Cretaceous Ichthyosaur

many ichthyosaur lineages continued cretaceous



restoration of platypterygius kiprijanovi – albian-cenomanian of kursk region (russia)

traditionally, ichthyosaurs seen decreasing in diversity further cretaceous, though had worldwide distribution. fossils period referred single genus: platypterygius. last ichthyosaur genus thought have become extinct in late cretaceous, during cenomanian 95 million years ago. ichthyosaurs have disappeared earlier other large mesozoic reptile groups survived until end of cretaceous. 2 major explanations given this. firstly, have been matter of chance. second explanation had extinction caused competition. less hydrodynamically efficient animals, mosasauridae , long-necked plesiosaurs, flourished. ichthyosaurian overspecialisation contributing factor extinction, possibly being unable keep fast-swimming , highly evasive new teleost fish, had become dominant @ time, against sit-and-wait ambush strategies of mosasaurids proved superior. model emphasised evolutionary stagnation, innovation shown platypterygius being ten fingers.

recent studies, however, show ichthyosaurs far more diverse in cretaceous thought. fragments referred platypterygius in fact represented diverse species. in 2012, concluded @ least 8 lineages spanned jurassic-cretaceous boundary, among them acamptonectes, sveltonectes, caypullisaurus, , maiaspondylus. in 2013, cretaceous basal thunnosaurian revealed: malawania. indeed, there radiation during cretaceous due increase of coastlines when continents further broke up.

the demise of ichthyosaurs has been described two-step process. first extinction event in beginning of cenomanian eliminated 2 of 3 ichthyosaur feeding guilds present, soft-prey specialists , generalists , leaving apex predator group, not particularly specialized. second major ichthyosaur extinction took place during cenomanian-turonian boundary event, anoxic event , eliminating apex predators, after single lineage survived, platypterygius hercynicus, disappeared shortly afterwards, 93 million years ago. ichthyosaur extinction pair of abrupt events rather long decline, related environmental upheavals , climatic changes in cenomanian , turonian. if so, not caused mosasaurid competition; large mosasaurs did not appear until 3 million years after ichthyosaur extinction, fill resulting ecological void. plesiosaurian polycotylidae perhaps filled of niches occupied ichthyosaurs, although had coexisted 19 million years. extinction result of ecological change , volatility caused changes in migration, food availability, , birthing grounds. part of cretaceous 1 in many other marine extinctions occurred, including of types of microplankton, ammonites, belemnites, , reef-building bivalves.