I recently started a fortress, and headed for the caverns only when my voracious appetite for charcoal meant the surface was bare of trees. I landed right in the middle of a large clearing, and set the trees there to be felled. In the meantime, I sent my military out to scout the cavern, so that it would hold no further secrets. There were two of them, fully armoured in bronze but carrying no weapon or shield, so they crept along the sides of the walls, to peer out without being seen. A low fault in the rock revealed a massive cave crocodile, slumbering and close. The first soldier retreated, but the second was seen on the way to the station point and charged by the enormous beast.
The first exchange meant nothing, the crocodile scraping its teeth on the soldier's gauntlet and gaining a bruise in return, and each missed the other until the crocodile barged the soldier to the ground with a stunning blow. Flailing and desperate, the soldier was ready to die when the scaly mass filling her view suddenly stilled, though not with the softness of death. She stood and began beating and beating it in the head, not noticing the oddly-angled rear toe mangled by a wild punch. The crocodile came to and she returned its earlier favour by biting it in the front foot, and the effort of throwing her off dropped it to the ground again.
Her fists were quickly joined by others, as dwarves threw aside their tools to give aid. Despite their efforts the beast's skull remained intact, and it was able to rear up and charge in the moments it awoke. Its jaws missed their mark each time, but the dwarves were tiring.
Up above, in the small enclosure between the two tombs, one dwarf remained. Ducim had not been called upon to restrain the cave crocodile, and was entering the the southern tomb when the sounds of shouting and running drew her ear. Refocusing, she sensed a presence about her waist, and looked down to see long rabbity ears and big liquid eyes over a smooth rounded snout. After sinking her pick into the kobold's spleen and cleaving off both its arms near the elbow, she strode towards the wall to see what the noise was about.
'Bolts! Venom!' they cried, and told her to drop the pick and take up a quiver while she waited for a weapon. Quickly the crossbow and bolts were made, and the bolts carried beyond the hall of skeletons to the room where the venom was kept. 'Tallow!' they cried, but the kitchen was empty. The turkeys and horses had long been butchered, and the only animals were the wild crocodile and a lone kestrel no bigger than a fist.
Quiet in the panic, Ducim put down the useless quiver and returned to her faithful pick. She took up the bloodied weapon, thought for a moment, and flipped it from her mining hand to her weapon hand.
The journey to the caverns was brief, Ducim being quick on her feet. The first blow to the crocodile's broad head bounced off hard, though a resounding crack rang out around the dwarves, and upon the second blow the beast's head tolled no more.
The corpse weighed a little over 1000L, and I now have lots of tallow.
The game has been modded to make the skull larger relative to the brain, so while you can one-shot a creature by severing its spinal cord it's a lot more difficult to jam the skull into the brain. Bones are as sensitive as ever.
It's interesting to note that a group of dwarves very like this one were able to take out a forgotten beast without needing a weapon to finish the job. Presumably, its better ability to stay conscious allowed the dwarves to aim attacks at its whole body, scoring enough hits on the lungs to wind it to death. The crocodile reached the 'having more trouble breathing' stage at least once, but spent most of its time unconscious and being uselessly headshotted.
There are other mods too, the most relevant of which is the addition of DFHack's greasing station. Had I not messed around trying to test it out, I could have had Ducim end the tale before the end of the third paragraph.