[chris (OP)]

A listener called in to a radio programme in which I was participating this week; unfortunately they ran out of time before he actually finished asking his question, or received an answer.

He was suggesting that air pressure changed, in some way, during geological time and this affected oxygen availability in the oceans and this accounts for the extinction of ammonite species.

What is the opinion of the forum usership on this one?

chris

[Don_1]

Both the ammonites and the Nautilus managed to survive the Permian mass extinction and again at the end of the Triassic they survive another mass extinction, but come the K-T boundary, only the Nautilus survives, yet the two species are very similar.

We do know that the K-T boundary brought about the extinction of most of the large animals, both terrestrial and aquatic, and many smaller creatures including a huge range of plankton.

Since ammonites began life as plankton, they would certainly have suffered from a shortage of young. Though the life cycle of the Nautilus is pretty much unknown, it is known that their eggs are large, so the young Nautilus would have a distinct advantage over the ammonite.

While the Nautilus is a deep sea dweller, rising to around 100m at night to feed on deep sea krill as they rise to feed, the ammonites are thought to have been shallow water dwellers which would not have gone deeper than around 100m. This is supported by the ammonites feeding habits, which include shallow water fish, molluscs and cephalopods. This would leave the ammonites, which would be much larger than the Nautilus, more prone to influence from the atmosphere.

The problem is, that we cannot be sure as to what caused the K-T event or the ramifications of the event, but I doubt it would have resulted in a radical change in pressure, if any at all. I think it is likely that the ammonites fell victim to similar circumstances to the dinosaurs; a lack of food, lack of young and, in the case of marine life, dissolved pollutants in the oceans close to the surface. These pollutants could have been both gaseous and solid and may have caused a significant reduction in dissolved oxygen levels, or could have simply poisoned shallow water creatures unable to go into deeper water unaffected by the problems in the atmosphere.

[chris (OP)]

Brilliant; thanks Don

[CliffordK]

I find it interesting that land and sea extinctions are so tightly tied together.

It would seem like shallow and deep sea oxygen would be somewhat different.

Shallow oxygen is likely controlled by things such as algae blooms and decomposers.  What we see today with dead zones caused by chemical fertilizers. 

I'm seeing that volcanic ash carries nutrients, and can cause an algae bloom.  Perhaps the same would be true with a large impact event. 

Algae, of course, is a double edged sword.  It does provide some oxygen, especially near the surface.  It is also nutritious.  However, as it sinks, it can feed decomposers and create an anoxic region.

Oxygen in the deep oceans is likely controlled by deep sea currents.  There have been hypothesized periods where a large ice melt can cause low density surface water, and effectively shut down the deep sea currents for a period of time, which could have devastating effects for the deep sea oxygen levels, as well as deep sea temperatures.

Anyway, it is quite possible that ocean extinction events could be associated with significant changes in oxygen levels.

[nicephotog]

Are all these creatures extincted using the same reproductive system e.g. eggs , reptiles, maybe some type of disease claimed them and maybe at the reproductive/infant stage?
Would it be possible to compare modern animals of an alike constructed type associate the needs bodily systems of their food gathering and reproductive cycles in terms of DNA contents to a disease or even microscopic disease/parasite system of that type?
http://www.windows2universe.org/headline_universe/olpa/diatoms_7jan09.html

http://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=112803&org=NSF
...Deep in the cold tundra of northern Canada, where it is dark much of the year, Siver recently had the opportunity to sample mud dating back 48 million years. The material lay deep in the bowels of a diamond mine under 150 feet of glacial material that covered the remains of an ancient lake. Viewing the mud sample under an electron microscope, Siver discovered a microorganism identical to those that exist today in the tropics. These tiny organisms had instantly proven that the area was once warm and tropical.

I suppose in retrospective they got the flu in many cases.

[Don_1]

Both the Nautilus and Ammonite  lay eggs, but the Nautilus lays a single large egg in deep water while the Ammonite lays many tiny eggs in much shallower water.

The hatching Nautilus is therefore already quite large, but the Ammonites are tiny plankton. Eventually, the Ammonite will outgrow the Nautilus, becoming perhaps twice the size. As already stated, the Nautilus is a deep sea dweller and the Ammonite remains in shallow waters.

In the case of the Ammonite and the Nautilus, I think it is the depth at which they live which is the most likely determining factor of survival, rather than size.

On dry land, the reptilians are laying eggs of all sizes. Some are buried, some in open nests.

Not all the reptilians fall foul of these mass extinctions. The Permian extinction saw the extinction of the Synapsids, but one group, the Clade Anapsids, survive. Later, in the Triassic mass extinction, the Chelonians, which descended from theses Clade Anapsids, survives again and later still their descendants survive the KT Boundary. They survive today in the shape of the modern Testudines, Tortoises and Turtles.

Since there is evidence that the Tortoise’s shell began to develop more than 250 million years ago, perhaps it was this adaptation which helped these animals survive where others did not. Perhaps it was also the Tortoises opportunistic feeding habit which gave it the edge, or its ability to go without water for long periods. Tortoises and turtles both bury their eggs and, in common with other reptiles, the young hatch fully formed, including a shell which, in most cases, rapidly hardens. But then most reptiles are hatched fully formed, so this may not be a determining factor in survival.

But not all the Tortoises survive the K-T Boundary, Basilemys sinuosa, for example became extinct. What was it about the anatomy of this tortoise that left it susceptible?

Since mass extinctions do not happen overnight, there must be a number of factors in play. It would certainly seem reasonable to theorise that during the long period of disturbance which causes mass extinctions, that animals might be more susceptible to bacterial, viral or parasitic attack. But I can’t see how any particular traits or anatomical construction of a species or an order might render it less or better equipped to survive. I might concede that the bacteria, virus and parasite might benefit from the decreased ability in their prospective hosts to fight off an attack, but would they not also have been subjected to the same problems?

[nicephotog]

But I can’t see how any particular traits or anatomical construction of a species or an order might render it less or better equipped to survive.

In terms of "anatomical construction" correct me if i'm wrong(easily) but most were the larger set of animals, although an interesting morphise size shift and extinction occured in Canidae of the borophaginae(however, only half way back to and after the K T Boundary), but in my terms of seeing it , it is similar to economics if your that large you must have as much dietry intake as required as minimum effective consumption and within a particular time frame that must be completed not later. All of them were a bit much to uphold at some time perhaps and had to injure each other to compete and that would lead to both malnutrition and death from low effective immunity to disease, while smaller creatures or members of the species may be able to survive, successfully ambush to compete and have adequate dietry intake to sustain themselves.
(After reading about the K T Boundary i wonder if Iridium constructed to match the meteor compond could be used with elephants to find the physical results?)

[Don_1]

While it would be true to say that the larger the animal, the more food it will require, it is a popular misconception that all dinosaurs were huge or even rather large. The Tyrannosaurus Rex would have weighed in at around 8 tons, but the not-so-celebrated Tyrannosaurus Raptorex  weighed just about 70 – 80kgs, or about half that of a modern Lioness and the Velociraptor would have weighed around 15kgs. All three were carnivores.

As far as the sauropods go, yes some were huge, very huge indeed and could weigh in at over 100 tons, but there were even small sauropods, such as the Europasaurus, which would have been much the same size and weight as a modern Ox.

But regardless of shape, size, anatomy and habitat, whether diurnal or nocturnal and whether herbivore or carnivore, they all succumb to the K-T Boundary.

While there is not a great deal known about the eating habits of dinosaurs, especially the carnivores, I think it would be reasonable to suggest that a large T.Rex might partake of a Triceratops or Stegosaurus then not need to eat again for some considerable time, just as modern reptiles do.

I would feel much happier to put this mass extinction down to wide spread causes rather than to a few odd factors. Pollution of the air, water and soil, food shortage, lack of light (UV especially), carcinogenic fall out and, yes, infection. In fact a whole catalogue of reasons, but it does seem that the reptilians were hardest hit.

[nicephotog]

nb: "sea currents" and circulation is done by convection.

Here's another one, The residue of the meteor imact is agreed to have committed a large enough chemical poisoning upon reptiles, but it may be better viewed as not so much the spread of the meteors material as the ability over time and generations for reptiles to not get past the poisonous surrounding by traveling to it not it reaching them.

As for ammonites, one science site said the oceans had fallen in depth around that time. If they fell quickly e.g. an earthquake or earthquakes caused large numbers of cracks and drained large quantities of sea water, that would be insantanious environment loss regardless of being able to be swept along in the water to where they settled after such an event.

If both gigantic earthquakes and the meteor occurred at the one time , then i suppose "Bob's ballbearing roller-skates and bananas" compamy may have thrown in volcanos too.

[Geezer]

My ammonites die off every year, but they seem to recover in the spring, unlike my nasturtiums.

[Don_1]

My ammonites die off every year, but they seem to recover in the spring, unlike my nasturtiums.

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