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Dyrosauridae was a successful clade of marine crocodyliforms that survived the Cretaceous–Paleogene biotic crises. The most important taxon from North America is Hyposaurus rogersii, a species firs...

The fossil crocodylomorph fauna of the Cenozoic of South America is very rich and diverse. Historically, few publications have been dedicated to providing an overall review of this fauna, with most reviews focusing on specific areas. However, the fact that many new species, taxonomic reviews and description of new specimens have been proposed in the last decade makes a comprehensive review of the fossil crocodylomorph fauna of the South American Cenozoic necessary. The only crocodylomorph lineages to have a fossil record comprising Late Cretaceous and Cenozoic deposits in South America is the Dyrosauridae. Sebecidae or its predecessors, however, are very likely to have inhabited the continent during the Cretaceous-Paleogene transition as well; both Dyrosauridae and Sebecidae are considered here to have survived the Cretaceous-Paleogene extinction while inhabiting South America. Caimaninae (Alligatoroidea) arrived either in the late Cretaceous or in the early Paleocene coming from North America. The fossil record of Caimaninae is present, however, only from the Paleocene. By the Eocene, there are no records of Dyrosauridae in South America; this group was globally extinct after the Eocene, possibly due to the global cooling that occurred by the end of the epoch. Sebecids and caimanines solely comprised the crocodylomorph fauna of the continent until the Miocene, where there are the first records of Gavialoidea (Gryposuchinae) and a possible first dispersion of Crocodyloidea, through the tentative tomistomines Charactosuchus and Brasilosuchus. Gryposuchinae likely arrived in the continent from Africa or from Asia during the Oligocene. Charactosuchus and Brasilosuchus may have come from North America where tomistomines lived from the Oligocene to the Pliocene. Sebecids were extinct after the middle Miocene; Charactosuchus, Gryposuchinae, Purussaurus, Mourasuchus and durophagous caimanines such as Gnatusuchus were extinct after the late Miocene. These extinctions are related to changes in the drainage basins caused by elevation of the Andes mountain range. Only the extant caimanine Caiman, Melanosuchus and Paleosuchus would survive the Miocene, being enriched by Crocodylus from the Pliocene onwards, which is likely that Crocodylus arrived in the American continents from Africa. The current fossil record indicates that these four genera comprise the extant crocodylian fauna of the continent since the Pliocene. Although our knowledge on crocodylomorph fossil fauna of the South American Cenozoic has increased continuosly, especially in the last decade, much yet must be done, especially on the taxonomy and phylogeny of Brasilosuchus and Charactosuchus, fieldworks in Paleogene and Pliocene localities, and the evolution of the specialized Caimaninae morphotypes.

Dyrosaurids were highly specialized, largely marine, relatives of living crocodylians, and one of the few archosaur lineages to survive the K-Pg extinction. Dyrosaurids lived during the Cretaceous to the Eocene and represent a unique combination of morphology and ecology not seen in living crocodylians. Little is known about their endocranial anatomy, leaving many questions about their neurosensory adaptations unaddressed. Recently, µCT (micro-computed tomography) scans were made of a well-preserved skull of Rhabdognathus, a Paleocene dyrosaurid from Mali. This marks the first time the braincase and neurosensory features of a dyrosaurid have been examined using CT. We focus our attention to three specific internal structures: the cranial endocast; the inner ear; and the paratympanic sinuses. The cranial endocast of Rhabdognathus revealed novel features including a unique conformation of its paratympanic system, a prominent dorsal venous system that communicates with the external skull table, extremely enlarged tympanic vestibules that meet at the midline of the endocranium, a prominent spherical cerebrum, and elongate olfactory tracts accounting for half the total endocast length. The bizarre laterally facing lateral Eustachian foramen of dyrosaurids is now understood to be a complex fossa including both a ventrally directed lateral Eustachian foramen and a laterally directed foramen for the basioccipital diverticulum. A novel median pterygopharyngeal canal was discovered connecting the pharynx to the adductor chamber. These revelations require a reinterpretation of the associated external foramina visible on the posterior of the skull in dyrosaurids and potentially their close relatives the pholidosaurids. The olfactory tract terminates in an enlarged olfactory region possessing complex bony projections—a unique morphology perhaps serving to increase surface area for olfaction. The inner ear of Rhabdognathus exhibits characteristics seen in both Pelagosaurus and Gavialis. The vestibule is spherical, as in Gavialis, but is significantly expanded. The semicircular canals are enlarged but pyramidal in shape as in the thalattosuchian Pelagosaurus. The proportion of the cochlear length to total endosseous labyrinth height is roughly 0.5 in Rhabdognathus implying that the hearing capabilities resemble that of thalattosuchians. A suite of expanded sense organs (e.g., bony olfactory lamina; hypertrophied vestibule of the inner ear), and the clear expansion of the cerebrum to a more symmetrical and spherical shape suggest that dyrosaurids possess neuroanatomical modifications facilitating an agile predatory near-shore ecology.

International audience; Following our fieldwork in Paleogene deposits of Togo, we herein report cranial as well as postcranial elements belonging to the family Dyrosauridae. This assemblage is dated to the Late Paleocene (Thanetian) from two quarries in southern Togo. The specimens include a partial skull presenting two large supratemporal fossae and a massive occipital condyle; long and slender isolated teeth; amphicoelous vertebrae including several articulated ones; and two osteoderms devoid of carina. The morphology of the partial skull reveals similarities with some African longirostrine forms such as Rhabdognathus spp., although this attribution cannot be confirmed. Longirostrine forms, known in the late Paleocene and early Eocene of the Iullemmeden basin (Nigeria, Niger, Mali, Algeria) and in the phosphates of Morocco and Tunisia, is only represented in Thanetian levels in Togo. Different palaeoenvironmental settings seem to have characterized the various African basins during the lower Eocene, with consequences for the geographic distribution of dyrosaurids. These dyrosaurid remains confirm the presence of the family in Togo during the Paleocene and underline the fossiliferous potential of the coastal sedimentary basin in Togo and in the bay of Benin.; Suite à nos travaux de terrain dans les dépôts du Paléogène du Togo, nous rapportons des éléments crâniens et post-crâniens appartenant à la famille des Dyrosauridae. Cet assemblage de crocodiliens est daté du Paléocène supérieur (Thanétien) affleurant dans deux carrières au Sud du Togo. Les spécimens décrits sont représentés par un crâne partiel présentant de grandes fosses supratemporales et un condyle occipital massif ; des dents isolées effilées et cannelées; des vertèbres amphicoeles dont plusieurs articulées ; et deux ostéodermes dorsaux sans carène. La morphologie des restes crâniens semble similaire à certaines formes africaines longirostres telles que Rhabdognathus spp., bien qu’une telle attribution générique ne puisse être confirmée. Les formes longirostres, connues au Paléocène supérieur et à l’Eocène inférieur dans le bassin des Iullemmeden (Nigéria, Niger, Mali et Algérie), dans les phosphates du Maroc et de Tunisie, ne sont représentées au Togo qu’au Thanétien. Des évolutions paléoenvironnementales différentes semblent avoir caractérisé les divers bassins d’Afrique à l’Eocène inférieur, et ont probablement influencé la distribution géographique des Dyrosauridae. Ces restes inédits de Dyrosauridae confirment, d’une part, la présence de ce groupe au Paléocène au Togo et accentuent, d’autre part, le potentiel fossilifère du bassin sédimentaire côtier du Togo et des dépôts contemporains de la baie du Bénin.

We describe a partial dyrosaurid skeleton recently prepared out of a limestone block discovered in the 1930s from Danian strata along the Atlantic coast of Senegal. The specimen, from a single individual, comprises nicely preserved elements of the appendicular and axial skeleton from the abdominal and sacral region, which enables us to refine our knowledge on some postcranial characteristics of the Dyrosauridae. Although Dyrosauridae are abundant in early Eocene deposits of North Africa, the present discovery in the Danian of Senegal fills a patchier record early after the K/Pg boundary and provides an important comparative data point with the few other Danian dyrosaurid records such asAtlantosuchusfrom nearby Morocco orGuarinisuchusandHyposaurusfrom Brazil and the USA, respectively.

Although the European dinosaur succession during the latest Cretaceous and its relationship with the Cretaceous-Paleogene (K-Pg) mass extinction has been the focus of recent work, other continental vertebrates, such as crocodylomorphs, have received less attention. The European continental record of crocodylomorphs in general, and of eusuchians in particular, is relatively dense through the Maastrichtian until the K-Pg boundary. Traditionally it has been argued that continental crocodylomorphs were minimally impacted by the K-Pg extinction, but they were substantially affected in Europe with the disappearance of endemic eusuchians such as Hylaeochampsidae, Allodaposuchus and their close relatives, and non-eusuchians such as Doratodon or Theriosuchus. Despite extensive sampling in Danian continental deposits, only scarce fragmentary crocodylomorph remains have been cited. It is not until the late Paleocene and Eocene that a recovery in continental crocodylomorphs is observed. The presence of taxa such as planocraniids, the alligatoroids Diplocynodon and Hassiacosuchus, and stem crocodyloids during this period provide the first reliable continental records of Crocodylia in Europe and is best explained by post-extinction immigration from Asia or North America. By contrast, marine forms such as Thoracosaurus are found on both sides of the K-Pg boundary in Europe. The adaptation of these marine animals to different environments, from shallow seas to more transitional or fluvial environments, could be the key to their success and survival across the K-Pg boundary, as seen in other marine crocodylomorph clades such as Dyrosauridae.

The enigmatic crocodyliform ‘Elosuchus’ felixi from the Echkar Formation (upper Albian to lower Cenomanian, Early–Late Cretaceous boundary) west of In Abangharit, Agadez District, Niger, is here re-described. Our assessment of the material shows that there are at least two taxa amongst the referred material: ‘E.’ felixi, including the holotype (an incomplete lower jaw) and two larger incomplete lower jaws; and an incomplete premaxilla, which we refer to Elosuchus sp. All other referred material is herein considered Crocodyliformes indeterminate. Based on our study of ‘E.’ felixi we refer it to a new genus, Fortignathus. A comparative study and updated phylogenetic analyses both suggest that F. felixi comb. nov. is a non-hyposaurine dyrosaurid or a dyrosaurid sister taxon. This is supported by four characteristics, including: inferred double festooned maxillae, a large gap between the D2 and D3 alveoli, gladius-shaped anterior dentary, and enlarged D4 alveoli that have a subrectangular cross section. The paucity of material means we refrain from referring F. felixi comb. nov. to Dyrosauridae. This species and suggestive material from the Cenomanian of Sudan allows us to formulate two hypotheses, however: (1) basal dyrosaurids were either freshwater or could live in both freshwater and saltwater ecosystems; and (2) Africa was their place of origin and dispersal.

International audience; New and nearly complete cranial remains of Pholidosaurus purbeckensis are described on the basis of specimens recovered from the Berriasian locality of Cherves-de-Cognac, France. Two skulls, associated mandibles and a set of dorsal osteoderms are available and allow a refinement of the anatomy of the genus, known otherwise from coeval deposits in Germany and England. Because of its longirostrine morphology, convergent with other crocodylomorph lineages, the phylogenetic relationships of Pholidosaurus are likely to be affected by Long Branch Attraction problems. Various tests of removing/excluding longirostrine lineages confirm that Dyrosauridae have a labile position and that their affinities with Pholidosauridae are weakly supported. Results from comparative anatomy and phylogenetic analyses recover Pholidosaurus as the basalmost member of Pholidosauridae, a group closely related to Goniopholididae. Pholidosaurus is recovered together with abundant remains of Goniopholis and with more limited remains of Theriosuchus. The paleoecology of Pholidosaurus and more generally, of Pholidosauridae, is discussed.

A well-preserved crocodyliform specimen from the Maastrichtian or Paleocene of Mali preserves the braincase and posterior dermatocranium. It is referred to Dyrosauridae on the basis of several derived features (a prominent anterior process of the postorbital, discrete occipital processes on the exoccipitals, significant quadratojugal contribution to jaw joint) and tentatively referred to Rhabdognathus on the basis of supratemporal fenestra shape. The lacrymal and prefrontal are relatively short compared with those published for other dyrosaurids. The palatines border the internal choanae anteriorly, and the choanae are divided by a midline septum derived from the pterygoids. The prefrontal pillars are mediolaterally broad and contact the palate ventrally. One stapes is preserved in place. The basicranial pneumatic system is very unusual, in that the anterior and posterior branches of the median eustachian canal are both separate at the palatal surface, and the pterygoids form part of the border for the anterior branch. The lateral eustachian openings lie within fossae on the lateral surface of the braincase and face laterally, with a descending process of the exoccipital nearly intersecting the opening. The braincase and surrounding dermal bones are elongate anteroposteriorly, and the postorbital's posterior ramus extends along the posterodorsal margin of the infratemporal fenestra. The quadrate ramus projects ventrally. These observations clarify character optimizations in previous phylogenetic analyses of Crocodyliformes.

Sabinosuchus coahuilensis, n. gen. et sp., is a marine crocodyliform from the Upper Cretaceous Sauz Creek Member or lower part of the Cuevas Creek Member of the Escondido Formation (Maastrichtian) near Sabinas in Coahuila, Mexico. The type specimen exhibits two synapomorphies of family Dyrosauridae: dentary alveolus 7 is reduced in size compared with the eighth, and the mandibular symphysis is nearly as wide as it is high for most of its length. Sabinosuchus coahuilensis is distinguished from all other known members of Dyrosauridae on the basis of three autapomorphic traits: the posterior section of the mandible is distinctly broad and flat, the mandibular rami are considerably longer than the symphysis, and the posterior mandibular alveoli are uniquely arranged. Sabinosuchus coahuilensis joins Hyposaurus rogersii as the second known North American dyrosaurid. Although the two were contemporaneous, they differed notably in rostrum length and shape; S. coahuilensis has a relatively shorter rostrum ...

We describe a new record of the dyrosaurid crocodyliform genus Hyposaurus, from the ?Campanian— Maastrichtian Shendi Formation of Sudan, based on a partial mandibular symphysis, two posterior portions of the upper jaw, and a fused frontal bone, all belonging to a single individual. The material can be assigned to Hyposaurus on the basis of the elliptical shape of the mandibular symphysis (wider than high) and the overall flat shape of the mandible. At the same time, the fossil material differs from other species of Hyposaurus in having (1) an enlarged eighth alveolus of the dentary relative to the other alveoli; (2) a reduced interalveolar space between the ninth and tenth alveoli; and (3) a prominent ridge and groove sculpturing on the dorsal side of the mandible along the symphyseal region. However, due to the fragmentary nature of the material, we refrain from drawing any higher-resolution taxonomic conclusions. The occurrence of Hyposaurus within the Shendi Formation represents the first reco...

This paper describes a new genus and species of dyrosaurid, Chenanisuchus lateroculi gen. et sp. nov. (Crocodyliformes, Mesoeucrocodylia) from the Thanetien (Late Palaeocene) of the Oulad Abdoun Basin, Morocco. This new taxon has a particularly short snout, as well as widely separated and laterally facing orbits. In the holotype, the mandible exhibits a retroarticular process that is strongly depressed posterior to the glenoid fossa, bringing the ventral margin of the medial wing of the articular to the same level as the ventral margin of the retroarticular process. This feature is shared with Congosaurus bequaerti, Dyrosaurus and isolated dyrosaurid material from Mali and Niger, but is absent in the putative closely related crocodyliforms, such as pholidosaurids and Terminonaris, and could be a dyrosaurid character.

Dyrosauridae is a clade of neosuchian crocodyliforms that diversified in terrestrial and aquatic environments across the Cretaceous-Paleogene transition. The postcranial anatomy of dyrosaurids has long been overlooked, obscuring both their disparity and their locomotive adaptations. Here we thoroughly describe of the postcranial remains of an unusually small dyrosaurid, Cerrejonisuchus improcerus, from the middle-late Paleocene Cerrejón Formation of Colombia, and we provide a wealth of new data concerning the postcranial anatomy of the key dyrosaurids: Congosaurus bequaerti and Hyposaurus rogersii. We identify a series of postcranial autapomorphies in Cerrejonisuchus improcerus (an elliptic-shaped odontoid laterally wide, a ulna possessing a double concavity, a fibula bearing a widely flattened proximal end, a pubis showing a large non-triangular distal surface) as well as functionally-important traits such as a relatively long ulna (85% of the humerus’ length), short forelimb (83% of hindlimb’s length), or thoracic vertebra bearing comparatively large lateral process (with widened parapophysis and diapophysis) along with strongly arched thoracic ribs allowing a more sturdy and cylindrical rib cage. These indicate a more terrestrial lifestyle for Cerrejonisuchus compared to the derived members of the clade. We also built a dataset of 187 traits on 27 taxa, that extensively samples the cranial and postcranial architectures of exemplar crocodyliforms. We analyze these data in via Principal Coordinate Analysis (PCoA) to visualize the postcranial morphospace occupation of Dyrosauridae, Thalattosuchia, and Crocodylia. Our data reveal the existence of a distinctive postcranial anatomy for Dyrosauridae that is markedly distinct from that of crocodylians. As a result, modern crocodylians are probably not good functional analog for extinct crocodyliformes. Postcranial data should also be more widely used in phylogenetic and disparity analyses of Crocodyliformes.