Meet the First Animals

The latest exhibition in our Contemporary Science and Society series, First Animals, tells the tale of Earth’s mysterious early animals, which evolved in the sea over half a billion years ago. Here, Dr Imran Rahman, Deputy Head of Research at the Museum, introduces some of the fossils that form a key part of this story.

From sponges to sea slugs and hagfish to humans, all animals alive today trace their roots back to a common ancestor that lived in the ocean more than 600 million years ago. We have no direct evidence of this first animal, but the fossil record reveals some of its earliest descendants. Our First Animals exhibition explores the evidence for Earth’s earliest animal life, attempting to answer the ‘what’, ‘when’, ‘how’ and ‘why’ of the origin of animals.

Yunnanozoon lividum from the Chengjiang fossil site had a long body with several filament-covered arches at the front and a fin-shaped structure towards the back. It cannot be confidently assigned to any known animal group.

First Animals features the oldest animals yet recovered from the fossil record, including specimens from 571-million-year-old rocks in Newfoundland, Canada. These represent the remains of originally entirely soft-bodied organisms, which have proven difficult to classify because they look so different to living species. However, new research on their anatomy and how they grew, including work by Museum researcher Dr Frankie Dunn, suggests they were early animals.

Charnia masoni consisted of alternating branches arranged along a frond. It is thought to be one of the oldest animal fossils yet found.

Microscopic fossils record the first animal skeletons, which first appeared about 550 million years ago. These include the remains of complete animals, as well as fragments such as spines and scales. Work by Museum researcher Dr Duncan Murdock using a particle accelerator to generate X-ray images of these tiny fossils has allowed us to reconstruct how the skeletons changed as they grew. This helps to establish the modern groups to which these ancient animals belonged, and unravels the mystery of why animals evolved hard skeletons when they did.

Virtual cross-sections through small shelly fossils created using X-ray imaging.

The most complete evidence for the early evolution of animals comes from sites of exceptionally-preserved fossils, or Lagerstätten, which retain impressions of soft tissue as well as hard parts, and include rare soft-bodied animals like worms and jellyfish.

First Animals brings together extraordinary specimens from three key fossil sites: Sirius Passet in northern Greenland (518 million years old), Chengjiang in Yunnan province, China (518 million years old) and Burgess Shale in British Columbia, Canada (508 million years old). This includes 55 unique fossils loaned by Yunnan University in China, as well as specimens from the University of Bristol and the Royal Ontario Museum.

The mollusc Halkieria evangelista from the Sirius Passet fossil site had a long body covered in hundreds of overlapping hard plates, with a large shell plate at either end.

The arthropod Haikoucaris ercaiensis from the Chengjiang fossil site had a semicircular head shield with a pair of large grasping appendages, a segmented body and a short tail.

The worm Ottoia prolifica from the Burgess Shale fossil site had a spiny proboscis and a long trunk that was divided into a series of fine rings.

These exceptionally-preserved fossils reveal the evolutionary diversification of life during the so-called ‘Cambrian explosion’. Through careful study of the fossils, scientists have begun to reconstruct the very first animal ecosystems, which are brought to life in the exhibition through a series of stunning digital reconstructions and the Cambrian Diver interactive installation. This allows visitors to explore a 360-degree oceanic environment in a virtual submersible craft, coming face-to-face with some of the first animals on Earth!

Digital reconstruction of the sea floor 518 million years ago, based on specimens from the Chengjiang fossil site, Yunnan province, China.
Video by Mighty Fossils.

 

First Animals is open until 24 February 2020. Entry is free, no booking required. www.oum.ox.ac.uk/firstanimals.

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