I noticed in my survival server that I have been getting a lot of pieces of triceratops bone, and no other species. I decided to test it so I spawned in about 950 blocks of ore and mined them. Out of that I got 2 triceratops arm bones, 2 triceratops skulls, 3 triceratops ribcage, 12 triceratops leg bones, 2 triceratops feet, 2 triceratops vertibrae (and of course a healthy amount of bones/biofossils/plant fossils etc) but no bone parts from any other species.

Playing 1.12.2, version 8.0.4.