Volcanism and the Rise of the Dinosaurs

Global paleogeographic setting during the Late Triassic. From X. Fu et al., 2020.

The Carnian Pluvial Episode (CPE), dated to 234–232 Ma, was a time of major turnover in the oceans and on land. It was characterized by global warming, ocean acidification, mega-monsoonal conditions, and a generalised increase in rainfall. In the marine sedimentary basins of the Tethys realm, an abrupt change of carbonate factories and the establishment of anoxic conditions mark the beginning of the climate change. This shift from arid to more humid conditions has been linked to the large-scale volcanism of the Wrangellia large igneous province (LIP). The widespread extinction caused by the CPE was followed by the first substantial diversification of dinosaurs.

Data from Central European Basin, Wessex Basin (United Kingdom), East Greenland (37), Morocco (38), Newark Basin (North America), and the Ischigualasto Basin (Argentina), indicate that increased rainfall resulted in the widespread expansion of the endorheic basins during the CPE. In the Jiyuan Basin, located in the southeast of the Ordos Basin, North China, an expanded Carnian lake succession offers a glimpse into this crucial interval.

 

Some representative palynological genera from the Jiyuan Basin (all scale bars = 20 μm). From Lu, Jing, et al., 2021

During the Early and Middle Triassic, North China was located in eastern Tethys. Later in the Triassic, the North China Plate collided with the South China Plate which resulted in extensive volcanism and the migration of the Ordos Basin depocenter continuously westward. High-resolution chemostratigraphy, palynological and sedimentological data indicate that four pulses of LIP volcanism were likely responsible for the global negative CIEs (carbon isotope excursion) that mark the CPE and drove major environmental changes.

The CPE also marks the first massive appearance of calcareous nannoplankton, while groups, like bryozoans and crinoids, show a sharp decline during this event. On land, palaeobotanical evidence shows a shift of floral associations towards elements more adapted to humid conditions (the palynological record across the CPE suggest at least 3–4 discrete humid pulses). During this interval, several families and orders make their first appearance: bennettitaleans, modern ferns, and conifer families (Pinaceae, Araucariaceae, Cheirolepidaceae), while key herbivorous groups such as dicynodonts and rhynchosaurs, which had represented 50% or more of faunas, disappeared.

Eoraptor lunensis, outcropping from the soil. Valle de la Luna (Moon Valley), Parque Provincial Ischigualasto, Provincia de San Juan, Argentina.

Followed the extinction of rhynchosaurs in most, or all, parts of the world, there was a burst of dinosaurian diversity in the late Carnian, represented by the upper Ischigualasto Formation and coeval units, with mostly carnivorous small- to medium-sized dinosaurs. Then, the long span of the early Norian, from 228.5–218 Ma, during which dicynodonts and sauropodomorph dinosaurs were the major herbivores. Finally, with the disappearance of dicynodonts, sauropodomorph dinosaurs became truly large in the middle and late Norian, from 218 Ma. This was followed by the extinction of basal archosaur groups during the end-Triassic mass extinction, 201 Ma, and the diversification of sauropods, larger theropods, ornithopods, and armoured dinosaurs subsequently, in the Jurassic.

 

References:

Lu, Jing, et al. Volcanically driven lacustrine ecosystem changes during the Carnian Pluvial Episode (Late Triassic), PNAS (2021). doi.org/10.1073/pnas.2109895118

X. Fu et al., A possible link between the Carnian Pluvial Event, global carbon-cycle perturbation, and volcanism: New data from the Qinghai-Tibet Plateau. Global Planet. Change 194, 103300 (2020) doi:10.1016/j.gloplacha.2020.103300

Michael J. Benton et al. The Carnian Pluvial Episode and the origin of dinosaurs, Journal of the Geological Society (2018). DOI: 10.1144/jgs2018-049

The Weissert Event

Paleogeographic map by C.R. Scotese, PALEOMAP project. From Cavalheiro et al., 2021

The continued fragmentation of Pangaea across the Late Jurassic and Early Cretaceous led to large-scale tectonic processes, on both regional and global scale, accompanied by some of the largest volcanic episodes in the history of the Earth, eustatic oscillations of the sea level, potentially heightened levels of anoxia, oceanic stagnation, and sulphur toxicity. The Weissert Event (~133 million years ago), linked with the main magmatic activity of the Parana`-Etendeka large igneous province (LIP), represents one of the most significant paleoceanographic events of the Early Cretaceous. This global perturbation in the C cycle is marked by a positive (+1.5‰) carbon isotope excursion (CIE) observed both in organic and inorganic records.

Global mean surface temperatures (GMSTs) and associated CO2 levels. From Cavalheiro et al., 2021.

A new study analyzed deep sea sediments obtained by the Ocean Drilling Program (ODP) from offshore Antarctica to reconstruct the paleotemperatures. The international team of researchers lead by Liyenne Cavalheiro combinded calcareous nannofossil data and chemostratigraphy, and found that that global temperatures declined by 3.0 °C (±1.7 °C) during the Weissert Event.

Calcareous nannoplankton represent a major component of oceanic phytoplankton. 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. Additionally, reconstructions of Cretaceous sea-surface temperatures (SSTs) have been revolutionised by the development of the organic palaeothermometer TEX86, based on the distribution of marine archaeal membrane lipids.

 

 

 

References:

Cavalheiro, L., Wagner, T., Steinig, S. et al. Impact of global cooling on Early Cretaceous high pCO2 world during the Weissert Event. Nat Commun 12, 5411 (2021). https://doi.org/10.1038/s41467-021-25706-0

Erba, E., Bartolini, A., & Larson, R. L. (2004). Valanginian Weissert oceanic anoxic event. Geology, 32(2), 149. doi:10.1130/g20008.1 

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

Forgotten women of Paleontology: Esther Richards Applin

Esther Richards Applin, 1944-1972. From Wikimedia Commons

In the 18th and 19th centuries women’s access to science was limited, and science was usually a ‘hobby’ for intelligent wealthy women. But 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. Later, the boom in the oil industry opened opportunities for women.
In 1920, E. T. Dumble, vice-president and general manager of the Rio Bravo Oil Company, put together a consortium agreement in Houston, which included his own company, the Texas Company, and Humble Oil Company. He hired Esther Applin née Richards, Alva Ellisor, and Hedwig Kniker to take charge of the company’s paleontological laboratory in Houston and solve the Gulf Coast stratigraphic problems. Macrofossils were too badly broken to be identifiable as to species, so Esther Applin turned her attention to the microfossils, especially foraminifera. It was the beggining of the micropaleontological revolution.

Esther Richards was born November 24, 1895, in in Newark, Ohio. She attended the University of California, Berkeley, and graduated with honors in paleontology in 1919. A year later, she moved to Houston to work for the Rio Bravo Oil company. In 1923, she married Paul L. Applin, a young geologist. In 1921, Esther presented a paper suggesting that microfossils could be use to stratigraphic correlation. Her study was ridiculed by Professor J.J. Galloway of the University of Texas, who stated: “Gentlemen, here is this chit of a girl, right out of college, telling us that we can use Foraminifera to determine the age of formation. Gentlemen, you know that it can’t be done.

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)

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, and even Galloway became a defender of this method. However, the role of these women was downplayed over time, and by 1975 the credit for this technology was shifted to four men.

Esther continued her work as a consulting paleontologist and subsurface geologist in Texas. She become a Fellow of The Geological Society of America, a charter member of the Society of Economic Paleontologists and Mineralogists, and a member o f the Mississippi Geological Society. In 1966, in recognition of her contributions to micropaleontology, she was made an honorary member o f the Mississippi Geological Society. She died on July 23, 1972.

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).

The braincase of Daspletosaurus.

Daspletosaurus torosus, holotype CMN 8506, Canadian Museum of Nature, Ottawa. From Wikepedia Commons

In 1970, Dale Russell described Daspletosaurus torosus. For decades, this specimen was regarded as the “prototypical” Campanian tyrannosaurine. It was discovered in 1921 by Charles Mortram Sternberg, who thought it was a new species of Gorgosaurus. But Daspletosaurus was heavier and more powerfully built than Gorgosaurus, and specilized in feeding on ceratopsians. A new study by a team of scientists from Canada and Argentina provides the first detailed study of the braincase of Daspletosaurus. The holotype of Daspletosaurus torosus (CMN 8506) from the Oldman Formation of Dinosaur Provincial Park, southern Alberta, includes a complete braincase. TMP 2001.36.1 (Daspletosaurus sp.) is a nearly complete skull and skeleton of an ontogenetically mature individual from the Oldman Formation. Both specimens were used to digitally reconstruct the brain, inner ear, and the braincase of Daspletosaurus and revealed extensive morphological variations. 

Cast of the skull of Daspletosaurus torosus in the Canadian Museum of Nature’s collections.

Our knowledge of dinosaurian braincases and the structure of their endocranial cavities has a surprisingly long history. The first well-preserved braincase (NHMUK R2501) was found almost 150 years ago in the Isle of Wight and was described as probably belonging to Iguanodon. In 1897, Charles William Andrews – using the same specimen – suggested that dinosaurian brains, and in particular their lobes and surface convolutions, were not closely pressed against the cranial wall. Almost sixty years later, John Ostrom published a study on the anatomy of the hadrosaurian dinosaurs of North America and reinforced the general opinion that they had brains that were not packed tightly within the braincase. In 1970, Dale Russell was the first to recognize taxonomic significance in the variation of the braincase morphology among tyrannosaurids.

The braincase of Daspletosaurus sp. (TMP 2001.36.1). From Carabajal et al., 2021

The new study reveals a set of characters useful to distinguish the genus Daspletosaurus from other tyrannosaurids: a deep midbrain flexure, the presence of an anterodorsal chamber of the basisphenoid recess, and the presence of a prohypophyseal sinus of the anterior tympanic recess at large body size Among the variations that potentially distinguish TMP 2001.36.1 from Daspletosaurus torosus are the short, vertical lagena, and the paired sinuses on the lateral wall of the basisphenoid recess (unique among tyrannosaurids), the entirely pneumatized paroccipital process (shared with Gorgosaurus), the well-developed crista tuberalis, and the curved ala basisphenoidalis. Additionally, the bottlenecked olfactory tract in TMP 2001.36.1 occurs mainly in smaller tyrannosaurids.

 

 

References:

Ariana Paulina Carabajal, Philip J. Currie, Thomas W. Dudgeon, Hans C.E. Larsson, and Tetsuto Miyashita. Two braincases of Daspletosaurus (Theropoda: Tyrannosauridae): anatomy and comparison. Canadian Journal of Earth Sciences. DOI: 10.1139/cjes-2020-0185

Russell, D.A. 1970. Tyrannosaurs from the Late Cretaceous of Western Canada. National Museum of Natural Sciences Publications in Palaeontology, 1: 1–32. DOI: 10.5281/zenodo.1040973

Introducing Ypupiara lopai

Restoration of two individuals of Ypupiara lopai. Credit: Guilherme Gehr

The iconic Velociraptor mongoliensis, described by Osborn in 1924, belongs to the Dromaeosauridae, a family of highly derived small to mid-sized theropod dinosaurs closely related to birds. Their fossils have been found in North America, Europe, Africa, Asia, South America and Antarctica. The group is characterized by the presence of long, three-fingered forelimbs that ended in sharp, trenchant claws, and a tail stiffened by the elongated prezygapophyses. In Gondwana, the clade Unenlagiinae is a diversification of dromaeosaurids. The group includes Buitreraptor and Austroraptor from Argentina. Ypupiara lopai from the Maastrichtian of the Bauru Group is the first unenlagiine dromaeosaurid species from Brazil.

The holotype (DGM 921-R) includes a partial preantorbital portion of a right maxillary, with three teeth in loci, and a partial posterior portion of a right dentary. The generic name means ‘the one who lives in the water’, an allusion to a Tupian myth about an aquatic creature. The specific name honors Alberto Lopa, the holotype’s discoverer. Ypupiara was found between the 40s and 60s in Peirópolis, near Uberaba, and placed in storage at the National Museum of Brazil. Unfortunately, the fossil was lost when the museum was consumed by a fire on 2 September 2018, but photographs of the specimen survived.

Right maxilla of DGM 921-R with details of teeth. Scale bar: 10 mm. From Brum et al., 2021.

Ypupiara is characterized by the morphology of the maxilla that exhibits a restrict number of neurovascular foramina on lateral surface, rectangular and anteroposteriorly expanded interdental plate, and teeth widely spaced and labiolingually compressed. Based on the ratio between the labiolingual and mediodistal diameters of the teeth more than 3/5, Ypupiara was classified as a sister-group of A. cabazai. It was suggested that unenlagiines consumed fish at least as part of their diet and potentially as the main source of food at least in Austroraptor due to its conidont dentition.

 

References:

Brum, Arthur Souza, Pêgas, Rodrigo Vargas, Bandeira, Kamila Luisa Nogueira, Souza, Lucy Gomes de, Campos, Diogenes de Almeida, & Kellner, Alexander Wilhelm Armin. (2021). A new Unenlagiinae (Theropoda: Dromaeosauridae) from the Late Cretaceous of Brazil. https://doi.org/10.1002/spp2.1375

Gianechini, Federico A and S. Apesteguía. (2011) “Unenlagiinae revisited: dromaeosaurid theropods from South America.” Anais da Academia Brasileira de Ciencias 83 1: 163-95 .

A brief history of Proboscideans

Lyuba, the best preserved mammoth mummy in the world, at the Field Museum of Natural History (From Wikimedia Commons).

In 1811, German zoologist Johann Karl Wilhelm Illiger introduced the taxonomic order Proboscidea for elephants, the American mastodon and the woolly mammoth. The proboscis, an elongated appendage from the head of an animal, is the most distinguishing feature of these mammals. They also have a highly specialized dentition, and tusks that formed from elongated upper incisors. The lineage arose in the Late Paleocene in Africa and spread across Eurasia and the Americas. Over their 60 million years of evolutionary history, proboscideans went from a few kilograms in the earliest representatives, to forms weighed up to 6-8 metric tons. Phosphatherium escuilliei, one of the earliest recognized proboscidean, stood about 30 centimetres with a body mass of 17 kilograms while Palaeoloxodon recki stood 4.27 metres tall and weighed 12.3 tonnes. Today, the clade is represented by only 3 species: the African forest elephant, Loxodonta cyclotis, the African bush elephant, Loxodonta africana and the Asian elephant, Elephas maximus.

Skull and upper dentition of Eritherium azzouzorum, the oldest and most primitive elephant relative. From Gheerbrant 2009

Traditionally, three major radiations have been recognized. The first radiation occurred between Paleocene-Oligocene and was restricted to Afro-Arabia. The second radiation involved the expansion of taxa that emerged between the Late Oligocene and the early Miocene outside Africa. The third radiation emerged at the end of the Miocene and extended through the Holocene epoch. The most primitive and smallest known proboscidean belong to the family Plesielephantiformes. The most diverse family was the Gomphotheriidae, which lived on all continents except Antarctica and Australia. The earliest Elephantiformes were similar in appearance to the first gomphotheres. The iconic mammoths were widespread in the northern hemisphere during the Last Ice Age and their remains inspired all types of legends.

Gomphotherium angustidens at Senckenberg Museum of Frankfurt. From Wikipedia Commons

The onset of C4 grass-dominated habitats around 8 Ma brought dramatic changes to the evolutionary context of megafauna communities. The adaptation to particular feeding habits is manifested in changes to the upper and lower incisors of proboscideans. Proboscideans in the first radiation were mostly browsers, whereas those in the second and third radiations were mostly grazers. Miocene forms, such as Gomphotherium angustidens and Rhynchotherium tlascalae are known to have slightly more hypsodont molars than Paleocene–Oligocene proboscideans.

A mammoth tooth on the riverbank on Wrangel Island. Image credit; Juha Karhu/University of Helsinki

In Europe, during the Pliocene, took place the extinction of the Deinotheriidae (they survived in Africa until the early Pleistocene), Mammutidae, and Gomphotheriidae. The Pliocene also witnessed the rise of stegodonts (Stegodontidae) and modern elephants (Elephantinae). During the Pleistocene, continental glaciars expanded and contracted over most of northern hemisphere causing dramatic ecological shifts. Most of the terrestrial megafauna became extinct. The extinction was notably more selective for large-bodied animals than any other extinction interval in the last 65 million years (dwarfed mammoths survived until 4000 years ago on Wrangell Island). Today, the greatest threat to elephants is loss of habitat and poaching for the illegal ivory trade.

 

References:

Cantalapiedra, J.L., Sanisidro, Ó., Zhang, H. et al. The rise and fall of proboscidean ecological diversity. Nat Ecol Evol (2021). https://doi.org/10.1038/s41559-021-01498-w

Gheerbrant, E (2009). “Paleocene emergence of elephant relatives and the rapid radiation of African ungulates”. Proceedings of the National Academy of Sciences of the United States of America. 106 (26): 10717–10721. doi:10.1073/pnas.0900251106.

Shoshani, J. (1998). Understanding proboscidean evolution: a formidable task. Trends in Ecology & Evolution, 13(12), 480–487. doi:10.1016/s0169-5347(98)01491-8 

Body and brain size evolution in genus Homo

 

Neanderthal skull (Image credit: Halamka/Getty Images)

Almost 2 million years ago in East Africa, hominin diversity reached its highest level with the appearance of the robust Paranthropus species, as well as the first specimens attributed to the genus Homo. This period is also marked by a dramatic increases in hominin body and brain size. Several theories have been developed to explain the interaction between African paleoclimate and early hominid evolution. The savannah hypothesis suggested that hominins were forced to descend from the trees and adapted to life on the savannah facilitated by walking erect on two feet. This idea was already outlined by Lamarck in his Philosophie zoologique (1809], where he describes in details how an early ancestor of primeval human abandons an arboreal life to adapt itself to open plains. More recently, the pulsed climate variability hypothesis highlights the role of short periods of extreme climate variability specific to East Africa in driving hominin evolution and subsequent dispersal events.  Now, a new study conducted by an interdisciplinary research team from Cambridge University and Tübingen University tested the influence of environmental factors on the evolution of body and brain size in the genus Homo over the last one million years.

Location and sample size (n) of body (squares) and brain size (triangles) estimates for individual Homo fossils used in the study by Will, M., Krapp, M., Stock, J.T. et al. 2021.

In the study, the team combines data from more than 300 fossils of the genus Homo divided into three taxonomic units: Mid-Pleistocene Homo, Homo neanderthalensis, and Pleistocene Homo sapiens distributed over the Old World. The environmental information for each fossil comes from a climate emulator (GCMET) that takes into account long-term, glacial-interglacial climate variation, caused by changes in the Earth’s orbit around the sun and in greenhouse gases.

The team found that temperature is a major predictor of body size variation, with larger-bodied individuals consistently occurring in colder climates. This increase in body size with decreasing environmental temperature is consistent with the Bergmann’s rule and could be explained because heat is dissipated more slowly in larger animals as the surface-area to volume ratio diminishes, so it would be a thermal advantage in colder habitats. They also found that brain size within Homo is less influenced by temperature suggesting that body and brain size are under different selective pressures.

 

References:

Will, M., Krapp, M., Stock, J.T. et al. Different environmental variables predict body and brain size evolution in Homo. Nat Commun 12, 4116 (2021). https://doi.org/10.1038/s41467-021-24290-7

Maslin M.A., C. Brierley, A. Milner, S. Shultz, M. Trauth, K. Wilson “East African climate pulses and early human evolution” Quaternary Science Reviews (2014). DOI:10.1016/j.quascirev.2014.06.012

Shultz S, Maslin M (2013) Early Human Speciation, Brain Expansion and Dispersal Influenced by African Climate Pulses. PLoS ONE 8(10): e76750. DOI: 10.1371/journal.pone.0076750

The realm of the Tyrant

Close up of “Sue” at the Field Museum of Natural History in Chicago, IL, 2009 (From Wikimedia Commons)

After the extinction of many carnivorous crurotarsan lineages (phytosaurs, ornithosuchids, and rauisuchians) at the Triassic–Jurassic boundary, theropod dinosaurs became the primary large-bodied flesh-eaters in terrestrial ecosystems. The group reached a great taxonomic and morphological diversity during the Jurassic and Early Cretaceous. Some major groups include Ceratosauria, Megalosauroidea, Spinosauridae; Carnosauria, and Coelurosauria. In the last decades, the study of Gondwanan non-avian theropods has been highly prolific, showing that the group reached a great taxonomic and morphological diversity comparable to that of Laurasia. Notwithstanding, there is a qualitative difference between Jurassic and Early Cretaceous assemblages relative to the latest Cretaceous (Campano-Maastrichtian) assemblages with abelisaurids dominating Gondwanan continents, and tyrannosaurids ruling Asiamerican ecosystems. 

Tyrannosaurus rex, the most iconic dinosaur of all time, and its closest relatives known as tyrannosaurids, comprise the clade Tyrannosauroidea, a relatively derived group of theropod dinosaurs, more closely related to birds than to other large theropods such as allosauroids and spinosaurids. The clade originated in the Middle Jurassic, approximately 165 million years ago, and was a dominant component of the dinosaur faunas of the American West shortly after the emplacement of the Western Interior Seaway (about 99.5 Mya). Over the past 20 years, new discoveries from Russia, Mongolia and China helped to build the Tyranosaurs family tree.

Skulls of the basal tyrannosauroids Guanlong (A), Dilong (B); Skulls of juvenile (C) and adult (D)Tyrannosaurus. (Adapted from Brusatte et. al., 2010)

All large-bodied carnivorous theropod dinosaurs passed through a wide range of body sizes. Therefore, the ecological niche of any given individual shifted throughout its lifetime. From the Jurassic through the early Late Cretaceous, this transformation occurred in the context of ecosystems in which the juveniles and subadults potentially competed with other theropod species with medium adult body sizes. But sometime after the Turonian something changed.

A new study by Thomas Holtz, a principal lecturer in the University of Maryland’s Department of Geology, surveyed the record of 60 dinosaur communities from the Jurassic and Cretaceous periods, revealing a drop-off in diversity of medium-sized predator species (50–1000 kg) in communities dominated by tyrannosaurs. On the other hand, the study also showed that the diversity of prey species did not decline. The proposed explanation for this phenomenon is the “tyrannosaurid niche assimilation hypothesis”. In this scheme, juvenile and subadult members of Tyrannosauridae were the functional equivalent of earlier middle-sized theropod carnivores. This absence of other potential mid-sized competitors in Campano-Maastrichtian Asiamerica could be a factor in some evolutionary transformations in Tyrannosauridae such as bite force and agility.

 

References:

Thomas R. Holtz, Theropod guild structure and the tyrannosaurid niche assimilation hypothesis: implications for predatory dinosaur macroecology and ontogeny in later Late Cretaceous Asiamerica, Canadian Journal of Earth Sciences (2021). DOI: 10.1139/cjes-2020-0174

Brusatte SL, Norell MA, Carr TD, Erickson GM, Hutchinson JR, et al. (2010) Tyrannosaur paleobiology: new research on ancient exemplar organisms. Science 329: 1481–1485. doi: 10.1126/science.1193304

Zanno, L., Makovicky, P. Neovenatorid theropods are apex predators in the Late Cretaceous of North America. Nat Commun 4, 2827 (2013). https://doi.org/10.1038/ncomms3827

 

The Herrerasaurian Radiation

Image from Ischigualasto Park (http://www.ischigualasto.gob.ar/)

The Triassic beds of Argentina and Brazil play a key role in the understanding of the origin and early diversification of Dinosauria. The first recorded dinosaurs include some predatory forms, such as the herrerasaurids from the lower Ischigualasto Formation in northwestern Argentina, and the Santa Maria formation in southern Brazil. In 1911, Guillermo Bodenbender briefly refers to the fossils of Ischigualasto, but intensive paleontological study of the Ischigualasto and Chañares Formations began only in the late 1950s. In Brazil, the fossil record of Triassic dinosaurs has greatly expanded since the discovery of Staurikosaurus in 1970.

Herrerasauridae is a basal clade of predatory, obligatorily bipedal dinosaurs recorded from the Upper Triassic of Argentina and Brazil. There are putative records of herrerasaurids from the mid-late Norian strata of Europe, North America, and from the Maleri Formation of India. The Herrerasaurid family includes Staurikosaurus, Gnathovorax, Herrerasaurus, Sanjuansaurus and possibly Frenguellisaurus. Staurikosaurus and Gnathovorax were recovered from the Hyperodapedon Assemblage Zone of the Santa Maria Supersequence in southern Brazil, whilst Herrerasaurus and Sanjuansaurus were collected from the lower levels of the Ischigualasto Formation, and Frenguellisaurus (considered by many authors as a junior synonym of Herrerasaurus) was collected from the upper levels of this unit. 

Skull of Herrerasaurus ischigualastensis (Sereno, 2013)

Herrerasaurus ischigualastensis is one of the best known Triassic dinosaurs and the largest dinosaur of the Ischigualasto Formation. It was described by Osvaldo Reig in 1963. Herrerasaurus was fully bipedal, with strong hind limbs, short thighs and long feet. The skull has a rectangular profile and a transversely narrow snout (Sereno and Novas, 1992). The presence of two sacral vertebrae and lack of brevis fossa made Herrerasaurus, and other herrerasaurids, a controversial group.

Due to this combination of features, including some traits that are nearly exclusive of theropod dinosaurs (e.g., serrated dentition, grasping hands, pubis with distal pubic boot, distal caudal prezygapophyses elongated), with some remarkable plesiomorphic traits (e.g., primitive-looking pelvic girdle and tarsus), the phylogenetic relationships of herrerasaurs are problematic. Some authors suggested that Herrerasauridae may constitute the sister group to Dinosauria, whereas others proposed theropod affinities for the group. Other proposal indicates that herrerasaurids may constitute a non-Eusaurischia branch of Saurischia.

 

The holotype of Daemonosaurus chauliodus (CM 76821). From Sues et al., 2011.

The putative North American herrerasaurs Tawa, Chindesaurus, Caseosaurus and Daemonosaurus, have been recorded from Norian to Rhaetian beds in different fossil sites in southwestern USA. Chindesaurus, from the Petrified Forest National Park in Arizona, shows several features of herrerasaurian affinities, while Tawa shares with Herrerasaurus, Sanjuansaurus and Gnathovorax several derived features that are considered diagnostic for Herrerasauria. These include: dorsoventrally deep jugal; cervical vertebrae with pronounced ventral keel; atrophied metacarpals IV and V; pubic shaft fan-shaped distally, resulting from the posterior flexion of the lateral margin of pubis; and anteroposteriorly expanded pubic boot. Among the features that Daemonosaurus shares with Herrerasauridae are: a dorsoventrally deep premaxilla, jugal dorsoventrally tall, and fang-shaped maxillary teeth.

The presence of herrerasaurs outside South America during the Late Triassic suggests the group was globally dispersed, contrasting with their apparent South America endemism. Furthermore, the recognition of Daemonosaurus as a herrerasaurian provides evidence that this clade survived into the Rhaetian and the group was likely one of the victims of the end-Triassic mass extinction.

References:

Novas, F.E., Agnolin, F.L., Ezcurra, Martí.D., Müller, R.T., Martinelli, Agustì., Langer, M., Review of the fossil record of early dinosaurs from South America, and its phylogenetic implications, Journal of South American Earth Sciences (2021), doi: https://doi.org/10.1016/j.jsames.2021.103341.

Pacheco C, Müller RT, Langer M, Pretto FA, Kerber L, Dias da Silva S. 2019. Gnathovorax cabreirai: a new early dinosaur and the origin and initial radiation of predatory dinosaurs. PeerJ 7:e7963 https://doi.org/10.7717/peerj.7963

Sues, Hans-Dieter, Nesbitt, Sterling J., Berman, David S., and Henrici, Amy C. 2011. “A late-surviving basal theropod dinosaur from the latest Triassic of North America.” Proceedings of the Royal Society B: Biological Sciences 278 (1723):3459– 3464. https://doi.org/10.1098/rspb.2011.0410

Leonardo and the Fossil Whale

Leonardo da Vinci: Self-portrait. From WikimediaCommons.

Leonardo di ser Piero da Vinci was the archetype of the Renaissance Man: artist, architect, musician, mathematician, engineer, inventor, anatomist, naturalist and geologist. A true polymath. He was born on April 15, 1452 in Vinci, a town in the lower valley of the Arno River. The majority of Leonardo’s scientific observations were in the Leicester Codex, a collection of writings from the 16th Century. Several excerpts from the Codex indicate that Leonard uses many ichnological principles that are still valid today.

The Codex Arundel is similar to the Codex Leicester. It was written between 1480 and 1518. In folio 155r, Leonardo recounted an experience in a cave in the Tuscan countryside: “Unable to resist my eager desire and wanting to see the great multitude of the various and strange shapes made by formative nature, and having wandered some distance among gloomy rocks, I came to the entrance of a great cave, in front of which I stood some time, astonished and unaware of such a thing. Bending my back into an arch I rested my tired hand on my knee and held my right hand over my downcast and contracted eyebrows, often bending first one way and then the other, to see whether I could discover anything inside, and this being forbidden by the deep darkness within, and after having remained there some time, two emo-tions arose in me, fear and desire: fear of the threatening dark cave, desire to see whether there were any wondrous thing within it”.

Reproduction of folios 155v (left corner) and 156r (right corner) of the Codex Arundel. From Collareta et al., 2020.

In the next folio, Leonardo described what appears to have been a fossil whale embedded in the walls of a cave:

“O powerful and once-living instrument of formative nature, your great strength of no avail, you must abandon your tranquil life to obey the law which God and time gave to creative nature. Of no avail are your branching, sturdy dorsal fins with which you pursue your prey, plowing your way, tempestuously tearing open the briny waves with your breast.

Oh, how many a time the terrified shoals of dolphins and big tuna fish were seen to flee before your insensate fury, as you lashed with swift, branching fins and forked tail, creating in the sea, mist and sudden tempest that buffeted and submerged ships…

O Time, swift despoiler of created things, how many kings, how many peoples have you undone? How many changes of state and circumstances have followed since thewondrous form of this fish died here in this winding and cavernous recess? Now unmade by time you lie patiently in this closed place with bones stripped and bare, serving as an armature for the mountain placed over you.”

Tuscan Pliocene fossil mysticetes: (a) ʽPelocetus sp.’ from Le Colombaie, near Volterra (original field sketch by G. Capellini, 1879); (b) Idiocetus guicciardinii from Montopoli (osteoanatomical plate reproduced after Capellini 1905). From Collareta et al., 2020.

In the folio 715r of the Codex Atlanticus, Leonardo described the same animal as ‘setoluto’, i.e. pro-vided with bristles – an observation that strongly evokes the presence of baleen, and as such, a positive identification of the ʽmarine monster’ with a baleen whale. A recent study suggests that Leonardo saw a fossil whale and recognised it as such, but the encounter was most likely along the flank of a hill, where cetacean remains from the Tuscan Pliocene are relatively common. Leonardo also made taphonomic observations on it and inferred that a considerable amount of time must have passed from the death of the whale in the marine realm to allow for its eventual discovery on land.

Leonardo’s legacy is extraordinary and his contributions to historical geology and ichnology are of special relevance. He wrote about the original horizontal arrangement of strata before Nicola Steno’s seminal work. He also provided the first organic observations on concepts such as actualism, taphonomy, and palaeocological inference. But because he never received a formal education in Latin or Mathematics, his writings were ignored by the scholars of the time. Five centuries after his death, Leonardo still surprises us.

References:

Collareta, A., Collareta, M., Berta, A., & Bianucci, G. (2020). On Leonardo and a fossil whale: a reappraisal with implications for the early history of palaeontology, Historical Biology, DOI: 10.1080/08912963.2020.1787403.

Etheridge, Kay. “Leonardo and the Whale.” In Leonardo da Vinci – Nature and Architecture,edited by C. Moffat and S.Taglialagamba, 89-106. Leiden: Brill, 2019.