Eocarcharia

Eocarcharia Temporal range: Early Cretaceous (Aptian–Albian), ~
Holotype postorbital
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Family:	†Spinosauridae (?)
Subfamily:	†Baryonychinae (?)
Genus:	†Eocarcharia Sereno & Brusatte, 2008
Type species
†Eocarcharia dinops Sereno and Brusatte, 2008

Eocarcharia (meaning "dawn shark") is an extinct genus of theropod dinosaurs from the Early Cretaceous (~Aptian–Albian age) Elrhaz Formation of Niger. The genus contains a single species, Eocarcharia dinops, to which several isolated skull bones have been referred. Eocarcharia was initially described as a basal member of the allosauroid family Carcharodontosauridae. However, later analyses indicated that the species hypodigm is chimaeric, comprising bones of multiple distinct taxa. Some of the Eocarcharia material, including the holotype specimen, likely belongs to a baryonychine spinosaurid. This would render Eocarcharia a spinosaurid genus, closely related to the coeval Suchomimus, with the definitively carcharodontosaur material belonging to a separate distinct taxon.

Discovery and naming

Reconstruction of the likely chimaeric hypodigm skull of Eocarcharia based on the initial interpretation of the material

In 2000, an expedition conducted by the University of Chicago led by American paleontologist Paul Sereno and funded by the National Geographic Society explored fossiliferous sandstone outcrops in a site known as Gadoufaoua on the western edge of the Ténéré Desert of Niger. These layers belong to the Elrhaz Formation, which dates to the Aptian and Albian ages of the Early Cretaceous, around 112 million years ago. During the expedition, skull bones consisting of: a maxilla (main tooth-bearing bone of the upper jaw) and two maxilla fragments, five postorbital (posterior orbit bones), a left frontal and prefrontal (skull roof bones), and five teeth of a theropod were collected in isolation. On the same expedition, a set of theropod postcranial elements consisting of three dorsal (back) vertebrae, two ribs, the sacrum, and the pelvis were found close to the maxilla of an abelisaurid. These remains were then transported to the University of Chicago for study and preparation before being returned to the Musee National du Niger and deposited under the catalog numbers. The skull elements were deposited under specimen numbers MNN GAD2-14, whereas the postcranial remains are under MNN GAD1-2 through MNN GAD1-8.

The cranial remains were believed to belong to the same species by Paul Sereno, who, with Jeffrey Wilson and Jack Conrad, later mentioned them in a 2004 paper as an undescribed carcharodontosaurid. Sereno and Steve Brusatte described one of the postorbitals, MNN-GAD2, as the holotype (name-bearing) specimen of a new genus and species of carcharodontosaurid in 2008, named Eocarcharia dinops. The generic name derives from the Ancient Greek words eos, meaning 'dawn', and karcharias, meaning 'shark', in reference to the shark-like teeth of Eocarcharia and its relatives. The specific name, dinops, is a Greek term meaning "fierce-eyed", in reference to the large orbital boss present on the postorbital above the eye.

In the same paper, Sereno and Brusatte named Kryptops palaios on the basis of the abelisaurid maxilla and the postcranial remains. They assigned the postcranial material to the same individual as the maxilla based on their close association and alleged basal abelisaurid features in the vertebrae and pelvis. In 2012, Matthew Carrano and colleagues considered Kryptops palaios to be a chimera (specimen composed of multiple species), and stated that its postcranial remains, especially the pelvis and sacrum, may actually belong to a carcharodontosaurid, possibly Eocarcharia. However, these bones do not overlap with the Eocarcharia holotype, which consists only of an isolated postorbital. This hypothesis was supported by later studies, who agreed that the postcranial remains belonged to an allosauroid, carcharodontosaurid, or a metriacanthosaurid.

Description

Based on the total fusion of the skull bones referred to Eocarcharia, Sereno & Brusatte identified them as having come from fully mature adult individuals. Referencing the more complete skulls and skeletons of other carcharodontosaurids (Acrocanthosaurus and Carcharodontosaurus), they determined that Eocarcharia was likely about half the linear size of the largest, more derived members of the family, at around 6–8 metres (20–26 ft).

Postorbital

Due to the possible chimeric nature of Eocarcharia, the only confidently known remains of Eocarcharia consist of the holotype postorbital as well as four referred postorbitals. However, the postorbital bears a thick, robust brow that likely resists breakdown due to its robusticity, leading to the preservation of these five postorbitals. This brow is the most prominent feature of the bone when viewed from lateral view, which is composed of two segments; an anterior portion with boxy dimensions and a posterior portion that forms an ovate orbital boss. This orbital boss is positioned above the posterodorsal edge of the orbit, a trait noted by Sereno and Brusatte to be diagnostic. However, the occurrence of an exaggerated orbital boss is also found in spinosaurids. This orbital brow is found in Mapusaurus and Giganotosaurus as well, however the orbital bosses of these genera are ossified as a distinct body from the rest of the postorbital. In contrast, the postorbital bosses of Carcharodontosaurus and Eocarcharia lack the extensive ossification seen in Mapusaurus and Giganotosaurus.

The margins of the postorbital make up segments of the borders of the orbit, laterotemporal fenestra, and supratemporal fenestra. Several of the postorbitals known from Eocarcharia preserve their lacrimal articular surfaces, which are 9 millimetres (0.35 in) deep and 12 millimetres (0.47 in) long. These articular surfaces are very small proportionally for a carcharodontosaurid, making this characteristic a diagnostic trait of Eocarcharia. In contrast, the point of contact between the postorbital and the frontal is rugose and bears a unique, plate-shaped process that interlocks with a matching concavity on the frontal. Another unique trait of Eocarcharia is that its bears a narrow facet which articulates the postorbital with the jugal, whereas carcharodontosaurids like Carcharodontosaurus have broader facets. Midshafts of ventral ramii in spinosaurids and megalosaurids are typically U-shaped in cross-section, whereas in Eocarcharia it is subtriangular in cross-section. An infraoribital process is also present on the ventral ramus of Eocarcharia, however it is distinct from those of other carcharodontosaurids in that it is small, distally-positioned, and rugose.

The frontal is known from Eocarcharia, which is proportionally very broad at its mid length, similar to that of Carcharodontosaurus. The supratemporal fossa (a depression along the temporal fenestra) is greatly exposed, in contrast to those of carcharodontosaurids, and has limited exposure from dorsal view. In ventral view, the anterior portion of the frontal is exposed and forms the roof of the olfactory section of the endocranium (part of skull that contains the brain). This portion of the frontal is narrow, in contrast to those of tetanurans which are typically broad.[1]

Paleobiology

Due to the fragmentary, chimeric, and indeterminate nature of the fossils of Eocarcharia, little can be directly known about the genus' paleobiology. In their 2008 description of Eocarcharia, Sereno and Brusatte noted the durable, robust physiology of the postorbital boss found in Eocarcharia. The brow was likely covered in keratin and displays large, intricate sutures between the postorbital and frontal that suggest it would be stable against lateral impacts. The laterosphenoid's head is placed in a socket in the postorbital which, although shallower than that of advanced carcharodontosaurids, would be able to handle increased stress. The brow is overbuilt and overdeveloped for purely display based on these characteristics. This led Sereno and Brusatte to hypothesize that the postorbital brows of Eocarcharia and carcharodontosaurids were used for intraspecific lateral head-butting. This feature is absent in allosauroids and most spinosauroids, however Ceratosuchops and Riparovenator also preserve large orbital bosses comparable to those in Eocarcharia. Although present in large tyrannosaurids, the postorbital bosses of Eocarcharia and carcharodontosaurids project laterally, further suggesting that they played a role in lateral head-butting.

Classification

As a carcharodontosaurid

Carcharodontosaurid maxilla referred to Eocarcharia

Speculative life restoration of Eocarcharia as a carcharodontosaurid

In their phylogenetic analyses, Sereno & Brusatte (2008) recognized Eocarcharia as an allosauroid theropod in an early-diverging position within the family Carcharodontosauridae. They noted that the resolution of their trees was more stable without Eocarcharia, since it could not be scored for most of the characters in their dataset. Regardless, their strict consensus tree recovered it as the sister taxon to the North American Acrocanthosaurus.

In a 2012 analysis of tetanuran theropods, Carrano, Benson & Sampson determined that specimen MNN GAD1-2, a pelvis and sacrum referred to Kryptops by Sereno and Brusatte, did not demonstrate anatomical features consistent with abelisaurids, but rather carcharodontosaurians. As such, they suggested that these remains could instead belong to Eocarcharia, though such a referral was tentative given the absence of overlapping material for comparisons. The referral of this specimen to Eocarcharia or the Carcharodontosauridae has not been supported in subsequent phylogenetic studies, which place it within the Metriacanthosauridae.

In their 2024 description of a new specimen of the giant carcharodontosaurid Taurovenator, Rolando et al. recovered Eocarcharia as an early-diverging member of the clade, branching after Neovenator. The results of their phylogenetic analyses are displayed in the cladogram below:

Carcharodontosauridae	Neovenator Eocarcharia Lajasvenator Acrocanthosaurus Carcharodontosaurinae Lusovenator Shaochilong Carcharodontosaurus saharicus Carcharodontosaurus iguidensis Giganotosaurini Tyrannotitan Giganotosaurus Mapusaurus Meraxes Taurovenator

The skull bones of Eocarcharia were not found in association and they belong to multiple individuals. As such, the taxonomic identity of these bones—and whether or not they can all be referred to the same taxon—has been debated. In their description of the carcharodontosaurid Tameryraptor, Kellermann, Cuesta & Rauhut (2025) scored the holotype postorbital (including a referred frontal with articular surfaces that match those of the postorbital) and referred maxilla as separate operational taxonomic units (OTUs) to test the likelihood that they belonged to the same taxon. In their analyses, both OTUs were consistently recovered in different positions, supporting their status as distinct taxa. The maxilla was reliably recovered as a carcharodontosauriform, either as a non-carcharodontosaurine carcharodontosaurid or as a metriacanthosaurid. On the other hand, the holotype was recovered in positions as a basal carcharodontosaur, or variably inside or outside of Carcharodontosauriformes. They interpreted these results as indicative of the referred maxilla skewing past analyses toward carcharodontosaur affinities for the taxon.

As a spinosaurid

Skull roof referred to Eocarcharia in dorsal and ventral (left) and lateral and medial (right) view

Reconstructed skull of the spinosaurid Suchomimus, a possible close relative of Eocarcharia

In 2024, Andrea Cau published the results of a comprehensive theropod phylogenetic framework. The following year, Cau and Paterna used an updated version of this dataset to analyze the relationships of Cretaceous theropods from Africa, especially those known from multiple specimens with minimal overlapping material. The researchers scored two separate OTUs for Eocarcharia: the referred maxilla and another comprising the skull roof material (including the referred frontal and prefrontal, and the holotype postorbital). As expected, the maxilla was found to have close affinities with early-diverging carcharodontosaurids. More surprisingly, the skull roof was recovered as the sister taxon to the coeval Suchomimus as a baryonychine within the Spinosauridae. These results were supported by the presence of at least seven shared traits in Eocarcharia and spinosaurids that are absent in carcharodontosaurs. Cau and Paterna further recognized that two of the autapomorphies (unique derived traits) proposed for Eocarcharia by Sereno and Brusatte are also uniquely shared with Ceratosuchops, a baryonychine from the Wessex Formation of the United Kingdom. Furthermore, the prefrontal bone has a feature seen in Baryonyx but not allosauroids. Given the discrepancies with the placement of Eocarcharia as a carcharodontosaur and the many similarities to Suchomimus, Ceratosuchops, and Riparovenator, the researchers considered it to be most parsimoniously regarded as a spinosaurid.

Cau and Paterna's phylogenetic results placed Eocarcharia as the sister taxon to Suchomimus. Both species differ in fourteen characters, precluding their taxonomic synonymization. This also provides further evidence to an observed trend of at least two spinosaurids coexisting in one ecosystem (e.g., Ceratosuchops and Riparovenator in the Wessex Formation). Since the maxilla OTU was recovered as distinct from the skull roof + holotype postorbital OTU, Cau and Paterna suggested that this bone—which demonstrates apparent allosauroid anatomy consistent with carcharodontosaurids—should be referred to a new taxon. Abbreviated results of their phylogenetic analysis are displayed in the cladogram below, with both Eocarchia OTUs indicated: the skull roof and holotype within the spinosaurid clade Ceratosuchopsini and the maxilla as a basal carcharodontosaurid. ⊞ buttons can be clicked to expand nodes.

Carnosauria

Megalosauroidea ⊞ Poekilopleuron Piatnitzkysaurus Marshosaurus Condorraptor Afrovenator Torvosaurus tanneri Megalosaurus Magnosaurus Duriavenator Wiehenvenator Vallibonavenatrix Leshansaurus Spinosauridae Ichthyovenator Sigilmassasaurus Spinosaurus (holotype) "Spinosaurus B" Spinosaurus (Kem Kem morph) Baryonychinae Baryonyx Ceratosuchopsini Suchomimus Eocarcharia (holotype + skull roof) Riparovenator Ceratosuchops ⊟ phylogenetic position of Eocarcharia (holotype + skull roof) Allosauroidea ⊞ Asfaltovenator Monolophosaurus Metriacanthosauridae Lourinhanosaurus Allosaurus Taurovenator (holotype) Siamraptor Piveteausaurus Concavenator Neovenator Carcharodontosauridae Eocarcharia (referred maxilla) Veterupristisaurus Lusovenator Lajasvenator Acrocanthosaurus Other carcharodontosaurids ⟹ ⊟ phylogenetic position of the referred "Eocarcharia" maxilla

Notably, spinosaurid similarities have been noted prior to the Cau and Paterna's 2025 analysis; in 2022, Sereno and colleagues figured a newly-discovered skull roof of Suchomimus. The similarity of this specimen to the postorbital and frontal of Eocarcharia was noted by Schade and colleagues the following year. In early 2025, Kellermann, Cuesta & Rauhut reinforced this comparison, claiming that the specimen may even be referrable to the genus. Cau and Paterna acknowledged these similarities, but noted characters more consistent with Suchomimus than Eocarcharia.

Paleoenvironment

Eocarcharia is known from the Elrhaz Formation. The depositional environment has been interpreted as being dominated by inland floodplains with high-energy river systems.

Eocarcharia likely coexisted in the Elrhaz Formation with several other dinosaurs. These include other theropods such as the spinosaurid Suchomimus, the abelisaurid Kryptops, and the abelisauroid Afromimus. Known sauropods from the locality include rebbachisaurid Nigersaurus and an unnamed titanosaur. Ornithischians include the dryosaurid Elrhazosaurus and the hadrosauriforms Ouranosaurus and Lurdusaurus. Crocodylomorphs such as Sarcosuchus, Anatosuchus, Araripesuchus, and Stolokrosuchus have also been discovered, in addition to ornithocheirid pterosaur and turtle remains. Freshwater bony fish, hybodont sharks, and freshwater bivalves are also known.

External links

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