In-utero Cannabalistic Fratricide?

June 21, 2005 1:45 PM

Help me prove I'm not crazy. I swear I saw a documentary about sharks, at one point in my past, and I swear this documentary mentioned that some species of sharks have single births due to the fact that though they are fish, their eggs hatch while still in the mother's 'womb'. Then it's every baby shark for itself, and many times sibling sharks devour one another before being born into the sea. Nobody believes me, and I can't seem to find anything to back up what I think I know.
posted by inging to science & nature (18 comments total)

This article seems to back that up.
posted by bshort1974 at 1:55 PM on June 21, 2005

I saw that, too, and it was a few years ago during Shark Week on the Discovery channel. I think I remember they had footage of this happening, from inside the shark's uterus. I might be crazy, though. And I know this doesn't narrow it down very much, sorry!
posted by peep at 2:00 PM on June 21, 2005

It does happen. Peep is right - they had endoscope footage of a tiny baby shark swimming round in the womb, in a weird soupy/vomity liquid, devouring its siblings. It's all about competition and threat.

It was during the same documentary that a small group of alpha chimpanzees (or gorillas, I can't remember) went on some crazed killing spree, running through a colony and grabbing baby chimps/gorillas and swinging them round their heads. The theme of the programme was obviously 'animals killing other animals'.
posted by nylon at 2:09 PM on June 21, 2005

I saw this tonight on BBC Prime on a program called Weird Nature. The sharks were Tiger Sharks or Sand Sharks or Sand-Tiger Sharks and the segment was filmed off the coast of South Africa. The journalist was bitten by a shark while filming underwater.

BBC Prime website doesn't have much info, only schedules.
posted by DelusionsofGrandeur at 2:14 PM on June 21, 2005

Maybe my girlfriend will chime in here with the authoritative "marine biology grad student" answer, but from what I recall this does happen but not with all sharks.
posted by pwb503 at 2:40 PM on June 21, 2005

I have no proof (other than the article bshort has provided), but I have the heard the same thing about tiger sharks.
posted by Specklet at 2:44 PM on June 21, 2005

Sharks are born live, rather than from laid eggs. . .just deal with it.
posted by Danf at 2:53 PM on June 21, 2005

Sharks are born live, rather than from laid eggs. . .just deal with it

Do a search on "oviparous" and "shark".
posted by joaquim at 3:14 PM on June 21, 2005

Sharks are born live, rather than from laid eggs

That will come as a shock to the many of us, me included, who've picked up shark egg cases on the beach.
posted by ROU_Xenophobe at 4:07 PM on June 21, 2005

It would have been more accurate to say, "Some sharks are born live, rather from laid eggs." There are oviparous and viviparous varieties of shark.

The in-womb-devouring thing is new to me, but fascinating. In biology, it seems to me, the truth is often stranger than fiction.
posted by salad spork at 5:06 PM on June 21, 2005

Considering the size and weight of the newborn, it appears that feeding on eggs or siblings is more effective than depending on the highly specialized yolk placenta.

bshort's link is awesome!
posted by croutonsupafreak at 5:24 PM on June 21, 2005

Yes, I like watching documentaries on sharks, and this is the tiger shark you're talking about. I saw it too, and always tell people about this whenever they talk about how miraculous "nature" is. :)
posted by madman at 9:35 PM on June 21, 2005

I dissected a shark in bio lab, and I can attest that there were baby sharks of varying sizes free in the body cavity. I did not dissect the babies to see if they contained even smaller sharks in their stomachs.
posted by ikkyu2 at 9:54 PM on June 21, 2005 [2 favorites has favorites]

Weird! I heard about this on the news last week. Australian scientists were looking at ways of producing more of this type of shark.. AH HAH!

Grey nurse sharks!

All the evidence you need.
posted by tomble at 1:39 AM on June 22, 2005

I recall seeing something about this on the Animal Planet channel, and the world's most extreme animals. They had the inside-o-scope with the gross soup. I'm fairly sure that the shark was the Thresher Shark, this seems to back me up, but I'm not 100% certain.
posted by borkencode at 3:43 AM on June 22, 2005

The term you're looking for is ovoviviparous.
posted by cgs06 at 6:10 AM on June 22, 2005

Sevengill sharks also birth live pups.
posted by agregoli at 9:33 AM on June 22, 2005

I'm pwb503's girlfriend and I used to teach a shark bio class and so have a little background in the subject matter.

There are three main types of shark development:
1. Oviparous: eggs are laid and juveniles hatch like most other fish. Examples: rays, skates (which are in the same class Chondrichthyes as sharks and other cartilaginous fish like ratfish) and lemon sharks. Those are most likely the egg cases you find on the beach ROU_Xenophobe. [If intact, you can frequently hold them up to a bright light and still see the young moving around inside.]
2. Viviparous: live birth, young feeds from placenta. Examples: Porbeagle, whale and blue.
3. Ovoviviparous: eggs form and then hatch within the mother. Examples: nurse, thresher.

The third case is when in-utero cannibalism can happen. In fact, most sharks have two uteri (and males have two genital organs called claspers), so the fight for dominance is happening in each uterus and then usually two juvenile sharks are born.

Sometimes the literature refers to all development that results in live young as "viviparous" even if that development is due to eggs hatching within the female, so it gets confusing.
posted by pwb503 at 11:44 PM on June 25, 2005