On the rise of the archosauromorphs

Proterosaurus speneri at Teyler’s Museum.

In the aftermath of the devastating Permo-Triassic mass extinction (~252 Ma), synapsid groups such as anomodonts and gorgonopsians and parareptiles such as pareiasaurs, were decimated and largely displaced by the archosauromorphs. The group, which include the ‘ruling reptiles’ (crocodylians, pterosaurs, dinosaurs, and their descendants, birds), originated during the middle–late Permian. The most basal archosauromorphs are Aenigmastropheus and Protorosaurus.

During the Triassic, the archosauromorphs achieved high morphological diversity, including aquatic or semi aquatic forms, highly specialized herbivores, massive predators, armoured crocodile-like forms, and gracile dinosaur precursors. The group constitutes an excellent empirical case to shed light on the recovery of terrestrial faunas after a mass extinction.

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

The massive volcanic eruptions in Siberia at the end of the Permian, covered more than 2 millions of km 2 with lava flows, releasing more carbon in the atmosphere. High amounts of fluorine and chlorine increased the climatic instability, which means that the Mesozoic began under extreme hothouse conditions. Isotope studies and fossil record, indicates that temperatures in Pangaea interiors during the Early Triassic oscillated between 30 and 40 degrees Celsius, with heat peaks in the Induan and during the Early and Late Olenekian. It was suggested that during that time there was a moderate oxygen depletion that caused the low body size of the amphibian and reptilian life-forms found in those rocks.

After the mass extinction event, a distributed archosauromorph ‘disaster fauna’ dominated by proterosuchids, established for a short time. In South Africa, Proterosuchus occurs only between 5 and 14 m above the PT boundary and a similar pattern has been documented for the synapsid Lystrosaurus. During the Olenekian (1–5 million years after the extinction), archosauromorphs underwent a major phylogenetic diversification with the origins or initial diversification of major clades such as rhynchosaurs, archosaurs, erythrosuchids and tanystropheids.

Stenaulorhynchus stockleyi, a rhynchosaur from the Middle Triassic (From Wikimedia Commons)

The Mid Triassic is marked by the return of conifer-dominated forests, and the end of an interval of intense carbon perturbations, suggesting the recovery and stabilization of global ecosystems. The Anisian (5–10 Myr after the extinction) is characterized by a high diversity among the archosauromorphs with the appearance of large hypercarnivores, bizarre and highly specialized herbivores, long-necked marine predators, and gracile and agile dinosauromorphs. This phylogenetic diversity of archosauromorphs by the Middle Triassic paved the way for the ongoing diversification of the group (including the origins of dinosaurs, crocodylomorphs, and pterosaurs) in the Late Triassic, and their dominance of terrestrial ecosystems for the next 170 million years.

 

 

References:

Ezcurra MD, Butler RJ. 2018 The rise of the ruling reptiles and ecosystem recovery from the Permo-Triassic mass
extinction. Proc. R. Soc. B 285: 20180361. http://dx.doi.org/10.1098/rspb.2018.0361

Ezcurra MD. (2016) The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms. PeerJ 4:e1778 https://doi.org/10.7717/peerj.1778

Holz, M., Mesozoic paleogeography and paleoclimates – a discussion of the diverse greenhouse and hothouse conditions of an alien world, Journal of South American Earth Sciences (2015), doi: 10.1016/j.jsames.2015.01.001

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Life finds a way.

 

Site M0077 in the Chicxulub crater as seen using gravity data. From Lowery et al., 2018.

In the late ’70, 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 an asteroid collided with the Earth and caused one of the most devastating events in the history of life. In 1981, Pemex (a Mexican oil company) identified Chicxulub as the site of this massive asteroid impact. The crater is more than 180 km (110 miles) in diameter and 20 km (10 miles) in depth, making the feature one of the largest confirmed impact structures on Earth.

The impact released an estimated energy equivalent of 100 teratonnes of TNT, induced earthquakes, shelf collapse around the Yucatan platform, and widespread tsunamis that swept the coastal zones of the surrounding oceans. The event also produced high concentrations of dust, soot, and sulfate aerosols in the atmosphere. The decrease of sunlight caused a drastic short-term global reduction in temperature (15 °C on a global average, 11 °C over the ocean, and 28 °C over land). While the surface and lower atmosphere cooled, the tropopause became much warmer, eliminate the tropical cold trap and allow water vapor mixing ratios to increase to well over 1,000 ppmv in the stratosphere. Those events accelerated the destruction of the ozone layer. During this period, UV light was able to reach the surface at highly elevated and harmful levels. Additionally, the vapour produced by the impact  could have led to global acid rain and a dramatic acidification of marine surface waters.

The Cretaceous/Palaeogene mass extinction eradicated almost three-quarters of the plant and animal species on Earth including non-avian dinosaurs, pterosaurs, marine reptiles, and ammonites. Global forest fires might have raged for months. Photosynthesis stopped and the food chain collapsed. Marine environments lost about half of their species, and almost 90% of Foraminifera species went extinct. But life always finds a way, and 30,000 years after the impact, a thriving ecosystem was present within the Chicxulub crater.

The evidence comes from the recent joint expedition of the International Ocean Discovery Program and International Continental Drilling Program. The team sampled the first record of the few hundred thousand years immediately after the impact within the Chicxulub crater. This sample includes foraminifera, calcareous nannoplankton, trace fossils and geochemical markers for high productivity. The lowermost part of the limestone sampled also contains the lowest occurrence of Parvularugoglobigerina eugubina, the first trochospiral planktic foraminifera, which marks the base of Zone Pα. This biozone was defined at Gubbio (Italy) to precisely characterise the Cretaceous/Paleogene boundary.

3 Early Danian foraminifer abundances and I/(Ca+Mg) oxygenation proxy. From Lowery et al., 2018.

P. eugubina was a low to middle latitude taxon with an open-ocean affinity and has an extremely variable morphology. Other foraminifer of the same genus (P. extensa, P. alabamensis) and Guembelitria cretacea were found at the same core. The nannofossil assemblage includes opportunistic groups that can tolerate high environmental stress such as Thoracosphaera and Braarudosphaera, but unlike the foraminifera, there are no clear stratigraphic trends in overall nannoplankton abundance. Discrete, but clear trace fossils, including Planolites and Chondrites, characterize the upper 20cm of the transitional unit. Nevertheless, the study also shows that photosynthetic phytoplankton struggled to recover for millions of years after the event.

Core samples also revealed that porous rocks in the center of the Chicxulub crater had remained hotter than 300 °C for more than 100,000 years. The high-temperature hydrothermal system was established within the crater but the appearance of burrowing organisms within years of the impact indicates that the hydrothermal system did not adversely affect seafloor life. These impact-generated hydrothermal systems are hypothesized to be potential habitats for early life on Earth and other planets.

 

Reference:

Christopher M. Lowery et al. Rapid recovery of life at ground zero of the end-Cretaceous mass extinction, Nature (2018). DOI: 10.1038/s41586-018-0163-6

Charles G. Bardeen, Rolando R. Garcia, Owen B. Toon, and Andrew J. Conley, On transient climate change at the Cretaceous−Paleogene boundary due to atmospheric soot injections, PNAS 2017 ; published ahead of print August 21, 2017 DOI: 10.1073/pnas.1708980114

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 CretaceousGeophys. Res. Lett.43,  doi:10.1002/2016GL072241.

 

 

Mary Anning, ‘the greatest fossilist the world ever knew’.

Duria Antiquior famous watercolor by the geologist Henry de la Beche based on fossils found by Mary Anning. From Wikimedia Commons.

By the 19th century, the study of the Earth became central to the economic and cultural life of Great Britain. 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. England was ruled by an elite, and of course, these scholarly activities only occurred within the upper echelon of British society. Notwithstanding, the most famous fossilist of the 19th century was a women of a low social station: Mary Anning.

Mary Anning 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 that they sold as “curiosities”. The source of those fossils was the coastal cliffs around Lyme Regis, part of a geological formation known as the Blue Lias.

The shore of Lyme Bay where Mary Anning did most of her collecting.

Invertebrate fossils, like ammonoids or belemnites, were the most common findings. But when Mary was 12, her brother Joseph found a skull protruding from a cliff and few month later, Mary found the rest of the skeleton. 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.

In 1819 the Annings were in considerable financial difficulties. They were rescued by the generosity of Thomas James Birch (1768–1829), who arranged for the sale of his personal collection, largely purchased from the Annings, in Bullock’s Museum in London.  The auction took place in May 1820, during which George Cuvier bought several pieces for the Muséum National d’Histoire Naturelle.

Mary Anning’s sketch of belemnites. From original manuscripts held at the Natural History Museum, London. © The Natural History Museum, London

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.

Autograph letter about the discovery of plesiosaurus, by Mary Anning. From original manuscripts held at the Natural History Museum, London. © The Natural History Museum, London

By the age of 27, Mary was the owner of a little shop: Anning’s Fossil Depot. Many scientist and fossil collectors from around the globe went to Mary´s shop. She was friend of Henry De la Beche, the first director of the Geological Survey of Great Britain, who knew Mary since they were both children and lived in Lyme Regis. De la Beche was a great supporter of Mary’s work. She also corresponded with Charles Lyell, William Buckland and Mary Morland, Adam Sedgwick and Sir Roderick Murchison.
It’s fairly to say that Mary felt secure in the world of men, and a despite her religious beliefs, she was an early feminist. In an essay in her notebook, titled Woman!, Mary writes:  “And what is a woman? Was she not made of the same flesh and blood as lordly Man? Yes, and was destined doubtless, to become his friend, his helpmate on his pilgrimage but surely not his slave…”

A) Mary Anning (1799- 1847) B) William Buckland (1784- 1856)

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 1829,  Mary Anning discovered Squaloraja polyspondyle, a fish. Unfortunately, the specimen was lost in the destruction of the Bristol Museum by a German bombing raid in November, 1940.
From her correspondence is clear that Mary learned anatomy by dissecting modern organisms. In a letter to J.S. Miller of the Bristol Museum, dated 20 January 1830, she wrote: “…I have dissected a Ray since I received your letter, and I do not think it the same genus, the Vertebrae alone would constitute it a different genus being so unlike any fish vertebrae they are so closely anchylosed that they look like one bone but being dislocated at two places show that each thin line is a separate vertebrae with the ends flat…”. 

Sketch of Mary Anning by Henry De la Beche.

Mary Anning, ‘the greatest fossilist the world ever knew’, 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.

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.

Mary Anning’s Window, St. Michael’s Church. From Wikimedia Commons.

In February 1850 Mary was honoured by the unveiling of a new window in the parish church at Lyme, funded through another subscription among the Fellows of the Geological Society of London, with the following inscription: “This window is sacred to the memory of Mary Anning of this parish, who died 9 March AD 1847 and is erected by the vicar and some members of the Geological Society of London in commemoration of her usefulness in furthering the science of geology, as also of her benevolence of heart and integrity of life.”

In 1865, Charles Dickens wrote an article about Mary Anning’s life in his literary magazine “All the Year Round”, where emphasised the difficulties she had overcome: “Her history shows what humble people may do, if they have just purpose and courage enough, toward promoting the cause of science. The inscription under her memorial window commemorates “her usefulness in furthering the science of geology” (it was not a science when she began to discover, and so helped to make it one), “and also her benevolence of heart and integrity of life.” The carpenter’s daughter has won a name for herself, and has deserved to win it.”

References:

Buckland, Adelene: Novel Science : Fiction and the Invention of Nineteenth-Century Geology, University of Chicago Press, 2013.

BUREK, C. V. & HIGGS, B. (eds) The Role of Women in the History of Geology. Geological Society, London, Special Publications, 281, 1–8. DOI: 10.1144/SP281.1.

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.

 

 

Lessons from the past: Paleobotany and Climate Change

 

From 1984–2012, extensive greening has occurred in the tundra of Western Alaska, the northern coast of Canada, and the tundra of Quebec and Labrador. Credits: NASA’s Goddard Space Flight Center/Cindy Starr.

For the last 540 million years, Earth’s climate has oscillated between three basic states: Icehouse, Greenhouse (subdivided into Cool and Warm states), and Hothouse. The “Hothouse” condition is relatively short-lived and is consequence from the release of anomalously large inputs of CO2 into the atmosphere during the formation of Large Igneous Provinces (LIPs), when atmospheric CO2 concentrations may rise above 16 times (4,800 ppmv), while the “Icehouse” is characterized by polar ice, with alternating glacial–interglacial episodes in response to orbital forcing. The ‘Cool Greenhouse” displays  some polar ice and alpine glaciers,  with global average temperatures between 21° and 24°C. Finally, the ‘Warm Greenhouse’ lacks of any polar ice, and global average temperatures might have ranged from 24° to 30°C.

Reconstructions of Earth’s history have considerably improved our knowledge of episodes of rapid emissions of greenhouse gases and abrupt warming. Several episodes of global climate change were similar in magnitude to the anthropogenically forced climate change that has occurred during the past century. Consequently, the development of different proxy measures of paleoenvironmental parameters has received growing attention in recent years. Paleobotany, the study of fossil plants in deep geological time, offers key insights into vegetation responses to past global change, including suitable analogs for Earth’s climatic future.

Monthly average atmospheric carbon dioxide concentration at Mauna Loa Observatory, Hawaii.

The main forces of climatic change on a global scale are solar forcing, atmospheric composition, plate tectonics, Earth’s biota, and of course, us. Human activity is a major driver of the dynamics of Earth system. Until the Industrial Revolution, the average global CO2 levels fluctuated between about 170 ppm and 280 ppm. But with the beginning of the Industrial Era, that number risen above 300 ppm, currently averaging an increase of more than 2 ppm per year. The average monthly level of CO2 in the atmosphere on last April exceeded the 410 ppm for first time in history. Thus we could hit an average of 500 ppm within the next 45 years, a number that have been unprecedented for the past 50–100+ million years according to fossil plant-based CO2 estimates. Therefore, the closest analog for today conditions is the Eocene, meaning greater similarities in continental configuration, ecosystem structure and function, and global carbon cycling.

Some of the best-studied intervals of global change in the fossil plant record include the Triassic–Jurassic boundary, 201.36 ± 0.17 Mya; the PETM, 56 Mya; and the Eocene–Oligocene boundary, 33.9 Mya.The first two events represent rapid greenhouse gas–induced global warming episodes; the last coincides with the initiation of the Antarctic ice sheet and global cooling leading to our current icehouse.

Time line of plant evolution (From McElwain, 2018)

During the PETM, compositional shifts in terrestrial vegetation were marked but transient in temperate latitudes and long-lived in the tropics. The PETM is characterized by the release of 5 billion tons of CO2 into the atmosphere, while temperatures increased by 5 – 8°C. High temperatures and likely increased aridity in the North American temperate biomes resulted in geologically rapid compositional changes as local mixed deciduous and evergreen forest taxa (such as Taxodium) decreased in relative abundance. These suggest that global warming has a marked effect on the composition of terrestrial plant communities that is driven predominantly by migration rather than extinction. However, it’s difficult to draw parallels with Anthropocene warming and vegetation responses because they are occurring at a minimum of 20 times faster than any past warming episode in Earth’s history.

In the early Eocene (56 to 49 Mya), a time of peak sustained global warmth, the Arctic Ocean was ice free, with a mosaic of mixed deciduous, evergreen (Picea, Pinus), and swamp forests, and with high densities of the aquatic fern Azolla. The Azolla bloom reduced the carbon dioxide from the atmosphere to 650 ppm, reducing temperatures and setting the stage for our current icehouse Earth. The eventual demise of Azolla in the Arctic Ocean is attributed to reduced runoff and a slight salinity increase.

The modern fern Azolla filiculoides (From Wikipedia)

The Earth’s poles have warmed and will continue to warm at a faster rate than the average planetary warming, because the heat is readily transported poleward by oceans and the atmosphere due to positive feedback effects involving snow cover, albedo, vegetation, soot, and algal cover in the Arctic and Antarctic. This phenomenon is known as “polar amplification”.

Recent studies about the greening of the Arctic indicates that increasing shrubiness has likely already had an unexpected negative impact on herbivore populations, such as caribou, by decreasing browse quality. Thus, it is important to predict how short-term temporal trends in Arctic vegetation change will continue under CO2-induced global warming. The paleobotanical record of high Arctic floras may provide broad insight into these questions.

References:

Jennifer C. McElwain, Paleobotany and Global Change: Important Lessons for Species to Biomes from Vegetation Responses to Past Global Change, Annual Review of Plant Biology  (2018), DOI: 10.1146/annurev-arplant-042817-040405

 

Ichthyornis and the evolution of the avian skull.

 

Ichthyornis skull

Birds originated from a theropod lineage more than 150 million years ago. By the Early Cretaceous, they diversified, evolving into a number of groups of varying anatomy and ecology. Much of birds anatomical variety is related to their skulls and in particulary with their beaks.

Discovered in 1870 by Benjamin Franklin Mudge, a professor from Kansas State Agricultural College and good friend of Othniel Charles Marsh, Ichthyornis, which means‭ ‘‬fish bird‭’‭, was a small early ornithuromorph from the Late Cretaceous of North America. Ornithuromorphs, include Gansus, Patagopteryx, Yixianornis, and Apsaravis, which form a grade on the line to Ornithurae, a derived subgroup that includes modern birds and their closest fossil relatives.

 

3D reconstruction of the skull of I. dispar (From Field et al., 2018)

The skull of I. dispar shows a transitional point in the evolutionary history of birds. The upper margin of the beak is concave in profile, a derived condition shared with living birds. The fused, toothless premaxillae have a terminal hook, and occupy the anterior quarter of the rostrum. Neurovascular foramina indicate the presence of a highly keratinized region of rhamphotheca called the premaxillary nail. The maxilla is plesiomorphically long. The dentition is extensive in both upper and lower jaws. A sulcus on the rostral half of the maxilla suggests a broad naso-maxillary contact and a correspondingly broad postnarial bar. The palatine is narrow and elongate, unlike that of Archaeopteryx and more stemward theropods. The quadrate exhibits two rounded capitular condyles that fit into cotyles on the prootic and squamosal bones to form a mobile joint with the cranium. The arrangement of the rostrum, jugal, and quadratojugal, the mobile suspensorium and the narrow, linear palatine all indicate that I. dispar possessed a fully functional avian cranial kinetic system.

The endocranial cavity appears essentially modern in sagittal section. The forebrain was enlarged and posteroventrally rotated while the optic lobes were inflated and laterally shifted, as in living birds. The squamosal exhibits an archaic, deinonychosaur-like morphology. The zygomatic process is deep and triangular in lateral view. The nuchal crest extends from the midline of the skull onto the zygomatic process, forming the upper edge of the squamosal bone, as in non-avialan theropods.

Darwin’s letter to Marsh (Yale Peabody Museum Archives)

Since its discovery, Ichthyornis has been viewed as a classical example of evolution, due to the combination of an advanced postcranial morphology and retention of toothed jaws. In a letter, dated August 31, 1880, Charles Darwin thanks Marsh for a copy of his monograph Odontornithes, which reported two contrasting bird genera: Hesperornis, which was about 1.8 metres tall, and Ichthyornis, which had an average wingspan of about 60 centimetres. In his letter, Darwin wrote: “I received some time ago your very kind note of July 28th, & yesterday the magnificent volume. I have looked with renewed admiration at the plates, & will soon read the text. Your work on these old birds & on the many fossil animals of N. America has afforded the best support to the theory of evolution, which has appeared within the last 20 years.”

 

References:

Daniel J. Field, Michael Hanson, David Burnham, Laura E. Wilson, Kristopher Super, Dana Ehret, Jun A. Ebersole & Bhart-Anjan S. Bhullar, Complete Ichthyornis skull illuminates mosaic assembly of the avian head, Nature (2018). nature.com/articles/doi:10.1038/s41586-018-0053-y
Xing Xu, Zhonghe Zhou, Robert Dudley, Susan Mackem, Cheng-Ming Chuong, Gregory M. Erickson, David J. Varricchio, An integrative approach to understanding bird origins, Science, Vol. 346 no. 6215, DOI: 10.1126/science.1253293.

 

A brief introduction to the Carnian Pluvial Episode.

Early-late Carnian (Late Triassic) palaeogeographic reconstruction showing some of the main vertebrate-bearing units (From Bernardi et al. 2018)

Dinosaurs likely originated in the Early to Middle Triassic. The Manda beds of Tanzania yielded the remains of the possible oldest dinosaur, Nyasasaurus parringtoni, and Asilisaurus, a silesaurid (the immediate sister-group to Dinosauria). However the oldest well-dated identified dinosaurs are from the late Carnian of the lower Ischigualasto Formation in northwestern Argentina, dated from 231.4 Ma to 225.9 Ma. The presence of dinosaurs, such as Panphagia, Eoraptor, and Herrerasaurus support the argument that Dinosauria originated during the Ladinian or earlier and that they were already well diversified in the early Carnian. Similarly, the Santa Maria and Caturrita formations in southern Brazil preserve basal dinosauromorphs, basal saurischians, and early sauropodomorphs. In North America, the oldest dated occurrences of vertebrate assemblages with dinosaurs are from the Chinle Formation. Two further early dinosaur-bearing formations, are the lower (and upper) Maleri Formation of India and the Pebbly Arkose Formation of Zimbabwe. These skeletal records of early dinosaurs document a time when they were not numerically abundant, and they were still of modest body size (Eoraptor had a slender body with an estimated weight of about 10 kilograms).

Trace fossil evidence suggests that the first dinosaur dispersal in the eastern Pangaea is synchronous with an important climate-change event named the “Carnian Pluvial Episode” (CPE) or “Wet Intermezzo”, dated to 234–232 Ma.

Skeleton of Eoraptor lunensis (PVSJ 512) in left lateral view. Scale bar equals 10 cm. From Sereno et al., 2013.

The Late Triassic is marked by a return to the hothouse condition of the Early Triassic, with two greenhouse crisis that may also have played a role in mass extinctions. Isotopic  records suggest  a global carbon cycle perturbation during the Carnian that was coincident with complex environmental changes and biotic turnover.

The CPE is often described as a shift from arid to more humid conditions (global warming, ocean acidification, mega-monsoonal conditions, and a generalised increase in rainfall). In the marine sedimentary basins of the Tethys realm, an abrupt change of carbonate factories and the establishment of anoxic conditions mark the beginning of the climate change. The CPE also marks the first massive appearance of calcareous nannoplankton, while groups, like bryozoans and crinoids, show a sharp decline during this event.

Palynological association from the Heiligkreuz Formation provide information on palynostratigraphy and palaeoclimate during the last part of the Carnian Pluvial Event (CPE). From Roghi et al., 2014

On land, palaeobotanical evidence shows a shift of floral associations of towards elements more adapted to humid conditions (the palynological record across the CPE suggest at least 3–4 discrete humid pulses). Several families and orders make their first appearance during the Carnian: bennettitaleans, modern ferns, and conifer families (Pinaceae, Araucariaceae, Cheirolepidaceae). The oldest biological inclusions found preserved in amber also come from the Carnian; and key herbivorous groups such as dicynodonts and rhynchosaurs, which had represented 50% or more of faunas, disappeared, and their places were taken by dinosaurs.

Despite the global significance of the CPE,  the trigger of the environmental change  is still disputed. Volcanic emissions from the Wrangellia igneous province and the dissociation of methane clathrates could be linked to the CPE. It seems that the combination of that events  would be the most likely explanation for the substantial shift of the C isotope excursion observed at the CPE.

 

References:

Massimo Bernardi et al. Dinosaur diversification linked with the Carnian Pluvial Episode, Nature Communications (2018). DOI: 10.1038/s41467-018-03996-1

Miller et al., Astronomical age constraints and extinction mechanisms of the Late Triassic Carnian crisis, Scientific Reports | 7: 2557 | (2017) DOI:10.1038/s41598-017-02817-7

Rogui et al. Field trip to Permo-Triassic Palaeobotanical and Palynological sites of the Southern Alps, Geo.Alp. 11. 29-84. (2014)

Paul C. Sereno, Ricardo N. Martínez & Oscar A. Alcober (2013) Osteology of Eoraptor lunensis (Dinosauria, Sauropodomorpha),Journal of Vertebrate Paleontology, 32:sup1, 83-179, DOI: 10.1080/02724634.2013.820113

Before Jurassic Park: The study of ancient DNA.

A tick entangled in a dinosaur feather (From Peñalver et al., 2017)

We all know the story. In the early 80’s, John Hammond, a shady entrepreneur, created the ultimate thematic park by cloning dinosaurs from preserved DNA in mosquitoes entombed in amber. The idea, as Michael Crichton acknowledged, was not new.

In 1982, entomologist George Poinar and electron microscopist Roberta Hess at University of California,  found exceptional evidence for the organic preservation of a 40-million-year-old fly in Baltic amber. They saw intact cell organelles, such as nuclei, and mitochondria, and wondered whether these results were replicable. After a letter from Poinar to a colleague, they received, a week later,  a 70–80 million-year-old wasp in Canadian amber. The wasp also revealed evidence of cellular structure. The realization that amber was a special source of cellular preservation caused them to wonder if it could be a source of molecular preservation, too.

Quagga mare at London Zoo, 1870, the only specimen photographed alive

Poinar and Hess joined forces with Allan Wilson, Professor of Biochemistry at Berkeley, and Russell Higuchi, a molecular biologist and postdoctoral researcher in Wilson’s lab. A year later, they embarked on the first experiment to test ideas about the preservation and extraction of DNA from insects in ancient amber. Poinar selected eight specimens that would potentially offer optimal preservation of DNA. In two of the eight insects were signs of DNA, but no hybridization experiments were done to determine whether the results were due to human contamination.

Soon, Wilson and Higuchi turned their attention to the quagga, a subspecies of plains zebra that went extinct in 1883. The study, lead by Russell Higuchi, used two short mitochondrial DNA sequences from the muscle and connective tissue from a 140 year-old quagga from the Natural History Museum in Mainz, Germany, and confirmed that the quagga was more closely related to zebras than to horses.
The survival of DNA in quagga tissue and in an Egyptian mummy created waves among the scientific community, and in the autumn of 1984, Wilson and his lab submitted to the National Science Foundation (NSF), the first official research proposal to search for DNA in ancient and extinct organisms. They wrote: “This is the first proposal to study the possible utility of DNA to paleontology. If clonable DNA is present in many fossil bones and teeth and in insects included in amber, a new field, molecular paleontology, can arise.”

 

Reference:

Jones, E.D., Ancient DNA: a history of the science before Jurassic Park; Studies in History and Philosophy of Biol & Biomed Sci (2018), https://doi.org/10.1016/j.shpsc.2018.02.001

Poinar, G. O., & Hess, R. (1982). Ultrastructure of 40-million-year-old insect tissue.
Science, 215(4537), 1241–1242. DOI: 10.1126/science.215.4537.1241

Higuchi R, Bowman B, Freiberger M, Ryder OA, Wilson AC. DNA sequences from the quagga, an extinct member of the horse family. Nature. 1984;312:282–284. doi: 10.1038/312282a0.

Peñalver, E. et al; Ticks parasitised feathered dinosaurs as revealed by Cretaceous amber assemblages, Nature Communications volume 9, Article number: 472 (2017)
doi:10.1038/s41467-018-02913-w

Introducing Tratayenia rosalesi

A speculative reconstruction of Tratayenia rosalesi. From Porfiri et al., 2018.

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 Fukuiraptor, Aerosteon, Australovenator, Megaraptor, Murusraptor, and Orkoraptor, 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. The enigmatic nature of this group has been a matter of discussion since the description of the first megaraptoran, Megaraptor namunhaiquii in 1990s . 

The phylogenetic position of Megaraptora is still controversial. But despite the lack of consensus, megaraptorans themselves remain a well-supported, monophyletic clade. Now, a new megaraptoran theropod dinosaur from the Upper Cretaceous of the Neuquén Group, sheds light on on these enigmatic predators.

Fossilized vertebrae and right hip bone of Tratayenia rosalesi. From Porfiri et al., 2018.

Tratayenia rosalesi is the first megaraptoran theropod described from the Santonian Bajo de la Carpa Formation of the Neuquén Group. The genus name is for Tratayén, the locality where the holotype was collected. The specific name honors Diego Rosales, who discovered the specimen in 2006.
The holotypic specimen (MUCPv 1162) consists of a well-preserved, mostly articulated series of dorsal and sacral vertebrae, two partial dorsal ribs, the right ilium, pubis and ischium fragments. Tratayenia is the first megaraptoran that unequivocally preserves the complete sequence of sacral vertebrae. The dorsal and sacral centra and neural arches of Tratayenia are unfused, suggesting that the specimen was a subadult at the time of death.

The elevated pneumaticity and morphological resemblance of the axial and pelvic elements of Tratayenia with Aerosteon riocoloradensis and Murusraptor barrosaensis suggests a particularly close relationships between these three taxa. Tratayenia is also the largest carnivorous taxon known from Bajo de la Carpa Formation, reinforcing the hypothesis that megaraptorids were apex predators in South America from the Turonian through the Santonian or early Campanian, following the extinction of carcharodontosaurids.

 

References:

Porfiri, J.D., Juárez Valieri, Rubé.D., Santos, D.D.D., Lamanna, M.C., A new megaraptoran theropod dinosaur from the Upper Cretaceous Bajo de la Carpa Formation of northwestern Patagonia, Cretaceous Research (2018), doi: 10.1016/j.cretres.2018.03.014.

Novas, F.E., 1998. Megaraptor namunhuaiquii gen. et. sp. nov., a large-clawed, Late Cretaceous Theropod from Argentina. Journal of Vertebrate Paleontology 18, 4-9.

Forgotten women of Paleontology: Elizabeth Anderson Gray

Elizabeth Anderson Gray (1831 – 1924) Image: The Trustees of the Natural History Museum, London

The nineteen century was the “golden age” of Geology. The Industrial Revolution ushered a period of canal digging and major quarrying operations. These activities exposed sedimentary strata and fossils, and the study of the Earth became central to the economic and cultural life of  Great Britain. 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”. 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. It was common for male scientists to have women assistants, but most of them went unacknowledged and become lost to history.  However, some women found the way to avoid that fate. One of those women was Elizabeth Anderson Gray.

Born in Alloway, Ayrshire, on February 21, 1831, Elizabeth Anderson Gray  is considered as one of the foremost Scottish fossil collectors of the late 19th and early 20th centuries. She had little formal schooling but as a girl joined her father, Thomas Anderson, in his hobby of fossil collecting. In 1856, she married a Glasgow banker, Robert Gray, co-founder of The Natural History Society of Glasgow. She took a geology course for women at Glasgow University and she trained her children to document their findings too. She was also friend of Jane Longstaff, a British malacologist and expert in fossil gastropods of the Palaeozoic. The Gray collections, considered important in studies of Ordovician fauna, were sold to institutions. In 1920 a major part of the collection was acquired by the British Museum for £2250. Charles Lapworth, in his work on the ‘Girvan Succession’ referred extensively to E. Gray’s collection in his stratigraphical correlations.

In 1900, Elizabeth Gray was made an honorary member of the Geological Society of Glasgow for her many contributions, and in 1903, she was awarded the Murchison geological fund in recognition of her skilful services to geological science. She continued gathering fossils until her death on 1924.

 

References:

BUREK, C. V. & HIGGS, B. (eds) The Role of Women in the History of Geology. Geological Society, London, Special Publications, 281, 1–8. DOI: 10.1144/SP281.1.

M. R. S. Creese (2007), Fossil hunters, a cave explorer and a rock analyst: notes on some early women contributors to geology, Geological Society, London, Special Publications, 281, 39-49. https://doi.org/10.1144/SP281.3

 

An early juvenile enantiornithine specimen from the Early Cretaceous of Spain

The slab and counterslab of MPCM-LH-26189

Mesozoic remains of juvenile birds are rare. To date, the only records are from the Early Cretaceous of China and Spain, from the mid-Cretaceous of  Myanmar, and from the Late Cretaceous of Argentina and Mongolia. The most recent finding from the Early Cretaceous of Las Hoyas, Spain, provide an insight into the osteogenesis of the Enantiornithes, the most abundant clade of Mesozoic birds. Previous records of Enantiornithes from the Las Hoyas fossil site include: Eoalulavis hoyasi, Concornis lacustris, and Iberomesornis romerali.

The latest specimen, MPCM-LH-26189, a nearly complete and largely articulated skeleton (only the feet, most of its hands, and the tip of the tail are missing), is very small. The specimen died around the time of birth, a crucial moment to study the osteogenesis in birds. The skull, is partially crushed, and is large compared to the body size. The braincase is fractured. The frontals and the parietals form a uniformly curved cranial vault. The cerebrocast shows a very slight inflation, suggesting that the cerebral anatomy of MPCM-LH-26189 falls in between that of the Archaeopteryx, and the putative basal ornithurine Cerebavis, whose telencephalic expansion is close to most extant birds. The cervical series is composed of 9 vertebrae. There are 10  thoracic vertebrae, and the sacrum appears to be composed of 5–6 vertebrae. The prezygapophyses of the mid-thoracic vertebrae extend beyond the cranial articular surface. The thoracic ribs are joint to the thoracic vertebrae. The two coracoids, the furcula, and three sternal ossifications are preserved. The furcula is Y-shapped. Both humeri, ulnae, and radii are also preserved.

Reconstruction of MPCM-LH-26189 by Raúl Martín

The osteohistological analysis of the left humerus shows a dense pattern of longitudinal grooves. Those grooves correspond to primary cavities, which open onto the surface of the cortex in young and fast-growing bone. The shaft of the tibia and radius show very-thin cortices. In addition,  the primary nature of the vascularisation, the round shape of the osteocytes lacunae and the uneven peripheral margin of the medullary cavity (with no endosteal bone), strongly suggests that the bone was actively growing when the bird died.

Enantiornithines show a mosaic of characters, reflecting their intermediate phylogenetic position between the basal-pygostylians and modern bird. In this clade, the sternum adopts an elaborate morphology, and in adult Enantiornithes, no more than eight free caudal vertebrae precede the pygostyle. The differences observed in the ossification of the sternum and the number of free caudal vertebrae in MPCM-LH-26189, when it compared to other juvenile enantiornithines, reveal a clade-wide asynchrony in the sequence of ossification of the sternum and tail, suggesting that the developmental strategies of these basal birds may have been more diverse than previously thought.

References:

Fabien Knoll, et al., “A diminutive perinate European Enantiornithes reveals an asynchronous ossification pattern in early birds,” Nature Communications, volume 9, Article number: 937 (2018) doi:10.1038/s41467-018-03295-9

Chiappe, L. M., Ji, S. & Ji, Q. Juvenile birds from the Early Cretaceous of China: implications for enantiornithine ontogeny. Am. Mus. Novit. 3594, 1–46 (2007).