Sunday, 28 July 2013

a flock of seagulls

One of the more pleasant aspects of the recent hot weather has been the opportunity, rarely granted to the long-suffering residents of these islands, to sit in the sun outside one’s local pub and enjoy a few beers. During one such sojourn at my own local, I found myself thinking about the Mesozoic era of the Earth’s history. This must sound like a bizarre juxtaposition of ideas, so an explanation of what triggered this train of thought is in order.

My home town, even though it is more than 30 miles from the nearest sea, has a large population of seagulls, many of which could be seen swooping and swerving overhead recently as the pub’s patrons basked in the unaccustomed warmth. Seagulls are highly adaptable creatures, so having any knowledge or experience of the sea is not essential to their continuing survival. Their behaviour is driven by only one imperative: the need for food.

So what’s the prehistoric connection? The Mesozoic era began with the last throes of the Permian mass extinction, 250 million years ago, when more than two-thirds of all land-based vertebrates and 95 percent of all ocean-dwelling species disappeared. During the Triassic period, the first of the three periods that comprise the Mesozoic era, the most significant replacements for these losses were reptiles, in the sea, in the air, and on the land.

In addition to the large reptiles that appeared during this period, there was also a group of smaller reptiles with some mammalian characteristics, known as therapsids. Towards the end of the Triassic, some of these had evolved into the first mammals, which were no bigger than small rodents that were unable to compete with the lumbering leviathans of the Jurassic period. These early mammals were therefore nocturnal, because reptiles are exothermic, meaning that they rely on the environment to maintain their body heat and are thus much less active at night.

Now, if we were to imagine the arrival of extraterrestrial visitors towards the end of the Cretaceous period, 70 million years ago, what would they have made of what they found here? They would not have been able to predict the precise direction in which evolution would have proceeded, but they would have concluded, surely, that the future lay with the big sauropods that dominated every landscape. The rat-like mammals that scurried around would not have registered as having any significance for future developments.

And they might well have been right, had it not been for the arrival of an extremely large meteorite 65 million years ago. When this unexpected projectile crashed into Mexico’s Yucat√°n Peninsula, the resulting explosion threw up huge quantities of dust. This had two effects: global temperatures plummeted; and the ensuing reduction in light levels severely inhibited plant photosynthesis. Both proved disastrous for the large reptiles: lower temperatures made it almost impossible to maintain body heat, especially if the body in question was extremely large; and reduced levels of photosynthesis meant that much less food was available for the big herbivorous dinosaurs, which in turn meant much less food for big carnivores such as the tyrannosaurs. They died out, leaving the way clear for mammals to take over the world.

We know that this was a worldwide phenomenon, because the thin layer of rock that marks the Cretaceous–Tertiary boundary can be seen on every continent, and this stratum can be linked definitively with a meteorite impact because it contains unusually high levels of iridium, an element that is rare here on Earth but relatively common as a constituent of meteorites.

If we imagine a second group of alien visitors to the planet now, what conclusions might they draw? They would surely note the environmental stresses induced by the dominant lifeform—an expanding population, resource depletion, pollution, etc.—so they might well conclude that, like the dinosaurs, Homo sapiens is doomed to extinction. If that really was their conclusion, they might then speculate on which creatures would fill the niche left behind. And this is where I return to the beer garden of the Agricultural Hotel, and the seagulls wheeling overhead. They have all the necessary attributes: adaptability, small size, audacity and speed of movement. And they will eat almost anything, stealing it if necessary, including food that has been discarded by humans (the main attraction for seagulls around these parts is a large landfill site). They are the ultimate opportunists.

This is all merely speculation, but humans shouldn’t forget that, like the dinosaurs, they haven’t been given any guarantees of their continuing survival, and we could still screw it all up, after which seagulls, or their descendants in the remote future, will inherit the Earth. The meek will have to look elsewhere.

12 comments:

  1. That was a chastening, if interesting read, Dennis. Is there a way we can metamorphose ourselves in sea gulls?

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    1. I’m afraid not Uma. I’m taking the long view here. The very long view.

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  2. I love the way sitting in a beer garden triggered a thoughtful look at Earth's evolutionary history.
    I sit in a beer garden and I think "I could murder a kebab"
    Great post.

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    1. I tend to do all my eating before I go to the pub Big D, especially on a Sunday afternoon, so hunger doesn’t interfere with the drinking.

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    2. totally agree with Big D, on this. How much did you drink Dennis in order to have such deep thoughts? :)

      I walk past Billingsgate quite a lot, and have noticed the vast amount of seagulls in this area. You'd think you was at the seaside on some days, although the River Thames is 2 mins away. I guess it's the fish.

      Maybe you can answer this Dennis. I've noticed that years ago we use to only see pigeons and small birds around but in the past few years, you rarely see them. What I do now see, are big massive black birds which I call crows (but not sure what they are) hanging around. They are at least twice the size of a pigeon with thick dark yellowish beaks and are harder to scare off. Could there be a reason for this?

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    3. Only six pints of Jennings’ finest Cumberland ale Rum, although that would have been augmented by some Electric Haze early in the proceedings.

      In the case of Billingsgate, it is definitely fish that attracts the gulls, but they are natural scavengers and will eat anything, including chips straight from the hands of drunks staggering home after a long session.

      Your mystery bird is definitely not a rook, carrion crow, jackdaw or raven, the commonest members of the crow family in Britain (their beak colours don’t match your description). Do these birds have long necks? If so, they could be cormorants, although I’ve noted in Hong Kong that they are easily spooked, which doesn’t square with being hard to scare off. You may find this link helpful.

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    4. Dennis, those black birds seem to have stubby necks almost as if it's real close to their shoulders. One thing for sure, you have to really chase them off otherwise they won't move. I'm going to check out your link now. Thanks mate.

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    5. I can’t offer any more suggestions Rum, so I hope the link is useful. Do let me know what you come up with.

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  3. Fascinating, Dennis. The current theory is that humanity is the highest development so far in the evolutionary chain. If the seagulls outlive us, that will certainly throw a monkey wrench in that theory.

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    1. The key phrase is “so far” Marty. I believe that if the human race survives the next 1000 years then it will survive indefinitely, but the coming millennium will be a dangerous period, and there are few species other than seagulls that are thriving amid the chaos wrought by the currently dominant species.

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  4. Thanks Dennis for sharing your excellent knowledge! I always believe, mother nature is the one do decide who survive, who would not. This geological knowledge seems to prove the idea.
    I wonder, how long have seagulls been existing as a species? Longer than humans (or homo sapiens)?

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    1. I can’t claim any expertise in the evolutionary history of seagulls Yunyi, but as far as I do understand the subject, the earliest seagulls appeared 25–30 million years ago, while the earliest species within the genus Homo (H. habilis) appeared only 2.4 million years ago (H. sapiens is a mere 100,000 years old).

      In the case of the various Homo species, evolution has been extraordinarily fast, but should humans disappear from the face of the Earth, the evolution of some other species will immediately kick into overdrive.

      As to which species that will be, my vote goes to the seagulls, which are not in fact a single species but a group of closely related genera.

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