The recent description of Utetitan zellaguymondeweyae marks a significant step forward in Late Cretaceous dinosaur research. This newly recognised titanosaurian sauropod lived during the Maastrichtian fauna stage in what is now Utah. Importantly, it challenges long-held assumptions about sauropod diversity in what we now know as North America.

For many years, palaeontologists believed that Alamosaurus sanjuanensis was the only sauropod present in North America during the final few million years of the Cretaceous. This idea always raised questions. After all, sauropods elsewhere often show multiple species living side by side. A single species persisting unchanged for such a long time seemed implausible.

The fossils that led to description of Utetitan come from the North Horn Formation, which dates to the very end of the Age of Dinosaurs. Although these remains were collected decades ago, they were historically placed within the Alamosaurus taxon. At the time, comparisons were difficult. Most sauropod fossils from the southwest and northern Mexico are fragmentary. Overlapping bones are rare. In addition, it is often difficult to compare fossil skeletons as they represent individuals at different growth stages.

A life reconstruction of Utetitan zellaguymondeweyae. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Utetitan zellaguymondeweyae

Recent re-examination of the material revealed something important. The Utah fossils differ consistently from Alamosaurus fossils found in New Mexico. These distinctions are anatomical, not simply related to ontogeny or taphonomy. As a result, the Utah skeleton was designated as the holotype of a new species, Utetitan zellaguymondeweyae.

The name Utetitan honours the native Ute peoples of the region. Whereas the species name honours the author’s (Gregory S. Paul) maternal grandmother Zella Guymon Dewey (1901–2002).

The holotype includes tail vertebrae, pelvic bones, limb elements, and a distinctive osteoderm. Consequently, Utetitan is one of the most informative Late Cretaceous sauropods known from North America. Its anatomy confirms its place within the Titanosauria clade.

Many Different Titanosaurs Lived in Late Cretaceous North America

Crucially, Utetitan changes how palaeontologists view Late Cretaceous ecosystems. Evidence now suggests that multiple titanosaurs lived in southwestern North America during the Campanian and Maastrichtian faunal stages of the Late Cretaceous. Furthermore, some fossils from Texas may belong to Utetitan. Other fossils do not. Older Campanian remains cannot be confidently assigned to either Alamosaurus or Utetitan. This suggests that there are many more titanosaur genera awaiting scientific description.

These titanosaurs may even represent a short-lived regional lineage. In semi-isolation, they could have evolved separately from titanosaurs elsewhere in the world. Interestingly, new skeletal reconstructions suggest that these animals were not as massive as earlier size estimates indicated.

Scale drawing of Alamosaurus.  Recent research suggests that Alamosaurus sanjuanensis may not have been as large as previously thought.  Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

From a biogeographical perspective, Utetitan supports the idea of late sauropod migrations into North America. Changing sea levels may have opened temporary land corridors. Through these routes, titanosaurs could disperse from other continents.

Ultimately, the Utetitan zellaguymondeweyae paper shows how revisiting old fossils can transform scientific understanding.

The scientific paper: “Stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the Late Cretaceous (Campanian-Maastrichtian) of southwestern North America” by Gregory S. Paul published as an open-access paper in Geology of the Intermountain West.

For models of Alamosaurus and other titanosaurs: Dinosaur Models.

Palaeontologists have described two new species of azhdarchid pterosaurs from Mongolia’s Gobi Desert. The Gobi Desert is famous for its numerous dinosaur fossils. However, pterosaur remains are very rare in Mongolian Mesozoic deposits. Researchers writing in the academic journal “PeerJ” identified azhdarchid pterosaur fossils.

The material consists of bones from the neck, and from these specimens two new species have been erected. The fossils come from two different localities (Bayshin Tsav and Burkhant). Originally collected in the 1990s, the fossils were described in detail in 2009 (Watabe et al). Yet, at the time the pterosaurs were not named, just described as indeterminate azhdarchids.

Azhdarchid Pterosaur Fossils

Subsequently, knowledge of azhdarchid pterosaur anatomy has improved. As a result, two distinct species have been named.  In a paper published in the autumn, researchers identified diagnostic features permitting the establishment of these two new species. The paper was written by researchers from the Universidade de São Paulo (Brazil), Shihezi University (China) and Hokkaido University (Japan).

Azhdarchid pterosaur fossils lead to the naming of two new taxa. The two new Mongolian taxa are compared to two of the largest azhdarchid pterosaurs. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Gobiazhdarcho tsogtbaatari: A Medium-Sized Pterosaur

The first species is named Gobiazhdarcho tsogtbaatari. It comes from the Burkhant locality of the Bayanshiree Formation. This pterosaur had an estimated wingspan of three to three and a half metres. It has been described as a medium-sized azhdarchid, with a wingspan roughly comparable to an Andean Condor (Vultur gryphus).  Fossils associated with this taxon include an atlantoaxis (fused neck vertebrae) and other cervical bones. These show it belonged to a lineage related to giants such as Quetzalcoatlus and Arambourgiania. In evolutionary terms, Gobiazhdarcho is a basal member of this quetzalcoatlid group, bridging gaps in the fossil record.

Its name reflects both its origin and scientific heritage. “Gobi” refers to the desert where it was found. “Azhdarcho” comes from Persian for dragon. The species name honours Mongolian palaeontologist Khishigjav Tsogtbaatar.

Tsogtopteryx mongoliensis: A Small Azhdarchid Pterosaur

The second species named in the paper is Tsogtopteryx mongoliensis. This pterosaur is notably small for an azhdarchid. Its estimated wingspan was approximately two metres, making it one of the smallest members of the Azhdarchidae family.  A single, partial mid-cervical vertebra is known for this species. Despite the limited material, distinct features show it belongs to a different pterosaur lineage than Gobiazhdarcho.  It was related to Hatzegopteryx. This lineage includes robust-necked azhdarchids previously known only from Europe.

The genus name combines the Mongolian word “Tsogt” (meaning mighty hero) with the Greek word pteryx which means wing. The species name references its discovery in Mongolia.

Azhdarchids Occupied Diverse Ecological Niches

The coexistence of Gobiazhdarcho and Tsogtopteryx in the same geological formation emphasises that azhdarchids occupied diverse ecological niches. Different body sizes suggest varied foraging behaviours and diets. This pattern echoes findings from other Upper Cretaceous deposits.  This study sheds fresh light on the diversity and phylogeny of azhdarchid pterosaurs. It reinforces the reoccurring pattern of coexistence between multiple, differently-sized azhdarchid species within the same palaeoenvironment.

The scientific paper: “Azhdarchid pterosaur diversity in the Bayanshiree Formation, Upper Cretaceous of the Gobi Desert, Mongolia” by R. V. Pêgas, Xuanyu Zhou​ and Yoshitsugu Kobayashi published in PeerJ.

For pterosaur models and other prehistoric animal figures: Pterosaur Models and Prehistoric Animal Figures.