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Unanswered Question about Cretaceous–Tertiary Extinction Event: 2

June 29, 2019 1 comment

In the previous part of this series, I wrote about how our current understanding of K-T extinction event and its immediate aftermath is rather incomplete. For starters, the most popular theory about what caused it is highly inadequate. We also do not understand why certain vertebrates such as “modern” birds aka Neornithes survived, but other sibling groups such as Hesperornithes, Ichthyornithes and Enantiornithes became extinct. This pattern of disappearance is especially odd since Enantiornithes were significantly more successful prior to the K-T event. Moreover, they were almost identical in general appearance, size range, flight characteristics and likely even possessed similar patterns of coloration and markings to birds that are still around.

Yes.. some had teeth within their beaks and many possessed vestigial claws within their wings. But otherwise, they were functionally identical to modern birds and their global distribution in the late-cretaceous strongly suggests that some could fly across oceans. They also occupied a far more diverse range of habitats than the ancestors of modern birds. So how did a group which was significantly more numerous, occupied a larger range of habitats and likely better at flying (at least then) become extinct while the less numerous group occupying a narrower range of habitats and not better at flying survive? This becomes even more relevant once you understand that the most popular “explanation” for who survived the K-T extinction revolves around adult body size, with those below 10-20 kg being more likely to survive than larger ones (YT video).

Since Neornithes and Enantiornithes had a very similar range of body sizes, something else was at work. And it gets better. Consider groups such as Ichthyornithes and Hesperornithes whose members were basically the late-cretaceous versions of seagulls and diving birds. How do pretty successful aquatic bird-like creatures become extinct when that extinction was more devastating to species living on land? Members of these two groups had access to a better, if still diminished, supply of food than their land-dwelling cousins. And as the discovery of the Qinornis fossil in early Paleocene shows, some non-Neornithes birds did survive. Are you starting to appreciate the inadequacy of currently explanations for why certain groups survived, while other didn’t?

Let us move on to the oceans, or more precisely who survived and who didn’t. While Mosasaurs disappeared after K-T extinction, others such as crocodiles, turtles and sharks survived. While some of you might believe that every Mosasaur species in the late Cretaceous was a 40-60 feet long beast, they came in a range of sizes and some such as Carinodens were about the size of alligators. Moreover, they occupied a range of ecological niches, had global distribution and some displayed specialized dentition. To out it another way, they were more numerous and diverse than crocodilians and were successful in many more environments ranging from the deep-water to shallow coastal areas and estuaries.And yet, it is the crocodilians (well.. some of them) who survived while all Mosasaur species went extinct.

And why did marine Turtles and some shark species make it through the K-T extinction? Why were bony fish the least affected by that extinction? Why did nautiloids, octopodes, squids and cuttlefish survive while the equally numerous belemnoids and ammonoids became extinct? Why did Choristodera (e.g Champsosaurus) survive the K-T extinction only to become extinct in the middle-to-late Eocene? If the direct and indirect effects of that comet/asteroid impact caused so much immediate worldwide damage to terrestrial plants (including flowering plants) how did bees survive? Things don’t look so straightforward and easy to explain now, do they? My point is that there are patterns in what survived and didn’t, but let us stop pretending they coalesce into a coherent theory to explain whatever happened at the time.

And why did most mammalian lineages survive the K-T event, but weren’t able to quickly occupy the niches left behind by all those extinct large animals? Why did it take almost 10-15 million years for mammals to finally reach the size we today associate with deer and pigs. And why were the large flightless birds such as Phorusrhacidae and Bathornithidae among the largest terrestrial carnivores in aftermath of that extinction. What accounts for the absence of large terrestrial mammalian predators in the first 15 million years after the K-T event? And ya.. I have a partial explanation for that, which I might write up in a future post. This become more unusual once you realize that the Earth was densely forested, very green and climatically pleasant place to live for about 15 million years after quickly recovering (within a million years) from the K-T extinction.

What do you think? Comments?

Unanswered Question about Cretaceous–Tertiary Extinction Event: 1

June 26, 2019 7 comments

As many readers know, I often don’t subscribe to widely-held and regurgitated explanations for phenomena, especially if they are obviously incomplete and not internally self-consistent. In my opinion, any theory or hypothesis which requires you to believe it based on the authority of some alleged experts is no different from religion. Let us now turn our attention to the topic of this post, namely why conventional explanations for what happened during the Cretaceous–Tertiary (K-T) extinction event are incomplete, misleading and often based on dubious reasoning. But before we go there, let us restate what we know for certain about that topic.

First, the extinction event in question did occur and resulted in the extinction of all non-avian dinosaurs, many large marine reptiles, pterosaurs and also a significant number of mammals and birds species. Second, it is almost certain that a comet or asteroid did hit the earth around that time. Some of you might ask, where is the controversy? Isn’t this the conventional explanation for the K-T extinctiont.. you know.. a comet/asteroid hits earth and kills all dinosaurs, pterosaurs, large marine reptiles but not all mammals and birds, who then took over ecological niches left open by those extinct groups. As it turns out, a lot more was occurring on earth at that time.

1] While the most popular current explanation revolves around an comet/asteroid impact being the cause of that extinction- it is not without problems. For starters, there is a peculiar gap between the youngest dinosaur fossils found and the impact. To put it another way, dinosaur fossils disappear from fossil record about 100 to 200 thousand years before the asteroid impact. While a few fragmentary dinosaur fossils found in one single location are a bit closer to the asteroid impact layer, one such instance is not enough to definitively claim that the impact was the cause of K-T extinction. It also does not help that the four major extinctions before it were caused by extremely massive and prolonged volcanic events.

As luck would have it, one of largest events of that type in last 100 million years was going on at around the same time. The Deccan traps, a large igneous province in south-west India, started forming about 200-300 thousand years before the asteroid impact. It goes without saying that a volcanic outpouring which can cover over a million square km with a layer of lava about 2 km thick (original extent) would also pump out a shitload of gasses such as carbon dioxide, sulfur dioxide, rock dust and other types of particulate matters into the atmosphere. The pretense that such a large geological event did not contribute to the K-T extinction is, in my opinion, largely due to latent racism within the scientific community.

This become more obvious once you realize that the timing of this flood basalt deposition (which began 200-300k years before impact) coincides with the loss of dinosaur from the fossil record in most parts of the world. And yes.. I am aware of more recent theories about how the impact could have caused or sped up the massive volcanic outpourings which formed Deccan traps. In any case, we cannot keep on pretending that the impact event (as defined by the iridium layer at end of K-T boundary) was the major, let alone only, cause of that extinction. The evidence simply does not back the impactor-only hypothesis and we are going to talk more about it now.

2] Another problem with the impact-only hypothesis is that it doesn’t explain certain peculiarities of the extinction pattern. Why did some birds survive the extinction, while non-avian dinosaurs did not? This question is far more complicated than it appears at first glance. Let me explain, most of you know that modern birds (descended from survivors of K-T event) evolved from theropod dinosaurs. But the relationship between the two is even closer than most realize. Tell me if the the following extinct dinosaurs look like birds or dinosaurs.. Eosinopteryx, Aurornis, Jinfengopteryx and Byronosaurus. Long story short, there are entire genera of dinosaur fossils which display features intermediate between classical dinosaurs and modern birds. The first three are from late Jurassic, while the fourth is from late Cretaceous. Dinosaurs with significant bird-like characteristics existed alongside archaic and, later modern, birds for millions of years.

More importantly, many of them were in the same size and weight range as modern birds. To make matters more complicated there is the category of what are popularly known as ‘archaic’ birds which were closer to modern birds than dinosaurs, but did not survive the K-T extinction. And then are groups such as the Enantiornithes, who also did not survive that extinction. Or maybe some semi-birds, such as Qinornis, did. The point I am trying to make is as follows: the degree of shared genetics, physiology, size and habitat overlap of bird-like dinosaurs and “true” birds makes it very hard to explain why one group survived but the others did not. And guess what.. there were tons of small to medium-sized dinosaurs with beaks (and no teeth) similar in size to emus, ostriches and even large pheasants. Some of you might attribute this to the ability of true birds to fly better than bird-like dinosaurs.

Well.. in that case, how do you explain the simultaneous extinction of pterosaurs who were even more accomplished flyers than modern birds. While some of the late cretaceous species, such as Quetzalcoatlus and Hatzegopteryx were truly massive creatures capable of intercontinental flight, many others were of a size we today associate with large seabirds. They were an immensely successful order of flying “reptiles” which originated sometime during middle-to-late Triassic (over 200 million years ago) and kept going until the K-T extinction event. They even shared the skies with what we would today call “true” birds for over 30 million years. If the ability to fly was what supposedly saved birds, it clearly did not work for pterosaurs who were much better flyers. Also, even the late cretaceous had pterosaurs not much bigger than large ducks or geese.

In the next part, I will go into why it is so odd that crocodilians survived the K-T event but Mosasaurs did not. And let us be clear about something else, not all of them were the 50-60 foot long creatures prominently displayed in documentaries about extinct species from the late cretaceous. Then there is the issue of why a decent number of mammalian species survived. While conventional explanations posit that they survived by being small, burrowing and being omnivorous- why do those factors not apply for small (chicken to dog-sized) omnivorous dinosaurs. And why did birds, who were far more exposed to the elements than either survive?

As you can see, our current understanding of the K-T extinction event is rather incomplete. We still don’t have a proper understanding of what combination of factors caused it and why it is noticeably bigger than the previous Triasic-Jurrasic extinction. We also do not fully understand why mammals and “modern” birds survived (at least some of them) it, but small bird-like dinosaurs and so-called “archaic” birds did not.. well, most of them- at least. In the upcoming part, I hope to tackle the issue of how body weight may have affected survival. Spoiler.. it still does not explain why small dinosaurs, archaic birds and small ornithurans became extinct while crocodilians did not. While I do not have any magical answers, we could start by acknowledging that a good portion of our current theories and hypothesis about that event are inadequate.

What do you think? Comments?