It was the year 916 when Arab Traders travelling along the eastern coast would discover an isolated atoll in the Indian Ocean, this atoll would later be in 1509 be first shown under the name of “Alhadra” on a Portuguese map of Madagascar. The name Aldabra is reported to have come from the Arabic word ‘Al-Khadra’ which means “the green”, in reference to the lagoon’s green reflection on the clouds above it. It wouldn’t be until 1742 where the French Captain Lazard Picault would make landfall on the worlds second largest Atoll, in 1814 the Atoll would pass from French possesion to become a part of the British colony of Mauritius, yet it would not be another 64 years until a scientific study was conducted on the Atoll, a hydrographic survey by the British Navy. The permission to commercially exploit the islands was given out on 1888.
More complicated going back and forth ended in the Island being given to the Republic of the Seychelles, to which it still belongs to this day. It became a UNESCO Natural World Heritage Site in 1982, an Important Bird Area by BirdLife International in 1998, Ramsar Wetland Site of International Importance by the Ramsar Convention in 2010 and an IOSEA marine turtle site in 2014. The Aldabra Atoll is now one of the most protected natural places on earth, with only 12 people living on the atoll at a time, mostly scientists and conservationists.
But what is so fascinating about this isolated Atoll in the Indian Ocean, part of a small unknown Island Republic? Aldabra is known as the jewel on the crown of the Seychelles, it represents a fascinatingly well preserved environment, almost untouched by the brutish human takeover of the natural world, Aldabra is home to the largest Population of giant Tortoises worldwide with estimates ranging from 100.000 to 150.00 animals of the Genus Aldabrachelys living on the atoll, more than humans live in the entire rest of the Seychelles. Aldabra is also one of only two known marine breeding site of Flamingos and the atoll’s lagoon is so large that the main island of Seychelles, Mahé, could fit inside it.
The atoll is considered one of the most biologically diverse and undisturbed raised coral atolls in the world, and for me particularly it’s interesting for it’s potential resemblance to the tropical islands of Southern Germany and Southern France. Back when 150 Million Years ago a vast shallow sea covered what today is the Jura Mountains and the Swabian and Franconian Alps.
The Islands that covered the northern edges of the Tethys are no more, but the amazing preservation of fossil remains and intense study of those and the surrounding rock allow is to paint an amazingly detailed picture of the past, one with gaping holes so big that you would think someone burned half of the picture, but a complete one nonetheless. The Solnhofen Archipelago consist of islands built on limestone made by the buildup of reefs, often times these islands surround basins, big dents in the seafloor which subsequently turn into lagoons as islands and reefs grow around them. The reef ecosystems are both familiar and alien, corals grow and prosper, but glass sponges which in the modern day are only found in the deep sea are represented en masse. Modern Reeffish are replaced by Pycondonts, some like Gyrodus giant, other reff fish are Coelacanths, Caturids. Barracudas are replaced by the likes of the Aspidorhynchids. Ammonites completely alien to us swim along Nautilus almost identical to what we have today.
The bizzare Pleurosaurus and various marine Turtles like Thalssemys, Eurysternum and Plesiochelys would also inhabit these reefs, hunting among the corals or like Thalassemys in the water around it, presumably.
The open oceans around the islands and sometimes the upper layers of the lagoons are inhabited by inrcredible animals like giant Pachycormids, Pliosaurs, fast swimming cephalopods resembling squid while themselves being more closely related to vampire squid and the enigmatic Metriorhynchids, like the huge Dakosaurus, or Teleosaurs like Machimosaurus and Aeolodon. Very rarely Plesiosaurs would also be found in the area.
Equally bizarre to us would be the terrestrial Flora and Fauna of the Islands, the only Birds are the bizarre Archaeopteryx and Alcmonavis, unlike anything we have today, sporting teeth and a long tail, the Skies instead are inhabited by a diverse amount of Pterosaurs like the famous Rhamphorhynchus and Pterodactylus, small terrestrial crocs like Alligatorellus, and relatives of the modern Tuatara inhabit the island together with the earliest relatives of the Geckota, like Ardeosaurus. The Vegetation on the Island is spiky and lowgrowing, adapted to the dry season the island experienced. Succulents in the stem and thick leafs are used to prevent water loss or store water. The extent of the vegetation is one of the biggest mysteries, it wasn’t until recently when bigger pieces of wood were found in Painten, so some small forest can atleast be expected on the bigger islands.
Now, comparing the Solnhofen Archipelago to the Aldabra Atoll is best done in stages, so we will look at different aspects of Geography, Meteorology and Biology in multiple sections were we go indepth into the similarities and differences of the two ecosystems.
The Climate and Weather
Both Aldabra and the Solnhofen Archipelago exhibit a tropical climate, the annual temperature does not deviate as greatly as for example modern day europe, but still a to a significant margin, summer maximum temperatures reach 32 degrees celsius, the minimum winter temperature is 22 degrees. Notable is the distinction of the dry and wet seasons, January, February, March and April in Aldabra receive up to 37 times as much rain as the dry season, sometimes rainfall is so little that almost desert like conditions are ruling the islands, which means that the heat and the sun are far more prevalent, despite the average temperature not changing to a significant degree.
Interestingly one main difference in this regard between Solnhofen and Aldabra might even be that Solnhofen during the wet season would experience more actual tropical storms, many of which could become Cyclones. Aldabras close proximity to the equator means that it rarely experiences such things, despite the extreme contrast between the dry and wet season. This does not apply to Solnhofen though, infact it’s in perfect condition to experience the full force of each storm with it sitting on the edge of the Tethys, it would be among the first places for Cyclones to make landfall if they didn’t do so already further east in Asia Minor. We have signs showing that these Cyclones travelled up all the way to Kimmeridge in the UK.
An islands freshwater after time gets contaminated with saltwater due to the saltwater leaking up trough the soil, basically destroying the freshwater source necessary for much of the islands biota to survive. The immense size of most islands on Aldabra prevent contamination with saltwater, but due to the extreme heat water still evaporates quickly, so the annual rain is quintessential in essentially stocking up the islands for the dry season, this creates small wetland biomes seperate to the mangroves, which is also how Aldabra manages to be a marine breeding site of Flamingos, we can expect equal dependance on annual rainfail in the Late Jurassic aswell.
Flora
Adaptions to the climatic conditions can be seen in Plants on both islands, infact the Solnhofen representative of Brachyphyllum (A form Genus so what is said here does not apply to all Brachyphyllum species whatsoever) and the in the Indian Ocean widespread Pemphis, especially Pemphis acidula, these two are incredibly similar plants despite not being closely related whatsoever! Both Taxa seem to be highly adaptive, Solnhofen like Brachyphyllum is found from Portugal to Poland, and there was no land bridge connecting most of the islands, and some like the islands around Nusplingen were pretty isolated aswell, and thats just what we have preserved! Similarly Pemphis is found from the Zanzibar Archipelago in Tanzania all the way to Cook Island in the Pacific! Pemphis is highly adaptable and depending on the conditions grows as a more densely branched bush, or as more sparsely growing low lying tree theres also enormous variation within leaf shape, as they can be both small, fleshy and succulent, or larger, flat.
While there are certainly multiple species of Brachyphyllum on the island, even Members of the same species have incredible Variation which may hint at similar adaptions to the modern Pemphis, while the leafs are not succulent in Brachyphyllum, the stem itself is, hinting at it having to survive both a long time without water, and or having to tolerate saltwater. The seeds of Pemphis are capable of floating on water, and often are propagated that way, this allowed the plant to colonize islands as desolate as Aldabra, Brachyphyllum may have employed a similar strategy where the cones of the plant could have also drifted across the oceans allowing it to colonize new land, coconut palms also employ a similar strategy.
Yet there is such a significant diversity of Brachyphyllum species present in the Solnhofen Archipelago, that one may wonder what other roles these plants may have filled in the ecosystems of the Late Jurassic. Over the decades multiple Genera have been erected for the various conifers of Solnhofen: Caulerpites, Thuites, Athrotaxites, Brachyphyllum, Palaeocyparis, Cupressinocladus and Watsoniocladus and quite frankly do I not want to get into that godless taxonomic hell-hole, but one thing is for sure, there were alot of different conifers inhabiting the Solnhofen Archipelago, certainly some of them made up the small forests of the islands, and others like the orthodox-Brachyphyllum were analogous to Pemphis. The next part is speculative but still plausible: A huge part of Aldabra is made up of mangrove forests which create a critical wetland environment, these mangroves cover 251 square kilometers (over half the area of the whole atoll) of the atoll. It’s possible that some of the Islands conifers occupied a similar niche in the local ecosystem, succulents can equally be an adaption to surving water salinity, and some of the conifers may aswell have formed coastal forests just like in Aldabra. Infact we already have what appear to be conifers growing like mangroves from the Toarcian of the Albanian Alps, furthermore leafs belonging to the genus Brachyphyllum and Pachypteris are even associated with mangrove like coaly root systems, in what appears to be an ancient early Jurassic mangrove forest! (Barbacka et al., 2019) Sadly we have yet to find direct evidence for this from any of the Solnhofen Localities, but that may be only due to most quarrys being located more center to the lagoon, and not at the edges where we would find such environments, sadly I cant look into the future, so time will tell.
Other notable plants from Solnhofen include the genus Cycadopteris while its phylogenetic relationship is a headache inducing mystery it’s still possible to deduce alot about this plant, what we have are mainly branches and leafs, those show thick and broad leafs perfect for storing water and maintaining it in the harsh dry season, we dont really know how this plant could have grown, if it were to be found on the beach or in the forests, it’s all speculation.
Zamites is also a common member of the Solnhofen Ecosystem, though strangely it seems to be entirely missing from some Localities, this Taxon is probably in a way similar to modern Palm Trees also common on Aldabra and isn’t really that notable here otherwise.
Other typical Mesozoic plants are also known from Solnhofen like various Cycads and extremely rare Gingkos but I dont want to go further into individual plants and instead look at how exactly we can imagine the small forests as a whole, that we would have possibly seen on Solnhofen and elsewhere. The forests of Aldabra nowadays are made up of broadleaf forests, with grasses but also ferns as groundcover, we can imagine something similar for the Late Jurassic just with conifers and ferns completely replacing grass, probably a wide array of other plants that would have made quite a spiky underbrush, during the dry season this forest would probably look uneventful and well dry, but during the seasonal rains the islands forests may have blossomed in a more intense green and brown.
The Lagoon
The gigantic lagoon of the Aldabra Atoll is a fascinating environenment, but here I want to start with the Solnhofen Archipelago and its nearby neighbours, in the past and for most of this blog I basically lump in all of the different Localitys of the Archipelago into one chunk, this is mostly useful when talking about terrestrial environments nearby, due to the extreme scarcity of remains from terrestrial settings. When talking about the lagoon it’s critical to make distinctions, because they are nothing alike, the Lagoons of Solnhofen, Painten and Eichstätt are big basins with water depths of up to 80 meters, this compared to the average depth of Aldabra, 5 meters is astounding, furthermore the deepest most point of the Aldabra lagoon is 20 meters below sea level, at the point where the channels lead into the shallower part of the lagoon. Yet there are 2 Localities extremely similar to Aldabra, the French Cerin, and the Bavarian Brunn.
Comparison of the depositional environment of Cerin to that of Aldabra are actually what inspired this post, characteristic is a big shallow lagoon, that with the tides fills and drains, even laying bare, we see this in both Cerin and Brunn, with cracks indicating drying of the seafloor being a common thing to, in Cerin even trackways showing Turtles both walking and or swimming in very shallow water or the dried seafloor, in this regard I was also curious about the famous Pterosaur Beach of Crayssac, which while resembling the lithographic limestones of Solnhofen superficially only preserve ichnofossils, sadly I personally was unable to find any interesting literature on what kind of environment it may have once been besides a “littoral mudflat”, so I wont be able to go further here.
(from Fabrigues et al., 2013)
The Lagoon of the Solnhofen Archipelago is lifeless, one of the factors as to why fossils preserve so well, live is restricted to microbial matts and sponges that would at the time be considered living fossils, as the closest relatives to these obscure Taxa are from the Cambrian. (Ammonella quadrata, Neochoiaella frattigianii) The Lagoons of Cerin and Brunn seem far more alive, with Crustacean and Worm borrows filling up entire layers of stone, we can probably expect an intense diversity of marine life here. So far we only uncovered a small part of both Cerin and Brunn, and furthermore we have no real clue how the shallower sections of the likes of Solnhofen and Painten would look like. What we see in Aldabra is multiple different ecosystems in one lagoon. In Aldabra we see dense microbial mats, patchy corals and big seagrass beds along completely barren sections exposing the carbonate sands which also formed the Solnhofen Limestone in the Jurassic. We have indication for all this from Solnhofen, Brunn and Cerin where especially microbial mats form a common but easy to overlook fossils. Patchy coral and sponge reefs are not directly preserved but to be expected, and seagrass beds were probably composed of Goniolina and Phylothallus Macroalgea, Goniolina is especially common in Brunn, so they may have made up a critical ecosystem builder in the shallower lagoons.
This and the other images in this row are from: Hamylton, Sarah & Hagan, A. & Bunbury, Nancy & Fleischer-Dogley, F. & Spencer, Tom. (2018). Mapping the lagoon at aldabra atoll, western Indian Ocean. Atoll Research Bulletin. 2018. 45-59.
Fauna
The Solnhofen Limestone is one of the most diverse fossil sites in the world, hundreds of species have been discovered between the slabs of rock, for example up to 230 species of Insects are known from Solnhofen, which is amazing when comparing it to the 1.000 species from Aldabra where we dont have to dig up every one of them out of rock and identify them based on that. Yet again though Aldabra proves how well of an modern analogue it is to Solnhofen by showing us the mostly intact ecosystem of a coral atoll. It is easy to imagine for example to have the Blacktip-Reef sharks of the atoll replaced with Hexanchiformes like Sphenodus, or Eonotidanus which would look like the modern Sevengill Shark Notorynchus.
But I dont want to talk too much about comparing the Marine Life here, it is clear that Fish are highly adaptable and can grow to be very similar to eachother based on their Niche without being related at all, the wonders of convergent evolution. We have more Tetrapods from Aldabra than Solnhofen of course, because Aldabra still exists and Solnhofen is a village in Bavaria world famous for its, notably, dead animals. Yet its still interesting to compare the Pterosaurs of the Solnhofen Archipelago to those of the Aldabra atoll. For example Pterodactylus, this most famous of Pterosaurs is certainly comparable to the broad ranged oystercatcher (Haematopus ostralegus) or the crab-plover (Dromas ardeola). Textural analysis of dental microwear on the teeth of pterosaurs and on modern reptiles indicate a varied diet for Pterodactylus, changing as the animal grows, but mostly concentrating on invertebrate prey the animal could find in the tidal zone. (Bestwick et al., 2020) This is further supported by the anatomy of Pterodactylus, with its big feet perfect for wading and not sinking into the sand.
Another Pterosaur with striking resemblance to a bird also found on Aldabra is Rhamphorhynchus, which bears such a striking resemblance to Frigate Birds. (Fregata) Aldabra is home to the worlds largest Frigate Bird colony, and Rhamphorhynchus is the most common Pterosaur of Solnhofen, both animal share comically large wingspans and both would probably be great soarers. Rhamphoryhnchus based on dental microwear is a generalist, catching anything it can from the water and just like Frigate Birds it was probably not afraid to bully smaller Pterosaurs to steal their food. The biggest distinguishing factor between the two is the strong ontogenetic change Rhamphorhynchus goes trough, where juveniles fill a completely different Niche to adults, which means that only adult Rhamphorhynchus are analogous to Frigate Birds while in a way juveniles are more analogous to Terns for example.
Another very interesting example is Anurognathus, though in this case its not only comparable to birds, the Madagascar Nightjar (Caprimulgus madagascariensis) but to Bats aswell like Paratriaenops pauliani. Judging by the amount of fossils we have, Anurognathus might seem like an incredibly rare member of the local ecosystem, but thats probably just a classic example of preservational bias, whereas the small and fragile body of Anurognathids is among the first things to fall apart, get swallowed by some dumb fish that rejects the notion of paleontology or to just get swept away into a basin where fossils just dont ever become a thing. It is easy to see what niche Anurognathus would fill, just like nightjars and bats a nocturnal hawking insectivore. There are probably multiple Anurognathids that lived on the Solnhofen Archipelago, if we ever find them though is something else.
I dont want to compare literally every Pterosaur from Solnhofen to a bird from the Seychelles, so im moving on to something else: Ostromia is a small Anchiornithid Theropod from Solnhofen, and infact the only flightless Avialan, with both Alcmonavis and the various Archaeopteryx species capable of powered flight. Ostromia in a way is probably very similar to the Aldabra rail, Dryolimnas cuvieri aldabranus the last remaining flightless bird of the Indian Ocean. The omnivorous diet of the Aldabra Rail overlaps with the diverse stomach content and pellets we have from the chinese Anchiornis, a close relative of Ostromia. The Aldabra Rail has been observed feeding on berries, flower petals, intertidal invertebrates, organic jetsam on beaches, turtle and tortoise eggs and hatchlings, skinks, geckos, crabs and carrion. It’s easy to imagine Ostromia exhibiting a similar lifestyle, as thats whats the best option for such an animal.
Both Archaeopteryx and Alcmonavis would have certainly been similarly generalist in contrast to the very specialized Pterosaurs, but do to both their flight capabilitys and Alcmonavis it’s size, which would have allowed both of them to exploit more niches. I do not want to talk too much about either of the two, infact I want to go back and write a seperate blogpost just on the Maniraptorans of Solnhofen.
Instead I now want to discuss the elephant in the room: Compsognathus, Juravenator and especially Sciurumimus. Nothing like these Taxa is known from any far-shore islands today, usually predators like these are what would drive local island fauna to extinction so their presence is especially perplexing, one of the most common themes of Island biogeography is a lack of big predators, it’s what enabled the Dodo afterall, yet here in Solnhofen we see 1 small Theropods, huge compared to the rest of the terrestrial Fauna and then Sciurumimus and Juravenator, who are both juvenile (potentially megalosauroid? not going intro that) and could have been even larger. I’ve looked at these animals as something completely normal for a long time and it’s now difficult for me to interpret what these three were doing, so I will probably write a seperate blog on these at some point. Which means we are now at our last segment.
Aldabra needs help
I hope that I by now have convinced you of the absolute wonder that is the Aldabra atoll, but sadly it’s still the 21st century and Aldabra and its inhabitants are at risk, climate change has caused immense coral bleaching around the island, and tons of plastic waste is landing on it’s shores, and Aldabras close proximity to one of the worlds busiest shipping lanes puts it at increasing risk of oil spills. Invasive species are a huge problem too, furthermore a lack of funds plagues the Seychelles Island Foundation.
It is possible to donate to the Seychelles Island Foundation to further it’s educational programs, conservation efforts and for security to protect the precious natural treasures of the Seychelles.
You can follow this link which will highlight what you can do or you can straight away contact info@sif.sc if you would like to make a donation.
Sources
Quite frankly I hate this section so you wont get any pretty academic citations here, enjoy website links:
http://www.jstor.org/stable/20456104
https://wikihmong.com/en/List_of_birds_of_Seychelles
https://en.wikipedia.org/wiki/Aldabra (ingenious I know)
https://www.nature.com/articles/s41467-020-19022-2
https://royalsocietypublishing.org/doi/10.1098/rsos.171800
The Save our Seas Foundation cannot be linked but will be noted here anyway
Additionally I used my way too expensive book: Solnhofen Ein Fenster in die Jurazeit
Kimmeridgian Times 