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

 

Mary Anning and the Hunt of Primeval Monsters.

mary_anning_plesiosaurus

Autograph letter concerning the discovery of plesiosaurus, from Mary Anning (From Wikimedia Commons)

Since the End of the 17th century to the beginning of the 19th, several discoveries of dinosaur remains and other large extinct ‘saurians’, were reported for first time. It was an exciting time full of discoveries and the concept of an ancient Earth became part of the public understanding. The most popular aspect of geology was  the collecting of fossils and minerals and the nineteenth-century geology, often perceived as the sport of gentlemen, was in fact, “reliant on all classes”.

The study of the Earth became central to the economic and cultural life of the Victorian Society and Literature influenced the pervasiveness of geological thinking. The Geological Society of London was founded on 13 October 1807 at the Freemasons’ Tavern, in the Covent Garden district of London, with the stated purpose of “…making geologists acquainted with each other, of stimulating their zeal, of inducing them to adopt one nomenclature, of facilitating the communications of new facts and of ascertaining what is known in their science and what remains to be discovered”. During this time, women were free to take part in collecting fossils and mineral specimens, and they were allowed to attend lectures but they were barred from membership in scientific societies. However, it was common for male scientists to have women assistants, often their own wives and daughters.

Plesiosaurus battling Temnodontosaurus (Oligostinus), front piece the Book of the Great Sea-Dragons by Thomas Hawkins.

Plesiosaurus battling Temnodontosaurus (Oligostinus), front piece the Book of the Great Sea-Dragons by Thomas Hawkins.

Mary Anning (1799-1847), was an special case. Despite her lower social condition, Mary became the most famous ‘fossilist’ of her time. She was born on Lyme Regis on May 21, 1799. Her father was a carpenter and an amateur fossil collector who died when Mary was eleven. He trained Mary and her brother Joseph in how to look and clean fossils. After the death of her father, Mary and Joseph used those skills to search fossils on the local cliffs,  that sold as “curiosities”. The source of the fossils was the coastal cliffs around Lyme Regis, one of the richest fossil locations in England and part of a geological formation known as the Blue Lias. The age of the formation corresponds to the Jurassic period. In 1811, she caught the public’s attention when she and her brother Joseph unearthed the skeleton of a ‘primeval monster’. They sold it for £23. Later, in 1819, the skeleton was purchased by Charles Koenig of the British Museum of London who suggested the name “Ichthyosaur” for the fossil.

On December 10, 1823, she discovered the first complete Plesiosaur skeleton at Lyme Regis in Dorset. The fossil was acquired by the Duke of Buckingham. Noticed about the discovery, George Cuvier wrote to William Conybeare suggesting that the find was a fake produced by combining fossil bones from different animals. William Buckland and Conybeare sent a letter to Cuvier including anatomical details, an engraving of the specimen and a sketch made by Mary Morland (Buckland’s wife) based on Mary Anning’s own drawings and they convinced Cuvier that this specimen was a genuine find. From that moment, Cuvier treated Mary Anning as a legitimate and respectable fossil collector and cited her name in his publications.

The holotype specimen of Dimorphodon macronyx found by Mary Anning in 1828 (From Wikimedia Commons)

On December of 1828, Mary found the first pterosaur skeleton outside Germany. William Buckland made the announcement of Mary’s discovery in the Geological Society of London and named Pterodactylus macronyx in allusion to its large claws. The skull of Anning’s specimen had not been discovered, but Buckland thought that the fragment of jaw in the collection of the Philpot sisters of Lyme belonged to a pterosaur.

In her later years, Mary Anning suffered some serious financial problems. She died of breast cancer on 9 March, 1847, at the age of 47. She was buried in the cemetery of St. Michaels. In the last decade of her life, Mary received  three accolades. The first was an annuity of £25, in return for her many contributions to the science of geology. The second was in 1846, when the geologists of the Geological Society of London organized a further subscription for her. The third accolade was her election, in July 1846, as the first Honorary Member of the new Dorset County Museum in Dorchester (Torrens, 1995). After her death, Henry de la Beche, Director of the Geological Survey and President of the Geological Society of London, wrote a very affectionate obituary published in the Quarterly Journal of the Geological Society on February 14, 1848, the only case of a non Fellow who received that honour.

References:

Davis, Larry E. (2012) “Mary Anning: Princess of Palaeontology and Geological Lioness,”The Compass: Earth Science Journal of Sigma Gamma Epsilon: Vol. 84: Iss. 1, Article 8.

Hugh Torrens, Mary Anning (1799-1847) of Lyme; ‘The Greatest Fossilist the World Ever Knew’, The British Journal for the History of Science Vol. 28, No. 3 (Sep., 1995), pp. 257-284. Published by: Cambridge University Press.

De la Beche, H., 1848a. Obituary notices. Quarterly Journal of the Geological Society of London, v. 4: xxiv–xxv.

Dickens, C., 1865. Mary Anning, the fossil finder. All the Year Round, 13 (Feb 11): 60–63.

 

A Brief Introduction to Conservation Paleobiology

Richard Owen stands next to the largest of all moa, Dinornis maximus (now D. novaezealandiae). From Wikimedia Commons.

Richard Owen stands next to the largest of all moa, Dinornis maximus (now D. novaezealandiae). From Wikimedia Commons.

Over the past 50 years, the pace and magnitude of human-induced global changes has accelerated dramatically. 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. 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 same drivers that contributed to ancient megafaunal and island extinctions.

The emerging discipline of conservation paleobiology is supplying necessary information to understand how ecosystems vary naturally through time and space and how they respond to major perturbations. The fossils that have provided such data include phytoplankton, zooplankton, fossil pollen, seeds, leaves, wood, invertebrate animals with hard parts, and vertebrate animals. They are particularly useful because they often show high fidelity to the living communities. Quaternary fossils have proven especially informative for addressing conservation questions, but useful information has also come from much older fossil deposits, reaching back millions of years.

1024px-bison_near_a_hot_spring_in_yellowstone

Bison near a hot spring in Yellowstone National Park (From Wikimedia Commons).

The analytical methods that allow comparing present with past fall into two main categories: taxon-based and taxon-free. Taxon-based methods rely on the presence, absence, or abundances of certain taxa and their underlying diversity. Taxon-free methods use metrics that reflect ecosystem function rather than structure. Depending on the availability of fossils and the type of conservation question being asked, one or the other approach may be more appropriate.

Taxon-based paleontological data are critical in deciding if a “natural” landscape represents a historical or a novel ecosystem. Historical ecosystems are those that still have at least 70% of the habitats that were present 500 years ago and that contain fewer than 5 people/km2. In the world’s first national park, Yellowstone National Park, USA, paleontological data influenced critical management decisions by demonstrating that Yellowstone preserves a historical ecosystem. Fossil deposits verified that almost all of the mammal species that had occupied the region for millennia are still present. Also, palynological records show that the current vegetation has persisted with only minor fluctuations in abundance of dominant taxa for at least 8000 years.

Lyuba, the best preserved mammoth mummy in the world, at the Field Museum of Natural History (From Wikimedia Commons).

Lyuba, the best preserved mammoth mummy in the world, at the Field Museum of Natural History (From Wikimedia Commons).

Taxon-free paleontological can often be related to environmental parameters with statistical significance data, and are critical for understanding whether certain ecosystems are approaching “tipping points,” as demonstrated by analysis of diatoms, pollen, and sediments from lake cores.

Fossils have also figured prominently  with efforts to reconstruct copies of species that humans have driven to extinction either recently (passenger pigeons) or in the deeper past (mammoths). Unfortunately, the ecosystems that supported many extinct species no longer exist, so survival outside of captivity would be difficult. In addition, preventing the extinction of extant species and habitats numbering in the thousands already is challenging, so the prospects of sustaining “de-extincted” species are poor at best. Media reports are presenting de-extinction in an optimistic framework, and conveying the impression that we face a real possibility of bringing mammoth back from extinction in  the near future. Of course, this is far from truth. We will never be able to recreate most extinct species in their purest form. Ultimately,  genetic engineering to simulate extinct life also raises ethical and legal concerns.

 

References:

Anthony D. Barnosky et al. Merging paleobiology with conservation biology to guide the future of terrestrial ecosystems. Science, 2017 DOI: 10.1126/science.aah4787

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

Braje, T.J., Erlandson, J.M., Human acceleration of animal and plant extinctions: A Late Pleistocene, Holocene, and Anthropocene continuum. Anthropocene (2013), http://dx.doi.org/10.1016/j.ancene.2013.08.003

Richmond, D.J., Sinding, M-H.S., Gilbert, M.T.P. (2016). The potential and pitfalls of de-extinction. — Zoologica Scripta, 45, 2236DOI: 10.1111/zsc.12212

Introducing Isaberrysaura

Isaberrysaura skull in lateral view and maxillary teeth (Adapted from Salgado et al., 2017)

Isaberrysaura mollensis gen. et sp. nov. is the first dinosaur recovered in the marine-deltaic deposits of the Los Molles Formation (Neuquén Province, Argentina), and the first neornithischian dinosaur known from the Jurassic of South America. So far, the South American record of Jurassic ornithischian dinosaurs was limited to a few specimens belonging to Heterodontosauriformes, a clade of small-sized forms that survived in Europe up to the Early Cretaceous. The name Isaberrysaura is derived from “Isa Berry” (Isabel Valdivia Berry, who reported the initial finding) and the Greek word “saura” (lizard).

The holotype of Isaberrysaura is an incomplete articulated skeleton with an almost complete skull, and a partial postcranium consisting of 6 cervical vertebrae, 15 dorsal vertebrae, a sacrum with a partial ilium and an apparently complete pubis, 9 caudal vertebrae, part of a scapula, ribs, and unidentifiable fragments. One of the most notable features of the discovery is the presence of permineralized seeds in the middle-posterior part of the thoracic cavity. The seeds were assigned to the Cycadales (Zamiineae) on the basis of a well-defined coronula in the micropylar region. The findings suggest the hypothesis of interactions (endozoochory) between cycads and dinosaurs, especially in the dispersion of seeds.

Gut content of Isaberrysaura mollensis gen. et sp. nov. (a–c), seeds of cycads (c), and other seeds (s); rib (r). From Salgado et al., 2017

The cranium of Isaberrysaura is reminiscent of that of the thyreophorans. The skull is estimated to be 52 cm long and 20 cm wide across the orbits. The jugal is triradiate and the nasals are ~20 cm long. There are two supraorbital bones; one is elongated (~10 cm), as in stegosaurs, and the other element interpreted as a posterior supraorbital is located on the posterior margin of the orbit. It has at least six premaxillary teeth, and there is no diastema between the premaxillary and the maxillary tooth row. Despite the many similarities between Isaberrysaura and the thyreophorans, the phylogenetic analysis indicates that Isaberrysaura is a basal ornithopod, suggesting that both Thyreophora and neornithischians could have achieved significant convergent features.

References:

Salgado, L. et al. A new primitive Neornithischian dinosaur from the Jurassic of Patagonia with gut contents. Sci. Rep. 7, 42778; doi: 10.1038/srep42778 (2017)

The legacy of Ernst Haeckel

Ernst Haeckel and his assistant Nicholas Miklouho-Maclay, photographed in the Canary Islands in 1866. From Wikimedia Commons.

Ernst Haeckel and his assistant Nicholas Miklouho-Maclay, photographed in the Canary Islands in 1866. From Wikimedia Commons.

Ernst Heinrich Philipp August Haeckel  was born on February 16, 1834, in Potsdam, Prussia. He wanted to be a botanist and his hero was Alexander Humboldt, but his father, a lawyer and government official, thought the career prospects in botany were poor. Following his father’s advice, he studied medicine at the University of Berlin and graduated in 1857.

The explorations of Humboldt and Darwin permanently impressed him, and in 1859, E. Haeckel travelled to Italy and  spent some time in Napoli, exploring and discovering his talent as an artist. Then he went to Messina, where began to study radiolarians. In 1864, he sent to Darwin, two folio volumes on radiolarians. Goethe was also a strong influence in Haeckel, and lead him to think of Nature in anthropomorphic terms.

Ernst Haeckel's ''Kunstformen der Natur'' (1904), showing Radiolarians of the order Stephoidea. From Wikimedia Commons.

Ernst Haeckel’s ”Kunstformen der Natur” (1904), showing Radiolarians of the order Stephoidea. From Wikimedia Commons.

He became the most famous champion of Darwinism in Germany and he was so popular that, previous to the First World War, more people around the world learned about the evolutionary theory through his work “Natürliche Schöpfungsgeschichte” (The History of Creation: Or the Development of the Earth and its Inhabitants by the Action of Natural Causes) than from any other source. He also wrote more than twenty monographs about systematic biology and evolutionary history. He formulated the concept of  ”ecology” and coined the terms of “protist”,  “ontogeny”, “phylum”, “phylogeny”,  “heterochrony”, and “monera”.

Along with many other scientists, Haeckel was asked by the managers of the Challenger Expedition to examine and report on the expedition’s collections specifically for radiolarians, sponges and jellyfish. Haeckel’s Report on Radiolaria took him almost a decade. He reported a total of 739 genera and 4318 species of Radiolaria (polycystines, acantharians and phaeodarians). 

Ernst Haeckel’s ”Kunstformen der Natur” showing various sea anemones classified as Actiniae. From Wikimedia Commons.

Ernst Haeckel’s ”Kunstformen der Natur” showing various sea anemones classified as Actiniae. From Wikimedia Commons.

His master work “Kunstformen der Natur” (Art forms of Nature) influenced not only science, but in the art, design and architecture of the early 20th century. Initially published in ten fascicles of ten plates each – from 1899 to 1904 -, coincided with his most intensive effort to popularise his monistic philosophy in Die Welträthsel and Die Lebenswunder.

But Haeckel was a man of contradictions. His belief in Recapitulation Theory (“ontogeny recapitulates phylogeny”) was one of his biggest mistakes. His affinity for the German Romantic movement influenced his political beliefs and Stephen Jay Gould wrote that Haeckel’s biological theories, supported by an “irrational mysticism” and racial prejudices contributed to the rise of Nazism. Despite those faults, he made great contributions in the field of biology and his legacy as scientific illustrator is extraordinary. In 1908, he was awarded with the prestigious Darwin-Wallace Medal for his contributions in the field of science.

After the death of his wife in 1915, Haeckel became mentally frail. He died on 9 August 1919.

References:

Robert J. Richards, The Tragic Sense of Life: Ernst Haeckel and the Struggle over Evolutionary Thought, (2008), University of Chicago Press.

Breidbach, Olaf. Visions of Nature: The Art and Science of Ernst Haeckel. Prestel Verlag: Munich, 2006.

Heie, N. Ernst Haeckel and the Redemption of Nature, 2008.

Aita, Y., N. Suzuki, K. Ogane, T. Sakai & Y. Tanimura, 2009. Study and reexamination of the Ernst Haeckel Radiolaria Collection. Fossils (Japanese Journal of the Palaeontological Society of Japan), 85, 1–2.

David Lazarus, The legacy of early radiolarian taxonomists, with a focus on the species published by early German workers, Journal of Micropalaeontology 2014, v.33; p3-19.

 

Liaodactylus primus and the ecological evolution of Pterodactyloidea.

Skull of the newfound species Liaodactylus primus (Credit: Chang-Fu Zhou)

Skull of the newfound species Liaodactylus primus (Credit: Chang-Fu Zhou)

Pterosaurs are an extinct monophyletic clade of ornithodiran archosauromorph reptiles from the Late Triassic to Late Cretaceous. The group achieved high levels of morphologic and taxonomic diversity during the Mesozoic, with more than 150 species recognized so far. During their 149 million year history, the evolution of pterosaurs resulted in a variety of eco-morphological adaptations, as evidenced by differences in skull shape, dentition, neck length, tail length and wing span. Pterosaurs have traditionally been divided into two major groups, “rhamphorhynchoids” and “pterodactyloids”. Rhamphorhynchoids are characterized by a long tail, and short neck and metacarpus. Pterodactyloids have a much larger body size range, an elongated neck and metacarpus, and a relatively short tail. Darwinopterus from the early Late Jurassic of China appear to be a transitionary stage that partially fills the morphological gap between rhamphorhynchoids and pterodactyloids.

Pterodactyloidea, the most species-diverse group of pterosaurs, ruled the sky from Late Jurassic to the end of Cretaceous. Liaodactylus primus, a new specimen, discovered in northeast China’s Liaoning province, documents the only pre-Tithonian (145–152 Ma) pterodactyloid known with a complete skull, shedding new light on the origin of the Ctenochasmatidae, a group of exclusive filter feeders, and the timing of the critical transition from fish-catching to filter-feeding, a major ecological shift in the early history of the pterodactyloid clade. The holotype specimen is a nearly complete skull (133 mm long) and mandibles, with the first two cervical vertebrae preserved in articulation with the skull. The elongation of the rostrum, almost half the length of the skull, is accompanied by a significant increase in the number of marginal teeth, giving a total of 152 teeth in both sides of the upper and lower jaws. The teeth are closely spaced to form a ‘comb dentition’, a filter-feeding specialization.

Pterodaustro guinazui cast (Museo Argentino de Ciencias Naturales)

Pterodaustro guinazui cast (Museo Argentino de Ciencias Naturales)

Liaodactylus is the oldest known ctenochasmatid, predating the previously Tithonian (152 Ma) record (Gnathosaurus and Ctenochasma from Germany) by at least 8–10 Myr . The Ctenochasmatidae, represents a long-ranged clade (160–100 Ma), and the only pterodactyloid clade that crossed the Jurassic-Cretaceous transition. The group includes the Early Cretaceous Pterodaustro from Argentina. Popularly called the ‘flamingo pterosaur’, Pterodaustro represents the most remarkable filter-feeding pterosaur known from the fossil record, with a huge number (more than 1000) of densely spaced ‘teeth’ (elastic bristles) in its lower jaws, for filtering small crustaceans, microscopic plankton or algae from open water along lake shores.

Pterosaurs display an extraordinary eco-morphological disparity in feeding adaptations, expressed in skull, jaws and dentition. The Late Triassic Eopterosauria, the basalmost pterosaur clade, were mainly insectivorous. Jurassic insectivores include the Dimorphodontia, Campylognathoididae and Darwinoptera, whereas the Anurognathidae were the only Jurassic insectivores that survived the Jurassic–Cretaceous transition, but became extinct in the Early Cretaceous. The rise of the ctenochasmatid clade was the first major ecological shift in pterosaur evolution from insectivorous-piscivorous to filter-feeding. During Cretaceous time,  the Eupterodactyloidea, a group of advanced pterodactyloids, engaged in a variety of feeding adaptations, including filter-feeding, fish-eating, carnivory and scavenging, herbivory including frugivory, durophagy and omnivory. The Early Cretaceous tapejarids may have been herbivorous, while the pteranodontids, with large skull but tapering and toothless jaws were suitable for seizing fish in open-water environments. Finally, the Late Cretaceous azhdarchids have been hypothesized as foragers feeding on small animals and carrion in diverse terrestrial environments.

Time-calibrated cladogram showing stratigraphic range, eco-morphological diversity of pterosaur clades. (Adapted from Zhou et al., 2017)

Time-calibrated cladogram showing stratigraphic range, eco-morphological diversity of pterosaur clades. (Adapted from Zhou et al., 2017)

References:

Chang-Fu Zhou, Ke-Qin Gao, Hongyu Yi, Jinzhuang Xue, Quanguo Li, Richard C. Fox, Earliest filter-feeding pterosaur from the Jurassic of China and ecological evolution of Pterodactyloidea, 

Andres, B., Clark, J., & Xu, X. (2014). The earliest pterodactyloid and the origin of the group. Current Biology, 24(9), 1011-1016.

WITTON, M. P., 2010 Pteranodon and beyond: the history of giant pterosaurs from 1870 onwards. In: Moody, R.T.J., Buffetaut, E., Naish, D., Martill, D.M. (Eds.), Dinosaurs and Other Extinct Saurians: A Historical Perspective. Geological Society, London, Special Publications 343, 287–311.

 

Sea-surface temperatures during the last interglaciation.

 

203_co2-graph-021116

The relentless rise of carbon dioxide (Credit: National Oceanic and Atmospheric Administration.)

A proverb of Confucius states “Study the past if you would divine the future.” Human activity ensures that our climate will become warmer in the next century and remain warm for many millennia to come which makes particularly pertinent the study of periods in which at least sectors of the Earth system may have been “warmer” than today. The last interglaciation (LIG, 129 to 116 thousand years ago) was one of the warmest periods in the last 800,000 years with an associated sea-level rise of 6 to 9 m above present levels . A new study by Jeremy S. Hoffman and colleagues, compiled 104 published LIG sea surface temperature (SST) records from 83 marine sediment core sites. Each core site was compared to data sets from 1870-1889 and 1995-2014, respectively. The analysis revealed that 129,000 years ago, the global ocean surface temperature was similar to the 1870-1889 average. But 125,000 years ago, the global SST increased by 0.5° ± 0.3°Celcius, reaching a temperature indistinguishable from the 1995-2014 average. The result is worrisome, because it shows that changes in temperatures which occurred over thousands of years, are now occurring in the space of a single century. The study also suggests that in the long term, sea level will rise at least six meters in response to the global warming.

Data from the study by Jeremy Hoffman et al. representing sample sites, sea surface temperatures, and historic carbon dioxide level

Data from the study by Jeremy Hoffman et al. representing sample sites, sea surface temperatures, and historic carbon dioxide level

The planet’s average surface temperature has risen about 2.0 degrees Fahrenheit (1.1 degrees Celsius) since the late 19th century. After the World War II, the atmospheric CO2 concentration grew, from 311 ppm in 1950 to 369 ppm in 2000. Glaciers  from the Greenland and Antarctic Ice Sheets are fading away, dumping 260 billion metric tons of water into the ocean every year. The ocean acidification is occurring at a rate faster than at any time in the last 300 million years, and  the patterns of rainfall and drought are changing and undermining food security which have major implications for human health, welfare and social infrastructure. In his master book L’Evolution Créatrice (1907), French philosopher Henri Bergson, wrote:  “A century has elapsed since the invention of the steam engine, and we are only just beginning to feel the depths of the shock it gave us.”

References:

J.S. Hoffman et al. Regional and global sea-surface temperatures during the last interglaciation. Science. Vol. 355, January 20, 2017, p. 276. doi: 10.1126/science.aai8464.

Past Interglacials Working Group of PAGES (2016), Interglacials of the last 800,000 years, Rev. Geophys., 54, 162–219, doi: 10.1002/2015RG000482. 

Bakker, P., et al. (2014), Temperature trends during the present and Last Interglacial periods—A multi-model-data comparison, Quat. Sci. Rev., 99, 224–243, doi: 10.1016/j.quascirev.2014.06.031.

Forgotten women of Paleontology: Emily Dix

 

Dr Emily Dix and her assistant Miss Elsie White.

Dr Emily Dix and her assistant Miss Elsie White.

In the 18th and 19th centuries women’s access to science was limited, and science was usually a ‘hobby’ for intelligent wealthy women. It was common for male scientists to have women assistants, often their own wives and daughters. But by the first half of the 20th century, a third of British palaeobotanists working on Carboniferous plants were women. The most notable were  Margaret Benson, Emily Dix, and Marie Stopes.

Emily Dix was born on 21 May 1904 in Penclawdd, in the beautiful area of the Gower Peninsula. At age 18, she gained the Central Welsh Board Higher Certificate in history, botany and geography, with distinctions in both history and botany. In 1925, she graduated with first class honours in Geology at the University College Swansea. After graduation, Emily continued at Swansea to research the geology of the western part of the South Wales Coalfield. Her work was supervised by Arthur E. Trueman, Professor of Geology at Swansea, and a pioneer in developing stratigraphical theory. Trueman realized that the only accurate way to use fossils for correlation was to divide the stratigraphical succession into biozones defined exclusively by the assemblages of species present, independently of the lithology in which they were found. Trueman’s main interest were  non-marine bivalves, so Emily’s early work was on the non-marine bivalves of the South Wales Coalfield.

Emily Dix during the 2nd International Carboniferous Congress in 1935 (From Burek and Cleal, 2005)

Emily Dix during the 2nd International Carboniferous Congress in 1935 (From Burek and Cleal, 2005)

Emily initially studied all aspects of the Late Carboniferous biotas in South Wales, but soon, she realized that plant fossils also had considerable biostratigraphical potential. Although, Paul Bertrand developed macrofloral biozones for the French coalfields in 1914, Emily used stratigraphical range charts for the first time in paleobotany recognising the need to separate biostratigraphy from lithostratigraphy. In 1926 Emily was awarded an MSc based on her Gwendraeth Valley work: ‘The Palaeontology of the Lower Coal Series of Carmarthen and the Correlation of the Coal Measures in the Western Portion of the South Wales Coalfield’.  In 1929 she was elected a fellow of the Geological Society, and a year later she was appointed Lecturer in Palaeontology at Bedford College in London, a position that she held for the rest of her working life. The same year, she attended the International Botanical Congress in Cambridge where she met W. Gothan, P. Bertrand, W. J. Jongmans and A. Renier, leaders in Upper Carboniferous palaeobotany at the time. Five years later, she attended the Second International Carboniferous Congress in Heerlen (The Netherlands) and she delivered papers on Carboniferous biostratigraphy. In 1936, Emily was invited to become the only female on an 11-man discussion group of the British Association for the Advancement of Science on Coal Measures correlation. She was clearly at the international forefront of the field.

Emily Dix in the Auvergne 1936 (seated fourth from right, see white arrow). From Burek and Cleal, 2005.

Emily Dix in the Auvergne 1936 (seated fourth from right, see white arrow). From Burek and Cleal, 2005.

At the start of the World War II, she was evacuated to Cambridge, along with the rest of Bedford College Geology Department. She lost a lot of valuable literature and other records in a London Blitz in May 1941. Fortunately, much of her collection of fossils survived.

At the end of the war, Emily suffered a mental breakdown. She was moved to a mental hospital run by the Quakers in the City of York. That was the end of her scientific career. She died in Swansea on 31 December 1972.

It was not until the late 1970s that her techniques were used again in Britain. Elsewhere in Europe, her approaches were adopted and can be seen in many of the papers presented at the International Carboniferous Congresses held at Heerlen during the 1950s and early 1960s.

References:

Burek, C. V. & Cleal, C. J. (2005) The life and work of Emily Dix (1904-1972). In: Bowden, A. J., Burek, C. V. & Wilding, R (ed.) History of palaeobotany: selected essays. Geological Society of London, Special Publication, 241, 181-196

Burek, C. V. (2005). Emily Dix, palaeobotanist – a promising career cut short. Geology Today, 21(4), 144-145

Climate model simulations at the end of the Cretaceous.

gg_60212w_crater

Artist’s reconstruction of Chicxulub crater 66 million years ago.

About thirty years ago, the discovery of anomalously high abundance of iridium and other platinum group elements in the Cretaceous/Palaeogene (K-Pg) boundary led to the hypothesis that a 10 km asteroid collided with the Earth and caused one of the most devastating events in the history of life. The impact created the 180-kilometre wide Chicxulub crater causing widespread tsunamis along the coastal zones of the surrounding oceans and released an estimated energy equivalent of 100 teratons of TNT and produced high concentrations of dust, soot, and sulfate aerosols in the atmosphere.

To model the climatic effects of the impact, a team of scientist from the Potsdam Institute for Climate Impact Research (PIK), use literature information from geophysical impact modeling indicating that for a 2.9 km thick target region consisting of 30% evaporites and 70% water-saturated carbonates and a dunite projectile with 50% porosity, a velocity of 20 km/s and a diameter between 15 and 20 km, a sulfur mass of 100 Gt is produced. This is about 10,000 times the amount of sulfur released during the 1991 Pinatubo eruption. Additionally, for a sulfur mass of 100 Gt, about 1400 Gt of carbon dioxide are injected into the atmosphere, corresponding to an increase of the atmospheric CO2 concentration by 180 ppm. There could be additional CO2 emissions from ocean outgassing and perturbations of the terrestrial biosphere, adding a total of 360 ppm and 540 ppm of CO2. The main result is a severe and persistent global cooling in the decades after the impact. Global annual mean temperatures over land dropped to -32C in the coldest year and continental temperatures in the tropics reaching a mere -22C. This model is supported by a migration of cool, boreal dinoflagellate species into the subtropic Tethyan realm directly across the K–Pg boundary interval and the ingression of boreal benthic foraminifera into the deeper parts of the Tethys Ocean, interpreted to reflect millennial timescale changes in the ocean circulation after the impact (Vellekoop, 2014).

A time-lapse animation showing severe cooling due to sulfate aerosols from the Chicxulub asteroid impact 66 million years ago (Credit: PKI)

A time-lapse animation showing severe cooling due to sulfate aerosols from the Chicxulub asteroid impact 66 million years ago (Credit: PKI)

References:

Brugger J., G. Feulner, and S. Petri (2016), Baby, it’s cold outside: Climate model simulations of the effects of the asteroid impact at the end of the Cretaceous, Geophys. Res. Lett., 43,  doi:10.1002/2016GL072241.

Alvarez, L. W., W. Alvarez, F. Asaro, and H. V. Michel (1980), Extraterrestrial Cause for the Cretaceous-Tertiary Extinction, Science, 208 (4448), 1095{1108, doi: 10.1126/science.208.4448.1095.

Galeotti, S., H. Brinkhuis, and M. Huber (2004), Records of post Cretaceous-Tertiary boundary millennial-scale cooling from the western Tethys: A smoking gun for the impact-winter hypothesis?, Geology, 32, 529, doi:10.1130/G20439.1

Johan Vellekoop, Appy Sluijs, Jan Smit, Stefan Schouten, Johan W. H. Weijers, Jaap S. Sinningh Damsté, and Henk Brinkhuis, Rapid short-term cooling following the Chicxulub impact at the Cretaceous–Paleogene boundary, PNAS (2014) doi: 10.1073/pnas.1319253111