Been hunting down some fossil Pokemon for your Pokemon GO collection? Now you have a rare opportunity to do so!

Niantic has announced that 7 km eggs will now ONLY hatch fossil Pokemon such as Omanyte, Kabuto, Aerodactyl, Lileep, Anorith, Cranidos, Shieldon, Tirtouga, and Archen. In the midst of this, 10 km eggs will now sometimes hatch Lucario’s pre-evolution form Riolu.

Here’s the full announcement below:

“Trainers,

It appears something strange has happened with the Eggs you can receive from Gifts: 7 km Eggs are now hatching only fossil Pokémon!

Here’s what we know so far.

• The fossil Pokémon Omanyte, Kabuto, Aerodactyl, Lileep, Anorith, Cranidos, Shieldon, Tirtouga, and Archen are now the only Pokémon hatching from 7 km Eggs.
• These fossil Pokémon will no longer be hatching from 2, 5, and 10 km Eggs.
• Riolu will now be hatching from 10 km Eggs.

We aren’t sure how long this phenomenon will last, but we can assure you that Spark is on the case. Be sure to follow us on social media, opt in to receiving push notifications, and subscribe to our emails to stay updated. Let’s GO!”

—The Pokémon GO team