Treasure trove from the Early Triassic

How did life respond to Earth’s greatest mass extinction? This is the subject of a new study in Science.

First some background. It has long seemed that the Early Triassic was a relatively boring time in the history of life, dominated by those “weedy” species that made it through the end-Permian catastrophe. A popular model of ecosystem recovery imagined a gradual refilling of the trophic “bucket,” beginning with the lowest levels and proceeding to higher and higher ones. The matter has remained obscure, though, in virtue of the death of lagerstätten from the earliest Triassic. (Lagerstätten provide privileged windows into the structure of past ecosystems. So, the dearth of lagerstätten from the earliest Triassic makes it difficult to assess the extent of trophic diversity during the first three million years of this period.)

But ask and you shall receive—or at least that’s how it seems to work in the rocks of South China. Back in 2015, paleontologist Xu Dai discovered the oldest Mesozoic lagerstätte in a succession of rocks near Guiyang. It dates to about a million years after the end-Permian extinction, and bursts with fish, shrimp, lobsters, ammonoids, sponges, conodonts and forams. This is a genuine treasure trove, which suggests a more rapid recovery from the end-Permian extinction than has previously been entertained. Maybe it was the case that more occupants of high trophic levels dodged the Permian extinction than we thought. Or maybe important elements of the modern marine fauna radiated quickly, despite inhospitable conditions in the earliest Triassic. At any rate, it seems that notions of a slow and stepwise recovery are no longer adequate. The story of earth’s greatest extinction just got more interesting, again.

For those interested in a quicker read, here’s a write-up from the news team at Nature (also, sadly, paywalled).

Oily blobs from the underworld

How many nails must be pounded into a coffin before it ceases to spring open? Find out now, in Science Advances!

Defenders of the biogenicity of the ~3.5 Ga Apex chert “microfossils” have been fighting a rearguard action since 2002, when Martin Brasier and colleagues published a damning reanalysis of the specimens and their geological context. These specimens were once thought to be the oldest known fossils in the fossil record. William Schopf, who described the specimens in a celebrated paper, claimed that they occurred in a sedimentary bedded chert, and more spectacularly (since they greatly predate evidence for significant oxygenation) that they may have been related to oxygen-producing cyanobacteria. But Brasier and colleagues showed that the specimens most likely originated in a hydrothermal setting, ruling out a cyanobacterial interpretation. They also showed, for example, that parts of the original specimens were cropped out of the published photographs (and not represented in the accompanying interpretive drawings), all of which led them to conclude that the putative fossils were in fact abiotic structures that formed around recrystallizing mineral grains during a series of hydrothermal events.

I am going to write about the Apex chert sometime, because what I have related is only the beginning of the story. But from my extreme outsider’s perspective, it seems that Brasier and friends gained the upper hand in 2002 and never relinquished it. (Martin Brasier died tragically in 2014, when a severely overtired man fell asleep at the wheel and collided with Brasier’s car. It is an extremely sad story, not least because it is impossible to read about the circumstances of the accident and not feel sorry for the man who caused the crash.) Anyway, this new publication is the latest chapter in the now thirty-year saga of these probably-not-actually-fossils. It argues that the carbon associated with the specimens is not biological in origin. But it also raises a question: where did the organic molecules in the chert come from? One possibility is from a reaction between water and rocks, an intriguing suggestion that nonetheless does not exclude the possibility that life existed during this time.

For the full story, follow the link above to the open-access article. A more accessible write-up can be found here.

A "Neo-Gouldian" argument for evolutionary contingency

The route from acceptance to publication is BJPS is a long one. As a result, there are many papers that are in the queue, waiting to be assigned an issue.

One that is nearing the front of the queue is this contribution from T.Y. William Wong, called “The Neo-Gouldian Argument for Evolutionary Contingency.” It is happy timing, since it was recently announced that the next MBL-ASU History of Biology Seminar will be called “Replaying Life’s Tape: Historical Contingency in the Life Sciences.”

Very roughly, the paper seeks to update Gould’s arguments about the contingency of life’s history in light of recent studies of Cambrian disparity and the selectivity of mass extinctions. I should say that this description is based entirely on the abstract: I haven’t had a chance to read the paper yet. But it seems likely to be interesting to readers of this blog.

Sexual jousting

This just in from PNAS: sexual combat in the Devonian!

In a new study, Alan Gishlick and Richard Fortey examine a genus of trilobites with trident structures protruding from their heads. They argue that the structures evolved for sexual jousting, which was big with trilobites back in the Devonian. Their key piece of evidence is a specimen that grew to maturity with a severely lopsided trident. This, the authors claim, is inconsistent with other functional interpretations of the structure. If the trilobite used the trident for feeding, it most likely wouldn’t have been able to reach maturity with a seriously deformed one. The same goes for defense. By contrast, animals often make it to sexual maturity with malformed “dueling equipment.” Here the authors enlist support from studies of mule deer and Rocky Mountain elk. Excellent.

For those who can’t get past the paywall, there is a nice write-up in the New York Times.

Sinosauropteryx turns 25, sort of

Earlier this week marked the 25th anniversary of this paper, which announced the discovery of Sinosauropteryx prima by Pei-ji Chen and colleagues. Sinosauropteryx was the first feathered dinosaur to be described in a scientific paper. (Or, if you’re a stickler for precision, it was the first non-avian dinosaur with a feather-like body covering to be described in a scientific paper.) So put on your party hats and read the commemorative piece by Kevin Padian if you can get past the paywall…

A sunburn for Gorgon

Breaking news from the latest Permian…

The end-Permian mass extinction, apart from being the largest extinction event in history, is one of the earth sciences’ greatest whodunits. Once thought to be a consequence of plate tectonic movement, it is now widely held that the main driver of the extinction was the magmatic event associated with the Siberian Traps large igneous province (but see this study from a couple years ago for an interesting wrinkle).

Now there’s this, from Science Advances; namely, “[in]direct evidence” of elevated UV radiation at the Permo-Triassic (P/Tr) boundary in Tibet. The evidence comes from pollen grains, which show a spike in the prevalence of ultraviolet absorbing compounds near the P/Tr boundary. This, in the words of the abstract, “suggest[s] a close temporal link between large-scale volcanic eruptions, global carbon and mercury cycle perturbations, and ozone layer depletion.” And this in turn supplies another potential cause of the environmental deterioration implicated in the land extinctions.

The article is open access, so you can read the whole thing by following the link, above.

A new addition to the stem bird aviary

An interesting article just appeared in Nature Ecology & Evolution. Here’s the short version. Researchers found a stem bird (a bird occupying an intermediate position in the phylogenetic tree between the oldest bird, Archaeopteryx, and the “true birds”) that helps bridge a large morphological gap in the fossil record. There’s a surface-level irony here given that Archaeopteryx is the OG intermediate form or “missing link.” But whenever you close a morphological gap you also create two new ones…

Anyway, the newly described bird, Cratonavis, is a mosaic of avian and non-avian characters, combining a relatively bird-like body with a more classically theropod-like skull. Don’t believe the news reports describing it as “bizarre”: I’m not even sure you could call it “unexpected.” Still, it is an interesting addition to a rapidly-filling aviary of stem birds. (Here’s a link to a non-technical write-up for anyone blocked by the paywall.)