@ehproque @david_chisnall I just keep getting surprised about how big the gap is between what I *think* is common knowledge and what actually is.
A while ago I had a conversation with someone who was astonished to find out that there are reptiles that bear live young. I *thought* this was common knowledge - especially here in Denmark, where 3 out of our 5 native reptile species do so.
I'm pretty sure that part of the definition I was taught in school was that they don't! So I have also learned something today.
@david_chisnall @ehproque Globally, about 20% of lizards and 30% of snakes bear live young.
In many of those (like the Eurasian common viviparous lizard), this is a pretty primitive form of live-bearing, where the mother basically just incubates some eggs (sometimes with vestigial shells!) inside her own body. Others (like blue-tongue skinks, such as Igor) have independently evolved an extremely advanced, mammal-like system, with placenta and umbilical cord and everything.
(Yes, Igor has a tiny bellybutton! It's just a very thin, almost invisible, line between some of his belly scales).
@david_chisnall @ehproque A little footnote on those skinks: Blue-tongues (Tiliqua) belong to the wider family Egerniinae, which all have that very advanced system for live birth. But this means that having children is *a lot* more risky and energy-expensive for females than in species where they can just bury some eggs somewhere and wander off. So there's been a strong selective pressure towards lower infant mortality rates than in most reptiles.
And - just like in mammals and birds - in most of those species this has led to advanced social behaviour. Shingleback skinks form lifelong monogamous pairs where both parents protect their young for a few months after birth. Prehensile-tailed skinks live in clan-like extended families with one or two parent pairs and their young of up to 4 years of age, all cooperating to defend their range, look out for predators and protect the youngest. Cunningham skinks and Gidgee skinks live in multigenerational underground tunnel complexes.
...and then there are the common blue-tongues (like Igor), who are entirely solitary and have solved the problem in a more classically reptilian manner: They are born with fully adult-level intelligence and learning ability. Adults have more learned experience to draw upon, but there is no difference (beyond the usual individual differences) between how well a 1-week-old and a 15-year-old bluey will do on a completely novel task.
