Last Chance to See, BBC2The Last Days of Lehman Brothers, BBC2Harper's Island, BBC3

Wit and repartee as Fry and friend seek the endangered manatee, while dull confusion reigns at soon-to-be-extinct Lehman Brothers

Dodos: adorable. The T Rex: awe-inspiringly terrifying (no, not Marc Bolan's big hair). Woolworths pick'n'mix: Amusingly delightful. And extinct, the lot of them. Which brings us, surreally enough, to this week's televisual treats.

Not quite extinct, but heading that way due to poachers, is the Ama-zonian manatee, as sweet as the dodo and the subject of the first episode in Stephen Fry's new series, Last Chance to See. Into the murky waters of a tributary of a tributary of a tributary of the great Brazilian river goes Fry, alongside zoologist Mark Carwardine.

The dynamic duo are picking up where Carwardine and Fry's friend, the late novelist Douglas Adams, began 20 years earlier, on the trail of various endangered species – though it soon becomes clear that Carwardine is a fair bit more dynamic than Fry: while the former is off in a tiny craft to photograph a potentially deadly emerald tree boa, Fry busies himself trying to get reception on his BlackBerry.

In fact, more than the hunt, it is the interplay between Carwardine and Fry ("I'm hot and I'm sweaty and I'd like to be in my hotel, but what am I moaning about? Mark told me to close the door last night because vampire bats might come in") that really makes this show. Carwardine is as knowledgeable about the natural world as Fry is about everything else, and their repartee is as joyously witty as one might expect.

Sorry, did someone mention manatees? Well, as it happens, the lugubrious behemoth (Hey! Enough about Stephen Fry already!) stays hidden in the wilds, but the two men are lucky enough to chance upon one towards the end of the programme ... albeit in a zoo. Nevertheless, its beguiling innocence immediately makes it clear why Fry is moved to opine that it would be positively indecent of us to let this wonderful creature die out.

Not quite so gentle (nor, would many say, are they so worthy of saving) are the financiers in The Last Days of Lehman Brothers. Corey Johnson, as Lehman boss Dick Fuld, has all the charm of a Tyrannosaur on heat and then some, as he battles to keep his bank afloat. Actually, more to the point, as he barks at his underlings. Because he doesn't really seem to spend that much time trying to save his business – just wandering around in his office, huffing a lot and putting in the one call, to US Treasury Secretary Hank Paulson, when all seems lost.

It's all very fast-moving, and at first comes across like a financial-catastrophe special of The Hustle with its strange choice of music and first-person narration (by a character who intermittently seems forgotten about), but for all that, it was hard not to get completely lost by a drama that decided not to name names. (Who were all those bankers in Paulson's get-together? Who's Fannie, for that matter? And what on earth are CDOs? And why does James Bolam have a strange Texan-via-Geordie twang? He's meant to be from Mississippi? Really?).

And, ultimately, it was hard not to be bored by what was one of the most important – and dramatic – events of the past year. The end of Lehman – and the programme – couldn't come soon enough. Maybe boardrooms just aren't cut out for TV specials. Better tell the producers at Dragons' Den.

No such problems over on Harper's Island, where guests at a wedding being held in a small community near Seattle are being bumped off with impressive alacrity – not to mention inventiveness. Thirteen episodes, 25 suspects, one killer. This is the pick'n'mix of extinction. Fizzy cola bottles or pineapple cubes? The flirty blonde or the annoying Englishman – who's going to get it next? As it happens, it's that bloke who used to be on LA Law (and chopped in half, no less), but it doesn't really matter, because this is pure confection for the eyes, a guilty pleasure there's no need to feel guilty about. It's glossy, it's sexy, it's Sunset Beach crossed with Scream, it's downright stupid. But, my goodness, is it fun. And it's one sure way to slash the guest list.