Saturday, 12 November 2022

Diplodocus: A history of reconstructions - Part 2

Here we are back again with a history of Diplodocus reconstructions! Last part we looked at the very first reconstructions of the genus, its predecessors and the fame and controversy that came with the various Dippy mounts. Today we will look at what happened after, as well as the many, sometimes weird ideas that have been made about the genus.

From Water to Land

Fig. 1

Starting from the 1920s onward, Diplodocus, like all sauropods, was interpreted as an erect-legged, but tail-dragging and mostly aquatic animal, with some researchers, such as William Diller Matthew, even going as far as saying that they never left the water by giving birth to live young. The most common interpretation about their diet was that they fed on soft aquatic plants, as their teeth seemed highly unsuited for chewing anything tougher. It was also thought that the head was too small to gather enough food to feed the giant body in bulk, hence why they were restricted to a very slow metabolism. But even back then, some questions about their diet came up, especially in relation to the bizarre, pencil-like teeth of Diplodocus with their blunt tips. In 1924, William Jacob Holland, the same man who supervised the Dippy mounts, proposed that Diplodocus may have actually primarily fed on mussels and other shelled animals, using the teeth to pluck them from rocks. The poor clams were then swallowed whole and crushed in a gizzard by gastroliths. Although he was the one proposing it, Holland himself was skeptical of the idea, as he correctly observed that no one has ever found mollusc shells in the stomach region of any sauropod skeleton. The idea still interestingly foreshadows some modern suggestions that Nigersaurus may have been a freshwater filter-feeder (Hallett & Wedel 2016).

Fig. 2

In the 30s, new specimens were being discovered, such as the Smithsonian’s USNM V 108655, adding to our knowledge about the genus. This specimen was originally assigned to the type species D. longus, but seems to more likely have been part of Diplodocus hallorum (Tschopp et al. 2015), which you might know better as “Seismosaurus”.


Fig. 3 & 4

The view of Diplodocus and other sauropods as aquatic grazers prevailed well into the 40s and 50s, as can be seen by these two paintings, the top one made by Mathurin Méheut for the French University of Rennes and the bottom one by none other than Zdeněk Burian.

Fig. 5

Already in the 50s, doubt began to appear about the classic watery sauropods. Kenneth Kermack’s (1951) studies showed that the laws of physics would have prevented them from using their long necks as a snorkel, like here in this Burian reconstruction of Brachiosaurus, as the water pressure on a fully submerged sauropod would have compressed its lungs so much that it would have been impossible for it to draw in air through its windpipe. If you want to test this yourself (though mind you that this is pretty unsafe), drop to the bottom of a pool and try drawing in air through a two-metre straw. Unfortunately, Kermack’s conclusions were either ignored by the paleontological community or dismissed by Edwin Colbert with the argument that whales can breathe while in the water just fine (Desmond 1975), ignoring the fact that whales do not have long necks and have to come very close to the water surface with nearly the whole body in order to take in air.

Fig. 6

In the late 60s, much change was on its way. In his influential paper The superiority of dinosaurs, Robert Bakker (1968) readdressed Kermack’s results and found various other flaws with the idea of sauropods having hippo-like lifestyles. Their hollow bones meant that they would have awkwardly floated on the water’s surface, whereas hippos and whales have heavy, solid bones in order to better sink. The feet of sauropods were also not adapted for muddy environments and, perhaps most importantly, many of their fossils were found in sediments that implied a very arid environment. Bakker reinterpreted the sauropods not only as fully terrestrial animals that ate the leaves of tall plants like giraffes do today, but also as metabolically highly active creatures, which used their bizarre teeth to rake off coniferous plant matter in massive bulk to then digest it in a gizzard (if sauropods truly used gastroliths to break down their food has come into question over the years (Wings & Sander 2007) and pure hindgut fermentation through a specialized caecum may be more viable (Hallett & Wedel 2016)). While not Diplodocus, Bakker used close relative Barosaurus to provocatively illustrate this new vision of sauropods, showing the animals with a proudly high-held neck, the tail well above ground, striding into the prehistoric savannah like giraffes. This roughly still remains the default interpretation of sauropod lifestyle, as many subsequent studies have confirmed its validity. But it was certainly not the end of mystery and debate around the life appearance of these animals.

Much noise about a nose

Fig. 7

One of the first questions trying to be unravelled during the Dinosaur Renaissance was that of the sauropod face. Most sauropods, especially Diplodocus, have their nares (the bony holes for the nostrils) on top of their skull right above the eyes. Classically, the nostrils were therefore placed right there as well, giving these animals a whale-like blowhole, which of course perfectly lined up with their original aquatic interpretation. With the knowledge that sauropods were actually land dwellers, the position of the nostrils became an intriguing mystery during the Dinosaur Renaissance. A sober take by McLoughlin (1979) was that the “blowhole” instead developed to more easily breathe while the mouth was submerged deeply in the spiky canopies of conifer trees. Giraffes, gerenuks and other high-browsing mammals of today also have retracted nostrils to not get stung in the nose by tree needles and in recent times this has even been put forth as an explanation for the sauropod-like skulls of litoptern mammals like famous Macrauchenia (Croft 2016).

Fig. 8

However, the most infamous take was of course that there never was a blowhole. Coombs (1975) was the first to argue that the retracted nares were actually evidence for a proboscis, based on the fact that animals like tapirs or elephants also have retracted nares to give a strong base for their trunks. Coombs himself did not illustrate this, but many after him did, such as Bakker (1986) above, who was open to the idea, but seems to have preferred the classic blowhole, with the explanation that the on-top nostril-position may have instead been useful for sound production. The sauropod trunk became a recurring phenomenon throughout many 70s and 80s books, mostly aimed at general audiences (read: children) to illustrate the degree of uncertainty in paleontological reconstructions. A trunked alternate history sauropod even appeared in Dougal Dixon’s The New Dinosaurs. Today the idea of the sauropod trunk is not taken seriously anymore, for good reason. No reptile group ever had the facial musculature required for such an organ and various details of the skull anatomy also speak against it.

Fig. 9

Nonetheless, researcher John Martin proposed a variation if it in 1996 with this 3D model of Diplodocus with prehensile lips. This never went anywhere and the exact reasoning and methods behind it remain obscure, though as Darren Naish noted, the position of the nostrils in this model is somewhat prophetic.

Fig. 10

For in 2001, Lawrence Witmer released an influential study, wherein he compared the fleshy nostril positions of various living reptiles and came to the conclusion that the position of it in sauropods and other dinosaurs was much more forward on the skull, close to the snout-tip, as in most other terrestrial vertebrates. In this view, the bony nostrils were just the base for an elaborate flesh-and-cartilage structure, not too dissimilar from what is seen in the noses of modern monitor lizards. This probably could have served a variety of functions, like sound production, thermoregulation and/or maybe housing a rete mirable, the same type of organ giraffes use to soften blood pressure when lowering their heads.

Fig. 11

Witmer’s hypothesis has become widely accepted among modern paleontologists and has now become a standard in paleoart. It should be mentioned, however, that not everyone has been on-board with this. Though open to the fleshy nose reconstructions, Hallett & Wedel (2016) still prefer the classic placement, for a rather succinct reason. Many of the giant, erect-necked sauropods would have had to bow their neck and head down to drink water at such an angle that, if the nostrils were truly at the front of the snout, they would have been submerged in the water, while if they were atop the head, the animal could have breathed more easily. In some ways this seems to go full circle to the old blowhole-interpretation, though it seems like a valid point to consider. The idea that retracted nostrils also made bulk-feeding on thorny trees easier could also still hold some water.

The Neck Wars

Fig. 12

A more well-known issue that arose in the 90s is the question of neck-posture. As a counter-movement to the increasingly more giraffe-like interpretation of sauropod lifestyle, paleontologists such as John Martin (1998) or Kent Stevens (1999) used computer model studies to argue that the sauropod neck was quite stiff and predominantly held in the osteologically neutral posture, meaning horizontally straight forward and largely unable to raise the head above shoulder-level, with the musculature actually being better adapted towards bending the neck down. In this view, sauropods such as Diplodocus were actually low-browsers, who evolved their necks to more easily forage the ground like living vacuum cleaners or giant geese without having to move much. This interpretation was famously immortalized by documentaries such as Walking with Dinosaurs.

 

Fig. 13

Although quite popular throughout the 90s and 2000s and still repeated in some popular sources here and there, this idea has come under quite a lot of criticism. Not only is the vertical lifestyle blatantly obvious in the skeleton of sauropods such as Giraffatitan, but almost all living tetrapods do not hold their necks in the osteologically neutral posture. Instead, muscles, ligaments and especially cartilage give a great deal more flexibility than would be expected from just the bones, with the neck more often than not being actually held diagonal curving upward when neutral (Taylor et al. 2009). A horizontally held, stiff neck would have also been a prime unprotected target for various predatory dinosaurs (Hallett & Wedel 2016). Even independently of the low-browsing hypothesis, the idea that sauropods evolved their long necks so they could just feed a lot without having to walk (as still repeated in recent popular media like Brusatte’s The Rise and Fall of the Dinosaurs) makes little sense, for no living large animal functions by this strategy (Hallett & Wedel 2016). The energy expended by walking up to a close food source is trivial, especially for large animals, as their larger steps alone mean they need to walk less, they actually use fewer calories relative to their size and need less food per kilogram than smaller animals (Hallett & Wedel 2016). So, if you feed from the ground, simply using your legs will always stay the more viable option rather than evolving a new hyperspecialized organ, which makes it far more likely that the sauropod neck instead evolved to reach hard-to-access food sources, such as tree canopies. Of course, one might point to ostriches, being long-necked grass-eaters, but their neck length evolved to compensate for their long legs, which they need to run away from predators (Bakker 1986), something which sauropods did not do.

Fig. 14

A perhaps final blow was dealt to the beam-necked sauropod idea with the 2020 computer-model study done by Vidal et al. on Spinophorosaurus. This study showed that the vertebrae of the pelvic area of this sauropod articulated into a concave wedge, which naturally lifted the spinal column of the animal diagonally upward and also meant the front limb girdle sat lower than usually reconstructed. This means that even in the osteologically neutral posture proposed by Stevens and others, the head and neck would have been pointing upward, quite ideal for high-browsing. That the musculature of the neck was adapted more for bending down makes even more sense in this light, as the ligaments and bones were already doing a great job holding it upright, meaning the animal only needed to exert muscular force when needing to bow down to drink. This has some rather far-reaching consequences, as Spinophorosaurus is generally classified as a basal eusauropod or at least a close relative of that group and the authors reason that this skeletal configuration would have applied to most if not all members of that clade. Since Eusauropoda comprises the Mamenchisauridae, the Diplodocoids (such as Diplodocus or Brontosaurus) and the Macronaria (Brachiosaurids and titanosaurs), this would mean that we have been reconstructing the majority of sauropod postures not diagonal enough (though some are already on their way to correct that).

Fig. 15

In general, it has therefore become popular again to depict Diplodocus and relatives (the animal depicted here seems to be a brontosaur) as high browsers. Sometimes by even using the double-beam chevron bones in their tails that Dippy derives its name from to prop themselves up onto their hindlegs in order to reach even higher into the treetops. This is by far not a new idea, though if this is something they did only occasionally or were specialized for doing regularly has in itself become a minor debate (see Foster 2020).

A final hurdle for the high-browsing camp is the question of how these giant animals handled their blood pressure, which is already a challenge for the much smaller giraffes. Most studies conclude that, in order to pump enough blood into the head of an erect-necked sauropod such as Diplodocus or Giraffatitan, the animals would have required gigantic hearts rivalling those of the largest cetaceans, which seems unlikely. This is today used as the main argument by beam-neck-supporters against sauropods raising their necks vertically. However, to paraphrase Naish (2021), it would be naïve to use this to discount every other evidence in favour of erect-neck postures without first assuming that these remarkable animals did not find solutions to these problems. Instead of having one giant heart, one proposal has been that sauropods may have had multiple pseudohearts along the neck which helped a more reasonably sized main heart with pumping, though such structures are virtually unknown in modern vertebrates, making it seem unlikely (Ganse et al. 2011). More likely, sauropods employed a wide array of smaller soft tissue adaptations, similar to what is seen in giraffes, to collectively lower the need for a large heart and deal with other blood pressure problems, like edema in the extremities. These adaptations were likely a combination of a rete mirabile, muscular venuous pumps, precapillary vasoconstriction, thicker blood vessel walls, extremely strong connective tissues, blood-cushions in the feet (as seen in horses), as well as blood with a much higher oxygen transport capacity (Ganse et al. 2011). That we will ever find evidence for any of this seems unfortunately unlikely, as such organs rarely fossilize. In the best case scenario, a baby sauropod maybe died and got preserved in a high-quality lagerstätte to the same degree as was the Scipionyx holotype and is now waiting to be uncovered.

The Headless Sauropod?

In terms of classification, a lot has also changed in the world of Diplodocus. First described in 1991, Seismosaurus hallorum soon became Diplodocus hallorum in the early 2000s, being a species even larger and longer than the famous D. carnegii, though suspected by some to be synonymous with the original D. longus. The problem with this is that D. longus has itself become a dubious taxon, on account of its original remains being too fragmentary. An attempt was therefore made in 2016 to strip D. longus off its status as the type species for the genus and instead grant D. carnegii the honour, but the proposal was rejected by the ICZN.

A more distressing revelation was made in 2015 by Tschopp et al., in the same study which also resurrected Brontosaurus as a valid genus. Analysing nearly all known remains referred to Diplodocus, they found that, due to the circumstances in which they were found and assigned, none of the skulls thought to belong to Diplodocus could be conclusively linked to the taxon or the species therein. All former Diplodocus skulls were either actually remains of the genus Galeamopus (as is the case with the original head of Dippy, USNM 2673) or could not be identified further than indeterminate Diplodocines, as is the case with USNM 2672, the skull you saw in Part 1 that was retroactively assigned by Marsh to the D. longus holotype. While there is a good chance that the latter ones do indeed come from Diplodocus (Tschopp et al. 2015), we cannot actually be sure until we find a new one firmly attached to a skeleton that is decisively Diplodocus.

In short, for now we do not know for certain what Diplodocus’ skull really looked like (though it likely did not differ too much from that of other diplodocids), which makes all the earlier nitty gritty debates about soft tissue placements rather funny in hindsight. It goes to show that even taxa we thought we knew well for a long time can still end up surprising us, sometimes even becoming more mysterious with time.

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Related Posts:

References:

  • Augusta, Josef: Tiere der Urzeit, Prag 1956.
  • Bakker, Robert Thomas: The superiority of dinosaurs, in: Discovery, 3, 1968, S. 11-22.
  • Bakker, Robert Thomas: The Dinosaur Heresies. New Theories Unlocking The Mystery of the Dinosaurs and Their Extinction, New York 1986.
  • Ballou, W. H.: Strange creatures of the past, in: The Century Illustrated Monthly Magazine, New York, 55, 1897, S. 15 -23.
  • Colbert, Edwin: Men and Dinosaurs, London 1968.
  • Coombs, Walter: Sauropod habits and habitats, in: Palaeogeography, Palaeoclimatology, Palaeoecology 17, 1975, p. 1-33.
  • Desmond, Adrian: The Hot-Blooded Dinosaurs. A revolution in Paleontology, London 1975.
  • Flammarion, Nicholas Camille: Le monde avant la création de l'homme: origines de la terre, origines de la vie, origines de l'humanité, Paris 1886.
  • Foster, John : Jurassic West. The Dinosaurs of the Morrison Formation and their World, Bloomington 2007 (Second Edition 2020).
  • Ganse, Bergita et al.: Body Mass Estimation, Thermoregulation, and Cardiovascular Physiology of Large Sauropods, in: Klein; Remes; Gee; Sander (Hg.): Biology of the Sauropod Dinosaurs. Understanding the life of Giants, Bloomington 2011, p. 105 – 115.
  • Gilmore, Charles Whitney: On a newly mounted skeleton of Diplodocus in the United States National Museum, in: Proceedings of the United States National Museum, 81, 1932, S. 1–21.
  • Hallett, Mark/Wedel, Mathew: The Sauropod Dinosaurs. Life in the Age of Giants, Baltimore 2016.
  • Hatcher, John Bell: Diplodocus Marsh, its osteology, taxonomy and probable habits, with a restoration of the skeleton, in: Mem. Carnegie Mus., 1, 1901, S. 1 – 63.
  • Hay, O. P., 1908. On the habits and the pose of sauropodous dinosaurs, especially of Diplodocus, Am. Nat., 42, pp. 672-881.
  • Holland, William Jacob: The osteology of Diplodocus Marsh with a special reference to the restoration of the skeleton of Diplodocus carnegiei Hatcher presented by Mr. Andrew Carnegie to the British Museum, in: Mem. Carnegie Mus., 2, 1905, S. 225 – 264.
  • Holland, William Jacob: A review of some recent criticisms of the restoration of sauropod dinosaurs, with special reference to that of Diplodocus carnegiei in the Carnegie Museum, in: Am. Nat., 44, 1910, S. 259 – 283.
  • Holland, William Jacob: The Skull of Diplodocus, in: Mem. Carnegie Mus., 9, 1924, S. 379 - 404.
  • Kermack, Kenneth: A note on the habits of the sauropods, in: Annual Magazine of Natural History, 12, 1951, S. 830 – 832.
  • Marsh, Othniel Charles: The Dinosaurs of North America, in: Annual Report of the US Geological Survey, 16, 1896, S. 135 - 415.
  • Martin et al.: Not cranes or masts, but beams: The biomechanics of sauropod necks, in: Oryctos, 1, 1998, S. 113 – 120.
  • Matthew, William Diller: Dinosaurs. With special reference to the American Museum collections, New York 1915.
  • Mcloughlin, John: Archosauria. A New Look at the Old Dinosaur, New York 1979.
  • Naish, Darren: Dinopedia. A Brief Compendium of Dinosaur Lore, Princeton 2021.
  • Osborn, H. F., and C. C. Mook. 1921. Camarasaurus, Amphicoelias and other sauropods of Cope. Memoirs of the American Museum of Natural History, n.s. 3:247-387 and plates LX-LXXXV.
  • Osborn, Henry Fairfield: Cope. Master Naturalist, Princeton 1931.
  • Popular Science Monthly, Vol. 72, 1908, S. 440.
  • Probst, Ernst: Tiere der Urwelt. Leben und Werk des Berliner Malers Heinrich Harder, Norderstedt 2014.
  • Russell, Dale: An Odyssey in Time. The Dinosaurs of North America, Minocqua 1988.
  • Stevens, Kent/Parrish, Michael:  Neck Posture and Feeding Habits of Two Jurassic Sauropod Dinosaurs, in: Science, 284, 1999, S. 798 – 800.
  • Taylor et al.: The long necks of sauropods did not evolve primarily through sexual selection, in: Journal of Zoology, 824, 2011, S. 1 – 12.
  • Tschopp, Emanuel/Mateus, Octavio/Benson, Roger: A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda), in: PeerJ, 3, 2015.
  • Vidal, Daniel; Mocho, Pedro; Aberasturi, Ainara, et al. : High browsing skeletal adaptations in Spinophorosaurus reveal an evolutionary innovation in sauropod dinosaurs, in: Scientific Reports, 10, 2020.
  • Wells, Herbert George: A Short History of the World, London 1922.
  • Wings, Oliver & Sander, Martin: No gastric mill in sauropod dinosaurs. New evidence from analysis of gastrolith mass and function in ostriches, in: Proceedings of the Royal Society, 274, 2007, S. 635 – 640.
  • Witmer, Lawrence: Nostril Position in Dinosaurs and Other Vertebrates and Its Significance for Nasal Function, in: Science, 293, 2001, 850 – 853.

Image sources:

  • Fig. 1: Holland 1924
  • Fig. 2: Gilmore 1932.
  • Fig. 3: Lescaze 2017.
  • Fig. 4 & 5: Augusta 1956.
  • Fig. 6: Bakker 1968.
  • Fig. 7 & 8: Bakker 1986.
  • Fig. 9: Junk in the trunk by Tetrapod Zoology.
  • Fig. 10 & 11: Hallett & Wedel 2016, p. 105 & 98.
  • Fig. 12: Stevens & Parrish 1999.
  • Fig. 13: Taylor et al. 2009.
  • Fig. 14: Vidal et al. 2020.
  • Fig. 15: Hallet & Wedel, p. 146.

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Sunday, 9 October 2022

Sparing a thought for some fossil plants or how I came to love Araucaria

Fig. 1: Giraffatitan brancai struggling to reach a particularly tall araucarian tree (Drawn by Me).

Plants. When was the last time you really put your mind’s focus on them? Despite giving us the food we eat and the oxygen we breathe, their presence around us and our usage of them is such a matter of fact that they do not really register as much more than scenery decoration in the stageplay that is ours, other people’s and animal’s lives. Michael Crichton’s Jurassic Park, of all things, put it quite well:

“People were so naïve about plants, Ellie thought. They just chose plants for appearance, as they would choose a picture for the wall. It never occurred to them that plants were actually living things, busily performing all the living functions of respiration, ingestion, excretion, reproduction – and defence. But Ellie knew that, in the earth’s history, plants had evolved as competitively as animals, and in some ways more fiercely. The poison of Serenna vermiformans was a minor example of the elaborate chemical arsenal of weapons that plants had evolved. There were terpenes, which plants spread to poison the soil around them and inhibit competitors; alkaloids, which made them unpalatable to insects and predators (and children); and pheromones, used for communication. […] People who imagined that life on earth consisted of animals moving against a green background seriously misunderstood what they were seeing. That green background was busily alive. Plants grew, moved, twisted, and turned, fighting for the sun; and they interacted continuously with animals – discouraging some with bark and thorns; poisoning others; and feeding still others to advance their own reproduction, to spread their pollen and seeds. It was a complex, dynamic process which she never ceased to find fascinating. And which she knew most people simply didn’t understand.”

It was just such a lack of understanding on my part that has recently led to some odd thoughts. You see, I was recently at an Ikea with my girlfriend and there I found a little, less than half a meter tall, plant, whose pot read Araucaria heterophylla. It was cheap, I liked the look of it and I had a vague understanding that araucarians are a very ancient plant group that has been around since the time of the dinosaurs, so I bought it. Once home with my new house organism, I looked up the species and was a bit shocked. A. heterophylla is not a small houseplant, instead I just bought the sapling of what is supposed to become a whole tree, which can potentially grow over 50 meters tall. Furthermore, because it is native to Norfolk Island, a territory of Australia, it can not survive winters outdoors in most European climates, so I will not be able to replant it in my garden should it become too large. Apparently, the saplings were only sold here around this time of the year so they could be used as Christmas trees before being thrown down the woodchipper immediately afterwards, as Christmas trees usually are. It may be “just” a plant, but an odd feeling of responsibility and pity overcame me upon learning this, as I am now taking care of an organism that is supposed to become quite large, while I am also unable to give it the proper conditions to truly thrive in. Sort of like buying a baby orca while you live in the desert.

Fig. 2: The new Araucaria heterophylla I now want to care for. The sauropod toy is by the way one of the original Lego dinosaurs from the 2001 line, which are great for posing. For the fossil in the background, read on.

In the process of looking up how to best care for this plant, I grew a new appreciation not just for the genus Araucaria, but also for the peculiarities and history of the wider family of the araucarians. Here are some things I would like to share with you. If you think some post about fossil plants will be a boring read, I will politely point out that I made a whole post about brachiopods not only work, but also got enough people to read and enjoy it that some are now making speculative evolution posts inspired by it.

Jurassic relicts

The family Araucariaceae, named after the Arauco Province in Chile, is part of the plant order Pinales, which today includes all living conifer trees, such as pines, redwoods and cypresses. All other conifers outside of Pinales are now extinct. Conifers, like ginkgos, cycads and gnetophytes, are part of the gymnosperms, whose cladistic definition is a bit confusing, as they classically also include the extinct seed ferns (pteridospermatophytes) that also gave rise to the angiosperm flowering plants, making the group paraphyletic. When excluding seed ferns and flowering plants, conifers, ginkgos, cycads and gnetophytes do seem to form a monophyletic clade called Acrogymnospermae. Within the conifers, the closest living relatives of the araucarians seem to be the podocarps and the closest relative of those two are the cypresses.

Fig. 3: Araucaria araucana growing around the Chilean volcano Llaima in the Conguillio National Park. Yes, this is also where the sixth episode of Walking with Dinosaurs was filmed.

Coniferous trees originated in the Carboniferous with cypress-like forms such as Walchia, gradually replacing the first fern and progymnosperm trees that had dominated in the Devonian. As the world became drier during the Permian, these tough, seed-bearing plants became more successful and went on to survive the catastrophic end of the Paleozoic without much problem, becoming the dominant group of land plants throughout the Mesozoic. A secret to their success compared to earlier plants groups might be their reproduction, as conifers have evolved a much faster and more direct form of fertilization between the male pollen and the female ovule than other gymnosperms.

Fig. 4: Fossil cones of Araucaria mirabilis from the Paleontological Museum of München.

When exactly the first araucarians evolved is a bit of a mystery, as it depends on the exact classification of certain taxa. If the leaf-taxon Brachyphyllum (as whole plants are rarely preserved, paleobotanists give fossils of specific plant parts, such as trunks and leaves, their own name, even if they come from the same organism) is indeed an early araucarian, their origin might also go as far back as the Late Carboniferous. The oldest definitive araucarian fossil, Araucaria mirabilis, “only” dates back to the Middle Jurassic. Throughout the rest of the Mesozoic, araucarians could be found in the whole world and they and their gymnosperm cousins saw wide success. Then they dramatically declined in the Late Cretaceous, a change often attributed to the rise and spread of angiosperms, whose insect-based pollination made their reproduction more efficient.

Fig. 5: Fossil scorpionflies (Mecoptera) may have been important pollinators of Mesozoic gymnosperms.

Today the flowering plants dominate in most tropical environments, while conifers such as pines only seem to remain dominant in harsher environments such as taigas, where the massive boreal forests form one of the world’s largest carbon sinks. Araucarians specifically have gone completely extinct in the northern hemisphere (except for two species in Malesia) and are now restricted to former Gondwanan landmasses such as South America, Australia and the islands that were once part of the sunken continent Zealandia. In some ways this displacement seems to parallel a similar pattern seen in the evolution of marine invertebrates, where once successful groups such as brachiopods and crinoids gradually disappear from the very productive shallows to migrate into the deep sea. However, just like that example, one has to wonder if we are really seeing here a fierce competition between gymnosperms and angiosperms, where the younger group is supposedly displacing the older one. Surely, taigas must have been a lot less common in the warmer Mesozoic than they are today, which would mean that the conifers were actually more successful at exploiting this new and expanding environment than their younger competitors. And while the insect-based pollination of angiosperms may be more efficient than wind-based pollination, many coniferous plants have independently evolved this form of pollination as well, likely even before the appearance of true flowering plants. Much evidence exists that already in the Early-to-Middle Jurassic, long before flowers and bees, the cheirolepidiacean conifers lived in symbiosis with mecopteran flies (Hallett & Wedel 2016) and such relationships may have even been common in various Mesozoic gymnosperms (Penalver et al. 2015).

Sauropod snacks?

One of the defining characteristics of araucarians, which I evidently failed to know beforehand, is that they grow exceptionally tall, with some specimens reaching 80 meters in height. While not as tall, the species Agathis australis can reach a wood volume of 517 cubic meters, making it the third largest tree in the world, only outmatched by redwoods and giant sequoias. Like their cousins, araucarians can also grow exceptionally old, up to a thousand years (Lüning et al. 2019)

Fig. 6: John C. McLoughlin’s (1979) depiction of Diplodocus feeding on what is implied in the text to be an araucarian.

The fact that araucarians have such incredibly tall-standing canopies, combined with the age they evolved their characteristic morphology in, has always made them prime candidates for co-evolution with sauropod dinosaurs. It is not difficult to imagine the canopies growing ever taller in response to ever-hungry sauropod maws, while the necks of the latter in turn grow even longer, until we reach the ridiculous proportions seen in both groups. There is at least some direct evidence for sauropods feeding on conifers, as in some of the only known coprolites attributed to them could be found the remains of various Mesozoic gymnosperms, including araucarians (Sonuksare et al. 2017). Microwear on the teeth of sauropods is also consistent with a coniferous diet (Hallett & Wedel 2016). Araucarians and relatives with their small, tough needles might seem like a poor diet at first, especially for such gigantic, energy-dependent organisms, but experiments by Hummel et al. 2008 show that through hindgut-fermentation, which sauropods most likely practiced, these plants could actually release a tremendous amount of energy if digested long enough. Basically, sauropods must have had a large hindgut chamber called a caecum in which araucarian and other pre-angiosperm plant matter was collected into a massive internal compost heap, where microorganisms and the heat created by their own decomposition worked tirelessly to turn them into a nutritious mush. This system meant that sauropod digestion worked best the more matter was piled onto the heap and the longer it was allowed to ferment, in turn creating a permanent bioreactor that continuously generated the required energy. This was maybe not just the method by which sauropods fuelled their huge sizes but may have also been a driving force in their gigantism, as a larger body and in turn larger caecum could generate more energy than a smaller one. Other results of the study are also fascinating, as they found that the most energetically rich plants sauropods could have fed on were horsetails, ginkgos, Angiopteris and araucarians. Horsetails and araucarians were especially singled out for their energy-content after longterm digestion, with low-growing horsetails likely having been the prime fodder for sauropod hatchlings while araucarians were likely the main food of adults. They also found that cycads, tree ferns and podocarps would have only made for poor food.

Fig. 7: The immense cone of A. bidwilli.

The strong association between sauropods and araucarians might put a new light onto the gradual decline of the latter. Surely, after over 100 million years of coexistence, the relationship between sauropods and araucarians must have been more complex than one just feeding on the other. One could easily imagine that sauropods sticking their tiny heads into the canopies while feeding and then wandering from tree to tree could have been used as a method of pollination. Furthermore, many modern trees also exploit large animals to disperse their seeds, the most prominent example to many readers probably being Persea americana, whose fruit, the avocado, was likely once adapted for being fed on by Pleistocene megafauna. Indeed, even some modern araucarian seeds, despite being largely carried by wind, are occassionally dispersed by animals, though often by smaller critters such as opossums and possums. The sheer size of their cones, however, seems ridiculously oversized for that purpose. Araucarians have possibly the largest cones among conifers, with the bunya pine (Araucaria bidwillii) having ones about the size of pineapples. Though cones are not the same as angiosperm fruit, could these maybe have originally evolved to be fed on by sauropods? The growing doubt about sauropods having used gastroliths to chew their food (Wings & Sander 2007) only adds further to the possibility of them having been prime seed-dispersers. If so, could the extinction of the sauropods have had a role in the global decline of araucarians?

Fig. 8: Could giant birds like the moa have helped with the dispersal of conifer seeds? It is possible, though there seems to be no evidence so far.

Jumping further off that idea, the continued existence of araucarians in the Gondwanan landmasses is also intriguing. Not too long ago, Australia and New Zealand were home to the large dromornithids and moas respectively. As large, flightless and herbivorous birds (though the latter is still debated in the case of Bullockornis), they would have been hindgut fermenters like the modern ostrich (and sauropods). Unlike ostriches, evidence exists that moas, with their stronger jaws, were not grazers but instead browsers capable of stripping the twigs of tall plants (Paul 1988). In these aspects, they could maybe be thought of as post-Mesozoic mini-sauropods. Could they therefore have coevolved with and helped smaller araucarians survive in the southern hemisphere by dispersing their seeds? The caveat with this idea is that there is no direct evidence from things like coprolites that these birds fed on araucarians or even conifers in general. Araucarians are also widespread in South America, which never had its own version of a giant herbivorous bird (unless some of the famous terror birds had a more flexible diet than previously thought, but there is no evidence for this).

Fig. 9: All the trunked reconstructions over the years really make one underappreciate how truly bizarre the skull of Macrauchenia was, in many ways resembling more a sauropod head than a mammal’s. I imagine all the arguments against trunks on sauropods should also apply here and indeed more recent research suggests this animal had more of a moose-like nose.

The continent did have other high browsers in the form of giant ground sloths like Megatherium, though their dentition seems to indicate more a diet of leaves, as in modern sloths, rather than conifer needles. Intriguing are instead the very sauropod-like skulls of long-necked South American litopterns such as Macrauchenia, which, by analogy, could mean that these mammals may have fed on coniferous plants, much like modern moose (here meaning Alces alces to avoid that old moose-elk mix-up). Data corroborating this is a bit lacking however. Older isotopic studies done on its tooth enamel resolved Macrauchenia as a mixed feeder (MacFadden & Shockey 1997), which would mean that, indeed like a moose, it could have fed on a variety of plants, including conifers like Araucaria. A newer study on the other hand suggests that it and other litopterns were more grazers instead (Oliveira et al. 2020). That last study was however based on tooth microwear, not isotopic data, and there is some evidence from sauropods that a diet of coniferous plants can produce wear-patterns that mistakenly suggest a grazing diet (Hallett & Wedel), so this could be a false positive.

The incredible Turkish araucarian gemstones

Sauropods (and possibly those that came after them) were not the only ones feeding on araucarians. Various human cultures have and still continue to eat the seeds of various species of Araucaria, such as A. araucana, A. angustifolia and A. bidwillii, including the Mapuche people of Chile and Argentina and the Aboriginal Australians. Beyond the culinary, these trees have also had more material uses. From their timber are made various utensils and vehicles and the Maori have used the resin of the genus Agathis to construct weapons (Neich 1966).

Fig. 10: Prayer beads made of oltustone.

The most extraordinary thing I found out though is the peculiar use of fossil araucarians in art. In the Erzurum Province of eastern Turkey, more specifically in the town of Oltu, mines have for centuries been excavating a special type of black gemstone. This so-called olutstone is globally only found in this region of Turkey and its special property is that upon excavation it is actually quite soft and therefore very easily carveable, only beginning to harden when exposed to air. It has thus been formed into a variety of utensils from jewellery all the way to prayer beads and smoking pipes. Upon closer examination, oltustone turns out to be a type of lignite (a sort of proto-coal) formed entirely out of the stems of Late Cretaceous araucarians. Even though they have been extinct in this part of the world since the age of dinosaurs, the araucarians thus managed to have an impact on the cultures of the northern hemisphere long before western explorers would rediscover their living members.

Fig. 11: If you are wondering about the fossil, it is a genuine Chirotherium footprint gifted to me by Torsten Scheyer from the Zoological Museum of Zürich. Apparently, it was found by a former student of his, but because that student did not keep notes nobody knows anymore where it came from, the lack of context now making it scientifically useless. He asked around the museum for anyone to take it home, because otherwise he would have had to throw it away for more storage. Moral of the story: If you find anything, write all the details down and take care of your notes! “The only difference between screwing around and science is writing it down”, to quote Adam Savage.

I now hope you have enjoyed this little journey through the world of araucarians and have grown more appreciation for fossil plants, as well as those that ate and used them. As for the little A. heterophylla, I will try my best to care for it. It will likely not grow tall into a sauropod feeder, though its seeds are edible, so one day it might feed me. The problem here is that, unlike most plants, Araucaria are not hermaphrodites but actually have split male and female sexes and can therefore not self-fertilize. I would therefore need a second plant of the opposite sex to make it produce seeds. The fact that I am even considering this means the plant is already manipulating a big, dumb animal into helping it with its reproduction. Maybe I am a sauropod?

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