Article: Bubble-headed trilobites, and a new olenid example
Several trilobites developed an inflated cephalic lobe with a distinctive bubble-like profile. This happened polyphyletically in at least seven families ranging from the Cambrian to the Silurian. We describe a new species of Ordovician (Tremadoc) olenid trilobite, Parabolinella bolbifrons, having this morphology. A review of other trilobites with apparently similar cephala shows that the bubble-headed appearance was derived in several different ways and probably acquired different functions. In deiphonine cheirurids, staurocephalids and Paraphillipsinella all, or only the frontal part of the glabella, is involved in the inflation. These species have rigidly attached conterminant hypostomes, and glabellar inflation may have matched a comparable inflation of the stomach. In the new species, as in several Cambrian examples with natant hypostomes, inflation is confined to a median area of the preglabellar field. This is unlikely to have involved any modification of the alimentary system.