On This Side of Paradise.

Stardate 3417.3. The Enterprise has arrived to the planet Omicron Ceti III to catalog the destruction suffered by an agricultural colony stablished in 2264. It was assumed that the colonists are dead because the planet was bathed in Berthold rays, a lethal form of radiation. Although there was no sign of animal life on the planet, the colonists were found alive and in excellent health. Mr. Spock, intrigued about the survival of the colony, is conducted by Leila Kalomi, a botanist he had met six years prior on Earth, to a field with very strange flowers which expelled some spores into his face. Spock begun to feel sick, and after a brief agonizing struggle, he smiled and confessed his love for Leila. Like Spock, all the members of the Enterprise that were exposed to the spores changed their behavior. The only one who resisted the effect of the spores was Captain Kirk.

Spock with Leila Kalomi (Image: CBS)

The key elements for the colony survival were the spores. The term ‘spores’ derived from the Greek word for seed. In a broad sense, spores are the reproductive structures of bacteria, fungi, algae, protists and land plants, adapted for dispersion and surviving for extended periods of time during unfavorable conditions.

The colonization of land by vascular plants in the Paleozoic was one of the most significant events in Earth’s history. We could hypothesize that terrestrial colonization was not possible prior to the evolution of the sporopollenin spore wall, and this adaptation is considered to be a synapomorphy of the embryophytes. Sporopollenin is the major component of the spore (and pollen) wall. This highly resistant biopolymer occurs in certain charophyceans, but is located in an inner layer of the zygote wall.

Cryptospores from the Early Middle Ordovician of Argentina (From Rubinstein et al., 2010)

Like their algal ancestors, all plant life cycle goes through both haploid (gametophyte) and diploid (sporophyte) stages. In vascular plants, the sporophyte generation predominates. The sporophyte produces the spores, which contain only a single copy of the chromosomes. The earliest dispersed spores attributable to terrestrial plants, termed cryptospores, are known from the Middle Ordovician. Cryptospores are believed to have been produced by bryophyte-like plants, but recently, they were interpreted as the product of a diverse group of mostly extinct plants, whose precise affinities to living clades remain unclear.

C. barrandei sp. nov., from Czech Republic (scale bar, 10 mm). From Libertín et al., 2018.

The description of Cooksonia barrandei (432 my, Czech Republic) shed light on the origins of the alternation of generations in land plants. The genus Cooksonia (named in honor of Isabel Cookson) is generally accepted as the oldest land plant, with a broad distribution in the Late Silurian and Early Devonian periods, including North America, North Africa, Europe, Asia and South America. Cooksonia barrandei (the species name is honoring Joachim Barrande, a famous French palaeontologist who lived in Prague), and is five million years older than the oldest previously described cooksonioids (427 mya). The plants were isosporous (produced only one kind of spore) and of small size, with a bent, isotomously branched axis with terminal branches completely preserved.

Star Trek has been a cult phenomenon for decades. The Original Series premiered on September 8, 1966, and has spawned five successor shows starting in the 1980s and several feature films , comic books, novels and an animated series. Star Trek also influenced generations of viewers about advanced science and engineering. “This side of Paradise” remains as one of the best episode of Star Trek. It was premiered on March 2, 1967. The title was taken by the final line of the poem “Tiare Tahiti” by Rupert Brooke: “Well this side of Paradise! …. There’s little comfort in the wise.”

References:

Libertín, Milan; Kvaček, Jiří; Bek, Jiří; Žárský, Viktor & Štorch, Petr (2018), “Sporophytes of polysporangiate land plants from the early Silurian period may have been photosynthetically autonomous”, Nature Plants, 4 (5): 269–271, doi:10.1038/s41477-018-0140-y

Rubinstein, C. V., Gerrienne, P., de la Puente, G. S., Astini, R. A., & Steemans, P. (2010). Early Middle Ordovician evidence for land plants in Argentina (eastern Gondwana). New Phytologist, 188(2), 365–369. doi:10.1111/j.1469-8137.2010.03433.x 

 

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A very short history of Dinosaurs.

Evolutionary relationships of dinosaurs. From Benton 2018.

On 20 February 1824, William Buckland published the first report of a large carnivore animal: the Megalosaurus. The description was based on specimens in the Ashmolean Museum, in the collection of Gideon Algernon Mantell of Lewes in Sussex, and a sacrum donated by Henry Warburton (1784–1858). One year later, the Iguanodon entered in the books of History followed by the description of Hylaeosaurus in 1833. After examined the anatomy of these three genera, Richard Owen erected the clade Dinosauria in 1842.

Dinosaurs likely originated in the Early to Middle Triassic. The closest evolutionary relatives of dinosaurs include flying pterosaurs and herbivorous silesaurids. Early ecological divergences in dinosaur evolution are signaled by disparity in dental morphology, which indicates carnivory in early theropods, herbivory in ornithischians, and omnivory in sauropodomorph (subsequently sauropodomorphs underwent a transition to herbivory).

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

The oldest dinosaurs remains are from the late Carnian (230 Ma) of the lower Ischigualasto Formation in northwestern Argentina. Similarly, the Santa Maria and Caturrita formations in southern Brazil preserve basal dinosauromorphs, basal saurischians, and early sauropodomorphs. In North America, the oldest dated occurrences of vertebrate assemblages with dinosaurs are from the Chinle Formation. Two further early dinosaur-bearing formations, are the lower (and upper) Maleri Formation of India and the Pebbly Arkose Formation of Zimbabwe. These skeletal records of early dinosaurs document a time when they were not numerically abundant, and they were still of modest size.

During the Late Triassic period numerous extinctions, diversifications and faunal radiations changed the ecosystems dynamics throughout the world. Nevertheless, dinosaurs exhibited high rates of survival. According to the competitive model, the success of dinosaurs was explained in terms of their upright posture, predatory skills, or warm-bloodedness. In the opportunistic model, dinosaurs emerged in the late Carnian or early Norian, and then diversified explosively. The current model contains some aspects of both the classic competition model and the opportunistic model. In this model, the crurotarsan-dominated faunas were replaced by a gradual process probably accelerated by the ecological perturbation of the CPE (Carnian Pluvial Episode).

Ingentia prima outcropping from the soil.

In the Jurassic and Cretaceous dinosaurs achieved enormous disparity. Sauropodomorphs achieved a worldwide distribution and become more graviportal and increased their body size. Gigantism in this group has been proposed as the result of a complex interplay of anatomical, physiological and reproductive intrinsic traits. For example, the upright position of the limbs has been highlighted as a major feature of the sauropodomorph bauplan considered an adaptation to gigantism. However, the discovery of Ingentia prima, from the Late Triassic of Argentina, indicates that this feature was not strictly necessary for the acquisition of gigantic body size.

Ornithischian were primitively bipedal, but reverted to quadrupedality on at least three occasions: in Ceratopsia, Thyreophora and Hadrosauriformes. The presence of early armored dinosaurs (thyreophorans) in North America, Asia, and Europe, but their absent from the southern African record, suggests some degree of provinciality in early ornithischian faunas.

Archaeopteryx lithographica, specimen displayed at the Museum für Naturkunde in Berlin. (From Wikimedia Commons)

Theropod dinosaurs also increased their diversity and exhibit a greater range of morphological disparity. The group underwent multiple parallel increases in brain size. The volumetric expansion of the avian endocranium began relatively early in theropod evolution. For instance, the endocranium of Archaeopteryx lithographica is volumetrically intermediate between those of more basal theropods and crown birds. The digital brain cast of Archaeopteryx also present an indentation that could be from the wulst, a neurological structure present in living birds used in information processing and motor control with two primary inputs: somatosensory and visual. The extensive skeletal pneumaticity in theropods such as Majungasaurus demonstrates that a complex air-sac system and birdlike respiration evolved in birds’ theropod ancestors. Anatomical features like aspects of egg shape, ornamentation, microstructure, and porosity of living birds trace their origin to the maniraptoran theropods, such as oviraptorosaurs and troodontids. In addition, some preserving brooding postures, are known for four oviraptorosaurs, two troodontids, a dromaeosaur, and one basal bird providing clear evidence for parental care of eggs.

Nonavian dinosaurs disappeared more or less abruptly at the end of the Cretaceous (66 mya). Birds, the only living dinosaurs, with more than 10,500 living species are the most species-rich class of tetrapod vertebrates.

 

References:

Benson, R. B. J. (2018). Dinosaur Macroevolution and Macroecology. Annual Review of Ecology, Evolution, and Systematics, 49(1).  doi:10.1146/annurev-ecolsys-110617-062231

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

Xing Xu, Zhonghe Zhou, Robert Dudley, Susan Mackem, Cheng-Ming Chuong, Gregory M. Erickson, David J. Varricchio, An integrative approach to understanding bird origins, Science, Vol. 346 no. 6215, DOI: 10.1126/science.1253293.

 

Introducing Caelestiventus hanseni.

A 3D printed model of Caelestiventus skull.

Pterosaurs were the first flying vertebrates appearing initially in Late Triassic. 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. Therefore, Triassic pterosaurs are extraordinarily rare and consists of fewer than 30 specimens, including single bones. With the single exception of Arcticodactylus cromptonellus from fluvial deposits in Greenland, the other specimens are known from marine strata in the Alps.

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.

a, Schematic silhouette of a dimorphodontid pterosaur in dorsal view. b, Preserved skull and mandible elements of C. hanseni. From Brooks B. Britt et al., 2018.

Caelestiventus hanseni, from the Upper Triassic of North America, is the oldest pterosaur ever discovered, and it predates all known desert pterosaurs by more than 65 million years. The generic name comes from the Latin language: caelestis, ‘heavenly or divine’, and ventus, ‘wind’. The species name, ‘hanseni’, honors Robin L. Hansen, a geologist, who facilitated work at the Saints & Sinners Quarry.

The holotype, BYU 20707, includes the left maxilla fused with the jugal, the right maxilla, the right nasal, the fused frontoparietals, the right and left mandibular rami, the right terminal wing phalanx and three fragments of indeterminate bones. The maxilla, jugal, frontoparietal, and mandibular rami of the specimen are pneumatic. The unfused skull and mandibular elements suggest that BYU 20707 was skeletally immature or had indeterminate growth. Based on the relationship between the length of the terminal wing phalanges and wing span in other non-pterodactyloid pterosaurs the new taxon would have a wing span greater than 1.5 m.

The holotype specimen of Dimorphodon macronyx found by Mary Anning in 1828 (From Wikimedia Commons)

Caelestiventus hanseni is placed as sister taxon to Dimorphodon macronyx. Both share the following derived features: a ventral blade along the dentary that forms a rostral keel and becomes a flange distally; a diastema between the second large mandibular tooth and the following smaller teeth; the overall morphology of the maxilla; the shape of the external naris and antorbital fenestra; the external naris by far the largest skull opening; the orbit smaller than the antorbital fenestra; and teeth with bicuspid apices. But despite their morphological similarity, C. hanseni and D. macronyx lived in very different environments. Dimorphodon, discovered by Mary Anning, was an island dweller in a humid climate and was preserved in the marine Blue Lias of southern England.

The significance of C. hanseni lies in its exceptional state of preservation, and its close phylogenetic relationship with Dimorphodon macronyx, indicating that dimorphodontids originated by the Late Triassic and survived the end-Triassic extinction event.

 

References:

Brooks B. Britt et al. Caelestiventus hanseni gen. et sp. nov. extends the desert-dwelling pterosaur record back 65 million years, Nature Ecology & Evolution (2018). DOI: 10.1038/s41559-018-0627-y

Learning from Past Climate Changes

In the last 540 million years, five mass extinction events shaped the history of the Earth. Those events were related to extreme climatic changes and were mainly caused by asteroid impacts, massive volcanic eruption, or the combination of both.  On a global scale the main forces behind climatic change are: solar forcing, atmospheric composition, plate tectonics, Earth’s biota, and of course, us. Human activity is a major driver of the dynamics of Earth system. From hunter-gatherer and agricultural communities to the highly technological societies of the 21st century, humans have driven the climate Earth system towards new, hotter climatic conditions. Until the Industrial Revolution, the average global CO2 levels fluctuated between about 170 ppm and 280 ppm. But with the beginning of the Industrial Era, that number risen above 300 ppm, currently averaging an increase of more than 2 ppm per year. The average monthly level of CO2 in the atmosphere in last April exceeded the 410 ppm for first time in history. Thus we could hit an average of 500 ppm within the next 45 years, a number that has been unprecedented for the past 50–100+ million years according to fossil plant-based CO2 estimates. This current human-driven change far exceed the rates of change driven by geophysical or biosphere forces that have altered the Earth System trajectory in the past, and it poses severe risks for health, economies and political stability. Learning from past climatic changes is critical to our future.

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

Microfossils from deep-sea are crucial elements for the understanding of our past and present oceans. Their skeletons take up chemical signals from the sea water, in particular isotopes of oxygen and carbon. Over millions of years, these skeletons accumulate in the deep ocean to become a major component of biogenic deep-sea sediments. The importance of microfossils as tool for paleoclimate reconstruction was recognized early in the history of 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.

Diatoms and radiolarians are susceptible to different set of dissolution parameters than calcareous fossils, resulting in a different distribution pattern at the sea floor and have been used for temperature estimates in the Pacific and in the Antarctic Oceans, especially where calcareous fossils are less abundant. Diatom assemblages are also used in reconstructions of paleoproductivity.

Scanning electron microscope image of different types of pollen grains. Image from Wikipedia.

Pollen and other palynomorphs proved to be an extraordinary tool to paleoenvironmental reconstruction too. Pollen analysis involves the quantitative examination of spores and pollen at successive horizons through a core, specially in lake, marsh or delta sediments, especially in Quaternary sediments where the parent plants are well known. This provide information on regional changes in vegetation through time, and it’s also a valuable tool for archaeologists because it gives clues about man’s early environment and his effect upon it.

Stomatal frequency of land plants, which has been shown in some species to vary inversely with atmospheric pCO2, has been used to estimate paleo-pCO2 for multiple geological time periods. Stomata are the controlled pores through which plants exchange gases with their environments, and play a key role in regulating the balance between photosynthetic productivity and water loss through transpiration.

Temple I on The Great Plaza and North Acropolis seen from Temple II in Tikal, Guatemala. From Wikimedia Commons

Paleoecological records indicate that the transition to agriculture was a fundamental turning point in the environmental history of Mesoamerica. Tropical forests were reduced by agricultural expansion associated with growing human populations. Also soil loss associated with deforestation and erosion was one of the most consequential environmental impacts associated with population expansion in the Maya lowlands. This environmental crisis ended with the collapse of the Classic Maya society.

Human activity has significantly altered the climate in less than a century. Since 1970 the global average temperature has been rising at a rate of 1.7°C per century, and the rise in global CO2 concentration since 2000 is 10 times faster than any sustained rise in CO2 during the past 800,000 years. Today the most politically unstable countries are also places where environmental degradation affected food production and water supply. Other human societies have succumbed to climate change – like the Akkadians – while others have survived by changing their behavior in response to environmental change. We have the opportunity to protect the future of our own society by learning from the mistakes of our ancestors.

References:

David Evans, Navjit Sagoo, Willem Renema, Laura J. Cotton, Wolfgang Müller, Jonathan A. Todd, Pratul Kumar Saraswati, Peter Stassen, Martin Ziegler, Paul N. Pearson, Paul J. Valdes, Hagit P. Affek. Eocene greenhouse climate revealed by coupled clumped isotope-Mg/Ca thermometry. Proceedings of the National Academy of Sciences, 2018; 201714744 DOI: 10.1073/pnas.1714744115

Nicholas P. Evans et al., Quantification of drought during the collapse of the classic Maya civilization, Science (2018); DOI: 10.1126/science.aas9871 

Will Steffen, et al.; Trajectories of the Earth System in the Anthropocene; PNAS (2018) DOI: 10.1073/pnas.1810141115