Behemoth is Baxter's Mammoth trilogy
Silverhair,
Longtusk and
Icebones collected together. Respectively, it follows the story of the last mammoths, the greatest mammoth and finally [...Pigs in space] mammooooooooths on Maaaaaaaaaaaaaaaaars! But, don't worry, Behemoth is very readable and not really that far fetched.
In Silverhair, a paltry group of mammoths find themselves pushed further and further into the inhospitable Northern icecap by marauding humans. This is the last family of mammoths and Baxter makes you feel their isolation and loss, and there is no little horror in seeing human actions from the point of view of the mammoths. This is the only slightly disconcerting issue I have with Behemoth. The anthropomorphic nature of the mammoth's behaviour, probably necessary for telling Baxter's story, just seems at odds with the animals in nature. I have no doubt of their ability to communicate and emote but these mammoths are opposable thumbs away from Euclidian mathematics and Pyramids!
In Longtusk, the hero of the mammoth's own cycle of creation is given centre stage. We follow the legendary mammoth, spoken of with reverence in the cycle, from young bull to saviour of the species. This story is set some 15,000 years ago just before the coming ice age and both the lives of the mammoths and the people they interact with are excellently presented. It is also nice to see a representation of ancient man that doesn't succumb to block-headed stereotypes, both Sapiens and Neanderthals come off as well rounded species and the progress and expansion of the Sapiens is frighteningly reminiscent of modern mans viral like spread over the Earth.
In Icebones, mankind has moved to and evacuated from Mars. We're not quite sure why man has departed and left behind a partially terraformed planet but the huge mammoths also left behind are like lost souls cast adrift. These are genetically engineered breeds, born without any natural instincts and solely reliant on their human masters for everything. Only Icebones, calf of the matriarch Silverhair from the first book remembers the nature of what mammoths are supposed to be. This is the story of how she leads a disparate group of tame and naive mammoths to better pastures, forging them into a herd and a family. Unfortunately, despite a well realised alien landscape, the story suffers for being a very long trek, with the petulant immature mammoths like squabbling kids in the backseat asking "Are we there yet?" every two minutes.
Overall I preferred the story of Longtusk, Silverhair is marginally less believable and Icebones simply drags too often. Longtusk is considerably more dynamic and full of adventure. That said all three books are enjoyable. Behemoth is a very easy read and Baxter conjures believable characters and environments. At the end I was left with a definite sadness that these creatures, such recent extinctions, are gone forever.