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Eurycephalosuchus
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Eurycephalosuchus
Eurycephalosuchus is an extinct genus of orientalosuchine alligatoroid from the Late Cretaceous Hekou Formation of China. Known from a well preserved skull and mandible alongside various postcranial remains, Eurycephalosuchus possessed a skull that was unusually short and broad skull, even by the standards of other orientalosuchines. Its skull table is also noted for being unusually short and its dentition features both elongated caniniforms and bulbous molariforms. Based on the size of the skull, Eurycephalosuchus may have been the smallest member of its lineage. The Hekou Formation was also home to two other crocodilians, the possibly related Jiangxisuchus and an indetermined member of Brevirostres. The genus Eurycephalosuchus is monotypic, containing only a single species: Eurycephalosuchus gannanensis.
The holotype of Eurycephalosuchus was discovered in 2021 at a construction site for the Qingfeng Pharmaceutical Manufactory in the Municipality of Ganzhou City, in China's Jiangxi Province. The type locality was located only 50 km (31 mi) northeast of the type locality of the related Jiangxisuchus. The specific strata that yielded the material are known belong to the Late Cretaceous redbeds, which were part of the early Maastrichtian Hekou Formation. The Hekou Formation is part of the larger Guifeng Group, although some previous studies such as the description of Jiangxisuchus originally referred to the redbeds as belonging to the Nanxiong Formation. The block of matrix that preserves the material contained a nearly complete skull with the attached mandible, 16 vertebrae and 15 ribs, a partial front limb and several osteoderms, all of which together are designated as specimen IVPP V 31110. There is some compression that affected the skull during preservation, pushing parts of the frontal and prefrontal bones over the rear edge of the nasal bone amongst other deformities. The same locality also yielded a shoulder blade articulated with a coracoid which are thought to belong to another type of crocodile, only described as being a member of Brevirostres and notably bigger than Eurycephalosuchus.
The name Eurycephalosuchus is a composite word of the Greek "eurys" meaning wide or broad, "kephale" meaning head and -suchus, derived from the Egyptian crocodile god Sobek. The species name on the other hand specifically points to Gannan, another name for Ganzhou, where the material was collected.
While members of Orientalosuchina are generally known for their short and blunt snouts, Eurycephalosuchus stands out for being short-snouted even by the group's standards. The holotype skull measures 14.31 cm (5.63 in) in dorsal cranial length, meaning measured from the tip of the snout to the rear end of the skull table. Accounting for the compression the fossil underwent, a fully intact skull might have measured around 14.81 cm (5.83 in), which is approximately the same as the maximum width across the quadratojugals. Measuring from the tip to the snout to the end of the quadrate condyle would render a skull only slightly longer than wide. Other parts of the skull likewise show bizarre proportions. The snout itself is short, only 9.63 cm (3.79 in) long, shorter than it is wide and making up less than half of the total skull length. The skull table, which is typically shorter than it is wide in crocodilians, takes this condition to an extreme. The length of this element is two thirds smaller than its width, with Wu and colleagues going as far as describing it as "unbelievably short", highlighting how this, much like the overall skull proportions, is unusual both for orientalosuchines and alligatoroids as a whole.
The premaxillae of Eurycephalosuchus are wider than long and almost entirely surround the external naris without forming a raised rim. However, given that the holotype is damaged it is not entirely clear whether or not the naris would have been a singular confluent opening that was wider than long as in Orientalosuchus or actually two openings separated by an elongated process of the paired nasal bones as in modern alligators and as has been proposed for the orientalosuchine Protoalligator. The posterior-most edge of the naris is formed by the nasals, with the premaxilla extending briefly along their edge to form short dorsal processes. A defining feature of orientalosuchines is the presence of a notch located at the contact of the premaxillae with the maxillae, a feature absent in modern alligators but present in true crocodiles. Such a notch is present in Eurycephalosuchus and similar in its anatomy to that of Orientalosuchus in being moderately deep and therefore different from the shallow notches seen in Dongnanosuchus and Jiangxisuchus. Right behind the premaxillae sit the maxillae, which are the broadest bones of the dorsal surface of the skull. When viewed from above the outer edges of the maxilla are sinuous, constricting at the contact with the premaxilla, reaching their greatest width around the large 5th maxillary tooth before constricting and broadening once again shortly behind it. Looking at the skull from the side shows that the maxillae exhibit a strongly concavo-convex ventral margin, a condition known as festooning. This results in two dental waves, which peak with the fifth and 12th maxillary teeth respectively. The maxilla continues backwards until meeting the lacrimal bone, inserting a small process between it and the nasals before sharply reducing into a lateral process that contacts the jugal bone.
Information on how the individual bones connect to another becomes harder to determine at the transition from the snout to the skull table due to the deformation of the holotype skull. Taphonomy has caused the broken frontal bone as well as the prefrontal bones to overlap the posterior ends of the nasals and parts of the lacrimals. The lacrimal bone is pointed towards the front, wedging itself into the maxilla, and broad towards the back, where the bone forms a process that contributes significantly towards the anterior margin of the orbits. The prefrontal likewise contributes to the eyesocket and is roughly triangular in shape based on the better preserved left side of the holotype. The frontal bone contributes a small part to the orbital margins and like in Dongnanosuchus is moderately broad between the eyesockets, with the interorbital septum being just a little broader than the space between the supratemporal fossae on the skull table. Though heavily distorted in the holotype, the eyesockets were clearly quite large compared to the supratemporal fossae and appear to have lacked the surrounding rim seen in Jiangxisuchus.
As is typical, the frontal broadens posteriorly as it enters the skull table and in orientalosuchine fashion just enters the supratemporal fossa. It contacts the rectangular postorbitals to either side along a oblique, concavo-convex suture and the single parietal bone at the midline between the fossae. Like the overall proportions of the skull, the supratemporal fossae too are wider than long. The bones that form the edge of the fenestra, sans the frontal, overhang the opening which differs from what is observed in any other member of Orientalosuchina that preserves this region of the skull. As in Dongnanosuchus, the space occupied by the parietal between the fossae is slightly narrower than the frontal is between the eyes. Also as in Dongnanosuchus it contacts the quadrate bone within the fossa and is simultaneously separated by it from the squamosal even though the two contact along an almost straight suture outside of the opening. The very back of the skull table is occupied by an exposed supraoccipital, which actually prevents the parietal from reaching the posterior margin.
The triradiate jugal bone contacts the maxilla and extends back to form part of the lower orbital margin and much of the ventral infratemporal fenestra. The bone consists of an anterior ramus which is broad but short, a thinner and longer posterior ramus and its contribution to the postorbital bar, which rises between orbit and infratemporal fenestra and joins the descending process of the postorbital. Its contact with the quadratojugal is oblique, with the dorsal contact taking place before the end of the infratemporal fenestra while the ventral contact is set much further back just before the mandibular condyle. The quadratojugal possesses a small spine that enters the fenestra and runs almost parallel its rear edge, something not known from any other orientalosuchines but similar to Brachychampsa. Like in Dongnanosuchus, Jiangxisuchus and Orientalosuchus, the foramen aëreum is located medially on the quadrate. Between the lateral and media condyles of the quadrate, the lateral is slightly larger.
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Eurycephalosuchus
Eurycephalosuchus is an extinct genus of orientalosuchine alligatoroid from the Late Cretaceous Hekou Formation of China. Known from a well preserved skull and mandible alongside various postcranial remains, Eurycephalosuchus possessed a skull that was unusually short and broad skull, even by the standards of other orientalosuchines. Its skull table is also noted for being unusually short and its dentition features both elongated caniniforms and bulbous molariforms. Based on the size of the skull, Eurycephalosuchus may have been the smallest member of its lineage. The Hekou Formation was also home to two other crocodilians, the possibly related Jiangxisuchus and an indetermined member of Brevirostres. The genus Eurycephalosuchus is monotypic, containing only a single species: Eurycephalosuchus gannanensis.
The holotype of Eurycephalosuchus was discovered in 2021 at a construction site for the Qingfeng Pharmaceutical Manufactory in the Municipality of Ganzhou City, in China's Jiangxi Province. The type locality was located only 50 km (31 mi) northeast of the type locality of the related Jiangxisuchus. The specific strata that yielded the material are known belong to the Late Cretaceous redbeds, which were part of the early Maastrichtian Hekou Formation. The Hekou Formation is part of the larger Guifeng Group, although some previous studies such as the description of Jiangxisuchus originally referred to the redbeds as belonging to the Nanxiong Formation. The block of matrix that preserves the material contained a nearly complete skull with the attached mandible, 16 vertebrae and 15 ribs, a partial front limb and several osteoderms, all of which together are designated as specimen IVPP V 31110. There is some compression that affected the skull during preservation, pushing parts of the frontal and prefrontal bones over the rear edge of the nasal bone amongst other deformities. The same locality also yielded a shoulder blade articulated with a coracoid which are thought to belong to another type of crocodile, only described as being a member of Brevirostres and notably bigger than Eurycephalosuchus.
The name Eurycephalosuchus is a composite word of the Greek "eurys" meaning wide or broad, "kephale" meaning head and -suchus, derived from the Egyptian crocodile god Sobek. The species name on the other hand specifically points to Gannan, another name for Ganzhou, where the material was collected.
While members of Orientalosuchina are generally known for their short and blunt snouts, Eurycephalosuchus stands out for being short-snouted even by the group's standards. The holotype skull measures 14.31 cm (5.63 in) in dorsal cranial length, meaning measured from the tip of the snout to the rear end of the skull table. Accounting for the compression the fossil underwent, a fully intact skull might have measured around 14.81 cm (5.83 in), which is approximately the same as the maximum width across the quadratojugals. Measuring from the tip to the snout to the end of the quadrate condyle would render a skull only slightly longer than wide. Other parts of the skull likewise show bizarre proportions. The snout itself is short, only 9.63 cm (3.79 in) long, shorter than it is wide and making up less than half of the total skull length. The skull table, which is typically shorter than it is wide in crocodilians, takes this condition to an extreme. The length of this element is two thirds smaller than its width, with Wu and colleagues going as far as describing it as "unbelievably short", highlighting how this, much like the overall skull proportions, is unusual both for orientalosuchines and alligatoroids as a whole.
The premaxillae of Eurycephalosuchus are wider than long and almost entirely surround the external naris without forming a raised rim. However, given that the holotype is damaged it is not entirely clear whether or not the naris would have been a singular confluent opening that was wider than long as in Orientalosuchus or actually two openings separated by an elongated process of the paired nasal bones as in modern alligators and as has been proposed for the orientalosuchine Protoalligator. The posterior-most edge of the naris is formed by the nasals, with the premaxilla extending briefly along their edge to form short dorsal processes. A defining feature of orientalosuchines is the presence of a notch located at the contact of the premaxillae with the maxillae, a feature absent in modern alligators but present in true crocodiles. Such a notch is present in Eurycephalosuchus and similar in its anatomy to that of Orientalosuchus in being moderately deep and therefore different from the shallow notches seen in Dongnanosuchus and Jiangxisuchus. Right behind the premaxillae sit the maxillae, which are the broadest bones of the dorsal surface of the skull. When viewed from above the outer edges of the maxilla are sinuous, constricting at the contact with the premaxilla, reaching their greatest width around the large 5th maxillary tooth before constricting and broadening once again shortly behind it. Looking at the skull from the side shows that the maxillae exhibit a strongly concavo-convex ventral margin, a condition known as festooning. This results in two dental waves, which peak with the fifth and 12th maxillary teeth respectively. The maxilla continues backwards until meeting the lacrimal bone, inserting a small process between it and the nasals before sharply reducing into a lateral process that contacts the jugal bone.
Information on how the individual bones connect to another becomes harder to determine at the transition from the snout to the skull table due to the deformation of the holotype skull. Taphonomy has caused the broken frontal bone as well as the prefrontal bones to overlap the posterior ends of the nasals and parts of the lacrimals. The lacrimal bone is pointed towards the front, wedging itself into the maxilla, and broad towards the back, where the bone forms a process that contributes significantly towards the anterior margin of the orbits. The prefrontal likewise contributes to the eyesocket and is roughly triangular in shape based on the better preserved left side of the holotype. The frontal bone contributes a small part to the orbital margins and like in Dongnanosuchus is moderately broad between the eyesockets, with the interorbital septum being just a little broader than the space between the supratemporal fossae on the skull table. Though heavily distorted in the holotype, the eyesockets were clearly quite large compared to the supratemporal fossae and appear to have lacked the surrounding rim seen in Jiangxisuchus.
As is typical, the frontal broadens posteriorly as it enters the skull table and in orientalosuchine fashion just enters the supratemporal fossa. It contacts the rectangular postorbitals to either side along a oblique, concavo-convex suture and the single parietal bone at the midline between the fossae. Like the overall proportions of the skull, the supratemporal fossae too are wider than long. The bones that form the edge of the fenestra, sans the frontal, overhang the opening which differs from what is observed in any other member of Orientalosuchina that preserves this region of the skull. As in Dongnanosuchus, the space occupied by the parietal between the fossae is slightly narrower than the frontal is between the eyes. Also as in Dongnanosuchus it contacts the quadrate bone within the fossa and is simultaneously separated by it from the squamosal even though the two contact along an almost straight suture outside of the opening. The very back of the skull table is occupied by an exposed supraoccipital, which actually prevents the parietal from reaching the posterior margin.
The triradiate jugal bone contacts the maxilla and extends back to form part of the lower orbital margin and much of the ventral infratemporal fenestra. The bone consists of an anterior ramus which is broad but short, a thinner and longer posterior ramus and its contribution to the postorbital bar, which rises between orbit and infratemporal fenestra and joins the descending process of the postorbital. Its contact with the quadratojugal is oblique, with the dorsal contact taking place before the end of the infratemporal fenestra while the ventral contact is set much further back just before the mandibular condyle. The quadratojugal possesses a small spine that enters the fenestra and runs almost parallel its rear edge, something not known from any other orientalosuchines but similar to Brachychampsa. Like in Dongnanosuchus, Jiangxisuchus and Orientalosuchus, the foramen aëreum is located medially on the quadrate. Between the lateral and media condyles of the quadrate, the lateral is slightly larger.