronic dinosaur kept in the Batcave as a trophy. The T. rex is a reminder from an early adventure on Dinosaur Island (Batman #35, from June 1946). In that story, Murray Wilson Hart, a wealthy industrialist creates an amusement park named Dinosaur Island, filled with robot replicas of dinosaurs and robotic cavemen, but a criminal takes control of the mechanical dinosaurs and attacks Batman and Robin. Eventually, the dynamic duo defeat the criminal and Batman take the T. rex as a souvenier.

A second and definitive version of Dinosaur Island appeared in the Spring 1960 issue of Star-Spangled War Stories #90. Based on The Land That Time Forgot by Edgar Rice Burroughs, the saga follows a group of American soldiers, stranded on an uncharted island during the Pacific War which they discover is populated by dinosaurs. The original novel was set on World War I and is a reminder of Jules Verne’s novel Journey to the Center of the Earth, and Arthur Conan Doyle’ s The Lost World.

Cover of The War that Time Forgot by Ross Andru & Mike Esposito

Almost three decades before Verne’s Journey to the Center of the Earth, Rodolphe Töpffer (1799- 1846) published a peculiar geological tale. Töpffer was a Swiss author considered the first comics artist.  In Journey to the Center of the Earth (1864), Jules Verne incorporated the knowledge of the time. Verne was inspired by Charles Lyell’s Geological Evidences of the Antiquity of Man and Lyell’s earlier ground-breaking work Principles of Geology.

Arthur Conan Doyle began to write The Lost World in 1911. One year later it was published in book form by Hoddar and Stoughton. By that time he already was one of the most popular author around the globe, thanks to his most iconic creation, Sherlock Holmes. Probably, one of the most influential works in Doyle’s novel was “Extinct Animals” by Ray Lankester,  Director of the Natural History Museum. The Lost World has much in common with Journey to the Centre of the Earth, and has contributed significantly to the fascination with dinosaurs and pterodactyls. Even more, the first full-length science fiction film was based on Conan Doyle’s novel.

 

References:

Conan Doyle, A. 1912. The Lost World. Hodder & Stoughton, London.

Verne, J. G. 1864. Voyage au centre de la Terre. Pierre Jules Hetzel, Paris.

Edgar Rice Burroughs, The Land That Time Forgot,  Blue Book Magazine, 1918

Batman #35, DC Comics, 1946

Star-Spangled War Stories #90, DC Comics, 1960

 

 

Solving the mystery of Megatherium diet.

Megatherium americanum, MACN.

Around 10,000 years ago, Argentina was home of numerous species of giant Xenarthrans, giant ground sloths (relative to tree sloth) and glyptodontids (relative to tiny extant armadillo). Sloths, characteristic of the mammal fauna of the Pleistocene of South America, show a great diversity with more than 80 genera, grouped in four families: Megatheriidae, Megalonychidae, Nothrotheriidae and Mylodontidae.

For more than a century different hypotheses on the dietary preferences of giant ground sloths have been proposed. In 1860, Owen gave an extensive explanations about their possible diet and behavior. He based his conclusions on the morphology of the skull, combined with peculiarities of the rest of the skeleton, but always by analogy with living tree sloth. He wrote: “Guided by the general rule that animals having the same kind of dentition have the same kind of food, I conclude that the Megatherium must have subsisted, like the Sloths, on the foliage of tree…”. In 1926, Angel Cabrera discussed the diet of Megatherium, rejecting some theories on myrmecophagy or insectivory, and agreed with Owen’s statements about a folivorous diet.

Megatherium americanum lower right tooth series. Scale bar: 5 cm (From M.S. Bargo and S.F. Vizcaíno, 2008)

The dietary preferences of extinct mammals can usually be evaluated through their tooth morphology, but the application of stable isotopes on fossil bones has yielded very important information to solve debates about the diet of extinct large mammal groups, by comparing the carbon and nitrogen isotopic composition of their bone collagen with those of coeval herbivorous and carnivorous taxa. Another isotopic approach is to mesure the difference between the carbon isotopic abundances of the collagen and the carbonate fractions of skeletal tissues. An animal with a herbivorous diet, exhibits significantly larger differences than a carnivore. The values measured on bone collagen from Megatherium, clearly fall in the same range as the large herbivores such as the equid Hippidion, the notoungulate Toxodon and the liptoptern Macrauchenia, for which there is no doubt about their herbivorous diet. Therefore, the hypotheses of insectivory or carnivory for these extinct mammals are not supported by the isotopic data.

 

References:

Hervé Bocherens et al. Isotopic insight on paleodiet of extinct Pleistocene megafaunal Xenarthrans from Argentina, Gondwana Research (2017). DOI: 10.1016/j.gr.2017.04.003

Bargo, M.S., Vizcaíno, S.F., 2008. Paleobiology of Pleistocene ground sloths (Xenarthra, Tardigrada): biomechanics, morphogeometry and ecomorphology applied to the masticatory apparatus. Ameghiniana 45: 175-196

Introducing Zhongjianosaurus.

 

Photograph of Zhongjianosaurus yangi holotype (From Xu & Qin, 2017).

Dromaeosaurids are a group of carnivorous theropods, popularly known as “raptors”. Most of them were small animals, ranging from about 0.7 metres in length to over 7 metres. They had a relatively large skull with a narrow snout and the forward-facing eyes typical of a predator. They also had serrated teeth, and their arms were long with large hands, a semi-lunate carpal, with three long fingers that ended in big claws. The earliest known representatives are from the Lower Cretaceous Jehol Group of western Liaoning, China. The most recent described dromaeosaurid is Zhongjianosaurus yangi. The new taxon was named in honor of  Yang Zhongjian, who is the founder of vertebrate paleontology in China.

The Early Cretaceous Jehol dromaeosaurids not only display a great size disparity, but also show a continuous size spectrum. Zhongjianosaurus represents the ninth dromaeosaurid species reported from the Jehol Biota. It was first reported in 2009, and is notable for its small size (about 25 cm tall), compact body, and extremely long legs.

Zhongjianosaurus yangi holotype. A. right scapulocoracoid in lateral view and furcula in posterior view; B. right humerus in anterior view; C. left ulna and radius in lateral view; D. ‘semilunate’ carpal, metacarpals II and III in ventral view and phalanges II-1 and -2 in lateral view; scale bars equal 5 mm (From Xu & Qin, 2017)

The holotype is an adult individual distinguishable from other microraptorines in possessing many unique features, most of them are present in the forelimbs. For example, the humerus has a strongly offset humeral head, a large fenestra near the proximal end, and a large ball-like ulnar condyle. Zhongjianosaurus also displays several other features which are absent in other Jehol dromaeosaurids. For instance, the uncinate processes are proportionally long and fused to the dorsal ribs, the caudal vertebral transitional point is located anteriorly, and the pes exhibits a full arctometatarsalian condition.

The coexistence of several closely related Jehol dromaeosaurids can be interpreted as niche differentiation. Tianyuraptor have limb proportions and dental morphologies typical of non-avialan carnivorous theropods, suggesting that they were ground-living cursorial predators, meanwhile Microraptor are more likely to have been arboreal or even gliding animals.

References:

Xu X , Qin Z C, 2017, in press. A new tiny dromaeosaurid dinosaur from the Lower Cretaceous Jehol Group of western Liaoning and niche differentiation among the Jehol dromaeosaurids. Vertebrata PalAsiatica

Xu X, 2002. Deinonychosaurian fossils from the Jehol Group of western Liaoning and the coelurosaurian evolution. Ph.D thesis, Beijing: Chinese Academy of Sciences. 1–322

Tilly Edinger vs. the nazis.

Tilly Edinger (Photo,Museum of Comparative Zoology, Harvard University, Cambridge, MA)

“Tilly” Edinger was born on November 13, 1897 in Frankfurt, Germany. She was the youngest daughter of the eminent neurologist Ludwig Edinger and Dora Goldschmidt, a leading social advocate and activist. In 1914, her father became the first Chair of Neurology in Germany, at the newly founded University of Frankfurt. He encouraged her to take science courses at the Universities of Heidelberg, Frankfurt, and Munich. Her research at Frankfurt was directed by Fritz Drevermann, director of the Senckenberg Museum. After her graduation in 1921, Edinger worked as an assistant in the Geological Institute of Frankfurt University. In 1927, she was  named Curator of Fossil Vertebrates at the Senckenberg. At that time, she had no colleagues in vertebrate paleontology in Frankfurt with the exception of Drevermann. She described the positive and negative aspects of that environment in a letter addressed to A. S. Romer: “all fossil vertebrates [at the Senckenberg Museum] are entirely at my disposition: nobody else is interested in them . . . On the other hand, this means that I am almost autodidact”. 

Among her early projects were descriptions the endocranial casts of Mesozoic marine reptiles, pterosaurs and Archaeopteryx.  In 1929,  she published Die fossilen Gehirne (Fossil Brains), the book that established Edinger’s membership in the German and international paleontological communities. This work would serve as the major scientific support for her wartime immigration to the United States.

Senckenberg Naturmuseum (Senckenberg Museum of Natural History)

After the death of German President Paul von Hindenburg on August 2, 1934, Chancellor Adolf Hitler became Führer of Germany. In the months following Hitler’s ascension to the power, the Nazis took control of all of the nation institutions. The universities were not excepted. Soon, Jewish professors were dismissed, arrested, or simply disappeared. At the time, Tilly Edinger was working  as curator of fossil vertebrates at the Senckenberg Museum of Natural History in Frankfurt, so the influence of the new rules on her professional life was slower than on many other persons of Jewish descent because the Senckenberg was a private institution, and her position there was unsalaried. She continued working at the Museum thanks to protective actions of Rudolf Richter, the invertebrate paleontologist who had succeeded Drevermann at the Senckenberg.

Although urged by friends to leave the country, she chose to stay, as did their brother, Friedrich, who later (1942) became a victim of the Holocaust. But, on the night of 9–10 November 1938, her paleontological career in Germany ended.  Nearly 100 Jews were killed and thousands were imprisoned in the infamous “Kristallnacht” (Night of the Broken Glass). Decided to leave Germany as soon as possible, she wrote to her childhood classmate Lucie Jessner, a psychiatrist who had immigrated first to Switzerland in 1933 and then to the United States in early 1938. Jessner contacted the eminent Harvard paleontologist Alfred S. Romer (1884–1973), writing: “My friend—Dr. Tilly Edinger, paleontologist in Frankfurt am Main, Germany—wants me to ask you about different matters, very important for her. She believes you might know her name by several of her papers and you might be friendly enough to give me the opportunity to speak with you”

Interior of Berlin’s Fasanenstrasse Synagogue, opened in 1912, after it was set on fire during Kristallnacht on November 9, 1938

With the positive response from Romer, Edinger applied for an American visa at the American Consulate in Stuttgart on 1 August 1938. Forced to look for another, short-term solution, she contacted Philipp Schwartz, a former pathology professor at the University of Frankfurt who had established the Notgemeinschaft Deutscher Wissenschaftler im Ausland (Emergency Association of German Scientists in Exile), a society dedicated to helping scientific refugees from Nazi Germany. Waiting for a solution, she wrote to Rudolf Richter to thank him for his supportive testimonial. She shared her conviction that “One way (England) or the other (United States), fossil vertebrates will save me”. 

Thanks to her pioneering works and the contacts she made from a previous trip to London in 1926, Edinger emigrated to England in May 1939. She started working at the British Museum of Natural History, alternately translating texts and working on her own paleoneurological projects. She described her life in London as considerably freer than in Germany: “It sounds funny, to one who was ‘at home’ not allowed to enter even an open museum, or a cinema, or a café, to apply the word ‘restrictions’ anywhere in the beautifully free life I am leading here”

Tilly Edinger and colleagues at the Museum of Comparative Zoology. Sitting left to right: Tilly Edinger, Harry B. Whittington, Ruth Norton, Alfred S. Romer, Nelda Wright, and Richard van Frank. Standing left to right: Arnold D. Lewis, Ernest E.Williams, Bryan Patterson, Stanley J. Olsen, and Donald Baird. (Photo: David Roberts, from Buchholtz, 2001)

In 1940, with the support of Alfred S. Romer, she moved to Massachusetts to take a position at the Harvard Museum of Comparative Zoology. By the early 1950s, she was not only the major contributor to the field of paleoneurology but also the mentor to a younger generation that was following in her footsteps. She received several honorary doctorates for her achievements, including Wellesley College (1950), the University of Giessen (1957), and the University of Frankfurt  (1964). She was elected president of SVP in 1963. Her last book: “Paleoneurology 1804-1966. An annotated bibliography”, was completed by several of her colleagues and is considered the necessary starting point for any project in paleoneurology.

 

References:

Buchholtz, Emily A.; Seyfarth, Ernst-August (August 2001), “The Study of “Fossil Brains”: Tilly Edinger (1897–1967) and the Beginnings of Paleoneurology”, Bioscience 51 (8)

Susan Turner, Cynthia V. Burek and Richard T. J. Moody, Forgotten women in an extinct saurian (man’s) world, Geological Society, London, Special Publications 2010, v. 343, p. 111-153

 

 

Introducing Daspletosaurus horneri

D. horneri holotype skull (MOR 590, Museum of the Rockies, Bozeman, Montana, USA)

Tyrannosaurus rex, the most iconic dinosaur of all time, and its closest relatives known as tyrannosaurids, comprise the clade Tyrannosauroidea, a relatively derived group of theropod dinosaurs, more closely related to birds than to other large theropods such as allosauroids and spinosaurids. All tyrannosaurs were bipedal predators characterized by premaxillary teeth with a D-shaped cross section, fused nasals, extreme pneumaticity in the skull roof and lower jaws, a pronounced muscle attachment ridge on the ilium, and an elevated femoral head. The clade was a dominant component of the dinosaur faunas of the American West shortly after the emplacement of the Western Interior Seaway (about 99.5 Mya).

Daspletosaurus horneri, a new species of tyrannosaurid from the upper Two Medicine Formation of Montana, is the sister species of Daspletosaurus torosus. The new taxon was named in honor of Jack Horner, and inhabited northern Laramidia (what is now southern Alberta and northern Montana) about 75 million years ago. Paleontologist Vickie R. Clouse discovered the first specimen in 1989 and more individuals were uncovered in the following decades. The so-called Two Medicine tyrannosaurinemade its first appearance in a study co-written by Jack Horner in 1992, about the phyletic evolution in four lineages of dinosaurs, including tyrannosaurs, from the Late Cretaceous of the American West.

Phylogenetic relationships of tyrannosaurines calibrated to geological time (From Carr et al., 2017)

The holotype of Daspletosaurus horneri (MOR 590) consists of a complete skull, partial pectoral limb, and nearly complete hindlimb; and is estimated to be ~9.0 m in total length and 2.2 m tall.  D. horneri has taller skull than  D. torosus. Because of the excellent quality of preservation of these fossils it was possible to study the type of soft tissue that covered the face (premaxilla, maxilla, nasal, lacrimal, jugal, postorbital, squamosal, dentary). The study revealed that many of the tyrannosaur’s skull features are identical to those of crocodilians. Given the skeletal similarities with crocodylians, tyrannosaurids had a highly sensitive facial tactile system that functioned in prey capture, and object identification and manipulation, for detecting the optimal temperature of a nest site, and, in courtship, tyrannosaurids might have rubbed their sensitive faces together as a vital part of pre-copulatory play.

 

References:

Thomas D. Carr, David J. Varricchio, Jayc C. Sedlmayr, Eric M. Roberts, Jason R. Moore. A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system. Scientific Reports, 2017; 7: 44942
doi:10.1038/srep44942

Horner, J. R., Varricchio, D. J. & Goodwin, M. B. Marine transgressions and the evolution of Cretaceous dinosaurs. Nature 358, 59–61 (1992) doi:10.1038/358059a0

 

Re-examining the dinosaur evolutionary tree.

Close up of “Sue” at the Field Museum of Natural History in Chicago, IL (From Wikimedia Commons)

In the nineteen century, the famous Victorian anatomist Richard Owen diagnosed Dinosauria using three taxa: Megalosaurus, Iguanodon and Hylaeosaurus, on the basis of three main features: large size and terrestrial habits, upright posture and sacrum with five vertebrae (because the specimens were from all Late Jurassic and Cretaceous, he didn’t know that the first dinosaurs had three or fewer sacrals). Later, in 1887, Harry Govier Seeley summarised the works of Edward Drinker Cope, Thomas Huxley and Othniel Charles Marsh, and subdivide dinosaurs into Saurischians and the Ornithischians. He wrote: The characters on which these animals should be classified are, I submit, those which pervade the several parts of the skeleton, and exhibit some diversity among the associated animal types. The pelvis is perhaps more typical of these animals than any other part of the skeleton and should be a prime element in classification. The presence or absence of the pneumatic condition of the vertebrae is an important structural difference…” Based on these features, Seeley denied the monophyly of dinosaurs.

Seeley’s (1901) diagram of the relationships of Archosauria. From Padian 2013

At the mid 20th century, the consensual views about Dinosauria were: first, the group was not monophyletic; second almost no Triassic ornithischians were recognised, so they were considered derived morphologically, which leads to the third point, the problem of the ‘‘origin of dinosaurs’’ usually was reduced to the problem of the ‘‘origin of Saurischia,’’ because theropods were regarded as the most primitive saurischians. But the discovery of Lagosuchus and Lagerpeton from the Middle Triassic of Argentina induced a change in the views of dinosaurs origins. Also from South America came Herrerasaurus from the Ischigualasto Formation, the basal sauropodomorphs Saturnalia, Panphagia, Chromogisaurus, and the theropods Guibasaurus and Zupaysaurus, but no ornithischians except a possible heterodontosaurid jaw fragment from Patagonia. The 70s marked the beginning of a profound shift in thinking on nearly all aspects of dinosaur evolution, biology and ecology. Robert Bakker and Peter Galton, based on John Ostrom’s vision about Dinosauria, proposed, for perhaps the first time since 1842, that Dinosauria was indeed a monophyletic group and that it should be separated (along with birds) from other reptiles as a distinct ‘‘Class”. In 1986, the palaeontologist Jacques Gauthier showed that dinosaurs form a single group, which collectively has specific diagnostic traits that set them apart from all other animals.

The dinosaur evolutionary tree (From Padian, 2017.

Phylogenetic analyses of early dinosaurs have  supported the traditional scheme. But a new study authored by Matthew Baron, David Norman and Paul Barrett, reach different conclusions from those of previous studies by incorporating some different traits and reframing others. Baron and colleagues, analysed a wide range of dinosaurs and dinosauromorphs, including representatives of all known dinosauromorph clades. 74 taxa were scored for 457 characters. The team  arrived at a dinosaur evolutionary tree containing one main branch that subdivides into the groupings of Ornithischia and Theropoda, and a second main branch that contains the Sauropoda and Herrerasauridae (usually positioned as either basal theropods or basal Saurischia, or outside Dinosauria but close to it). The union between ornithischians and theropods is called Ornithoscelida. The term was coined in 1870 by Thomas Huxley for a group containing the historically recognized groupings of Compsognatha, Iguanodontidae, Megalosauridae and Scelidosauridae.

From Baron et al., 2017.

The synapomorphies that support the formation of the clade Ornithoscelida includes: an anterior premaxillary foramen located on the inside of the narial fossa; a sharp longitudinal ridge on the lateral surface of the maxilla; short and deep paroccipital processes; a post-temporal foramen enclosed within the paroccipital process; a straight femur, without a sigmoidal profile; absence of a medioventral acetabular flange; a straight femur, without a sigmoidal profile; and fusion of the distal tarsals to the proximal ends of the metatarsals.

Of course, those results have great implications for the very origin of dinosaurs. Ornithischia don’t begin to diversify substantially until the Early Jurassic. By contrast, the other dinosaurian groups already existed by at least the early Late Triassic. If the impoverished Triassic record of ornithischians reflects a true absence, ornithischians might have evolved from theropods in the Late Triassic (Padian, 2017). The study also suggest that dinosaurs might have originated in the Northern Hemisphere, because most of their basal members, as well as their close relatives, are found there. Furthermore, their analyses places the origin of dinosaurs at the boundary of the Olenekian and Anisian stages (around 247 Ma), slightly earlier than has been suggested previously.

 

References:

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. Dividing the dinosaurs. Nature 543, 494–495 (2017) doi:10.1038/543494a

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).

Seeley, H. G. On the classification of the fossil animals commonly named Dinosauria. Proc. R. Soc. Lond. 43, 165171 (1887).

Huxley, T. H. On the classification of the Dinosauria, with observations on the Dinosauria of the Trias. Quarterly Journal of the Geological Society, London 26, 32-51. (1870).

 

Mammalian dwarfing during ancient greenhouse warming events.

Bighorn Basin, Wyoming (Image: University of New Hampshire, College of Engineering and Physical Sciences)

The Paleocene-Eocene Thermal Maximum, known as PETM (approximately 55.8 million years ago), was a short-lived (~ 200,000 years) global warming event due to a rapid rise in the concentration of greenhouse gases in the atmosphere. It was suggested that this warming was initiated by the melting of methane hydrates on the seafloor and permafrost at high latitudes. This event was accompanied by other large-scale changes in the climate system, for example, the patterns of atmospheric circulation, vapor transport, precipitation, intermediate and deep-sea circulation, a rise in global sea level and ocean acidification.

The second largest hyperthermal of the early Eocene, known as ETM2, occurred about 2 million years after the PETM (approximately 53.7 Ma). Another smaller-amplitude hyperthermal, identified as “H2,” appears in the marine record about 100,000 years after ETM2 (approximately 53.6 Ma).

Sifrhippus sp. restoration in the Naturhistoriska Riksmuseet, Stockholm, Sweden (From Wikimedia Commons)

Dwarfing of mammalian taxa across the Palaeocene-Eocene Thermal Maximum (PETM) was first described in the Bighorn Basin, Wyoming. The basin has a remarkably fossil-rich sedimentary record of late Palaeocene to early Eocene age. The interval of the Paleocene–Eocene Thermal Maximum is represented by a unique mammalian fauna composed by smaller, but morphologically similar species to those found later in the Eocene. Diminutive species include the early equid Sifrhippus sandrae, the phenacodontids Ectocion parvus and Copecion davisi. 

Fossils of early equids are common in lower Eocene deposits of the Bighorn Basin, making a comparison between the PETM and ETM2 hyperthermal events possible. Using tooth size as a proxy for body size, researchers found a statistically significant decrease in the body size of mammals’ during the PETM and ETM2. Teeth in adult mammals scale proportionally to body size. For instance, Sifrhippus demonstrated a decrease of at least 30% in body size during the first 130,000 years of the PETM, followed by a 76% rebound in body size during the recovery phase of the PETM. Arenahippus, an early horse the size of a small dog, decreased by about 14 percent in size during the ETM2. (D’Ambrosia et al., 2017)

Arenahippus jaw fragment (Image credit: University of New Hampshire)

Body size change during periods of climate change is commonly seen throughout historical and geological records. Studies of modern animal populations have also yielded similar body size results. Tropical trees, anurans and mammals have all demonstrated decreased size or growth rate during drought years. In the case of mammals, the observed decrease in the average body size could have been an evolutionary response to create a more efficient way to reduce body heat.

The combination of global warming and the release of large amounts of carbon to the ocean-atmosphere system during the PETM has encouraged analogies with the modern anthropogenic climate change, which has already led to significant shifts in the distribution, phenology and behaviour of organisms. Plus, the consequences of shrinkage are not yet fully understood. This underlines the urgency for immediate action on global carbon emission reductions.

 

 

References:

Abigail R. D’Ambrosia, William C. Clyde, Henry C. Fricke, Philip D. Gingerich, Hemmo A. Abels. Repetitive mammalian dwarfing during ancient greenhouse warming events. Science Advances, 2017; 3 (3): e1601430 DOI: 10.1126/sciadv.1601430

Rankin, B., Fox, J., Barron-Ortiz, C., Chew, A., Holroyd, P., Ludtke, J., Yang, X., Theodor, J. 2015. The extended Price equation quantifies species selection on mammalian body size across the Palaeocene/Eocene Thermal Maximum. Proceedings of the Royal Society B. doi: 10.1098/rspb.2015.1097

Burger, B.J., Northward range extension of a diminutive-sized mammal (Ectocion parvus) and the implication of body size change during the Paleoc…, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2012), http://dx.doi.org/10.1016/j.palaeo.2012.09.008