As ever, IMO: “Eaters of Dead”, and “13th Warrior” – the novel (which I’ve read) though well-written, as anything by Crichton: I thought it basically – to put it most charitably, not for me. Author hijacking Ibn Fadlan from IMO interesting genuine-historical scenario, to be taken up to the Northlands by the Vikings whom he fleetingly, in real life, encountered on the Volga – to go and re-enact with them, the Beowulf scenario, with Grendel and his mother being relict Neanderthals; fine for those who like such stuff, but for me, “I don’t want to know”. And for me, if the novel is “not wished” – the film, which I’ve seen, was totally dire. (I approached both novel and film, hoping to enjoy – but it didn’t happen.)
Relatively-recent Elasmotheriums -- agree, very much in the “if-only” realm. I first heard of this engaging if not-nice-to-know-up-close-and-personal creature, via another Internet board, whereon all manner of things are discussed. Learned thereof (with Wikipedia references) from a very nice and to my mind highly knowledgeable lady – self-styled “amateur palaeontologist” – who often posts on that board. Her “what-if” scenario given thereby, postulated the “Elasmo” being conserved by successive rulers, likely as being a very exciting quarry for hunting (thus worth keeping in existence for future generations of hunters), for a long, long time. Her personal end-point for the scenario, was the chaos of the c. 1918 – 1922 Russian Civil War. More optimistic scenario-merchants, could have the beast surviving that “bottleneck” – the USSR was, at least in theory, strongly pro-nature conservation... obviously it all never happened, and even if Ibn Fadlan’s informants circa 920 AD were telling him about a creature which was still live-and-kicking right then; it didn’t remain so for very long thereafter.