Introducing Notatesseraeraptor frickensis.

Notatesseraeraptor frickensis at the Sauriermuseum Frick. (From Wikimedia Commons)

Over the last two decades our knowledge of the fossil record of early theropod dinosaurs has greatly improved. However, there are different hypotheses about their relationships. Theropods are relatively abundant in post-Carnian Triassic faunas, including the European Liliensternus, the South American Zupaysaurus, and the North American Coelophysis. Those taxons represent the earliest major radiation of Neotheropoda. Two primitive branches of this clade are the Coelophysoidea and the Dilophosauridae. More recent studies suggest that at least some members of the ‘traditional Coelophsoidea’ are more closely related to the tetanurans and that the Dilophosauridae may represent a second clade of early non-averostran neotheropods. Notatesseraeraptor frickensis gen. et sp, from the Late Triassic of Switzerland, provides new clues about the relationships of the early theropods.

The new specimen belong to an immature individual of length 2.6–3.0 m, and it was collected in 2006 from Gruhalde clay pit in Frick (Aargau, Switzerland), a place well known for its abundant, articulated Plateosaurus material. The genus name derives from the Latin “nota” meaning feature and “tesserae”, a word used to describe glass, or other material used in the construction of a mosaic, in reference to the interesting mixture of characters found in the fossil.

Skeletal anatomy of N. frickensis gen. et sp. nov. From Zahner and Brinkmann, 2019.

The new specimen was described based on a cranium (SMF 09-2) and partial postcranial skeleton (SMF 06-1). The cranium is proportionally long and low as is commonly found in traditional coelophysoid-grade neotheropods. But in contrast to coelophysids, the premaxillary tooth crowns of N. frickensis are all strongly recurved, laterally compressed and bear fine serrations. The postcranial skeleton includes two articulated forelimbs, 13 dorsal, four sacral and four proximal caudal vertebrae; cervical, dorsal and sacral ribs; chevrons; gastralia; and even stomach contents ( a well-preserved maxilla of the rhynchocephalian Clevosaurus). The preserved postcranial elements share most of their morphological similarities with ‘Syntarsus’ kayentakatae. N. frickensis has plesiomorphically long forelimbs. The radius is about three-quarters of the length of the humerus. The manus is composed of four digits, whereas the fourth is reduced to a very slim metacarpal. The shape of the ilium are similar to those found in Coelophysis.  

The phylogenetic analyses, with emphasis on early neotheropods, suggests that Notatesseraeraptor is a basal member of Dilophosauridae, a clade that comprises Dilophosaurus, and Cryolophosaurus.

 

References:

Marion Zahner; Winand Brinkmann (2019). “A Triassic averostran-line theropod from Switzerland and the early evolution of dinosaurs”. Nature Ecology & Evolution. doi:10.1038/s41559-019-0941-z

Martín D. Ezcurra, and Federico L. Agnolín (2017). Gondwanan perspectives: Theropod dinosaurs from western Gondwana. A brief historical overview on the research of Mesozoic theropods in Gondwana. Ameghiniana 54: 483–487. https://doi.org/10.5710/102.054.0501

 

Advertisements

Hesperornithoides miessleriis and the evolution of flight.

Primary blocks of Hesperornithoides specimen WYDICE-DML-001. Images taken by Levi Shinkle. From Hartman et al., 2019.

Birds originated from a theropod lineage more than 150 million years ago. Their evolutionary history is one of the most enduring and fascinating debates in paleontology. In recent years, several discovered fossils as well as innovative studies of living bird behavior, have enriched our understanding of early paravian evolution and flight origins. The discovered fossils demonstrate that distinctive bird characteristics such as feathers, flight, endothermic physiology, unique strategies for reproduction and growth, and a novel pulmonary system have a sequential and stepwise transformational pattern, with many arising early in dinosaur evolution, like the unusually crouched hindlimb for bipedal locomotion,the furcula and the “semilunate” carpal that appeared early in the theropod lineage.

The new paravian theropod, Hesperornithoides miessleriis, from the Late Jurassic Morrison Formation of east–central Wyoming, provides new clues about paravian relationships, as well as the acquisition of flight-related characters in stem avians. Nicknamed “Lori”, and with an estimated length of 89 cm, the new specimen is significantly smaller than other relatively complete theropods from the Morrison Formation. Hesperornithoides lived in a wetland environments with herbaceous plants, but no trees. The habitat, combined with limb proportions indicate that the new specimen was clearly terrestrial.

Association of skeletal elements of Hesperornithoides miessleriis assembled from 3D scans of specimen blocks. Scale bar = 6 cm. From Hartman et al., 2019

Hesperornithoides exhibits the following combination of characters: pneumatic jugal; short posterior lacrimal process; quadrate forms part of lateral margin of paraquadrate foramen; small external mandibular fenestra, humeral entepicondyle >15% of distal humeral width; manual ungual III subequal in size to ungual II; mediodistal corner of tibia exposed anteriorly. The holotype (WYDICE-DML-001) is a partially articulated skeleton consisting of an almost articulated skull, five cervical vertebrae, isolated anterior dorsal rib, portions of 12 caudal vertebrae, five chevrons, partial left scapula and coracoid, portions of the proximal left humerus and distal right humerus, left ulna and radius, radiale, semilunate carpal, left metacarpals I–III, manual phalanges III-2 and 3, manual unguals I, II, and III, ilial fragment, most of an incomplete femur, right and left tibiae and fibulae, left astragalus and calcaneum, portions of right and left metatarsal packets, left pedal phalanges III-1, III-2, III-3, IV-1, IV-2, IV-3, IV-4, and pedal unguals II and III and the proximal portion of IV. The cranial elements are preserved in a separate “skull block”, whereas the axial skeleton is distributed across three blocks.

The acquisition of powered flight in birds was preceded in the course of paravian evolution by a complex sequence of anatomical and functional innovations, and many characters associated with avian flight evolved in a terrestrial context. For this reason, a refined and robust phylogeny of paravians is imperative in order to elucidate the sequence of evolutionary stages that resulted in the acquisition of major avian traits.

 

References:

Hartman S, Mortimer M, Wahl WR, Lomax DR, Lippincott J, Lovelace DM. 2019A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flightPeerJ 7:e7247 https://doi.org/10.7717/peerj.7247

Agnolin FL, Motta MJ, Egli FB, Lo Coco G, Novas FE. 2019. Paravian phylogeny and the dinosaur-bird transition: an overview. Frontiers in Earth Science 6:252 https://www.frontiersin.org/articles/10.3389/feart.2018.00252/full

Marine ecosystems have entered the Anthropocene

Sampling of foraminifera found in a sediment core from the Caribbean, dating back to before the Industrial Revolution. CREDIT MICHAL KUCERA

Anthropogenic climate change and ocean acidification resulting from the emission of vast quantities of CO2 and other greenhouse gases pose a considerable threat to ecosystems and modern society. Planktonic foraminifera are a group of marine zooplankton that made their first appearance in the Late Triassic. Although, identifying the first occurrence of planktonic foraminifera is complex, with many suggested planktonic forms later being reinterpreted as benthic. They are present in different types of marine sediments, such as carbonates or limestones, and are excellent biostratigraphic markers. Their test are made of  globular chambers composed of secrete calcite or aragonite, with no internal structures and different patterns of chamber disposition: trochospiral, involute trochospiral and planispiral growth. During the Cenozoic, some forms exhibited supplementary apertures or areal apertures. The tests also show perforations and a variety of surface ornamentations like cones, short ridges or spines. The phylogenetic evolution of planktonic foraminifera are closely associated with global and regional changes in climate and oceanography.

John Murray, naturalist of the CHALLENGER Expedition (1872-1876) found that differences in species composition of planktonic foraminifera from ocean sediments contain clues about the temperatures in which they lived. The ratio of heavy and light Oxygen in foraminifera shells can reveal how cold the ocean was and how much ice existed at the time the shell formed. Another tool to reconstruct paleotemperatures is the ratio of magnesium to calcium (Mg/Ca) in foraminiferal shells. Mg2+ incorporation into foraminiferal calcite  is influenced by the temperature of the surrounding seawater, and the Mg/Ca ratios increase with increasing temperature.

Planktonic foraminifera from the Sargasso Sea in the North Atlantic Ocean. (Photograph courtesy Colomban de Vargas, EPPO/SBRoscoff.)

Analyzing previously collected sediment samples from over 3,500 sites around the world’s ocean, researchers found that the composition of the planktonic foraminifera has changed significantly since the pre-industrial period. The shifts in planktonic foraminifera are indicative of a more-general phenomenon across marine ecosystem, with zooplankton communities shifting poleward by an average 374 miles as a result of warming ocean temperatures.

Human activity is a major driver of the dynamics of Earth system. After the World War II, the impact of human activity on the global environment dramatically increased. Ocean warming reduces the solubility of oxygen, and raises metabolic rates accelerating the thermal stratification.

References:

Jonkers, L., Hillebrand, H., & Kucera, M. (2019). Global change drives modern plankton communities away from the pre-industrial state. Nature. doi:10.1038/s41586-019-1230-3

Forgotten women of paleontology: Hildegarde Howard

Hildegard Howard with fossil bird from the Rancho La Brea.

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). Unfortunately, women were not become members of these societies for over 300 years. Yvonne Choquet-Bruhat became the first woman to be elected to the Paris Academy of Science in 1979. Although the Royal Society was less rigid in terms of memberships than the Paris Academy of Science, it was not until 1945 that the first women were admitted as fellows of the Royal Society: the X-ray crystallographer Kathleen Yardley Lonsdale (1903–1971), and biochemist and microbiologist Marjory Stephenson (1885-1948).

Despite the barriers, between 1880 and 1914, some 60 women contributed papers to Royal Society publications. Meanwhile, in the United States, geology was a marginal subject in the curricula of the early women’s colleges until an intense programme was started at Bryn Mawr College in the 1890s.

Hildegard Howard measures specimens from the Rancho La Brea Collection. Image from The Natural History Museum of Los Angeles County Archives.

Florence Bascom was one of the pioneers when geological education at universities became available to women. She received her PhD degree from Johns Hopkins University in 1893 by special dispensation, as women were not admitted officially until 1907; while Carlotta Joaquina Maury attended Cornell University, where she became one of the first women to receive her PhD in paleontology in 1902.

When Hildegarde Howard began attending the Southern Branch of the University of California (now known as the University of California at Los Angeles), women were still barred from scientific societies. She was born on April 3, 1901 in Washington D.C., but moved to Los Angeles at the age of 5. Her main interest was journalism, until she met her first biology instructor, Miss Pirie Davidson. In 1921, Hildegarde obtained a part-time job working for Dr. Chester Stock, sorting bones from Rancho La Brea in the basement of the Los Angeles Museum of History, Science and Art (now known as the Natural History Museum of Los Angeles County). One year later, she went to Berkeley to finish her degree.

Dr. Hildegarde Howard, in her office in 1961.Copyright Natural History Museum of Los Angeles County

In 1928, she obtained her Ph.D. degree. Her dissertation, entitled “The Avifauna of Emeryville Shellmound”, became one of her most popular works, and remained as the principal reference of its kind until the appearance of the first edition of Nomina Anatomica Avium in 1979. She obtained a permanent position with the museum in 1929. Although she was a curator, she did not receive that official title until 1938. Through that decade, she wrote twenty-four papers on fossil birds in the American Southwest. She was promoted to the curator of Avian Paleontology in 1944, and she would serve in that role until 1951, when she was promoted to Chief Curator of Science, She became the first woman to receive the Brewster Medal for outstanding research in ornithology in 1953.

Hildegarde Howard officially retired in 1961, although continued research on fossil birds, publishing her last paper in 1992. During her extraordinary career, Dr. Howard described 3 families, 13 genera, 57 species, and 2 subspecies, and remains highly regarded as one of the foremost experts in her field. She died on February 28, 1998.

 

References:

Campbell Jr., Kenneth. 2000c. “In Memoriam, Hildegarde Howard 1901-1998.” The Auk, vol.117, no.3, 775-779.

 

Introducing Kaijutitan, the strange beast.

The entrance to the town of Rincón de los Sauces.

Since the discovery of dinosaur remains in the Neuquen basin in 1882, Argentina has gained the title of Land of the Giants. The tittle was reinforced by the discoveries of titanosaurs like Argentinosaurus, Dreadnoughtus, Notocolossus, Puertasaurus, and Patagotitan. The study of this diverse group of sauropod dinosaurs embrace an extensive list of important contributions, which started with Richard Lydekker’s pioneering work on Patagonian dinosaurs, and by the classic Friedrich von Huene monograph on Argentinean saurischians and ornithischians.

Titanosaurus were a diverse group of sauropod dinosaurs represented by more than 30 genera, which included all descendants of the more recent common ancestor of Andesaurus and Saltasaurus. The group includes the smallest (e.g. Rinconsaurus, Saltasaurus; with estimated body masses of approximately 6 tonnes) and the largest sauropods known to date. They had their major radiation during the middle Early Cretaceous. The evolution of body mass in this clade is key element to understand sauropod evolution.

 

Cranial elements of MAU-Pv-CM-522/1. From Filippi et al., 2019.

Kaijutitan maui, is the first basal sauropod titanosaur from the Sierra Barrosa Formation (Upper Coniacian, Upper Cretaceous). The holotype (MAU-Pv-CM-522) consists of cranial, axial, and appendicular elements presenting an unique combination of plesiomorphic and apomorphic characters. The generic name Kaijutitan is derived from Kaiju, Japanese word that means “strange beast” or “monster”, and titan, from the Greek “giant”.  The species name refers to the acronym of the Museo Municipal Argentino Urquiza, Rincon de los Sauces, Neuquén, Argentina.

The cranial elements of this specimen include the complete neurocranium (the supraoccipital, exoccipital, left paraoccipital process, left exoccipital-opisthotic-prootic complex, left laterosphenoid and orbitosphoid, and basioccipital-basisphenoid complex). The impossibility of recognizing clear sutures suggest an ontogenetic adult stage of the specimen. One of the most notable autapomorphies exhibited by Kaijutitan is the anterior cervical vertebra with bifid neural spine, a feature usually found in diplodocids and dicraeosaurids. Unfortunately, the femur and humerus of Kaijutitan maui are incomplete, therefore the body mass of this titanosaur can only be estimated by comparison with other titanosauriforms. Kaijutitan would have had a body mass similar or intermediate to that of Giraffatitan (38.000 kg) and Notocolossus (60.398 kg).

 

References:

Filippi, L.S., Salgado, L., Garrido, A.C., A new giant basal titanosaur sauropod in the Upper Cretaceous (Coniacian) of the Neuquén Basin, Argentina, Cretaceous Research, https://doi.org/10.1016/j.cretres.2019.03.008.

Meet Iberodactylus.

Partial rostrum of Iberodactylus andreui. From Holgado et. al, 2019

Pterosaurs were the first flying vertebrates. The group achieved high levels of morphologic and taxonomic diversity during the Mesozoic, with more than 200 species recognized so far. From the Late Triassic to the end of the Cretaceous, 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. Because of the fragile nature of their skeletons the fossil record of pterosaurs is strongly biased towards marine and lacustrine depositional environments.

Pterosaurs have 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, and ruled the sky from the Late Jurassic to the End Cretaceous.

Comparison of the rostrum of Iberodactylus andreui with a cast of a skull of Hamipterus tianshanensis. From Holgado et al., 2019

The record of Iberian pterosaurs is scarce, but a new taxa from the Lower Cretaceous of Spain reveals an unexpected relationship with Hamipterus tianshanensis from the Lower Cretaceous of China. Iberodactylus andreui gen. et sp. nov., was recovered at Los Quiñones site, close to the village of Obón (Teruel, Spain), at the end of the 1980s by Javier Andreau. The holotype (MPZ-2014/1) consists of the anterior portion of the rostrum (~198 mm in length), and includes a partially preserved premaxillary crest, and a fragment of the maxillary bone with several fragmentary teeth. The specimen preserved its original 3D shape, although exhibits frequent fractured bones, that added to the eroded bone surfaces, reveal an external thing layer of cortical bone of 1.5 mm. The robustness and height of the premaxillary crest, suggest that MPZ-2014/1 may represent a male specimen.

The most striking feature of MPZ-2014/1 is the premaxillary crest. This crest exhibits well-developed elongated, sub-vertical striae and sulci, anteriorly curved, a combination that is quite similar to Hamipterus tianshanensis from the Berriasian-Albian of China. It was suggested that the sulci could be interpreted as a trait related to the attachment of the rhamphotheca, as in the case of some extant birds.

Origin and radiation of the clade Anhangueria during the Early Cretaceous. From Holgado et al., 2019

Phylogenetic analyses indicate that Hamipterus tianshanensis and Iberodactylus andreui gen. et sp. nov. form a monophyletic group, the Hamipteridae fam. nov., that falls within the Anhangueria, sharing with other anhanguerians the presence of a lateral expansion on the rostral tips. Anhanguerians has been recorded elsewhere in the Early Cretaceous of Europe, however Iberodactylus is not closely related to any known European anhanguerian, suggesting that the clade Anhangueria could have ancestral connections to eastern Laurasia.

Other tetrapod lineages are recorded in the Iberian Peninsula with close affinities to Asian faunas. Those lineages include titanosauriforms, crocodyliforms, enanthiornitean birds, and the gobiconodontid mammal Spinolestes xenarthrosus related to Gobiconodon and Repenomamus.

Reference:

Borja Holgado, Rodrigo V. Pêgas, José Ignacio Canudo, Josep Fortuny, Taissa Rodrigues, Julio Company & Alexander W.A. Kellner, 2019, “On a new crested pterodactyloid from the Early Cretaceous of the Iberian Peninsula and the radiation of the clade Anhangueria”, Scientific Reports 9: 4940

The mounting of the cast of Diplodocus carnegii at the Museo de La Plata.

Diplodocus carnegii at the Museo de La Plata, 1912 (From Otero and Gasparini, 2014)

Diplodocus carnegii at the Museo de La Plata, 1912 (From Otero and Gasparini, 2014).

Diplodocus is one of the most popular dinosaurs of all time. The first remains of a Diplodocus were found by Benjamin Mudge and Samuel Wendell Williston, in the Upper Jurassic outcrops of Cañon City, Colorado, United States, in 1877. One year later, Othniel Charles Marsh named the species Diplodocus longus on the basis of remains of the hind limb and tail. The name Diplodocus means ‘double beam’ in reference to the particular two-pronged morphology of the posterior hemal arches. D. carnegii, was discovered in 1899 during an expedition carried out by the Carnegie Museum to the Upper Jurassic Morrison Formation of Wyoming. John Bell Hatcher dedicated the new species of to Andrew Carnegie.

A sketch from the of Diplodocus carnegii, which Carnegie had framed and mounted on a wall at his castle in Scotland.

William Jacob Holland, director of the Carnegie Museum, sent a sketch of the skeleton of Diplodocus to Andrew Carnegie. At the time, the steel tycoon was at his Castle, Skibo, in Sutherland County, Scotland. The King Edward VII of England, saw the sketch and asked Carnegie to give him a specimen for the British Museum of Natural History in London. Holland proposed to Carnegie to make a life-sized replica of D. carnegii to be given to the British Museum of Natural History. On May 12, 1905, the long skeleton was unveiled to a crowd of 300 people, and became an instant star.

Mounting of the cast of Diplodocus carnegii at the Museo de La Plata, Argentina. Arthur Coggeshall and William Holland are second and third from left (Adapted from ‘Caras y Caretas’ magazine, 1912).

Nine replicas of D. carnegii were made and donated to kings and presidents of Europe and Latin America. On November of 1911, Argentinean president Dr. Roque Saenz Peña communicated to Andrew Carnegie his request to have a replica of D. carnegii. His request was accepted, and on July 1, 1912, 34 boxes containing the cast of the animal were sent to Argentina on the S.S. ‘Sallust’. William Holland and Mr. Arthur Coggeshall were in charge of mounting the replica. The site where the replica would be mounted in the Museo de La Plata, would be the Sala III, which was dedicated to invertebrates and plants. Holland insisted that the plans used for the mounting of D. carnegii at Vienna were followed in mounting the skeleton in La Plata. After the skeleton was mounted, the Director of the Museum, Dr. Samuel Lafone-Quevedo, gave a speech expressing his gratitude to Andrew Carnegie and his representatives, in which William Holland was designated an Honorary Member of La Plata University.

Reference:

Alejandro Otero and Zulma Gasparini “The History of the Cast Skeleton of Diplodocus carnegii Hatcher, 1901, at the Museo De La Plata, Argentina,” Annals of Carnegie Museum 82(3), (2014). doi: http://dx.doi.org/10.2992/007.082.0301

BARRETT, P., P. PARRY, AND S. CHAPMAN. 2010. Dippy: The Tale of a Museum Icon. Natural History Museum, London. 48 pp.

 

Introducing Moros intrepidus, the harbinger of doom.

Moros intrepidus. Credit: Jorge Gonzalez

Tyrannosauroidea, the superfamily of carnivorous dinosaurs that includes the iconic Tyrannosaurus rex, originated in the Middle Jurassic, approximately 165 million years ago, and was a dominant component of the dinosaur faunas of the Northern Hemisphere. All tyrannosaurs were bipedal predators characterized by premaxillary teeth with a D-shaped cross section, fused nasals, extreme pneumaticity in the skull roof and lower jaws, a pronounced muscle attachment ridge on the ilium, and an elevated femoral head. But for most of their evolutionary history, tyrannosauroids were mostly small-bodied animals and only reached gigantic size during the final 20 million years of the Cretaceous. Now, the discovery of a new, diminutive tyrannosauroid, Moros intrepidus gen. et sp. nov., shed lights on the successful radiation of Campanian tyrannosauroids.

The holotype (NCSM 33392), preserves a partial right hind limb including portions of the femur, tibia, second and fourth metatarsals, and phalanges of the fourth pedal digit. It was recovered from the lower Mussentuchit Member (6–7 m above the Ruby Ranch contact), upper Cedar Mountain Formation, Emery County, Utah, USA. This small-bodied, gracile-limbed tyrannosauroid lived about 96 million years ago. The name derived from Greek word Moros (an embodiment of impending doom) in reference to the establishment of the Cretaceous tyrannosauroid lineage in NA, and the Latin word intrepidus (intrepid), in reference to the hypothesized intracontinental dispersal of tyrannosaurs during this interval.

Bone microstructure of M. intrepidus (NCSM 33392). From Zanno et al., 2019.

NCSM 33392 derives from a skeletally immature individual (6-7 years) nearing adult size . According to the histological analysis, M. intrepidus exhibits a moderate growth rate, similar to Guanlong, a more primitive tyrannosauroid from the Late Jurassic of China. By contrast, large-bodied, tyrannosaurines from the last stages of the Cretaceous, like Gorgosaurus, were already triple their masses at similar ages. M. intrepidus suggests that North American tyrannosauroids were restricted to small sizes for a protracted period of ~15 million years and at some point at the Turonian, they embarked on a trend of rapid body size increases, to became the top predators of the Cretaceous.

 

References:

Zanno, L.E, Tucker, R.T., Canoville, A., Avrahami, H.M., Gates, T.A., Makovicky, P.J. (2019), Diminutive fleet-footed tyrannosauroid narrows the 70-million-year gap in the North American fossil record, Communications Biology, DOI: 10.1038/s42003-019-0308-7

Introducing Bajadasaurus pronuspinax.

Bajadasaurus reconstruction (Museo Municipal Ernesto Bachmann, Villa El Chocón, Neuquén).

Dicraeosauridae is a family of mid-sized sauropod dinosaurs characterized by a distinctive vertebral column with paired, long, neural spines. 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. Dicraeosauridae includes  Amargasaurus, Pilmatueia, Suuwassea, and Brachytrachelopan. Now, the description of Bajadasaurus pronuspinax gen. et sp. nov., from the Early Lower Cretaceous of Bajada Colorada Formation in Northern Patagonia, Argentina), shed new light on the function of its spines and the defense behavior in sauropod dinosaurs.

Bajadasaurus was discovered in 2013, by a team of paleontologists from CONICET, Fundación Félix de Azara, Universidad Maimónides, and Museo Paleontológico Ernesto Bachmann. The generic name derived from Bajada (Spanish, in reference to the locality Bajada Colorada) and saurus (Greek, lizard). The specific name derived from pronus (Latin, bent over forward) and spinax (Greek, spine), referring to the anteriorly pointed, curved, neural spines of the cervical vertebrae.

Skeletal elements of Bajadasaurus pronuspinax. From Gallina et al., 2019.

The holotype, MMCh-PV 75, includes a nearly complete skull (left maxilla, left lacrimal, both prefrontals, both frontals, both parietals, both postorbitals, both squamosals, left quadratojugal, both pterygoids, both quadrates, supraoccipital, exoccipital-opisthotic complex, basioccipital, basisphenoid, both prootics, both laterosphenoids, both orbitosphenoids, both dentaries, left surangular, both angulars, both splenials, left prearticular, left articular, isolated upper tooth row), both proatlases, atlantal neurapophyses, axis and the fifth cervical vertebra.

The skull of Bajadasaurus is gracile, with dorsally exposed orbits, dorsoventrally compressed occipital condyle, extremely narrow basipterygoid processes, elongate and slender anterior processes of the squamosals, medially extended post-temporal fenestrae, short lateral temporal fenestrae and a reduced dentition in the maxilla and dentary, that largely differs from other known taxa within Dicraeosauridae. But the most striking feature of Bajadasaurus is the presence of extremely long cervical neural spines that curve anteriorly. Amargasaurus exhibit the same development of cervical neural spine elongation as Bajadasaurus, but the spines of the former point backwards rather than forwards. Dicraeosaurus and Brachytrachelopan show anteriorly inclined neural spines in the cervical vertebrae, but the spines are much shorter than in Bajadasaurus.

A group of Bajadasaurus. Illustration: Jorge A. González.

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, including interpretations 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. Those explanation, except the last one, require that these long and extremely gracile bone projections, now recognized in Bajadasaurus as well, can support enough physical stress to avoid fracturing. Bone is stronger and stiffer in passive situations, however, horns and other keratin-based materials are tougher and highly resistant to impact-related fractures. Therefore, the keratinous sheath in Amargasaurus and perhaps Bajadasaurus provides a better mechanical solution against a potential fracture.

 

References:

Gallina, Pablo A., Apesteguía, Sebastián, Canale, Juan I., Haluza, Alejandro (2019), A new long-spined dinosaur from Patagonia sheds light on sauropod defense system, Scientific Reports volume 9, Article number: 1392 DOI: https://doi.org/10.1038/s41598-018-37943-3

Janensch, W. Die Wirbelsäule der Gattung Dicraeosaurus. Palaeontographica Supplement 7, 37–133 (1929).

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).

The hyperthermals of the geological record

During the last 540 million years five mass extinction events shaped the history of the Earth. Those events were related to extreme climatic changes. The geological records show that large and rapid global warming events occurred repeatedly during the course of Earth history.
Our planet’s climate has oscillated between two basic states: the “Icehouse”, and the “Greenhouse”, and superimposed on this icehouse–greenhouse climate cycling, there are a number of geologically abrupt events known as hyperthermals, when atmospheric CO2 concentrations may rise above 16 times (4,800 ppmv). Although each hyperthermal is unique, they are consequence from the release of anomalously large inputs of CO2 into the atmosphere and are relatively short-lived (with the exception of the Permian–Triassic boundary).

A summary of the most significant hyperthermals in the last 300 Myr. From Foster et. al., 2018.

The emplacement of large igneous provinces (LIPs) is commonly associated with hyperthermals, for example, the Siberian Traps at the P–T boundary. The CO2 emissions caused global warming. The SO2 emissions on mixing with water vapour in the atmosphere, caused acid rain, which in turn killed land plants and caused soil erosion. Warmer oceans melted frozen methane located in marine sediments which pushed the global temperatures to higher levels. Additionally, the increased continental weathering induced by acid rain and global warming led to increased marine productivity and eutrophication, and so oceanic anoxia, and marine mass extinctions.

The hyperthermal at the P–T boundary was associated with the most severe terrestrial and oceanic mass extinction of the last 541 Myr, where 96% of species became extinct. It comprises two killing events, one at the end of the Permian (EPME) and a second at the beginning of the Triassic, separated by 60000 years. In terms of carbon isotope excursion, the P–T boundary hyperthermal and the PETM share many similarities, but the warming after the P-T boundary was more extreme and extended for longer than PETM.

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

The End-Triassic Extinction is probably the least understood of the big five. It has been linked to the eruption of the Central Atlantic Magmatic Province (CAMP), a large igneous province emplaced during the initial rifting of Pangea. Most mammal-like reptiles and large amphibians disappeared, as well as early dinosaur groups. In the oceans, this event eliminated conodonts and nearly annihilated corals, ammonites, brachiopods and bivalves. In the Southern Hemisphere, the vegetation turnover consisted in the replacement to Alisporites (corystosperm)-dominated assemblage to a Classopollis (cheirolepidiacean)-dominated one.

The early Toarcian Oceanic Anoxic Event (T-OAE; ∼183 mya) in the Jurassic Period is considered as one of the most severe of the Mesozoic era. The T-OAE is thought to have been caused by increased atmospheric CO2 triggered by Karoo–Ferrar volcanism. Results from the Paris Bassin indicates that the increasing greenhouse conditions may have caused acidification in the oceans, hampering carbonate bio-mineralisation, and provoking a dramatical loss in the CO2 storage capacity of the oceans.

Tentative changes in mid-latitude vegetation patterns during OAE2. (a) Araucariaceae, (b) other conifers incl. Cheirolepidiaceae, (c) Cupressaceae, (d) angiosperms incl. Normapolles-producing forms, (e) ferns. From Heimhofer et al., 2018.

The early Aptian Oceanic Anoxic Event (OAE1a, 120 Ma) represents a geologically brief time interval characterized by rapid global warming, dramatic changes in ocean circulation including widespread oxygen deficiency, and profound changes in marine biotas. During the event, black shales were deposited in all the main ocean basins. It was also associated with the calcification crisis of the nannoconids, the most ubiquitous planktic calcifiers during the Early Cretaceous. Their near disappearance is one of the most significant events in the nannoplankton fossil record.

The mid-Cretaceous Oceanic Anoxic Event 2 (OAE2, 93 Ma) marks the onset of an extreme phase in ocean temperatures known as the “Cretaceous thermal maximum”. It has been postulated that the OAE2 was triggered by a massive magmatic episode.

Comparison of the effects of anthropogenic emissions (total of 5000 Pg C over 500 years) and PETM carbon release (3000 Pg C over 6 kyr) on the surface ocean saturation state of calcite. From Zeebe, 2013

The Paleocene-Eocene Thermal Maximum (PETM; 55.8 million years ago), was a short-lived (~ 200,000 years) global warming event attributed to a rapid rise in the concentration of greenhouse gases in the atmosphere. It was suggested that this warming was initiated by the melting of methane hydrates on the seafloor and permafrost at high latitudes. During the PETM, around 5 billion tons of CO2 was released into the atmosphere per year, and temperatures increased by 5 – 9°C. This event was accompanied by other large-scale changes in the climate system, for example, the patterns of atmospheric circulation, vapor transport, precipitation, intermediate and deep-sea circulation and a rise in global sea level. But unlike other hyperthermals, the PETM is not associated with significant extinctions.

Anthropogenic climate change and ocean acidification resulting from the emission of vast quantities of CO2 and other greenhouse gases pose a considerable threat to ecosystems and modern society. The combination of global warming and the release of large amounts of carbon to the ocean-atmosphere system during the PETM has encouraged analogies to be drawn with modern anthropogenic climate change. The current rate of the anthropogenic carbon input is probably greater than during the PETM, causing a more severe decline in ocean pH and saturation state. Also the biotic consequences of the PETM were fairly minor, while the current rate of species extinction is already 100–1000 times higher than would be considered natural. This underlines the urgency for immediate action on global carbon emission reductions.

References:

Foster GL, Hull P, Lunt DJ, Zachos JC. (2018) Placing our current‘hyperthermal’ in the context of rapid climate change in our geological past. Phil. Trans. R. Soc. A 376: 20170086 http://dx.doi.org/10.1098/rsta.2017.0086

Benton MJ. (2018) Hyperthermal-driven mass extinctions: killing models during the Permian–Triassic mass extinction. Phil. Trans. R. Soc. A 376: 20170076. http://dx.doi.org/10.1098/rsta.2017.0076

Penn, J. L., Deutsch, C., Payne, J. L., & Sperling, E. A. (2018). Temperature-dependent hypoxia explains biogeography and severity of end-Permian marine mass extinction. Science, 362(6419), eaat1327. doi:10.1126/science.aat1327 

Ernst, R. E., & Youbi, N. (2017). How Large Igneous Provinces affect global climate, sometimes cause mass extinctions, and represent natural markers in the geological record. Palaeogeography, Palaeoclimatology, Palaeoecology, 478, 30–52. doi:10.1016/j.palaeo.2017.03.014

Turgeon, S. C., & Creaser, R. A. (2008). Cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode. Nature, 454(7202), 323–326. doi:10.1038/nature07076

Ulrich Heimhofer, Nina Wucherpfennig, Thierry Adatte, Stefan Schouten, Elke Schneebeli-Hermann, Silvia Gardin, Gerta Keller, Sarah Kentsch & Ariane Kujau (2018) Vegetation response to exceptional global warmth during Oceanic Anoxic Event 2, Nature Communications volume 9, Article number: 3832

Zeebe RE and Zachos JC. 2013 Long-term legacy ofmassive carbon input to the Earth system: Anthropocene versus Eocene. Phil Trans R Soc A 371: 20120006. http://dx.doi.org/10.1098/rsta.2012.0006.