Triassic ammonoids of Northeast Asia: Diversity and evolutionary stages

Biogeography of Triassic Ammonoids

“…However, we provide evidence here with BSN analyses (Fig. 7.6) that a biogeographical latitudinal structure of faunal relationships persists during the Ladinian along the eastern Panthalassa, although possibly somewhat weaker than during the Anisian (see also Konstantinov 2008). A marked differentiation between the Tethys and Panthalassic basins is also confirmed by the NP-MANOVA and ANOSIM comparisons (Table 7.1), again indicative of rather heterogeneous distributions of ammonoids during the Ladinian.…”

“…7.1). The Spathian/Anisian boundary is characterized by a marked faunal turnover associated with the radiation of mid-Triassic families such as Arcestidae (Dagys et al 1979;Monnet and Bucher 2005;Konstantinov 2008;Balini et al 2010). During the Anisian, latitudinal differentiation of assemblages seems to be maintained at levels comparable to the Smithian or Spathian (Galfetti et al 2007c;Balini et al 2010), which suggests a lingering tight link between the SST gradient and the LGGR.…”

“…The Triassic remains one of the most interesting and intriguing periods for ammonoid evolution as it is marked by successive episodes of intense radiation and marked extinction associated with sudden biogeographic changes often closely related to major climatic and oceanographic changes (e.g. Tozer 1982;Dagys 1988;Dagys and Ermakova 1990;Brayard et al 2006Brayard et al , 2007bBrayard et al , 2009aMonnet and Bucher 2006a;Galfetti et al 2007a;Konstantinov 2008;Zakharov et al 2008;Balini et al 2010;Monnet et al 2013;Zakharov and Moussavi Abnavi 2013). The end of the Triassic is also marked by the enigmatic appearance of the first heteromorphs and a further nearannihilation at the Triassic/Jurassic boundary (~ 201 Ma).…”

Evolutionary Trends of Triassic Ammonoids

“…2.3) are characterized by four long-term successive diversity oscillations of declining magnitude, which are probably shaped by global climatic and oceanographic changes (Brayard et al 2006;Galfetti et al 2007b;Konstantinov 2008). As highlighted by Brayard et al (2009), in the first oscillation, during the Olenekian, ammonoid generic diversity reached values (~ 110) higher than those for the Permian.…”

“…The latter ends with a marked diversity decline before the Jurassic. Additional studies have explored the diversity of Triassic ammonoids but with lower time resolution, smaller datasets and/or more restricted geographic scope (e.g., Yang and Wang 2000;Konstantinov 2008;Brühwiler et al 2010;Zakharov and Abnavi 2013). …”