Credit: Charles Mitchell, University at Buffalo, SUNY
A colony of Rectograptus intermedius, a diplograptine graptolite species that thrived before the Ordovician mass extinction. Graptolites were able to secret a collagen-like substance that they could then shape into tubes (each about 0.5 mm wide), spines and other shapes. Paleontologists have studied fossil graptolites, which are found the world over, for more than 150 years.