Today biodiversity hotspots cluster mainly in the tropics. The high diversity in tropical floral and faunal communities is regarded as a product of low extinction (“museum”) and relative higher origination rates (“cradle”) due to higher molecular evolution compared to higher latitudes.

The Tethys Ocean reigned an extensive tropical area for a major part of the Phanerozoic. Sediments deposited in this tropical ocean and the fossils included are a treasure trove for palaeontologists. They allow glimpses into past biodiversity hotspots, into past faunal and floral communities and into centers of evolution.

Although the Tethyan realm is primarily known for exquisite marine fossil records, here the focus is on the vegetation of the surrounding continents. Plant macrofossil sites adjacent to the Tethys testify not only the early evolution of typical Mesozoic plant groups in the late Permian (Corystospermales, Bennettitales, and the conifer family Podocarpaceae in Jordan) but also the radiation of some of these groups in the Anisian and Carnian deposits of Austria and northern Italy. In contrast to the plant macrofossil sites surrounding the Tethys, plant microfossils are transported into the Tethys by rivers and deposited in marine sediments. These document for example plant survival during the Permian–Triassic mass extinction in South China or the Middle to Late Triassic biogeographical differentiation of the flora.

The extraordinary genus Crickites is chronologically restricted to the uppermost Frasnian (Upper Devonian, UD I–L), occurring exclusively during the Upper Kellwasser Crisis, often in large numbers and with remarkable body size (> 40 cm). Morphological features place it within the Gephuroceratidae, distinguished particularly by its characteristic suture with a high ventrolateral saddle. Unlike most other representatives of this family, which exhibit biconvex growth lines, Crickites - along with its much thinner sister genus Clauseniceras - is characterized by exclusively convex growth lines. Additionally, the conch is unusually wide and becomes progressively wider through ontogeny. Crickites ranks among the largest known ammonoids of the Devonian, thriving during a time of severe ecological changes now recognized as one of the major mass extinction events in Earth’s history. This apparent paradox of a global spreading followed by rapid extinction, raises significant evolutionary and palaeoecological questions. The genus shows a wide distribution, from Cr. lindneri in the Canning Basin (NW Australia), to Cr. holzapfeli in the Rhenish Mountains (Germany), and supposed Cr. rickardi in the Appalachians (North America). A major challenge, however true for all gephuroceratids, is the unresolved taxonomy and systematic classification. Contributing factors include a historically fragmented and inconsistent research history, the loss of type material, and the lack of precise diagnoses. To date, it remains unclear how many and which species are validly assigned to Crickites. Therefore, this study provides the first comprehensive revision of this important yet poorly understood fossil group.

The Permian–Triassic mass extinction (PTME) is characterized by the highest extinction rates in marine communities in the entire Phaneozoic. As the event coincides with extreme environmental perturbations such as rapid global warming, most palaeobiological studies assume all extinctions during the PTME occurred as primary loss of taxa directly caused by physical environmental stress. However, secondary extinction cascades triggered by changes in ecological interactions can be as, if not more, important drivers of species loss. Herein, we modelled food webs of marine communities across the PTME using the most comprehensive occurrence dataset from the western Tethyan tropical deposits at Meishan, China, at a very high stratigraphical resolution to infer secondary extinctions. Using robustly inferred predator-prey networks for each time interval, we classified extinctions as secondary under the following conditions: i) a predator became extinct when prey diversity declined, ii) a primary consumer (e.g., filter feeders) became extinct following a decrease in primary productivity, iii) a species within the trophic network became extinct following either increased predation pressure (increased normalized out-degree) or a loss of resources (declined normalized in-degree). Based on these classifications, the majority of the extinctions can be attributed to secondary extinction due to perturbations in primary productivity or changes in trophic interactions. Modelling trophic interactions in these extinct communities reveals the importance of considering evidence for secondary extinctions to better understand the processes giving rise to biodiversity patterns in deep time.

Robust time scale is essential for understanding geological processes and biotic evolution. Following the Permian-Triassic mass extinctions, the Early Triassic recorded a series of climatic, environmental and biotic events. However, the tempo of these events remains poorly constrained.

In this work, we present four new high-precision zircon U-Pb dates from the Induan in South China using high precision CA-ID-TIMS techniques. We then adopted coupled Bayesian eruption age and Bayesian age-depth models to interpret these dates and built age model, based on which, we provided, for the first time, absolute time estimations for the Griesbachian-Dienerian and Induan-Olenekian boundaries, i.e. 251.562 +0.090/-0.101 Ma and 250.626 +0.140/-0.214 Ma, respectively.

Then, we applied the same analytical approach on published U-Pb dates of 25 ash beds. The resulting age-depth models, combined with biostratigraphic data, allow us to update age estimations for all Early Triassic stage/substage boundaries. The new time scale shows significant differences from those based on cyclostratigraphy, as well as some minor differences from the low MSWD weight mean age interpretations.

The timing of three negative and four positive excursions of Early Triassic carbon isotope were precisely constrained based on the new age models. The new age models also provide a robust timeline to evaluate biotic evolution in the aftermath of the Permian-Triassic mass extinction. For instance, the first remarkable biotic rebound in the late Griesbachian is ~0.3 Myr after the Permian-Triassic mass extinction, much faster than expectation.

Triassic plankton already resembled modern communities to a considerable degree. After the end-Permian extinction, primary producers rebounded quickly: acritarchs and prasinophytes dominate Early Triassic successions, and the first calcareous nannoliths, including true coccoliths, appear by the late Norian to Rhaetian in the western Tethys and British Columbia. Calcispheres may record encysting algae, while oberhauserellid foraminifers are considered precursors of planktonic globigerinids. Unambiguous dinoflagellate cysts emerge in Middle Triassic strata of Western Australia.

Zooplankton diversified at the same pace. Radiolarians regained pre-extinction richness by the Anisian and Ladinian, with spectacular faunas in the Buchenstein Formation of the Dolomites. Planktonic crinoids, documented by masses of micro-ossicles from the Cassian Formation, formed a conspicuous suspension-feeding tier. Meroplankton was equally abundant: protoconchs show that most Cassian gastropods produced planktotrophic larvae, and echinoderms with similar larval strategies (holothurians, echinoids, ophiuroids) are widespread from Ladinian time onward, even though pluteus or auricularia ossicles are only sporadically preserved. Throughout the period, prolific ammonite populations imply a constant flux of cephalopod paralarvae that nourished higher trophic levels.

Far from being radiolarian-only, Triassic plankton already contained most of the elements that later structured Mesozoic, and ultimately modern, marine food webs.