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Crocodylomorpha
Crocodylomorpha
Crocodylomorpha
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Crocodylomorphs
Temporal range: Late Triassic–Present, 235–0 Ma
Skeleton of Terrestrisuchus, an early crocodylomorph
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauria
Clade: Pseudosuchia
Clade: Paracrocodylomorpha
Clade: Loricata
Clade: Crocodylomorpha
Hay, 1930
Type species
Crocodylus niloticus
Laurenti, 1768
Subgroups

Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. Extinct crocodylomorphs were considerably more ecologically diverse than modern crocodilians. The earliest and most primitive crocodylomorphs are represented by "sphenosuchians", a paraphyletic assemblage containing small-bodied, slender forms with elongated limbs that walked upright, which represents the ancestral morphology of Crocodylomorpha. These forms persisted until the end of the Jurassic.[1] During the Jurassic, crocodylomorphs morphologically diversified into numerous niches, with the subgroups Neosuchia (which includes modern crocodilians) and the extinct Thalattosuchia adapting to aquatic life, while some terrestrial groups adopted herbivorous and omnivorous lifestyles. Terrestrial crocodylomorphs would continue to co-exist alongside aquatic forms until becoming extinct during the Miocene.

Evolutionary history

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Life restoration of Hesperosuchus from the Late Triassic (Carnian) of North America, an early branching, so-called "sphenosuchian" crocodylomorph

The earliest lineages of Crocodylomorpha are placed into the paraphyletic "Sphenosuchia", which are characterized by slender bodies with elongate legs. The oldest known crocodylomorph is Trialestes, known from the Late Triassic (Carnian-Norian) of Argentina, around 231–225 million years ago,[2] the last groups of "sphenosuchians" persisted until the end of the Jurassic.[1] During the Jurassic, crocodylomorphs diversified, including the emergence of herbivorous and omnivorous forms,[3] as well as the aquatically adapted Neosuchia and Thalattosuchia, with Thalattosuchia and several groups of neosuchians becoming adapted to a marine lifestyle over the Jurassic and Cretaceous[4] During the Cretaceous, the Notosuchia were a diverse group across the Southern Hemisphere occupying many diverse ecologies.[5] Modern crocodilians, a subgroup of Neosuchia, emerged during the Late Cretaceous.[4] Crocodylomorph diversity was severely reduced by the end-Cretaceous extinction event.[5] The last group of terrestrially adapted crocodylomorphs was the Sebecidae, a group of large predatory notosuchians which persisted in South America until the middle Miocene around 12 million years ago.[6][4]

Taxonomy and phylogeny

[edit]

Historically, all known living and extinct crocodiles were indiscriminately lumped into the order Crocodilia. However, beginning in the late 1980s, many scientists began restricting the order Crocodilia to the living species and close extinct relatives such as Mekosuchus. The various other groups that had previously been known as Crocodilia were moved to Crocodylomorpha and the slightly more restrictive Crocodyliformes.[7] Crocodylomorpha has been given the rank of superorder in some 20th and 21st century studies.[8]

The old Crocodilia was subdivided into the suborders:

Mesosuchia is a paraphyletic group as it does not include eusuchians (which nest within Mesosuchia). Mesoeucrocodylia was the name given to the clade that contains mesosuchians and eusuchians (Whetstone and Whybrow, 1983).

The previous definitions of Crocodilia and Eusuchia did not accurately convey evolutionary relationships within the group. The only order-level taxon that is currently considered valid is Crocodilia in its present definition. Prehistoric crocodiles are represented by many taxa, but since few major groups of the ancient forms are distinguishable, a conclusion on how to define new order-level clades is not yet possible. (Benson & Clark, 1988). Crocodylomorpha in the modern sense, as defined by Paul Sereno in 2005, is phylogenetically defined as the most inclusive clade containing Crocodylus niloticus (the Nile crocodile), but not Rauisuchus tiradentes, Poposaurus gracilis, Gracilisuchus stipanicicorum, Prestosuchus chiniquensis, or Aetosaurus ferratus.[9]

Phylogeny

[edit]

Below is a cladogram of most known crocodylomorphs from Stephan F. Speikeman in 2023.[10] The modern consensus is that "sphenosuchians" form a paraphyletic assemblage leading towards the more derived Crocodyliformes. The basal crocodylomorph Saltoposuchidae was defined by Speikman, 2023 as the most inclusive clade containing Saltoposuchus connectens, but not Sphenosuchus acutus, Carnufex carolinensis, and Trialestes romeri. The clade Solidocrania was established by Alexander A. Ruebenstahl and colleagues in 2022 to unite crocodyliforms with their closest "sphenosuchian" relatives who both share similarly reinforced skulls. This clade was defined as the least inclusive clade including Junggarsuchus sloani, Almadasuchus figarii, and Macelognathus vagans.[11] The following cladogram was published by Juan Martín Leardi in 2025.[12]

Crocodylomorpha

Biology

[edit]

The Crocodylomorpha comprise a variety of forms, shapes, and sizes, which occupied a range of habitats. As with most amniotes, Crocodylomorphs were and are oviparous, laying eggs in a nest or mound, known from strata as old as the Late Jurassic.[13] Adult size varies widely, from about 55 cm long in Knoetschkesuchus to much larger dimensions, as in Sarcosuchus. Most crocodylomorphs were carnivores, but many lineages evolved to be obligate piscivores, such as the extant gharials.

In some forms, like Hesperosuchus and Terrestrisuchus, metatarsal V still had one or two phalanges,[14] but in Crocodyliformes all metatarsal V phalanges have been lost.[10]

References

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Sources

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Crocodylomorpha

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Crocodylomorpha is a diverse of pseudosuchian archosaurs that encompasses all living crocodylians (crocodiles, alligators, caimans, and gharials) and their extinct relatives, originating in the Period approximately 230 million years ago during the upper stage. Defined phylogenetically as the most inclusive group containing Crocodylus niloticus (the ) but excluding Poposaurus gracilis (a rauisuchian), this is characterized by early members that were small, slender, terrestrial predators with long legs adapted for agile running, contrasting with the more robust, forms seen in modern survivors. Over its more than 200-million-year history, Crocodylomorpha has exhibited remarkable adaptability, occupying terrestrial, , and fully aquatic niches across global environments. The evolutionary history of Crocodylomorpha is marked by multiple radiations following mass s, beginning with basal "sphenosuchian" forms in the that filled top predator roles before the dominance of large theropod dinosaurs. Major diversification occurred in the after the end-Triassic , giving rise to subgroups such as the marine-adapted thalattosuchians (e.g., teleosaurids and metriorhynchids with streamlined bodies and paddle-like limbs) and the more crocodyliform-like protosuchians. By the , disparity peaked with the emergence of notosuchians—highly varied forms including herbivorous, burrowing, and terrestrial carnivores—and the ancestors of modern eusuchians, reflecting ecological opportunities in fragmented landmasses and shifting climates. Body size followed a multi-peak pattern, with an early disparity peak in the driven by small atoposaurids and large teleosaurids, followed by a gradual decline through the due to extinctions of small-bodied lineages, though mean sizes increased in clades. Crocodylomorpha demonstrated resilience through major events, surviving the end-Triassic and Cretaceous-Paleogene (K-Pg) boundaries with minimal long-term impact compared to other s, though diverse lineages like thalattosuchians and most notosuchians vanished by the end of the . Post-K-Pg, the clade's morphological and ecological diversity sharply declined, with only the crown-group Crocodylia—encompassing alligatoroids, crocodyloids, and gavialoids—diversifying in the , primarily as semiaquatic ambush predators in freshwater and coastal habitats. As of 2025, 26 species persist, representing a fraction of the group's former glory, yet their fossil record underscores Crocodylomorpha's role in understanding evolution, niche partitioning, and recovery from global catastrophes.

Evolutionary history

Origins in the Triassic

Crocodylomorpha emerged during the , with the earliest known fossils dating to the stage approximately 235–227 million years ago. These initial records include basal sphenosuchians such as Carnufex carolinensis from the Pekin Formation in , representing one of the oldest documented members of the clade. Similarly, Saltoposuchus connectens from the Tübingen Formation in exemplifies early crocodylomorph morphology, though its fossils are slightly younger within the stage. These small-bodied forms, typically under 2 meters in length, indicate a rapid initial appearance following the diversification of pseudosuchian archosaurs. Key adaptations distinguishing crocodylomorphs from their archosaur ancestors included a fully erect limb posture, which enhanced terrestrial mobility and stamina compared to the more sprawling gait of earlier pseudosuchians. Elongated hindlimbs further supported agile, cursorial locomotion, allowing these early crocodylomorphs to inhabit diverse terrestrial environments. Dentition showed early signs of anisodonty, with differentiated teeth suited for grasping prey, marking a shift toward specialized carnivory inherited and refined from archosaur forebears. By the and stages (approximately 227–201 million years ago), crocodylomorphs underwent an initial radiation, evidenced by fossils from the in , where taxa like Hesperosuchus agilis and cf. Sphenosuchus sp. document increased diversity in fluvial and settings. In , the Los Colorados Formation yields remains of non-crocodyliforms such as Pseudhesperosuchus jachaleri and protosuchids, highlighting a broad Pangaean distribution during this interval. This expansion coincided with arid to semi-arid habitats across the , where seasonal river systems and ephemeral lakes supported small, agile predators amid the early stages of continental rifting. These conditions, characterized by hot, dry climates with intermittent wet phases, facilitated the ecological niche occupancy by basal crocodylomorphs before their further diversification in the .

Mesozoic diversification and key radiations

The Triassic-Jurassic mass extinction event approximately 201 million years ago triggered a rapid radiation of crocodylomorphs, the sole surviving pseudosuchian lineage, leading to significant morphological disparity by the Early Jurassic. This diversification was marked by the emergence of thalattosuchians, a clade that adapted to fully marine environments during the Jurassic. Teleosaurids, such as Teleosaurus, inhabited coastal and nearshore habitats with robust, armored bodies suited for ambush predation in shallow waters, while metriorhynchids like Metriorhynchus and Geosaurus evolved streamlined forms, reduced armor, and paddle-like limbs for open-ocean pelagic lifestyles, representing one of the most extreme aquatic specializations among archosaurs. Early neosuchians, basal relatives of modern crocodylians, also arose, exemplified by semi-aquatic forms such as Goniopholis from the Late Jurassic Morrison Formation in North America, which featured generalized skulls for versatile feeding in riverine and floodplain ecosystems. In the , crocodylomorph diversity peaked with expansions into terrestrial and semi-aquatic niches, particularly in , where notosuchians exhibited remarkable morphological innovation. Protosuchians, early crocodylomorphs with terrestrial traits, persisted in some regions, but notosuchians dominated with adaptations for upright posture, varied locomotion, and specialized dentitions reflecting omnivorous, herbivorous, or insectivorous diets. For instance, Anatosuchus minor from the of possessed a broad, overhanging snout with low-pressure sensory pits, enabling it to forage for small , amphibians, and in shallow waters or mudflats. Similarly, Pakasuchus kapilimai from the mid-Cretaceous of displayed mammal-like teeth, including shearing and grinding molars for processing diverse terrestrial prey such as and small vertebrates, highlighting with early mammals. Pholidosaurs, long-snouted neosuchians like Pholidosaurus, occupied semi-aquatic habitats in with elongated rostra for piscivory, bridging basal and advanced crocodyliform forms. Key radiations underscored crocodylomorphs' ecological versatility, including the rise of giant apex predators in coastal environments. Deinosuchus, an enormous alligatoroid reaching over 10 meters in length, preyed on large dinosaurs and marine reptiles along the in , evidenced by bite marks on hadrosaur and tyrannosaurid bones, and tolerated brackish to saltwater conditions. Fossil assemblages from iconic sites illustrate this diversification: the yielded neosuchians like Goniopholis amid fluvial deposits; the preserved exceptionally detailed thalattosuchians such as Cricosaurus in lagoonal settings; and the in contained diverse crocodyliforms, including the aberrant Stomatosuchus with its filter-feeding pouch-like snout, in deltaic and coastal facies. These adaptations allowed crocodylomorphs to exploit a broad array of niches, from fully aquatic to predominantly terrestrial, before the end-Cretaceous extinction.

Cenozoic survival and modern forms

The Cretaceous–Paleogene (K–Pg) extinction event at approximately 66 million years ago resulted in the extinction of most non-crocodylian crocodylomorph lineages, though recent evidence indicates brief survival of at least some notosuchians into the early . Only members of the crown-group Crocodylia, particularly within , survived long-term into the . This survival is attributed to the ecological versatility of eusuchians, which allowed them to persist through the mass extinction that eliminated most other pseudosuchians; a 2025 study further highlights the clade's resilience across multiple extinctions due to ecomorphological adaptability. Post-K–Pg, eusuchian lineages underwent diversification, marking a recovery phase amid the recovery of continental ecosystems. In the , early alligatoroids and crocodyloids emerged and diversified primarily in and . For instance, the alligatoroid represents one of the earliest definitive records of the genus in , known from Late Eocene deposits in , indicating an expansion of alligatoroid forms during this period. In , Paleogene assemblages include basal alligatoroids such as and Hassiacosuchus, alongside stem crocodyloids and planocraniids, reflecting a radiation of these groups in temperate to subtropical environments following the . These fossils document the initial establishment of modern crocodylian body plans and ecological roles. During the and into the , crocodylomorphs—now predominantly crocodylians—migrated toward tropical regions as global climates cooled, adapting to warmer, wetland-dominated ecosystems in the . became prominent among some lineages, exemplified by Purussaurus, a caimanine from South American deposits that reached lengths of approximately 12 meters, serving as a top predator in fluvial systems. This period saw crocodylians integrate into contemporary ecosystems, with their diversity stabilizing around 25 extant species today, shaped by biogeographic shifts and climatic constraints. Recent analyses estimate the divergence of the crown-group Crocodylia between 100 and 80 million years ago, aligning with origins and supporting the survival of these lineages through the K–Pg boundary. These estimates, derived from integrated morphological and genetic data, highlight the deep evolutionary history leading to modern forms.

Taxonomy and systematics

Classification and major groups

Crocodylomorpha is defined as the most inclusive containing Crocodylus niloticus but excluding Poposaurus gracilis, encompassing the crown-group Crocodylia (extant crocodilians) and various stem-groups such as basal forms and intermediate taxa. This clade originated in the and includes approximately 26 extant species alongside a rich diversity of extinct relatives that exhibited terrestrial, semiaquatic, and fully aquatic lifestyles. The classification of crocodylomorphs traces back to , who in the 10th edition of Systema Naturae (1758) placed the within the genus Lacerta as Lacerta crocodilus, grouping it among based on superficial morphological similarities rather than phylogenetic relationships. Over the 19th and early 20th centuries, evolved through hierarchical groupings like orders and families, often emphasizing anatomical features such as skull structure, but these systems lacked explicit consideration of evolutionary ancestry. The shift to cladistic approaches in the mid-20th century, influenced by Willi Hennig's principles, emphasized monophyletic groups defined by shared derived characters; A. D. Walker's 1968 erection of Crocodylomorpha as a uniting Crocodylia with sphenosuchians marked a key transition, later refined in cladistic analyses by Jacques Gauthier in 1986. Major subgroups of Crocodylomorpha include basal sphenosuchians, which represent early terrestrial forms from the to , and crocodyliforms such as Protosuchia, early basal crocodyliforms with primitive features like upright limb posture. Mesoeucrocodylia, defined as all crocodyliforms more closely related to Crocodylus niloticus than to Protosuchus richardsoni, encompasses more derived forms, uniting Notosuchia (primarily terrestrial, diverse in the with adaptations like herbivory) sister to Neosuchia (semiaquatic, leading to the extant branch ). Other notable subgroups are Thalattosuchia, a marine radiation with paddle-like limbs, and Neosuchia, which includes as the crown group containing all living crocodylians (, Crocodylidae, and ). Among extinct families, Goniopholididae, basal neosuchians characterized by robust skulls and semiaquatic habits, ranged from the to the across . Dyrosauridae, a mesoeucrocodylian group with elongated snouts and marine affinities, persisted from the () through the Middle Eocene, surviving the Cretaceous-Paleogene extinction and achieving a global distribution in the .

Phylogenetic relationships

The phylogenetic relationships within Crocodylomorpha have been elucidated through numerous cladistic analyses, revealing a basal where non-crocodyliform crocodylomorphs, often referred to as sphenosuchians, represent the earliest-diverging lineages and serve as the to all more derived crocodylomorphs. These basal forms, such as Hesperosuchus and Litargosuchus, exhibit primitive archosaurian features including slender builds and terrestrial adaptations, with no evidence of for Sphenosuchia itself in recent parsimony-based trees. Following this split, Protosuchia emerges as an early offshoot within , comprising basal crocodyliforms like Protosuchus that retain small body sizes and generalized morphologies, positioned as successive outgroups to more advanced clades in comprehensive morphological datasets. Key debates persist regarding the placement of certain groups, notably Thalattosuchia, whose is generally supported by shared cranial and postcranial traits such as elongated snouts and paddle-like limbs adapted for , but whose exact position remains contentious. Early analyses recovered Thalattosuchia as the to , while others nest it within Neosuchia; recent expanded from the 2020s, incorporating broader sampling, support positions either as basal crocodylomorphs, within Neosuchia, or to Mesoeucrocodylia, depending on dataset and outgroup choice, highlighting the influence of outgroup choice on tree topology. Similarly, Notosuchia exhibits debated affinities, with some lineages showing convergent evolutionary trends toward terrestrial mammal-like adaptations, including heterodont dentition, ziphodont teeth for shearing, and upright posture, suggesting niche overlap with mammalian herbivores and carnivores in Gondwanan ecosystems during the . Central to crocodylomorph interrelationships is the node Mesoeucrocodylia, defined as all crocodyliforms more closely related to niloticus than to Protosuchus richardsoni, which unites Notosuchia (encompassing sebecids in consensus topologies) with the crown-group radiation of and via Neosuchia. This clade is characterized by derived features like procoelous vertebrae and enhanced , marking a major diversification in the . In simplified form:

Crocodylomorpha ├── Basal crocodylomorphs (incl. sphenosuchians, paraphyletic) └── [Crocodyliformes](/page/Crocodyliformes) ├── Protosuchia (basal crocodyliforms) └── Mesoeucrocodylia ├── Notosuchia (incl. [Sebecidae](/page/Sebecidae)) └── Neosuchia ├── Thalattosuchia (debated position) └── [Eusuchia](/page/Eusuchia) └── Crocodylia ├── [Alligatoroidea](/page/Alligatoroidea) ├── [Gavialoidea](/page/Gavialoidea) └── [Crocodyloidea](/page/Crocodyloidea)

Crocodylomorpha ├── Basal crocodylomorphs (incl. sphenosuchians, paraphyletic) └── [Crocodyliformes](/page/Crocodyliformes) ├── Protosuchia (basal crocodyliforms) └── Mesoeucrocodylia ├── Notosuchia (incl. [Sebecidae](/page/Sebecidae)) └── Neosuchia ├── Thalattosuchia (debated position) └── [Eusuchia](/page/Eusuchia) └── Crocodylia ├── [Alligatoroidea](/page/Alligatoroidea) ├── [Gavialoidea](/page/Gavialoidea) └── [Crocodyloidea](/page/Crocodyloidea)

This structure reflects consensus from large morphological matrices, with over 500 characters supporting the basal splits and major nodes. Recent phylogenetic studies in the , leveraging high-resolution CT scans to reveal internal cranial anatomy such as neurovascular structures and endosseous labyrinths, have further refined relationships within Notosuchia by confirming as a derived of terrestrial predators within Mesoeucrocodylia, rather than basal offshoots, with close affinities to other notosuchians like baurusuchids. Recent phylogenetic updates (2024) have clarified definitions within Notosuchia, addressing contentious positions of clades like . For instance, analyses of Sebecus icaeorhinus and related taxa demonstrate shared choanal and palatal features with other notosuchians, supporting their integration as late-surviving terrestrial predators in faunas.

Anatomy and morphology

Skeletal adaptations

Crocodylomorphs exhibit a remarkable postcranial evolution, transitioning from the lightweight, builds of early forms to the robust, semi-aquatic or terrestrial adaptations seen in later clades. Basal crocodylomorphs, such as those in Sphenosuchia, possessed gracile skeletons with elongated hindlimbs and a relatively long, flexible tail, enabling a fully terrestrial lifestyle with potentially facultative or high-speed quadrupedal locomotion similar to contemporaneous theropod dinosaurs. In contrast, more derived crocodyliforms, particularly eusuchians, developed a quadrupedal stance with a sprawling or semi-erect , characterized by shortened, muscular limbs and a barrel-shaped trunk supported by broad ribs, adaptations suited to predation in aquatic or semi-aquatic environments. Limb modifications among crocodylomorphs reflect diverse ecological niches. Early sphenosuchians featured elongated hindlimbs relative to forelimbs, with slender long bones and reduced phalangeal counts, enhancing cursoriality on land. In marine-adapted thalattosuchians, particularly metriorhynchids, fore- and hindlimbs evolved into paddle-like structures through hyperphalangy and flattened elements, facilitating propulsion in pelagic environments while retaining some terrestrial capability in basal teleosauroids. Osteoderm armor, consisting of dermal ossifications embedded in the skin, emerged early in crocodylomorph evolution and became more extensive in neosuchians, forming paravertebral rows that provided structural reinforcement and protection, with histological evidence of woven bone deposition for rapid growth. The of crocodylomorphs shows clade-specific variations in vertebral morphology and counts. Notosuchians, such as Simosuchus clarki, display a shortened with a reduced number of caudal vertebrae—fewer than in any other known crocodylomorph—resulting in a compact presacral region and potentially aiding in burrowing or terrestrial maneuvering. Across the group, vertebral fusion patterns vary, with eusuchians exhibiting co-ossification in the sacrals and proximal caudals for enhanced stability during locomotion, while basal forms maintain greater flexibility in the cervical and dorsal series. Body size in Crocodylomorpha spans a wide range, from small basal forms around 1 meter in length, such as Terrestrisuchus gracilis, to gigantic species exceeding 10 meters, exemplified by Sarcosuchus imperator, which reached estimated lengths of 11–12 meters and masses over 8 tons based on vertebral and limb scaling. This disparity peaked during the , with subsequent clades showing adaptive peaks in size corresponding to ecological shifts.

Cranial and dental features

Crocodylomorphs exhibit a skull configuration inherited from their ancestors, characterized by the presence of upper and lower temporal fenestrae, an anterior to the orbit, and a mandibular fenestra on the lower , which collectively lighten the skull and accommodate jaw musculature. In basal crocodylomorphs such as sphenosuchians, these fenestrae are prominent, contributing to a lightweight cranium suited for , though the is reduced or lost in more derived crocodyliforms like those in the lineage leading to modern forms. A key evolutionary modification in Crocodylomorpha is the loss of the postfrontal bone, which occurs as a synapomorphy defining the and results in the extending posteriorly to contact the squamosal, simplifying the dorsal skull roof in advanced taxa. Dentition in crocodylomorphs is thecodont, with teeth deeply socketed in alveoli for secure anchorage, a condition that enhances biting efficiency across the group. Basal crocodylomorphs and early crocodyliforms typically possess homodont, conical teeth adapted for piercing and grasping prey, reflecting a carnivorous diet similar to that of extant crocodylians. In contrast, derived notosuchians evolved pronounced heterodonty, featuring multicusped, leaf-shaped, or molariform posterior teeth that facilitated grinding and herbivory, as seen in taxa like Simosuchus clarki and Pakasuchus kapilimai, where this adaptation arose independently at least three times during the . Palatal structures in crocodylomorphs underwent significant evolution, particularly in neosuchians and eusuchians, where an ossified secondary formed by the , , and pterygoid bones separates the nasal and oral cavities, allowing aquatic respiration while the mouth remains submerged. The choanae, or internal nares, shifted posteriorly in eusuchians to a position at the rear of the , positioned within a deep , which further supports semi-aquatic lifestyles by directing airflow efficiently. This secondary palate represents a derived feature that evolved convergently in some early-branching crocodylomorphs, enhancing predatory ecology in environments. Sensory adaptations in the crocodylomorph include the on the dorsal surface, which in some taxa houses a associated with circadian rhythms and light detection, though this structure is reduced or absent in crown-group crocodylians. Precursors to electroreception are evident in cranial features such as enlarged foramina for the , which innervate integumentary sensory organs capable of detecting pressure and chemical cues, adaptations that likely originated in semi-aquatic ancestors for prey localization. These cranial openings facilitated the evolution of multimodal sensing, integrating with postcranial sensory systems in modern crocodylians.

Paleobiology and ecology

Diet and feeding mechanisms

Early crocodylomorphs, particularly basal forms like sphenosuchians, exhibited diets centered on insectivory and small-scale carnivory, as inferred from their multicusped teeth showing wear patterns consistent with processing hard-shelled invertebrates and small vertebrates. Tooth morphology in these taxa, including conical crowns with fine serrations and evidence of proal jaw movement, further supports a predatory lifestyle targeting agile, terrestrial prey such as insects and lizards during the Late Triassic. Specialized feeding adaptations emerged in later crocodylomorph lineages, with teleosaurids displaying piscivorous habits evidenced by their elongate, conical teeth suited for grasping slippery and isotopic signatures indicating marine prey sources. In contrast, advanced notosuchians evolved herbivory, as seen in clarki, where complex, leaf-shaped and biomechanical analyses of oral processing capacity reveal adaptations for grinding material, marking multiple independent transitions to plant-based diets within Crocodylomorpha. Apex predatory strategies characterized large neosuchians like , with bite force estimates reaching approximately 102,800 N based on extrapolations from extant crocodylian scaling and robusticity, enabling it to subdue large dinosaurs through crushing bites. evidence, including bite marks on hadrosaur bones and strength analyses, suggests these giants employed death-roll maneuvers analogous to modern crocodylians, twisting to dismember prey despite their massive size. Stable isotope analyses, particularly δ13C values from tooth enamel and bone apatite, provide evidence of dietary niche shifts across crocodylomorph , with early terrestrial forms showing enriched δ13C signatures from C3 plant-based prey chains, transitioning to depleted values in aquatic thalattosuchians reflecting marine or freshwater piscivory. These isotopic patterns highlight ecological diversification, from terrestrial carnivory in notosuchians to semi-aquatic opportunism in later eusuchians.

Locomotion, habitat, and behavior

Early crocodylomorphs exhibited terrestrial locomotion characterized by an erect limb posture, enabling a "high walk" gait similar to that observed in modern crocodilians during rapid movement. This adaptation, inferred from skeletal features such as elongated forelimbs and a more upright hindlimb stance in basal forms like sphenosuchians, allowed for efficient overland travel and potentially faster pursuits compared to the sprawling posture of more basal pseudosuchians. In contrast, thalattosuchians developed specialized aquatic locomotion, relying on lateral undulation of a hypocercal tail for propulsion during swimming, with reduced limbs functioning more as stabilizers than primary thrust generators. Habitat preferences among crocodylomorphs underwent significant shifts over time, beginning with riparian and terrestrial environments in the , where early taxa like Protosuchus inhabited riverine floodplains and forested margins. By the , thalattosuchians, particularly metriorhynchids, achieved fully pelagic marine lifestyles, supported by adaptations including hypertrophied salt-excreting glands that facilitated in saltwater environments. In the , certain lineages such as notosuchians occupied arid inland habitats, with fossils from semi-arid basins like Brazil's Group indicating tolerance for dry, seasonal conditions through behavioral adjustments like burrowing or . Behavioral inferences for extinct crocodylomorphs derive primarily from trace fossils and taphonomic evidence. Nesting traces, such as mound-like structures associated with protosuchians, suggest reproductive behaviors involving site selection near water bodies for egg deposition and incubation. Bonebeds containing aggregated juveniles, as seen in some crocodyliform assemblages, imply possible or social grouping, where adults may have protected young from environmental stressors or predators. Trackways further reveal ambush-oriented behaviors, with crocodyliform prints showing slow, deliberate quadrupedal progression and tail drags indicative of stealthy approaches in shallow aquatic settings, consistent with bottom-walking to maintain for surprise attacks.

Diversity and distribution

Extinct taxa and biogeography

Crocodylomorpha encompasses a diverse array of extinct taxa that dominated ecosystems, with notable examples including the giant pholidosaurid imperator from the of northern , which reached lengths of approximately 11-12 meters and likely preyed on large vertebrates in riverine habitats. Another distinctive form is Armadillosuchus arrudai, a notosuchian from the of known for its extensive dermal armor resembling that of armadillos, suggesting adaptations for terrestrial life and defense against predators. Similarly, Mourasuchus nativus, a caimanine from the of , exhibited a broad, flat and specialized indicative of filter-feeding on small aquatic prey, growing to over 10 meters in length. Biogeographic patterns among extinct crocodylomorphs reveal strong continental affinities, with notosuchians predominantly restricted to Gondwanan landmasses such as , , , and , where they diversified into terrestrial and herbivorous forms during the . In contrast, neosuchians showed greater Laurasian distribution in , , and , often occupying semiaquatic niches. Dyrosaurids exemplify transatlantic dispersal, originating in during the and colonizing and in the via marine routes across the widening . The temporal distribution of crocodylomorph diversity peaked during the , driven largely by the radiation of notosuchians and eusuchians in fragmented and . Following the breakup of , regional intensified, as vicariance isolated lineages on southern continents, leading to unique adaptive radiations such as burrowing and mammalian-mimic forms in . Gaps in the crocodylomorph fossil record are evident, particularly in , where sampling is underrepresented compared to other continents, potentially underestimating diversity in Laurasian neosuchians during the . Recent discoveries highlight previously unrecognized high-latitude distributions and Gondwanan connections.

Living crocodylians and conservation

Living crocodylians, comprising the crown group Crocodylia, are represented by 25 recognized (as of 2025) distributed across three families: with 8 (such as the , Alligator mississippiensis), Crocodylidae with 15 (such as the , Crocodylus niloticus), and with 2 (the , Gavialis gangeticus, and the , Tomistoma schlegelii). These exhibit a distribution, primarily in freshwater and brackish habitats across the , , , and , with the highest diversity concentrated in and northern , where up to six can co-occur in shared ecosystems. However, some populations face challenges from ; for instance, in , introduced Burmese pythons (Python bivittatus) compete with native for prey resources, exacerbating pressures on local food webs. Conservation efforts for living crocodylians are coordinated by the IUCN SSC Crocodile Specialist Group, which assesses statuses via the ; of the 25 species, 11 are classified as threatened (7 Critically Endangered, 1 Endangered, 3 Vulnerable) as of 2025, representing significant risk primarily from habitat loss due to , drainage, and river damming, as well as illegal for skins and meat. Notable conservation efforts include those for the (Crocodylus intermedius), listed as Critically Endangered with a wild population estimated at 250-1,500 individuals (fewer than 100 in as of 2025), supported by reintroduction programs and measures in protected areas of and , though populations remain critically low despite some stable subpopulations. Despite these threats, sustainable management has led to downlistings for species like the , from Endangered to Least Concern, highlighting the potential for recovery when habitat protection and enforcement are prioritized. Human-crocodylian interactions encompass both conflicts and benefits, with economic value derived from regulated farming operations that produce high-quality leather for luxury goods and meat for consumption, generating millions in annual revenue while reducing incentives for wild harvesting through CITES-compliant ranching programs. Ecologically, crocodylians serve as keystone predators that regulate prey populations and maintain biodiversity; for example, American alligators create "gator holes" that provide critical refugia for fish, birds, and amphibians during dry periods, functioning as ecosystem engineers in wetland habitats. These roles underscore their importance in supporting broader trophic dynamics and nutrient cycling in tropical and subtropical ecosystems.

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