COMPARING PATTERNS OF PHANEROZOIC GENERIC ORIGINATION AND THEIR POSSIBLE CONSTRAINTS: IS THERE A RELATIONSHIP TO ENVIRONMENTAL CHANGE?

One of the conundrums faced by paleobiologists is attempting to elucidate the potential roles that physical, chemical, thermal, and biologic constraints have placed on the history of life. In order to investigated this issue, we compare the timing of genera origination through the Phanerozoic derived from Sepkoski's (2002) compendium of fossil marine animal genera with data ‘binned' using intervals of different duration(e.g., periods, subperiods, epochs, and substages) against various factors (i.e., temporal variation in sea level, mean global temperature, mean global isotopic curves of δ¹⁸O and δ¹³C, and global anoxic events) as well as mass extinctions events. Our results show found that: (i) Given that the global physical factors curves are generally relatively poorly resolved and only cover general details, there is a good correlation between the physical factors and the origination pattern only when the latter are plotted at low stratigraphic resolution (i.e, periods and subperiods). (ii) The distribution of origination peaks and troughs change when the temporal resolution used is increased, generally producing a more even origination pattern at higher resolution levels (i.e., substages). (iii) Peaks in the number of originations have a better correlation with the lesser extinction event aftermaths than with the ‘great five' aftermaths. This suggests two potential explanations: (1) the lesser events produced more evolutionary opportunities; or (2) a biotic recovery was delayed due to the stronger intensity and hence greater biotic impact of the larger events. Finally (iv) the so-called ‘Pull of the Recent' is more pronounced for low-temporal-resolution data, but as the temporal resolution is increased this effect weakens. Although some changes in the rate of variation among of various factors match with some origination peaks, these partial result let us to conclude that there are not a set of clear ‘rules' that govern origination patterns through the Phanerozoic. This reflects the need for more refined proxy data to more fully reconstruct the Earth's environment and its changes as well as the extreme difficulty of attempting to unravel not only what roles various factors play in governing origination, but how these various components interact with each other and the biota to produce evolutionary change.