2019-11-07 01:37:00
Some 110 million years ago, at the beginning of the Cretaceous, the climate of northeastern Brazil was tropical, similar to that of today. The vegetation, among which cycads and conifers abounded, was adapted to dry environments. The region was inhabited by crocodiles, dinosaurs, turtles and a great variety of pterosaurs, among which Thalassodromeus stands out for its large size.
We only know of this species from a broken skull and some dubious fragments, but it is enough to distinguish it from other known species. The skull fragments were collected in 1983 near the Brazilian town of Santana do Cariri, in the Araripe Basin, but the new species, Thalassodromeus sethi, was not described until 2003. The generic name, Thalassodromeus, means “sea runner.” , because the authors of the description, the Brazilian paleontologists Alexander Kellner and Diogenes de Almeida Campos, found similarities between the beak and the skull of Thalassodromeus and those of the American skimmer (Rynchops niger), a bird of the coasts and rivers of America; and they proposed that the way of feeding of both species was the same. The American skimmer flies low above the surface of the water, with the tip of its lower jaw submerged to catch small fish, insects, crustaceans, and mollusks by feel. But biomechanical studies indicate that the energy required for this type of fishing would be excessive for any pterosaur weighing more than a kilo, and furthermore, the stresses that the jaws of Thalassodromeus would have suffered with this mode of feeding would have been too great. In fact, the aluminum model that was used as the beak of Thalassodromeus broke in tests. The specific name sethi alludes to the Egyptian god Set, because, according to Kellner and Almeida, the large bony crest that adorns the head of this pterosaur vaguely resembles, seen from the side, the crown of Set, one of the mitres worn by the Egyptian pharaohs. . Although other paleontologists have since pointed out that the crest is more like another Egyptian crown, that of the god Amun, adorned with two long parallel feathers. The describers of the species were not very successful with the name, but, once published, a scientific name remains. Such are the rules of zoological nomenclature.
The skull of Thalassodromeus is huge and very robust, with sharp-edged toothless jaws and strong musculature. It is one of the largest skulls among known pterosaurs, with a length of more than one meter and forty centimeters, and proportionally to body size, one of the largest of all vertebrates. It has a fusiform, aerodynamic shape, adapted for flight. The beak-shaped jaws are 65 centimeters in length; it is not clear if they were straight or the end curved up or down; the state of conservation of the fossil does not allow to determine it.
The crest extends from the end of the upper jaw backwards and upwards. It is very flat and light, with a thickness that varies between one centimeter at the base and the front, and one millimeter at the rear end, which is marked by a characteristic V-shaped indentation, which is what makes one think of the crown of Amun with its two feathers. In adults, the crest is nearly twice the length and height of the rest of the skull.
The surface of the Thalassodromeus crest bears highly visible grooves that are virtually identical to those that appear in many living animals on bones that are lined with keratin, such as the beaks of birds and the horn cores of some mammals. We can deduce that the crest of this pterosaur was also covered with a keratin sheath, so its size in life could be even larger. There is also a very deep groove on each side of the skull, which runs longitudinally along the crest, from the midpoint of the beak upwards and backwards, and which is surely the mark of the junction line of two keratin plates, as also occurs in the beak of some birds. These two plates must have been clearly distinguishable in the animal’s life, and perhaps even had different colors.
According to studies on the growth of the crest of thalassodromid pterosaurs, the group to which Thalassodromeus belongs, the upper plate is shorter in young specimens and does not cover the skull, and is separated from the longer rear plate. The rearward crest growth above the skull is quite late, and is related to sexual maturation.
Several functions have been proposed for the Thalassodromeus crest, which are not incompatible with each other. The network of blood vessels on its extensive surface indicates that it could be used for thermoregulation, to dissipate the heat produced in moments of intense activity, such as hunting and flying. But the wing membranes and air sacs that occupy the hollow bones of pterosaurs are more effective at controlling temperature than a crest. Another possible function is the exhibition, for the recognition of the members of the own species, to scare away the predators or in the nuptial parades; for this, the crest would surely be colored, and in the latter case it could be different in each sex; At the moment, as we only have one copy, we cannot know. No aerodynamic studies have been done to find out if the crest could be used in flight as a rudder, although its late development makes it unlikely that this was its primary function.
Although we only know of the skull of Thalassodromeus, it is estimated to have been as tall as a human, with a wingspan of about fifteen feet. As in other pterosaurs, its body was covered in hair-like fibers. It is assumed that, like its closest relatives, it had hind legs almost as long as its forelegs, if we do not take into account the long finger that supports the wings. This allowed him to move on the ground with ease. The most recent hypotheses suggest that, with its strong jaws, Thalassodromeus fed on land, similar to storks, and was capable of killing and devouring relatively large prey, especially if its bill was curved. A curved bone is less resistant to compression than a straight one, but much more resistant to other types of stress. So it could break more easily when hitting head-on, giving a peck, but it would have been capable of biting and holding large prey. As the state of the beak of the only fossil that we know of is not good enough to know its shape for sure, we will have to wait for more fossils to appear to elucidate the mode of feeding of this great pterosaur.
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