The Early Aptian Oceanic Anoxic Event.

120moll

The Early Cretaceous (Aptian Age), 120 Ma.

The geological records show that large and rapid global warming events occurred repeatedly during the course of Earth history. The growing concern about modern climate change has accentuated interest in understanding the causes and consequences of these ancient abrupt warming events. The early Aptian Oceanic Anoxic Event (OAE1a, 120 Ma) represents a geologically brief time interval characterized by rapid global warming, dramatic changes in ocean circulation including widespread oxygen deficiency, and profound changes in marine biotas. During the event, black shales were deposited in all the main ocean basins. It was also associated with the calcification crisis of the nannoconids, the most ubiquitous planktic calcifiers during the Early Cretaceous. Their near disappearance is one of the most significant events in the nannoplankton fossil record.

sin-titulo

Scanning electron microscope photos of different nannofossil assemblages from Early Cretaceous chalks from the North Sea (adapted from Mutterlose & Bottini, 2013)

Calcareous nannoplankton represent a major component of oceanic phytoplankton. Their calcareous skeletons can be found in fine-grained pelagic sediments in high concentrations and the biomineralization of coccoliths is a globally significant rock-forming process. The ‘nannoconid decline’ is related to the emplacement of the Ontong Java Plateau (OJP). The  CO2 released by the flood basalts was the main player in the climatic events. However, records from the Pacific and Tethys realms demonstrate that during OAE 1a the  major shift in global oceanic osmium composition occurs well after the onset of the nannoconid crisis. Previous studies argued that the nannoconid crisis was caused by ocean acidification due to numerous pulses of CO2 and methane. The Ontong Java Plateau is a massive, submerged seafloor.  It covers an area of about 1,900,000 square kilometers. It  was emplaced ca. 120 Ma, with a much smaller magmatic pulse of ca. 90 Ma. The CO2 release was too late, and too gradual, to have caused the calcification crisis in the nannoconids by ocean acidification

References:

Naafs, B. D. A. et al., Gradual and sustained carbon dioxide release during Aptian Oceanic Anoxic Event 1a, Nature Geosci. http://dx.doi.org/10.1038/ngeo2627 (2016)

Jenkyns, H. C. (2010), Geochemistry of oceanic anoxic events, Geochem. Geophys. Geosyst., 11, Q03004, doi:10.1029/2009GC002788.

Sea level regulated tetrapod diversity dynamics through the Jurassic/Cretaceous interval.

The Jurassic/Cretaceous Boundary

Map of the Jurassic/Cretaceous Boundary by C. Scotese.

The Jurassic/Cretaceous (J/K) boundary, 145 Myr ago, remains as the less understood of major Mesozoic stratigraphic boundaries. Sedimentological, palynological and geochemical studies, indicate a climatic shift from predominantly arid to semi arid conditions in the latest Jurassic to more amicable humid conditions in the earliest Cretaceous. The continued fragmentation of Pangaea across the Late Jurassic and Early Cretaceous led to large-scale tectonic processes, on both regional and global scale, accompanied by some of the largest volcanic episodes in the history of the Earth; eustatic oscillations of the sea level; potentially heightened levels of anoxia, oceanic stagnation, and sulphur toxicity; along with two purported oceanic anoxic events in the Valanginian and Hauterivian. There’s also evidence of three large bolide impacts in the latest Jurassic, one of which might have been bigger than the end-Cretaceous Chicxulub impact.

Painting of a late Jurassic Scene on one of the large island in the Lower Saxony basin in northern Germany (From Wikimedia Commons)

Painting of a late Jurassic Scene on one of the large island in the Lower Saxony basin in northern Germany (From Wikimedia Commons)

The J/K interval represents a period of elevated extinction, and involves the persistent loss of diverse lineages, and the origins of many major groups that survived until the present day (e.g. birds). The magnitude of this drop in diversity ranges from around 33% for ornithischians to 75–80% loss for theropods and pterosaurs. Mammals suffered an overall loss of  diversity of 69%. Crocodyliforms suffered a major  decline across the Jurassic/Cretaceous boundary in both the marine and terrestrial realms; while non-marine turtles declined by 33% of diversity through the J/K boundary. In contrast, lepidosauromorphs greatly increased in diversity (48%) across the J/K boundary, reflecting the diversification of major extant squamate clades, including Lacertoidea, Scincoidea and Iguania.

In the marine realm, sauropterygians and ichthyosaurs show evidence for a notable decline in diversity across the J/K boundary, which continued into the Hauterivian for both groups.

Stratigraphic ranges of major Jurassic–Cretaceous theropod (A), sauropod (B), and ornithischian (C) dinosaur clades through the Middle Jurassic to Early Cretaceous (From Tennant et al,. 2016)

Stratigraphic ranges of major Jurassic–Cretaceous theropod (A), sauropod (B), and ornithischian (C) dinosaur clades through the Middle Jurassic to Early Cretaceous (From Tennant et al,. 2016)

Eustatic sea level is the principal mechanism controlling the Jurassic–Cretaceous diversity of tetrapods. Rising sea levels leads to greater division of landmasses through creation of marine barriers, modifying the spatial distribution of near-shore habitats and affecting the species–area relationship, which can lead to elevated extinctions. This fragmentation can also be a potential driver of biological and reproductive isolation and allopatric speciation, the combination of which we would expect to see manifest in the diversity signal. Additionally, the diversity of fully marine taxa was more probably affected by the opening and closure of marine dispersal corridors, whereas that of terrestrial and coastal taxa was more probably dependent on the availability of habitable ecosystems, including the extent of continental shelf area (Tennant, et al., 2016).

References:

Tennant J,P., Mannion P. D., Upchurch P., Sea level regulated tetrapod diversity dynamics through the Jurassic/Cretaceous interval, Nature Communications, ISSN: 2041-1723 DOI: 10.1038/ncomms12737

Tennant, J. P., Mannion, P. D., Upchurch, P., Sutton, M. D. and Price, G. D. (2016), Biotic and environmental dynamics through the Late Jurassic–Early Cretaceous transition: evidence for protracted faunal and ecological turnover. Biol Rev. doi:10.1111/brv.12255 

Butler, R. J., Benson, R. B. J., Carrano, M. T., Mannion, P. D. & Upchurch, P. Sea level, dinosaur diversity and sampling biases: investigating the ‘common cause’ hypothesis in the terrestrial realm. Proc. R. Soc. B 278, 1165–1170 (2011).

“Where No Dinosaur Has Gone Before”

The Starship Enterprise flies over an orange planet in 'The Man Trap,' the premiere episode of 'Star Trek,' which aired on September 8, 1966. (CBS via Getty Images)

The Starship Enterprise flies over an orange planet in ‘The Man Trap,’ the premiere episode of ‘Star Trek,’ which aired on September 8, 1966. (CBS via Getty Images)

Star Trek has been a cult phenomenon for decades. The Original Series premiered on September 8, 1966, and has spawned four successor shows starting in the 1980s and 13 feature films , comic books, novels and an animated series. Star Trek also influenced generations of viewers about advanced science and engineering. Of course, geology played an important role on the show. In the episode “That Which Survives”, we met the senior geologist D’Amato when the USS Enterprise investigates a planet similar to Earth . Unfortunately, D’Amato was soon killed by the hologram of a beautiful woman, Losira, the last survivor of a Kalandan outpost.

Lieutenant D'Amato, the senior geologist aboard the USS Enterprise serving under Captain James T. Kirk.

Lieutenant D’Amato, the senior geologist aboard the USS Enterprise serving under Captain James T. Kirk.

Every incarnation of Star Trek introduced several alien life forms, including the Gorn, a reptilian alien race, a common motif in mythology, folklore, science fiction, conspiracy theories, ufology, and cryptozoology. In the episode “Distant Origin” (Star Trek: Voyager, 1997), the Voth, an ancient civilization in the Delta Quadrant, discovered  the remains of a human Voyager crew member on the planet Hanon IV. Voth scientist Gegen believes he finally has confirmation of his “distant origin” theory. According to Gegen, the Voth actually migrated to the Delta Quadrant from an original planet far away. Later, we discovered that the Voth presumably descended from Parasaurolophus.

The episode, a metaphor for the relationship between Galileo Galilei and the Catholic Church, plays with the infamous “Dinosauroid  Hypothesis” (a.k.a. Sapient Dinosaurs). In the early 1980s, paleontologist Dale Russell, curator of vertebrate fossils at the National Museums of Canada, in Ottawa, speculates about a possible evolutionary path for Troodon, suggesting that it could have evolved into intelligent beings similar in body plan to humans. Troodon, a relatively small theropod, comparable in size to Deinonychus and Unenlagiahad a very large brain for its size, stereoscopic vision, raptorial hands and an enlarged sickle− shaped claw on the foot, indicative of a predatory lifestyle. In the novel First Frontier (Star Trek, Book 75) written by Diane Carey and Dr. James I. Kirkland, a paleontologist who discovered the famous Utahraptor, we found that the U.S.S. Enterprise is caught in an alternative reality where the Earth is a vast jungle-like paradise  ruled by the Clan Ru, an alien race, descendant of Earth’s raptor dinosaurs. The Clan Ru posses two fingers on each hand with an opposable thumb as in Russell’s model for Troodon evolution.

Sin título

 

References:

Russell, D. A., & Séguin, R. 1982. “Reconstruction of the small Cretaceous theropod Stenonychosaurus inequalis and a hypothetical dinosauroid.” Syllogeus 37, 1-43.

Junchang Lü; Li Xu; Yongqing Liu; Xingliao Zhang; Songhai Jia; Qiang Ji (2010). “A new troodontid (Theropoda: Troodontidae) from the Late Cretaceous of central China, and the radiation of Asian troodontids.” Acta Palaeontologica Polonica. 55 (3): 381–388. doi:10.4202/app.2009.0047.

Diane Carey, James I. Kirkland, First Frontier (Star Trek, Book 75) Paperback, August 1, 1995.

A brief introduction to the Carnotaurus family tree.

 

Skull and neck of Carnotaurus sastrei

Skull and neck of Carnotaurus sastrei (From Novas et al., 2013)

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 oldest records of abelisauroid theropods are from the Early Jurassic. These ceratosaurian theropods exhibit spectacular cranial ornamentation in the form of horns and spikes; and strongly reduced forelimbs and hands. The group was erected by Jose Bonaparte with the description of  Abelisaurus Comahuensis. 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, from Cenomanian (Ilokelesia, Xenotarsosaurus, and Ekrixinatosaurus) to Campanian–Maastrichtian (Abelisaurus, Carnotaurus, Aucasaurus, and Noasaurus).

Abelisauroidea has been divided into two main branches: the Noasauridae and the Abelisauridae. The Noasauridae are known from Cretaceous beds in northern Argentina, Madagascar, India, and Niger. They are small and slender with sizes that range from 1 to 3 metres in length. The best-preserved and most complete noasaurid is Masiakasaurus knopfleri from the Maastrichtian of Madagascar. The Abelisaurids are medium to large, robust animals, such as the Carnotaurus and the Majungasaurus of Madagascar. The group exhibits short, round snouts; thickened teeth; short, stocky arms; and highly reduced forearms.

Masiakasaurus on display at the Royal Ontario Museum.

Masiakasaurus on display at the Royal Ontario Museum.

Carnotaurus sastrei is the most advanced member of Abelisauridae. It was collected in the lower section of La Colonia Formation, Chubut Province, Argentina, by an expedition led by Argentinian paleontologist José Bonaparte. In 1985, Bonaparte published a note presenting Carnotaurus sastrei as a new genus and species and briefly describing the skull and lower jaw. The skull of Carnotaurus is complete, measuring 60 cm from the tip of the premaxillae to the distal tip of the paroccipital process. The most distinctive features of Carnotaurus are the two robust conical horns that extend from the frontals. The horns are dorsoventrally compressed, and 146 mm long on both sides. The dorsal surface of each horn is ornamented with a series of longitudinal grooves. Because relatively few abelisaurid braincases are known, the description of the Carnotaurus braincase is important for understanding the variability of this structure within the clade (Carabajal 2011). C. sastrei would have had a comparatively weak muscle-driven bite.

The forelimbs of Carnotaurus show an extreme reduction, proportionally greater than the reduction observed in tyrannosaurids, although the radius, ulna and humerus are very robust. The hand has four digits, including a large, conical-shaped metacarpal IV lacking an articulation for a phalanx.

 

References:

Novas, F.E., et al., Evolution of the carnivorous dinosaurs during the Cretaceous: The evidence from Patagonia, Cretaceous Research (2013), http://dx.doi.org/10.1016/j.cretres.2013.04.001

Bonaparte, José F.; Novas, Fernando E.; Coria, Rodolfo A. (1990). “Carnotaurus sastrei Bonaparte, the horned, lightly built carnosaur from the Middle Cretaceous of Patagonia”, Contributions in Science (Natural History Museum of Los Angeles County) 416.

Mazzetta, Gerardo V.; Fariña, Richard A.; Vizcaíno, Sergio F. (1998). “On the palaeobiology of the South American horned theropod Carnotaurus sastrei Bonaparte”, Gaia 15: 185–192.

Ruiz, Javier; Torices, Angélica; Serrano, Humberto; López, Valle (2011). “The hand structure of Carnotaurus sastrei (Theropoda, Abelisauridae): implications for hand diversity and evolution in abelisaurids”. Palaeontology 54 (6): 1271–1277.

Late Cretaceous and modern diatom ecology: implications for our changing oceans

Sin título

Photomicrographs of diatom resting spores. Scale bars =10 mm (From Davies and Kemp, 2016)

Diatoms are unicellular algae with golden-brown photosynthetic pigments with a fossil record that extends back to Early Jurassic. They live in aquatic environments, soils, ice, attached to trees or anywhere with humidity, and their remains accumulate forming diatomite, a type of soft sedimentary rock. The most distinctive feature of diatoms is their siliceous skeleton known as frustule that comprise two valves. The formation of this opaline frustule is linked  in modern oceans with the biogeochemical cycles of silicon and carbon.

Past fluctuations in global temperatures are crucial to understand Earth’s climatic evolution. During the Late Cretaceous the global climate change has been associated with episodes of outgassing from major volcanic events, orbital cyclicity and tectonism before ending with the cataclysm caused by a large bolide impact at Chicxulub, on the Yucatán Peninsula, Mexico. Following a major diatom radiation after the Cenomanian-Turonian anoxic event, the development of the first extensive diatomites provides the earliest widespread geological evidence for the rise to prominence of diatoms in ocean biogeochemistry. Studies of the greenhouse Cretaceous climates are especially topical since such warm, high CO2 periods of the past are often invoked as potential analogues for present warming trends (Davies and Kemp, 2016).

A. Chain of Stephanopyxis turri (From

A. Chain of Stephanopyxis turri (From Davies and Kemp, 2016)

Because their abundance and sensitivity to different parameters,  diatoms play a key role in Paleoceanography, particularly for evidence of climatic cooling and changing sedimentation rates in the Arctic and Antarctic oceans and to estimate sea surface temperature. Like Stephanopyxis, a common planktonic genus in the present oceans distinguished by its long stratigraphic range from the Albian to modern. Stephanopyxis can be found in tropical or warm water regions and evidence suggests a similar ecological adaptation during the Cretaceous. Meanwhile, resting spore development is generally associated with the onset of unfavourable environmental conditions and sporulation generally occurs in response to a sudden change in one or more environmental factors.

Since the start of the Industrial Revolution the anthropogenic release of CO2 into the Earth’s atmosphere has increased a 40%. In this context, warming of the present surface ocean is  leading to increased stratification in both hemispheres. Based on traditional views of diatom ecology, ocean stratification would  lead to decreased diatom production and a reduced effectiveness of the marine biological carbon pump. But recent ocean surveys, and records of the stratified seas of the Late Cretaceous, suggest that increased stratification may lead to increased rather than decreased diatom production and export. This would then result in a negative-rather than positive feedback to global warming (Davies and Kemp, 2016).

 

References:

A. Davies, A.E.S. Kemp, Late Cretaceous seasonal palaeoclimatology and diatom palaeoecology from laminated sediments, Cretaceous Research 65 (2016) 82-111

Martin, R. E. and Quigg, A. 2012 Evolving Phytoplankton Stoichiometry Fueled Diversification of the Marine Biosphere. Geosciences. Special Issue on Paleontology and Geo/Biological Evolution. 2:130-146.

Forgotten women of Paleontology: Erika von Hoyningen-Huene

Erika von Huene in the lates 1920s at the Tuebingen University.

Erika von Huene at the Tuebingen University.

Erika Martha von Hoyningen-Huene was born in Tübingen, Germany, on September 30, 1905.  Descendant of a noble Baltic German family, Erika grew up in a deeply religious home. Her father,  Professor Dr Friedrich Freiherr (Baron) von Hoyningen, better known as Friedrich von Huene (1875–1969), was a world expert palaeontologist, whose life and research were strongly influenced by his beliefs. Von Huene wrote several books, papers and articles, spanning 65 years, but he never gained a full professorial position. Instead, he took the position of  Konservator at the University of Tübingen. As a young girl, Erika helped her father in the Institute and Museum of Geology and Palaeontology and studied under his strong influence.

She was one of only two female vertebrate palaeontologists in the pre-World War II history of Germany.  She completed her doctorate under the supervision of Prof. Dr Edwin Hennig in 1933, the same year that Hitler came to power. She later contributed with George Gaylord Simpson with her pioneering work on early mammals. But  the Nazi regime affected her life and work. During those difficult years, her father used his influence to help persecuted colleagues, such as ‘Tilly’ Edinger. However, after the events that followed the infamous “Kristallnacht” (Night of the Broken Glass), Tilly Edinger’s paleontological career in Germany ended abruptly.

Friedrich on Huene contemplating the placement of a rib on a South African dicynodont specimen (From Turner 2009)

Friedrich von Huene contemplating the placement of a rib on a South African dicynodont specimen (From Turner 2009)

When World War II began, Erika moved to Berlin invited by her former professor Otto H. Schindewolf, and carried out some work for him in the geological survey. After the war ended, Erika lost her job. For a time, she assisted his father and published her last paper in 1949. Her last years were devoted to managing nursing homes in Tübingen and Berlin. She died in Berlin, almost a week after her father’s death, on April 9, 1969.

During her scientific career, Erika wrote only seven papers. She suffered the consequences of the discrimination against women in Germany and finally gave up. In the year that Erika gained her doctorate, promotion for women in Germany was denied and women in higher positions were downgraded, and by the time  the war ended and men returned to their jobs, most women returned to the “safety of their homes”.

References:

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

S. Turner, 2009, Reverent and exemplary: ‘Dinosaur man’ Friedrich von Huene (1875-1969), Geological Society London Special Publications 310(1):223-243

Murusraptor barrosaensis, a new species in the megaraptorid clade.

Body reconstruction of Murusraptor barrosaensis (From Coria et al., 2016)

Body reconstruction of Murusraptor barrosaensis (From Coria et al., 2016)

Patagonia has yielded the most comprehensive fossil record of Cretaceous theropods from Gondwana, including Megaraptora, a clade of medium-sized and highly pneumatized theropods represented by Megaraptor, Orkoraptor and Aerosteon, and characterized by the formidable development of their manual claws on digits I and II and the transversely compressed and ventrally sharp ungual of the first manual digit (Novas et al, 2013). The enigmatic nature of this group has been a matter of discussion since the description of the first megaraptoran, Megaraptor namunhaiquii. For years, Megaraptor has been alternatively interpreted as belonging to different theropod lineages: as basal coelurosaurians (Novas,1998), basal tetanurans (Calvo et al.,2004; Smith et al., 2008), and allosauroids closely related with carcharodontosaurids (Smith et al., 2007; Benson et al., 2010; Carrano et al., 2012). The main reason for so many different interpretations is the incomplete nature of most available megaraptorid skeletons and the little information about their cranial anatomy.

Murusraptor barrosaensis, from the Upper Cretaceous of Neuquén Province, Argentina, belongs to a Patagonian radiation of megaraptorids together with Aerosteon, Megaraptor and Orkoraptor. Murusraptor, meaning “Wall Raptor”, was discovered in a canyon wall in 2001 during an expedition to Sierra Barrosa in northwestern Patagonia. The holotype specimen includes much of the skull, axial skeleton, pelvis and tibia. The braincase is intact and most of the sutures are still visible, indicating that this was not a fully mature animal.

Different appendicular elements of Murusraptor in their original burial positions (From Coria et al., 2016)

Different appendicular elements of Murusraptor in their original burial positions (From Coria et al., 2016)

Murusraptor barrosaensis is unique in having anterodorsal process of lacrimal longer than height of preorbital process; sacral ribs hollow and tubelike; short ischia distally flattened and slightly expanded dorsoventrally.

Murusraptor shares with all Megaraptoridae two unambiguous synapomorphies: teeth with no enamel wrinkles (interpreted as a reversion to primitive condition in Theropoda); and anterior caudal vertebrae with neural arch bearing prominent centrodiapophysial laminae that define a deep infradiapophysial fossa. Murusraptor also exhibits some characters that are interpreted as convergencies of this taxon with non-tyrannosauroid theropods, including lacrimal with a small pneumatic recess; and a highly pneumatic braincase (Coria et al., 2016)

References:

Rodolfo A. Coria, Philip J. Currie. A New Megaraptoran Dinosaur (Dinosauria, Theropoda, Megaraptoridae) from the Late Cretaceous of Patagonia. PLOS ONE, 2016; 11 (7): e0157973 DOI: 10.1371/journal.pone.0157973

Porfiri, J. D., Novas, F. E., Calvo, J. O., Agnolín, F. L., Ezcurra, M. D. & Cerda, I. A. 2014. Juvenile specimen of Megaraptor (Dinosauria, Theropoda) sheds light about tyrannosauroid radiation. Cretaceous Research 51: 35-55.

 

Introducing Gualicho.

Gualicho shinyae, at the Centro Cultural de la Ciencia.

Gualicho shinyae, at the Centro Cultural de la Ciencia.

The Cretaceous beds of Patagonia have yielded the most comprehensive record of Cretaceous theropods from Gondwana and includes at least five main theropod lineages: Abelisauroidea, Carcharodontosauridae, Megaraptora, Alvarezsauridae, and Unenlagiidae. The best represented theropod clades in the Late Cretaceous terrestrial strata of the Neuquén Basin are the Abelisauroidea and the Carcharodontosauridae. The  Abelisauroidea has been divided in two main branches: the Noasauridae which includes the small-sized abelisauroids, and the Abelisauridae which comprises medium to large-sized animals, like the popular Carnotaurus sastrei. The group exhibits strongly reduced forelimbs and hands, stout hindlimbs, with a proportionally robust and short femur and tibia.  The Carcharodontosauridae includes the largest land predators in the early and middle Cretaceous of Gondwana, like the popular, Giganotosaurus carolinii. The group evolved large skulls surpassing the length of the largest skull of Tyrannosaurus rex.  Another common trait is the fusion of cranial bones. Gualicho shinyae gen. et sp. nov, a partially articulated mid-sized theropod (about 7.6m long and 450kg in weight) represents a new tetanuran theropod taxon from the Huincul Formation.

Articulated right foot of the holotype of Gualicho shinyae during excavation (from Apesteguía et al., 2016)

Articulated right foot of the holotype of Gualicho shinyae during excavation (from Apesteguía et al., 2016)

The new specimen exhibits a new and unusual combination of characters observed in various remotely related clades including ceratosaurs, tyrannosaurids, and megaraptorans. The didactyl manus with a semilunate distal carpal are indicative of derived tetanuran affinities, while the expanded posterior margin of the metatarsal III proximal articulation, are shared with ceratosaurs. The reduced forelimbs with didactyl manus are similar to those of the tyrannosaurids. However, in tyrannosaurids, the carpal elements are reduced and proximodistally flattened, whereas in Gualicho the semilunate and scapholunare carpals retain a more complex shape typical of the carpal elements of most non-coelurosaurian tetanurans. In addition, the manus of Gualicho differs from tyrannosaurids in having a proportionately more robust metacarpal I with a rectangular, rather than triangular, proximal articulation in end view (Apesteguía et al., 2016).

Left humerus of the of the holotype specimen of Gualicho shinyae (MPCN PV 0001) in (A) anterior, (B) posterior, (C) proximal, and (D) distal views. Abbreviations: dpc, deltopectoral crest; ics, intercondylar sulcus; it, internal tuberosity; msh, scar for insertion of m. scapulohumeralis (From Apesteguía et al., 2016).

Left humerus of the of the holotype specimen of Gualicho shinyae (MPCN PV 0001) in (A) anterior, (B) posterior, (C) proximal, and (D) distal views. Abbreviations: dpc, deltopectoral crest; ics, intercondylar sulcus; it, internal tuberosity; msh, scar for insertion of m. scapulohumeralis (From Apesteguía et al., 2016).

Gualicho shares several derived characters with the African theropod Deltadromeus, including reduced distal humeral articulations, and an expanded lobe bearing a medial trough on the proximocaudal aspect of the fibula. The faunal resemblances between strata in the Neuquén and San Jorge Basins of Patagonia and North African Cenomanian beds are intriguing, but difficult to interpret due to a lack of well sampled, age equivalent strata elsewhere.

Gualicho was discovered on a paleontological expedition led by Sebastian Apesteguía in 2007. The name derived from the Gennaken (Northern Tehuelche languaje) watsiltsüm, an old goddess now considered a source of misfortune. The name was chosen to reflect the difficult circumstances surrounding the discovery and study of the specimen. The specific name honors Ms. Akiko Shinya, Chief Fossil Preparator at the Field Museum.

References:

Apesteguía S, Smith ND, Juárez Valieri R, Makovicky PJ (2016) An Unusual New Theropod with a Didactyl Manus from the Upper Cretaceous of Patagonia, Argentina. PLoS ONE 11(7): e0157793. doi: 10.1371/journal.pone.0157793

A Tale of Two Exctintions.

The permian triassic boundary at Meishan, China (Photo: Shuzhong Shen)

The Permian Triassic boundary at Meishan, China (Photo: Shuzhong Shen)

Extinction is the ultimate fate of all species. The fossil record indicates that more than 95% of all species that ever lived are now extinct. Over the last 3 decades, mass extinction events  have become the subject of increasingly detailed and multidisciplinary investigations. In 1982, Jack Sepkoski and David M. Raup identified five major extinction events in Earth’s history: at the end of the Ordovician period, Late Devonian, End Permian, End Triassic and the End Cretaceous. These five events are know as the Big Five.

The end-Permian extinction is the most severe biotic crisis in the fossil record, with as much as 95% of the marine animal species and a similarly high proportion of terrestrial plants and animals going extinct . This great crisis occurred 252 million years ago (Ma) during an episode of global warming. The End-Triassic Extinction  is probably the least understood of the big five. 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. Although it’s almost impossible briefly summarize all the changes in biodiversity associated with both extinction events, we can describe their broad trends.

 

Flow chart summarizing proposed cause-and-effect relationships during the end-Permian extinction (From Bond and Wignall, 2014)

Flow chart summarizing proposed cause-and-effect relationships during the end-Permian extinction (From Bond and Wignall, 2014)

Both extinction events are commonly linked to the emplacement of the large igneous provinces of the Siberian Traps and the Central Atlantic Magmatic Province. Massive volcanic eruptions with lava flows, released large quantities of sulphur dioxide, carbon dioxide, thermogenic methane and large amounts of HF, HCl, halocarbons and toxic aromatics and heavy metals into the atmosphere. Furthermore, volcanism contribute gases to the atmosphere, such as Cl, F, and CH3Cl from coal combustion, that suppress ozone formation. Acid rain likely had an impact on freshwater ecosystems and may have triggered forest dieback. Mutagenesis observed in the Lower Triassic herbaceous lycopsid Isoetales has been attributed to increased levels of UV-radiation. Charcoal records point to forest fires as a common denominator during both events. Forest dieback was accompanied by the proliferation of opportunists and pioneers, including ferns and fern allies. Moreover, both events led to major schisms in the dominant terrestrial herbivores  and apex predators, including the late Permian extinction of the pariaeosaurs and many dicynodonts and the end-Triassic loss of crurotarsans (van de Schootbrugge and Wignall, 2016).

Aberrant pollen and spores from the end-Triassic extinction interval (scale bars are 20 μm). (a) Ricciisporites tuberculatus from the uppermost Rhaetian deposits at Northern Ireland (adapted from van de Schootbrugge and Wignall, 2016)

Aberrant pollen and spores from the end-Triassic extinction interval (scale bars are 20 μm). (a) Ricciisporites
tuberculatus and b) Kraeuselisporites reissingerii (adapted from van de Schootbrugge and Wignall, 2016)

During the end-Permian Event, the woody gymnosperm vegetation (cordaitaleans and glossopterids) were replaced by spore-producing plants (mainly lycophytes) before the typical Mesozoic woody vegetation evolved. The palynological record suggests that wooded terrestrial ecosystems took four to five million years to reform stable ecosystems, while spore-producing lycopsids had an important ecological role in the post-extinction interval. A key factor for plant resilience is the time-scale: if the duration of the ecological disruption did not exceed that of the viability of seeds and spores, those plant taxa have the potential to recover (Traverse, 1988). Palynological records from across Europe provide evidence for complete loss of tree-bearing vegetation reflected in a strong decline in pollen abundance at the end of the Triassic. In the Southern Hemisphere, the vegetation turnover consisted in the replacement to Alisporites (corystosperm)-dominated assemblage to a Classopollis (cheirolepidiacean)-dominated one.

Comparison of extinction rates for calcareous organisms during the end-Permian and end-Triassic extinction event (from van de Schootbrugge and Wignall, 2016)

Comparison of extinction rates for calcareous organisms during the end-Permian and end-Triassic extinction event (from van de Schootbrugge and Wignall, 2016)

Rapid additions of carbon dioxide during extreme events may have driven surface waters to undersaturation. Acidification affects the biogeochemical dynamics of calcium carbonate, organic carbon, nitrogen, and phosphorus in the ocean and interferes with a range of processes, including growth, calcification, development, reproduction and behaviour in a wide range of marine organisms like foraminifera, planktonic coccolithophores, pteropods and other molluscs,  echinoderms, corals, and coralline algae. Both extinction events led to near-annihilation of cnidarian clades and other taxa responsible for reef construction, resulting in ‘reef gaps’ that lasted millions of years. Black shales deposited across both extinction events also contain increased concentrations of the biomarker isorenieratane, a pigment from green sulphur bacteria, suggesting that the photic zone underwent prolonged periods of high concentrations of hydrogen sulphide. Following the end-Triassic extinction, Early Jurassic shallow seas witnessed recurrent euxinia over a time span of 25 million years, culminating in the Toarcian Oceanic Anoxic Event.

 

References:

BAS VAN DE SCHOOTBRUGGE and PAUL B. WIGNALL (2016). A tale of two extinctions: converging end-Permian and end-Triassic scenarios. Geological Magazine, 153, pp 332-354. doi:10.1017/S0016756815000643.

BACHAN, A. & PAYNE, J. L. 2015. Modelling the impact of pulsed CAMP volcanism on pCO2 and δ13C across the Triassic-Jurassic transition. Geological Magazine, published online

Retallack, G.J. 2013. Permian and Triassic greenhouse crises. Gondwana Research 24:90–103.

 

Once upon a time, there was a Dodo.

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

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

The Dodo (Raphus cucullatus Linnaeus, 1758) a giant, flightless pigeon endemic to the Mascarene island of Mauritius, became extinct just three centuries ago. As one of the earliest species to be identified as extinct, the Dodo gained tremendous celebrity throughout the nineteenth and twentieth centuries. It was first used as the prime example of a species wiped out by recent human activity in the Penny Magazine (Broderip 1833; reprinted in the Penny Cyclopaedia), where the author wrote that: “The agency of man, in limiting the increase of the inferior animals, and in extirpating certain races, was perhaps never more strikingly exemplified than in the case of the Dodo. That a species so remarkable in its character should become extinct, within little more than two centuries, so that the fact of its existence at all has been doubted, is a circumstance which may well excite our surprise, and lead us to a consideration of similar changes which are still going on from the same cause.”

Much greater public awareness of the Dodo’s demise followed publication of the monograph The Dodo and Its Kindred (Strickland and Melville 1848). Shortly after, a life-size reconstruction of a Dodo was displayed in 1851 at the Great Exhibition in London and later exhibited at the Crystal Palace at Sydenham. Even Lewis Carroll featured the Dodo as a character in Alice’s Adventures in Wonderland and firmly established the bird as a popular figure in Victorian culture.

The Oxford dodo head (From Wikimedia Commons)

The Oxford dodo head (From Wikimedia Commons)

In 1828, John Duncan, curator at the Ashmolean Museum, described a desiccated dodo head and foot held at the museum. In 1842, John Theodore Reinhardt, a Danish professor, examined a second dodo skull at the Copenhagen Museum and concluded that it was a giant pigeon. Prior to Reinhardt’s proposal, the Dodo had variously been considered a diminutive ostrich, a rail, or even a kind of vulture.

The publication of ‘Alice’s Adventures in Wonderland’ coincided with a spectacular discovery of subfossil dodo bones from a marsh called the Mare aux Songes in Mauritius in 1865.  George Clark, discoverer of the fossil site, sent consignments of bones initially to Richard Owen  and subsequently to Alfred Newton. A year later, Owen described the bones in Memoir on the Dodo. He reconstructed the bird using the most famous of the contemporary Dodo paintings, one by the Dutch artist Roelandt Savery. Three years later, Owen rectified his mistake by reconstructing the bird in a natural more upright position.

Amateur naturalist and barber Louis Etienne Thirioux (1846–1917),  collected two of the most important dodo skeletons known to science around the turn of the 19th century. Thirioux’s dodos were discovered in the foothills and valleys of Le Pouce and surrounding mountains, but their exact provenance has not been recorded.

Owen’s (1866) original reconstruction of the dodo.

Owen’s (1866) original reconstruction of the dodo.

In 1896, Hilaire Belloc wrote a beautiful poem about the dodo in his Bad Child’s Book of Beasts.

The Dodo used to walk around,
And take the sun and air.
The sun yet warms his native ground –
The Dodo is not there!

The voice which used to squawk and squeak
Is now for ever dumb –
Yet may you see his bones and beak
All in the Mu-se-um.

References:

Kenneth F. Rijsdijk, Julian P. Hume, Perry G. B. De Louw, Hanneke J. M. Meijer, Anwar Janoo, Erik J. De Boer, Lorna Steel, John De Vos, Laura G. Van Der Sluis, Henry Hooghiemstra, F. B. Vincent Florens, Cláudia Baider, Tamara J. J. Vernimmen, Pieter Baas, Anneke H. Van Heteren, Vikash Rupear, Gorah Beebeejaun, Alan Grihault, J. (Hans) Van Der Plicht, Marijke Besselink, Juliën K. Lubeek, Max Jansen, Sjoerd J. Kluiving, Hege Hollund, Beth Shapiro, Matthew Collins, Mike Buckley, Ranjith M. Jayasena, Nicolas Porch, Rene Floore, Frans Bunnik, Andrew Biedlingmaier, Jennifer Leavitt, Gregory Monfette, Anna Kimelblatt, Adrienne Randall, Pieter Floore & Leon P. A. M. Claessens (2015) A review of the dodo and its ecosystem: insights from a vertebrate concentration Lagerstätte in Mauritius, Journal of Vertebrate Paleontology, 35: sup1, 3-20, DOI: 10.1080/02724634.2015.1113803

Turvey, S. T.; Cheke, A. S. (2008). “Dead as a dodo: The fortuitous rise to fame of an extinction icon”. Historical Biology 20 (2): 149–163