Burning Dinosaurs & CO2
The Triassic–Jurassic boundary 200 million years ago marked the beginning of the dinosaurs’ dominance of the entire planet. Following the worst ever extinction event at the end of the Permian, 252 mya, dinosaurs started showing up in the fossil record around 245 mya but did not spread to all areas of the globe until the end of the Triassic. A new study in the Proceedings of the National Academy of Sciences (PNAS) posits one possible explanation for why the spread of dinosaurs was stymied. Sadly, this interesting but not conclusive report was immediately seized upon by climate alarmists as a cautionary tale about atmospheric CO2 levels. A news item in Science online labels modern levels “alarming” and implies that a fiery fate, like the one that held the dinosaurs at bay for so long ago, awaits us all.
Geologists and paleontologists divide Earth's past into many different time periods, based on changes in strata—the rock record. For example, the Triassic-Jurassic boundary is marked by a major extinction in the marine realm. This event, one of the five largest extinctions since complex life evolved 550 mya, is especially well documented in the European Alps. At least half of the species now known to have been living on Earth at that time went extinct. This event vacated terrestrial ecological niches, allowing the dinosaurs to assume the dominant role during the Jurassic period.
This event happened quickly in geologic terms, taking less than 10,000 years. While the extinction of sea life was most pronounced, it has also been suggested that there was a major biotic crisis among land species. The Late Triassic is characterized by the appearance in the fossil record of many of the "modern" clades of continental tetrapods, including dinosaurs, mammals, turtles, lepidosaurs, frogs and salamanders. These new lifeforms co-existed with various older groups from earlier in the Triassic and even the preceding Permian period. Near or at the Triassic-Jurassic boundary many groups and families disappeared or experienced major losses in diversity. Surprisingly, dinosaurs did not show any losses of lineages at this transition as shown in the figure below.
Why it took dinosaurs so long to spread to all corners of the world is a qustion that has vexed paleontologists for quite some time. In a new paper in PNAS, titled “Extreme ecosystem instability suppressed tropical dinosaur dominance for 30 million years,” an interdisciplinary team led by J. H. Whiteside, a geochemist at the University of Southampton, has put forth a novel explanation—raging fires, arid conditions, and high temperatures kept big dinosaurs out of the area that would become North America for millions of years. Here is the article abstract:
A major unresolved aspect of the rise of dinosaurs is why early dinosaurs and their relatives were rare and species-poor at low paleolatitudes throughout the Late Triassic Period, a pattern persisting 30 million years after their origin and 10–15 million years after they became abundant and speciose at higher latitudes. New palynological, wildfire, organic carbon isotope, and atmospheric pCO2 data from early dinosaur-bearing strata of low paleolatitudes in western North America show that large, high-frequency, tightly correlated variations in δ13Corg and palynomorph ecotypes occurred within a context of elevated and increasing pCO2 and pervasive wildfires. Whereas pseudosuchian archosaur-dominated communities were able to persist in these same regions under rapidly fluctuating extreme climatic conditions until the end-Triassic, large-bodied, fast-growing tachymetabolic dinosaurian herbivores requiring greater resources were unable to adapt to unstable high CO2 environmental conditions of the Late Triassic.
The researchers claim their work is the first large-scale study to incorporate multiple prehistoric climate indicators with the fossil record of both early dinosaurs and related species. Working at a fossil rich location in northern New Mexico, known as the Ghost Ranch, the authors think they have pieced together the answer to what held the dinosaurs back until the end of the Triassic. During the Late Triassic period between about 215 million and 205 million years ago, Ghost Ranch and surrounding regions were subject to carbon dioxide levels many times modern levels. These regions, which were much closer to the equator at the time (see the figure below), were subject to raging wildfires and extreme fluctuations in temperature and vegetation growth. All of this made life inhospitable for larger dinosaurs.
This is, to our knowledge, the first multiproxy study of climate and associated faunal change for an early Mesozoic terrestrial ecosystem containing an extensive vertebrate fossil record, including early dinosaurs. Our detailed and coupled high-resolution records allow us to sensitively examine the interplay between climate change and ecosystem evolution at low paleolatitudes during this critical interval of Earth's history when modern terrestrial ecosystems first evolved against a backdrop of high CO2 in a hothouse world. We demonstrate that these terrestrial ecosystems evolved within a generally arid but strongly fluctuating paleoclimate that was subject to pervasive wildfires, and that these environmental conditions in the early Mesozoic prevented large active warm-blooded herbivorous dinosaurs from becoming established in subtropical low latitudes until later in the Mesozoic.
The paper is getting good if cautious reviews from fellow scientists. The team’s interpretation of ancient climatic conditions “are certainly convincing,” said Michael Benton, a paleobiologist at the University of Bristol, quoted in Science. Hans-Dieter Sues, a paleobiologist at the Smithsonian Institution’s National Museum of Natural History, called the new study is a “very important contribution,” but cautioned that it focused on “a single restricted area.”
“We need comparable information from a wider range of sites to test their generality,” Sues stated. In a similar vein, Nick Fraser, a paleontologist at the National Museums of Scotland, added: “No one locality or region can be regarded as the Holy Grail, but this is an excellent starting point.”
So far so good. But then the news article in Science online steps over the line. Under a bombastic headline, “Raging fires, high temps kept big dinosaurs out of North America for millions of years,” Michael Balter, a staff writer for Science and NYU journalism professor, jumps over the line of supportable scientific speculation and tries to turn the research paper into a cautionary tail about global warming. Along with lurid artwork, the article implies modern day atmospheric CO2 levels are in someway comparable with conditions during the Late Triassic.
“They found that Ghost Ranch was a hothouse during the Late Triassic, with mean annual temperatures as high as about 28°C,” he writes. “Carbon dioxide levels ranged between about 1200 and 2400 parts per million (ppm), many times higher than the already alarming 400 ppm Earth is experiencing today and the estimated 280 ppm just before the Industrial Revolution.”
What do modern CO2 levels have to do with the subject of the paper? In what way are modern levels “already alarming” when the levels in the report are three to six times current concentrations? Obviously, Mr. Balter is implying that rising atmospheric CO2 will lead the modern world to a calamity similarly to the one that faced the dinosaurs of the Triassic. Does this conjecture have any basis in fact? Let's find out.
As noted by the authors of the PNAS paper, the distribution of land was much different during the Triassic. The area in question was located close to the equator and the ancient super continent Pangaea was just starting to break up. The world was experiencing hothouse conditions, meaning there were no icecaps at the poles, and much of the continental land mass suffered hot arid conditions. It was a much different world back then. Over time it would change into a world more amicable for the evolving dinosaurs, though the world of the Jurassic and subsequent Cretaceous would still not be recognizable to modern humans.
Other changes were happening at the end of the Triassic. Pollen and spores from terrestrial plants show that there was a dramatic change from high-diversity palynofloras to assemblages almost entirely made up of cheirolepidaceous conifers (Corollina or Classopollis). In other words, the nature of Earth's vegetation was changing dramatically. Perhaps this is why Natural History Museum of Utah paleontologist Randall Irmis stated scientists “haven’t found a single [plant-eating] dinosaur” near the equator during the Triassic, not a carbon dioxide induced conflagration as reported in the PNAS article.
Further more, it should be noted that life during the Triassic was bouncing back after the worst extinction event in the history of the planet. And even though the planet was hot and arid, with atmospheric CO2 levels as high as 2400 ppm life flourished. Obviously the much higher CO2 levels were not toxic or catastrophic.
Bottom line is that we are talking about an alien planet here, a world as different from our own as any in a science fiction movie. The arrangement of the continents, the existence of mountain ranges that were not present 200 mya, radical changes in vegetation and the fact that our planet is still in an Ice Age make any comparison between the impact of ancient carbon dioxide levels and today's ludicrous.
It has been well known for a long time that CO2 levels in the distant past were "many times higher than the already alarming 400 ppm Earth is experiencing today." That anyone would published an article linking Triassic wildfires, dinosaurs and CO2 to anthropogenic global warming is beyond contemptible. Balter's hidden message is that we could all become human flambé in the near future, just like the poor dinosaurs. The Science article co-opted a real scientific paper for propaganda purposes, a lame attempt to push the climate alarmist agenda and a scientifically unethical act.
Be safe, enjoy the interglacial and stay skeptical.