Showing posts with label Robert Bakker. Show all posts
Showing posts with label Robert Bakker. Show all posts

Saturday, 9 August 2025

Wilfarth's Great Tides and the Dinosaurs - Part 3

Go here for Part 2!

And so we continue with Martin Wilfarth and his alien visions for the Mesozoic:

“The herbivorous Kickoff-Breathers”

Die herbivoren Abstossatmer (Iguanodontidae)

…and birds?

Coming now to the Ornithischia. Wilfarth imagines the ancestor of the ornithischians as a small “saltopodid” that adapted to living in more isolated but large tidepools that connect with the ocean only for a short time during flow. Plankton was sparse here, and so were the filter-feeding invertebrates that most of the saurischians fed on. So these small dinosaurs instead began feeding on water plants, which was an easy transition, as he notes, because they are softer than terrestrial plants that have woody support-structures (Wilfarth 1949a, p. 54). As the ancestral, pencil-like front teeth were useless for herbivory, they were lost and instead the lips hardened, becoming eventually a true beak supported by a predentary bone. Hence why Wilfarth sees the name Predentata as equally valid as Ornithischia. Being small animals in deep tidal lakes, made even deeper during flow, the animals needed to jump up a far distance to breathe. Grazing underwater in a crouched position, the pubis was already below the femur and could therefore be used to pull the leg back for a powerful upwards jump (see fig. 2). Exploiting this, the early ornithischians retroverted their pubis so that the pubo-femoral muscle could be used even more effectively to help with jumping. The downside of this was that these ornithischians consequently lost the bipedal balancing function of their pelvis and could only move anymore on land either quadrupedally or by hopping (Wilfarth 1949a, p. 54). But as tidal ranges lowered and carnivorous dinosaurs became a bigger threat, some re-developed bipedalism by evolving the additional praebubis or neopubis bone at the anterior base of the pubis, which picked up again the lost lever-function.   

Fig. 1: Underwater Iguanodon. This is one of my favorite illustrations in the book, because of how well-drawn the dinosaurs are here. There is a nice, scaly texture to them that is strangely lacking in the others. Though I am guessing that was to deliberately invoke iguanas? (Source: Wilfarth 1949a, p. 56).

As already mentioned (see part 1), unlike other workers of his time, Wilfarth did not view the ornithischian pelvis as arising independently from the saurischian one:

“That the ancestor of the ornithischians already was a lever-pelvis saurian, one can see by the retroverted pubis already being true levers, meaning longer than they would have to be for a basket-pelvis. If we count all saurians with a lever-pelvis as dinosaurs, so we may conclude that the ornithischians and birds must descend from a saurischian.” (Wilfarth 1949a, p. 52, translated by me).

Apart from speaking in favour of dinosaur monophyly here, your interest must surely be piqued by the mention of birds. I bet you did not see that coming. Yes, indeed, Wilfarth believed that birds descend from dinosaurs, a fact we all know today but an idea that would have been regarded as highly unorthodox in the 1940s, thanks to Gerhard Heilmann and Othenio Abel, who, contra Huxley, had popularized the idea that birds only share a common ancestor with dinosaurs among the Pseudosuchia. Wilfarth goes even further by claiming that the birds actually descend from the hypothetical small tidal proto-ornithischians just discussed:

“The birds probably branch off at the point on the evolutionary line to the ornithischian at which the retroverted pubis had been gained, but the herbivorous diet has not or not fully been adopted yet. In the birds must then have occurred an arboreal episode in their evolutionary line. The little saurischian who was destined to become the progenitor of the birds then probably climbed up the tree as an insectivore. Here a neopubis was not gained, because here there was no necessity for it.” (Wilfarth 1949a, p. 55, translated by me).

The idea that birds might descend from the ornithischian dinosaurs was semi-popular among some paleontologists of the early 1900s, mostly due to the shape of their pelvis, but was strongly rejected by Gerhard Heilmann (1926) on the basis of the ornithischian pelvis only bearing a resemblance to that of ratites, whose skeletons are greatly derived from those of ancestral birds like Archaeopteryx, as well as ornithischians supposedly not having clavicles that could have evolved into the avian furcula. Wilfarth surely was aware of Heilmann’s writings, given that he heavily references his artwork, so it is interesting that he either disagreed with or ignored these conclusions. Sadly, there is no greater elaboration than what you have just read. Wilfarth was not the only one proposing a bird-dinosaur ancestral relationship during the pre-Ostrom “Dinosaur Doldrums”, but those proposals, made by the likes of Carl Vogt, Robert Wiedersheim and Percy Lowe, were even more unorthodox and therefore taken even less seriously. They suggested that birds are actually polyphyletic, with the flying forms descending from Heilmann’s pseudosuchians or even pterosaurs and the ratites directly descending from the ostrich-dinosaurs. So Wilfarth seems a bit saner in comparison, even if he identified the wrong dinosaur group as the bird-ancestors. The bird-ornithischian link would be revived one last time by Peter Galton in 1970, who, just like Wilfarth, concluded that, while true ornithischians with their praepubis were too derived to have been the direct bird-ancestors, they still could have shared a close immediate ancestor similar to Lesothosaurus. Galton himself gave this idea up by the mid-80s (Norman 1985, p. 193).

Fig. 2: The reversion of the ornithischian pubis was to facilitate better jumps, according to Wilfarth (Source: Wilfarth 1949a, p. 53).

The first specific ornithischian group discussed by Wilfarth are the iguanodonts, whom he interprets as larger versions of the ancestral kick-breathers, though now so large that they merely needed to stand up to breathe. Just as with Plateosaurus and the sauropods, the characteristic thumb-claw of Iguanodon he interprets as another tool for the animals to anchor themselves in the sediment while feeding (Wilfarth 1949a, p. 56). During flow, the animal evaded sharks with its strong paddle-tail, during ebb it ran away from the theropods with its strong hindlegs.

“The Backplate Saurians”

Die Rückenplattensaurier (Stegosauridae)

Dinosaurs usually get the short end of the stick in old paleontological texts, but no group ever gets an end as short as the stegosaurs. With their small brains, supposedly useless, extraneous backplates and mismatched legs, many old writers saw these animals as destined for extinction. It is therefore quite refreshing to see that Wilfarth, in his own weird way, actually shows them quite a bit of appreciation, seeing them as expertly adapted to their supposed habitat. It should be noted that Wilfarth here seems to treat ankylosaurs as a type of stegosaur, probably following Marsh’s original definition of Stegosauria.

Fig. 3: Kentrosaurus using its thagomizer as an anchor against the current (Source: Wilfarth 1949a, p. 62).

Especially the backplates have given many early researchers headaches and there have even been some who claimed they were maladaptive traits, a consequence of genetic degeneracy out of control, with Frederic Brewster Loomis writing in 1905 (p. 842): “With such an excessive load of bony weight entailing a drain on vitality, it is little wonder that the family [Stegosauridae] was short-lived”. Wilfarth sees the plates instead as ingenious hydrodynamic structures, a beneficial adaptation for the intertidal zone (which is at least one step above being aerodynamic). To Wilfarth, stegosaurs inhabited shallow waters with strong currents. Feeding against the current, the backplates helped direct the water, so that it would flow over the back and press the animal down, so it could retain a firm grip to the ground instead of being carried away. (Wilfarth 1949a, p. 59 – 60). One wonders if the spikes on Wiwaxia could have worked like that.

Wilfarth is very open to the thagomizer of stegosaurs and ankylosaurs having been used as a defensive weapon (amusingly more against sharks than against theropods), though he thinks that could not have been its only function. Using Kentrosaurus (written here as “Kentrurosaurus”, which was Edwin Hennig’s preferred spelling to avoid confusion with Centrosaurus), Wilfarth notes that many contemporary reconstructions are wrong in showing the tail-spikes of stegosaurs as pointing straight up (Wilfarth 1949a, p. 58 – 59) and instead were splayed more to the side and pointing back. This is still the preferred view today. Where it gets weird is that Wilfarth asserts that therefore the most likely function of the thagomizer was as an anchor or stake in the sediment, as a further countermeasure against strong currents (Wilfarth 1949a, p. 57 – 58). This extends even to the tail-clubs of the ankylosaurs.

The unusually long hindlegs in comparison to the arms are of course another obvious adaptation towards having to rear up in shallow water in order to breathe. Interesting is here that Wilfarth makes special note of the neck-armour many stegosaurs had, which in his view protected the throat during this vulnerable moment (Wilfarth 1949a, p. 63 – 64).

“The Neck-Shield Saurians”

Die Nackenschildsaurier (Ceratopsia)

The earliest ceratopsians, like Leptoceratops, Wilfarth still interprets as primarily aquatic, on account of their deep, laterally flattened tails, something he does for other dinosaurs too. It should be noted that this was pretty common for paleontologists at the time, especially in regards to hadrosaurs, and it took until the Dinosaur Renaissance for some to point out that the dinosaur tail does not resemble the paddle-tails of crocodilians, especially since the deepest sections tend to be close to the body instead of mid- or end-part of the tail.

Fig. 4: Triceratops gracefully grazing in shallow water. In the background an individual lifts its head above the waves to breathe (Source: Wilfarth 1949a, p. 65).

The forms appearing in the Late Cretaceous he however regards as the dinosaurs with the least aquatic adaptations (Wilfarth 1949a, p. 65). Which of course makes sense, because the Great Tides had greatly diminished by this point. Instead of swimming or living submerged, the ceratopsians were merely waders of knee-high waters, grazing on aquatic plants during flow and otherwise prowling the beaches for other plants during ebb. The characteristic neck-frill Wilfarth interprets as a specific adaptation towards that lifestyle. While he does not go full John C. McLoughlin  he does still view the shield as primarily an attachment site for strong neck and shoulder muscles, allowing the skull to quickly pivot around its ball-and-socket-joint with the spine. This “hinge-skull” or “Klappschädel”, as he calls it, allowed the ceratopsians to efficiently lift their snout above water when they needed to take a breath, again according to Wilfarth’s motto that dinosaurs used elaborate bone constructions in order to save on muscle-work. The question of why they would evolve such an unusual hinge-skull instead of simply repositioning their nostrils like other semi-aquatic animals would do, Wilfarth does not address. On the topic of nostrils, Wilfarth writes on the unusually huge ceratopsian nares, believing that, just as with the sauropods, these must have housed elaborate soft tissue structures:

“The bony nasal opening in the ceratopsians is very big. Despite that, this fact has so far been ignored and reconstructions of the neck-shield saurian have always (with the exception of Lull 1933) drawn them a usual small nostril. These ornithischians have simply always been viewed as Mesozoic replacement-rhinoceroses, and for an only-land animal such a huge nasal opening is of course inconceivable. For a shallow-water-dweller and a hinge-skull-breather however, a huge nasal opening, which can be quickly widely opened and then shut close again, was very important.” (Wilfarth 1949a, p. 67, translated by me).

Semi-aquatic interpretations of ceratopsians have popped up here and there again in the decades following Wilfarth, but, as with most dinosaurs, evidence is abundant that these were purely terrestrial animals. However, the large nostrils that he addresses here still present a mystery for paleoartists to this day. While some still continue to reconstruct them with simple, slit-like nostrils, it has become popular to speculate that they may have housed large, inflatable air sacs, used for visual communication as seen in some birds.

Fig. 5: Triceratops using its headshield as a muscle-lever to lift its huge nostrils above the water (Source: Wilfarth 1949a, p. 65).

The nose horn, Wilfarth sees primarily as a means of protecting the large, fleshy and therefore sensitive nostrils. The brow horns in some species, however, he believes primarily evolved as a means of giving the eyes shade, so that they could look more clearly through the water’s surface (Wilfarth 1949a, p. 69), I guess similar to the wings of a black heron. Though he also goes into detail on how the numerous horns on the ceratopsian skull could also be used in defence against sharks, marine reptiles and theropods (Wilfarth 1949a, p. 69 – 70).

That Wilfarth regards the ceratopsians as the least aquatic dinosaurs is of course interesting if we remember (from part 1) his cryptozoological article on the Sanderson reports from African. Of course he would view these as the dinosaurs most likely to survive into the modern day, as they would be best suited for coping with the loss of the Great Tides.

“The Trunkbreathers”

Die Rüsselatmer (Hadrosauridae)

The hadrosaurs are the one group that Wilfarth has focussed the most on, writing papers on the supposed hadrosaur-trunk as far back as 1938. His hypothesis has notably changed and evolved over the years in response to criticism. Perhaps responding to Sternberg’s critique, where Sternberg erroneously claimed that Wilfarth imagined the hadrosaurs having a trunk like an elephant, Wilfarth writes:

“That is why I name the sub-family Hadrosaurinae here “Peaktrunkers” [Original: Spitzenrüssler], although the term “trunk” is dangerous. All the world immediately thinks of an elephant’s trunk, which is used as a tool for gathering food. This is obviously not what is meant here. The expanded breathing-nose, which is the subject here, is solely used for respiration. Also in length and mobility the breathing-nose cannot compete with the elephant’s trunk. As is often the case, here too the right word is missing for a previously unknown apparition. Nose is too little, trunk too much. There is nothing left but to use the term trunk here, because it has to be emphasized that we are dealing here with significantly more than a nose.” Wilfarth (1949a, p. 74, translated by me).

I believe the closest that Wilfarth imagined here for the hadrosaurs is something like the breathing proboscis seen on the snouts of modern softshell turtles. It should be noted that, for the time, this was pretty much the only unorthodox idea Wilfarth espoused about the hadrosaurs. Other supposed aquatic features cited by him, such as deep paddle-tails and alleged webbing on the hands of hadrosaur mummies, were also used by plenty of other contemporaneous researchers to support an amphibious lifestyle for these dinosaurs. And unlike other researchers, Wilfarth did not relegate the hadrosaurs to the waters because he thought they could only eat soft aquatic plants. He does mention that the complex tooth-batteries in their jaws would have been just as effective in function as the molars of mammals (Wilfarth 1949a, p. 54), which I think is somewhat notable, as that would later become an important talking point in the Dinosaur Renaissance.

Fig. 6: An early, trunk-nosed hadrosaur walking upright across the tidal bottom, feeding on aquatic plants drifting in the water. The pose seems inspired by Charles Knight's original reconstruction of Trachodon (Source: Wilfarth 1949a, p. 74). 

The hadrosaurs he imagines as evolving from an ornithischian similar to Iguanodon, but adapted to the shallow-water conditions of the Late Cretaceous. They no longer needed to rear up or fulfil breath-jumps in order to breathe and instead, convergently to the ceratopsians, evolved adaptations that allowed them to keep their nostrils above the water during feeding. The simplest of these forms were the aforementioned “Spitzenrüssler”, Hadrosaurinae, to which Wilfarth counts forms like Hadrosaurus (synonymous to him with Trachodon), Edmontosaurus and Claosaurus. These differed from the iguanodonts by having deep, vacuous nares, which Wilfarth again sees as an indicator for elaborate soft-tissue structures, in this case an inflatable, short, forward-facing proboscis. That these spaces probably did house some sort of elaborate nostril structure is still a popular speculation today, though, as with the ceratopsians, something like inflatable display sacs were probably more likely. Wilfarth makes special note of the hook-like squamosal bones at the back of the skull of hadrosaurs, which he interprets as a lever-like structure, again similar to the ceratopsian neck-frill, that allowed the animals to quickly clap back their heads for quick breaths (Wilfarth 1949a, p. 83). The zygapophses in the neck vertebrae he interprets as a further stabilizing feature to better make the animal withstand strong currents (Wilfarth 1949a, p. 82 – 83). The general feeding mode of hadrosaurines he imagines as walking bipedally through shallow water and feeding, from below, on drifting plants on the water’s surface.

Fig. 7: Wilfarth's supposed evolution of the hadrosaur trunk. Beginning with forward-facing, extendable nostrils in Claosaurus, pointing backwards in Kritosaurus, becoming a large, fleshy structure in lambeosaurines, before then ossifiying in Parasaurolophus. As the description indicates, Wilfarth was unsure where the fleshy nostrils would have actually connected with the inner skull, speculating if a secondary opening atop the skull was a sort of new naris (Source: Wilfarth 1949a, p. 85).

With the water constantly splashing against the nose, the trunk eventually began facing backwards and started to retract, as seen in supposed transitional forms like Kritosaurus. This eventually resulted in the evolution of the “Helmettrunkers” (Helmrüssler), the Lambeosaurinae. In Wilfarth’s view, the headcrest on animals like Corythosaurus was the basis for fleshy trunk extending from the top of the head, allowing the animal to feed on plants and breathe in water even in a crouched-over position. Wilfarth remains ambiguous on where he thinks the connection of the fleshy nostrils into the skull would have run. In his sketches he seems to prefer a secondary skull opening in the crest he labelled 5b, but as he cannot find it in every hadrosaur skull, he is also open to the trunk having been connected to the original nares at the front of the snout (Wilfarth 1949a, p. 85), which would seem much more sensible if you asked me.

Fig. 8: Corythosaurus in breathing and feeding position (Source: Wilfarth 1949a, p. 78).

The end-point of this evolution were then eventually forms like Parasaurolophus. The idea that Parasaurolophus’ famous headcrest acted as a form of snorkel is not actually unique to Wilfarth. Alfred Sherwood Romer, yes that Romer, in his famous textbook on vertebrate paleontology, already had this idea in 1933. Though without any fleshy bits, instead thinking there must have been an actual hole at the end of the crest. Wilfarth’s original interpretation was ironically very different. In his 1938 paper on hadrosaurs, he originally speculated that the whole headcrest of this dinosaur was connected by muscles and ligaments to the neck and shoulders, acting similarly to the hinge-skulls of the ceratopsians. This was of course an extreme interpretation he was strongly criticized for (Wiman 1942), though it is interesting from the perspective of the modern discussions on the placement of the nuchal ligaments, such as in Bertozzo et al. 2020. Shortly after publication, Wilfarth gave this idea up (Wiman 1942), so I guess you at least cannot say that he was not receptive to criticism.

Fig. 9: Parasaurolophus, able to breathe and feed at the same time thanks to its crest (Source: Wilfarth 1949a, p. 84).

Instead, again following the idea that dinosaurs preferred replacing muscle-work with bone construction, the crest of Parasaurolophus actually represents an ossification of the breathing trunk that in forms like Corythosaurus was still made out of flesh and muscle (Wilfarth 1949a, p. 82 – 83). This made it the most specialized and efficient of the hadrosaurs, able to feed in shallow water, even on all fours, while being able to breathe at the same time. But even that did not save it from extinction.

The Great Dying

Wilfarth’s assessment of the End-Cretaceous mass extinction is as brief as it is succinct and his evaluation of different hypotheses reads as surprisingly modern, systematically going through all the ideas that were popular during his time before coming to his own conclusions. Funny for us today is that he labels it the Great Dying, which is now a term more reserved for the End-Permian mass extinction.

First Wilfarth addresses the idea that competition with mammals wiped out the dinosaurs, something proposed, for example, by Baron Franz Nopsca. He, quite correctly, counters this with the remark that dinosaurs were not the only animals that went extinct and that mammals could have hardly also been competing with the marine reptiles and pterosaurs.

Next is the idea that disease could have been the main cause, an idea first championed by Roy Lee Moodie and long after even by Robert Bakker. Here again, Wilfarth notes that epidemics could have hardly wiped out both the dinosaurs and also all the other giant reptiles, as well as so many invertebrates like ammonites.

Third is the idea of “racial senility” or “phylogeronty”. This was an idea very popular in the early 20th century, endorsed by some leading paleontologists like Richard Swann Lull and Arthur Smith Woodward, who claimed that whole lineages could “age” like a single person, meaning that the longer they existed the more their genome would deteriorate and grow out of control, leading to the evolution of maladaptive features and eventually extinction (Benton 1990). Proponents of this idea often liked to point at the odd and excessive features on the skulls of dinosaurs, like the hadrosaur headcrests or the ceratopsian neckfrills, or at the strange shell-shapes of the heteromorph ammonites, as evidence that the genetics of these animals had gone awry with age, like the Ottomans and Byzantines growing more decadent as their empire neared its end (Bakker 1986, p. 52). That this idea was once so popular, and that it still subconsciously lingered on in popular imaginings of prehistory long after, is pretty baffling, as it falls apart when you think about it for just a minute. All life on Earth shares the same common ancestor, so at any point in time all lifeforms also share the same evolutionary age of their genes. Wilfarth, who we have seen views all the odd features of dinosaur anatomy as beneficial adaptations for their lifestyle, points exactly this out when he criticizes the concept of racial senility and asks why the dinosaurs should have grown senile, but crocodiles, snakes, lizards and turtles still have not. Adding to that: “Should this senility have extended to the ammonites and so on? Lingula, a brachiopod, has from the Cambrian until today not grown senile” (Wilfarth 1949a, p. 87, translated by me).

The fourth idea he addresses is that other animals ate all the dinosaur eggs. Here he correctly points out that it would be highly unusual for the number of egg-eaters to increase so suddenly and also the obvious fact that many of the marine reptiles did not even lay eggs but gave live birth.

Fifth is the idea that a sudden drop in global temperatures could have led to the extinction of the various cold-blooded animals, which was an idea that would prove to be popular all the way into the 1970s (Benton 1990). Here, Wilfarth brings up the pretty valid point that the early Cenozoic was still just as tropical as the Mesozoic (Wilfarth 1949a, p. 87) and that by the same logic there should also no longer be any snakes and crocodiles today. Indeed, today we know that the Palaeocene and Eocene were actually even warmer than the Cretaceous.

Last, he comes to the also popular idea that orogenies were the main cause, the many new mountain chains building up in the Late Cretaceous draining the swamps that the dinosaurs supposedly inhabited. Again, he points out that many animals went extinct that obviously were not swamp-dwellers, but funnily enough he also points out a very valid inconsistency, which is that many of the proponents of this idea did not view certain dinosaur groups, like the coelurosaurs and carnosaurs, as swamp-dwellers (Wilfarth 1949a, p. 87).

 Thus, Wilfarth comes to the conclusion that you probably could have imagined. By the beginning of the Cenozoic, the Moon had drifted away so far from the Earth that it led to an end of the Great Tides and therefore also the unique intertidal ecosystem that used to cover a large part of the continents. Thus, it came to a collapse of the shallow-water planktonic community, followed by an extinction of invertebrates and in turn marine reptiles and, of course, the dinosaurs (Wilfarth 1949a, p. 87 – 88), which were then succeeded by the fully terrestrial fauna of the Cenozoic. Wilfarth ends his book poetically: “The Great Tides formed the dinosaurs, with the Great Tides they also faded.” (Wilfarth 1949a, p. 88).

Fig. 10: How you supposedly get a Parasaurolophus out of a Corythosaurus, with a speculative transitional form (Source: Wilfarth 1949a, p. 80).

Of course, the base assumption, that dinosaurs were intertidal-dwellers, is wrong and today we definitely know that a catastrophic asteroid impact spelled doom for the Mesozoic, but on its own, Wilfarth’s conclusion is quite sober, especially compared to the other ideas of the time. Why? Because, normally, the biggest driver for the extinction of species is habitat loss, a fact that is more relevant today than ever. While I think human activity certainly was a factor in the extinction of the mammoth, what is often overlooked is that the entire biome these animals inhabited, the mammoth steppe, is also almost completely gone due to climatic and ecological changes.

On another note, it is interesting that Wilfarth here unknowingly tried to resurrect arguably the first hypothesis for the K-Pg mass extinction. Georges Cuvier (1825) was one of the first naturalists of the early 19th century who recognized a major faunal change between the Secondary and Tertiary ages. However, dinosaurs were barely known by that time and so most of the lifeforms known to him from the Age of Reptiles were plesiosaurs, crocodiles, ichthyosaurs and turtles. So he thought that during this period most life was still aquatic or amphibious and went extinct due to a sudden drop in sea levels, with the mammals of the Tertiary Age being Earth’s first true dry-land fauna. How Cuvier and his ilk imagined their alien Age of Reptiles would be a topic for a whole other series of blogposts, though Mario Lanzas has given a good impression.

Assessing Wilfarth

This ends Wilfarth’s vision of the Mesozoic and the lifestyle of dinosaurs. There are obviously some details I would have liked to know more from him. Like, what was going on on dry land during this time? Is this where the first mammals and birds were biding their time until the fall of the Great Tides? How much more extreme were conditions during the Permian? How exactly do pterosaurs and marine reptiles fit into the Great Tides? Except for an image description there is also a sore lack of any stratigraphical arguments from dinosaur-bearing sites that Wilfarth could have addressed.

But in the end how do we want to evaluate Martin Wilfarth? Obviously, he was quite unorthodox and eccentric and his insistence on the validity of his hypothesis and how it supposedly answers so many questions all at once bears all the hallmarks that we today associate with pseudoscience. And most importantly: He was wrong. At the same time, his hypothesis was based on some true uncertainties of his time and some of the things he used as arguments, such as the supposed aquatic adaptations in sauropods and hadrosaurs, were really not all that different from what leading contemporaneous experts were already claiming. He just dared to go a few steps farther down the aquatic paradigm.

Fig. 11: Wilfarth pointing out the unusually vacuous bony nostrils of Iguanodon and Edmontosaurus, speculating that these must have housed large, unusual, fleshy noses with special functions (Source: Wilfarth 1949a, p. 73).

What I hope I was able to show is that there are also things that can be appreciated about Wilfarth’s body of work. He was one of the few scientists in the 1940s who tried to specialize in dinosaurs, at a time when most vertebrate paleontologists were decidedly neglectful of the group. In a recovering post-war Germany, mind you. In the process, he made some points, which, even if they were ignored by his contemporaries, would prove quite prophetic for later dinosaur research. In Wilfarth’s work we find such prescient ideas, unpopular for his time but very familiar today:

  • Dinosaurs were successful, complex animals.
  • Dinosaur anatomy was sophisticated and its oddities were efficient adaptations to their environment and lifestyle, not degenerate features brought about by “racial senility”.
  • Dinosaurs did not go extinct due to incompetence or due to being inferior to mammals.
  • Dinosaurs are monophyletic.
  • Birds descend from dinosaurs.
  • Dinosaur young changed lifestyle and ecology as they grew up.
  • Dinosaurs had stiff backs and balancing tails that worked like a seesaw.
  • Plateosaurus was an obligate biped.
  • Sauropods held their spine up in a slight concave curve and regularly reared up onto their hindlegs.
  • The large nares on sauropod, ceratopsian and hadrosaur skulls were likely supporting elaborate soft-tissue structures.
  • Small theropods were fast and agile.
  • Large theropods were active hunters.
  • Stegosaurs were competently adapted animals, not mistakes of nature.
  • The spikes on thagomizers faced sideways.
  • The horns on ceratopsian skulls were formidable defensive weapons.
  • Hadrosaur dentition was complex and just as efficient as that of herbivorous mammals.

It is true that a broken clock strikes right twice a day, but this is a bit more than that, don’t you think? While Wilfarth’s framework as a whole was wrong, it is nonetheless fascinating that the lens with which he viewed the dinosaur skeleton still was able to make him see some features that much later researchers would discover, while being ignored by his contemporaries. And does that not say something about the philosophy of science? In his famous work The Structure of Scientific Revolutions, Thomas Kuhn argued that the worldview a scientist operates in is more important than the data he works with, as only with a change in worldview can he sometimes see things he would not have seen otherwise (some interpreters of Kuhn have gone as far as arguing that he claimed that when the worldview changes, it is the world itself that actually changes). Wilfarth pointing out features that other contemporaries seem to have ignored, such as the highly unusual noses of dinosaurs, would seem to support this. But another point Kuhn argued is that, due to the crucial unintelligibility or incommensurability between worldviews (“planet” is a very different term for a geocentrist than it is for a heliocentrist), scientists will ultimately diverge and break away from each other with each revolution, producing not a progress towards what we would call truth, but a progress away from a common starting point, akin to darwinistic speciation. If all sciences were nearing truth, he argued, we would see them converge into a single grand unified theory, instead of what we actually see: Each discipline splitting up into more and more sub-disciplines, some of which incompatible with each other (such as quantum physics vs. relativity theory).

Wilfarth’s tidal paradigm is incompatible with the warmblooded paradigm of the thinkers of the Dinosaur Renaissance. But not necessarily incommensurable, as the word “dinosaur” would have meant pretty much the same to a Wilfarth and a Bob Bakker, but not to an Edwin Colbert. And they both also made common observations that the researchers of the older swamp paradigm did not. Is that then not a notable convergence? Like pterosaurs and birds both evolving wings, just in different configurations, due to adapting to the same constraints of aerodynamics? Maybe, contra Kuhn, worldviews can convergently adapt to the same underlying constraints, some adapting better to reality than others, implying that there is some sort of truth that can be progressed towards. Or maybe I am just waxing philosophical again because I don't know how to end this section. Here's a meme:

Fig. 12: And so the cruel king stands there among the tides, enjoying the crocodile cacophony or perhaps just the aquatic ambiance, awaiting the arrival of his gangplank galleon

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Related articles:

Further Reading:

References:

  • Benton, Michael: Scientific Methodologies in Collision. The History of the Study of the Extinction of the Dinosaurs, in: Evolutionary Biology, 24, 1990, p. 371-400.
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  • Desmond, Adrian: The Hot-Blooded Dinosaurs. A revolution in Paleontology, London 1975.
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  • Ekman, Martin: A Concise History of the Theories of the Tides, Precession-Nutation and Polar Motion (From Antiquity to 1950), in: National Land Survey. Division of Geodetic Research, S-801, 1993, p. 585 – 617.
  • Fulda, Ernst: Die Entstehung der Zechsteinsalze nach der Grossflutenhypothese von Martin Wilfarth, in: Kali, 32, 1937a.
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  • Vidal, D.; Mocho, P.; Aberasturi, A.; Sanz, J. L.; Ortega, F.: High browsing skeletal adaptations in Spinophorosaurus reveal an evolutionary innovation in sauropod dinosaurs, in: Scientific Reports, 10, 2020.
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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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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.
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