An introduction to Vetulicolians

The Vetulicolians are an obscure group of extinct deuterostomes- the group of animals that includes acorn worms, echinoderms, and chordates. How these mysterious creatures specifically fit into this group has long vexed researchers ever since it was determined that the first specimen, Vetulicola cuneata, was not a bivalved arthropod. Through anatomical comparisons and various fossils revealing the presence of notochords, researchers eventually determined that vetulicolians were chordates related to the tunicates, or sea squirts, and the larvaceans.

   As far as we humans know, vetulicolians were temporally restricted to the Cambrian Period of the Paleozoic Era.

Here's a little introduction to the variety of vetulicolians. There will be more to come in future posts.

The Wedge-faced Ancientworm
(note: most prehistoric creatures don't get a common name like our modern animals. They have to content themselves with scientific nomenclature. But we figured such oddballs deserved some memorable everyday names.)

Species: Vetulicola cuneata
Phylum: Chordata
Subphylum: Vetulicolia
Class: Vetulicolida
Family: Vetulicolidae
Size: 9 cm
Time period: Cambrian, 515 million years ago
Location: Chengjiang County, Yunnan Province, China

Vetulicola was the first identified member of this group. Similar in size to a large goldfish, it was originally described as a "bivalved crustacean" but the articulation of the carapace was unlike anything seen in other arthropods. The shell comes to a spike-like point on the bottom and a hard, inflexible, shark-like fin on top. The mouth is covered by a beak-like structure called the "oral disk". Along its flanks are five diamond-shaped holes that are believed to be gill openings.

The living animal would have resembled a wooden clog converted into an ice skate with an oar-shaped tail emerging from the heel. Unlike chordates, the anus opens at the very tip of this tail.

A few Vetulicola fossils were discovered with small epibionts growing on the end of their tails. These passengers, called Cotyledion tylodes, belong to a small, relatively obscure group of invertebrates called entoprocts, which resemble tiny tentacled shaving brushes. Their presence on Vetulicola's hind end led some researchers to conclude that the Wedge-faced Ancientworm was a burrower with Cotyledion settling on its exposed tail tip poking up out of the mud. However, the streamlined, fish-like anatomy of vetulicolians in general suggests that they were more likely active swimmers in the open water. Most likely Coytledion larvae attached to the tail-tips of swimming vetulicolids- much as modern barnacles attach to the bellies and head of humpback whales- and survived on a diet of their host's feces in a case of "waste not, want not" commensal symbiosis.

There'll be more vetulicolians coming soon, but if you'd like to learn more right now, here's a book all about them.