Wilfarth's Great Tides and the Dinosaurs - Part 2

Go here for part 1!

And so we return to Martin Wilfarth and his highly unorthodox ideas of intertidal dinosaurs. Let us jump right in with the next major group:

“The Breath-Neck Saurians”

Die Atemhalssaurier (Sauropoda)

As the tidal levels sank in the Jurassic, down to a range of about 10 metres (Wilfarth 1949a, p. 35), it was no longer needed for dinosaurs to perform breath-jumps or rear onto their hindlegs and especially the large plateosaurs could simply lift up their long necks to breathe. But bipedalism on land restricted how long their neck could be, so they eventually became quadrupedal to free themselves of that restraint (Wilfarth 1949a, p. 39 – 40).

Fig. 1: Wilfarth's reconstruction of Diplodocus both in bipedal and quadrupedal posture. It looks strangely modern if one just thinks away the water. Their whip-tails are buried in the sediment to act as anchors (Source: Wilfarth 1949a, p. 34).

As you could have probably guessed, Wilfarth identifies the sauropods as the most aquatic of the dinosaurs, staying in water even during ebb and only coming onto land to lay eggs. In this he is ironically also the least radical for his time. The idea of sauropods being too heavy for land and therefore aquatic or amphibious has its roots all the way back to the description of Cetiosaurus by Richard Owen and most of the leading experts during Wilfarth’s time would have agreed that these animals would have spent most of their lives in water, using their long necks as snorkels. Some, like William Diller Matthew (1915) arguably went even further than Wilfarth by claiming that sauropods gave live birth and therefore never had any reason to come onto land. Even the idea that sauropods were not herbivores but actually fed on shellfish predates Wilfarth and goes back to William Jacob Holland (1924). The only difference between these paleontologists and Wilfarth is that they interpreted sauropods as living in freshwater, whereas Wilfarth (1938a, p. 277 & 1949a, p. 50) argued that the bottoms of freshwater lakes and rivers are too uneven to be suitable for a huge wading, non-swimming animal, as it meant the legs would constantly be of the wrong length for the needed lifestyle. Instead, they were adapted for the even tidal flats.

Fig. 2: A diagram showing how an aquatic Diplodocus could have returned from a breathing posture back into a feeding posture against the current by using its buried tail for support (Source: Wilfarth 1949a, p. 48).

Today the idea that sauropods could have used their necks as snorkels, and therefore be aquatic as envisioned in the previous century, is disproven by simple physics. Kenneth Kermack (1951) showed that on a sauropod fully submerged all the way up to the head, the water pressure on the lungs would have been so large that it would have been impossible for it to draw in air through the windpipe. Though of course this only came out after Wilfarth’s book and was initially even dismissed by leading paleontologists like Edwin Colbert, until being picked up again by Robert Bakker in the 70s.

Fig. 3: How a sauropod whipped up and down between eating and breathing by using its hips like a seesaw. "Hehehe, going back for more" (Source: Wilfarth 1949a, p. 45).

Wilfarth is once again quite observant about details of sauropod anatomy, though the way he interprets these details as aquatic adaptations is not always logical. For example, he claims that the recurved claws on the feet of sauropods were made to safely anchor the huge animal in the soft ground, which is essentially the same interpretation that is still widely accepted today (Hallett & Wedel 2016). But Wilfarth then also claims that this precludes these feet from having been used for walking on land, with the animal supposedly tripping over its own claws if it did so. I do not really understand his reasoning here, especially considering that tortoises have the same type of recurved claws on their feet and they live on land. Likewise, Wilfarth notes the almost fingerless hands of sauropods, arguing that this also made them unsuited for terrestrial locomotion, or walking in general, and that the sauropods were essentially still bipedal animals that used their forelegs merely as support-structures during worm-grazing, supported by the anchoring thumb-claw (Wilfarth 1949a, p. 39 – 40).

Fig. 4: Wilfarth pointing out the strange gaps between the vertebral spines that are produced by the common, hunched over reconstructions of sauropods and using these to argue that the animals actually held their tails and back in an upright, concave position (in water), closing the gaps (Source: Wilfarth 1949a, p. 47).

A funny thing is that his reconstruction of Diplodocus, with it rearing up onto its hindlegs and holding its spinal column in a straight line with the tail well above ground, looks almost modern if one just thinks away the water. And I believe there is a peculiar reason for that. Wilfarth notes the fused vertebral spines above the pelvis form a noticeable gap between those of the tail and back. He argues that this shows that the animal’s spine was generally not held in the convex posture, with the curved back and drooping tail you often see in old art, but that in life these gaps were closed, by the animal having its tail and back actually lifted up in a slight concave position (1949a, p. 47). Even if his misguided interpretation of this feature is that the sauropods regularly reared up in the water in order to breathe, the observation itself is remarkably prescient and actually predicts much later work. Vidal et al. 2020 used essentially the same observation in the sauropod Spinophorosaurus to argue that eusauropods have traditionally been reconstructed as too horizontal, with the pelvic vertebrae indicating that the front of the body was actually neutrally held up diagonally, as in giraffes, supporting the modern notion of these animals as high-browsers.

Fig. 5: Modern skeletal reconstruction of Spinophorosaurus, showing that, essentially, Wilfarth was right in thinking that the sauropod spine formed a light concave at the hip (Source: Vidal et al 2020).

Wilfarth’s discussion of sauropod facial anatomy is also interesting in the modern day. Of course, the high nares on diplodocoids he interprets as a sort of whale-like blowhole, as was the style at the time. Ever since Witmer 2001 it has become unpopular to reconstruct the fleshy nostrils of these dinosaurs as sitting directly atop the nares, being instead shifted towards the snout-tip as in other reptiles and connected to the nares by a big, fleshy structure. I personally remain agnostic on this issue. There has been some pushback against an elaborate nose in recent years, mostly in online discourses by paleoartists, as there is no obvious sign on the snout of diplodocoids of any attachment sites for such an external flesh- or cartilage structure. As Hallett & Wedel (2016) and before them McLoughlin (1979) have argued, a blowhole might still make sense even in a terrestrial context, as it would have allowed the animal to more easily browse thorny trees or keep the nose dry when having to curve the neck and head down to drink. Where Wilfarth is again quite modern is in the discussion of macronarian noses. As he notes, their nares are so unusual and spacious that they simply must have housed big, elaborate soft-tissue structures (prefiguring Witmer 2001), that aided in breathing: “The nose of Brachiosaurus can be imagined balloon-like and extendable. Since the nasal bar is very narrow, one can conclude that the fleshy nose looked like a uniform structure. A well-functioning breathing-nose allowed the sauropod to exploit the wave-troughs and in turn significantly save on neck-length, since in the wave-trough the water surface is closer to the bottom.” (Wilfarth 1949a, p. 52, translated by me). Unfortunately for us he provides no illustrations of what he thinks that might have looked like.

Regarding sauropod dentition, Wilfarth argues that the teeth of animals like Diplodocus were spaced too far apart to have worked efficiently as rakes, therefore interpreting them not as herbivores but again as faunivorous “flesh-grazers” of the worm lawns, like the earlier plateosaurs (Wilfarth 1949a, p. 41 – 43). The conspicuous space between the teeth has interestingly been pointed out again in the modern day, though this time to support the idea that some sauropods may have had a supporting beak-like structure covering their teeth (Wiersma & Sander 2017).

Fig. 6: Wilfarth's thoughts on sauropods in water were oddly prescient. The ones about sauropods on land... not so much. Deja vu (Source: Wilfarth 1949a, p. 38).

Where Wilfarth’s ideas (apart from the snorkel-neck) have aged the worst is in regards to sauropods on land. Here he argues that, because they did not have a well-developed femoral head, sauropods could not have walked on erect legs like other dinosaurs. Thus, he reconstructs the sauropod mother coming to land to lay her eggs as crawling on her belly. This of course recalls earlier reconstructions made by Hay, Tornier and Harder. Though Wilfarth (1938a, p. 270 – 271) notably criticizes Tornier for reconstructing Diplodocus with sprawled-out legs like a crocodile, because, like Holland before him, he accurately points out that this would have disarticulated the legs. So instead, he reconstructs the crawling legs as crouched and angled in line to the body. I guess this is marginally better than Tornier’s monstrosity, but would have made for an even more awkward gait.

Wilfarth distinguishes three major groups of sauropods, which lived at different water-levels. First there are the Schlickgrundbewohner (“Silt-bottom-dwellers”) which are roughly synonymous with the Diplodocoidea. These he imagines as inhabiting the deepest depths, during ebb even venturing out into the parts of the ocean that stayed permanently inundated. They spent their lives continually following the ebb and flow, up and down the tidal flats, systematically fauna-grazing on the way by digging up worms. They preferred grazing against the current, so that the silt-clouds their digging produced would not blind them. To breathe, they regularly reared up onto their hindlegs, using their whip-tails as an additional anchor in the silt like their saurischian ancestors did.

Next are the Sandgrundbewohner (“Sand-ground-dwellers”) in which Wilfarth includes smaller, more robust forms like Brontosaurus and Camarasaurus. These lived at shallower depths with stronger currents and mostly fed on above-ground critters like brachiopods and crinoids. They evolved more elaborate noses that allowed them to quickly breathe in and close their nostrils again during wave-throughs, so that they did not need to rear up to breathe like the diplodocoids.

Third are the Hocharmsaurier (“High-arm-saurians”) like Brachiosaurus (Wilfarth refers here mostly to Janensch’s Brachiosaurus brancai, which is today its own genus Giraffatitan). These Wilfarth regards as the only true quadrupeds among the sauropods, having completely given up the practice of rearing up to breathe and thereby also losing the whip-like anchoring tail. Instead, these saurians, in response to the lowering tidal range, came to solely rely on the length of their neck to breathe, hence why their fleshy nose became even more elaborate than in the sand-ground-dwellers.

“The Mudflatwalkers”

Die Wattenläufer (Struthiomimidae)

Fig. 7: A little coelurosaur running over a pavement of seashells after the tide has already retreated (indicated by the streamlines around the clams, as Wilfarth likes to point out). The dinosaur itself is directly based on a reconstruction of Compsognathus drawn by Gerhard Heilmann, though with the cute little detail that Wilfarth's version has a slight fin around the tail. (Source: Wilfarth 1949a, p. 16). 

Whereas the sauropods became more aquatic with the lowering tidal range of the Jurassic, the coelurosaurs that descended from the podokesaurids became more terrestrial. That these animals were mostly terrestrial runners Wilfarth (1949a, p. 18) cannot deny, due to their fused metatarsals, reduced toes and general similarity to birds. Though he argues that they still were not pure dry-land-animals. For one, the dry land during this time would still have been pretty poor in food sources compared to the tidal zone, for the other, he doubts that the long tails of these animals really were purely used for balance, because the very similar birds can walk bipedally without needing a long tail. Instead, the coelurosaur tails must have still served an additional swimming purpose, helping the animal traverse tidepools or escape from larger predators. He also has conflicting views on the hollow bones, noting, in comparison with the pneumatic bones of birds, that this is again another sign for a terrestrial lifestyle, though bizarrely he also speculates if the hollow cavities could have been filled with water during flow in order to make the animal heavier (Wilfarth 1949a, p. 15).

Fig. 8: Struthiomimus stealing eggs on the beach. Instead of a redraw, this is directly taken from one of Osborn's papers. Which is sad, because I would have liked seeing an ornithomimid with a swimming tail (Source: Wilfarth 1949a, p. 17).

Wilfarth interprets the coelurosaurs of the later Mesozoic as beach-runners, always following the ebb and flow so that they could scavenge on the stranded animals left behind by the retreating waters or digging up small aestivating animals from their burrows. Additionally, he speculates that forms like Struthiomimus could have dug up and fed on the eggs of other dinosaurs or fished for small animals in tidepools. Being constantly on foot and also needing to run away from larger carnivores, he muses that they must have been quite fast Wilfarth 1949a, p. 17) and, similar to Heilmann, his illustrations indeed show the animals being active and dynamic, with the tail held well above the ground as in modern reconstructions. Compare this with other contemporary depictions like Disney’s Fantasia.

“The Big-Chunk-Predators”

Die Grossstückräuber (Megalosauridae)

Fig. 9: A Ceratosaurus feeding on a small ornithischian as the tide slowly approaches in the background. While Wilfarth says this is based on the Knight reconstruction, it reminds me more of a Heilmann piece (which also copied Knight), where the prey animal was Camptosaurus (Source: Wilfarth 1949a, p. 22).

The big predatory theropods (what Von Huene and others would have called carnosaurs), Wilfarth imagines as evolving in the Late Triassic from small-fauna-pluckers similar to Plateosaurus, that, unlike the sauropods, responded to the lowering tidal range by becoming more terrestrial. These theropods first lived like larger versions of the beach-runners, following the tides to scavenge on stranded fish and reptiles, before Jurassic forms like Ceratosaurus and Allosaurus evolved short necks and huge jaws, becoming active hunters of other dinosaurs. While, as with the coelurosaurs, Wilfarth interprets these animals as mostly terrestrial animals, having obvious walking feet, he cannot wholly separate them from the sea. He argues again, using birds, that the long tails of these animals were simply too long to have served purely as counterbalance, and would have actually been a hindrance on land, as them being dragged around on the ground would have been an obvious risk for injuries. Nor could they have been a purely vestigial feature from an aquatic ancestor, as the tails seemingly became longer with time, with Tyrannosaurus of the low-tide Late Cretaceous having the most terrestrial feet yet also the longest tail, with its huge pubic foot, Wilfarth (1949a, p. 25 – 27) speculates, purely serving to keep the massive tail off the ground so it could not be injured. Ergo, the tail, despite its hindrance on land, must have kept a vital purpose, which Wilfarth claims was to be a propeller for swimming, allowing the big theropods to keep up their pursuit even if a hadrosaur or ostrich-dino fled into the water. This basically makes them big, mean, bipedal crocodiles.

Fig. 10: Tyrannosaurus rex standing in the surf zone of the retreating tide, perhaps pining for the fjords. Obviously based on the original reconstruction of the animal by Charles R. Knight (Source: Wilfarth 1949a, p. 27).

The big flaw in Wilfarth’s argument is that he bases the supposed extraordinary tail-length of Tyrannosaurus solely off the famous (or rather infamous) AMNH 5027 skeletal mount, the original 1917 reconstruction of T. rex by Henry Fairfield Osborn. You may know it as the skeleton that served as the basis for the Jurassic Park logo. What Wilfarth does not seem to have known is that this mount was basically a Frankenstein’s monster, the museum having cobbled together parts of different specimens to fill out gaps in the incomplete skeleton, in the process adding way too many vertebrae to the tail than were present in the real animal (something funnily enough referenced in the original Jurassic Park novel). Wilfarth thus seems to have fallen victim to another person’s mistake, making it doubly ironic when he calls out paleoartists for not accurately portraying the tail-length of T. rex and accusing them of an actualistic bias (Wilfarth 1949a, p. 25 – 26).

Fig. 11: The famous T. rex mount AMNH 5027. The long, serpentine tail Wilfarth interprets as a feature used for swimming, not knowing that the tail-length in this mount was unknowingly exaggerated by the constructors (Source: Wilfarth 1949a, pl. 1).

From a certain point of view Wilfarth still prefigures some thinkers of the Dinosaur Renaissance (apart from saying that tail-dragging theropods don’t make sense), like Gregory S. Paul (1988, p. 44 – 47), who debunked the old myth that hadrosaurs and sauropods could just flee into the water to escape their pursuers, because theropods could in any case easily swim as well if they had to.

Be sure to continue with part 3, where we look at how Wilfarth interpreted the ornithischian dinosaurs as aquatic and speculates on why the dinosaurs went extinct!

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Related articles:

• Wilfarth's Great Tides and the Dinosaurs - Part 1 
• Wilfarth's Great Tides and the Dinosaurs - Part 3 
• The Alien Prehistoric World Trope - Part 2
• The weirdest things people have thought about pterosaurs
• The Ridoculus History of Sprawl-legged Diplodocus  
• Diplodocus: A history of reconstructions - Part 1
• Diplodocus: A history of reconstructions - Part 2   
• Why Brachiopods are actually pretty cool 
• Paleopods: The myth of the predatory prosauropods that kinda turned out to be true
• "Hawkinspunk" Spinosaurus

Further Reading:

• Alien Planetology 
•  A Vast Quantity of Evidence Confirms that Non-Bird Dinosaurs were not Aquatic by Darren Naish
• Dinosaur Sex Lakes, Too Big to Walk and the Bizarre Theories of Brian Ford by C. M. Kosemen

References:

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• Bonnan, Matthew & Senter, Phil: Were the basal sauropodomorph dinosaurs Plateosaurus and Massospondylus habitual quadrupeds?, in: Barrett, P.M.; Batten, D.J. (eds.): Evolution and Palaeobiology of Early Sauropodomorph Dinosaurs (Special Papers in Palaeontology 77), Oxford 2007, p. 139–155.
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Skull drawing of Kaatedocus siberi

Just a random drawing I did of the Kaatedocus siberi HQ2, a diplodocid discovered by the Swiss Siber-team at the Howe Quarry of Wyoming. This is just something I did because I was bored and is not at all accurate to the real thing (as I am still inexperienced at drawing things from life), so it should not be used as a reference.

Dinosaur Books that Made Us - Eyewitness Dinosaur

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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• The Alien Prehistoric World Trope: Part 2 - Dinosaurs become movie monsters
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• Visiting the Sauriermuseum Aathal - Part 1: The Howe Quarry Dinosaurs
• Diplodocus: A history of reconstructions - Part 1
• Sparing a thought for some fossil plants or how I came to love Araucaria

References:

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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.