The weird and wonderful of the Cambrian (Part 17): Vetulicola cuneata – a strange, segmented drifter of the early Cambrian seas

Jon Trevelyan (UK)

This is the seventeenth in my series of short articles on fossils of the Cambrian. Vetulicola cuneata is one of the most enigmatic animals from the Early Cambrian, known from the celebrated Chengjiang biota of China. Living around 518 million years ago, it represents a body plan so unusual that its evolutionary position puzzled researchers for decades.

With a wedge-shaped anterior section, a segmented tail, and a large terminal opening interpreted as a primitive pharynx, Vetulicola sits close to the origins of chordates – our own distant lineage. Whether regarded as an early deuterostome – a major group of animals that includes chordates (and ultimately vertebrates) and their relatives – or more specifically as a stem chordate, it offers an extraordinary glimpse into a period of evolutionary experimentation unlike anything seen before or since.

Discovery and appearance

The first fossils of Vetulicola cuneata were described in the late 1990s from the Maotianshan Shales near Chengjiang, Yunnan Province. The preservation is exceptional: flattened impressions showing fine details of the body wall, internal chambers, and segmentation. These fossils brought immediate attention because Vetulicola didn’t resemble any known phylum.

The organism was around 6-8cm long and consisted of two main regions.

1. A large, box-like anterior section shaped roughly like a wedge or inflated shield. This part of the body was soft, inflated, and divided into four broad lobes or flanges along the sides. At the front lay a wide, slit-like mouth or opening leading to the pharyngeal chamber.
2. A narrow, segmented posterior tail, muscle-like in appearance, composed of seven or more repeated units. This posterior region lacked limbs or appendages, but shows clear evidence of lateral compression, suggesting stabilising movement through the water.

There are no eyes or sensory organs preserved, but the body plan suggests a swimming or drifting filter-feeder, rather than an active predator or burrower.

Interpretation and Classification

Few Cambrian animals have caused as much evolutionary head-scratching as Vetulicola. Early hypotheses placed it among arthropods, jellyfish or even anomalocarid relatives. The real turning point came when researchers realised that the large front opening and the structures inside it were part of a simple filtering throat, which is a feeding system characteristic of deuterostomes, the group that later gave rise to chordates, echinoderms and hemichordates.

Modern interpretations view Vetulicola as a stem deuterostome positioned close to the base of the group that would eventually give rise to chordates. The large anterior body may have housed a pharynx perforated by gill slits. Water drawn in through the mouth would have passed across filter structures and been expelled laterally. This places Vetulicola in a critical evolutionary zone, alongside other early deuterostomes like Yunnanozoon and Haikouella, although its precise relationships remain debated.

The segmented tail suggests muscular propulsion, but its limited flexibility implies it was more of a stabiliser or steering organ than a primary swimming appendage. Vetulicola probably hovered or cruised slowly through quieter water, filtering suspended particles.

Significance

Vetulicola cuneata is significant for several reasons.

1. A glimpse of early deuterostome evolution: its pharyngeal architecture suggests that filter-feeding was a core lifestyle among early members of the group that led to chordates.
2. Evidence of unusual Cambrian body plans: the stark difference between the inflated anterior and the segmented posterior highlights the experimental nature of Cambrian evolution.
3. Insights into feeding and ecology: Vetulicola lived in relatively quiet, deeper parts of the Chengjiang sea, where fine organic material drifted down. Its morphology suits a slow, energy-efficient filter-feeding lifestyle, rather than rapid swimming or burrowing.
4. Important complement to other Chengjiang chordate-adjacent forms: alongside Yunnanozoon, Haikouella, Myllokunmingia and Haikouichthys, Vetulicola forms part of a cluster of early deuterostomes that together illuminate the early origin of features such as gill slits, muscular tails, and basic segmentation.

Conclusion

Vetulicola cuneata stands as one of the most distinctive animals of the Cambrian explosion – an organism whose strange combination of features captures a transitional moment in the history of deuterostomes. Its wedge-shaped anterior, filtering pharynx, and segmented posterior offer a rare window into how some of the earliest relatives of chordates lived and fed. In the shimmering seas of Cambrian China, Vetulicola was part of a vibrant ecosystem of innovating body plans, marking one of the first chapters in the evolution of complex animals.