Wednesday, April 09, 2008

Nowt so queer as (Earth) folks - Part 1

Here's another archived post brought across from my now defunct Worlds of Possibility blog. Enjoy.

However 'alien' we might envisage extraterrestrial life to be, the real thing will undoubtedly trump our imaginations. We only have to look at how diverse and extraordinarily weird life on this planet can be to see that. So I thought it would be interesting to look at several examples of Terran weirdness ... just to accentuate this point. And I'm starting with that most ancient of fish - the shark.

In recent years, our deep sea exploration cameras have provided startling visuals of some of the planet's odder sharks, like the Goblin Shark and the Frilled Shark. But did you know that even the most common sharks have some really strange traits - such as having two penises and foetal cannibalism?

Sharks have two claspers (pterygopodia) that develop on the anterior region of the ventral flippers. The name is a bit misleading as they are not used for grasping - rather they 'clasp' together to make a pseudo-penis. Each has a cartilaginous support and a groove on their inner edge and, during copulation, the two come together to form a channel through which the sperm is passed. So I suppose you could say that sharks have two half-penises - unlike snakes and lizards that really do have two functional penises.

And then there's the issue of intrauterine cannibalism. Some sharks lay eggs in a leathery case (the mermaid's purse we find washed up on beaches). Others bear live young. In some species (e.g. The Great White, Mako, Thresher and Basking Sharks), the first embryos to hatch eat the other eggs found in the oviduct, a phenomenon called oophagy. But in other species, such as Sand Tigers, the embryos actually fight amongst themselves inside the womb and the victors eat the weak. This strategy means that only the strongest and largest young are born, which gives them a great start in the world of predator-prey relationships.

But if you want real weirdness in sharks, you have to take a trip back into prehistory to look at some of the designs that were tried but didn't make it to the present day - such as Heliocoprion, a shark with an extraordinary lower jaw. Some scientists believe that this was a kind of spiral 'conveyor belt', in which new teeth would advance to replace old ones. But the true arrangement and purpose of the teeth remains a mystery. Some scientists have also suggested that it may have operated like a spiked whip, possibly curled underneath the lower jaw like a weapon-heavy elephant trunk.

And then there was Stethacanthus which, on the whole, looked like a modern shark except for its outrageous dorsal fin. Shaped like an ironing board, the top of this fin was covered in rough, tooth-shaped scales (denticles) that matched a similar patch of skin on the snout. Scientists believe that it was used as part of a courtship display ... or maybe it was supposed to mimic a huge mouth and make the creature appear more frightening?

Just goes to show ... there's nowt so queer as (Earth) folks.

Fossil shark reconstructions by Todd Marshall

1 comment:

Anonymous said...

I think that when we see the strange species wich lived in the ancient past, as these weird chondrichtyans, one stars to think... whoa! maybe ANYTHING was possible! and then... one tends to extrapolate in the hypothetical alien forms... but we have one problem... even if these forms are strange, weird, and... (my english vocabulary has no more words...), they are based in a "basic" bauplan (or body plan), being this the idea of the Phyllum classification (I started to think this after reading the Burguess post...). So, most aliens from movies show derivations from the known "bauplans"... Aliens and predators are basically tetrapods (at least in the adult form of the Xenomorphs, Facehuggers seem more Arthropodous-like, asi the adult exoskeleton), Giant spiders are... just that! flying creatures are in general vertebrate like with bat-pterosaur-bird features (sometimes mixed). But in general restricted to these phyla.
During the cambrian explotion more bauplans existed (Gould's disparity), proposed as "different tries of producing metazoan life", and several of these bauplans became extinc during scarce time (poor Hallucigenia). Maybe one interesting aproach to propose hypothetical alien living forms would be using as a basis the unsuccesful (I think I'm mispelling) bauplans, and "upgrade" them using hypothetical but feasible "evolutionary changes"...
I dunno... if someday I decide to start representing hypothetical life forms, I would start with Burguess Creatures... after all, the lived, at least for a little time (talking geologically, obviously)

Ezekiel Vera http://paleovera.googlepages.com/