In a recent comic, The Oatmeal asked tumblr to blame their service outages on an imaginary animal like twitter's Fail Whale and promptly came up with one, the Tumbeasts.
What's awesome is that Tumblr actually did end up using his artwork on their error page. This is what it looks like:
Mad props to the Oatmeal and Tumblr for this stellar addition to my fail pet collection!
And thanks to michaelk for pointing it out to me!