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.

Forgotten women of Paleontology: Maria Pavlova

María Pávlova (1854-1938). From Wikimedia Commons

The first half of the 1860s was an extraordinary time in Russian history. After the Crimean War Tsar Alexander II took  steps to set the Russian Empire on the path of modernization. In 1868, Russian feminists submitted a request to the rector of the St. Petersburg University to open higher women’s course. The rector agreed, but the Minister of Education demoted the status of the courses to “public lectures”. A year later, Julia Lermontova and Sofia Kovalevskaya obtained permission to attend classes at Heidelberg University in Germany. Only in 1876, Alexander II authorized the creation of higher women’s courses with the same curricula as men’s universities. Finally, the University Courses for women opened on October 2, 1878 in St. Petersburg. Historian K. N. Bestuzhev-Rumin was appointed the first director of the courses (in his honor the courses were unofficially called “Bestuzhev’s”).

Maria Vasillievna Pavlova, nee Gortynskaia, was the first Russian woman to achieve significant national and international success in vertebrate paleontology. She was born in Ukraine in 1854. Her father was a state provincial doctor who encouraged her to study science. In 1870, she graduated from the Kiev Institute of Noble Maidens. Three years later she married a rural doctor N.N. Illich-Shishatsky. In the summer of 1880, after the death of her husband she traveled to Paris to attend classes at the Sorbonne. She studied zoology, botany, geology, and paleontology under the guidance of Albert Gaudry, receiving the grade of specialist in paleontology in 1884. She later worked in the Paris Museúm d’historie naturelle. In 1886 she married with the young geologist A.P. Pavlov and returned to Russia. At the request of her husband, Maria was allowed to put in order the paleontological collection of the Geological Cabinet of Moscow University, where she worked for more than 30 years.

M.V. Pavlova at her desk at the Paleontological Museum of Moscow State University. 1920s. From Bessudnova and Lyubina, 2019.

Her first scientific work was a description of the ammonites collected by Pavlov in the Volga region but all of her subsequent research focused on vertebrate fossils. She studied the fossil fauna of the Novaya Zemlya islands, and the “hipparion fauna” of the southwestern regions of European Russia. In 1897 she was one of only two women invited to join the Organizing Committee and presentations of the International Geological Congress (IGC) held in St. Petersburg. Between 1887-1906 the nine issues of her celebrated Studies in the Paleontological History of Hoofed Animals were published. Later she published her monograph Les éléphants fossils de la Russie, followed by her two-volume of Mammifères tertiaires de la nouvelle Russie, co-authored with Aleksei Pavlov. Maria often acquired material for her research from private individuals and exchanged casts of fossil animals with famous foreign paleontologists and museum curators.

In order to introduce paleontology to a wider audience, Maria translated into Russian Henry Neville Hutchinson’s Extinct Monsters and Melchior Neumayer’s Die Stämme des Tierreichs. In 1910, Pavlova was invited to head the department of paleontology at Moscow University. It was the first experience of systematic teaching of paleontology in Moscow. In 1925 she was elected a corresponding member of the Russian Academy of Sciences (in the same year it was renamed into the Academy of Sciences of the USSR). In 1926, the Geological Society of France awarded the Pavlovs with the gold medal  for their geological and paleontological works. She went on her last geological expedition in 1931, to the Volyn district, near Khvalynsk, a place of a mass accumulation of bones of fossil mammoths, elephants and rhinos.

She died on December 23, 1938.

 

References:

Valkova, O. (2008). The Conquest of Science: Women and Science in Russia, 1860–1940. Osiris, 23(1), 136–165. doi:10.1086/591872

Bessudnova Z.A., Lyubina G.I. Main lady of russian paleontology. To the 165th anniversary of the honorary academician Maria V. Pavlova. // Вестник Российской академии наук. – 2019. – Vol. 89. – N. 6. – P. 621-628. doi: 10.31857/S0869-5873896621-628

 

Introducing Llukalkan aliocranianus

Photograph of the materials in the field. Image credit: Federico Gianechini

The Abelisauridae represents the best-known carnivorous dinosaur group from Gondwana. Their fossil remains have been recovered in Argentina, Brazil, Morocco, Niger, Libya, Madagascar, India, and France. The group was erected by Jose Bonaparte with the description of  Abelisaurus Comahuensis. These theropods exhibit spectacular cranial ornamentation in the form of horns and spikes and strongly reduced forelimbs and hands. The Argentinean record of abelisauroid theropods begins in the Middle Jurassic (Eoabelisaurus mefi) and spans most of the Late Cretaceous. The clade includes Carnotaurus sastrei, Abelisaurus comahuensis, Aucasaurus garridoi, Ekrixinatosaurus novasi, Skorpiovenator bustingorryi, Tralkasaurus cuyi and Viavenator exxoni. Llukalkan aliocranianus, a new furileusaurian abelisaurid from the Bajo de la Carpa Formation (Santonian) in northwestern Patagonia, is an important addition to the knowledge of abelisaurid diversity.

 

Reconstruction of the complete skull and mandible of Llukalkan aliocranianus. Scale bar: 5 cm. From Gianechini et al., 2021

The new specimen was found near the site where the remains of Viavenator exxoni were recovered at La Invernada fossil area, 50 km southwest of Rincón de los Sauces city, Neuquén province, Argentina. This site has provided a valuable theropod record. Other taxa discovered at La Invernada include the titanosaurian sauropods Bonitasaura salgadoi, Traukutitan eocaudata, and Rinconsaurus caudamirus, pterosaurs, multiple crocodyliforms, snakes, and turtles.

The holotype (MAU-Pv-LI-581) is an incomplete but partially articulated skull with a complete braincase. The generic name derived from the word Llukalkan, “one who scares or causes fear” in Mapudungun language. The specific name aliocranianus means “different skull” in Latin.  Llukalkan exhibits some similarities with Viavenator, that include: elongate and robust olfactory tracts; large and horizontally oriented olfactory bulbs; cerebral hemispheres clearly delimited in lateral view; a tongue-shaped floccular process of cerebellum posteriorly projected and reaching the level of the posterior semicircular canal; and elongate and ventrally projected passage for the rostral middle cerebral vein. Additionally, Llukalkan has a small pneumatic recess caudal to the columellar recess, which is identified as a poorly developed caudal tympanic recess. This taxon also presents a T-shaped lacrimal with jugal ramus lacking a suborbital process, that differs significantly from the lacrimal of other abelisaurids.

 

References:

Federico A. Gianechini, Ariel H. Méndez, Leonardo S. Filippi, Ariana Paulina-Carabajal, Rubén D. Juárez-Valieri & Alberto C. Garrido (2021): A New Furileusaurian Abelisauridfrom La Invernada (Upper Cretaceous, Santonian, Bajo De La Carpa Formation), NorthernPatagonia, Argentina, Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2020.1877151

Introducing Ninjatitan zapatai, the earliest known titanosaur

Anterior caudal vertebra of Ninjatitan zapatai. Scale bar equals 10 cm. From Gallina et al., 2021

Titanosauria is the most diverse sauropod clade represented by nearly 80 genera described worldwide, the vast majority of which were recovered from Upper Cretaceous sediments of Argentina. It has been suggested that the titanosaurian origin took place around 135 million years ago in South America. The study of this diverse group of large, long-necked, herbivorous dinosaurs embrace an extensive list of important contributions, which started with Richard Lydekker’s pioneering work on Patagonian dinosaurs.

The discovery of Ninjatitan zapatai, a new specimen from the Lower Cretaceous Bajada Colorada Formation (Berriasian–Valanginian) of north Patagonia, supports the hypothesis that the group was already established in the Southern Hemisphere and reinforces the idea of a Gondwanan origin for Titanosauria. Ninjatitan lived 140 million years ago and reached 20 meters in length (65 feet). The firs remains were discovered in 2014 by technician Jonatan Aroca. The holotype (MMCh-Pv228) includes an incomplete anterior–middle dorsal vertebra, a middle dorsal centrum, and anterior caudal centra with the base of neural arches preserved, a complete left scapula, a fragmentary distal femur, and a nearly complete left fibula of a single individual. The generic name honors the Argentine paleontologist Sebastián “Ninja” Apesteguía. The species name refers to Mr. Rogelio “Mupi” Zapata, in recognition for his work as a technician of the Museo Municipal Ernesto Bachman.

Left scapula of Ninjatitan zapatai. Scale bar equals 10 cm. From Gallina et al., 2021.

Despite the fragmentary nature of the new taxon, three derived characters of Ninjatitan support its possition within the clade Titanosauria: 1) presence of procoelous anterior caudal centra; 2) pneumatized neural arch of anterior caudal vertebrae; and 3) position of the acromial process near the glenoid level. The position of Ninjatitan, as a basal titanosaur, extends the origin of this clade by at least 10 Myr.

The Berriasian–Valanginian Bajada Colorada Formation of Neuquén Province, Patagonia Argentina, has provided novel information in the last years that helps to elucidate the evolutionary history of different sauropod lineages. The first sauropod taxon recognized from this unit was the diplodocid Leinkupal laticauda. The second taxon is the recently described dicraeosaurid Bajadasaurus pronuspinax.

References:

Pablo Ariel Gallina, Juan Ignacio Canale, & José Luis Carballido (2021).The earliest known titanosaur sauropod dinosaur. Ameghiniana58(1), 35–51 http://dx.doi.org/10.5710/AMGH.20.08.2020.3376

Sander PM, Christian A, Clauss M, et al. Biology of the sauropod dinosaurs: the evolution of gigantism. Biol Rev Camb Philos Soc. 2011;86(1):117-155. doi:10.1111/j.1469-185X.2010.00137.x

Rewriting the Mammoth Family Tree

Mammuthus primigenius, Royal British Columbia Museum. From Wikipedia Commons

From Siberia to Alaska, mammoths were widespread in the northern hemisphere during the Last Ice Age and their remains inspired all types of legends. Their lineage arose in Africa during the late Miocene, and first appeared in Europe almost three million years ago. Eventually they dispersed to North America via Beringia, during the Middle Pliocene to Early Pleistocene. Their evolution during the Pleistocene is usually presented as a succession of chronologically overlapping species. M. meridionalis (southern mammoths) arose about 2–1.7 million years ago and was replaced by M. trogontherii (steppe mammoths), which evolved in eastern Asia around 2–1.5 million years ago. Although the relationship among these taxa are uncertain, the prevailing view is that M. columbi (Columbian mammoths) must have arisen from M. trogontheri, which must also be the ancestor of the earliest known examples of M. primigenius (woolly mammoths). A new study by an international team of paleontologists and geneticists offers a glimpse into the origin and evolution of woolly and Columbian mammoth. They used genomic data more than one million years old. So far, the oldest genomic data recovered were from a horse specimen dated to 780–560 thousand years ago.

The researchers recovered genome data from three Early-Middle Pleistocene mammoth molars preserved in Siberian permafrost. The samples were recovered by the late Andrei Sher (Russian Academy of Sciences, Moscow) from the well-documented Olyorian Suite of northeastern Siberia in the 1970s. The first specimen (referred to as ‘Krestovka‘) is morphologically similar to the steppe mammoth (originally defined from the Middle Pleistocene of Europe). It was discovered in 1973 in a cliff exposure along the right side of the Krestovka River. The second specimen (referred to as ‘Adycha’) was recovered in 1976 from a gravel bar in the Adycha River and shows M. trogontherii-like morphology. The third specimen (referred to as ‘Chukochya’) was found in 1971 in a riverbank on the right side of the Bolshaya Chukochya River, and has a morphology consistent with an early form of woolly mammot.

Krestovka specimen showing measurement positions: W = crown width, H = crown height, LL = lamellar length, ET = enamel thickness. From van der Valk et al, 2021

 

Analysis of the DNA suggested that two evolutionary lineages of mammoths inhabited eastern Siberia during the later stages of the Early Pleistocene. One of these lineages is represented by the Krestovka specimen (dated 1.65 Ma), and the second lineage comprises the Adycha specimen (dated 1.3 Ma) along with all Middle and Late Pleistocene woolly mammoths. The results also indicate that the Columbian mammoth is a product of admixture between woolly mammoths and a previously unrecognized ancient mammoth lineage, represented by the Krestovka specimen. This hybridization event took place around 420,000 years ago. The new findings indicate that before the hybridization event North American mammoths belonged to the Krestovka lineage. Previously, a DNA study of the complete mitochondrial genome of Columbian mammoths suggested that interbreeding between late Pleistocene taxa could serve as an indicator of major ecological events, including those surrounding the megafaunal extinctions.

The iconic woolly mammoth evolved into a cold-tolerant, open-habitat specialist through a series of adaptive changes like hair growth, and white and brown fat deposits. The study found that the genes related to these features were present in both the Adycha (87%) and Chukochya (89%) genomes. The findings are suported by the tooth shape of all these northern species that is adapted to grazing   in a cold, open environment.

 

References:

van der Valk, T., Pečnerová, P., Díez-del-Molino, D. et al. Million-year-old DNA sheds light on the genomic history of mammoths. Nature (2021). https://doi.org/10.1038/s41586-021-03224-9

Laura Arppe, Juha A. Karhu, Sergey Vartanyan, Dorothée G. Drucker, Heli Etu-Sihvola, Hervé Bocherens. Thriving or surviving? The isotopic record of the Wrangel Island woolly mammoth population. Quaternary Science Reviews, 2019; 222: 105884 DOI: 10.1016/j.quascirev.2019.105884

Enk, J.; Devault, A.; Widga, C.; Saunders, J.; Szpak, P.; Southon, J.; Rouillard, J. M.; Shapiro, B.; Golding, G. B.; Zazula, G.; Froese, D.; Fisher, D. C.; MacPhee, R. D. E.; Poinar, H. (2016). “Mammuthus population dynamics in Late Pleistocene North America: divergence, phylogeography, and introgression”. Frontiers in Ecology and Evolution. 4. doi:10.3389/fevo.2016.00042.

Enk, J., Devault, A., Debruyne, R. et al. Complete Columbian mammoth mitogenome suggests interbreeding with woolly mammoths. Genome Biol 12, R51 (2011). https://doi.org/10.1186

 

The Middle Eocene Climatic Optimum and the Patagonian floras.

Spore-pollen species from the Eocene of southern South America. From Fernandez et al., 2021

The geological records show that large and rapid global warming events occurred repeatedly during the course of Earth history. Ecological models can predict how biodiversity is affected by those events, but only the fossil record provides empirical evidence about the impact of rising temperatures and atmospheric CO2 on species diversity.

The Middle Eocene Climatic Optimum (MECO, ~40 Ma) was a transient period of global warming that interrupted the general cooling trend initiated at the end of the early Eocene climate optimum (EECO, ~49 Ma). The MECO is related to major oceanographic and climatic changes in the Neo-Tethys and also in other oceanic basins, and lasted about 500–600 Kyr. The MECO altered the pelagic ecosystem with repercussions on the food web structure. The lack of nutrients in the surface waters led to a significant decrease in planktonic foraminiferal accumulation rates, while autotroph nannoplankton accumulation rates remained stable.

Relative frequency of the most common plant groups across the MECO and Late Eocene. From Fernández et al., 2021

The MECO also influenced terrestrial biotas. A new study quantify the response of the floras of southern Patagonia to this warming event. The samples were collected from the Río Turbio Formation in southern Patagonia. The terrestrial palynological assemblage revealed a clear inverse relationship between the abundance of ferns and angiosperms. At the beginning of the MECO, ferns highly increase in abundance (with Cyatheaceae, Dicksoniaceae, and Osmundaceae as the most frequent families), while the abundance of angiosperms decreases dramatically. Podocarpaceae also increases from ~5 % to ~20%. At the core of MECO, ferns drop to a minimum, and angiosperms become dominant. Finally, at the end of the MECO ferns rise again to maximum values and angiosperms decrease.

Palynological analysis also revealed that floras in southern Patagonia were in average ~40% more diverse during the MECO than pre-MECO and post-MECO intervals. The penetration of neotropical migrant species to the highest latitudes along with the persistence of southern Gondwanan natives may have triggered the gradual increasing diversity that can be observed across the MECO.

 

References:

Fernández, D.A., Palazzesi, L., González Estebenet, M.S. et al. Impact of mid Eocene greenhouse warming on America’s southernmost floras. Commun Biol 4, 176 (2021). https://doi.org/10.1038/s42003-021-01701-5

Giorgioni, M., Jovane, L., Rego, E.S. et al. Carbon cycle instability and orbital forcing during the Middle Eocene Climatic Optimum. Sci Rep 9, 9357 (2019). https://doi.org/10.1038/s41598-019-45763-

Sonal Khanolkar, Pratul Kumar Saraswati & Karyne Rogers (2017) Ecology of foraminifera during the middle Eocene climatic optimum in Kutch, India, Geodinamica Acta, 29:2,181-193, DOI: 10.1080/09853111.2017.130084