The global drop in biodiversity is one symptom of our current environmental crisis and a driver of conservation efforts. However, what should our starting point for biodiversity be; against which we can measure the current loss? Fifty, 500, 5000 years ago? And what about new species? In the last year alone 18,000 new species have been described (some of them are fossils!). And what about under-explored realms, such as the deep-sea? Well new research published in Frontiers in Marine Science demonstrates that our current knowledge of deep-sea life is heavily biased. This biases the species-richness of the deep-sea towards wide-ranging species that were described earlier in the exploration of the ocean depths.