Is this the strangest egg in the world? The shell contains no egg white, yoke or embryo, nor even chocolate. No bird will ever hatch from it. Instead it is filled with a stony mineral. Which creature laid it, and what was expected to emerge from it? The only thing that comes to mind is a stone eater, from Nora Jemisin’s volcanic masterpiece The Fifth Season. But that is from another world.
There is a story here. This is about an Easter egg hunt with a difference. Forget about bunnies. Think dinosaurs.
Easter is the season of eggs and rabbits. Actually, those are a bit of an add-on. The importance of eggs came from a religious prohibition on eating eggs in the week before Easter – eggs harvested during that week would be kept, decorated and given to the children at Easter. (In some countries, including Ukraine, the eggs are painted red.) The Easter bunny stems from a German tradition but was originally a hare, not a rabbit. Easter has become a mismatch of traditions. The word Easter itself has a Germanic origin, although the precise meaning has been lost in time (a likely meaning is ‘dawn’); strangely, the word is now only used in English. Chocolate as an Easter tradition was a commercial invention. (The modern redefinition of Easter egg as a hidden quirk in computer games has nothing to do whatsoever with Easter and helps to keep you hooked a bit longer, to be exposed to more adverts.)
Behind all these traditions (except the commercial one) is the season of new beginnings, a restart, regrowth or resurrection after the desolation and perhaps hunger of winter. Many cultures celebrate this, each in their own way. Spring is when the world springs to new life. Originally this was seen as the start of the year, in a tradition which goes back at least four millennia. The 12 constellations of the zodiac form a procession with the bull at the head: at the time the constellations were invented the bull was April. The oldest parts of the bible use spring as the start of the year, while parts written after about 600BC have the year starting in autumn. In England, the start of the year was in March as late as the 17th century, something that causes confusion for the dating the Bristol flood. But the most important part of Easter remains those eggs – nowadays made from chocolate rather than cholesterol, although one can wonder which is unhealthier.Eggs are of course far older than Easter. The silly question of what came first, the chicken or the egg, has a clear answer. The oldest egg that has been found (microscopically small) is from 600 million year ago whilst chickens spread around the globe only in the last 2 millennia. Although eggs are thought of as associated with birds, many other animals do lay eggs, from sea horses to snakes. It is rare among mammals though: only the platypus and several species of echidnas, both limited to Australia and New Guinea, are egg layers. In spite of our confused Easter traditions, bunnies are not known for their eggs.
Dinosaurs, like the birds that descended from them, laid eggs. One may wonder whether they also sat on them (which would be one way to explain their extinction). We own a dinosaur egg. Actually, we own a clutch of them, acquired in mysterious circumstances. We know roughly where they were found. Our eggs are adopted from a duck-billed dinosaur mother (whom obviously we never met) from some 80 million years ago. The fossil eggs are very useful in school science talks – it is amazing how many of the children recognize them as belonging to dinosaurs!
Fossilized dinosaur eggs are surprisingly common. The eggs come in a variety of shapes, from spherical to very strongly elongated, and are not quite as large as you might expect from such a large reptile: ostrich eggs can be larger. The shells are up to 5 mm thick, depending on species, and in most cases the egg has the same curvature at both ends, unlike the pear shaped eggs of most birds. (Egg-shaped eggs can only be produced one per ovary at a time. Symmetric eggs roll of the egg bandwagon in one go.)
Most known dinosaur eggs come from only a few types of dinosaurs, mainly from the Cretaceous. Most are in fact late Cretaceous (100 – 66 million years ago), as are our eggs. There is a simple cause: the earlier dinosaurs mainly had soft-shelled eggs, like turtles, which don’t fossilize well. The hard-shelled eggs (with a thick calcite layer) developed in some species (independently from each other) and perhaps never in others. This may be related to how the eggs were cared for: whether dug into the sand, as in turtles, or kept in nests or clutches on the surface.
Most fossilized eggs have been found in clutches on the ground. (Not in trees, for obvious reasons.) The eggs are surprisingly strong. Even an ostrich egg is strong enough to stand on (don’t do this when mother is anywhere near!) and dinosaur eggs were a lot thicker. Still, it would be unwise for a very large dinosaur to just sit on her eggs. No shell weak enough to allow hatching could have withstood that kind of pressure. But many dinosaurs (at least those with hard-shelled eggs) did stay with their eggs. There is one known fossil of a clutch of eggs with the remains of a mature dinosaur, which is interpreted as the dinosaur either protecting the nest or even brooding. How normal that was we do not known, but it is assumed that this was not uncommon behaviour, at least among some species. Smaller oviraptorosaurs laid their eggs close together: calculations indicate they could sit on the eggs without breaking them. Larger oviraptorosaurus species instead left an opening in the middle of the eggs, meters wide. These dinosaurs were much too heavy to directly sit on the eggs: the nests suggest they would have sat on the ground in between the eggs, covering the eggs without putting too much of their weight on it. Oviraptors were feathered – perhaps to be benefit of the eggs rather than the parents. But the home care was not universal: no adult titanosaur bones have yet been found near any of their eggs. Was food an issue? A dinosaur needed to eat a lot and the vegetation would quickly have run out when staying in one place, especially if they were flocking together. So many things we don’t know!
We do not know how widespread brooding was among dinosaurs, but it seems a good bet that the hard-shelled eggs were hard-shelled for a reason. Soft-shelled eggs are more likely to have been left to it by the absent-minded parent. Good parents are also more likely to leave fossils!
We know very little about dinosaur parental care after hatching. Behaviour doesn’t fossilize well. As the eggs appear to have survived mostly complete, it is likely that the young immediately left the nest. (A growing baby dinosaur would have trampled the egg shells to bits.) Afterwards, it may have been a matter of staying out of the way. The young might have been too small (perhaps 10 cm) to be easily visible (let alone guardable) to a 10-meter long mother! They were in charge of finding their own food. There are some cases where a large number of bones from immature dinosaurs were found together, of different species. Perhaps these flocked by size rather than by species. But that is where our knowledge ends. The mortality rate for the first year or so will have been close to 100%: young dinosaurs would not have had it easy. Growth rates were typically around a doubling per year although this varied widely between species. Some (for instance the tyrannosaurus) grew large through a growth spurt, others quietly grew large over decades. I guess it might have been best not to be a tyrannosaur half the size of the neighbour, as this would make you seem like a good bet for a satisfying meal!
To fossilize an egg
Eggs don’t really need fossilizing. The shells (at least if hard-shelled) are already made from calcite, so in a way they are oven-ready to become fossils. Survival of the whole egg shell does require that they were left reasonably undisturbed. I guess being sat on by mother dinosaur would in most cases do that! An egg-eating snake might think twice before risking that.
Eggs were laid in favourite places. There are some 200 sites in the world where dinosaur eggs are found, and where they are found they can be very common, even in stacked layers. Fossilized dinosaur eggs had been laid in sand (either beach or dunes) or on flood plains. Ours were laid on a flood plain in an area with meandering rivers, a bit like the area of the Dinosaur National Monument. This would have been a semi-arid plain with good plant growth near water, but subject to occasional flooding which could cover the eggs in sediment. Slow floods (sheet-flooding) would leave the eggs in place within the nest. A fast flood would scatter them randomly over short distances. A flash flood would shatter the eggs and move the fragments over large distances. All of this is seen in fossilized eggs. Fossil eggs were mostly buried in sandstone or mudstone. Instead of sediment, volcanic ash could also do the job. The main constraint for fossilization is that the sediment or ash should not have been too acid as this would dissolve the shell. Acid rain might also have been a problem for the egg survival.
Once safely buried, the inside decomposes whilst the egg shell survives. Sediment can now enter the shell through any holes. This provides interior support to the empty egg shell against the weight of the sediment above. But in many cases, this was too little or too late, and only the lower half of the shell survived whilst the top half collapsed. When you see a fossil egg in the shop embedded in a sandstone matrix, be aware that it may be displayed upside down. In those cases, only the bottom side was cleaned from the rock. The top half was not excavated because it may be in much worse shape – or may even be missing.
[Not all dinosaur eggs for sale come from the ground. They are also made in factories. It takes more expertise than I have to recognize a fake egg from a real one! The rule of thumb is that if it looks too good to be true, it probably is too good to be true, regardless of how expensive.]
Finding embryos inside a dinosaur egg is a rare occurrence. The hatchling would have emerged through a hole in the egg, but much of the shell stays behind. The sediment that covers them is oblivious to the hole, or even whether the egg is full or empty.
Volcanic ash can be a perfect egg fossilizer. It is both lightweight (thus allowing the egg to stay intact) and an effective deterrent against egg predators. In contrast, lava is not recommended as it plays havoc with eggs. Fried eggs don’t make good fossils.
Volcanic rocks are often riddled with holes, like an inedible version of a Swiss cheese. Gasses within the lava creates those holes while the lava solidifies. It can also happen in sediment with organic material: as the material decomposes, a hole is left behind. And some materials come with pre-formed holes: coral comes to mind.
Nature abhors a vacuum. Where there is a hole, something will try to fill it. Water percolates through the rock and dissolves minerals. It enters the holes and stays there: over time, the dissolved minerals begin to cover the walls with a solid layer. Dissolved silica is deposited as agate. The image below shows such agate inside a coral. The silicon is deposited in layers, and these are often clearly visible in the agate. A wide variety of colours are possible, depending on the trace elements and the crystal structure. But be aware that agate can also be artificially coloured to make it more saleable.
Agate makes for a popular gem. As an aside, the name comes from the river Drillo in Sicily. The association may not be immediately obvious, but at the time (350 BC when Sicily was a Greek colony) this river was known as Achates.
Agate commonly forms from volcanic material. The original agates in the Drillo river were from the ash of Etna. The ash can be SiO2-rich (rhyolite) or SiO2-poor (andesite, basalt). SiO2-rich agate forms the spherical so-called ‘thundereggs’, while agate in basalt forms in less regular cavities. In all cases, they are formed at some distance from the original eruption, such as at the margins of ignimbrites, and require interaction with water. Making an agate is a slow process, in fact one that has not yet been replicated in the lab. But it has happened a lot in the real world. The oldest agate dates from more than 3 billion years ago – they are as old as diamond.
The agate egg
The National History Museum in London has a large collection of minerals – almost 200,000 items. (It is also well known for its meteorite collection.) Only a small fraction is on display. One of the items kept in storage was a beautiful spherical agate, donated in the late 19th century. It was recently selected to be displayed not to the public, but in an area open to members of the museum. The rooms here are named after Mary Anning, of Jurassic coast fame.
The agate in question is shown at the top of the post, on a photo provided by the museum (with apologies for the background colour apparently inspired by our Blue Lagoon revamp). The agate completely fills a thin shell of spherical rock. That in itself is unusual: the holes filled by agate are typically more irregularly shaped. The story from the museum tells how the curator noticed the similarity to another specimen seen in France. It shared the shape, the thin rim and the dark agate towards the centre. The French specimen was obviously also an agate, but the rim was classified as a dinosaur egg! This combination is uncommon but not entirely unheard of. It turned out that this was also the explanation for National History specimen: a dinosaur egg had been agatised.
The fossil museum egg clearly shows the impression of other eggs: it had been part of a clutch. It is not clear whether the egg had hatched: there may be a hole at the back in the image on the top of the post but it is not clear whether this is original or made investigating the content. The egg was found in ancient volcanic ash associated with a volcanic eruption. The embryo (if not yet hatched) would have succumbed quickly when the ash cut off the air supply but the ash layer was not deep enough to crush the egg. Some time after the explosion, water began to enter the egg and the deposition started. It turned an unborn dinosaur into a fossil gem, a true Easter egg.
It all happened in India.
India has several sites with fossil dinosaur eggs. Some of the sites are among the largest collections in the world. One of the fossils shows an egg, a hatched baby dinosaur – and a snake with a wide open jaw, ready to eat either the unfortunate 50-cm hatchling or one of the other eggs. All had been buried together in a sudden mudslide. So now we know that young dinosaurs had to survive scary predators.
The first dinosaur in India had been found in 1828. William Henry Sleeman discovered bones of what later became known as a Titanosaurus Jainosaurus, (one of over 100 species of titanosaurus now known) from a site on the slope of the hills above Jabalpur. Detailed surveys of this site were done a century later, most famously by Barnum Brown of the American Museum of National History. Brown was already known for the first discovery of Tyrannosaurus Rex. On the steamship to India he met a young woman, and on arrival they married. Lilian and Barnum Brown spend their honeymoon collecting dinosaur fossils. Lilian later wrote a book about it, with the title “I married a dinosaur” and sub-title The light-hearted story of a strange honeymoon in Indian and Burmese jungles, hunting big game that had been dead for million of years. The bottom line was perhaps to be wary of whirlwind romances! Barnum was too pre-occupied to properly write up all the discoveries. But although there was a detailed older description by William Sleeman of the location, the vegetation and the monsoon rains has changed the region and the site of the original fossil and Barnum Brown’s excavations was lost. In “The Age of Dinosaurs in the Land of Gonds”, Chatterjee describes how he went to locate it: “One day, after a futile week-long search, Sibani sat on a rock for our midday lunch break. I suddenly realized that was no rock my wife was sitting on, it was in fact a sauropod femur! The site matched perfectly with Captain Sleeman’s 1828 description of the bone bed close to his bungalow, where he found fossil fragments of animals and plants in the sediments below the Deccan Trap.”
India had separated from Africa, Antarctics and later Madagascar by the start of the late cretaceous, carrying with it its cargo of dinosaurs. The diversity of species in India was not great, but there were a lot of them and they evolved into a unique community while the continent drifted north into the Tethys. If you are desperate for Bruhathkayosaurus, Rajasaurus or Jubbulpuria, cretaceous India is the place to go. There were different species of dinosaurs well known from other continents: titanosaurs, abelisaurs, ankylosaurs. The final, youngest layer with dinosaur fossils is the Lameta formation which is widespread in western and central India and dates from the late cretaceous.
The Indian continent at the time was still much closer to Africa than to Asia, and was some 20 degrees south of the equator. It was larger than India is now: as much as half of the continent has since been lost in the Himalaya crumple zone. It was similar in size to Australia.
Now the trouble began. As India moved north, it approached a hot spot. Once it began to overrun this, the heat melted the bottom of the plate and eruptions flooded the newly formed continent. The Deccan traps had begun, to the detriment of the local dinosaurs.
The Deccan traps are among the largest continental flood basalts, although part of the lava is off-shore in the Arabian sea. The eruption was associated with the rifting between India and the Seychelles. The eruptions lasted for 8-10 million years but most of the eruption happened within a 1 million year period.
The traps contain multiple individual flows or sheets, separated by sediments. Those sediments are called intertrappean beds, and they are meters thick. They must have taken centuries to millennia to accumulate: the Deccan eruption clearly was intermittent. The iridium layer from the Chicxulub asteroid impact which put a full stop to Dinosaurian existence has been found in one of these sediment layers, a 6-meter deep intertrappean bed. That the Deccan traps had a role in the dinosaur extinction is not in doubt. That it was the sole cause is a much more controversial position, although it has been argued and it may have been true locally in India. For the worldwide extinction event, the Deccan traps has an alibi. It wasn’t there.
The Deccan traps erupted in several phases. The first phase started around 67.5 million years ago, and the later phases happened 65.1, 63.2 and 62.8 million years. 50%-75% of the volume of the Deccan eruptions came a few hundred thousand years after the asteroid impact. The dates do depend on where in the Deccan traps (and how) they are measured. The above dates are measured in the western provinces. In the northern Malwa plateau, the first phase is dated to 66.35 to 66.05 million years, followed by a brief interlude before the eruption resumed at 65.95 million years. Global temperatures increased at 66.5 million years, suggesting the Deccan traps were well underway by that time but went back to normal at 66.1 million years indicating a reduction in eruption rate. The Chicxulub asteroid impact was 66.0 million years ago. A new warming spike happened 25,000 yr before impact but this was smaller and short-lived. Immediately after the asteroid impact, temperatures dropped like a stone. The timeline indicates that the Chicxulub asteroid impact occurred during a lull in the eruption. Indeed, the location of the iridium layer in the intertrappean bed shows that the Deccan traps had been taking a break. The location of the Deccan eruption moved around over time with a tendency to move southwards while India migrated north. It is possible that the eruption continued somewhere in the traps, but at a much reduced rate.
Global environments were unstable in this era. Sea levels had been falling, perhaps because India was passing over the hot spot which previously had been pushing up the sea floor. In America, a sea arm of climatic importance dried up. The significant warming half a million years before impact suggests that the first Deccan phase started furiously with a lot of CO2 emission but tapered off over time. It was a hard time to be a dinosaur. Large animals may not be quick in adjusting to ecological changes. It is hard to learn to eat grass when you are build to eat trees! (Some dinosaurs did indeed manage to eat both.)
The Deccan and the egg
Back to the present-day Easter egg hunt. Dinosaur extinction worldwide may be dated to a quiet time in the Deccan eruption, but any dinosaur in India would already have had a bad time. There are a lot of complete but empty eggs in India: was this because of a low hatching rate? That could be related to Deccian pollution of the atmosphere and water. One can imagine young Indian dinosaurs en masse disrupting dinosaur society in their extinction rebellion protests.
Our egg was found somewhere in central India (according to the museum), and was associated with Deccan ejecta. There is no reason to associate it with the main extinction event itself: we are probably looking for an early eruption phase. It would also not have been within a lava bed as that would have ruined the egg. We are looking for ash. The location of the find is not reported, other than ‘in the centre of India’. A plausible location may be in the north central parts of the Deccan traps where the eruption was focussed in its early phase, in a region not covered by later eruptions. This would date the egg to the 1 million years or so before Chicxulub.
An interesting aside is that this is the same area where Jabalpur is located, which is where William Sleeman found his titanosaurus which Chatterjee’s wife rediscovered. The egg was originally found somewhere between 1817 and 1843, which is around the same time. And best of all, the egg appears to be that of a titanosaurus.
I decided to check this. The museum wrote that the egg had been discovered by Charles Fraser who lived in India between 1817 and 1843. It should be possible to find out where this person had lived! A search showed up a Charles Fraser, Lieutenant-Colonel, 1799-1868, who had worked as an Indian administrator from 1817 to 1843. That was our man. The blurb at the National Archives said that Fraser was in the Bengal Civil Service during 1817-46, served in Saugor and Nerbudda Territories, and was Commissioner of the Saugor Division 1837-43. These territories were captured by the British in 1818, with the Territories being set up in 1820 (so the starting date was a bit jumping the gun) – and the capital of the region was Jabalpur. The guess was right!
Fraser had left the territories in 1843 but apparently stayed in India until 1846. As the find was dated to the period 1817-1843, it places it within these territories. There was an uprising in the area in 1842, and after this a new governor took over – our friend Sir William Sleeman! In fact Sleeman had worked in the same administration as Fraser since 1820, though in more senior positions. His find of the titanosaurus was in the local Lameta formation. It seems plausible that Charles Fraser found his ‘stone’ in the same region. It is tempting to think of them exploring together, William Sleeman finding dinosaur bones sticking out from the hill slope while Charles Fraser stumbled over a strange looking stone – the titanosaurus’ very egg! But that would be too good to be true.
Jabalpur is located just north of the Amarkantak plateau, southeast of the Malwa Plateau. The latter is well dated, as mentioned above. The Armakantak has given some younger (post-asteroid) dates but the titanosaur find shows that there were also Deccan eruptions before. Those older dates still need to be measured. It seems plausible that they will be co-eval with the voluminous Malwa eruption, but that remains to be proven. Fraser is reported to have lived in Saugor from 1831 to 1833 and possibly later as well and this is on the edge of the Malwa plateau itself: it is entirely possible that the egg was found there.
Could Charles Fraser have recognized the stone as a dinosaur egg? Why did he collect the strangely round stone and open it up? Did he expect to find agate, or was he hoping for an embryo? The word ‘dinosaur’ had not been invented yet but that is a minor detail. The first confirmed dinosaur egg was discovered only in 1923, a century later. So Fraser might have had a suspicion, especially since there were apparently several such stones together, but he could not have known for certain.
As an aside, Jabalpur was a major centre in the kingdom of the Gonds, the region after which Gondwana (‘land of the Gonds’) is named. It seems kind of appropriate.
Fossilizing an egg within the Deccan traps is only the beginning. Any child knows that an egg is for opening, to find the treasure inside (and hoping it will be chocolate!). This egg is special because of the agate stone eater inside. How did that get there?
The museum wrote that the agate formed shortly after the egg was laid. That is conjecture. Agate has been found in the Deccan traps: it formed within cavities in the basalt and has been unearthed in mines. But this agate did not form during the Deccan eruptions themselves. It has been dated variously to 55, 45 and 22 million year ago, many millions of years later. This is probably climate related: the agate formed from weathering of the basalt, and it required a ready supply of water to the holes in the basalt. It took a long time for the right conditions to occur, depending on climate change and of course on the slow drift north. The rainfall and water pathways may have varied over time. Perhaps this is why we have not been able to make agate in the laboratory. We lack the patience.
In the case of our egg, we can therefore also assume that the agate filling also came much later than the egg. The minerals were deposited inside the egg as much as tens of millions of years after the reptile that had laid the egg had gone extinct. And much later still a mammal called Charles Fraser found the egg and resurrected it, to end up in a museum room named after that most famous of dinosaur hunters: Mary Anning.
An Easter egg hunt
And that is the story of our Easter egg. It tells of a time when the world was different, and when a continent was adrift in a foreign sea. The long reign of the dinosaurs would very soon be ending. The animal that laid the egg was oblivious to the disaster that was coming. The egg was never to hatch – whether from volcanic pollution or volcanic ash is perhaps a moot point. But although the world around it succumbed to fire and wind, and the dinosaurs disappeared into history, the egg remained and waited for better times. In the new Spring that was to come, a new season of the Earth, a treasure would grow inside, shaped by the very volcano that had killed the egg.
But the biggest treasure of the agatised dinosaur egg is the story it has to tell. It is a story of endings and beginnings. That is Easter.
Albert, April 2023
Read also Death of dinosaurs