Thomas Galfetti

Good Genes and Good Luck: Ammonoid Diversity and the End-Permian Mass Extinction

“Rapid” Recovery The Permian-Triassic extinction 252 million years ago was Earths most severe biotic crisis since the Precambrian and is thought to have depressed diversity in its wake for millions of years. Brayard et al. (p. 1118; see the Perspective by Marshall and Jacobs) show, however, that ammonoids, a large group of marine organisms that were severely affected, recovered remarkably quickly. Only 1 million years after the extinction, ammonoids had recovered to levels higher than in the Permian, compared with the 10-million-year biotic recovery period for other benthic organisms. The Triassic recovery seems to include several cycles, but the immediate recovery of ammonoids may have left them as one of the most diverse groups in the earliest Triassic. In contrast to other groups, ammonoid diversity recovered within 1 million years of the end-Permian extinction to levels higher than before. The end-Permian mass extinction removed more than 80% of marine genera. Ammonoid cephalopods were among the organisms most affected by this crisis. The analysis of a global diversity data set of ammonoid genera covering about 106 million years centered on the Permian-Triassic boundary (PTB) shows that Triassic ammonoids actually reached levels of diversity higher than in the Permian less than 2 million years after the PTB. The data favor a hierarchical rather than logistic model of diversification coupled with a niche incumbency hypothesis. This explosive and nondelayed diversification contrasts with the slow and delayed character of the Triassic biotic recovery as currently illustrated for other, mainly benthic groups such as bivalves and gastropods.

Smithian-Spathian boundary event: Evidence for global climatic change in the wake of the end-Permian biotic crisis

One of the most important carbon cycle perturbations following the end-Permian mass extinction event straddles the Smithian-Spathian boundary (SSB) (Olenekian, Early Triassic). This anomaly is characterized by a prominent positive carbon isotope excursion known from Tethyan marine rocks. Its global signifi cance is established here by a new high paleolatitude record (Spitsbergen). Paleontological evidence, such as Boreal palynological data (Barents Sea, Norway) and global patterns of ammonoid distribution, indicates a synchronous major change in terrestrial and marine ecosystems near the SSB. The reestablishment of highly diverse plant ecosystems, including the rise of woody gymnosperms and decline of the formerly dominating lycopods, is interpreted as an effect of a major climate change. This hypothesis is supported by modeling of ammonoid paleobiogeography, the distribution patterns of which are interpreted as a proxy for sea surface temperatures (SST). The latest Smithian thus appears to have been a time of a warm and equable climate as expressed by an almost fl at pole to equator SST gradient. In contrast, the steep Spathian SST gradient suggests latitudinally differentiated climatic conditions. We propose that this drastic climate change and the global carbon cycle perturbation were triggered by a massive end-Smithian CO2 injection. The SSB event could therefore represent one of the causes for stepwise and delayed recovery of marine and terrestrial biotas in the wake of the end-Permian biotic crisis.

PALAEOECOLOGICAL CHANGES AFTER THE END-PERMIAN MASS EXTINCTION: EARLY TRIASSIC OSTRACODS FROM NORTHWESTERN GUANGXI PROVINCE,SOUTH CHINA

Early Triassic (Griesbachian to Spathian) ostracod faunas are here first discovered and described form the Guangxi Province, South China. Thirty-seven species belonging to fourteen genera are recognized. Seven species are new: Bairdia fengshanensis n.sp., Bairdia wailiensis n.sp., Liuzhinia guangxiensis n.sp., Ptychobairdia luciaae n.sp., Ptychobairdia aldaae n.sp., Paracypris jinyaensis n.sp. and Paracypris gaetanii n.sp. The Griesbachian assemblage from the basal microbial limestone is well diversified and does not suggest any abnormal palaeoenvironmental conditions in terms of salinity, temperature or oxygen content. Particularly, the ostracods are typical of well oxygenated water and do not reflect any anoxia. Dienerian and Smithian ostracods are evidenced for the first time and the assemblages suggest less favourable palaeoenviromental conditions. Diversity and abundance of ostracod assemblages recovered from the Spathian on. The main taxonomic turnover among ostracod assemblages occurred seemingly between the Griesbachian and the Spathian.

Timing of recovery from the end-Permian extinction: Geochronologic and biostratigraphic constraints from south China: COMMENT AND REPLY: COMMENT

[Lehrmann et al. (2006)][1] recently interpolated a new age of 247.2 Ma for the Early-Middle Triassic boundary in Guandao (Guizhou Province, south China) where four new U-Pb ages were measured from ash layers bracketing this boundary as defined by conodonts. Along with previous data of [Lehrmann et