WI Marine Dinos Never Became Extinct?

Small nitpick, so-called "marine dinosaurs" are NOT DINOSAURS. The great marine reptiles belonged to a completely different reptillian clade. The amniotes (reptiles, mammals, and birds) are usually classified according to temporal fenestration, which is probably the most reliable method of phylogenetic classification. The major amniote classes are anapsids, diapsids, and synapsids. The anapsids include all basal amniotes and the original reptiles. Today, anapsids are represented by testudines (turtles and tortoises). Diapsids include most reptiles and all birds. Synapsids include the mammals and the extinct pelocosaurs (such as dimetrodon) and mammal-like reptiles.

The dinosaurs, as well as birds, pterosaurs, crocodiles, lizards, mososaurs, and snakes are all diapsids. However, plesiosaurs are euryapsids and ichtyosaurs parapsids. The parapsid condition is similar to the euryapsid condition, and parapsid skulls might be a variation of the euryapsid type. Both in turn were derived from the diapsid condition. Parapsid reptiles evolved either from euryapsids (most likey) or independently from sea-going diapsids.

The following link explains it better:
http://tolweb.org/notes/?note_id=463

See also:
http://tolweb.org/Amniota/14990

A cladistic classification of amniotes follows.

ANAPSID
  • testudines (turtles, tortoises)
DIAPSID
  • squamates
    • lizards, snakes, mososaurs
    • tuatras
  • archosaurs
    • crocodiles
    • pterosaurs
    • dinosaurs & birds
  • marine reptiles
    • plesiosaurs (euryapsid)
    • ichtyosaurs (parapsid)
SYNAPSIDS
  • pelycosaurs (including dimetrodon)
  • therapsids
    • monotremes
    • mammals
There are several key differences between marine reptiles and dinosaurs. Aside from the fact that dinosaurs are archosaurs and are far more closely related to birds than any living or extinct reptile outside of archosauria, it is now understood that dinosaurs, like pterosaurs, were in fact endothermic (warm blooded) like mammals and birds (actually, their metabolism was like birds). The major groups of marine reptiles: euryapsid-derived plesiosaurs and ichtyosaurs, and the snake-like mososaurs were probably all ectothermic (cold blooded). We are reliably certain that mososaurs were cold blooded because mososaurs were squamates who evolved from a lizard-like ancestor. I am not as certain about plesiosaurs and ichtyosaurs, but I think they had a metabolism like that of sharks. [The distinction between ectothermy and endothermy is probably more a matter of degree than of kind. Virtually all animals produce SOME heat in metabolism. Most lifeforms produce very little heat, but endotherms produce a great deal, so much so that they may maintain a constant temperature.] Plesiosaurs and ichtyosaurs probably were able to maintain a warmer body temperature than the surrounding water by virtue of their sheer size and bulk, which would allow them to enter cold waters, but their inability to maintain a high enough body temperature (due to a fundamentally ectothermic metabolism) would keep them from thriving in cold climates. Therefore, the marine reptiles would be confined to sub-tropical seas.

Originally Posted by jacobus
Might humanity have come to revere the sea monsters, and worship them as gods? Would the faithful have left human victims chained at the shore as a sacrifice, like Andromeda was left for Cetus? Or would we execrate them as some kind of demons?

If such practices were to happen, they would likely be abandoned were Christianity or Islam (or whatever ATL equivalent) became widespread. Instead, such creatures would probably be classed as "leviathans," viewed as frightening sea monsters, but not as deities.

Originally Posted by TMOT1955
I'm not sure they really did become extinct.

Looks like we have a believer in Nessie! :rolleyes:

Originally Posted by TMOT1955
My personal belief is that The Loch Ness Monster (Nessie) isn't just one individual but is instead a small community or group of individuals. The same with Chessie and Champie supposedly spotted in The Chesapeake Bay and in Lake Champlain.

I think in fairly large but isolated bodies of water like Loch Ness, it may be possible for a small number of such dinosaurs to have adapted and survived and their offspring are still with us a species little changed in say 100 million years.

Well, they would pretty much have to be! One would need numerous individuals to reproduce, at least if Nessie, Champ, the Ogopogo monster, et all, are living beings and not paranormal phenomena. There can not be just one such creature, which is another problem with the Loch Ness Monster "theory." There may be more than enough biomass in Loch Ness to support a single large adult plesiosaur, probably even two. However, for the species to continue, there must be a large population, which would likely starve. If the global population of plesiosaurs were small enough, then the genetic variability would be minimized, thus explaining how an animal can exist for 80 million or so years relatively unchanged. There is of course one obvious problem. Such small, constrained populations tend to go extinct! This is why the Loch Ness Monster, Champ, and other supposed living plesiosaurs can not be plesiosaurs, or any other extinct marine reptile.

My take is that the reason why belief in the Loch Ness Monster is so prevalent is because it is so deeply rooted in the folklore and mythology of Scotland. The archetype of the being is derived from the mythical kelpie, or "water horse" of Celtic paganism. The kelpies were supernatural beings or phantasmic entities, perhaps lake deities or the ghosts of virgin maidens, or the like. A version of the myth persisted when Keltic peoples like the Irish, Scots, Picts, and Welsh were converted to Christianity. According to Adomnan, Saint Columba encountered a "water beast" in the vicinity of Loch Ness. The paranormal nature of the creature explains why the Nessie is referred to in the singular, it is always THE Loch Ness Monster. While I think that the modern Nessie mythos is tied to the kelpies of Britannic mythology, it was only recently that the Loch Ness Monster was understood to be a natural creature.

In pre-Christian times, the kelpie was a deity or fantasm. In Christian times, it was a demonic being encountered by St. Columba. In modern times, the myth took on a "scientific" nature, and early in the 20th century, paleontology was a new field. The discovery of dinosaur and marine reptile fossils influenced the belief that the alleged creature of Loch Ness is a surviving descendent of a prehistoric animal. The Loch Ness myth is purely a product of the imagination, or perhaps influenced by a natural phenomenon, such as a seismic phenomenon or school of fish, mistaken for a beast.

Originally Posted by Emperor Qianlong
Actually, one of the peculiar features about dinosaurs is that none* of them were aquatic.

Depends on your definition of aquatic. Aquatic like cetaceans, or aquatic like hippopatami. While all dinosaurs were terrestrial animals, none were aquatic in the sense of "ocean-dwelling" (there were no flippered dinosaurs), there is strong evidence that some dinosaurs were very capable swimmers, and that some of the large sauropods may have been amphibious or "aquatic" in the sense of hippos and crocs. It is theorized that some sauropod dinosaurs like diplodocus or the apatosaurs and brachiosaurs spent a great deal of time in lakes or rivers.

However, you are correct that the marine reptiles were NOT dinosaurs, or even closely related, though many laypeople have the habit of referring to all the great Mesozoic and Permian reptiles as "dinosaurs."

Originally Posted by Weaver
The problem is that reptiles are not mammals. Whilst lions and orcas are relatively rare, crocodiles and other predator reptiles are not.

There is a very basic difference between mammalian and reptile predators...reptiles are very numerous. Whilst I have in the past travelled for days in Southern Africa seeing never a lion or any other predator, I would not be game to attempt to swim across any of our estuarine rivers in Northern Australia...there are literally dozens in every stretch of river just waiting for a chance.

Strange to say a modern time traveller would be very likely to be able to dodge the odd T-Rex on land (warm-blood), he would be foolish in the extreme to swim across a stretch of ocean.

Very true, ectothermic predators would be far more common than endothermic predators. In fact, the ratio of carnivorous dinosaurs to suitable prey or carrion animals was relatively low, comparable to the ratio of predatory or scavenger mammals to herbivores, further evidence that the dinosaurs were warm blooded. Marine reptiles were almost certainly entirely ectothermic, and would be able to survive on less food. Compare the frequency of crocodiles and constrictor snakes with relatively rare lions, tigers, or jaguars... or sharks to orcas.

Personally, I think that for any large marine reptile of the Mesozoic to survive would be bordering on ASB territory. Of course a more plausible reptillian sea monster might be derived from extant lizards or snakes. Monitor lizards or sea-going constrictors might make a good candidate to replace the mososaurs. I am not sure if giant sea turtles can evolve into a substitute plesiosaur.
 
Small nitpick, so-called "marine dinosaurs" are NOT DINOSAURS. The great marine reptiles belonged to a completely different reptillian clade. The amniotes (reptiles, mammals, and birds) are usually classified according to temporal fenestration, which is probably the most reliable method of phylogenetic classification. The major amniote classes are anapsids, diapsids, and synapsids. The anapsids include all basal amniotes and the original reptiles. Today, anapsids are represented by testudines (turtles and tortoises). Diapsids include most reptiles and all birds. Synapsids include the mammals and the extinct pelocosaurs (such as dimetrodon) and mammal-like reptiles.

The dinosaurs, as well as birds, pterosaurs, crocodiles, lizards, mososaurs, and snakes are all diapsids. However, plesiosaurs are euryapsids and ichtyosaurs parapsids. The parapsid condition is similar to the euryapsid condition, and parapsid skulls might be a variation of the euryapsid type. Both in turn were derived from the diapsid condition. Parapsid reptiles evolved either from euryapsids (most likey) or independently from sea-going diapsids.

The following link explains it better:
http://tolweb.org/notes/?note_id=463

See also:
http://tolweb.org/Amniota/14990

A cladistic classification of amniotes follows.

ANAPSID
  • testudines (turtles, tortoises)
DIAPSID
  • squamates
    • lizards, snakes, mososaurs
    • tuatras
  • archosaurs
    • crocodiles
    • pterosaurs
    • dinosaurs & birds
  • marine reptiles
    • plesiosaurs (euryapsid)
    • ichtyosaurs (parapsid)
SYNAPSIDS
  • pelycosaurs (including dimetrodon)
  • therapsids
    • monotremes
    • mammals
There are several key differences between marine reptiles and dinosaurs. Aside from the fact that dinosaurs are archosaurs and are far more closely related to birds than any living or extinct reptile outside of archosauria, it is now understood that dinosaurs, like pterosaurs, were in fact endothermic (warm blooded) like mammals and birds (actually, their metabolism was like birds). The major groups of marine reptiles: euryapsid-derived plesiosaurs and ichtyosaurs, and the snake-like mososaurs were probably all ectothermic (cold blooded). We are reliably certain that mososaurs were cold blooded because mososaurs were squamates who evolved from a lizard-like ancestor. I am not as certain about plesiosaurs and ichtyosaurs, but I think they had a metabolism like that of sharks. [The distinction between ectothermy and endothermy is probably more a matter of degree than of kind. Virtually all animals produce SOME heat in metabolism. Most lifeforms produce very little heat, but endotherms produce a great deal, so much so that they may maintain a constant temperature.] Plesiosaurs and ichtyosaurs probably were able to maintain a warmer body temperature than the surrounding water by virtue of their sheer size and bulk, which would allow them to enter cold waters, but their inability to maintain a high enough body temperature (due to a fundamentally ectothermic metabolism) would keep them from thriving in cold climates. Therefore, the marine reptiles would be confined to sub-tropical seas.
May I say I'm glad to see another taxonomy geek on the board!
 
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