Cariocecus bocagei

Lore & Background

The partial skull of Cariocecus was discovered in 2016 by Pedro Marrecas in a limestone outcrop of the Papo Seco Formation, 200 meters from the 'Praia do Areia do Mastro' locality on the Setúbal Peninsula. The specimen was prepared at the Royal Belgian Institute of Natural Sciences in 2024 and μCT-scanned before being accessioned in Portugal. In 2025, Filippo Bertozzo and colleagues named and described the species, establishing it as the first iguanodontian skull from Portugal, as previous Portuguese iguanodontians (Draconyx, Eousdryosaurus, Hesperonyx) were known only from postcranial remains.

The skull shows several unusual traits. The maxilla and jugal are completely fused, unlike all other ornithopods, possibly allowing the animal to chew tougher materials. A large bony brow (supraorbital) projected low over the eye, likely protecting it from damage and sun glare, giving an 'eagle-eyed' appearance. The skull also lacks a nasal crest, unlike some relatives. Based on incomplete fusion of skull bones, the individual was not yet skeletally mature, though its orbit size matched adult proportions.

Reader's Guide

Cariocecus bocagei is significant as the first iguanodontian skull from Portugal, filling a gap in the fossil record of European hadrosauroids. Its unique fused maxilla-jugal complex and low supraorbital suggest specialized feeding and visual adaptations. Phylogenetic analysis places it as a close relative of the English hadrosauroids Brighstoneus and Comptonatus, forming a clade near the base of Hadrosauroidea. This relationship was confirmed in a 2026 study of the Chinese hadrosauroid Haolong. The Papo Seco Formation also yielded the spinosaurid Iberospinus and fragmentary remains of other dinosaurs, pterosaurs, turtles, and fish, deposited in a shallow marine to continental environment. Cariocecus thus contributes to understanding the diversity and biogeography of Early Cretaceous ornithopods in Europe.

Did You Know?

• Cariocecus is the fourth definitive iguanodontian named from Portugal, but the first with a skull.
• The generic name references the Iberian war deity Cariocecus, and the specific name honors Portuguese naturalist José Vicente Barbosa du Bocage.
• The maxilla and jugal of Cariocecus are completely fused, a trait not seen in any other ornithopod.
• The holotype skull was μCT-scanned to study internal anatomy, revealing replacement teeth in the maxilla.

Discovery and the Long Road to Description

In 2016, a partial articulated ornithopod skull was unearthed by Pedro Marrecas from a limestone outcrop belonging to the Papo Seco Formation, situated roughly 200 metres from the Praia do Areia do Mastro shoreline on the Setúbal Peninsula in Sesimbra Municipality, Portugal. The specimen then entered a long period of preparation and study. In 2024, Stéphane Berton at the Royal Belgian Institute of Natural Sciences worked on the fossil and subjected it to micro-CT scanning to reveal internal and obscured anatomical details. After this work, the specimen was transferred to the Sociedade de Historia Natural in Torres Vedras, where it was permanently accessioned as SHN.832. The skull preserves a remarkable amount of structure: portions of both premaxillae, the nasals, frontals, nearly the entire basicranium, and numerous bones from the right side including the maxilla, jugal, ectopterygoid, lacrimal, prefrontal, supraorbital, and postorbital. Nine years after its initial recovery, Filippo Bertozzo and colleagues formally described the animal as a new genus and species in 2025, establishing SHN.832 as the holotype.

An Unusual Face Among Ornithopods

Cariocecus bocagei stands apart from every other known ornithopod through three unique anatomical characters. Most strikingly, the rostral ramus of the jugal bone is entirely fused to the maxilla, forming a single undivided unit with no visible separation line between the two elements. In all other ornithopods these two bones remain distinct. Second, the supraorbital bone articulates only with the lacrimal, whereas in other members of the group it also contacts the prefrontal. This bone sat very low over the eye socket, lending the animal a distinctive eagle-eyed profile that may have shielded the eye from both physical trauma and solar glare. Third, viewed from behind, the top edge of the supraoccipital bears three small knobs. The overall skull profile is low with a flattened cranial vault, and unlike close relatives such as Brighstoneus, Cariocecus lacked a nasal crest. The maxilla holds seventeen tooth positions, with twelve erupted teeth visible and one replacement tooth per socket identified through micro-CT imaging.

A New Chapter in Portugal's Dinosaur Record

Cariocecus bocagei marks a significant milestone in the Portuguese fossil record. It is the fourth definitive iguanodontian named from the country, following Draconyx in 2001, Eousdryosaurus in 2014, and Hesperonyx in 2024, all of which come from the Jurassic Lourinhã Formation and are known only from postcranial remains. What sets Cariocecus apart is that it is the first Portuguese iguanodontian to preserve a skull, and the first iguanodontian skull ever recovered from Portugal. The generic name honours Cariocecus, an Iberian and Lusitanian war deity later syncretised with Mars and Ares under Roman rule; the name also nods to the skull's superficial resemblance to goats and horses, animals ritually sacrificed to that deity. The specific epithet bocagei commemorates Portuguese naturalist José Vicente Barbosa du Bocage and his scholarly contributions. The animal is thought to be a close relative of the English hadrosauroids Brighstoneus and Comptonatus. Additional fragmentary iguanodontian material from the Papo Seco Formation, including isolated teeth, a maxilla fragment, four caudal vertebrae, and a femur tip, remains unclassified beyond Iguanodontia or Styracosterna indeterminate.

Life in the Barremian Shallows

Cariocecus bocagei lived during the Barremian age of the Early Cretaceous in what is now the Setúbal Peninsula region of Portugal. Its remains come from the Papo Seco Formation, a deposit recording a shallow marine to continental environment. The fossil assemblage from this formation is diverse: alongside Cariocecus it has yielded the spinosaurid Iberospinus, fragmentary coelurosaurian theropods, titanosauriform sauropods, pterosaurs, turtles, crocodyliforms, fish, and aquatic shelled invertebrates, painting a picture of a rich coastal ecosystem. The holotype individual was not fully grown; sutures between nearly all skull bones had not yet co-ossified, indicating it had not reached skeletal maturity. Based on a reconstruction model informed by its presumed relatives Brighstoneus and Comptonatus, the skull base measured an estimated 42.3 centimetres. Remarkably, a linear regression comparing orbit-to-skull ratios across eighteen ornithopod species suggested that despite its immaturity, this animal had already attained the expected adult eye-socket size, implying it was a medium-sized iguanodontian that likely foraged during daylight hours under the shade of its prominent supraorbital brow.