The end-Triassic extinction: A tale of Death and Global Warming.

A basaltic lava flow section from the Middle Atlas, Morocco. From Wikimedia Commons.

For the last 540 million years, five mass extinction events shaped the history of the Earth. The End-Triassic Extinction (ETE) is typically attributed to climate change associated with degassing of basalt flows from the central Atlantic magmatic province (CAMP) emplaced during the initial rifting of Pangea. 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.

The emplacement of CAMP started c. 100,000 years before the end-Triassic event and continued in pulses for 700,000 years. Three negative organic C-isotope excursions (CIEs) have being recognized at the end-Triassic: the Marshi, the Spelae, and the top-Tilmanni CIEs. A recent study published in Nature estimated that a single short-lived magmatic pulse would have released about 5 × 1016 mol CO2, roughly the same total amount of projected anthropogenic emissions over the 21st century, causing an increase of about 2 °C in global temperatures, and an oceanic pH decrease of about 0.15 units over 0.1 kyrs, suggesting that the end-Triassic climatic and environmental changes, driven by CO2 emissions, may have been similar to those predicted for the near future.

A normal fern spore compared with mutated ones from the end-Triassic mass extinction event. Image credit: S LINDSTRÖM, GEUS

These massive volcanic eruptions with lava flows, also released large quantities of sulphur dioxide, thermogenic methane and large amounts of HF, HCl, halocarbons and toxic aromatics and heavy metals into the atmosphere, resulting in global warming, and ozone layer depletion. The high concentrations of pCO2 are indicative of ocean acidification suggesting that this may have been a marine extinction mechanism especially in relation to the scleractinian corals. Mutagenesis observed in plants and their reproductive cells (spores and pollen) were likely caused by mercury, the most genotoxic element on Earth .

The new study confirms the abundance of CO2 (up to 105 Gt volcanic CO2 degassed during CAMP emplacement) and indicates that at least part of this carbon has a middle- to lower-crust or mantle origin, suggesting that CAMP eruptions were rapid and potentially catastrophic for both climate and biosphere. Since the industrial revolution, the wave of animal and plant extinctions that began with the late Quaternary has accelerated. Australia has lost almost 40 percent of its forests, and almost 20% of the Amazon has disappeared in last five decades.Calculations suggest that the current rates of extinction are 100–1000 times above normal, or background levels. If we want to stop the degradation of our planet, we need to act now.

 

References:

Capriolo, M., Marzoli, A., Aradi, L.E. et al. Deep CO2 in the end-Triassic Central Atlantic Magmatic Province. Nat Commun 11, 1670 (2020). https://doi.org/10.1038/s41467-020-15325-6

Sofie Lindström et al. Volcanic mercury and mutagenesis in land plants during the end-Triassic mass extinction, Science Advances (2019). DOI: 10.1126/sciadv.aaw4018}

Davies, J., Marzoli, A., Bertrand, H. et al. End-Triassic mass extinction started by intrusive CAMP activity. Nat Commun 8, 15596 (2017). https://doi.org/10.1038/ncomms15596

The Forest Out of Time

An artist’s impression of Antarctica as a swampy rainforest between 92m and 83m years ago. (Credit: Alfred-Wegener-Institut/James McKay)

 

Past fluctuations in global temperatures are crucial to understand Earth’s climatic evolution. During the mid-Cretaceous, Earth’s climate was extraordinarily warm with temperatures in the tropics as high as 35 degrees Celsius, particularly during the Turonian to Santonian stages (93.9–83.6 Ma), with increasingly high sea levels and numerous epicontinental seas. The interval was characterized by extensive deposition of organic carbon (OC) rich black shales across a wide range of marine settings. Because marine proxies dominate records of past temperature reconstructions, our understanding of continental climate is relatively poor. Now, researchers from the UK and Germany discovered evidence of a temperate rainforest in West Antartica. The new finding offers a window into the terrestrial conditions of the extreme southern latitudes during this period.

The evidence comes from a core of sediment drilled into the seabed near the Pine Island and Thwaites glaciers in West Antarctica. One section of the core revealed a network of fossil plant roots, and countless traces of pollen and spores from plants, including the first remnants of flowering plants ever found at these high Antarctic latitudes. Pollen assemblage is dominated by the conifer tree families Podocarpaceae and Araucariaceae. The abundant tree ferns includes Cyathea. The presence of Sterisporites antiquasporites (Bryophyta, Sphagnum) suggest the temporary existence of a peat swamp. This coincides with increasing Peninsulapollis pollen.

 

West Antarctica. Image: Unsplash/Henrique Setim

Pollen and other palynomorphs proved to be an extraordinary tool to palaeoenvironmental reconstruction. In 1921, Gunnar Erdtman, a Swedish botanist, was the first to suggest this application for fossil pollen study. Like spores, pollen grains reflects the ecology of their parent plants and their habitats and provide a continuous record of their evolutionary history. Based on the palynomorph assemblage, the researchers found that the annual mean air temperature was around 13 degrees Celsius, and the average temperature of the warmest summer month was 18.5°C, whereas the amount and intensity of rainfall were similar to those in today’s Wales.

The mid-Cretaceous was an interval of intense climatic, tectonic and biotic changes across Gondwana. The break-up of the supercontinent and the rise of angiosperms caused a global floral turnover. Antarctica is particularly important because it preserves rock sequences that record the climate during the break-up of the supercontinent and the climate changes during the onset of continental-scale glaciation.

 

References:

Klages, J.P., Salzmann, U., Bickert, T. et al. Temperate rainforests near the South Pole during peak Cretaceous warmth. Nature 580, 81–86 (2020). https://doi.org/10.1038/s41586-020-2148-5

Forster, A. et al. Tropical warming and intermittent cooling during the Cenomanian/Turonian Oceanic Anoxic Event (OAE 2): sea surface temperature records from the equatorial Atlantic. Paleoceanography 22, PA1219 (2007). DOI:10.1029/2006PA001349

Introducing Dineobellator notohesperus

Life reconstruction of Dineobellator notohesperus. Artwork by Sergey Krasovskiy

 

The iconic Velociraptor mongoliensis, described by Osborn in 1924, belongs to the Dromaeosauridae, a family of highly derived small to mid-sized theropod dinosaurs closely related to birds. Their fossils have been found in North America, Europe, Africa, Asia, South America and Antarctica. They first appeared in the mid-Jurassic Period, but their fossil record in North America is very poor near the time of their extinction prior to the Cretaceous-Paleogene boundary. The group is characterized by the presence of long, three-fingered forelimbs that ended in sharp, trenchant claws and a tail stiffened by the elongated prezygapophyses.

The description of Dineobellator notohesperus, a new specimen discovered in 2008 in New Mexico, offers a glimpse into the biodiversity of Dromaeosaurids at the end of the Cretaceous. The generic name is derived from the Navajo word Diné, in reference to the people of the Navajo Nation, and the Latin suffix bellator, meaning warrior. The specific name is derived from the Greek word noto, meaning southern, or south; and the Greek word hesper, meaning western.

 

Skeletal reconstruction of Dineobellator notohesperus. From Jasinski et al., 2020

 

The holotype (SMP VP-2430), similar in size to Velociraptor and Saurornitholestes, includes elements of the skull, axial, and appendicular skeleton. The nearly complete right humerus measures 185.78 mm, with an estimated total length of 215 mm. The presence of quill knobs in Dineobellator provides further evidence for feathers throughout Dromaeosauridae. This new specimen co-existed with numerous other theropods, including caenagnathids, ornithomimids, troodontids, and tyrannosaurids.

Dineobellator exhibits some features in the forelimbs that suggest greater strength capabilities in flexion, in conjunction with a relatively tighter grip strength in the manual claws, while the possession of opisthocoelous proximal caudal vertebrae may have increased the agility of Dineobellator and thus may have implications for its predatory behavior, particularly with respect to the pursuit of prey.

 

References:

Jasinski, S.E., Sullivan, R.M. & Dodson, P. New Dromaeosaurid Dinosaur (Theropoda, Dromaeosauridae) from New Mexico and Biodiversity of Dromaeosaurids at the end of the Cretaceous. Sci Rep 10, 5105 (2020). https://doi.org/10.1038/s41598-020-61480-7

Senter, P., Kirkland, J. I., DeBlieux, D. D., Madsen, S. & Toth, N. New dromaeosaurids (Dinosauria: Theropoda) from the Lower Cretaceous of Utah, and the evolution of the dromaeosaurid tail. PLoS One 7, e36790 (2012). https://doi.org/10.1371/journal.pone.0036790

Osborn, Henry F. (1924a). “Three new Theropoda, Protoceratops zone, central Mongolia”. American Museum Novitates. 144: 1–12. http://hdl.handle.net/2246/3223

 

Introducing Asteriornis maastrichtensis

 

Three-dimensional image of the skull of Asteriornis maastrichtensis.
Image credit: Daniel J. Field, University of Cambridge

The earliest diversification of extant birds (Neornithes) occurred during the Cretaceous period. After the mass extinction event at the Cretaceous-Paleogene (K-Pg) boundary, the Neoaves, the most diverse avian clade, suffered a rapid global expansion and radiation. A genome-scale molecular phylogeny indicates that nearly all modern ordinal lineages were formed within 15 million years after the extinction, suggesting a particularly rapid period of both genetic evolution and the formation of new species. Today, with more than 10500 living species, birds are the most species-rich class of tetrapod vertebrates. The description of a new neornithine from the Late Cretaceous of Belgium shed new light on the evolution of birds.

Asteriornis maastrichtensis is a small member of the clade Pangalloanserae, the group that includes Galliformes and Anseriformes, with an estimated body weight of about 400 grams. The holotype (NHMM, 2013 008) includes a nearly complete, articulated skull with mandibles, and associated postcranial remains preserved in four blocks. The new specimen, dated between 66.8 and 66.7 million years ago, was collected in 2000 by Maarten van Dinther. The generic name is derived from the name of the Asteria, the Greek goddess of falling stars, and the Greek word ornis for bird. The specific name maastrichtensis honors the provenance of the holotype, the Maastricht Formation (the type locality of the Late Cretaceous Maastrichtian stage).

Artist’s reconstruction of Asteriornis maastrichtensis.
Illustration: Phillip Krzeminski

Asteriornis exhibits caudally pointed nasals that overlie the frontals and meet at the midline of the skull, and a slightly rounded, unhooked tip of the premaxilla. The new specimen reveals a previously undocumented combination of ‘galliform’ and ‘anseriform’ features that emphasizes the modular nature of the skull and bill of crown birds. The narrow and elongate hindlimbs and provenance from nearshore marine sediments suggest that Asteriornis might have had a shorebird-like ecology.

 

References:

Field, D.J., Benito, J., Chen, A. et al. Late Cretaceous neornithine from Europe illuminates the origins of crown birds. Nature 579, 397–401 (2020). https://doi.org/10.1038/s41586-020-2096-0

A Short History of the Early Female Geoscientists from Argentina

Mathilde Dolgopol de Saez. Image credit: Asociación Paleontológica Argentina (A.P.A.)

Women have played various and extensive roles in the history of geology. Unfortunately, their contribution has not been widely recognised by the public or academic researchers. In the 18th and 19th centuries women’s access to science was limited, and science was usually a ‘hobby’ for intelligent wealthy women. Early female scientists were often born into influential families, like Grace Milne, the eldest child of Louis Falconer and sister of the eminent botanist and palaeontologist, Hugh Falconer; or Mary Lyell, the daughter of the geologist Leonard Horner. They collected fossils and mineral specimens, and were allowed to attend scientific lectures, but they were barred from membership in scientific societies. Thanks to the pioneer work of these women, the 20th century saw the slow but firm advance of women from the periphery of science towards the center of it.

Edelmira Inés Mórtola (1894-1973)

In Argentina, during the 1870s, public schools were organized and expanded for the training of teachers in different cities of the country. North American teachers were hired, some of whom promoted among their students the interest in pursuing university studies. Cecilia Grierson (1859-1934) was the first woman to earn a PhD in Medicine and Surgery in 1889. She was an important reference for other women, collaborating in the women’s movement in the early twentieth century.

The first papers in natural sciences signed by women were published around 1910. Edelmira Inés Mórtola was the first woman to earn her Ph. D in geology in Argentina, in 1921. She was also the first woman to work for the Dirección General de Minas, Geología, e Hidrología (DGMGH) in 1919. She focus on teaching and was an inspiring figure for young women. In 1924, she was appointed Professor at the Universidad de Buenos Aires (UBA). The Museum of Mineralogy “Dr. E. Mórtola “, that she helped to organize, honors her extraordinary career. She died on May 28, 1973.

Noemí Violeta Cattoi. Image credit: Asociación Paleontológica Argentina (A.P.A.)

Mathilde Dolgopol de Saez was born on March 6, 1901. She was one of the first female paleontologist from Argentina (graduated in 1927), along with Ana Cortelezzi (1928?), Dolores López Aranguren (1930), Andreína Bocchino de Ringuelet (1930?) y Enriqueta Vinacci Thul (1930). Unfortunately, only her thesis and the one of López Aranguren were formally published. The mayor part of her research was focused on fossil fish and birds. She died on June 27, 1957.

Noemí Violeta Cattoi was born in Buenos Aires on December 23, 1911. She received her PhD degree in Natural Science at the University of Buenos Aires, but before her graduation she was trained at the Museo Argentino de Ciencias Naturales. She was head of Paleozoology at the Museum, and adjunt professor at the Museo de la Plata. Her research was mainly focused on extinct birds and mammals from South America. She was also one of the founding member of the Asociación Paleontológica Argentina (A.P.A), along with María Bonetti de Stipanicic, Andreína B. de Ringuelet, Elsa F. de Alvarez and Hildebranda A. Castellaro. Noemí Cattoi died on January 29, 1965.

Reference:.

Rafael Herbst, Luisa M. Anzótegui, Las mujeres en la paleontología argentina, Revista del Museo de La Plata (2016) Volumen 1, Número Especial: 130-13 DOI:https://doi.org/10.24215/25456377e024

GARCIA, Susana V.. Ni solas ni resignadas: la participación femenina en las actividades científico-académicas de la Argentina en los inicios del siglo XX. Cad. Pagu [online]. 2006, n.27, pp.133-172 https://doi.org/10.1590/S0104-83332006000200007.

Link: https://www.apaleontologica.org.ar/

Introducing Tralkasaurus cuyi, the thunder lizard.

Photo: AFP/MUSEO ARGENTINO DE CIENCIAS NATURALES

The Abelisauridae represents the best-known carnivorous dinosaur group from Gondwana. Their fossil remains have been recovered in Argentina, Brazil, Morocco, Niger, Libya, Madagascar, India, and France. The group was erected by the legendary paleontologist Jose Bonaparte with the description of  Abelisaurus Comahuensis. These theropods exhibit spectacular cranial ornamentation in the form of horns and spikes and strongly reduced forelimbs and hands. The clade includes Carnotaurus sastrei, Abelisaurus comahuensis, Aucasaurus garridoi, Ekrixinatosaurus novasi, Skorpiovenator bustingorryi, Eoabelisaurus mefi and Viavenator exxoni.

Abelisauroids were traditionally divided into two main clades: large-sized Abelisauridae, and small-sized Noasauridae. Although represented by relatively well-known skeletons, the phylogenetic relationships within abelisaurids remain debated. The Argentinean record of abelisauroid theropods begins in the Middle Jurassic (Eoabelisaurus mefi) and spans most of the Late Cretaceous. Now, a new abelisaurid from the upper section of the Huincul Formation (Cenomanian-Turonian) at the Violante Farm fossil site, Río Negro province, northern Patagonia, Argentina, is an important addition to the knowledge of abelisaurid diversity.

Map of El Cuy region showing the Violante farm fossil site. From Cerroni et al., 2020.

The holotype MPCA-Pv 815 is represented by an incomplete specimen including a right maxilla, distorted and incomplete dorsal, sacral and caudal vertebrae, cervical ribs, and pubis. Tralkasaurus is a medium-sized abelisaurid, much smaller than large abelisaurids as Abelisaurus and Carnotaurus. The name derived from Tralka, thunder in Mapudungun language, and saurus, lizard in Ancient Greek. The specific name “cuyi” derived from the El Cuy, the geographical area at Rio Negro province, Argentina, where the fossil was found.

This four-meter-long (13-foot-long) theropod exhibits a unique combination of traits, including deeply incised and curved neurovascular grooves at the lateral maxillary body that originate at the ventral margin of the antorbital fossa, and shows an extensive antorbital fossa over the maxillary body that is ventrally delimited by a well-marked longitudinal ridge that runs from the promaxillary fenestra level towards the rear of the maxilla.
Because body mass is usually indicative of an ecological niche, the new taxon probably occupied a different ecological niche within the predatory guild.

 

References:

Cerroni, M.A., Motta, M.J., Agnolín, F.L., Aranciaga Rolando, A.M., Brissón Egli, F., & Novas, F.E. (2019). A new abelisaurid from the Huincul Formation (Cenomanian-Turonian; Upper Cretaceous) of Río Negro province, Argentina. Journal of South American Earth Sciences https://www.sciencedirect.com/science/article/abs/pii/S0895981119304766

Introducing Thanatotheristes degrootorum, the Reaper of Death

Thanatotheristes degrootorum. Illustration by Julius Csotonyi

Tyrannosauroidea, the superfamily of carnivorous dinosaurs that includes the iconic Tyrannosaurus rex, originated in the Middle Jurassic, approximately 165 million years ago, and was a dominant component of the dinosaur faunas of the Northern Hemisphere. 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. But for most of their evolutionary history, tyrannosauroids were mostly small-bodied animals and only reached gigantic size during the final 20 million years of the Cretaceous. To explain their geographic dispersal through Laurasia, one phylogenetic hypothesis suggested a scenario where basal tyrannosaurids (i.e., albertosaurines and Daspletosaurus) occurred in northern locations (Alberta and Montana) and derived tyrannosaurids (i.e. Bistahieversor, Lythronax, and Teratophoneus) occurred farther south (New Mexico and Utah), with the Tyrannosaurus evolving from the southern group during the Maastrichtian.

The recently described Thanatotheristes degrootorum, from the middle Campanian of the Foremost Formation of Alberta, Canada, is the oldest tyrannosauroid known from Canada and is approximately 2.5 million years older than Gorgosaurus libratus and Daspletosaurus torosus from the Oldman and Dinosaur Park formations. This new specimen provides a new tool to understand the evolution and paleogeographic distribution of Tyrannosauridae.

Jaw bones of Thanatotheristes degrootorum. Image credit: Jared Voris

The holotype (TMP 2010.5.7) includes the right maxilla, right jugal, right postorbital, right surangular, right quadrate, right laterosphenoid, left frontal, and both dentaries. The presence of a well-developed ornamentation on the maxilla suggests the individual was probably sexually mature. A referred specimen (TMP 2018.016.0001) is based on a partial right maxilla from a subadult individual, and it was found approximately 10 km northeast of Hays, Alberta. The name derived from Thanatos the Greek god of death, and theristes (Greek), harvester or reaper. The specific name honors John and Sandra De Groot, who discovered the holotype specimen.

The new taxon is one of the earliest tyrannosaurid from North America, and is roughly equivalent in age to Dynamoterror dynastes from the Menefee Formation of northern New Mexico, but is slightly younger than Lythronax argestes from the Wahweap Formation of southern Utah.

Thanatotheristes skull. Image credit: Jared Voris

Phylogenetic analysis suggests that Thanatotheristes is most closely related to Daspletosaurus. Together, they form the clade Daspletosaurini, a group of long and deep-snouted tyrannosaurines. Thanatotheristes differs from Daspletosaurus in several characters. For instante, in Thanatotheristes the contact surface for the jugal on the postorbital is braced by a robust ridge that extends to the posterior margin of the postorbital. Furthermore, Thanatotheristes lacks two synapomorphies diagnostic for Daspletosaurus. First, the posterior bifurcation of the antotic crest of the laterosphenoid is an indistinct ridge rather than a prominent shelf-forming crest. Second, the symphyseal surface of the dentary only displays low anteroposterior ridges and lacks large interlocking bony projections.

The addition of more basal tyrannosaurid clades reveals that at least five major lineages evolved within Tyrannosauridae, with different skeletal morphotypes linked to differences in paleoecology, such as prey composition or hunting/feeding strategies.

 

References:

Voris, J.T., Therrien, F., Zelenitsky, D.K., Brown, CM., A new tyrannosaurine (Theropoda:Tyrannosauridae) from the Campanian Foremost Formation of Alberta, Canada, provides insight into the evolution and biogeography of tyrannosaurids, Cretaceous Research, https://doi.org/10.1016/j.cretres.2020.104388.

 

Climate Change and the legacy of the Challenger expedition

SEM images of selected planktonic foraminifera specimens; (i) T. trilobus (Tara), (j) G. ruber (Tara), (k) G. ruber (Challenger), (l) G. bulloides (Challenger), (m,n) G. ruber test cracked to reveal wall texture (Tara), (o,p) G. ruber test cracked to reveal wall texture (Challenger). From Fox et al., 2020.

It all began in 1868, with British naturalist William B. Carpenter and Sir Charles Wyville Thomson, Professor of Natural History at Edinburgh University. They persuaded the Royal Society of London to sponsor a prolonged voyage of exploration across the oceans of the globe. But it was not until 1872 that Royal Society of London obtained the use of the HSM Challenger from the Royal Navy. The ship was modified for scientific work with separate laboratories for natural history and chemistry. The cost of expedition was £200,000 – about £10 million in today’s money. The expedition was led by Captain George Nares and the scientific work was conducted by Wyville Thomson assisted by Sir John Murray, John Young Buchanan, Henry Nottidge Moseley, and the German naturalist Rudolf von Willemoes-Suhm. From 1872 to 1876, Murray developed a pioneering device which could register the temperature of the ocean at great depths, and assisted in the collection of marine samples. After the dead of Thomson in 1882, John Murray became director and edited the Challenger Expedition Reports. 

The science and ship crew of the HMS Challenger in 1874.

 
The planktonic foraminifera collected during the HMS Challenger expedition are part of the historical collection of the Natural History Museum, London. Their importance as tool for paleoclimate reconstruction was recognized early in the history of oceanography. The samples collected almost 150 years ago provide an extraordinary opportunity to understand the effects of one of the most urgent questions of our time with regards to anthropogenic environmental change: ocean acidification. 
 
Planktonic foraminifera are a group of marine zooplankton with a shell composed of secrete calcite or aragonite, with no internal structures and different patterns of chamber disposition (trochospiral, involute trochospiral and planispiral growth); with perforations and a variety of surface ornamentations like cones, short ridges or spines. Their shells take up chemical signals from the sea water, in particular isotopes of oxygen and carbon. Over millions of years, these skeletons accumulate in the deep ocean to become a major component of biogenic deep-sea sediments. By comparing the sediment samples from the HMS Challenger Expedition (1872–1876) with the recent Tara Oceans expedition material (2009–2016), the researchers found that the composition of the planktonic foraminifera has changed significantly since the pre-industrial period, and revealed that all modern specimens had up to 76% thinner shells than their historic counterparts.
 
 
 

Nano-CT representative reconstructions and measurements for Neogloboquadrina dutertrei from Tara (a–c), and Challenger (d–f). From Fox et al., 2020.

Ocean acidification affects the biogeochemical dynamics of calcium carbonate, organic carbon, nitrogen, and phosphorus and interferes with a range of processes including growth, calcification, development, reproduction and behaviour in a wide range of marine organisms like planktonic coccolithophores, foraminifera, echinoderms, corals, and coralline algae. Additionaly, ocean acidification can intensify the effects of global warming, in a dangerous feedback loop. Since the Industrial Revolution the pH within the ocean surface has decreased ~0.1 pH and is predicted to decrease an additional 0.2 – 0.3 units by the end of the century. 

After the World War II, the impact of human activity on the global environment dramatically increased. This period associated with very rapid growth in human population, resource consumption, energy use and pollution, has been called the Great Acceleration. In the coming decades, the ocean’s biogeochemical cycles and ecosystems will become increasingly stressed by ocean warming, acidification and deoxygenation. This scenario underlines the urgency for immediate action on global carbon emission reductions.

 

References:

Fox, L., Stukins, S., Hill, T. et al. Quantifying the Effect of Anthropogenic Climate Change on Calcifying Plankton. Sci Rep 10, 1620 (2020). https://doi.org/10.1038/s41598-020-58501-w

Jonkers, L., Hillebrand, H., & Kucera, M. (2019). Global change drives modern plankton communities away from the pre-industrial state. Nature. doi:10.1038/s41586-019-1230-3

Wyville Thompson, C. The Voyage of the “Challenger”. The Atlantic. 2 volumes (1878).

Dohrn, Anton. (1895). The Voyage of HMS “Challenger” A Summary of the Scientific Results. http://doi.org/10.1038/052121a0

 

 

From Mantell to de Ricqlès: A brief history of Paleohistology

Bone microstructure of M. intrepidus (NCSM 33392). From Zanno et al., 2019.

The aim of Paleohistology is the study of the microstructure of fossilized skeletal tissues. Despite that the organic components of mineralised tissues decay after death, the inorganic components of bone preserve the spatial orientation of organic components such as osteocyte lacunae, vascular canals, and collagen fibres.

The techniques for the microscopic study of biological tissues began in 1828, when two British scientists, Henry Witham and William Nicol, experimented by grinding sheets of petrified tree trunk into traslucents sheets so that they could viewed under the microscope. Few years later the new technique was applied to fossil vertebrates by Agassiz. In 1849, John Thomas Quekett published his most important paper on the histological structure of bone in mammals, birds, reptiles, and fish. He described vascular canals, lacunae and canaliculi, and trabecular endosteal bone.

Dorsal dermal spine of the Hylaerosaurus (From Mantell, 1850a. Plate XXVII)

The next important advance was the first clear description of dinosaur bone microstructure: Hylaerosaurus made by British paleontologist Gideon Mantell in 1850. In his work, Mantell provides a drawing of a thin section from a “dorsal dermal spine” of Hylaerosaurus. The same year, Mantell described a transverse thin section from a humerus of Pelorosaurus, and notes that the bone exhibits an “intimate structure beautifully preserved; the bone cells, and Haversian canals, are as distinct as in recent bones.” In 1871, John Phillips described the structure of pterosaur bones from the Stonesfield ‘Slate’ (Bathonian, Middle Jurassic, England) and noted that pterosaur bones contained longitudinal “Haversian canals” and figured “lacunae… with many short excurrent somewhat branched tubules”.

Detail of the humerus of Vegavis iaai (MACN-PV 19.748) in polarised light. Scale = 1 mm. (From G, Marsà et al., 2017)

A century later, the introduction of hard plastic resins, the development of tungsten carbide microtome blades, the use of very thin diamond-edged saw blades, and the examination of bone tissue with surgically implanted orthopedic devices fostered new methods for studying the histology of fully mineralized bone.

Armand de Ricqlès, in the 1960s and 1970s, observed that paleohistological features could be correlated with growth rates and thus could indirectly shed light on the thermal physiology of extinct organisms. He based his conclusions on the neontological observations of Rodolfo Amprino. Quantitative studies confirmed that avascular bone is deposited more slowly than vascular bone, and radial bone is deposited faster than laminar bone. De Ricqlès early histological examinations of dinosaur bones suggested that they did not grow in a manner similar to extant cold-blooded reptiles (which deposit poorly vascularized cortical bone, interrupted by many lines of arrested growth). On the contrary, the evidence indicated that dinosaurs had a physiology that more closely approximated that of extant, fast-growing, endothermic birds. He included pterosaurs in a discussion on reptile bone histology and emphasised the structural similarities with bird bones such as the large diaphyseal medullary cavities enclosed by a dense cortex, with spongiosa in the epiphyseal region. The studies conducted by de Ricqlès opened a new path for paleohistology and his work continues to influence the field today.

Recent

References:
Bailleul AM, O’Connor J, Schweitzer MH. 2019. Dinosaur paleohistology: review, trends and new avenues of investigation. PeerJ 7:e7764 https://doi.org/10.7717/peerj.7764

Quekett J. (1849) On the intimate structure of bone, as composing the skeleton, in the four great classes of animals, viz., mammals, birds, reptiles, and fishes, with some remarks on the great value of the knowledge of such structure in determining the affinities of minute fragments of organic remains. Transactions of the Microscopical Society of London. 1849;2(1):46–58. doi: 10.1111/j.1365-2818.1849.tb05102.x.
Mantell Gideon Algernon (1850) XVII. On a dorsal dermal spine of the Hylæosaurus, recently discovered in the strata of Tilgate Forest140 Phil. Trans. R. Soc. http://doi.org/10.1098/rstl.1850.0018

Mantell Gideon Algernon (1850b) XVI. On the pelorosaurus; an undescribed gigantic terrestrial reptile whose remains are associated with those of the iguanodon and other saurians in the strata of Tilgate Forest, in Sussex140Phil. Trans. R. Soc. http://doi.org/10.1098/rstl.1850.0017

De Ricqlès (1969) De Ricqlès A. L’histologie osseuse envisagée comme indicateur de la physiologie thermique chez les tétrapodes fossiles. Comptes Rendus Hebdomadaires des Séances de l’Academie des Sciences, Serie D: Sciences Naturelles. 1969;268:782–785

Introducing Wulong bohaiensis, the dancing dragon

Wulong bohaiensis. From Poust et al., 2020

Birds are the most species-rich class of tetrapod vertebrates. They originated from a theropod lineage more than 160 million years ago. The evolutionary history of Birds is at the root of the paravian radiation, when dromaeosaurids, troodontids, and avialans were diverging from one another. Within the clade Paraves we found the morphology and soft tissue changes associated with the origin of modern avian flight. One of this key changes was the difference of nearly four orders of magnitude in body size, a pivotal element in the origin of powered avian flight. 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.
The Jehol Biota included two formations: the Yixian Formation, and the Jiufotang Formation, and contain the most diversified avifauna known to date. Among them are the long bony-tailed Jeholornis, only slightly more derived than Archaeopteryx, and many fossils of troodontids like Mei long, Sinovenator changii, Sinusonasus magnodens and Jinfengopteryx elegans. Now, the recently described Wulong bohaiensis, from the Jiufotang Formation, shed new light on the evolution of Birds. This small, feathered dromaeosaurid theropod lived in the Early Cretaceous (Aptian) and was discovered by a farmer more than a decade ago. The holotype (D2933) is a complete articulated skeleton (only some ribs are missing)and exhibits special preservation of keratinous structures.

An X-ray of Wulong showing wrist and vertebra detail on the right. (Poust et al., 2020)

Wulong (meaning “dancing dragon”) is distinguished by the following autapomorphic features: long jugal process of quadratojugal, cranially inclined pneumatic foramina on the cranial half of dorsal centra, transverse processes of proximal caudals significantly longer than width of centrum, presence of 30 caudal vertebrae producing a proportionally long tail, distally located and large posterior process of the ischium, and large size of supracoracoid fenestra (>15% of total area). The holotype has several gross osteological markers of immaturity like the unfused dorsal and sacral vertebrae, but mature feathers are present across the entire body of Wulong.

The feathered dinosaurs from the Jehol Biota are key to understand the origin of birds and dinosaur behavior. In modern birds development of ornamental feathers is generally timed to co-occur with sexual maturity. The presence of such elaborate feathers in the immature Wulong demonstrates that nonavian dinosaurs had a very different strategy of plumage development then their living relatives.

References:

Poust, AW; Gao, C; Varricchio, DJ; Wu, J; Zhang, F (2020). “A new microraptorine theropod from the Jehol Biota and growth in early dromaeosaurids”. The Anatomical Record. American Association for Anatomy. doi:10.1002/ar.24343