380 MESOZOIC/End Cretaceous Extinctions Figure Cretaceous Paleocene, stage level extinction patterns for marine invertebrate families Data tabulated from Benton (1993) The Fossil Record London: Chapman & Hall In fact, overall Maastrichtian brachiopod family richness is less than a third that of bryozoans, and the actual number of brachiopod families that became extinct during this stage was comparably reduced Among echinoderms, irregular echinoid families bore the brunt of the Maastrichtian extinction pulse Taken as a whole, it is difficult to avoid the impression that marine invertebrates were being subjected to much longer-term extinction pressures than their protistan counterparts with the Maastrichtian representing the apotheosis of trends that first become evident in the early part of the Late Cretaceous Moreover, once the Maastrichtian catharsis was reached, it had relatively less overall effect on marine invertebrate family-level diversity than did the protistan reductions As for the patterns of species-level extinction distributions, despite two decades of intensive study the fine-scale extinction pattern is known only for ammonites in two Late Maastrichtian sections (Seymour Island, Antarctica and Zumaya, Spain) In both cases extinctions observed extinction horizons are not concentrated at the K–T boundary, but rather are spread throughout the entire interval (see Figure 2) Marine Vertebrates This group, largely comprising fish, ichthyosaurs, mosasaurs, sauropterygians, and marine turtles, has rarely received much attention in Maastrichtian extinction studies despite the iconic status of mosasaurs and plesiosaurs as stereotypic K–T victims One sometimes also sees ichthyosaurs mentioned as participants in the end-Cretaceous extinction event, but this is erroneous The last ichthyosaur became extinct in the Albian Overall (Figure 7), marine vertebrates