One thing to remember about obsidian is that it's extremely sharp and can be sharpened by hand (with extreme care) to be I believe a few molecules thick, if not monomolecular.
According to someone who seemed to know a great deal about the subject, there are instances of Mesoamerican people cutting charging horses in half with obsidian swords around the time of Cortez.
Also, Cortez and the Spaniards were so surprised by the effectiveness of obsidian javelins in penetrating proofed steel breastplates that he did some testing himself and proved it.
Mythbusters semi-debunked the horse thing. It took multiple swings to decapitate their fake horse, and the greatest effect was achieved by using the sword like a saw. However, they did acknowledge that they weren't experts in Aztec sword techniques.
However, the rest of this is well worth researching. Faith healers and charlatan doctors used to use palmed obsidian blades to make near-invisible, unnoticeable incisions on their patients for demonstrations, and for a while there was interest in using obsidian blades for modern surgery because of their ridiculous fine edge (though steel proved easier to sterilize and thus won out).
It's pretty neat stuff, actually.
Does anyone know if it's possible to make megabeasts breed?
I believe the answer for this is "no", though it might be possible through the same venues as "mermaid farming" for the ones that are sapient and come in both sexes.
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Lastly, thanks to everyone who offered advice on my shooting gallery. I made all three targets into shooting ranges, and now my marksdorfs are coming to practice.