# Rapid growth in a large Cambrian apex predator

## TL;DR

This study reveals that a 520-million-year-old Cambrian predator grew extremely fast, suggesting a unique life strategy during the Cambrian explosion.

## Contribution

The paper provides the first quantitative analysis of the post-embryonic growth of a Cambrian apex predator.

## Key findings

- Appendages of Amplectobelua symbrachiata grew isometrically with an estimated maximum size of 90 cm.
- The species exhibited rapid growth compared to modern arthropods.
- The growth pattern supports the idea of an evolutionary 'arms race' during the Cambrian explosion.

## Abstract

Despite the importance of ontogenetic data on early diverging euarthropods to our understanding of the ecology and evolution of past life, the data are distinctly lacking, as reconstructing life histories of fossil animals is often challenging. Here we report the growth trajectory of frontal appendages of the apex predator Amplectobelua symbrachiata, one of the most common radiodont arthropods from the early Cambrian Chengjiang biota (c. 520 Ma) of China. Analysis of 432 specimens (9.1–137.1 mm length; 1.3–25.6 mm height) reveals that appendages grew isometrically, with an estimated maximum size of the whole animal of c. 90 cm. Individuals grew rapidly compared to extant arthropods, as assessed using the electronic length-frequency analysis (ELEFAN) approach. Therefore, we show that the Cambrian apex predator A. symbrachiata was an extremely fast-growing arthropod, with an unusual life history strategy that formed as part of the escalatory ‘arms race’ that shaped the Cambrian explosion over 500 Ma.

The post-embryonic development of a 520 million years ago apex predator was quantitively described, which revealed that Amplectobelua symbrachiata was an extremely fast-growing arthropod with an unusual life history strategy.