This paper presents the first quantitative study of the Early Jurassic
recovery of ammonoids after the end-Triassic mass extinction based on
detailed U-Pb ID-TIMS (isotope dilution thermal ionization mass
spectrometry) geochronology from ash bed zircons placed within a clear
phylogenetical and biochronological framework at the subzonal and
species level. This study was triggered by the discovery of a rich
Peruvian succession of ammonites, deposited concomitantly with an
unusually large number of ash beds. Two major phases of
rediversification are observed during the Psiloceras spelae and
Angulaticeras zones that correspond to positive peaks in the delta
C-13(org) curve, providing a possible link between biodiversity and the
global carbon cycle.
In the case of the post-extinction recovery, the development of the
earliest Hettangian ammonites occurs within the genus Psiloceras, which
begins with the occurrence of P. spelae and then explodes into worldwide
development of smooth psiloceratids of the Psiloceras planorbis group
s.l. This rapid biodiversification likely occurred less than 100 ka
after the end-Triassic crisis; the genus Psiloceras occupied all the
possible ecological niches worldwide, from the Pacific deep waters to
the NW European shallow deposits and also in some rare Tethyan
occurrences like at Germig in Tibet. This global dispersion allowed the
differentiation of the group in several major phyla, the
Schlotheimiidae, Discamphiceratinae, Arietitidae and Lytocerataceae,
which were the roots of all other Jurassic and Cretaceous ammonites. (C)
2012 Elsevier B.V. All rights reserved.