Ammonite extinctions , Ammonites are one of the most recognisable fossils of our prehistory, Ammonoids reigned supreme in their habitat for hundreds of millions of years, surviving from the Devonian period 417-354 m.y.a; through many extinction events, their final demise coinciding with the extraordinary 'KT boundary' Ammonite extinction event at the end of the cretaceous period approximately 65 m.y.a.

Heteromorph ammonites of the extinction

 

Throughout these evolving stages of this cephalopoda group several extinctions would redefine the habits of the marine invertebrate which would develop into the most strange shaped phragmacones (shells), and also great sizes, by the end of the Cretaceous. The largest types recorded up to 8 feet 6 inches (2.6m), Pachydiscus seppenradensi was discovered in a limestone quarry near the town of Munster Germany C.1895, of Campanian stage, late (upper) Cretaceous Period, around 83-72 m.y.a;  discovered by Theodore Nopco. Theodore sold the ammonite to Professor Dr. Hermann Landois (for 125 gold Marks, the average annual salary at the time was 650 Marks), the Dr. founder of the Westphalian Provincial Museum of Natural History.

The now fossilised specimen weighs about 3500kg! It is believed that perhaps even larger ammonite lived. It is also theorised ammonites of this monumental size may have lived a more sedate deep water-shelf life, whereas their smaller cousins were pelagic.

The ammonite group evolved during the Devonian period, named after the county, Devon in England. The first major blow to the ammonite group was during the Frasnian stage. The Kellwasser event, close to the Frasnian – Fammenian boundary (375 mill yrs ago) and often referred to as the ‘Devonian extinction/Ammonite extinction’ event. Later in the period, again in the Famennian stage another event saw the demise of not only marine life, the Hangenberg event affected marine and land environments.

The ammonites became so diverse after the initial Ammonite extinction in the Frasnian stage, due to the lack of competition perhaps, they filled the oceans and ranged globally. Interestingly palaeontologists and geologist found the ammonite a useful aid for dating rock strata, rather than the other way around, this primarily due to the proliferation of ammonites. It wasn’t always so, in the early days of the science of Stratigraphy. William Smith and John Hutton (both scholars equally termed the father of modern day geology, at various times), noted in the late eighteen century, as they studied the geology of Britain, the importance of the inclusions of fossils in the rock layers. Over the last two centuries many same type ammonites have been found in the rock formations of several continents, thus it has transpired rather than date the rock, then date the fossils contained therein, the fossils have come to define the date of each rock layer, making identification of the age of rock layers expedient for modern day geologists and historically aiding the formulation of tectonic plate movements.

After the Devonian extinction event the Permian period erupted with more bad news for the ammonite population. In this period two major extinction events are noted, firstly ‘Olsens Gap’ (around 270 - 260 mill yrs ago), it has been difficult to ascertain exactly how long the gap occurred being close to the second major event and so theorist have accessed that more than one event rolled over millions of years, as pulses, these pulses continue through the period several times through the fossil record. An even greater mass Ammonite extinction took place extinguishing almost all the Ammonites, including the goniatites. The ‘Great Permian Extinction’ signalled the end of other life forms including the trilobites, a major invertebrate group. The event was almost for life on our planet, a total extinction event, approximately 96% of marine life, 83% of genera became extinct. A deteriorating climate, anoxic oceans, with possible impact and volcanic events which over millions of years contributed to the catastrophe. It is estimated it took up to 30 million years for life on earth to recover from this apocalyptical period. However the great survivor ammonites did survive along with brachiopods and nautiluses and of course the reptiles along with several other groups. Some of the main ammonite groups to survive are the Ceratitina and Phylloceratina which prospered and diversified through the Triassic period.

Post the ‘Great Dying’, the Triassic again was no friend to the ammonites. By the early Triassic in the Olenekian stage approx 249-247 m.y.a., another extinction event altered life patterns, the Smithian-Spathian extinction occurred. Around the tropics many species disappeared as surface temperatures reached an estimated 40°C. Later by the end of this period of time the boundary of the Triassic - Jurassic Period saw once again a major extinction event close the age. No slow degradation this time an abrupt 10,000 year event. Now was the age of the Dinosaurs to enter stage and proliferate terrestrially, while in the oceans our friends the ammonites lost one major group Ceratitina, however the family of ammonites survived to once more diversify throughout the Jurassic like never before.

The ages of the Jurassic and Cretaceous would define the ammonites like no other period before, up until the infamous KT boundary. KT meaning the Cretaceous-Tertiary, 'K' scientifically is the 
symbol for the Cretaceous (named Cretaceous after the Belgian geologist Jean d’Omalius d’Halloy C.1822 after his work identified it from chalk strata of the Paris basin), the K is from the German language, 
derived from the Latin 'creta' (chalk) and in German 'kreide' (chalk), so named the infamous ash layer found around the world donating the abrupt Ammonite extinction level event.