TLATOPHULOS: new hadrosaurid from MEXICO

Article by Filippo Bertozzo

The day in which a new hadrosaur is presented to the public, after a long time of study and research, is certainly a celebration. But when a new parasaurolophine is introduced, even with a skull bordering on perfection, it’s a day to remember in the annals!

This week, world paleontology was positively shaken by the publication of Tlatolophus galorum, a new hadrosaur from the Upper Campanian of Mexico. The publication is by Ramìrez-Velasco et al. on Cretaceous Research.

This dinosaur, of considerable size (an estimated total length of 12 meters, with the skull estimated at 1.79 m), was found in 2013 in the Cerro del Pueblo Formation, near Presa de San Antonio (Coahuila, northern Mexico), and consists of the aforementioned skull, some bones of the limbs and pelvis, and an almost complete vertebral series of the tail. The description now published refers only to the skull, while the other elements of the skeleton are still in the preparation and study phase.

Tlatolophus means “word crest”, referring to its comma form which, in Aztec iconography, resembles the glyph of “word”. Galorum, on the other hand, is dedicated to two local families, Garza and Lòpez: “ga” recalls Jesùs Garza Arocha who encouraged the discovery of this find, and “lorum” is dedicated to the Lòpez family for their help during the excavation and their dedication to the defense of the Mexican paleontological heritage.

Undoubtedly, the most impressive feature of this specimen is its crest, formed by the premaxillary and nasal bones, with a slight participation of the prefrontal. The crest is very reminiscent of that of Parasaurolophus, although the terminal part expands to form a sort of plate (while, we recall, in Parasaurolophus it is more tubular). The authors also point out the similarity between the shape of the nasal, elongated posteriorly and expanded in the terminal portion, to that of Tsintaosaurus, a Chinese hadrosaur that became famous in the 90s for its characteristic “pole” crest, then changed to a more circular shape. As pointed out in the study, the shape of the crest fills a morphological gap in the evolution of these structures in Lambeosaurinae (that is, that group of hadrosaurs with “empty” cranial crests, containing the passage of the respiratory tract). The nasal, in fact, lengthens but maintains a ventral position; the nasal process of the premaxillary extends beyond the orbital area (a characteristic present in the lambeosaurin tribe but later lost in Parasaurolophus and other derivative parasaurolophins), and bends anteriorly (a characteristic present in Tsintaosaurus and Amurosaurus, later lost in the derived lambeosaurins). The discovery of a crest so widened and curved like a comma, different from the tubular crests like Parasaurolophus and from the “helmeted” Corythosaurus-style ones, suggests two evolutionary scenarios: 1), the comma crests were present at the beginning of the evolution of Lambeosaurinae, or 2) this morphology was acquired independently in both Tsintaosaurus and Tlatolophus.

The discovery of a parasaurolophino in Mexico extends the geographic range of this group southward, and adds to the local hadrosaur fauna that so far consists of Magnapaulia, Velafrons and Kritosaurus. Furthermore, the phylogenetic analysis proposed in the study suggests that parasaurolophins originated in North America (contrary to the Asian origin previously proposed by other authors) from a Lambeosaur ancestor in the mid-Upper Cretaceous, eventually reaching Asia (Charonosaurus). and Europe (Blasisaurus) towards the end of the Maastrichtian.

Obviously the question does not end there. Much remains to be said in the evolution of parasaurolophins, undoubtedly among the most fascinating but also among the rarest and most mysterious hadrosaurs, but possible new future findings could help us better understand the evolution and ecology of these wonderful animals!

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