Sir David Attenborough has said the death of the last male northern white rhino is "another catastrophe and another warning signal".
The 91-year-old was speaking following the death of Sudan, the 45-year-old last male of his species in Kenya earlier this week.
He said the problems facing those protecting other endangered animals was "huge" as the world was now so crowded.
Sir David said: "It's another catastrophe and another warning signal.
"The last male has gone so that's another obituary that you have to put down. It's another extinction which is our doing."
The naturalist and filmmaker said: "It applies across the Animal Kingdom. We've being going on about the way in which human beings have been exterminating species for a long time. And we started doing in the 17th century with the dodo. We exterminated that along with a number of other crimes of that sort which are our responsibility.
"But now the problems are huge, simply because the world is so crowded there's not the space for things."
Sir David was speaking at the opening of a new dinosaur exhibition at the Yorkshire Museum, in York, where he said he was "mystified" about why his Blue Planet II programme has had such a worldwide impact on the debate over the use of plastics.
He said: "I'm as mystified as anybody else as to why it's had that impact. I think it came at a particular moment, when people are concerned and there's a worldwide concern about what's happening. And that series just pressed that button."
Sir David was visiting the Yorkshire Museum to open the Yorkshire's Jurassic World exhibition, which takes visitors on an journey back through 150 million years of Yorkshire "to discover lost giants and the changing worlds they inhabited".
He tried out the state-of-the-art virtual reality headsets, clearly enjoying the experience as he joked with the staff.
The veteran broadcaster said he grew up loving fossils and still found them exciting.
He said: "Going up to a rock and hitting it with a hammer and it falls open and you see the most
beautiful, perfect shell that nobody's seen for for 150 million years - if that isn't romantic, I don't know what is.
"Certainly, as a boy I was absolutely fixated with fossils. I collected them and I suppose I learned the rudiments of biology out of viewing fossils."
:: The Yorkshire's Jurassic World exhibition opens to the public on Saturday