Earliest Triassic ichthyosaur from Spitsbergen

Ichthyosaurus figure at Crystal Palace. From Wikimedia Commons

Ichthyosaurs were iconic marine reptiles that roamed the Mesozoic oceans for some 160 million years. They were characterized by an elongated body, a relatively small head, a long snout, flipper shaped limbs, and dolphin-like tail flukes. Recent studies indicates that they form the clade Ichthyosauromorpha with Hupehsuchia, a group of Early Triassic marine reptiles that inhabited the South of China. The clade arose after the devastation of the end-Permian mass extinction event (EPME, ~252 Ma). Although, there is a wide anatomical gap between Ichthyosauriformes and the Hupehsuchia. A new study  from the Uppsala University and the University of Oslo with new ichthyopterygian material recoverd from the Arctic island of Spitsbergen recalibrates the time and origin of this clade.

Computed tomography image and cross-section showing internal bone structure of vertebrae from
PMO 245.975. Image credit: Øyvind Hammer and Jørn Hurum

The fossil remains designated as PMO 245.975  includes  11 articulated vertebral centra, 15 indeterminate bone fragments, limb and/or limb girdle elements. The centra of PMO 245.975 are comparable with vertebrae from ‘middle-sized’ ichthyopterygian skeletons. Aditionally, their internal organization is also entirely cancellous with a dense circumferentially oriented trabecular network (1). Those features indicates fast growth, elevated metabolism and a fully oceanic lifestyle, evidencing that the earliest ichthyopterygian ancestors must have rapidly adapted as oceanic apex predators.

The new materials were initially recovered in 2014 in the Lower Triassic Sassendalen Group strata in Flowerdalen, Svalbard, Norway. and predate the late Smithian crisis (LSC, ∼249.6 Ma). The LSC is characterized by successive global biotic and environmental changes, including a dramatic positive carbon isotopic excursion, oceanic anoxia and a cooling event. This crisis is one of the most severe known for some nekto-pelagic organisms such as ammonoids.

 

References:

Kear, B. P., Engelschiøn, V. S., Hammer, Ø., Roberts, A. J., & Hurum, J. H. (2023). Earliest Triassic ichthyosaur fossils push back oceanic reptile origins. Current Biology: CB, 33(5), R178–R179. https://doi.org/10.1016/j.cub.2022.12.053 (1)

Nakajima, Y., Shigeta, Y., Houssaye, A., Zakharov, Y. D., Popov, A. M., & Sander, P. M. (2022). Early Triassic ichthyopterygian fossils from the Russian Far East. Scientific Reports, 12(1), 5546. https://www.nature.com/articles/s41598-022-09481-6

Motani, R., Jiang, D. Y., Tintori, A., Ji, C., & Huang, J. D. (2017). Pre-versus post-mass extinction divergence of Mesozoic marine reptiles dictated by time-scale dependence of evolutionary rates. Proceedings of the Royal Society B: Biological Sciences, 284(1854), 20170241. https://royalsocietypublishing.org/doi/full/10.1098/rspb.2017.0241

Thorne, P. M., Ruta, M., & Benton, M. J. (2011). Resetting the evolution of marine reptiles at the Triassic-Jurassic boundary. Proceedings of the National Academy of Sciences, 108(20), 8339-8344. https://doi.org/10.1073/pnas.1018959108

 

Lessons from the past: The Great Dying, a model for the current biodiversity loss

 

Permian Seafloor. Photograph by University of Michigan Exhibit Museum of Natural History.

Extinction is the ultimate fate of all species. The fossil record indicates that more than 95% of all species that ever lived are now extinct. Individuals better adapted to environments are more likely to survive and when a species does fail, it is called a background extinction. Occasionally extinction events reach a global scale, with many species of all ecological types dying out in a near geological instant. Those catastrophic events are known as mass extinctions.

During the last 540 million years five mass extinction events shaped the history of the Earth. The Permian-Triassic mass extinction (PTME) is the most severe biotic crisis in the fossil record, with as much as 95% of the marine animal species and a similarly high proportion of terrestrial plants and animals going extinct . This great crisis occurred 252 million years ago (Ma), and is linked to the emplacement of the large igneous province of the Siberian Traps.

Flow chart summarizing proposed cause-and-effect relationships during the end-Permian extinction (From Bond and Wignall, 2014)

Massive volcanic eruptions with lava flows, released large quantities of sulphur dioxide, carbon dioxide, thermogenic methane and large amounts of HF, HCl, halocarbons and toxic aromatics and heavy metals into the atmosphere. Acid rain likely had an impact on freshwater ecosystems and may have triggered forest dieback. Ocean warming reduced the solubility of oxygen, and raised metabolic rates accelerating the rate of oxygen consumption. Those climatic conditions: global warming, ocean acidification, and marine deoxygenation, are similar to the human-driven environmental disruptions that we are facing today.

An international team of researchers from the California Academy of Sciences, the China University of Geosciences (Wuhan), and the University of Bristol, examined fossils from South China (a shallow sea during the Permian-Triassic transition)  and recreated the ancient marine environment using simulated food webs to represent the ecosystem before, during, and after the PTME.

The permian triassic boundary at Meishan, China (Photo: Shuzhong Shen)

The new study indicates that in the first phase of the extinction community stability slightly decreased despite the loss of more than half of taxonomic diversity, while community stability significantly decreased in the second phase (about 60,000 years after the first biodiversity crissis) because ecosystems are more resistant to environmental change when there are multiple species that perform similar functions. Once the last species in each role began to go extinct, the ecosystem rapidly collapsed.

Since the industrial revolution, the wave of animal and plant extinctions that began with the late Quaternary has accelerated. Calculations suggest that the current rates of extinction are 100–1000 times above normal, or background levels. We are in the midst of the so called “sixth mass extinction event”. If we want to stop the degradation of our planet, we need to act now.

 

 

 

References:

Huang, Y., Chen, Z. Q., Roopnarine, P. D., Benton, M. J., Zhao, L., Feng, X., & Li, Z. (2023). The stability and collapse of marine ecosystems during the Permian-Triassic mass extinction. Current Biology. DOI: 10.1016/j.cub.2023.02.007

Bond, David P.G., Wignall, Paul B., (2014). “Large igneous provinces and mass extinctions: An update” https://doi.org/10.1130/2014.2505(02)