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On “Campilognathoidids”

August 10, 2013

Necrophiliac Caviramus homosexuality by Elijah Shandseight (aka Smnt2000).

Necrophiliac Caviramus homosexuality by Elijah Shandseight (aka Smnt2000).



Previously, I have talked about Campylognathoides
, a very weird and large non-pterodactyloid pterosaur from the Toarcian Jurassic of Europe. I was indeed ignorant of severel unique traits like it’s massive, very powerful wings appearently similar to those of falcons and maybe indicative of a similar flight style. More importantly, I neglected the fact that this animal might have had close relatives in some of the strangest lineages of pterosaurs to have ever existed.

The curved jaw ones

When not considered the only member of it’s kind, Campylognathoides is occasionally shoved in with Eudimorphodon, Caviramus, Carniadactylus and Austriadactylus in the clade Campylognathidae/oidea. This decision is not widely agreed upon and indeed these animals have been placed at numerous grades in Pterosauria, particularly Campylognathoides proper and Eudimorphodon (see the Novialoidea hypothesis, for instance). Nonetheless, these pterosaurs generally share some anatomical traits, like oversized, posteriorly flared sterna, large temporal openings, elevated coronoid processes and, uniquely among pterosaurs, molariforme teeth (except for Campylognathoides), which implies a common ancestry. However, it would not be surprisingly if these traits evolved independently among several pterosaurs. Thus, for the sake of safety, it’s best to use the terms between brachets.

If a common pterosaur lineage, “Campylognathoidea/idae” was the first major pterosaur radiation: most members of the group are known from the late Triassic from the Norian and Rhaetian periods, composing most of the know Triassic pterosaur diversity. They survived the cataclysms at the end of the Triassic, and lasted up to the Toarcian, 80 million years later, before being systematically replaced by rhamphorhynchids as the dominant pterosaurs (or not). Notably, a great part of their temporal range is actually something of a Lazarus situation: most of the described specimens are from the Norian, with Campylognathoides being almost alone in the mid-Jurassic, with some scat remains here and there. Of course, since the Early Jurassic is dirt poor in terms of pterosaur diversity, this can hardly be surprising, but still an 80 million year almost-gap is impressive.

While little work has been done on the inner phylogeny of the group, Austriadactylus and Caviramus share several traits, such as their unusually slender wings (see below) and headcrests, while Campylognathoides, despiste being otherwise more “typical”, is both sufficiently displaced in time and with enough oddness of it’s own – such as it’s unusually large [for a pterosaur] fibula, that reaches down to the ankle – to possibly belong to another singular branch of the clade’s tree. Thus, the group is probably composed of two or three branches: “austriadactyliformes” and “eudimorphodontiformes“, with Campylognathoides being either part of the latter or an independent lineage. If “Campylognathoidea/idae” is paraphyletic or polyphyletic, research on how these clades fit within Pterosauria would then take place.

First great aeronauts

“Campylognathoidids” have the distinction of being the first pterosaurs to have truly become specialised for an aerial lifestyle: Preondactylus and similar things were generalised flyers, while dimorphodontids were leaning towards Galliforme-like terrestriality, both to be expected from basal pterosaurs*. “Campylognathoidids”, by contrast, bear large wings and well developed sterna, no doubt indicative of aerial prowess and spending a great portion of their time flying.

*Anurognathids, some of the most powerful flyers among pterosaurs, might have also evolved in the Triassic given their rather basal features, though since we know little about their evolution we will ignore them.

“Campylognathoidid” wings come in two flavours: the “robust wings” seen in most of the clade – most extreme in Campylognathoides – and the “slender wings” seen in Caviramus and Austriadactylus. The “robust wings” bear similar arm element, pteroid and metacarpal porportions to those of Preondactylus, but they are much more robust and larger, the humerus in particular possessing very large dectopectoral crests and shafts much thicker than those of other early pterosaurs; such extreme anatomy is only comparable to that of ornithocheiroids. “Slender wings”, bu contrast, go in the exact opposite direction, bearing rather thin and long arm bone elements, with the humerus being so slender in Caviramus that it’s 20 times longer than it is wide, and is unique among pterosaurs for being thinner than the femur. In both forms, the wing finger is consistently very long, composing as much as 79% of the wing length, a reccord among pterosaurs, with rhamphorhynchine rhamphorhynchids at 67% and ornithocheirids and pteranodontids at 60%. No wonder, thus, that earlier studies (such as Rayner and Hazlehurst 2013) thought that these animals occupied an “extreme flight niche unseen in modern flyers”. The two wing forms seem to correlate to two types of flight style, both witnessed in species that spend most of their time in the air:

– “Robust wings” have been compared to those of falcons and molossid bats, having long wings with emphasis on the long, narrow dystal region, wider medial region and extremely robust wing bones and muscles. These animals are specialised for rapid powered flight with very strong and quick flight strokes, achieving high speeds and incredible manouverability.

– “Slender wings” are almost certainly correlated to extensive soaring flight, with minimal flight strokes. They are in particular similar to those of seabirds, which also bear rather slender arm bone elements and exceptionally long arms, though for the moment adaptations like “locks” in the articulations – adaptations seen in some seabirds and ornithocheiroids pterosaurs – are so far unknown. Caviramus at least seems to have long hindlimbs, implicating that the wing could have been significantly braod and thus useful for soaring in inland settings, though it could also simply be an indication of terrestrial adaptations (though see below).

Both models implicate that these animals spend most of their lives in the air, being the first vertebrates to have truly specialised for long flights and perhaps even resting on the air. The “robust winged” “campylognathoidids” certainly could take off both quickly and frequently, the robust wing musculature and bones being an example exaptation for animals relying on powerful quadrupedal launch. The “slender winged” model, by contrast, bears defenitely weaker arm bone elements, and may even pose issues as the humerus is thinner than the femur, the opposite condition for animals vaulting like pterosaurs and bats do – most likely they could still launch quadrupedally, though how frequently and if it needed specific modifications is still not researched.

In regards to terrestrial locomotion, Campylognathoides is rather relevant due to it’s preserved pelvis. With a ventrally fused pelvic construction, it could walk in an erect posture like other pterosaurs. “Campylognathoidids” would have probably been fairly competent walkers, particularly Caviramus with it’s long, gracile limbs, though Eudimorphodon has been interpreted as having a glenoid that would have prevented the forelimb from rotating under the body, offering it a sprawling posture in the forelimbs; suffice to say, this is controversial. At least Eudimorphodon and Carniadactylus could probably climb, having antungal sesamoids. Campylognathoides has a fibula that is rather long for a pterosaur, almost touching the ankle; whereas this was an atavism, or held a function in terrestrial locomotion, remains unknown.

First crests

Austriadactylus by Julio Lacerda, here with a rather conservative headcrest size.

Austriadactylus by Julio Lacerda, here with a rather conservative headcrest size.

“Campylognathoidids” are also the first pterosaurs with crests, with Caviramus and Austriadactylus bearing bony crests on their snouts: in the former, it is roughly triangular and projects anterodorsally from the snout tip, while in the latter it runs across the dorsal edge of the skull, forming a semi-rectangular look as it becomes taller near the end of the snout. In both forms, the crests bear fibrous bone, similar to that in the crests of of scaphognathines wukongopterids, ctenochasmatoids, dsungaripteroids and tapejarids, suggesting that they supported larger keratinous crests, unfortunately so far unpreserved. Other “campylognathoidids” might have also beared similar crests, as pterosaurs like Pterodactylus indicate that keratinous crests may form regardless of there being a bony crest underneath. Should it be a feature unique to “austriadactyliformes”, however, it either implies that they are an independent pterosaur clade closer to crest-bearing forms, or a remarkable case of convergent evolution; with both rhamphorhynchines and ornithocheiroids seemingly lacking keratinous crests, it’s entirely possible that they evolved at least four independent times among pterosaurs.

With so few specimens, it’s unclear if any sexual dimorphism was present, though the crests, as with those of most pterosaurs, almost certainly served in interspecific competition, bearing no observable aerodynamic use.

Feeding strategies

Eudimorphodon skull, showcasing the odd adaptations for mastication like it's molariformes, it's unfused mandibular symphysis, it's massive temporal fenestrae.

Eudimorphodon skull, showcasing the odd adaptations for mastication like it’s molariformes, it’s unfused mandibular symphysis, it’s massive temporal fenestrae.

“Campylognathoidids”, as usual, have historically been depicted as fish eaters. This is not an entirely inaccurate depiction for Eudimorphodon, which has been found with scales belonging to Parapholidophorus, and was probably more than capable of capturing fish on the wing. Howwever, while Eudimorphodon might have been a dedicated piscivore – and even then, this is pure speculation, as other decidely less piscivorous flying sauropsids, like Microraptor, have also been found with fish remains, implying opportunistic shore scavenging instead of dedicated piscivory -, “campylognathoidids” probably weren’t oriented towards piscivory above any other lifestyle.

For starters, “campylognathoidids” were capable of a trick both uneeded for piscivory and in fact generally degraded or outright lost in dedicated piscivores: mastication. Uniquely among pterosaurs*, “campylognathoidids” developed molariforme teeth, which were multicuspid – as much as five cusps in individual teeth -, tightly packed as to create a cutting edge, with wrinkled enamel and with perfect occlusion. This in particular seems to have been taken to an extreme in Caviramus, where the molariformes are so tightly packed that they offset and overlap, and in Eudimorphodon, which bears an unfused mandibular symphysis, allowing a wider range of jaw motion, including lateral chewing. Tooth-on-tooth and possible tooth-on-food abrasion have been detected, to the point that wearing off until the crowns are stunted is well present, indicating extensive mastication; most of it is located at the back of the jaws, where the biting force would have been strongest, as predicted for a masticating animal. Likewise, the unusually massive “campylognathoidid” temporal fenestrae and coronoid processes indicate the presence of very large jaw muscles, perhaps of the largest proportionally to any pterosaur. Austriadactylus and Eudimorphodon have a strange pair of large, fang-like teeth in the upper jaw amidst the molariformes, a situation also seen in Preondactylus, clearly indicating it to be a basal characteristic among pterosaurs. The function of these “molar fangs” is unknown, but may have aided in piercing large prey.

*Dsungaripterids show adaptations similar to those of masticators, though they are thought to have just crushed food, rather than actually chewing it.

Mastication generally evolves in endothermic tetrapods, as means to grind food up to make digestion as fast and easy as possible. It generally either occurs in dedicated herbivores, or highly metabolic opportunists, particularly when dealing with insect carapaces. “Campylognathoidids”, lacking obvious adaptations for herbivory, being flying vertebrates and almost certainly basally small as the smallest forms have wingspans of 70 cm, almost certainly fit the latter category, and mastication would presumably have evolved in order to provide for the high metabolic demands of powered flight at a faster scale.

Uniquely among “campylognathoidids”, Campylognathoides lacks molariforme teeth, it’s dentition being fairly typical for a pterosaur: unserrated, single-cusped, with smooth enamel and occuring widely spaced in much smaller numbers. Being among the last “campylognathoidids” with a large temporal gap between clearly preserved “campylognathoidid” teeth, it’s unknown if Campylognathoides is unusual for the standards of the clade, or if “campylognathoidids” might have gradually lost mastication, maybe due to the pressures of an aerial lifestyle and maybe competitive pressure from other pterosaur groups like rhamphorhynchids, whose simpler dentition would have saved weight. It is also entirely possible that masticating “campylognathoidids” disappeared in the Triassic extinctions, and only the non-masticating forms surviving into the Jurassic. The fact that no other group of pterosaur would have developed mastication seems to imply that the competitive pressures to remain lightweight might have been a factor, though it could simply not have occured for no particular reason.

Known “campylognathoidids” appear to show a fair variety of foraging strategies. Carniadactylus, with it’s small size, piercing molariformes and yet little evidence of extensive abrasion, has been thought to be an insectivore. With “robust wings”, it may have been able to hunt aerial insects, a feat earlier pterosaurs would have been too clumsy on the air to practise, and further enhanced in another type of pterosaur, the anurognathids, hough regardless it might have fed mostly on terrestrial invertebrates anyways. Eudimorphodon, being larger and exhibiting extensive tooth wear, probably had a more diverse diet, feeding on vertebrates. It’s sprawling posture might imply that it foraged primarily on the wing, which could explain it’s so far seemingly piscivorous diet, hunting fish from the air; in particular, the “molar fangs” could have been used to hold slippery prey, being located in an area where the biting force was higher and being large enough to pierce their prey. Nonetheless, it might have had a more diverse diet than that, as again extensive mastication and piscivory don’t seem to mix much. Like Campylognathoides below, it might have been capable of hawking other pterosaurs in the air, and maybe also terrestrial prey in the manner of a predatory bat.

Considerably larger and with “slender wings”, Austriadactylus seems to have been a terrestrial forager, being seemingly less capable of hunting on the wing, preying on tetrapods and use it’s “molar fangs” to break the spines of small sauropsids and mammals. Caviramus seems to have taken terrestrial foraging further, however: with it’s long, almost stilk-like limbs and it’s more complex and numerous molariformes, it was almost certainly a terrestrial omnivore, feeding on invertebrates, tetrapods and plant matter would would have been triturated by it’s multicuspid teeth. It’s gracile arms and legs might have made it one of the best walkers and runners among non-pterodactyloid pterosaurs, and based on it’s slender limb elements I’m tempted to compare it to maned wolves and seriemas. Rather importantly, Caviramus bears deep pits at the mandibular tip (Stecher 2008), which may either support a small beak, or, more plausibly, some form of sensory tissues, or maybe even the indication of lips!

Campylognathoides has been previously described by me as a sort of azhdarchid analogue, based off Padian (2009), an idea that relies on it’s jaws and teeth, similar to those of other terrestrially foraging non-pterodactyloid pterosaurs such as scaphognathines, unlike the “fish grabs” of piscivorous pterosaurs. Indeed, Campylognathoides does not seem to bear adaptations for piscivory, at least specifically, and another pterosaur, the rhamphorhynchid Dorygnathus, seems to have been the main piscivore in their ecosystem, leaving Eudimorphodon as the only possibly piscivory inclined “campylognathoidid”. Instead, Campylognathoides might have been more of a terrestrial animal, as it’s long fibula might have aided in strengthening the hindlimbs and it’s powerful arms would allow quick launching. However, with it’s extensive aerial adaptations and very large wings, Campylognathoides might have also been capable of hawking other pterosaurs in the air, making it the pterosaurian version of a falcon, and maybe even strike slow moving terrestrial targets. Its large wings might also have allowed it to carry prey proportionally large to it’s body size, making it truly a pterosaur of prey.

Aside from the implication that the two Campylognathoides species might different growth stages, we have little in the way of “campylognathoidid” fossil samples to understand their growth rates or sexual dimorphism. While the described specimens are few, they do showcase that these animals were the dominant pterosaurs of the Triassic, unambiguously important to the ecosystems of the last stages of the period, and may or may not have remained the most imporant pterosaur lineage until the Toarcian.

Final thoughts

The Candeleros Formation of Argentina bears an unique case of Cenomanian non-pterodactyloid pterosaur remains(!). So far, I have read little into it, and it appears little work has been done in regards it’s apomorphies, but wouldn’t it be a shock it the already 80 million year gap between “campylognathoidid” fossils stretched even more?

REFFERENCES

– “Pterosaurs: Natural History, Evolution, Anatomy”. Mark P. Witton (2013)

– Stecher (2008)

– Padian (2009)

– Padian (1983a)

– Hazlehurst et Rayner (1992)

– Darren Naish (2008)

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