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

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.