Habitat preferences of dinosaurs from the Ibero-Armorican Island during the Late Cretaceous

The habitat preferences of different members within fossil communities are an important aspect of understanding ancient ecosystems. The preferences of different biological groups help researchers infer their diets, living spaces, and interactions with other organisms sharing the same habitat.

However, due to the rarity of fossils, preservation and sampling biases make it very difficult to accurately estimate the habitat preferences of ancient organisms. For example, the Late Cretaceous dinosaur fauna of North America is often considered to be well sampled and extensively studied. Nevertheless, the issue of determining the paleolatitude and paleoenvironmental context of these fossils was not resolved until around 2019. Even so, the habitat preferences inferred from North American dinosaur faunas have often been treated as representative of dinosaurs globally, and have even been used as evidence suggesting a global decline in dinosaur diversity during the Late Cretaceous. Subsequent studies conducted on a global scale, however, have produced results that conflict with this interpretation.

Building on this issue, one study focused on the island environments of Europe during the Cretaceous, when rising sea levels formed an archipelago. By comparing these island ecosystems with continental environments, researchers examined whether dinosaur habitat preferences were influenced by the size of available land areas.

The Ibero-Armorican Island was located in what is now southern France, Spain, and Portugal, and during the Late Cretaceous it was the largest island in the European archipelago. This region contains abundant dinosaur fossils. From the final two stages of the Cretaceous—the Campanian and the Maastrichtian—at least several hundred fossils have been discovered. These fossils occur in a variety of depositional environments. Through detailed geological, stratigraphic, and paleontological analyses conducted in the region, researchers were able to integrate fossil data to reconstruct the composition of local dinosaur communities and the habitat preferences of different dinosaur groups.

Dinosaurs of the Ibero-Armorican Island (Image source：NSaurio，採用 CC BY-SA 4.0 授權）

In this study, a total of 747 fossil records were analyzed, including skeletal fossils, egg fossils, and trace fossils, originating from 28 different geological formations. These fossils represent six dinosaur groups: Titanosauria, Rhabdodontidae, Hadrosauroidea, Nodosauridae, Maniraptora, and Abelisauroidea. The depositional environments of the Ibero-Armorican domain were divided into two categories: coastal environments and inland lowlands. Based on fossil occurrences and paleoenvironmental information, researchers recorded two types of values: first, the number of occurrences of each taxonomic group within a particular environment; and second, the estimated number of individual organisms within that environment based on skeletal fossils.

The results show that, with the exception of Abelisauroidea, the other five groups displayed a preference for inland lowland environments. The ratios of coastal to inland occurrences are as follows: Titanosauria and Rhabdodontidae, 1:4; Hadrosauroidea, 3:7; Nodosauridae, 1:9; Maniraptora, 2:3; and Abelisauroidea, 1:1.

Data for Titanosauria indicate that if only skeletal fossils are considered, titanosaurs appear to prefer coastal environments. However, when all fossil evidence is taken into account, their preference shifts toward inland lowlands. This may be because dense vegetation in lowland environments provided better concealment for juveniles and abundant food resources, making lowlands suitable nesting areas for titanosaurs. This interpretation is broadly consistent with findings from other regions. In contrast, trace fossils of titanosaurs are more commonly found in coastal areas elsewhere, which may reflect taphonomic bias.

The results for Hadrosauroidea conflict with findings from other regions. In addition, Rhabdodontidae show an even stronger restriction to inland environments than hadrosauroids and occur in lower numbers. Although both groups coexisted for a period—indicating ecological niche differentiation—rhabdodontids disappeared completely by the end of the Cretaceous. This extinction may be related to their more restricted distribution and strong competition from hadrosauroids.

The results for Nodosauridae conflict with some global studies but agree with research from other parts of Europe. Nodosaurids appear to be the group with the strongest preference for lowland environments. However, it should be noted that nodosaurids also have the smallest sample size among the groups studied, and their results may therefore be influenced by sampling and preservation biases.

Among theropod dinosaurs, Maniraptora show a stronger preference for lowland environments, whereas Abelisauroidea do not. Maniraptoran groups such as Dromaeosauridae and Troodontidae are also significantly more abundant than abelisaurids. The only theropod nest fossil discovered in the study occurs in a coastal environment. This may indicate a nesting preference similar to that proposed for titanosaurs. However, a single specimen is clearly insufficient to draw firm conclusions. This scarcity may reflect the higher trophic level of theropods, which naturally occur in lower numbers. Additionally, unlike many other dinosaur groups, theropods did not cover their nests, making them more susceptible to destruction.

Habitat preference ratios of the six dinosaur groups from the Ibero-Armorican Island (Image source：Vázquez López, B. J et al. (2025).，採用 CC BY 4.0 授權）

Overall, among the six dinosaur groups studied from the Ibero-Armorican Island, all except Abelisauroidea show a clear preference for inland lowland environments. These results partly agree with, and partly contradict, findings from other regions. Furthermore, the extinction of Rhabdodontidae may have been related to competition with Hadrosauroidea, an issue that warrants further investigation. While the conclusions of this study provide valuable insights, they may still be affected by preservation and sampling biases. Additional fossil discoveries and further research will be necessary to test these interpretations.

（Author: Bai Leng）

Reference:

Vázquez López, B. J., Sellés, A., Prieto-Márquez, A., Vila, B. (2025). Habitat preference of the dinosaurs from the Ibero-Armorican domain (Upper Cretaceous, south-western Europe). Swiss Journal of Palaeontology.