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

Reimagining Amargasaurus

Amargasaurus cazaui. MACN

Dicraeosauridae is a family of mid-sized sauropod dinosaurs characterized by a distinctive vertebral column with paired, long, neural spines. Argentinian dicraeosarids include Amargasaurus cazaui, Pilmatueia faundezi and Bajadasaurus pronuspinax. The group was first described in 1914 by Werner Janensch with the discovery of the nearly complete skeletons of Dicraeosaurus in the expeditions to the upper Jurassic beds of Tendaguru, Tanzania. The discovery of Amargasaurus cazaui in 1991, from the Early Cretaceous beds of La Amarga Formation of Northern Patagonia, renewed the discussion on the peculiar vertebral anatomy of these sauropod dinosaurs.

The hyperelongated hemispinous processes of dicraeosarids were interpreted by some authors as a support structure for a thermoregulatory sail, a padded crest as a display and/or clattering structure, a dorsal hump, or as internal cores of dorsal horn. A new study lead by Ignacio Cerda tested these hypotheses using internal microanatomy and bone microstructure from the holotype of Amargasaurus, and a fragmentary dicreaosaurid specimen (MOZ-Pv 6126-1, consisting of an almost complete anterior dorsal vertebra) also from the La Amarga Formation (Barremian–Aptian, Lower Cretaceous).

Skeletal silhouette of Amargasaurus cazaui. From Cerda et al., 2022.

Despite that the organic components of mineralised tissues decay after death, the inorganic components of bone preserve the spatial orientation of organic components such as osteocyte lacunae, vascular canals, and collagen fibres. Armand de Ricqlès, in the 1960s and 1970s, observed that paleohistological features could be correlated with growth rates and thus could indirectly shed light on the thermal physiology of extinct organisms. Previous paleohistological studies in dicraeosarids revealed particular histological features regarding the vascularization pattern and cortical resorption. 

Bone histology of hyperelongate hemispinous processes of Amargasaurus cazaui. From Cerda et al., 2022

The hemispinous processes from Amargasaurus and MOZ-Pv 6126-1 essentially consist of compact bone tissue. The study lead by Ignacio Cerda also found that secondary remodelling is profuse not only in the perimedullary region but also in the outer cortex. The histological features analized comprise a highly vascularized fibrolamellar bone interrupted with CGMs (cyclical growth marks), presence of obliquely oriented Sharpey’s fibres, and abundant secondary osteons irregularly distributed within the cortex. 

The spatial distribution and orientation of the Sharpey’s fibres indicate the presence of an important system of interspinous ligaments, covered by the integumentary system, which resulted in the formation of a prominent cervical sail in this taxon. However, there is not anatomical or histological evidence that support the presence of a keratinized sheath. The new study also suggests that the cervical sail in Amargasaurus could be used as a display device, a term that includes ‘intraspecific agonistic, deterrent, or sexual display structures’. Unfortunately, the dicraeosaurid record is still too scarce to determine the existence of sexual dimorphism in this clade.

 

References:

Ignacio A. Cerda, Fernando E. Novas, José Luis Carballido, Leonardo Salgado (2022): Osteohistology of the hyperelongate hemispinous processes of Amargasaurus cazaui (Dinosauria: Sauropoda): Implications for soft tissue reconstruction and functional significance. In: Journal of Anatomy. DOI: 10.1111/joa.13659

Windholz, G. J., & Cerda, I. A. (2021). Paleohistology of two dicraeosaurid dinosaurs (Sauropoda; Diplodocoidea) from La Amarga Formation (Barremian–Aptian, Lower Cretaceous), Neuquén Basin, Argentina: Paleobiological implications. Cretaceous Research, 128, 104965. doi: 10.1016/j.cretres.2021.1049

Salgado, L. & Bonaparte, J. F. Un nuevo saurópodo Dicraeosauridae, Amargasaurus cazaui gen et sp. nov., de la Formación La Amarga, Neocomiano de la provincia del Neuquén, Argentina. Ameghiniana 28, 333–346 (1991).

Windholz, G. J., Baiano, M. A., Bellardini, F., & Garrido, A. (2020). New Dicraeosauridae (Sauropoda, Diplodocoidea) remains from the La Amarga Formation (Barremian–Aptian, Lower Cretaceous), Neuquén Basin, Patagonia, Argentina. Cretaceous Research, 104629. doi: 10.1016/j.cretres.2020.10462

 

Testing the aquatic spinosaurid hypothesis

This is the only photographic proof of German researcher Ernst Stromer’s discovery of Spinosaurus. Image from the Washington University in St. Louis

The Spinosauridae is a specialized group of large tetanuran theropods known from the Berriasian to the Cenomanian of Africa, South America, Europe and Asia. The group is characterised by a long, narrow skull, robust forelimbs with a hooked thumb claw, and tall neural spines forming a dorsal sail.  Spinosauridae has been divided in two clades Baryonychinae (including Suchomimus, Baryonyx and Cristatosaur), and Spinosaurinae. Baryonyx walkeri, described by Alan Charig and Angela Milner in 1983, is the oldest unquestionable spinosaurid. The ecology of the group has been debated since the original discovery of Spinosaurus aegyptiacus in 1911. Although Stromer’s original description of Spinosaurus was published in 1915, a more complete detailed picture of its anatomy, evolution, and biogeography only begun to emerge in recent decades with the discovery of a partial skeleton of a subadult individual of S. aegyptiacus in the Cretaceous Kem Kem beds of south-eastern Morocco. At the time of deposition, this part of Morocco was located on the southern margin of the Tethys Ocean and it was characterized by an extensive fluvial plain dominated by northward flowing rivers and terminating in broad deltaic systems on Tethys’ southern shores. The discovery of this new skeleton of Spinosaurus has challenged the paradigma about the restriction of non-avian dinosaurs to terrestrial environments. Previous paleo-histological studies suggested that Spinosauridae had a strong relationship with aquatic environment. Now, a new study published in Nature, indicates that they were aquatic specialists.

Osteohistology variation among the analysed spinosaurid taxa. From Fabbri et al., 2022

Since the works of Nopcsa and Heidsieck in 1934, it has been suggested that the secondary adaptation of tetrapods to an aquatic environment induced modifications of the inner architecture and histological characteristics of bones. Using femora and dorsal ribs to test the correlations between bone density and ecology of these animals, the team lead by Dr. Matteo Fabbri built a dataset of 291extinct and extant amniote species, including mammals, marine reptiles and birds.

Bone density is associated with buoyancy control. Many studies on avian microanatomy had already established a relationship between high bone compactness (i.e., considerable degree of osteosclerosis) and diving behavior. The presence of high bone density in Spinosaurus and Baryonyx supports the hypothesis that spinosaurids were aquatic specialists. Additionally, the highly specialized morphology of the Spinosaurus tail allowed it to function as a propulsive structure for aquatic locomotion. The anterior positioning of the center of mass within the ribcage may have also enhanced balance during aquatic movement. On the other hand, Suchomimus exhibits hollower bones and it was more adapted to a life hunting in shallow water.

References:

Fabbri, M., Navalón, G., Benson, R.B.J. et al. Subaqueous foraging among carnivorous dinosaurs. Nature (2022). https://doi.org/10.1038/s41586-022-04528-0

HONE, D. W. E. and HOLTZ, T. R. (2017), A Century of Spinosaurs – A Review and Revision of the Spinosauridae with Comments on Their Ecology. Acta Geologica Sinica, 91: 1120–1132. doi: 10.1111/1755-6724.13328

Ibrahim, N., Sereno, P. C., Dal Sasso, C., Maganuco, S., Fabbri, M., Martill, D. M., Zouhri, S., Myhrvold, N., Iurino, D. A. (2014). Semiaquatic adaptations in a giant predatory dinosaur. Science, 345(6204), 1613–1616. doi:10.1126/science.1258750 

Aureliano, T., Ghilardi, A.M., Buck, P.V., Fabbri, M., Samathi, A., Delcourt, R., Fernandes, M.A., Sander, M., Semi-aquatic adaptations in a spinosaur from the Lower Cretaceous of Brazil, Cretaceous Research (2018), doi: 10.1016/j.cretres.2018.04.024

First Triassic records of pterosaurs in the southern hemisphere.

Pachagnathus and Yelaphomte. Image credit: Jorge Blanco

Pterosaurs were the first flying vertebrates. 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. By the Mid-Jurassic, pterosaurs had a worldwide distribution, but their known record is markedly biased toward the northern hemisphere. The description of two new specimens from Quebrada del Barro Formation in north-western Argentina are the first unequivocal Triassic records of pterosaurs in the southern hemisphere. Previous to this new work, the only record of a Triassic pterosaur in southern hemisphere was Faxinalipterus minima, from the Caturrita Formation in southern Brazil, although now is considered as a basal Ornithodira.

Pachagnathus benitoi, partial mandibular symphysis in right and left view. From Martinez et al., 2022

Yelaphomte praderioi was a small pterosaur. The holotype (PVSJ:914) is represented by a partial rostrum with the anterior part of both maxillae and palatine, and the posterior portion of both premaxillae. The highly fused bones of the rostrum may indicate its maturity and adult size. The generic name derived from the Allentiac language (spoken by the Huarpe) and means beast of the air, referring to the extreme pneumaticity of the rostrum of the new species and its capacity to flight. The specific name honors Angel Praderio, who discovered the new specimen.

Pachagnathus benitoi was a moderate-sized pterosaur. The holotype (PVSJ:1080) is a partial mandibular symphysis lacking anterior end, preserving one tooth and three alveoli from the the left side, and the roots of three teeth and two alveoli from the right side. The name comes from the words “Pacha” (Earth, in Aymara languaje) and “gnathus” (jaws, in Greek). The specific name honours Benito Leyes, who found the first fossils in Balde de Leyes.

 

References:

Martínez, R.N., Andres, B., Apaldetti, C. and Cerda, I.A. (2022), The dawn of the flying reptiles: first Triassic record in the southern hemisphere. Pap Palaeontol, 8: e1424.https://doi.org/10.1002/spp2.1424

Martínez, R.N., C. Apaldetti, G. Correa, C.E. Colombi, E. Fernández, P. Santi Malnis, A. Praderio, D. Abelín, L.G. Benegas, A. Aguilar-Cameo & O.A. Alcober. 2015. A new Late Triassic vertebrate assemblage from northwestern Argentina. Ameghiniana 52: 379–390.

Eunice Foote, climate change, and the Matilda Effect

Eunice Foote, née Newton (1819–1888), Photo credit: WSKU Public Radio News for Northeast Ohio

The birth of modern science was hostile to women’s participation. The world’s major academies of science were founded in the 17th century: the Royal Society of London (1662), the Paris Académie Royale des Sciences (1666), and the Berlin Akademie der Wissenschaften (1700), but women were not become members until the 20th century. Often, the work of women were invisibilized. In the 18th and 19th centuries women’s access to science was limited, and science was usually a ‘hobby’ for intelligent wealthy women. In 1993, science historian Margaret W. Rossiter coined the term “Matilda effect” to describe the bias against acknowledging the achievements of those women scientists. Some cases illustrating the Matilda effect include those of Agnes Pockels, Eunice Foote, Nettie Stevens, Lise Meitner, Rosalind Franklin, and Jocelyn Bell Burnell.

Eunice Foote’s paper in the American Journal of Science and Arts. Royal Society

Eunice Newton Foote was born on July 17, 1819, in Goshen, Connecticut. She published just two papers, in 1856 and 1857. In her first paper, “Circumstances affecting the heat of the sun’s rays,” she suggested that greater amounts of carbon dioxide (CO2) in the atmosphere would increase Earth’s temperature. That statement was made five years before John Tyndall demonstrated that gases such as methane and carbon dioxide absorbed infrared radiation, and could trap heat within the atmosphere. In a Scientific American article from 1856, which discusses the contribution of women to the advancement of science, it was suggested that Eunice Foote’s experiment, exposing tubes containing different gases to the sun, was designed to test the hypothesis that carbon dioxide concentrations in the atmosphere lead to global warming and can explain warm periods in the geologic past. The article also offers a glimpse of the early nineteenth century understanding of climate change in the geologic past.

Women and men who signed the Declaration of Sentiments at first Woman’s Rights Convention, July 19-20, 1848. From Wikimedia Commons.

Eunice Foote was also part of the women’s-rights movement. She and her husband, Elisha Foote, a judge, inventor, and mathematician, were part of the first woman’s rights convention. Along with Lucretia Mott, Elizabeth Cady Stanton and Frederick Douglas, they signed the Seneca Falls Declaration in 1848. Douglas described the document as the “grand movement for attaining the civil, social, political, and religious rights of women.

Eunice Foote died on 30 September 1888. A summary of her work was published in the 1857 volume of Annual of Scientific Discovery by David A. Wells, who wrote: “Prof. Henry then read a paper by Mrs. Eunice Foote, prefacing it with a few words, to the effect that science was of no country and of no sex. The sphere of woman embraces not only the beautiful and the useful, but the true.”

 

References:

Foote, Eunice, 1856. Circumstances affecting the heat of the Sun’s rays: Art. XXXI, The American Journal of Science and Arts, 2nd Series, v. XXII/no. LXVI, November 1856, p. 382-383.https://ia800802.us.archive.org/4/items/mobot31753002152491/mobot31753002152491.pdf 

Rossiter, M. W. (1993). The Matthew Matilda Effect in Science. Social Studies of Science, 23(2), 325–341. http://www.jstor.org/stable/285482

Jackson, Roland. (2019). Eunice Foote, John Tyndall and a question of priority. Notes and Records: The Royal Society Journal of the History of Science, 0(0), 20180066. https://doi.org/10.1098/rsnr.2018.0066

Ortiz, J. D., & Jackson, R. (2020). Understanding Eunice Foote’s 1856 experiments: heat absorption by atmospheric gases. Notes and Records: The Royal Society Journal of the History of Science. doi:10.1098/rsnr.2020.0031

Scientific Ladies.—Experiments with Condensed Gases. (1856). Scientific American, 12(1), 5–5. http://www.jstor.org/stable/24947406

Introducing Guemesia ochoai

Right lateral view of the braincase of Guemesia ochoai. Scale bar: 5 cm. From Agnolín et al, 2022.

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 theropods exhibit spectacular cranial ornamentation in the form of horns and spikes, and strongly reduced forelimbs. 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 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. The Argentinean record of abelisauroid theropods begins in the Middle Jurassic with Eoabelisaurus mefi, and spans most of the Late Cretaceous. The clade includes Carnotaurus sastrei, Aucasaurus garridoi, Ekrixinatosaurus novasi, Skorpiovenator bustingorryi, Tralkasaurus cuyi, Viavenator exxoni, Niebla antiqua, and Llukalkan aliocranianus. All of them are from the Cretaceous of Patagonia.

Map indicating the locality that yielded Guemesia ochoai. From Agnolín et al, 2022.

Guemesia ochoai is the first definitive abelisaurid theropod from Northwestern Argentina. The holotype (IBIGEO-P 103) is represented by a nearly complete braincase, with parietals, frontals, supraoccipital, basioccipital, exoccipital-opisthotic complex, basisphenoid-parasphenoid, prootics, laterosphenoids, and orbito-sphenoids. It was recovered from Los Blanquitos Formation (Campanian, Late Cretaceous), near Amblayo town, Salta province, Argentina. The name honours General Martin Miguel de Güemes who defended northwestern Argentina during the War of Independence, and Javier Ochoa, technician of the Museo Regional “Florentino Ameghino,” who discovered the specimen. The braincase of Guemesia is small compared to other abelisaurids. Unfortunately, the absence of postcranial elements makes impossible to perform histological analysis and to corroborate if the specimen reached somatic maturity. The cranial endocast has a total length of 73 mm from the base of the olfactory tract to the foramen magnum, and the volume is 47.6 cm3 (almost 70% smaller than the cranial endocasts of Carnotaurus and Viavenator). But the most striking feature of Guemesia is a row of foramina close to the midline of the fused frontals that is unknown in other abelisaurids. These rows may be linked to a zone of thermal exchange.

References:

Federico L. Agnolín et al, First definitive abelisaurid theropod from the Late Cretaceous of Northwestern Argentina, Journal of Vertebrate Paleontology (2022). DOI: 10.1080/02724634.2021.2002348

Meet Dearc sgiathanach

 

Dearc sgiathanach. Scale bars: 30 mm. Adapted from From Jagielska et al., 2022.

Pterosaurs were the first vertebrates to evolve powerful flight. Their reign extended to every continent and achieved high levels of morphologic and taxonomic diversity during the Mesozoic, with more than 200 species recognized so far. During their 149 million year history, the evolution of pterosaurs resulted in a variety of eco-morphological adaptations, as evidenced by differences in skull shape, dentition, neck length, tail length and wing span. The oldest-known pterosaurs appear in the fossil record about 219 million years ago. Most Triassic and Jurassic 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. Pterosaurs have traditionally been divided into two major groups, “rhamphorhynchoids” and “pterodactyloids”. Rhamphorhynchoids are characterized by a long tail, and short neck and metacarpus. Pterodactyloids have a much larger body size range, an elongated neck and metacarpus, and a relatively short tail. Dearc sgiathanach, a newly described rhamphorhynchine pterosaur from the Isle of Skye, Scotland, is the largest known Jurassic pterosaur.

Postcranial skeleton and dentition of Dearc sgiathanach. From Jagielska et al., 2022

Discovered in 2017 by Amelia Penny, the holotype (NMS G.2021.6.1-4), a well preserved, articulated, skeleton, was found at Rubha nam Brathairean (Brothers’ Point), Isle of Skye, in north-west Scotland, in the Lonfearn Member of the Lealt Shale Formation (Bathonian, Middle Jurassic). The specimen is almost complete with the exception of the anterior and dorsal portions of the cranium, the end of the tail, hindlimbs elements, and parts of the wings. The name comes from the Scottish Gaelic language and has a double meaning: “winged reptile” and “reptile from Skye.”

Dearc sgiathanach includes the following autopomorphies: vomers with “trident-shaped” precapillary contact, a pre-choana depression on the palatal surface of the maxilla, and enlarged optic lobes. Bone histology indicates that the specimen belong to a juvenile individual. Based on the proportions of humerus length and skull length of Rhamphorhynchus and Dorygnathus, the research team lead by Natalia Jagielska, estimated the wingspan of Dearc sgiathanach at >2.5 m. Phylogenetic analysys places Dearc sgiathanach within the clade Angustinaripterini. The new specimen suggests that many “pterodactyloid” features convergently evolved in other groups, and hightlights that the Middle Jurassic was a time of increasing diversification in pterosaur history.

References:

JAGIELSKA, Natalia, et al. A skeleton from the Middle Jurassic of Scotland illuminates an earlier origin of large pterosaurs. Current Biology, 2022. DOI: 10.1016/j.cub.2022.01.073

Introducing Abditosaurus kuehnei, the ‘forgotten reptile’ 

Abditosaurus kuehnei. Image credit: Oscar Sanisidro / Museu de la Conca Dellà

Towards the end of the Cretaceous, France, Spain and Portugal formed the Ibero-Armorican Island. This region holds one the most complete sauropod dinosaur communities and provides clues to understand the events that differentiate the Ibero-Armorican vertebrate assemblages from those of other European islands. The recently described Abditosaurus kuehnei from the Late Cretaceous of Catalonia is the most complete titanosaur skeleton discovered in Europe so far. The new taxon support the migration hypothesis and shed new light on the palaeobiogeographic events between the European archipelago and Godwana. 

Abditosaurus reached 17,5 meters in length (57 ft) with a body mass of 14,000 kg. The holotype, an associated, semi-articulated, partial skeleton, includes several isolated teeth, 12 cervical vertebrae, 7 dorsal vertebrae, 3 chevrons, scapular and pelvic bones, right tibia, parts of the femurs and a complete humerus. The new specimen exhibits an unusual combination of characters not seen in other Ibero–Armorican titanosaurs, like a very robust humerus with a distally expanded deltopectoral crest, a synapomorphy of Saltasauridae. The generic name is derived from the Latin word ‘Abditus’ (means forgotten), and the Greek word “sauros” (lizard). The specific name ‘kuehnei’ honours Professor Walter Georg Kühne who discovered the specimen.

Fossil elements of Abditosaurus kuehnei collected during the 2012-2014 excavations. Image credit: Rubén Contreras. From Vila et al., 2022.

Phylogenetic analyses indicates that Abditosaurus is a saltasaurid lithostrotian titanosaur. Saltasaurinae, a clade from South America and Africa, includes Neuquensaurus, Saltasaurus and Paralititan. The arrival of Abditosaurus to Europe via a dispersal event from Africa ocurred after a regressive event during the Early Maastrichtian(70.6 Ma) that affected the central Tethyan margin and northern Africa.

The history of Abditosaurus began in 1954. Walter Kühne, one of the most renowned specialists on fossil mammals in Europe, found the bones near Orcau (Tremp Basin, Catalonia, Spain), and sent to the Instituto Lucas Mallada in Madrid. In 1955, Kühne revisited the site and collected ten more bones. Unfortunately, the site fall out in oblivion until 1986. when a team led by Josep Vicenç Santafé from the Institut de Paleontologia de Sabadell (Barcelona) found part of a sternal plate and three dorsal ribs. Between 2012 to 2014, a team from the Institut Català de Paleontologia, the Universidad de Zaragoza, and the Museu de la Conca Dellà re-excavated the locality and recovered the remaining axial and appendicular elements. Finally, after 6 decades, the sauropod discovered by Kühne was completely collected in 2014.

References:

Vila, B., Sellés, A.G., Moreno-Azanza, M., Razzolini, N.L., Gil-Delgado, A., Canudo, J.I., Galobart, À. Nature Ecology & Evolution (2022). DOI: 10.1038/s41559-021-01651-5.

Fondevilla, Victor, et al. Chronostratigraphic synthesis of the latest Cretaceous dinosaur turnover in south-western Europe. Earth-Science Reviews (2019) https://doi.org/10.1016/j.earscirev.2019.01.007