Chance discovery contributes to origins and evolution focus | Curator of Micropalaeontology

When I first came to the Museum I dreamt that one day someone would bring something in for identification that I would recognise to be a really important find. The contents of a consultancy sample back in 2005 helped to make my wish come true. This post tells of the discovery and subsequent publication of a significant species of early fossil fish from Oman that provides information on the origins and evolution of life on our planet, one of the main focus areas of Museum science.

Montage of photos showing close ups of fossil plates and scales
Examples of plates and scales of the early fish Sacabambaspis

Very occasionally I get consultancy rock samples sent to me for dissolving to find microfossils. This is so that we can provide the age for a rock formation or details about fossil environments or climate. And so it was that Alan Heward, then of Petroleum Development Oman (PDO), sent me a sample in 2005 for analysis to try to find age diagnostic conodonts. Conodonts are extinct phosphatic microfossils that look like teeth and are used extensively for dating rocks that are roughly 500-205 million years old.

Initially I was disappointed as the sample failed to dissolve in the bath of acetic acid (the acid you find in vinegar) that I was using to release specimens. However, when I looked under the microscope at the small residue that had been produced I saw tiny oak leaf like crenulated structures that I immediately recognised as fragments of early fish.

Photo showing the structures in alignment on a black background
Some of the tiny crenulated structures from the first sample. The largest are just under 2mm in length

I knew that Dr Ivan Sansom of the University of Birmingham was studying early fossil fish like the one under my microscope so I took images of the tiny specimens and sent them to him by e-mail. Within a minute he was on the phone asking where I had got them, suggesting a visit to find more and check out the geological setting from which they had come. I had discovered tiny fragments of an early arandaspid fish called Sacabambaspis.

A line drawing of the reconstruction of Sacabambaspis and a photo of its fossil scale inset
Reconstruction of the early fish Sacabambaspis and (inset) a scanning electron microscope image of a Sacabambaspis scale from the Ordovician of Oman. Reconstruction published with permission from Ivan Sansom, University of Birmingham.

Prior to my Oman discovery, examples of Sacabambaspis had been recorded from Argentina, Bolivia and Australia so we know that this particular fish lived on the continental margins of the ancient supercontinent of Gondwana. In the Ordovician period about 450 million years ago, Gondwana was an amalgamation of what we currently know as Africa, South America and Australia with some parts of China and the Middle East.

These examples all come from very similar geological settings suggesting that they lived in a very shallow sea. Complete specimens from the type area in Bolivia suggest that these early fish were probably poor swimmers, scrabbling around on the bottom of the shallow sea, filtering for food.

Coloured illustration depicting the Gondwanan supercontinent
Palaeogeography of the Gondwanan supercontinent roughly 498 million years ago, showing locations of Sacabambaspis discoveries in Oman (4), Bolivia (1), Argentina (2) and Australia (3)

The Oman discoveries showed that Sacabambaspis was present all around the margins of the ancient continent of Gondwana and not just in the southern regions as had previously been shown by the findings from South America and Australia. Previously it had been suggested that they originated in Australia and spread northwards but the Oman specimens suggest that this may not be the case.

Dr Sansom funded a trip to Oman in 2006, supported by Alan Heward of PDO, to collect further samples for dissolving. Until the last morning of the trip, we had not found any suitable samples but, just as we were about to leave, I looked down and saw next to my foot a rock with tiny fragments of what looked like arandaspid fish plates and scales. It wasn’t until my return to London that I found I needed to have my first pair of glasses…

Photograph of Giles Miller and Felicity Heward in Oman
With Felicity Heward at Wadi Daiqa, holding two large slabs of rock covered with fish scales and plates. Sadly the one that Felicity was holding was lost in the post between Oman and London but the Hewards have collected and donated plenty of material since.

We returned the following year, this time funded by the Museum with additional support from PDO. Subsequent laboratory work on this material and several donations from further field collecting by Alan Heward, have yielded an excellent suite of specimens from Oman that are now part of the Palaeontology collections here at the Museum.

Several samples have also yielded conodonts. We have published papers on the fish and other fossil material but there remains much to be written up, including a paper on the Amdeh Formation that has yielded all these finds. Now I have finished this post I feel inspired to get on a write up the rest of this fauna with my collaborators!

If you have a natural history object that you want identified by a Museum scientist then you can post an image on our Identification forum. Alternatively you can make an appointment to bring your specimen into the Angela Marmont Centre for UK Biodiversity. And, if you can’t get to London then why not try your local museum? Maybe you will also be lucky and find something that is new to science or provides important evolutionary evidence for the early origins of life.