Featured image: Landscape mountain sky by Enrique Lopez Garre, Pixabay License.
Paper: A paraphyletic ‘Silesauridae’ as an alternative hypothesis for the initial radiation of ornithischian dinosaurs
Authors: Rodrigo Muller and Maurício Garcia
Dinosaurs dominated terrestrial ecosystems for nearly 170 million years in the Mesozoic. There were three major groups of dinosaurs. The long-necked sauropodomorphs, which included the largest animals ever to live on land, could grow as long as a Boeing 737 aircraft. The meat-eating theropods, which included the famous Tyrannosaurus rex, have evolved into the modern dinosaurs: birds. And the bird-hipped ornithischians, an assorted group of herbivorous dinosaurs, evolved some of the most bizarre anatomy known in evolutionary history. This ranged from the plate-backed Stegosaurus, to the thumb-spiked Iguanodon, and from the exaggerated crests of Triceratops to the walking coffee table that is Ankylosaurus.
Continue reading “The early evolution of the bird-hipped dinosaurs”
Paper: A 23 m.y. record of low atmospheric CO2
Featured image: Modern vascular land plants (Raphanus sativus), growing in a carbon dioxide experiment (Figure 1A from Jahren et al., 2008)
Authors: Ying Cui, Brian A. Schubert, A. Hope Jahren
Carbon dioxide is a greenhouse gas, trapping warmth within the Earth’s atmosphere. Sixty years of measurements on Hawaii’s Mauna Loa summit have shown rising amounts of carbon dioxide in our atmosphere. In addition, the carbon dioxide levels in our modern atmosphere are significantly higher than those we have seen on Earth over the last 800,000 years, according to measurements on bubbles of ancient air trapped in Antarctic ice. When combined with measurements of global temperatures, these direct measurements are irrefutable evidence for rapid modern climate change. However, understanding our current position relative to Earth’s climate farther back in time is trickier, since scientists have to estimate atmospheric composition indirectly (through a “proxy”). A new study tackles this problem with a new method of estimating past carbon dioxide, showing that modern carbon dioxide levels have been unprecedented since at least 7 million years ago.
Continue reading “New 23 million year record of atmospheric carbon dioxide highlights current human influence on the atmosphere”
Featured image: The earliest examples of life on Earth are microbial buildups known as stromatolites, like these 1.8 Ga old examples from Great Slave Lake, Canada. What changed on our planet for organisms to evolve from microbes to macroscopic lifeforms?
Paper: Ediacaran reorganization of the marine phosphorus cycle
Authors: Laakso, T.A., Sperling, E.A., Johnston, D.T., and Knoll, A.H.
This is a guest post by Akshay Mehra and Danielle Santiago Ramos. Contact us to submit a guest post of your own!
The history of life on Earth—as recorded in the rock record—stretches back to more than 3.5 billion years ago (Ga). The earliest fossilized remains of living organisms appear in the form of stromatolites, which are laminated constructions built in part (or completely) by microbes. While there have been some tantalizing hints that living organisms were mobile by 2.1 Ga (Albani et al., 2019) and multicellular by 1.6 Ga (Bengston et al. 2017), what is definitively known is that by ~750 million years ago (Ma), complex microscopic lifeforms were widespread on our planet. As time progressed, life became macroscopic. Then, during the Cambrian Era (beginning 539 Ma), most modern phyla (i.e. a grouping of organisms based on body plans) appeared in a flurry of diversification so drastic that it has been nicknamed “the Cambrian explosion.” Scientists are still trying to understand what combination of physical and biological processes may have driven the Cambrian explosion.
Continue reading “Did a change in phosphorus cycling lead to the diversification of macroscopic life?”