Simon’s Backup Weblog


Two (Fossilised) Heads Are Better Than One…

Posted in Uncategorized by Simon Bisson on December 20, 2006

From BBC News:

Scientists have found what is thought to be the first example of a two-headed reptile in the fossil record.

The abnormal animal, belonging to a group of aquatic reptiles, was unearthed in northeastern China and dates to the time of the dinosaurs.
[…]
This animal was a choristoderan, an extinct reptile that reached a length of one metre in adulthood and was characterised by a long neck – two in this case.

The animal’s spinal column divided in two at the point where the neck emerges from the body. This formed two long necks that ended in two skulls.

It’s all quite amazing and what I suspect will be a unique find (especially considering how difficult fossilisation actually is).

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6 Responses to 'Two (Fossilised) Heads Are Better Than One…'

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  1. hunkymouse said,

    It leaves on speculating on how common such freaks were, then, compared with now. One sample, as you say, doesn’t help much!

    But it does seem as if DNA has many different mechanisms designed to eliminate transcription errors, and I presume that the first DNA didn’t necessarily have all these mechanisms. Was mutation more common long ago? Is the existence of this fossil less surprising than it may be?

  2. inamac said,

    Fascinating. It’s difficult to tell from the photos whether this was a live animal, a stillbirth, or a fossilisation in the egg (the posture suggests the latter – though you’d expect some fossil indication of the shell/case). In the latter cases it may not be that uncommon – you still get live two-headed snakes occasionally, and probably a relatively high number of foetal deaths.

    Neither the fossil record, nor current records of unborn mutations are sufficiently complete to be able to say how rare/common this is.

  3. rowanf said,

    There was a two headed snake living quite happily for many years in the San Francisco at the California Academy of Sciences. I think it has passed now, but it didn’t seem to hinder it particularly to be bicephalos.

  4. sclerotic_rings said,

    Well, bugger. You beat me to it. And here I thought I was all clever to spot it before anyone else did…

  5. sclerotic_rings said,

    Having seen plenty of examples of this with live reptiles (mostly turtles, but the occasional snake and lizard), it’s not common, but it’s not as incredibly rare as in mammals or birds. I suspect that it was live for a short time: the lack of calcification in the skulls suggests that it was probably a few weeks or months old when it died, which happens to be about the general life expectancy of such a specimen. (In this case, it’s not so much a mutation as it is an example of insufficient gene expression. As with all other two-headed animals, what you’re looking at here is an animal that would have been twins had the genes been working during cell differentiation.)

  6. sclerotic_rings said,

    Actually, I’d figure that such freaks were that common back then as now: it’s very rare in mammals or birds (most such cases miscarry or die in the egg before they ever get the chance to face the outside world), but it’s actually much more common in turtles than most people expect. (I know a local turtle breeder who shows off red-eared sliders, Blandings turtles, snapping turtles, and Florida softshell turtles, and he has at least four or five two-headed turtles at each show that have hatched from this year’s batches. Since that extra head usually indicates undeveloped or underdeveloped intestines or livers, most survive a few days at most before dying, and the others might last a year with extra care. I don’t think he’s had one that’s survived to adulthood yet: for some reason, snakes are more likely to see that happen than turtles or lizards.)


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