Dr Charlie Underwood (UK)
Shark enamel are amongst essentially the most iconic and wanted of fossils. Nevertheless, for many of us, amassing them generally is a troublesome and even disagreeable process. I’m positive that the majority collectors in northern Europe are acquainted with choosing their means over slipped cliffs of clay, in the teeth of a freezing winter gale, to collect the few treasures that erosion leaves on the beach. Alternatively, the more dedicated are used to carrying hundreds of kilos of clay home and painstakingly passing it through a sieve before even knowing if there are any fossils there.
But it is not all like this. There are a number of places in the world where the vagaries of sedimentology have allowed bone-beds (or phosphorites) to develop, within which vertebrate fossils, and shark teeth in particular, are hundreds of times more abundant than in a normal marine sediment. By far the most extensive of these deposits are in Morocco.
Below the dusty scrub and parched farmland of northern Morocco lie the largest reserves of mineral phosphate known. Vast complexes of open-cast mines, one stretching for nearly 30km, have been cut into these deposits, with a network of conveyor belts transporting the phosphate sand and rock to the processing factories turning the rock into fertilizer. These great phosphate deposits were laid down in a sea saturated with nutrients and teeming with life. As a result, the phosphates are crammed with the fossilised phosphatic bones and teeth of fish, sharks and a host of other extinct vertebrates.
As the phosphate rock is dug up, fossils are exposed in their millions. Many of the better ones are collected by the mine workers and sold on to wholesalers. These fossils eventually find their way to mineral shows and curio shops across the globe. Indeed, the pale yellow to buff-coloured shark teeth from these mines are amongst the most widely sold of all fossils. Of course, it is not just shark teeth that turn up in these mines, as remains or rays, bony fish and reptiles are all common.
Although phosphates with abundant shark remains are common in a number of places, such as along the US eastern seaboard and the Pacific coast of South America, the Moroccan deposits are unique amongst the deposits worked for fossils in that they span an extensive period of time. Although the age of the phosphates varies somewhat from place to place, in the area around Khouribga, from where most of the fossils originate, the phosphates range in age from latest Cretaceous (Late Maastrichtian) to Early Eocene (Ypresian). As a result, different levels in the mines yield a huge range of fossils from the Late Cretaceous, Palaeocene and Eocene.
Sixty eight million years ago, Morocco lay on the southern margin of the great tropical ocean of Tethys, part of which would, one day, become the Mediterranean Sea. For millions of years, this had been getting narrower as Africa and India moved northwards, changing ocean currents to force nutrient-rich waters up from the ocean floor and onto the flooded northern edge of the African continent. Within these warm and productive seas, great blooms of plankton formed the basis of a food chain, at the top of which lived the mosasaurs. However, while the ocean conditions that created this environment persisted for 18 million years, the mosasaurs and their contemporaries did not. The tumultuous events that occurred at the end of the Cretaceous period (65 million years ago) wiped out many of the inhabitants of these rich seas, from tiny plankton to the giant reptiles.
After the demise of so many of the inhabitants of the world’s oceans, new animals evolved to take their place, with new groups of fish, sharks and reptiles replacing the animals of the Cretaceous. Even now, as survivors of the great end Cretaceous extinction evolved into new forms during the Palaeocene, another global upheaval was to occur. The end Palaeocene (65mya)saw one of the most dramatic rises in global temperatures known, as methane, a powerful greenhouse gas that was previously trapped in the deep ocean, was released into the atmosphere. During all of this time, the phosphates, with their abundance of fossils, continued to be deposited, leaving an unrivalled record of the changes in marine vertebrate faunas across these two events.
How are the fossils collected?
Rules covering the access to land owned by the OCP (the crown-owned mining company) effectively prevent anyone, other than the mine workers, from collecting material in the field. Therefore, they, and the dealers they sell to, are the only source of the fossils. The Moroccan phosphates are extremely condensed, with the entire sequence being less than 20m thick. The rocks themselves range from loose and uncemented phosphate sand to very hard, calcite-cemented phosphate with chert nodules. The mining operation concentrates on the soft levels that can be easily dug out, with the harder material usually being heaped up in vast spoil tips.
The main soft units have been numbered Couche 0 to 3, from the top downwards. In addition, there are several other, thin, soft units above this that are not worked. The lowest and thickest of the soft units is Maastrichtian in age (65 to 70 million years ago). These rocks are usually yellowish in colour and composed largely of finely broken fish bones. Although soft enough for digging, these sediments cannot easily be dry-sieved, and so the fossils are typically gathered by surface collecting.
The most highly sought after fossils are the remains of mosasaurs, with partial skeletons and skulls being relatively frequent finds. Isolated teeth are far more common, but most of these get used to make rather nasty faked jaws, comprising ‘bones’ made of plaster and/or bone fragments and real teeth.The only shark teeth collected here in large quantities are of Squalicorax, although teeth of Serratolamna, Hexanchus and the ray, Rhombodus, are all commonly seen for sale. In addition, other ‘things of interest’ are commonly collected, usually attached to an oval slab of the rock. These are mostly pieces of bony fish skull or skeleton, but rostral teeth of sclerorhychid sawfishes are also collected.
The Palaeocene rocks (60mya) are only soft enough to be worked in some places, and so Palaeocene fossils are not that commonly seen. These rocks are the probable source of most of the best fossil crocodiles, with beautifully preserved skulls being regularly found. However, as with the mosasaurs, there are lots of rather unconvincing fakes and composites about.
Where soft phosphate sands (known as Couche 2) are present, they are sometimes soft enough to be dry-sieved in the field. This involves the soft sediment being shovelled into a coarse sieve (probably about 8mm mesh) and the teeth and other fossils being picked out of this. The main targets are the rare, serrated, teeth of Palaeocarcharodon. In the process, many other teeth are collected, to be later sold by the kilo. Even rarer, and more sought after than the Palaeocarcharodon teeth, are those of the giant cow shark, Notidanodon. As with the other valuable specimens, these teeth are commonly repaired or composites made from pieces of several teeth.
The rocks of around the Palaeocene-Eocene boundary (55mya) are represented by a bed of very hard, calcite cemented, oolitic phosphate, commonly containing pebbles of green mudstone. This bed is the source of many of the reptile fossils from the area, as well as rare remains of giant sea birds (Odontopteryx) and mammals. It also contains large numbers of huge examples of teeth of the shark, Otodus, and is the source for most Otodus teeth attached to matrix seen for sale. Some of these teeth are present as associated dentitions, scattered on the sea floor when the shark decayed.
Probably, the most widely collected layer for shark teeth is the early Eocene Couche 1. This is a very soft, oolitic phosphate sand containing vast numbers of fossils. This is sieved in the mines, often by mine workers during their lunch break. The large teeth of Otodus, and ‘unusual’ teeth of the nurse shark Nebrius and the cow sharks Hexanchus and Weltonia, are put to one side. What is left is a fascinating mix of shark and ray teeth, fish bones and teeth, and small bones and other remains of crocodiles, sea snakes and birds.
Higher levels of the phosphates are rarely worked, and so fossils from these units are very rarely seen.
I want some of those …
The inability to access the sites directly means that all fossils come through a dealer, or more commonly, a whole string of middle men. It is possible to visit the dealers directly, but there are only a couple of geological tour operators who have the knowledge, and the trust of the dealers, to allow this to happen. In addition, the distance from Khouribga to any of the other major geological sites in Morocco makes a visit there impractical for many visitors. Despite that, visiting the area is fascinating. Some of the whitewashed adobe farmhouses have been almost completely given over to store rooms and workshops filled with fossils.
The floors of some rooms are covered with crocodile and mosasaur skulls and partial skeletons, others covered in trays of identical sized Otodus teeth destined for the jewellery trade, still more stacked with crudely faked mosasaur jaws, turtles, crocodile skulls and ‘pizzas’ (damaged shark teeth stuck onto a disk of reconstituted rock to resemble an associated set). However, the most interesting rooms are those filled with ‘other stuff’ – boxes of assorted maastrichtian fossils on small rock slabs, trays of mixed rarities (unusual shark teeth, bits of reptile, ray tooth plates and all manner of other items), matchboxes of small shark teeth and crates of ‘kilo mix’, the leftovers of the sieving operations once the most valuable fossils have been removed. Not only can fossils be bought at the dealers’ houses – just waiting at a road junction is often enough for someone to appear with a tray of fossils or, if you are really lucky, you meet someone on the way home from the mine, allowing access to the whole and unsorted results of a day’s work.
However, there is no need to visit Morocco to get hold of these fossils. There are a number of importers bringing material into Europe and North America, some shipping container loads of fossils at one time. Although you can get these fossils from many outlets, if you want quality specimens, I would recommend buying directly from one of the importers. The fossils will have been shipped legally with correct paperwork and, even if they import them, the importers will know which fossils are faked or ‘improved’. For larger fossils, remember that what you see is what you get.
If there is a crocodile skull half exposed from the rock and still in its plaster jacket, do not expect to be able to prepare it further. More likely than not, the other side was destroyed by digging machinery, and it has been exposed to show the good side. Never trust something that appears too cheap, and look closely – some workshops have boxes of broken bits of Otodus, so if there is a large tooth with a lateral cusp or root lobe missing, it can be replaced. If you want anything that is cheap(ish), unlikely to be messed about with too much, and will give you a great collection, I would suggest buying some kilo mix. Perfect teeth can work out costing almost nothing, and you never know what may be in there.
In most cases, I would be happy to say that I am not a supporter of the trade in fossils, as I have seen the damage that can be done to fragile sites and the ‘loss’ of scientifically important specimens. However, in the case of this material, I consider that there is no case to answer. The fossils that are traded here would otherwise be made into fertilizer along with the rest of the rock, and they bring much needed money into the impoverished communities of the area. In addition, some fossils, such as mammals, have legal protection, and it could even be considered that the presence of so many low price shark teeth on the market has reduced the collecting pressure on other sites.
So what have I got?
Cretaceous material is usually easily recognised. Shark teeth are often yellow in colour with white roots, and the rock ranges from cream to orange and is made largely of tiny bone shards. In addition, most of the fossils are of species that became extinct at the end of the period. The rock is usually too hard to dry sieve, but not durable. Therefore, if you have a specimen attached to a slab of rock, it will have been hardened, probably with a water soluble glue (but sometimes acetone soluble hardener is used). If the fossil is robust enough to be removed from the rock, break the remaining rock down in water and sieve it; you will probably get several beautifully preserved tiny teeth.
Most of the Tertiary phosphates are oolitic and usually a buff colour, although some are white or dark reddish purple. For larger specimens, such as reptiles, it is usually possible to get some small shark teeth from the matrix to give a general age for the specimen. Most Palaeocene sharks are supplied either as isolated teeth of species that only existed in that period, or, uncommonly, as kilo mix. This tends to be (from the little I have seen) quite low diversity, and dominated by a couple of species of quite large teeth (a large sand tiger, probably Hypotodus, small Otodus, although these are usually removed to be used in jewellery, and Cretalamna). There are relatively few bits of ‘non shark’, and the teeth are often a very pale colour. This tends to be more expensive than the Eocene kilo mix because of the larger average size of the teeth.
Most, but not all, of the Otodus and other fossils embedded in very hard, pale, oolitic phosphate are basal Eocene age (55mya)and come from the hard layer between Couches 1 and 2. If there are greenish mudclasts present, these are diagnostic as they are not found (as far as I know) at other levels. As with the Maastrichtian specimens, breaking down the matrix will yield a number of small shark and ray teeth. I broke down a fist-sized piece of this and got teeth (some broken I admit) of 11 species of sharks and rays. Due to the hardness, it is necessary to use dilute acetic (or formic) acid, following the normal precautions.
Most of the loose teeth that are for sale come from Couche 1. The larger or more unusual teeth are usually separated during collection, and are likely to be sold individually. What is left is sold off as kilo mix. This varies from pristine, with only a few teeth taken out, to heavily contaminated and mixed with all the well preserved material removed. There will always be a little contamination during collection, either through mixing caused by the excavation machinery, or the collectors picking up teeth they see lying about on the way to and from the site.
More contamination happens when the dealers make up weight of a box by grabbing a few handfuls from another box. Usually, though, the contamination from these is restricted to the occasional Cretaceous tooth, and is easy to recognise. Worse is when the sample is interfered with further down the chain and, at this stage, many of the larger teeth may be removed and sold separately. Most of the kilo mix I have seen for sale in internet auction sites is of this type. The less dealers have handled the samples, the less likely this is to happen. In many cases, the best samples look the worst; if there are lots of bits of bone, nodules and pieces of rock in the box, it is likely that is has not been ‘tidied up’ and is pretty much as it was when it left the miner. Generally, these samples are a pale buff colour, or may be reddish if they are from near the base of the bed.
There are a lot of ‘non shark’ items, and often about a third of the sample is not composed of shark teeth. Of these items, the commonest are teeth, usually broken but sometimes complete or articulated, of bat rays. There are several species referred to as Myliobatis, as well as rarer Aetobatus and Pseudaetobatus. Less common are rostral teeth of sawfishes. There are common bony fish remains, with teeth and jaw fragments of pycnodonts, Cybium and Phyllodus all being frequent, as well as catfish fin spines and fish bones. The commonest tetrapod remains are the vertebrae of sea snakes, although pieces of crocodile, turtle and bird are all common.
Shark teeth are dominated by the sand tigers Striatolamia and two species of Brachycarcharias. Teeth of other genera, such as Jaekelotodus, Cretalamna, Serratolamna, Otodus and at least one undescribed species, are also likely to be present. You may even be lucky enough to have a sample where the cow and nurse shark teeth have been left in. Of course, for each species of these larger sharks and rays, there are maybe five with teeth too small to have been collected by this method. Hopefully, in time, it will be possible to get hold of these samples as well, as this is where (in my opinion) the real fun is.
As I write this, a storm is lashing southern Britain. For once, I am not weighing up which of nearby beaches will produce the best fossils with the least chance of getting soaked and cold, but I am instead sorting through a box of hundreds of amazing Moroccan fossils in the warm and dry.
Dr Charlie Underwood has published a large number of publications in particular on sharks and fish, but also covering a wide array of subjects and carried out a field study in Madagascar for Madagascar Hunt Oil Company from in 1998.
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