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Description
Reconstruction of the anterior half of the metriorhynchid Dakosaurus andiniensis from the Late Jurassic of Argentina.

Dakosaurus is one of the most famous genera of metriorhynchid crocodylomorphs, the remains of which are found in great numbers in Europe and have also been found in Mexico and Argentina. The name was given to the animal in 1856 and means "biter lizard". The type species is D. maximus. This metriorhynchid stands out among related forms with a high skull and large teeth of the ziphodont type, characteristic of many predatory reptiles.

The species depicted in the figure was mentioned in the literature back in 1985, and named in 1996. It originates from the Vaca Muerta formation in Neuquén province (Argentina). The holotype consisted of an isolated rostrum, but in 2009 two new specimens were described, including an entire skull with a jaw. Because of its size and terrible appearance, the animal was nicknamed "Godzilla". The skull of D. andiniensis is very large and extremely massive, with a short and high muzzle. The eye socket is rounded and quite large, a sclerotic ring has been preserved in it, occupying 56% of the height of the eye socket. The lower jaw is high and with a smooth, not scalloped upper edge. The teeth are very large, flattened from the sides and with serrated edges. In 2012 , the work of Young and co-authors was published (anatomypubs.onlinelibrary.wile… ), in which the wear of Dakosaurus teeth is studied - damaged crown tops and worn distal and mesial surfaces of teeth. Damage to the tips of the teeth indicates feeding with large prey, implying tearing it apart and, accordingly, contact with the bone. The wear of the sides of the crown is associated with the overlapping occlusion of the teeth, reminiscent of the teeth of modern killer whales. Small pits on the edges of the jaws also speak in favor of such a bite. The skull of D. andiniensis just shows such a closure of teeth.

Another detail is the salt glands. They are used to remove excess salt from the body when the animal drinks a lot of salt water, and are found in modern sea turtles, marine iguanas and crested crocodiles. They have also been found in metriorhynchids such as Geosaurus. In 2021, a paper was published on the anatomy of the Dakosaurus's antorbital fenestra, which presumably housed the salt gland: anatomypubs.onlinelibrary.wile… Paleontologists found that this hole has an extension (diverticulum) located under the eye socket between the jaw muscles, the movement of which could squeeze out excess salt.

Finally, Dakosaurus (although not the pictured species) has known skin impressions (palaeo-electronica.org/content… ). They indicate a wrinkled texture and the absence of scales. In addition, there is a curious detail - rounded seals and recesses have been preserved on the skin. It is assumed that these are skin parasites and traces of their vital activity, respectively.

In this work, I tried to accommodate all this data. Despite choosing the option with minimal soft tissues around the mouth, I did not make crocodilian integument on the Dakosaurus's head. Although there is some roughness on the nasal bones of the Argentine species, it is too weak to conclude that there is a strong keratinization. As a result, I came to smooth coverings that improve the streamlining.

Black ballpoint and gel ink pens and black colored pencil, 2023.

Description
Reconstruction of the anterior half of the metriorhynchid Dakosaurus andiniensis from the Late Jurassic of Argentina.

Dakosaurus is one of the most famous genera of metriorhynchid crocodylomorphs, the remains of which are found in great numbers in Europe and have also been found in Mexico and Argentina. The name was given to the animal in 1856 and means "biter lizard". The type species is D. maximus. This metriorhynchid stands out among related forms with a high skull and large teeth of the ziphodont type, characteristic of many predatory reptiles.

The species depicted in the figure was mentioned in the literature back in 1985, and named in 1996. It originates from the Vaca Muerta formation in Neuquén province (Argentina). The holotype consisted of an isolated rostrum, but in 2009 two new specimens were described, including an entire skull with a jaw. Because of its size and terrible appearance, the animal was nicknamed "Godzilla". The skull of D. andiniensis is very large and extremely massive, with a short and high muzzle. The eye socket is rounded and quite large, a sclerotic ring has been preserved in it, occupying 56% of the height of the eye socket. The lower jaw is high and with a smooth, not scalloped upper edge. The teeth are very large, flattened from the sides and with serrated edges. In 2012 , the work of Young and co-authors was published (anatomypubs.onlinelibrary.wile… ), in which the wear of Dakosaurus teeth is studied - damaged crown tops and worn distal and mesial surfaces of teeth. Damage to the tips of the teeth indicates feeding with large prey, implying tearing it apart and, accordingly, contact with the bone. The wear of the sides of the crown is associated with the overlapping occlusion of the teeth, reminiscent of the teeth of modern killer whales. Small pits on the edges of the jaws also speak in favor of such a bite. The skull of D. andiniensis just shows such a closure of teeth.

Another detail is the salt glands. They are used to remove excess salt from the body when the animal drinks a lot of salt water, and are found in modern sea turtles, marine iguanas and crested crocodiles. They have also been found in metriorhynchids such as Geosaurus. In 2021, a paper was published on the anatomy of the Dakosaurus's antorbital fenestra, which presumably housed the salt gland: anatomypubs.onlinelibrary.wile… Paleontologists found that this hole has an extension (diverticulum) located under the eye socket between the jaw muscles, the movement of which could squeeze out excess salt.

Finally, Dakosaurus (although not the pictured species) has known skin impressions (palaeo-electronica.org/content… ). They indicate a wrinkled texture and the absence of scales. In addition, there is a curious detail - rounded seals and recesses have been preserved on the skin. It is assumed that these are skin parasites and traces of their vital activity, respectively.

In this work, I tried to accommodate all this data. Despite choosing the option with minimal soft tissues around the mouth, I did not make crocodilian integument on the Dakosaurus's head. Although there is some roughness on the nasal bones of the Argentine species, it is too weak to conclude that there is a strong keratinization. As a result, I came to smooth coverings that improve the streamlining.

Black ballpoint and gel ink pens and black colored pencil, 2023.