Eocarcharia Dinops

''Eocarcharia'' (meaning "dawn shark") is an extinct genus of theropod dinosaurs found in what is now the western Ténéré Desert of Niger. It is known from several skull bones collected in 2000 by an expedition to the Early Cretaceous (Aptian–Albian ages) Elrhaz Formation (Gadoufaoua locality) led by American paleontologist Paul Sereno. They were then described in 2008 by Sereno and Steve Brusatte. The genus contains a single species, ''Eocarcharia dinops''. Sereno and Brusatte identified the remains as a new carcharodontosaurid, but later studies suggested that the species is chimaeric, comprising bones of multiple unrelated taxa. Some of the ''Eocarcharia'' material, including the holotype (name-bearing) specimen, likely belongs to a baryonychine spinosaurid. This would render ''Eocarcharia'' a member of this group, closely related to the coeval ''Suchomimus''. Meanwhile, the definitively carcharodontosaurid bones, a and teeth, belong to a separate distinct taxon.

Little is known about ''Eocarcharia'' due to its fragmentary and chimeric nature. When considered a carcharodontosaurid, it was estimated to be long, making it smaller than derived carcharodontosaurids like ''Giganotosaurus,'' and ''Carcharodontosaurus''. The (bone behind the orbit) is robust with a large brow, a distinct characteristic of ''Eocarcharia''. It was possibly covered in keratin and used for head-butting with other individuals of its species. ''Eocarcharia'' lived in an environment with rivers and vast floodplains alongside many other dinosaurs, pterosaurs, crocodylomorphs, and freshwater animals.

Discovery and naming

In 2000, American paleontologist Paul Sereno led an expedition conducted with the University of Chicago and funded by the National Geographic Society. The purpose of this trip was to explore fossiliferous sandstone outcrops in a site on the western edge of the Nigerian Ténéré Desert known as Gadoufaoua. These rock layers belong to the Elrhaz Formation, dating to the Early Cretaceous. During the expedition, several isolated theropod skull bones were collected, including a maxilla (main tooth-bearing bone of the upper jaw) and two maxilla fragments, five (bone behind the orbit), two —one articulated with the left and one with a partial ( bones)— and five teeth. 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 MNN GAD2-14.

In 2008, Sereno and Steve Brusatte described all of the remains as belonging to a new genus and species of carcharodontosaurid, named ''Eocarcharia dinops''. They established one of the postorbitals, MNN-GAD2, as the holotype (name-bearing) specimen. The generic name, ''Eocarcharia'', derives from the Ancient Greek words , meaning , and , meaning , referencing the early-diverging nature of ''Eocarcharia'' in relation to its 'shark-toothed' relatives. The specific name, , is a Greek term meaning "fierce-eyed", referring to the postorbital ornamentation above the eye.

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. The only remains confidently referrable to ''Eocarcharia'' consist of the holotype postorbital, four referred postorbitals, a left frontal, and a left prefrontal. Referencing the more complete skulls and skeletons of other carcharodontosaurids like ''Acrocanthosaurus'' and ''Carcharodontosaurus'', they determined that ''Eocarcharia'' was likely about long, half the linear size of the largest, more derived members of the family. Similar estimates were supported by later publications.

Posterior skull

The postorbital bears a thick, robust brow that, likely due to its robusticity, preserves well. This brow is composed of two segments; an anterior (front) portion with boxy dimensions and a posterior (back) portion that forms an ovate orbital boss (a large, thick bony mass). This orbital boss is positioned above the posterodorsal (top back) edge of the orbit, a trait noted by Sereno and Brusatte to be diagnostic (a distinct feature of a species). However, the occurrence of an exaggerated orbital boss is also found in spinosaurids. An orbital boss is also found in ''Mapusaurus'' and ''Giganotosaurus'', though 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 orbit edges, the , and the . Several of the postorbitals known from ''Eocarcharia'' preserve their articular surfaces (part of the postorbital that articulates with the lacrimal), which are deep and long. These articular surfaces are very small and deep 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 (projection of bone) that interlocks with a concavity on the frontal. Another diagnostic trait of ''Eocarcharia'' is that its bears a narrow facet which articulates the postorbital with the (cheekbone), whereas carcharodontosaurids like ''Carcharodontosaurus'' have broader facets. Midshafts of the ventral (bottom) ramus (a branch of bone) 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 (away from body core)-positioned, and rugose.

The frontal is known from ''Eocarcharia'', which is proportionally very broad at its mid length, similar to that of ''Carcharodontosaurus''. In dorsal view, the supratemporal (a depression along the temporal fenestra) is greatly exposed, another diagnostic characteristic. 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. Notably, a prefrontal is also preserved. Independent prefrontals are absent in advanced carcharodontosaurids as they are typically coosified with the lacrimals into a single element, whereas in genera like ''Acrocanthosaurus, Eocarcharia,'' and ''Concavenator'', they are unfused. The prefrontal bears an extended process engineered to articulate with the deep, squared articular notch on the frontal. On the ventral (bottom) side of the frontal, theropods typically feature an extended process. that travels along the posteromedial (back inner) portion of the bone. ''Eocarcharia'' lacks this characteristic and is instead enlarged, distinct, and lacks the ossification.

Referred maxilla and teeth

One nearly complete maxilla and two central maxilla portions were initially referred to ''Eocarcharia'' and definitively belong to a carcharodontosaurid or closely allied taxon. The dentary has 15 alveoli (tooth sockets). It is generally flat, which would have given this taxon a relatively narrow snout. (small pits and grooves) cover the external surface. The , a depression on the side of the maxilla, is pierced by three fenestrae (holes), the largest of which is the subtriangular promaxillary fenestra, followed by the maxillary fenestra, which is subequal in size. A smaller round accessory fenestra is present above these two. Most of the alveoli in the complete maxilla preserve replacement teeth. The are transversely compressed. Unlike many carcharodontosaurid teeth, those referred to ''Eocarcharia'' are not blade-shaped and they lack straight posterior (cutting edges on the back of the crown) and enamel wrinkles with high relief.

Classification

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 the same 2008 paper, Sereno and Brusatte named '' Kryptops palaios'' on the basis of an abelisaurid maxilla and 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.

In their 2024 description of a new specimen of the giant carcharodontosaurid ''Taurovenator'', Rolando and colleagues 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:

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

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.

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''. They also commented on the possibility that some of the other specimens traditionally referred to ''Suchomimus'' may actually belong to ''Eocarcharia''.

Paleobiology

Due to the fragmentary, chimeric, and indeterminate nature of the fossils of ''Eocarcharia'', little can be directly known about its paleobiology. In their 2008 description, Sereno and Brusatte noted the thickness and robustness of the postorbital bosses. The brow was likely covered in keratin, extending its size. It also 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 stress. This combination of stress adaptations illustrate that the brow was for more than purely display purposes. This led the authors to hypothesize that the postorbital brows of ''Eocarcharia'' and carcharodontosaurids were used for intraspecific lateral head-butting. This brow is absent in allosauroids and most spinosaurids, however the spinosaurids ''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.

Paleoecology

''Eocarcharia'' is known from the Elrhaz Formation of the Tegama Group in an area of the Nigerian Ténéré Desert called Gadoufaoua. The Elrhaz Formation consists mainly of fluvial sandstones with low relief, much of which is obscured by sand dunes. The sediments are coarse- to medium-grained, with almost no fine-grained horizons. ''Eocarcharia'' lived about 120 to 112 million years ago, during the Aptian to Albian ages of the mid-Cretaceous. It likely lived in habitats dominated by inland floodplains (a riparian zone).

''Eocarcharia'' lived alongside several other dinosaurs. These included other theropods, such as the spinosaurid and probable close relative ''Suchomimus'', ''Kryptops'' (known from a chimeric combination of abelisaurid and allosauroid material), and the putative noasaurid ''Afromimus''. Several megaherbivores like the hadrosauriforms ''Ouranosaurus'' and ''Lurdusaurus'', dryosaurid ''Elrhazosaurus'', and two sauropods, the rebbachisaurid ''Nigersaurus'' and an unnamed titanosaur, have been unearthed from Gadoufaoua. Together, these comprise one of the few associations of megaherbivores with a balance of sauropods and large ornithopods. Crocodylomorphs like ''Sarcosuchus'', ''Anatosuchus'', ''Araripesuchus'', and ''Stolokrosuchus'' also lived there. In addition, remains of an ornithocheirid pterosaur, turtles, bony fish, a hybodont shark, and bivalves have been found. The aquatic fauna consists entirely of freshwater inhabitants.

See also

* ''Kryptops''
* 2008 in paleontology

References

{{Taxonbar, from1=Q29574600, from2=Q132487

Carcharodontosauridae
Dinosaur genera
Albian dinosaurs
Fossil taxa described in 2008
Taxa named by Paul Sereno
Taxa named by Stephen L. Brusatte
Dinosaurs of Niger