During one of our hikes in northern Ras Al Khaimah, we came across a group of remarkable fossil-bearing stones. One slab was roughly half a metre in both length and width and was far too heavy to carry away for further study.
The surface contained a dense, tangled pattern of tubes, ridges and branching forms. At first glance, it looked like a collection of burrows or worm casts preserved in stone.
A field observation, not a final identification
Without close photographs, a measured section and expert examination, the fossil cannot be identified with certainty. The interpretations below are possibilities based on its appearance and the known marine fossils of the wider region.
A fossil too large for the backpack
The size of the slab immediately made collection impractical, and leaving it in place was the right decision. Large fossil-bearing rocks are more useful in their geological context than removed from the outcrop.
The surrounding rock appeared to contain several different fossil textures. Some were tubular or branching, while others looked like small grains, fragments or shell-shaped inclusions.
A fossil is not only an object. Its position in the rock is part of the story.
Burrows, casts and trace fossils
The tangled structures may represent trace fossils, also called ichnofossils. These preserve the activity of an organism rather than the organism's body.
Common trace fossils include burrows, feeding trails, resting marks, footprints and borings. A burrow may later fill with sediment that becomes more resistant than the surrounding rock, leaving a raised cast after erosion.
Identifying the animal that produced a burrow is often difficult. Different organisms can make similar structures, and the same animal may produce different traces depending on its behaviour and the consistency of the seafloor.
- Burrows
- Feeding trails
- Resting traces
- Walking tracks
- Borings
- Sediment-filled casts
Could trilobites have made the traces?
Trilobites were extinct marine arthropods whose name means “three lobes,” referring to the three longitudinal sections of their exoskeleton.
Trilobites lived from the Cambrian Period until the end of the Permian, approximately 521 to 252 million years ago. Their body fossils usually show a segmented exoskeleton, but trilobites also left trace fossils as they crawled, rested and fed on the seafloor.
Recognised trilobite trace fossils include Cruziana, Rusophycus and Diplichnites. These can preserve paired grooves, scratch marks or repeated impressions produced by limbs.
The tangle is not automatically a trilobite fossil
A branching burrow network without diagnostic scratch marks cannot be confidently attributed to trilobites. Worm-like animals, crustaceans and other burrowers may produce similar patterns.
Trilobite activity therefore remains an interesting possibility, but not a confirmed identification from the information available.
How old are the rocks?
Fossil-rich carbonate rocks in the wider Hajar Mountains include Permian and Triassic marine formations. Modern geological timescales place the Permian at approximately 299 to 252 million years ago and the Triassic at approximately 252 to 201 million years ago.
Older literature may give different numerical boundaries, such as 286–208 million years, because geological timescales have been refined over time.
A broad regional age does not prove the age of an individual loose block. Confirming that requires knowing the exact formation and whether the rock was found in its original bed or transported by erosion or floodwater.
Fusulinids: cigar-shaped microfossils
Some of the small elongated forms in the rock could be fusulinids. Fusulinids were marine foraminifera—single-celled organisms that built chambered shells.
Many fusulinids are spindle-shaped or resemble tiny grains of rice or small cigars in cross-section. They were especially common during the late Carboniferous and Permian and became extinct at the end of the Permian.
Although they are called microfossils, larger specimens can be visible to the naked eye in limestone. Their rapid evolution makes them useful for dating and correlating Permian rocks.
Crinoids: sea lilies, not sea urchins
The rock may also contain fragments of crinoids. Crinoids are marine echinoderms related to sea stars and sea urchins, but they are not themselves sea urchins.
Many crinoids have a flower-like body supported by a stalk, which explains the common name “sea lily.” Their stalks are built from numerous circular or star-shaped plates called columnals.
After death, the skeleton often breaks apart, leaving small discs, rings or short stem fragments scattered through limestone.
Corals, shells and a mixed marine community
Permian marine limestone in the Oman Mountains is known to contain a varied fossil community, including corals, bivalves, brachiopods, gastropods, crinoids and fusulinids.
A single slab can therefore appear to be a confusing mixture. Some shapes may be complete fossils, while others are broken fragments, cross-sections or burrows cutting through earlier material.
This mixture is valuable because it reflects a living marine environment rather than an isolated organism. The rock may record a shallow sea, reef-associated habitat, storm deposit or seafloor repeatedly disturbed by burrowing animals.
How to examine a fossil in the field
Good fossil identification begins with careful observation rather than immediate collection. Take photographs with a scale and record the surrounding rock and bedding.
- Photograph the entire slab.
- Add a ruler, coin or trekking pole for scale.
- Take close-ups from several angles.
- Photograph the surrounding outcrop.
- Record whether the rock is loose or still in place.
- Note the colour, grain size and rock type.
- Record approximate location privately.
- Consult a geologist or palaeontologist.
Light from the side
Low-angle sunlight or a torch held from the side can reveal ridges, grooves and scratch marks that disappear under flat overhead light.
Leave large fossils where they belong
Fossils and geological formations may be protected by local law or fall within protected, archaeological or privately owned areas.
Removing a large slab can damage the outcrop and destroy information about its position. It can also be dangerous: heavy rocks may cause injury or destabilise a slope.
- Do not hammer or break an outcrop without permission.
- Do not remove fossils from protected areas.
- Do not publish precise locations of vulnerable sites.
- Never attempt to carry an unsafe rock.
- Photograph and report important finds instead.
Final thoughts
The northern Hajar Mountains preserve the remains of seas that vanished hundreds of millions of years ago. A single stone may contain burrows, shell fragments, corals, crinoids and tiny foraminifera all mixed together.
Our fossil slab may represent a dense network of trace fossils, perhaps accompanied by fusulinids and other marine remains. Trilobites are possible participants in the wider geological story, but the tangled structures cannot be assigned to them with confidence without diagnostic evidence.
The most honest fossil identification sometimes ends with a question mark— and that question is what makes the discovery exciting.
Further reading
DubaiHiking.org Editorial Team
DubaiHiking.org shares UAE hiking stories, geological discoveries and responsible outdoor knowledge from the Hajar Mountains and beyond.
