h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

...fire storm... ...global...




At any rate, that started me thinking on the conditions immediately following the Chixalub impact, just about every tree on the planet either knocked down or burned, global winter due to dust suspended in the atmosphere as well as smoke, offset somewhat by greenhouse gas emissions, half the oxygen in the atmosphere gone missing, a point established by means of studies of air bubbles trapped in amber laid down before and after the KT impact, for which I have yet to see a really adequate explanation.

Where did that oxygen go?

What happened to it?




Next I was thinking in terms of surviving lineages of animals, two lineages of shrews, one with eyelashes, one with cat-like whiskers, giving rise to modern placental herbivores and modern placental carnivores respectively, along with miscellaneous other shrews, the archaic group of placental mammals or sloth family which pre-existed the KT disaster, only one marsupial, a mouse sized honey possum, two varieties of monotremes, the echidna and the platypus, the monotreme (or therapsid) equivalents of the hedge-hog and the muskrat, the only surviving groups of egglaying mammals, representing a once thriving mammalian group which included among other species, the pterodactyls (compare the beak structures of the pterodactyl and the echidna, you should see what I mean), apparently only one lineage of birds.

Unfortunately, the KT object hit right in the middle of the monotreme/therapsid range.

One can kind of picture an echidna with an egg in the pouch dropping everything and furiously digging in along with miscellaneous armadillos and panglolins and anteaters doing the same, way off on the other side of Gondwanaland (which hadn't broken up yet, South America, Australia and Papua-New Guinea, Antarctica, the Indian Plate and the Arabian Plate, New Zealand and Madagascar still connected to Africa, none connected to Laurentia, which had already broken up into North America and Eurasia, Gondwanaland at the time actually considerably larger than Eurasia, the Chixalub impact site on the extreme southern tip of the North American land mass, an island continent with the sea all around) as the firestorm broke out, the platypus not liking the smell of the air as it emerged from the submerged entry to its burrow retreating and damming up the entrance.




Next I was thinking in terms of what the surviving animal groups had in common, and hit upon two things, first, they were overwhelmingly of insectivorous habit, second, most had strong adaptations for coping with hypoxic conditions, burrowing animals, birds adapted to high altitude flight, plesiosaurs adapted to deep diving at sea*.

Many have suggested that it was the loss of half the atmospheric oxygen that was the main driver of the KT extinctions.





*Plesiosaurs didn't go extinct with KT disaster, instead surviving in the fossil record till about 30 million years ago. Many authorities think they never went extinct at all, instead evolving into modern serpents, which first appear in the fossil record about 30 million years ago.

Dimetrodons not only appear in many dinosaur books, there was one in Blackgang Chine too.

My favourite dinosaur has to be the polacanthus - I have an original 'Walking With Dinosaurs' model of one.

Part of the attraction has to be the dramatic names, right? The more dramatic the name, the more memorable. No-one had heard of a Velociraptor before Jurassic Park, but since then everyone pictures a super-quick predator. 'Brontosaurus' is an exciting name in exactly the way that 'Apatosaurus' isn't. 'Apatosaurus' sounds like giant Brontosaurus droppings - which is why the name 'Brontosaurus' will live on no matter what the palaeontologists say the official name is. Similarly, though Smilodon was not a tiger, 'Sabre Tooth Tiger' sounds cool.

<BB<

I always called it Snaggletooth. Maybe I got confused with Snagglepuss.

Brachiosaurus or Stegosaurus doesn't sound very cool though. I also agree that Ankylosaurus deserves more love.
A lot of it is also about a skewed view of the dinosaurs. There were a lot of small dinosaurs too, but we don't see them so often. Also the fossils of big animals tend to be better preserved. So we are mostly exposed to the big dinosaurs, which seem even more amazing since we have so little megafauna today.

When the first Hypsilophodon were found on the Isle of Wight in 1849 it was assumed that they were juvenile Iguanodon for a good 20 years.

Besides which, I suppose it is much easier to spot really, really big bones rather than quite small ones. Are small bones more likely to be washed away in river beds, crushed under the weight of rocks on top (many fossils are quite cracked), swallowed by predators etc and so less likely to survive?

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>That's right, nevermind the experts. They're hidebound.<

Or maybe they've actually devoted their lives to studying their subject, know a shedload about bone structures, evolutionary trees and such and therefore are in a much better position to form a stance on it than you or I.

As I understand it noone actually claims birds are dinosaurs, they are merely the only surviving ancestors of dinosaurs.

This 'birds ancestors of dinosaurs' thing never excited me - it's all relative. I see people quoting facts like 'the human is more closely related to the petunia than it is to the elephant' and wonder what I'm supposed to do about it.

With respect to survivability of bones in the ground, basing this on experience with a garden composter and kitchen waste, the bones usually decompose within a year.

In the wild, they're quickly disposed of by small animals, including worms and insects, but also small rodents and birds, especially if weathered and crumbly.

The most spectacular fossil finds are usually in locations protected from the elements or media with preservative properties of some kind.

A comment on paleontology, irrespective of type or geological age, the evidence, at least in the popular literature is usually plotted against only the contemporary map of today's world, rather than compared and contrasted with the geography of the times in which the fossils were laid down.

Example, tracing movements of early humanity out of Africa, the early hominins are shown migrating around the Black Sea, which didN't exist as a sea until about 6800 BC.

Land bridges, when they form, are not only highways for animals, but also for diseases that are thought by some to have contributed to some of past species extinction events.

When access to geographical territories either opens or closes, it always means evolutionary change give sufficient time, though of opposite kinds, either increased rate of extinction, or increased rate diversification.




Notes on old smilodon, though the evidence is still sketchy, they apparently lived in troops of about 50, with social structures more like modern hyenas than any modern big cat.

Team players, in other words.

Hmmm... In that case, am I the only one to wonder what the collective noun is for sabre-tooth tigers?

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How about a pride or a pack of mis-named carnivores? From the evidence of the La Brea tar pits, Smilodon didn't have stripes and hence wasn't any kind of tiger. In fact, there's no evidence that any species of pre-historic cat had stripes. I don't know where 'sabre-toothed tiger' came from as a name, but it's just wrong.

It might not be a particularly accurate name, but it’s a brilliant brand and piece of PR.

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...mind the short hind legs, like those of wolverines or hyenas.

The high rpm they could develop made them lightning fast on a short sprint...

"Where did that oxygen go? What happened to it?"

Perhaps it was consumed in the global firestorm. Fire needs oxygen too, you know.




>That's right, nevermind the experts. They're hidebound.<

"Or maybe they've actually devoted their lives to studying their subject, know a shedload about bone structures, evolutionary trees and such and therefore are in a much better position to form a stance on it than you or I."


You seem awfully defensive about this.



"As I understand it noone actually claims birds are dinosaurs, they are merely the only surviving ancestors of dinosaurs."

Yes, they are claiming birds are dinosaurs.

And they're right to do so, because according to conventional definitions of cladistic groupings, any, um... hierarchy... of animal that evolved from any higher-order hierarchy of animal is also considered a part of that same, higher-order hierarchy of animal.

Hence, all hominids are also primates, all conifers are also trees, all rodents are also placental-mammals, all kangaroos are also marsupial-mammals, and all birds (having evolved from dinosaurs) are ALSO DINOSAURS.

I understand how it all works. I'm not arguing with the logic of it.



To clarify my position: This same method, taken to its extreme, means that all birds alive today are also considered reptiles. This, despite the fact that they have ABSOLUTELY NOTHING IN COMMON WITH OTHER REPTILES.

As such, I believe that our methods of categorization would be better served by acknowledging that once an animal-group evolves past a certain point, it becomes completely unrecognizable from its original, higher-order group. And therefore it should instead be split off from that group and become a founder of its own group.

Hence, in MY proposed system, the ornithischian dinosaurs (which eventually evolved into true birds) would still be part of the dinosaur-group. But, once you reach Archaeopteryx and have actual, FLYING birds, THEN no further descendants would be considered dinosaurs. They would just be birds.

I would also take them out of the reptiles, were it in my power.



I hope that clears that up.

Mr X, archaeopteryx are not a good cut-off point between birds and dinosaurs. Some archaeopteryx fossils have been found without clear feather impressions and these fossils have been mislabelled compsognathus (which lived at around the same time). This means that, at that stage in avian evolution, the distinction between bird and dinosaur was not sufficiently clear-cut to tell one from the other.

...helpful hint on differentiating 'bird-like' and 'mammal-like' reptiles, count their toes.

Turles have five, making them 'mammal-like,while crocodiles have three, making them 'bird-like'.

Turtles have got a common ancestry with crodilians and many features in common, but apparently the two groups differentiated some time in the Silurian, or shortly after, in an age when there weren't even any proper reptiles as yet.

Its possible to demonstrate bird-like and mammal-like traits even with amphibians.




Clarification on the term 'lineage' as I used it above, that doesn't necessarily indicate a single species, but can denote a group of closely similar species with a common ancestry, as with the Galapagos finches, for example.

Can you cite something that shows expert paleantologists claiming that then Mr X?

All the serious literature I've read reports birds as the only surviving clade resulting from dinosaurs - that is NOT paleantologists claiming that birds are dinosaurs.

Press reports on what scientists claim are usually horrifically inaccurate. A news reports claiming that 'scientists say birds are surviving dinosaurs' is either most likely a misunderstanding of what the scientists actually find or (more charitably)

I'm not being defensive, I have an aversion to non-experts dismissing the findings of experts in a peer-reviewed science without reasonable foundation - like actually having studied it *properly* themselves.
If you're going to blithely dismiss the consensus of world experts in a subject you better have a pretty extraordinary foundation of evidence and expertise yourself.
Maybe you have that, but that's not how it's coming across to me. In which case I'm pretty likely to blithely dismiss your opinion versus world expert consensus.

...(more charitably) them explaining something to lay people in terms they might follow - leading it to be 'slightly inaccurate'.

Pfft (to myself) - OK, I've actually read your post properly now - actually rather embarrassingly, I see what you mean and now I generally agree. Apologies.


Thanks for clearing it up like that. It was the one liner dismissiveness earlier that raised my hackles.

*shuffles off*

**



"Mr X, archaeopteryx are not a good cut-off point between birds and dinosaurs. Some archaeopteryx fossils have been found without clear feather impressions and these fossils have been mislabelled compsognathus (which lived at around the same time). This means that, at that stage in avian evolution, the distinction between bird and dinosaur was not sufficiently clear-cut to tell one from the other."


Oh whatever, you know what I mean.





"Can you cite something that shows expert paleantologists claiming that then Mr X?"

Virtually every documentary on the subject ever made, since the connection was firmly established.

Also I happen to have a textbook on the subject here with me. (Titled "The Evolution and Extinction of the Dinosaurs, by David E. Fastovsky and David B. Weishampel" if you want to know.)

Incidentally it was the Theropoda who evolved into birds, not the Ornithischia, so please let me make that one correction.


Also -- rather more importantly -- I took a class on the subject in college and my teacher, who IS a practicing paleontologist, is the one who explained all this to me in the first place.

I nevertheless disagree with his reasoning, for the reasons I've outlined above. While I completely agree that it's wiser to heed more authoritative sources, on any subject, than so-called "amatuers" of those subjects, I also don't believe it's in anyone's best interest to hold their word up as some infallible doctrine. Humans make mistakes no matter educated they are.

If that still bothers you, then that's your business. Please do not hound me.