Halloween Special X: The legend of a Patagonian Monster

Primo Capri and his Plesiosaur. Photo: Rafael Soriani, 1922

On December 10, 1823, Mary Anning discovered the first complete Plesiosaur skeleton at Lyme Regis in Dorset. Noticed about the oddity of the specimen, George Cuvier wrote to William Conybeare suggesting that the find was a fake produced by combining fossil bones from different animals. But despite their unusual body plan Plesiosaurs were a highly successful group of Mesozoic marine reptiles. Their four limbs are enlarged and modified as propulsive flippers, the trunk is short and stiff, and proportional head size seems to vary inversely with neck length.

The idea of surviving plesiosaurs was popularize in the works of Jules Verne and Sir Arthur Conan Doyle. “The Monster of Lake LaMetrie” (1899), a short story by Wardon Allan Curtis, features an encounter between a scientist and a plesiosaur that has been cast up from the hollow center of Earth.  The modern emergence of the Loch Ness monster in the 1930s was deeply influenced by these stories and films like The Lost World (1925) and King Kong (1933).  Even now, the discovery of fossil remains of plesiosaurs from the freshwater fluvial deposits of the mid-Cretaceous Kem Kem Group of Morocco sparked some sensationalist headlines about the Loch Ness Monster. But a decade before the media frenzy around Nessie, there was an argentinian expedition to hunt a living plesiosaur.

Clemente Onelli (courtesy of Archivo General de la Nación, Argentina). From Brinkman and Vizcaíno, 2014

Clemente Onelli (courtesy of Archivo General de la Nación, Argentina). From Brinkman and Vizcaíno, 2014

It all began in January, 1922, when Martin Sheffield, a flamboyant American hunter and gold prospector living in Patagonia, wrote a letter to Buenos Aires Zoo Director, Clemente Onelli. In the letter, Sheffield claimed that he saw a very strange creature in a lake near Esquel, a small Patagonian town in the foothills of the Andes: “I have been able to see, in the middle of the lake, an enormous animal with a head like a swan and enormous size and the movement in the water makes me suppose a crocodile body.

Sheffield’s account and similar reports from Laguna Epuyén led Onelli to think that the mysterious creature could be a plesiosaur. He organized an expedition to capture the beast alive and bring it back to the zoo in Buenos Aires. Onelli also invited Elmer S. Rigg, an associate curator of palaeontology at the Field Museum of Natural History in Chicago. Riggs, like most of the scientific community utterly discredited that a plesiosaurus was still alived. However, some people took it seriously. That was the case of Dr. Albarracin, President of the Society for the Protection of Animals. He demanded that the Minister for the Interior stop the expedition, under the law 2786, which prohibits the hunting of rare animals.

A report from the Plesiosaur expedition. Scientific American 127: 2

Despite the fail of the expedition, the fever around the plesiosaur did not stop. Primo Capraro, a businessman from Bariloche, used a float with the figure of a plesiosaur making it parade through the streets of the town. Rafael D’Agostino (music) and Amílcar Morbidelli (lyrics) wrote a tango about the creature. And one hundred years later the stories around the monster continued. The last reported sighting was on August, 2020.

 

References:

Brinkman, Paul & Vizcaíno, Sergio. (2014). Clemente Onelli’s sketch map and his first-hand, retrospective account of an early fossil-hunting expedition along the Río Santa Cruz, southern Patagonia, 1888–1889. Archives of natural history. 41. 326-337. 10.3366/anh.2014.0251.

MATTERS, L., (1922). An antediluvian monster: Is the Argentine Plesiosaurus a fake or a scientific marvel?? Scientific American 127: 2

The enigmatic Scleromochlus and the origin of pterosaurs.

Life reconstruction of Scleromochlus taylori. Image credit: Gabriel Ugueto

Pterosaurs were the first flying vertebrates, and their reign extended to every continent and achieved high levels of morphologic and taxonomic diversity during the Mesozoic. The oldest-known pterosaurs appear in the fossil record about 219 million years ago. Most Triassic pterosaurs are small but already had a highly specialized body plan linked to their ability to fly: shoulder girdle with strongly posteroventrally enlarged coracoid braced with the sternum and laterally facing glenoid fossa; forelimb with pteroid bone and hypertrophied fourth digit supporting a membranous wing; and pelvic girdle with prepubic bone and strongly developed preacetabular process.

Due to the fragile nature of their skeletons and the absence of fossils with transitional morphologies, the origin of pterosaurs is one of the most elusive questions in vertebrate paleontology. In 2020, a study led by Martin Ezcurra demonstrated a close relationship between Lagerpetidae and Pterosauria, and found Scleromochlus as the earliest-diverging pterosauromorph. The recognition of lagerpetids as the sister taxon to pterosaurs provides clues to study the origin of Pterosauria, its specialized body plan and flying abilities.

The newly anatomical features of Scleromochlus taylori. From Foffa et al., 2020.

Scleromochlus taylori, from the early Late Triassic of Scotland, is a tiny reptile with extremely long hindlimbs known from seven largely articulated skeletons on small slabs. It was discovery in 1907 by Arthur Smith Woodward who identified Scleromochlus as a small bipedal running or leaping dinosaur. As early as 1914, Huene interpreted Scleromochlus as an arboreal climbing and leaping pseudosuchian close to the origin of pterosaurs.  A new study led by Dr Davide Foffa support the hypothesis that the first flying reptiles evolved from small, potentially bipedal, cursorial ancestors.

Using microcomputed tomographic techniques, the team led by Dr Davide Foffa, provides new key information of Scleromochlus anatomy. The skull length of Scleromochlus is ~50% of the presacral vertebral column length, as in early pterosaurs; the maxilla has an anterior process that tapers to a point and has a weakly concave anterior margin; the occipital neck is extremely short; the pubis is less than 50% the length of the femur; the femoral head is ‘hook-shaped‘; and the length of metatarsal V is less than half length of metatarsal III.

 

References:

Foffa, D., Dunne, E.M., Nesbitt, S.J. et al. Scleromochlus and the early evolution of Pterosauromorpha. Nature (2022). https://doi.org/10.1038/s41586-022-05284-x

Ezcurra, M.D., Nesbitt, S.J., Bronzati, M. et al. Enigmatic dinosaur precursors bridge the gap to the origin of Pterosauria. Nature (2020). https://doi.org/10.1038/s41586-020-3011-4

Bennett SC.  Reassessment of the Triassic archosauriform Scleromochlus taylori: neither runner nor biped, but hopperPeerJ 8:e8418 (2020) https://doi.org/10.7717/peerj.8418

An 80-million-year-old fossilized braincase from an enantiornithine bird

MPM-334-1 is a diminutive basicranium of a skeletally mature enantiornithine bird. From Chiappe et al., 2022.

Birds are extraordinarily intelligent and they can rival mammals in terms of relative brain size and behavioural complexity. The clade 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. Recent studies have shown that corvids and some parrots are capable of cognitive achievement comparable to those of great apes. They manufacture and use tools, solve puzzles, and plan for future needs. Futhermore, they share with humans and a few other animal groups a rare capacity for vocal learning.

Over the last decades, several discovered fossils of theropods and early birds have enriched our knowledge of the evolution of the avian skull. Now, the discovery of an exceptionally well preserved braincase from an Upper Cretaceous (~80 Ma) enantiornithine bonebed in southeastern Brazil shed light on the early evolution of the avian braincase, brain and inner ear.

Enantiornithine braincase MPM-334-1 from the Late Cretaceous of southeastern Brazil; (a) Ventral view, (b) dorsal view. From Chiappe et al., 2022

Enantiornithes are the most diverse group of Mesozoic birds. The clade shows a mosaic of characters, reflecting their intermediate phylogenetic position between the basal-pygostylians and modern bird, and their remains, ranging from the size of hummingbirds to turkeys, have been collected on every continent except Antarctica. MPM-334-1 (Museu de Paleontologia de Marília, São Paulo State) is a diminutive basicranium of a skeletally mature enantiornithine bird. The endocast comprises impressions from the external surfaces of most of the medulla, parts of the cerebellum, and the ventral portion of the optic tectum.

MPM-334-1 displays a mosaic combination of plesiomorphic dinosaurian traits and a set of endocranial transformations: a flexed brain that are remarkably similar to those of extant birds, a ventralized foramen magnum and ‘crown-like’ endosseous labyrinth. The new study lead by Luis Chiappe, suggest a more complex scenario for the evolution of the avian skull and central nervous system than had previously been understood, with key features of the modern avian endocranium evolving much earlier than what was formerly thought. 

 

References:

Chiappe LM, Navalón G,Martinelli AG, Nava W, Field DJ. 2022 Fossil basicranium clarifies the origin of theavian central nervous system and inner ear. Proc. R. Soc. B289: 20221398. https://doi.org/10.1098/rspb.2022.1398

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).

Introducing Elemgasem nubilus

Elemgasem nubilus. Image credit: Abel Germán Montes

Abelisauroidea is the best known carnivorous dinosaur group from Gondwana. The clade was erected by the legendary paleontologist Jose Bonaparte with the description of Abelisaurus Comahuensis. These ceratosaurian theropods 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. 

The Cretaceous beds of Patagonia holds an extraordinary record of abelisaurids, although there is a paucity during the whole Coniacian.  This lack of specimens during this interval is a worldwide phenomenon. Thus, the Late Cretaceous record of abelisaurids is represented by two intervals: the Cenomanian–Turonian, with taxa from Argentina, Africa and Madagascar, and the Santonian–Maastrichtian, with taxa from Argentina, Brazil, Africa, Madagascar and India. Elemgasem nubilus, from the Portezuelo Formation of Argentina, is the first abelisaurid from the Turonian–Coniacian interval. The new specimen increases the diversity of this clade at a time of significant turnover in the tetrapod fauna of South America, marked by global climate change, and mass extinction events recorded worldwide in the marine realm.

Femur histology of Elemgasem nubilus. From Baiano et al., 2022.

The holotype (MCF-PVPH-380), discovered in 2002, includes several axial and appendicular elements, and exhibits the following features: a marked rugosity on the lateral surface of the fibula, a high lateral surface and a high proximolateral wall of the calcaneum, as well as posterior caudal centra with oval articular surfaces and a groove on the ventral surface. Osteohistological analysis of the femur and phalanx III-2 indicates that this new specimen was at least 8 year old and had achieved sexual maturity but was still growing.

Elemgasem measured about 4 meters (13 feet) long. The genus name refers to the Tehuelche god Elemgasem, the ‘owner’ of the animals and founder of the northern Tehuelche people. The specific name nubilus comes from the Latin ‘foggy days’ in reference to the climatic conditions during the palaeontological expedition when this specimen was discovered.

Location map and geological strata from which the specimen Elemgasem nubilus MCF-PVPH-380 holotype was recovered. From Baiano et al., 2022.

In the Late Cretaceous Abelisauridae splits in the clade Majungasaurinae and and the clade Brachyrostra. Post-Coniacian brachyrostrans constitute a natural group, Furileusauria. Phylogenetic analysis recovered Elemgasem as an unstable taxon, occupying all possible positions within Furileusauria, or as a sister taxon of this clade. 

Elemgasem nubilus lived about 90 million years ago in one of the most phylogenetically diverse fauna from the middle Late Cretaceous of South America, which includes crocodiles, pterosaurs, ornithopods, and four distinct lineages of tetanuran theropods, such as Megaraptor, the alvarezsaurid Patagonykus, the dromaeosaurids Neuquenraptor, Pamparaptor and Unenlagia, and an indeterminate neornithine. 

 

 

References:

Mattia A. Baiano, Diego Pol, Flavio Bellardini, Guillermo J. Windholz, Ignacio A. Cerda, Alberto C. Garrido & Rodolfo A. Coria Elemgasem nubilus: a new brachyrostran abelisaurid (Theropoda, Ceratosauria) from the Portezuelo Formation (Upper Cretaceous) of Patagonia, Argentina (2022). https://doi.org/10.1002/spp2.1462 

Jakapil kaniukura, the shield bearer

Jakapil kaniukura. Image credit: Pepe Mateos/Agencia Telam

The Late Cretaceous of Argentina is represented by a high diversity and abundance of Theropoda and Sauropoda, while ornithischian remains are scarce and are mainly represented by hadrosaurids. Thyreophora is a clade of ornithischian dinosaurs that includes stegosaurs, ankylosaurs and basal forms as Emausaurus ernsti, Scutellosaurus lawleri, and Scelidosaurus harrisonii. The group is characterized by the presence of a postcranial dermal armour extending from the neck to the tip of the tail. Their fossil record is mainly known from the northern hemisphere, and its presence in the Gondwanan continents remains poorly known with some skeletal remains and tracks in South America, Africa, Madagascar, Australia, New Zealand and Antarctica. Basal thyreophorans could be bipedal or combine bipedal and quadrupedal locomotion, while stegosaurs and ankylosaurs were obligate quadrupeds.

Jakapil kaniukura is the first definitive thyreophoran species from Argentina. The first remains were found in 2014, in the upper beds of the Candeleros Formation at the ‘Rinconada de la Piedra Blanca’ in Rio Negro Province, Argentina. The genus name Jakapil (Ja-Kapïl: shield bearer), comes from the ‘gananah iahish’, Puelchean or northern Tehuelchean language. The specific epithet, comprising kaniu (crest) and kura (stone), comes from the Mapudungun language and refers to the diagnostic ventral crest of the mandible.

 

Holotype of Jakapil kaniukura. From Riguetti et al., 2022.

The holotype (MPCA-PV-630), with an estimated living mass of 4-7kg (9-15lb), is a partial skeleton of a subadult individual that includes fragmentary cranial bones, a nearly complete left lower jaw, partial vertebral elements, a complete dorsal rib, a partial coracoid, a nearly complete left scapula, a partial right scapula, two partial humeri, a possible partial right ulna, and more than forty osteoderms.

The skull of Jakapil is incomplete. The premaxilla, maxilla and mandible reveal a short skull in comparison with most non-ankylosaurid thyreophorans. The mandible resembles that of heterodontosaurids and basal ceratopsians. The basipterygoid processes are not close to the midline. The ventral process is small and carries a foramen. The predentary is pyramidal-shaped with a rounded apex, and two large and rounded lateral processes. The most striking feature is the presence of a ventral crest of the mandible. The axial elements are similar to those of Scelidosaurus. The humeri are strongly reduced in size. The femoral fragments also resemble those of basal ornithischians. Despite the incompleteness of the material, the overall limb dimensions and estimations suggest a bipedal stance in Jakapil.

 

References:

Facundo J. Riguetti, Sebastián Apesteguía & Xabier Pereda-Suberbiola (2022) A new Cretaceous thyreophoran from Patagonia supports a South American lineage of armoured dinosaurs. https://doi.org/10.1038/s41598-022-15535-6

Introducing Meraxes gigas

Meraxes gigas. Image credit: J. Gonzalez

The Cretaceous beds of Patagonia have yielded the most comprehensive record of Cretaceous non-avian theropods from Southern Hemisphere, which includes at least five main theropod lineages: Abelisauroidea, Carcharodontosauridae, Megaraptora, Alvarezsauridae, and Unenlagiidae. These record facilitates the understanding of the origin, evolution, and radiation of theropods from Gondwana. The first remains of dinosaurs were found near Neuquen city by an officer army in 1882 and were sent to Florentino Ameghino, the “founder father” of Argentinian paleontology.

Carcharodontosauridae includes the largest land predators in the early and middle Cretaceous of Gondwana, like the popular, Giganotosaurus carolinii. Members of this theropod family were first recorded in Cenomanian beds of Africa. The group possess widely fenestrated skulls, and in some cases with heavily sculptured facial bones. Another common trait is the fusion of cranial bones. Meraxes gigas, a new specimen from the Upper Cretaceous of northern Patagonia, Argentina, is the most complete carcharodontosaurid ever found and provides new information about the skull length in Giganotosaurus.

Reconstruction of the skeleton of Meraxes. From Canale et al., 2022

The holotype (MMCh-PV 65) is represented by a nearly complete skull without mandibles, pectoral and pelvic girdles, fore- and hindlimbs, fragments of cervical and dorsal vertebrae, complete sacrum, and proximal and middle caudal vertebral series. The first remains were discovered in 2012 in the Upper Cretaceous Huincul Formation of northern Patagonia, Argentina. The new specimen weighed more than 4 tons and measured up to 11 meters (36 feet) long. Histological analysis indicates that this dinosaur was an adult of 45-53 years of age at death.

The name comes from Meraxes, a dragon of the Song of Ice and Fire saga (by George R.R. Martin), with golden eyes and silver scales, named for a god of the Valyrian Freehold. The specific name “gigas” (gigant in Greek) makes reference to the size of the species.

Skull of Meraxes. Image credit: Fundación Azara

The skull of Meraxes is profusely ornamented and has a total length of 127 cm. This is the most complete cranium of any Carcharodontosaurinae. Applying scaling equations and measurements taken from Meraxes, the team lead by Dr. Juan Canale from the Museo Paleontológico Ernesto Bachmann, has estimated the size of the Giganotosaurus skull. The results indicate a length of 163 cm, one of the biggest theropod skulls ever found.

Meraxes also preserves near-complete forelimbs which are about half the length of the femur, a feature comparable to late tyrannosaurids and abelisaurids. This reveals a trend towards forelimb reduction in megapredatory theropod. Quantitative analyses suggest that this evolutionary convergence is especially pronounced between forelimb ratios of Meraxes and the tyrannosauroid Tarbosaurus.

References:

Canale, J.I. et al., New giant carnivorous dinosaur reveals convergent evolutionary trends in theropod arm reduction. Current Biology (2022). doi:10.1016/j.cub.2022.05.057

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

Forgotten women of Paleontology: Ava C. Ellisor

 

Alva C. Ellisor at her laboratory in 1946

At the beginning of 20th century, many universities started admitting women, with different motivations, including the lack of men following WWI and the Soviet Revolution. The oil and gas industry, long stereotyped as a male profession, also openned to women. In 1919, E. T. Dumble, vice-president and general manager of the Rio Bravo Oil Company, called the geology department at the University of California at Berkeley and asked Professor Bruce Clark for the name of his best man in paleontology. Clark said, “I haven’t a man, would a woman do?”. A year later, Dumble hired Esther Applin (née Richards). Almost at the same time, Wallace Prat, hired Alva Ellisor to build a paleontology department for Humble Oil Company. In 1921, Raymond Baker, from The Texas Company, hired Hedwig Kniker. As part of the consortium agreement between these companies, Richards, Ellisor and Kniker started working on macropaleontologic solutions to solve the Gulf Coast stratigraphy. Dumble believed that macrofossils were the key to understand the chaotic Tertiary stratigraphy of the Gulf Coast. But macrofossils were too badly broken to be identifiable as to species, so Ellisor and Richards turned their attention to the microfossils, especially foraminifera. It was the beggining of the micropaleontological revolution.

Hedwig Kniker, Esther Applin and Alva Ellisor. From Wikipedia

Alva Christine Ellisor was one of the first female stratigrapher in U.S. She was born on April 26, 1892, in Galveston, Texas. In 1915, she received her Bachelor of Arts Degree in Geology from The University of Texas. After graduating, she taught science at Ball High School in Galveston. In 1918 Ellisor began working as a professor at the University of Texas. A year later, she worked as a geologist for the Kansas Geological Survey. In 1920 she began to work for Humble Oil & Refining Company, until her retirement in 1947.

Hedwig Kniker, Esther Richards and Alva Ellisor. From Gries, 2020

In 1924, at a meeting of the American Association of Petroleum Geologists (AAPG), Alva Ellisor, Esther Applin née Richards, and Hedwig Kniker presented their seminal paper: Subsurface stratigraphy o f the Coastal Plain of Texas and Louisiana. Since then, Micropaleontology was quickly embraced by industry. However, the role of these women was downplayed over time, and by 1975 the credit for this technology was shifted to four men.

From left to right: Esther Richards, John Suman, James L. Ballard, Alva Ellisor at Hidalgo Bluff near the Brazos River Botton. (From R.R.Gries. 2018)

Ellisor was one of the founders of the Houston Geological Society in 1923. She was also one of the founding member of the Society of Economic Paleontology and Mineralogy (SEPM) in 1927, along with Richards and Kniker. In 1929 she was elected a Fellow of the Geological Society of America. In 1962, she received the Distinguished Alumni Award from the Geology Department of The University of Texas at Austin. Thomas Barrow, senior vice president at Exxon Corporation, remarked her contributions to the field: “Miss Ellisor not only had to prove to her company, but also to convince the rest of the geologic profession that micropaleontology was important”.

She died on September 22, 1964 in Galveston, Texas.

References:

Richards Applin, Esther; Ellisor, Alva E.; Kniker, Hedwig T. (1925). “Subsurface Stratigraphy of the Coastal Plain of Texas and Louisiana”. American Association of Petroleum Geologists Bulletin. 9 (1): 79–122.

Gries, Robbie Rice (2018). “How female geologists were written out of history: The micropaleontology breakthrough”. Women and Geology: Who Are We, Where Have We Come from, and Where Are We Going?. doi:10.1130/2018.1214(02).

Gries, R. R. (2020). Buried Discoveries of Early Female Petroleum Geologists. Geological Society, London, Special Publications, SP506–2019–216. doi:10.1144/sp506-2019-216 

The ‘ghost’ fossils of the future past

Fossil Coccolithophores. Image Credit: S.M. Slater, P. Bown et al / Science journal

Calcareous nannoplankton represent a major component of oceanic phytoplankton, ranging in size from 0.25 to 30 μm. The first records are from the Late Triassic. 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. This heterogeneous group includes coccoliths, discoasters and nannoconids. They are crucial elements for our understanding of past and present oceans. Their skeletons take up chemical signals from the sea water, in particular isotopes of oxygen and carbon.  In the Jurassic and Cretaceous oceans, the calcareous nannoplankton was the most efficient rock-forming group, for that reason the characterization of calcareous nannofloras in OAE (Oceanic Anoxic Events) intervals are used to improve our understanding of the marine ecosystem and biological processes such as photosynthesis (biological pump) and biomineralisation (carbonate pump) that affect the organic and inorganic carbon cycle, as well as adsorption of atmospheric CO2 in the oceans (Erba, 2013). 

Schematic representation of a generic coccolithophore cell. From Flores & Sierro, 2013.

Coccolithophores are unicellular marine golden-brown algae differing from other Chrysophyta in having two flagella and a third flagella-like appendage called a haptonema. They also posses calcified scales, called coccoliths, at some stage in their life as a protective armour that eventually falls to the ocean floor to build deep-sea ooze and fossil chalks. Declines in the abundance of nannofossils through several past global warming events were linked to biocalcification crises caused by climate change and ocean acidification. Now, a new study presents a global record of ‘ghost’ nannofossils that reveals that  nannoplankton were more resilient to past warming events than traditional fossil evidence would suggest.

Scanning electron microscope images of calcareous nannofossil imprints preserved on the surface of organic matter; Toarcian (including T-OAE interval), Yorkshire, UK. From Slater et al., 2022

The new study focused on the Toarcian Oceanic Anoxic Event (T-OAE ∼183 mya) considered as one of the most severe of the Mesozoic era. This event is associated with a major negative carbon isotope excursion, mass extinction, marine transgression and global warming caused by massive volcanism in the Southern Hemisphere. Previous studies had indicated that during the peak of this event calcareous nannofossils collapsed due to ocean acidification. But the new research have found that these fossils had been overlooked due to their tiny size and their mode of preservation.

Ghost nannofossils  in rocks from the T-OAE, OAE1a and OAE2. Credit: S.M. Slater et al., 2022

After their death, nannofossils were buried in soft sediment at the bottom of the sea, while their imprints were preserved in the surfaces of other organic matter, such as pollen or spores. These imprints—or “ghost”—nannofossils were found in sediments through the TOAE in the UK, Germany, Japan and New Zealand, but also from two similar global warming events in the Cretaceous: the early Aptian Oceanic Anoxic Event (OAE1a, 120 Ma) from Sweden, and the Oceanic Anoxic Event 2 (OAE2, 94 Ma) from Italy. These findings provide new tools to understand how the calcareous nannoplankton respond to warming events.

 

References:

S. M. Slater, P. Bown, R. J. Twitchett, S. Danise, V. Vajda, Global record of ‘ghost’ nannofossils reveals plankton resilience to high-CO2 and warming, Science (2022). www.science.org/doi/10.1126/science.abm7330

Elisabetta Erba, Calcareous nannofossils and Mesozoic oceanic anoxic events, Marine Micropaleontology 52 (2004) 85 – 106 https://doi.org/10.1016/j.marmicro.2004.04.007

Doney, D. S. Busch, S. R. Cooley, K. J. Kroeker, The impacts of ocean acidification on
marine ecosystems and reliant Human communities. Annu. Rev. Environ. Resour. 45, 83
112 (2020).
doi:10.1146/annurevenviron012320083019

J.-A. Flores, F.J. Sierro, Flores, PALEOCEANOGRAPHY, BIOLOGICAL PROXIES| Coccolithophores. (2013): 783-794, https://www.sciencedirect.com/science/article/pii/B9780444536433002818

 

Maip macrothorax, the shadow of the death

Maip macrothorax. Image credit: Agustín Ozán

Patagonia has yielded the most comprehensive fossil record of Cretaceous theropods from Gondwana, including Megaraptora, a clade of medium-sized and highly pneumatized theropods characterized by their elongate skulls, and the formidable development of their manual claws on digits I and II. The enigmatic nature of this group has been a matter of discussion since the description of Megaraptor namunhaiquii in 1990s . Other representatives of the clade are Aoniraptor libertatem, Aerosteon riocoloradensis, Australovenator wintonensis, Murusraptor barrosaensis, Tratayenia rosalesi and Orkoraptor burkei. The phylogenetic position of Megaraptora is still controversial. But despite the lack of consensus, megaraptorans themselves remain a well-supported clade. Now, a new megaraptoran theropod dinosaur from the Upper Cretaceous of the Santa Cruz Province, Argentina, sheds light on on these enigmatic predators and their evolutionary radiation.

Maip macrothorax is a large-bodied megaraptorid from lower Maastrichtian Chorrillo Formation in Santa Cruz Province, Argentina. The holotype (MPM 21,545) includes the axis (only lacking both prezygapophyses and its right postzygapophysis), several dorsal and caudal vertebrae, three incomplete cervical ribs, numerous incomplete or fragmentary dorsal ribs, numerous gastral elements, left coracoid, distal end of a second metatarsal, and fragments of the scapula. The generic name, Maip, is derived from an evil entity in Aonikenk mythology that represents “the shadow of the death”. The specific name, macro, derives from the Greek word makrós (meaning long), and the Latin word thorax (meaning chest) in reference to its wide thoracic cavity (which has, approximately, more than 1.20 m width).

Axis of Maip in lateral (A, A´), anterior (B, B´), posterior (C, C´), dorsal (D, D´) and ventral (E, E´). Scale bar: 5 cm. From Aranciaga et al., 2022

The new specimen was discovered in 2019, but due the outbreak of the COVID-19 pandemic in early 2020 the dig was temporarily interrupted. The most striking feature of Maip is its large size. Maip macrothorax was between nine and 10 meters (30-33 feet) and weight about 5 tons. Several vertebrae and ribs of Maip show striations or rugosities interpreted as the attachment sites for the costovertebral and costotransversarium ligaments, a condition not commonly observed in other theropods.

The new study, lead by Aranciaga Rolando, recovered two new clades comprising some derived megaraptorids from South America. The first one, Clade A, comprises Megaraptor, Murusraptor, most of the Cenomanian–Turonian Patagonian forms with 6 or 7 m in length. The second one, Clade B, includes Orkoraptor, Tratayenia, Aerosteon and Maip, most of the Santonian through Maastrichtian megaraptorids from South America, with 8 or 10 m in length. This clade is supported by two synapomorphies: dorsal vertebrae with a bifurcated lamina anterior to the transverse process and forming an accessory fossa, and round and large articular facets of pre- and postzygapophyses of proximal caudal vertebrae. Additionally, the work suggests that after the Turonian, megaraptorids showed an increase in the body size and (with other theropod groups) replaced carcharodontosaurids in the role of apex predators within the Southern continents in the course of the Late Cretaceous.

 

References:

Aranciaga Rolando, A.M., Motta, M.J., Agnolín, F.L. et al. A large Megaraptoridae (Theropoda: Coelurosauria) from Upper Cretaceous (Maastrichtian) of Patagonia, Argentina. Sci Rep 12, 6318 (2022). https://doi.org/10.1038/s41598-022-09272-z

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

Pterosaurs and the origin of feathers

Reconstructed T. imperator skeleton, National Museum of Brazil. From Wikimedia Commons

Feathers were once considered to be unique avialan structures linked to birds evolutionary success. Primitive theropods, such as Sinosauropteryx and the tyrannosaurs Dilong and Yutyrannus, and some plant-eating ornithischian dinosaurs, such as Tianyulong, and Kulindadromeus are known from their spectacularly preserved fossils covered in simple, hair-like filaments called ‘protofeathers’. Other integumentary filaments, termed pycnofibres, has been reported in several pterosaur specimens. The discovery of integumentary structures in other pterosaurs, such as Pterorhynchus wellnhoferi (a rhamphorhynchoid pterosaur), and other exquisitely preserved specimens from China, suggest that all Avemetatarsalia (the wide clade that includes dinosaurs, pterosaurs and close relatives) were ancestrally feathered.

A new specimen of an adult Tupandactylus imperator, a tapejarid pterosaur from north-eastern Brazil, preserves extensive soft tissues which provides more evidence that pterosaurs had feathers. The fossil, originally poached from an undetermined outcrop of the Early Cretaceous Crato Formation, was in privated hands for an unknown period of time and later deposited at the Royal Belgian Institute of Natural Sciences (RBINS). The fossil was repatriated to Brazil early this year.

Details of the cranial crest of MCT.R.1884 and the scanning electron microscope images of melanosomes (g-i). Scale bars, 50 mm (a); 5 mm (b); 2 mm (c); 250 μm (d–f); 2 μm (g–i). From Cincotta et al., 2022.

The new specimen (MCT.R.1884) comprises the posterior portion of the cranium and the remains of a soft tissue cranial crest preserved on five separate slabs. Two types of fibrous integumentary structures were present. The monofilaments (approximately 30 mm long and 60–90 μm wide) resemble those present in the anurognathid Jeholopterus ningchengensis and the ornithischian dinosaur Tianyulong. The most striking feature is the presence of fossil melanosomes with diverse morphologies that supports the hypothesis that the branched integumentary structures in pterosaurs are feathers.

Melanosomes are granules of the pigment melanin. The diverse shape of the melanosomes recovered from the skin fibres in the crest, monofilaments and branched feathers resembles that in the skin of extant birds and mammals. This is an indication that pterosaurs had the genetic machinery to control the colors of their feathers.

References:

Cincotta, A., Nicolaï, M., Campos, H.B.N. et al. Pterosaur melanosomes support signalling functions for early feathers. Nature (2022). https://doi.org/10.1038/s41586-022-04622-3