1000kg titanoboa (on land) vs 300kg lion
Titanoboa (1000kg) vs lion (300kg) on land: Titanoboa was a huge prehistoric snake that was twice as long as a modern anaconda and several times as heavy. Titanoboa was bigger around than an oil barrel along much of its body. It was an ambush predator capable of overcoming large prey items (crocodiles, large turtles, perhaps large terrestrial animals) in its mighty coils. Constrictors are fantastic hunters, but are poor fighters on land without the benefit of ambush. Titanoboa's mobility and stamina will be limited on land, and a practiced combatant like a lion can cause trouble for it. A lion is one of the better fighters among cats, as it is charged with the protection of the pride (from other predators and other male lions). Lions are endowed with the typical big cat attributes (strength, quickness, agility, athleticism, jaws & claws, killing know-how, etc.), and commonly deal with dangerous adversaries (Cape buffalo, zebra, crocodiles, hyenas, etc.). This fight will be akin to a decent-sized snow leopard (55kg) taking on a green anaconda (182kg). The lion will need to immediately attack the skull or spine in an attempt to land a crushing bite before Titanoboa latches onto it with its jaws (Titanoboa's head was about the size of a beer keg), but never having dealt with a contrictor of this size, may not know that this is what it needs to do. A jaguar, for example, is an expert reptile killer and would have a decent chance of dispatching a contrictor over 3 times its own weight on land because it will know what it needs to do. A lion is skilled at hunting certain animals because it has learned to do so, but one may attack the Titanoboa in a haphazard fashion if it's unaware of the danger the snake poses. The lion will have trouble escaping from the Titanoboa's bite once it latches on, and may not be able to ward off the coiling action of the constrictor before it's too late. Titanoboa will also be the much stronger animal, and the lion won't be able to control the positioning of this battle (something it usually does in most battles it engages in) once the fight becomes a close-quarters one. If the lion uses its quickness to avoid Titanoboa's strike while appearing to be a threat to the snake (to make the snake feel like it needs to actively defend itself), it will be able to fatigue the constictor and move in for the kill. But, again, the lion may not know that this is what he needs to do. If these 2 animals are placed together to do battle without any time to adapt (in regards to dealing with each other), the massive Titanoboa will have the edge. Not being accustomed to one another will be a bigger hindrance to the lion, and it will be more apt to make a mistake. If the 2 animals are allowed to share the same habitat over many years and adapt to one another, the lion will be able to make the kill on land more times than not because it will know what it needs to do. As it stands now, the lion will not have the experience needed to be favored. Edge to Titanoboa.