On the evolutionary history of jawed vertebrates from the late Ordovician to the early Silurian age and discovery of the Konservat-Lagersttte
Molecular studies suggest that the origin of jawed vertebrates was no later than the Late Ordovician period (around 450 million years ago (Ma))1,2. Together with disarticulated micro-remains of putative chondrichthyans from the Ordovician and early Silurian period3,4,5,6,7,8, these analyses suggest an evolutionary proliferation of jawed vertebrates before, and immediately after, the end-Ordovician mass extinction. The earliest complete fossils of jawed fishes for which a reconstruction of their appearance could be obtained came from in the late Silurian. The dearth of articulated, whole-body fossils from before the late Silurian has long rendered the earliest history of jawed vertebrates obscure. The new discovery of the Konservat-Lagersttte is marked by the presence of a variety of well-preserved jawed fishes with complete bodies from the early Silurian age. The dominant species, a ‘placoderm’ or jawed stem gnathostome, which we name Xiushanosteus mirabilis gen. et sp. nov., combines characters from major placoderm subgroups14,15,16,17 and foreshadows the transformation of the skull roof pattern from the placoderm to the osteichthyan condition10. The chondrichthyan Shenacanthus vermiformis is related to the Shenacanthus. The armor plates show extensive, unknown, and large median plate, which can be combined with a conventional chondrichthyan bauplan18. Together, these species reveal a previously unseen diversification of jawed vertebrates in the early Silurian, and provide detailed insights into the whole-body morphology of the jawed vertebrates of this period.
A study published in Science today says that a large amount of fossils found in southern China represent a complex marine environment from the dawn of modern life. The organisms of the Guiyang biota lived around 251 million years ago, just one million years after the world’s worst known mass-extinction event, at the end of the Permian period. This shows that the ecosystems recovered more quickly than previously thought.
The fossils were discovered in 2015 by paleontologist and China University of Geosciences student, Xu Dai. Before the COVID-19 pandemic halted fieldwork, he and his associates collected more than 1,000 fossils of whole fish, ancient lobsters, and prehistoric crab-like creatures from a layer of black Shale in Guizhou province.
Volcanic ash in the layer dates to 250.8 million years ago. That makes the Guiyang biota the oldest known fossil assemblage from the Mesozoic era, the interval between the Permian–Triassic mass extinction and the Cretaceous–Paleogene mass extinction that wiped out non-avian dinosaurs 66 million years ago.
The extinction of large swathes of life at the end of the 16th century is sometimes referred to as the mother of mass extinctions. The event is thought to have been caused by global warming triggered by volcanic activity that heated Earth’s atmosphere and acidified the oceans.
Benton says that the emerging picture is of a time in which ecosystems recovered swiftly before being hit by repeated temperature shocks throughout the first eight million years of the early Triassic period. “What’s now coming out is even more extraordinary, that the rate of recovery can be really super-fast, unexpectedly, against the backdrop of really grim conditions,” he says. But Benton, too, thinks that self-sufficient organisms would have come first, followed by species that consumed those animals, and then apex predators.
According to the co-author, a rapid shift of predatory fishes suggest that the complex Ecosystem didn’t disappear during the mass extinction.
Dai is going to return to the Guiyang sites in the middle of the year to see what else he will yield after three years of no fieldwork. He is also keen to find sites — perhaps on the Tibetan Plateau — that hold fossils that lived during the one million years between the Permian mass extinction and the Guiyang biota.