pearl-nautilus:

Sphenodiscus lenticularis, Fox Hills Formation, South DakotaLate Cretaceous (~ 70 mya) This specimen displays the extraordinarily intricate suture patterns that are characteristic of this species. Also evident is part of the beautifully iridescent nacreous layer. A laterally flattened ammonite, this animal is thought to have been a relatively fast swimmer. 
source:

pearl-nautilus:

Sphenodiscus lenticularis, Fox Hills Formation, South Dakota
Late Cretaceous (~ 70 mya) 
This specimen displays the extraordinarily intricate suture patterns that are characteristic of this species. Also evident is part of the beautifully iridescent nacreous layer. A laterally flattened ammonite, this animal is thought to have been a relatively fast swimmer. 


source:

(via s-a-d-e-s)