Like the Milian, Leos and Ocirin, the Tigrus is one of the 9 original eggs (as featured in Eggdoku) released when the site was created, but has not been actually finalized or released as a species.
A Tigrus egg featured in Eggdoku
Like the Milian, there has been no concept art of the Tigrus, though its name would suggest it to have been intended as a tiger-like creature. When the Igneo was first released some users thought this to be the species that was intended to be the Tigrus (given the Igneo's look as a classic large predatory feline), but that has never been confirmed.
It is currently unknown if this species has been dropped or will at some point be developed and released.