Asynchronous trilobite extinctions at the early to middle Cambrian transition

Abstract

Trilobites appeared and diversified rapidly in the Cambrian, but it is debated as to whether their radiations and extinctions were globally synchronous or geographically restricted and diachronous. The end of the early Cambrian is a classic example—it has traditionally been defined by the extinction of olenellid and redlichiid trilobites and the appearance of paradoxidid trilobites. Here we integrate the global biostratigraphy of these three trilobite groups with high-precision tuff and tandem detrital zircon U-Pb age constraints to falsify prior models for global synchronicity of these events. For the first time, we demonstrate that olenellid trilobites in Laurentia went extinct at least 3 Ma after the first appearance of paradoxidids in Avalonia and West Gondwana (ca. 509 Ma). They also disappeared before the extinction of redlichiids and prior to the base of the Miaolingian at ca. 506 Ma in South China. This indicates that these three trilobite groups (paradoxidids, olenellids, and redlichiids) and their associated biotas overlapped in time for nearly 40% of Cambrian Epoch 2, Age 4. Implications of this chronological overlap are: (1) trilobite transitions were progressive and geographically mediated rather than globally synchronous; and (2) paleontological databases underestimate the diversity of the early Cambrian. This ∼3 Ma diachroneity, at a critical time in the early evolution of animals, also impacts chemostratigraphic and paleoclimatic data sets that are tied to trilobite biostratigraphy and that collectively underpin our understanding of the Cambrian Earth system.

Quantitative comparison of geological data and model simulations constrains early Cambrian geography and climate

“…refs. [21][22][23][24] and could be examined in future studies. The four configurations we tested are briefly described here.…”

“…refs. 18,19,[21][22][23][24][25][26][27][28][29][30][31][32][33] . These include variants of the 'Antarctocentric' paradigm [25][26][27][28]30,31 , characterised by a portion of West Gondwana lying at or near the South Pole, and an 'equatorial' configuration 18,19,21,33 in which all the major palaeocontinents, including West Gondwana, occupy low to mid-palaeolatitudes (Fig.…”

An outer shelf shelly fauna from Cambrian Series 2 (Stage 4) of North Greenland (Laurentia)

“…Immediately overlying olenellid-bearing strata (Buen Assemblages 2–4 of Peel and Willman, 2018) that underlie the Aftenstjernesø Formation were attributed to the Dyeran Stage (Peel and Willman, 2018). The boundary between these two North American stages has been equated with the boundary between Cambrian Stages 3 and 4 of the international standard, but Geyer (2019) reviewed difficulties associated with this correlation, with the Montezuman-Dyeran boundary now placed low in Stage 3 (Sundberg et al, 2020).…”

Paleomagnetic insights into the Cambrian biogeographic conundrum: Did the North China craton link Laurentia and East Gondwana?

“…The trilobite biozones, including the Hsuchuangia-Ruichengella, Sunaspis laevis, Poriagraulos natum, and Bailiella lantenoisi zones, indicate that the strata are of the Wuliuan Stage (Zhu et al, 2019, and references therein), which is estimated to be ca. 506-503.5 Ma based on new isotopic ages (Karlstrom et al, 2020;Sundberg et al, 2020).…”