Living Dinosaurs (re: mountain species)

You have a point that the peaks of mountains are not ideal for fossil preservation, but what about mountain lakes, mountain meadows, mountain valleys and mountain streams at lower elevations than the summit? They are certainly quite suitable. Corrosion can actually help. A mudslide from the peaks can help bury and preserve fossils at slightly lower elevations.

That of course depends on whether there will be global warming or whether there will be another ice age. I surmise that if one were to perish in the heart of Anarctica, one's remains will be preserved for quite some time until the action of plate tectonics move the land mass away from the Anarctic circle, or until a firestorm from another meteorite hit melts the ice.

I am curious. What is your take on the lack of chimpanzee fossils?

Sure, some kingsnake species are also found at high altitudes, but diversity of reptilian life usually decreases rapidly at high elevations, especially in forested areas in North America.

Too heavy to be suitable ancestors for a flyer.

Deinonychus is about the size of a human. Most gliding mammals are much smaller. Dumbo may be the only heavy bodied flyer that ever existed, but it is a cartoon. To be suitable ancestors for birds, a dinosaur has to be not much bigger than a gliding squirrel for feathers to have any aerodynamic effect.

To say that the hummer is a dinosaur, you first have to show that it is at least descended from a dinosaur. Firstly, Mayr and Ashlock (1991) are unconvinced that birds are descended from dinosaurs, showing that not every one subscribes to the orthodoxy. Secondly, recently discovered evidence (Ruben et al. 1999) shows that Scipionyx and Sinosauropteryx, two very different theropods, have a diaphragm and hepatic piston respiratory system similar to living crocodilians and mammals. Together with the developmental evidence of the hand published by Burke and Feduccia in Nature in Nov. 1997, the new evidence shows that theropods are probably more closely related to crocodilians than they are to the birds.

John Ruben of Oregon State Univ. remarked that a change from the hepatic piston system to the living birds' air sac system would be impossible, since the transitional animal would have a life-threatening hernia, or hole, in its diaphragm. Some cladists have argued that birds evolved the air sac system from the hepatic pistion system, but this scenario is both ad hoc and highly unlikely physiologically. I predict over the next few years, many museums will quietly rearrange their exhibits so that birds are no longer claimed to be direct descendants of dinosaurs. Either that or many prestigious museums will risk becoming the laughing stock among knowledgeable scientists.

If you want to see a living dinosaur, the crocodylians-not the birds-are the closest things to one. Birds are warm blooded; dinosaurs and crocs are cold-blooded. Birds are feathered; dinosaurs and crocs have scales. Birds have air sacs; dinosaurs and crocs have a diaphragm. Those who claim that birds are dinosaur descendants or 'living dinosaurs' are simply barking up the wrong tree.

The problem is that orogenically active areas are poor at preserving sediments over long time periods. Continued uplift or erosion as the uplift dies down are both apt to remove such limited deposits. There may well be a few preserved Cretaceous sedimentary bodies formed in montane environments. All those I am personally aware of, however, are Tertiary, and the Neogene is much better represented among these than the Paleogene. Paleobotanists working in western North America (plants have much better fossil record than vertebrates) have found a few, mostly Pliocene deposits of montane sediments, but have mostly had to guess about what might have been growing in the mountains, or work from water-worn cone scales and such.

This is not to say that montane environments in a tropical climate would necessarily be cold - look at modern tropical mountains. The high Andes are chilly, sure, but even much lower mountains offer a very different set of adaptive pressures from tropical lowlands, and tropical mountain ranges often have an impressive amount of endemism and striking adaptations to crag habitats and such. There's no real reason that there shouldn't have been montane dinosaurs, in the strict sense, excluding birds, but we'll be very lucky to recover significant fossils of them. We have little or no idea about montane birds of the Cretaceous, either, regardless of whether we consider their sister group to lie within the Theropods or among the Archosauria _s. lat._ or elsewhere.

Dinosaurs have been found in Alaska and Australia. The Alaskan dinosaurs WERE within their contemporary Arctic circle. I suspect that some of the Australian dinosaurs were antarctic. You could prove your point about frozen carcases fossilizing IF you can prove the Alaskan and Australian fossils were frozen PRIOR to being fossilized. Since plant material is found in the same locations however, I doubt that happened.

and if you throw in a high-elevation rainforest you can quadruple the number of small vertebrate species. Is anyone going to discuss AMBER as a fossil known from high elevation forests?

<snipped-inane arguement of yes tehy are-no they're not sparked due to size considerations - dinosaurs must be too LARGE to be flyers>

What POSSIBLE proof do you have that dinosaurs smaller than that which have been found COULD NOT exist? I want a biological reason.

What is the average size of pre K/T mammal fossils? How many are known? Is the preservation bias of tiny pre K/T mammals prehaps due to the simple fact that they BURROWED-that they NESTED IN HOLES IN TREES? Both conditions will increase the likelyhood of fossilization of an animal that died in sito.

What has been surmised about dinosaurs? -Open habitats Why WOULD we see tiny dinosaurs preserved?

wrote...

That was why I thought mountain valleys may be better than mountain tops in preserving fossils. Continued erosion can send tremendous amounts of sediments into the valleys, burying whatever fossils which may be present deeply.

Perhaps the fossils are buried so deeply that most of them cannot be found. It may take millions of years of erosion to expose them again.

Sure, mountainous areas are like terrestrial islands. Montane populations are often prevented from interbreeding with other populations on other mountain tops. The mountains of se. Arizona have been described as 'island' habitats for this reason. The intervening landscape is too hot and dry for many montane species to cross except during glacial periods. Tiger salamanders in the Great Basin are often isolated on different mountain tops. Genetic studies have shown that there is little interbreeding between populations.

There is a very good physiological reason. Ruben et al. argue that the dinosaurs have the nasal passages, lung structures and diaphragm of cold blooded crocodilians, not the nasal passages and air sacs characteristic of modern endothermic birds. If they were ectothermic, they probably won't survive in the cold mountain habitats.

According to a paper by Chinsamy et al. (1994, Nature 368:196-197), a Mesozoic bird was probably cold-blooded because it has growth rings in its bones. If that is the case, endothermy probably did not evolve in Archaeopteryx either. It is very probable that endothermy evolved among birds in the Tertiary or at best late Cretaceous. Hence it is a good reason why montane birds are unknown from the Cretaceous. They haven't evolved the ability to cope with montane climates yet.

Without meaning to get dragged into the bird/dino origins debate, I'd still like to point out that Ruben has been somewhat misquoted here. Although Ruben likes to use his dino evidence to argue for the non-homology of theropod and bird respiratory systems, he never says (nor does he mean to imply

Ruben et al. did not say these mucscles were homologous between crocs and theropods in his article, but they did not say they were not either. There are three possibities for the similarities: convergence, parallelism and synapomorphy. Convergence is rather unlikely because of the rarity of this system in extant tetrapods and the fact that early Triassic crocodylomorphs were terrestrial beasts with upright postures, implying greater activity levels and need for respiratory efficiency than the extant crocs (Ruben et al. 1999 Science). So this feature may have arisen early in the evolution of the thecodonts or basal archosaurs. Their similarities are most likely evidence of synapomorphy or at least parallellism.

If this respiratory system arose early in thecodont evolution, then it opens the possibility that may be crocodilians are more closely related to theropods than either of them are to the Ornithischians. There are few characters uniting the 2 traditional dinosaurian groups except perhaps upright posture. Perhaps the similarities between the Saurischia and Ornithishcia are convergences or plesiomorphies associated with that posture. If the Ornithischians can converge upon the modern Aves in pelvic structure, I see little reason why 'dinosaurian' characters cannot also be convergences. In two of his books, Carroll (1988, Vertebrate Paleontology and Evolution; 1997 Patterns and Processes of Vertebrate Evolution) does not formally recognize the Dinosauria (Ornithischia + Saurischia) as a taxon, perhaps with good