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Reptilian relationships

Discussion in 'Herp Awareness' started by kremlinator, Aug 3, 2006.

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  1. kremlinator

    kremlinator Banned User

    I admit it. I grew up thinking that all reptiles lay eggs and that it is a character uniting them. Upon entering university (when my obsession really began) I learned that some are ovoviviparous, meaning that they keep the eggs inside them and they hatch inside the mother without ever forming a calcified shell. This seems entirely plausible, of course. Lots of snakes do it, I'm sure some of the snake keepers at this site will be fast to confirm this.

    A month after getting my first herp, I got her a mate. Twitch, my Gold Skink, got "gravid", or so I thought. I walked in one day to see a live birth in action, complete with both parents being gentle to the youngins. I thought it was weird; the babies didn't have yolk sacs and it looked an aweful lot to resemble the placenta that came out when my guinea pigs had babies in grade 5. Weird.

    Turns out, the genus Mabuya, according to studies done by Dr. Vitt (who was kind enough to send a bunch of articles for my research) is a bit of an extreme, but only in South America. My gold skinks are from southeast Asia and are exempt from this extremity. However, the model organism, M. heathi, is placentotrophic. What does that mean? Here's the gist: This and other south american Mabuya have a placenta which provides the baby with roughly 99% of the nutrients straight from the mother. The baby doesn't grow much until the placenta forms. What's even neater is that babies only 4 months old get pregnant every year and their little bodies explode with growth to accomodate the growing fetus. It has been speculated that since Teiids (that is, tegus and relatives) run the roost in South America because of higher metabolisms, the skinks (which are restrained to microhabitats that teiids can't use) developed this reproduction as a response to increased egg theivery. Kind makes you stop to think, doesn't it? A placental lizard! What's next, a mammal that lays eggs? Oh wait...nevermind. :)


    I also want to clear this up: Turtles and Crocodilians aren't true reptilians. Reptilians are paraphyletic. That means that they don't all come from a common ancestor that is a lowest common denominator. For example: Crocodiles are related to birds and dinosaurs, as they have a fourth trochanter on their femurs- this among other adaptations mean they are in a group called "Archosaurs", which are distinctly NOT in "Eureptilia" (true reptiles). Turtles may be even farther removed from this. It is unclear if they are diapsids (with 2 temporal openings in the back of the skull) or anapsids (with no openings in the back of the skull). Well, their skull technically HAS no openings for starters...but that could be secondarily lost. However, their closest relatives....errr....what LOOKS Like their closest relatives, the procolophonids, are extinct, but turtles appear soon after they diappear from the fossil record...weird. They are anapsids and look VERY turtley. Oh yeah, by the way, all reptiles and archosaurs are diapsids. So turtles, which I suspect (and certain authors agree with me convincingly) are anapsids, are further removed from true reptiles and even crocodiles. Besides, what kind of an animal has a development in the skeleton that rotates the shoulder girlde INSIDE the ribs! Only known animal to do that, and it occurs AFTER the bones are formed (with the shoulder girdle on the outside) and then ROTATES IN before birth. Had to get that off my chest, just drives me nuts when people assume turtles and snakes are closely related.
     
  2. kremlinator

    kremlinator Banned User

    I forgot to mention that in M.heathi, the eggs that are transferred from the ovaries to the womb are roughly the same size as mammalian eggs, which means they were small. They looked like parasites at first, but upon further inspection, they were actually evenly spaced eggs! The sizing of the migrating eggs, as I understand it, is something that seperated reptilian and mammal eggs as they left the ovaries. So much for that difference, eh?
     
  3. caudalis_sa

    caudalis_sa Elite Member

    dude...and did you know reptiles are cold blooded! Amazing!

    but seriously..this might interest you...some skinks of the mabuya genus here in South Africa are oviparous and viviparous depending on their locality. For example the cape skink(mabuya capensis) is mainly ovoparous but in a few locations such as Pretoria and Port Elizabeth they lay eggs...quite amazing!
     
  4. kremlinator

    kremlinator Banned User

    Yes, I've heard of that selective ability to be ovoviviparous and oviparous. See, in that case it wouldn't be true viviparitry (placentation) at all but instead it would be an internal, uncalcified egg held within the mother...she would likely supply almost no nutrients to it after it has formed it's own yolk sac. I believe that the selection to withhold the egg is related to predator abundance (and therefore pressure), because withholding the egg is harder on the mother but if it prevents the babies from being eaten in the egg, it's worth it only if the predators are in greater numbers.

    Reptiles are COLD blooded!? Next thing you'll tell me that mammals are warm blooded! CRAZY!
     
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