The Evolution of the Avian Brain after the K-Pg mass extinction.

Ernst Haeckel – Kunstformen der Natur (1904), plate 99: Trochilidae .

Birds are extraordinarily intelligent. Studies have shown that corvids and some parrots are capable of cognitive achievement comparable to those of great apes. They manufacture and use tools, solve puzzles, and plan for future needs. Futhermore, they share with humans and a few other animal groups a rare capacity for vocal learning. Previous studies have shown that bird brains have more neurons than mammalian brains and have very high neuronal densities.

Birds and mammals have undergone remarkable encephalization, in which brain size has increased without corresponding changes in body size. Brain size has been correlated with major evolutionary innovations like cognition, flight, environmental adaptability and enhanced sensory capabilities. But the early evolutionary history of the hyperinflated brain that distinguishes birds from other living reptiles remains elusive. Using a large dataset comprising more than 2,000 birds and non-avian dinosaurs, a team of scientist lead by Daniel Ksepka reconstructed part of that story. Their results indicate that the avian brain size was profoundly impacted by the K-Pg mass extinction event.

Avian Brain-Body Size Evolution. From Ksepka et al., 2020.

The earliest diversification of extant birds (Neornithes) occurred during the Cretaceous period and after the mass extinction event at the Cretaceous-Paleogene (K-Pg) boundary, the Neoaves, the most diverse avian clade, suffered a rapid global expansion and radiation. Today, with more than 10500 living species, birds are the most species-rich class of tetrapod vertebrates.

The new findings reveal at least seven brain-body scaling events in birds right after the mass extinction event. The initial shift in the expansive neoavian radiation appears to have been driven by larger brains and smaller bodies, since the evolution of large brains provide a buffer against frequent or unexpected environmental changes via enhanced capacity for flexible behavioral responses. Birds only reached their apex in relative brain size during the Neogene when crown corvids and crown parrot radiated. Song-birds (including corvids), and hummingbirds (Trochilidae) are the only major groups of birds known to be capable of vocal learning, an ability controlled by additional brain pathways not found in other birds.

 

References:

Ksepka et al., Tempo and Pattern of Avian Brain Size Evolution, Current Biology (2020), https://doi.org/10.1016/j.cub.2020.03.060

Kabadayi, C., & Osvath, M. (2017). Ravens parallel great apes in flexible planning for tool-use and bartering. Science, 357(6347), 202–204. doi:10.1126/science.aam8138 

Lee, M.S.Y., Cau, A., Naish, D., and Dyke, G.J. (2014). Dinosaur evolution.Sustained miniaturization and anatomical innovation in the dinosaurian an-cestors of birds. Science345, 562–566 DOI: 10.1126/science.1252243

 

The end-Triassic extinction: A tale of Death and Global Warming.

A basaltic lava flow section from the Middle Atlas, Morocco. From Wikimedia Commons.

For the last 540 million years, five mass extinction events shaped the history of the Earth. The End-Triassic Extinction (ETE) is typically attributed to climate change associated with degassing of basalt flows from the central Atlantic magmatic province (CAMP) emplaced during the initial rifting of Pangea. Most mammal-like reptiles and large amphibians disappeared, as well as early dinosaur groups. In the oceans, this event eliminated conodonts and nearly annihilated corals, ammonites, brachiopods and bivalves.

The emplacement of CAMP started c. 100,000 years before the end-Triassic event and continued in pulses for 700,000 years. Three negative organic C-isotope excursions (CIEs) have being recognized at the end-Triassic: the Marshi, the Spelae, and the top-Tilmanni CIEs. A recent study published in Nature estimated that a single short-lived magmatic pulse would have released about 5 × 10¹⁶ mol CO₂, roughly the same total amount of projected anthropogenic emissions over the 21st century, causing an increase of about 2 °C in global temperatures, and an oceanic pH decrease of about 0.15 units over 0.1 kyrs, suggesting that the end-Triassic climatic and environmental changes, driven by CO2 emissions, may have been similar to those predicted for the near future.

A normal fern spore compared with mutated ones from the end-Triassic mass extinction event. Image credit: S LINDSTRÖM, GEUS

These massive volcanic eruptions with lava flows, also released large quantities of sulphur dioxide, thermogenic methane and large amounts of HF, HCl, halocarbons and toxic aromatics and heavy metals into the atmosphere, resulting in global warming, and ozone layer depletion. The high concentrations of pCO₂ are indicative of ocean acidification suggesting that this may have been a marine extinction mechanism especially in relation to the scleractinian corals. Mutagenesis observed in plants and their reproductive cells (spores and pollen) were likely caused by mercury, the most genotoxic element on Earth .

The new study confirms the abundance of CO₂ (up to 10⁵ Gt volcanic CO₂ degassed during CAMP emplacement) and indicates that at least part of this carbon has a middle- to lower-crust or mantle origin, suggesting that CAMP eruptions were rapid and potentially catastrophic for both climate and biosphere. Since the industrial revolution, the wave of animal and plant extinctions that began with the late Quaternary has accelerated. Australia has lost almost 40 percent of its forests, and almost 20% of the Amazon has disappeared in last five decades.Calculations suggest that the current rates of extinction are 100–1000 times above normal, or background levels. If we want to stop the degradation of our planet, we need to act now.

 

References:

Capriolo, M., Marzoli, A., Aradi, L.E. et al. Deep CO₂ in the end-Triassic Central Atlantic Magmatic Province. Nat Commun 11, 1670 (2020). https://doi.org/10.1038/s41467-020-15325-6

Sofie Lindström et al. Volcanic mercury and mutagenesis in land plants during the end-Triassic mass extinction, Science Advances (2019). DOI: 10.1126/sciadv.aaw4018}

Davies, J., Marzoli, A., Bertrand, H. et al. End-Triassic mass extinction started by intrusive CAMP activity. Nat Commun 8, 15596 (2017). https://doi.org/10.1038/ncomms15596

The Forest Out of Time

An artist’s impression of Antarctica as a swampy rainforest between 92m and 83m years ago. (Credit: Alfred-Wegener-Institut/James McKay)

 

Past fluctuations in global temperatures are crucial to understand Earth’s climatic evolution. During the mid-Cretaceous, Earth’s climate was extraordinarily warm with temperatures in the tropics as high as 35 degrees Celsius, particularly during the Turonian to Santonian stages (93.9–83.6 Ma), with increasingly high sea levels and numerous epicontinental seas. The interval was characterized by extensive deposition of organic carbon (OC) rich black shales across a wide range of marine settings. Because marine proxies dominate records of past temperature reconstructions, our understanding of continental climate is relatively poor. Now, researchers from the UK and Germany discovered evidence of a temperate rainforest in West Antartica. The new finding offers a window into the terrestrial conditions of the extreme southern latitudes during this period.

The evidence comes from a core of sediment drilled into the seabed near the Pine Island and Thwaites glaciers in West Antarctica. One section of the core revealed a network of fossil plant roots, and countless traces of pollen and spores from plants, including the first remnants of flowering plants ever found at these high Antarctic latitudes. Pollen assemblage is dominated by the conifer tree families Podocarpaceae and Araucariaceae. The abundant tree ferns includes Cyathea. The presence of Sterisporites antiquasporites (Bryophyta, Sphagnum) suggest the temporary existence of a peat swamp. This coincides with increasing Peninsulapollis pollen.

 

West Antarctica. Image: Unsplash/Henrique Setim

Pollen and other palynomorphs proved to be an extraordinary tool to palaeoenvironmental reconstruction. In 1921, Gunnar Erdtman, a Swedish botanist, was the first to suggest this application for fossil pollen study. Like spores, pollen grains reflects the ecology of their parent plants and their habitats and provide a continuous record of their evolutionary history. Based on the palynomorph assemblage, the researchers found that the annual mean air temperature was around 13 degrees Celsius, and the average temperature of the warmest summer month was 18.5°C, whereas the amount and intensity of rainfall were similar to those in today’s Wales.

The mid-Cretaceous was an interval of intense climatic, tectonic and biotic changes across Gondwana. The break-up of the supercontinent and the rise of angiosperms caused a global floral turnover. Antarctica is particularly important because it preserves rock sequences that record the climate during the break-up of the supercontinent and the climate changes during the onset of continental-scale glaciation.

 

References:

Klages, J.P., Salzmann, U., Bickert, T. et al. Temperate rainforests near the South Pole during peak Cretaceous warmth. Nature 580, 81–86 (2020). https://doi.org/10.1038/s41586-020-2148-5

Forster, A. et al. Tropical warming and intermittent cooling during the Cenomanian/Turonian Oceanic Anoxic Event (OAE 2): sea surface temperature records from the equatorial Atlantic. Paleoceanography 22, PA1219 (2007). DOI:10.1029/2006PA001349