Tribrachidium lived during a period of time called the Ediacaran, which ranged from 635 million to 541 million years ago. This period was characterized by a variety of large, complex organisms, most of which are difficult to link to any modern species. It was previously thought that these organisms formed simple ecosystems characterized by only a few feeding modes, but the new study suggests they were capable of more types of feeding than previously appreciated.
Once Guillermo del Toro gets his act together and shoots At the Mountains of Madness, this actual fossil from an organism predating most complex life forms and "difficult to link to any modern species" should definitely feature somewhere:
Link to the article on EurekAlert!, which has been for years one of my favorite RSS feeds in the world.
Anyway, increasingly tired references aside, the first complex organisms fascinate me, their sheer diversity and possibility. Sure, the present biosphere is weird and ridiculous and fabulous, but it's one possible outcome among many, and the strangeness and beauty of those possible presents is haunting. Like those 3 AM thoughts about who we could have been had we made different choices (some worse, some better — hard to say which ones are more painful to imagine — and some too strange to allow for a comparison); this is like that, except for the whole of us, of this.
Some worlds worse, some worlds better; hard to say which ones would be more painful if we could imagine them.