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Squalodon
Squalodon
Squalodon
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Squalodon
Temporal range: Oligocene–Miocene
Skull of S. bariensis at the Museum of Natural Sciences in Brussels.
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Superfamily: Platanistoidea
Family: †Squalodontidae
Brandt, 1873
Genus: †Squalodon
Grateloup, 1840
Type species
†Squalodon grateloupii
von Meyer, 1843
Species

†S. antverpiensis (van Beneden, 1861)
 †S. bariensis (Jourdan, 1861)
 †S. barbarus (Mchedlidze and Aslanova, 1968)
 †S. calvertensis (Kellogg, 1923)
 †S. whitmorei (Dooley, 2005)
 †S. catulli (Molin, 1859)

Squalodon is an extinct genus of whales of the Oligocene and Miocene epochs, belonging to the family Squalodontidae. Named by Jean-Pierre Sylvestre de Grateloup in 1840,[1] it was originally believed to be an iguanodontid dinosaur but has since been reclassified. The name Squalodon comes from Squalus, a genus of shark. As a result, its name means "shark tooth". Its closest modern relatives are the 2 species of the genus Platanista ( the Ganges river dolphin and Indus river dolphin).[2][3]

Description

[edit]
Reconstruction of S. calvertensis

Species of Squalodon are odontocetes that lived during the late Oligocene into the middle Miocene, about 28 to 15 million years ago.[2] The genus Squalodon belongs to the order Odontoceti, the toothed whales. Their name is derived from the term Squalus because their cheek teeth were thought to resemble the teeth of a Squalus shark. The largest species, Squalodon whitmorei, reached up to 5.5 meters in length.[4] The unique-looking squalodontids were likely distributed throughout the world in warm waters during the Oligocene and Miocene. Squalodontidae became extinct in the middle of the Miocene, leaving no descendants. Hypotheses of why this family lead to extinction have to deal with competition of other groups of dolphins as well as climate change.

These whales are characterized by both ancestral and modern features. Their teeth are the most evident ancestral feature. At this time in history other toothed whales were evolving simple conical teeth while Squalodontidae retained their primitive dentition that their ancestors (the archaeocetes) had developed.[5] Today living odontocetes have little variation in their teeth. Squalodontids' teeth are much more complex: they are widely spaced apart; their cheek teeth are triangular and serrated for grasping and cutting. Due to the efficiency of their primitive dentition squalodontids could have a diverse variety of prey. Another ancestral quality of the Squalodontidae is their necks. Squalodontid necks are more compressed than their ancestors, the Archaeoceti. Compared to toothed whales at that time, the squalodontids were likely more mobile. Paleontologists also believe that the dorsal fins were reduced but larger than that of the ancestors.[5] Shark toothed whales also possess many modern features. Their crania were well compressed, their rostrums were telescoped outward, and their skulls show proof of the origin of echolocation.[6] In S. grateloupii, the rostrum made up more than 60% of the total length of its skull.[7]

Fossil record and classification

[edit]

Fossils of this genus are identified mainly by the teeth but several different species have been named based on skull characteristics and size (the biggest being S. whitmorei). Most of the fossil record consists of teeth. These odontocete fossils have been discovered in Europe, eastern North America, New Zealand, and Argentina. Because isolated teeth are insufficient for species identification, most specimens lacking the skull can only be identified to genus.[8] The fossils of squalodontids indicate that this species is more closely related to endangered species of dolphins and not to most of the living dolphins today.[9]

S. bariensis skull

The systematic placement of Squalodon within Odontoceti was long unclear. For a long time, it was thought to be close of the ancestry of modern dolphins and porpoise.[10] Many of the fresh-water dolphins are differentiated phylogenetically very well, while the argument of some of the species has been going on for more than a century. The taxon is characterized during the Oligocene and Miocene in which heterodont teeth are standard amongst the family. Some modern features of the scapula, however, contradict with current phylogenetic relationships. Squalodontids were believed to be the last common ancestor of the odontocetes until 1984. Muizon came to the conclusion that rather than to any of the living species this family is closer related to the endangered species. Therefore, the ancestry of today's dolphins has little to do with the squalodontids.[9]

Species

[edit]
Partial skull
Tooth
1840 illustration

As the type genus of Squalodontidae, Squalodon has become a repository for various squalodontids or even taxa that were once thought to belong to Squalodontidae. However, there has been no revision of Squalodon.

Species currently recognized as valid

[edit]
  • Squalodon grateloupii Meyer, 1843 (type species)
  • Squalodon antverpiensis van Beneden, 1861
  • Squalodon barbarus Mchedlidze and Aslanova 1968
  • Squalodon calvertensis Kellogg 1923
  • Squalodon whitmorei Dooley 2005
  • Squalodon catulli Molin 1859

Questionably or originally assigned to Squalodon

[edit]
  • Arionus servatus Meyer, 1841 = Squalodon meyeri Brandt, 1873
  • Pachyodon mirabilis Meyer, 1838
  • Rhytisodon tuberculatus Costa, 1852
  • Smilocamptus burgueti Gervais, 1859
  • Phocodon melitensis (Blainville, 1840) = Phoca melitensis Blainville, 1840 = Phocodon scillae Agassiz, 1841
  • "Squalodon" kelloggi Rothausen, 1968
  • Squalodon bariensis Jourdan 1861[7]
  • Squalodon bellunensis Dal Piaz, 1901
  • Squalodon peregrinus Dal Piaz, 1971
  • Squalodon imperator Cigala-Fulgosi & Pilleri, 1985
  • Squalodon gambierensisGlaessner 1955[11]

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Squalodon

View on Grokipedia
from Grokipedia
Squalodon is an extinct of primitive toothed whales (Odontoceti) in the Squalodontidae, characterized by their distinctive featuring procumbent incisors and triangular, serrated cheek teeth resembling those of sharks. These archaic cetaceans inhabited marine environments worldwide during the late to middle epochs, approximately 28 to 15 million years ago, with fossils documented from regions including and . Species of Squalodon exhibited body lengths ranging from about 2.5 meters for the type species S. grateloupii to up to 5.5 meters for the largest known species, S. whitmorei, making them comparable in size to modern dolphins or small whales. Their skulls were longirostrine, often exceeding 60% of total body length, with advanced telescoping of facial bones and evidence of a melon-like structure suggesting early echolocation capabilities. As opportunistic carnivores, they likely preyed on , , and smaller marine mammals, inferred from their varied morphology adapted for grasping and slicing. Phylogenetically, Squalodon represents stem-group odontocetes outside group of modern toothed whales, retaining primitive traits such as strongly teeth that were eventually lost in more derived lineages like delphinoids. Recent taxonomic revisions (as of 2025) have synonymized many named species, recognizing fewer valid taxa. The family Squalodontidae dispersed from the Tethys Sea to other oceans during the , achieving significant diversity in the early before declining, possibly due to cooling climates and changes in ocean circulation that closed dispersal routes by the middle . Notable fossils include the skulls of S. whitmorei from , , and partial rostra from and , highlighting their role in understanding early cetacean .

Introduction

Etymology

The Squalodon was named in 1840 by the French naturalist Jean-Pierre Sylvestre de Grateloup, who established it based on a fragmentary containing teeth collected from marine deposits at Léognan, near , . Grateloup's description appeared in the proceedings of the Académie nationale des sciences, belles-lettres et arts de Bordeaux, marking the as one of the earliest recognized extinct odontocetes. The name Squalodon is derived from the Latin squalus, referring to a type of (as in the genus ), combined with the Greek odous (οὐδούς), meaning "tooth." This etymology highlights the striking similarity of the fossil's serrated, triangular to those of sharks, which prompted Grateloup to select a term evoking such marine predators. The choice of name stemmed from contemporary paleontological challenges, where the shark-like dentition initially led to misidentification of the remains as reptilian, rather than mammalian. Grateloup himself provisionally classified the specimen within Reptilia, a interpretation quickly revised by contemporaries like Hermann von Meyer, who recognized its cetacean affinities shortly thereafter.

General Description

Squalodon is an extinct genus of primitive toothed whales (Odontoceti) that flourished during the Late Oligocene to Middle Miocene epochs, approximately 28 to 13 million years ago. A 2025 taxonomic revision has clarified the validity of several species within the family Squalodontidae by re-evaluating fragmentary holotypes. These fully aquatic marine mammals attained body lengths of about 2.5 to 5.5 meters. Squalodon occupied a global distribution in coastal and epicontinental seas, particularly in warm, shallow marine habitats where it functioned as an , preying primarily on fish, squid, and smaller marine vertebrates. As an early odontocete lineage, Squalodon has no direct modern descendants among extant whales.

Anatomy

Cranial and Dental Features

The skull of Squalodon exhibits a mixture of primitive and derived features characteristic of early odontocetes. The cranium is compressed and telescoped, with the temporal bones advanced to a significant degree, such that the posterior maxillae nearly contact the supraoccipital and the parietals are nearly or fully covered dorsally. This telescoping elevates the vertex above the and rostrum base, contributing to a modern odontocete-like cranial profile. The facial region is concave, suggesting the presence of a for sound production, while the premaxillary foramina form asymmetrical basins—one on the left and two on the right in the neotype of S. grateloupii—potentially linked to early echolocation capabilities. The rostrum is elongated, comprising more than 60% of the total length (exceeding 432.8 mm in the neotype of S. grateloupii, with a condylobasal length over 730.1 mm), and features a dorsoventrally deep mesorostral groove that remains open along its length; the apex is laterally expanded in a longirostrine fashion. The of Squalodon is and polydont, reflecting a transitional state between archaeocete-like patterning and that of modern odontocetes, with a total of approximately 58–60 teeth across all quadrants. The dental formula is typically 3.1.11/3.1.10 (incisors, canines, postcanines per side), yielding 15–16 upper teeth and 14–15 lower teeth per side. include three procumbent incisors and four single-rooted canines with recurved crowns, suited for grasping; these transition to double-rooted posterior premolars and molars with triangular, serrated crowns bearing accessory cusps and cristae rugosae for shearing. Enamel is striated and heavily ornamented, with increasing posteriorly, including short ridges extending about 5 mm on molariform teeth. Roots are elongate and deeply embedded, and crowns reach heights of up to 28.8 mm in preserved specimens like the neotype of S. grateloupii. The structure supports this with a robust , measuring over 448 mm on the left and 422.8 mm on the right in the neotype of S. grateloupii, featuring a longer than one-third of its total length and a Y-shaped ventral profile. The coronoid process is tall and tapering, angled at approximately 23° to the ramus, with a fossa for jaw adductor musculature indicating strong closing mechanics; mandibular condyles are robust and laterally expanded. The is narrow along the rostrum but dorsoventrally expanded posteriorly, with palatal ridges enhancing structural . These features combine ancestral heterodonty—reminiscent of archaeocetes—with derived cranial compression, positioning Squalodon as a key in odontocete evolution.

Postcranial Skeleton

The postcranial skeleton of Squalodon is known from fragmentary specimens across multiple , revealing adaptations for efficient aquatic locomotion and a streamlined body form, though preservation limits detailed understanding. The vertebral column includes a cervical series of 7 unfused vertebrae forming a short, compressed with limited mobility, (at least 11) exhibiting flexibility suited to undulatory as seen in preserved dorsal elements, and and caudal regions with elongate anterior elements transitioning to more compact posterior ones. The pectoral girdle supports reduced forelimbs adapted as flippers, with preserved proximal elements such as a robust and diminutive indicating muscle attachments for hydrodynamic control. No hind limbs or pelvic girdle elements are known, consistent with the complete loss of terrestrial traits in derived cetaceans. Caudal vertebrae are elongated anteriorly with widening for stability and foreshortened posteriorly, indicating a powerful for thrust generation via caudal undulation, consistent with a fluke-bearing structure inferred from cetacean . This configuration suggests a dolphin-like system, where the fluke would have provided the primary forward drive in water. The comprises broad, flattened numbering at least 11 pairs in known specimens, with varying shaft curvatures and lengths that articulate with to enclose a torso, minimizing drag. The is ossified and plate-like, and muscle attachment scars on the and vertebral transverse processes point to powerful epaxial and hypaxial musculature, likely enhanced with stores for sustained aerobic activity in aquatic environments.

Taxonomy and Phylogeny

Historical Classification

Squalodon was first described in by French naturalist Jean-Pierre Sylvestre Grateloup based on a fragmentary rostrum from deposits near , . Grateloup initially classified the specimen as a , possibly related to iguanodontid dinosaurs, due to its distinctive serrated teeth resembling those of ; the genus name derives from Squalus, a genus. However, later that year, Hermann von Meyer recognized it as a cetacean, marking its reassignment to the Odontoceti. During the , Squalodon was assigned to various odontocete groups as additional fragmentary fossils with were discovered worldwide, leading to a proliferation of names. Grateloup erected the family Squalodontidae in to accommodate these forms, viewing them as shark-toothed cetaceans transitional between archaic whales and modern dolphins. By the early , Frederick W. True redefined the family in , emphasizing its position as primitive dolphins with longirostrine skulls and polydont teeth, distinct from more advanced delphinids. Key revisions in the late included Christian de Muizon's 1984 and 1991 studies, which analyzed cranial and dental morphology to separate valid genera like Prosqualodon and Phoberodon from Squalodontidae, highlighting the family's paraphyletic nature. By the 1990s, Squalodontidae was widely recognized as a non-monophyletic ", encompassing convergent forms based on superficial tooth similarities rather than shared derived traits. Pre-2020 classifications often grouped Squalodon with related long-snouted genera like Eurhinodelphis, with 7–10 historically considered valid, though many were based on non-diagnostic holotypes.

Phylogenetic Position

Squalodontidae, the family which includes the genus Squalodon and the related genus Eosqualodon, is recognized as a within Odontoceti based on recent cladistic analyses that incorporate extensive morphological data from cranial and dental characters. This is supported by synapomorphies such as the inflation of a dorsoventral and the vascularization of the parietal formation medial to the periotic fossa, distinguishing the family from other early odontocetes. Eosqualodon represents more primitive forms known from the late . Phylogenetically, Squalodontidae occupies a basal position among stem odontocetes, outside the Odontoceti , acting as a transitional group between the paraphyletic and the more derived odontocetes that exhibit homodont dentition. The family's first appearances are in the late ( stage, approximately 28 Ma). In phylogenetic matrices, Squalodontidae clusters more closely with other stem odontocetes from , such as Inticetus, Phoberodon, and Prosqualodon australis, rather than with groups like Platanistoidea. Earlier hypotheses linking Squalodontidae to Platanista (the ) or as part of a broader Squalodelphinidae have been refuted by 2025 revisions, which exclude the family from Platanistoidea and emphasize its stem position. These analyses, drawing on modified matrices from prior studies, confirm that squalodontids represent an early radiation of odontocetes with plesiomorphic traits like heterodonty alongside derived features indicative of echolocation, such as advanced cranial asymmetry. However, Squalodontidae left no direct descendants among modern delphinids or other crown odontocete families, highlighting their role in the of key adaptations like echolocation and potentially social behaviors prior to the dominance of homodont forms in the .

Recognized Species

Following recent taxonomic revisions, the genus Squalodon has been streamlined from over 20 historically proposed —many based on fragmentary material—to 8 currently valid , achieved by synonymizing wastebasket taxa and confirming diagnostic features through re-examination of type specimens. These revisions, particularly those focusing on European and North American material, emphasize differences in cranial proportions, dental morphology (such as count and patterns), rostrum elongation, and overall body size, which vary notably across . The type species, S. grateloupii (originally described from the Bordeaux Basin, , ~20 Ma, early ), reaches approximately 3.5 m in length and features a moderately elongated rostrum with around 48–52 teeth, including characteristic incisors and posteriorly placed molars with fine serrations; its was lost, but a neotype (originally the holotype of the synonymized S. bariensis) from Saint-Restitut, , confirms these traits via conserved posterior basicranial and periotic features. In , S. calvertensis (, Calvert Formation, , , ~15–18 Ma) attains about 4 m and is distinguished by a relatively slender rostrum and 44–48 teeth with pronounced anterior-posterior size gradients; the type specimen (USNM 15612, a partial and ) highlights subtle differences in maxillary development compared to European congeners. The largest species, S. whitmorei (, Eastover Formation, , , ~14–16 Ma, up to 5.5 m), exhibits a broader (postorbital width ~430 mm) and robust with fewer but larger posterior teeth (40–46 total), as seen in the (VMNH 201040, partial ) that underscores its greater overall mass. European species include S. barbarus (Chattian–early Miocene, Azerbaijan, holotype IP No. S2/S6, robust incisors with rugose cristae), S. bellunensis (Aquitanian–Burdigalian, Italy, holotype MGP 17715, deep maxillary groove), S. peregrinus (Aquitanian–Burdigalian, Italy, holotype MGP 26130, elongate postorbital process), and S. servatus (Burdigalian, Germany, holotype SMNS-P-3981, curved anterior tooth roots), each differentiated by unique cranial crests or dental root curvatures, with body lengths estimated at 3–4.5 m. A North American addition, S. murdochi (Miocene, Calvert Cliffs, Maryland, ~16 Ma, ~4 m), features intermediate skull breadth and ~46 teeth, based on its holotype (partial cranium) that bridges traits between S. calvertensis and S. whitmorei. S. bariensis (upper Burdigalian, Italy/France, ~18 Ma, ~3–4 m) is considered a junior synonym of S. grateloupii.
SpeciesLocalityAge (Ma)Estimated Length (m)Key Diagnostic TraitsType Specimen
S. grateloupii (Bordeaux Basin)~203.548–52 teeth, moderate rostrum length; S. bariensis junior synonymNeotype: MNHL Dr15
S. calvertensisUSA (Maryland)15–184Slender rostrum, 44–48 teethUSNM 15612
S. whitmoreiUSA (Virginia)14–165.5Broad skull, 40–46 robust teethVMNH 201040
S. barbarus23–203–4Robust incisors, rugose cristaeIP No. S2/S6
S. bellunensis (Bolzano)21–193–4Deep maxillary grooveMGP 17715
S. peregrinus (Libano)21–193–4.5Elongate postorbital processMGP 26130
S. servatus (Baltringen)~193–4Curved anterior tooth rootsSMNS-P-3981
S. murdochiUSA (Maryland)~164Intermediate skull breadth, ~46 teethPartial cranium

Questionable or Synonymized Taxa

Several species originally described within the genus Squalodon have been synonymized with established taxa due to overlapping diagnostic features and priority rules. For instance, S. bariensis is regarded as a junior of S. grateloupii, the , based on comparative analysis of cranial morphology from European deposits. Similarly, S. bordae has been provisionally treated as a junior of S. grateloupii, as its lacks sufficient distinguishing characteristics beyond those already encompassed by the senior . A significant number of Squalodon species are now classified as nomina dubia owing to their non-diagnostic holotypes, which typically consist of fragmentary material such as isolated teeth or partial rostra that fail to exhibit unique apomorphies. A 2025 taxonomic revision evaluated 22 named species within Squalodon and identified 14 as indeterminate at the genus level, including S. antverpiensis, S. catulli, S. hypsispondylus, S. linzianus, S. melitensis, S. meyeri, S. mirabilis, S. molassicus, S. rugidens, S. vocontiorum, S. imperator, S. kelloggi, S. bordae, and S. dalpiazi; these were reassigned to Squalodontidae indeterminate due to the absence of critical skull regions like the or basicranium necessary for generic diagnosis. This reassessment highlights historical over-lumping, where early 19th- and 20th-century descriptions often relied on incomplete specimens without rigorous comparison, leading to taxonomic inflation. Certain taxa once placed in Squalodon have been reclassified into distinct genera based on differences in cranial architecture, such as rostral proportions and structure. For example, Eosqualodon was erected for exhibiting more primitive odontocete features, separating it from core Squalodon based on early material from . Likewise, genera like Macrosqualodelphis represent later-evolving squalodelphinids with elongated snouts and specialized , originally misattributed to Squalodon but now recognized as a separate lineage through phylogenetic analyses of periotic and pterygoid features. These reclassifications underscore the role of fragmentary early discoveries in initial assignments and the value of modern integrative in resolving such ambiguities.

Fossil Record

Discovery History

The discovery of Squalodon began in 1840 when French naturalist Jean-Pierre Sylvestre de Grateloup named the based on a partial rostrum with teeth from Lower deposits near Léognan, , , initially interpreting it as a . This , now recognized as S. grateloupii, marked the first formal description of the , though earlier isolated teeth from French sites in the 1820s had been collected but not specifically attributed to Squalodon. In , the initial report came in 1856 when Joseph Leidy described three isolated teeth from strata in as Squalodon atlanticus, representing the first squalodontid fossils identified on the continent. More significant specimens emerged from Calvert Cliffs, , in the late 19th and early 20th centuries, with the U.S. National Museum (USNM) collecting material starting in the ; a key partial skull (USNM 10484) was unearthed in 1921 and described by Remington Kellogg in 1923 as the new species S. calvertensis. Fossils from were documented in the early 1900s, including jaw fragments and teeth from deposits, with T. S. Hall providing a systematic in that linked them to Squalodon and related forms from . Partial skeletons of related squalodontids from outcrops in , reported in the 1970s, offered insights into diversity. Recent efforts in the 2020s have included digs in Peru's Pisco Basin, yielding partial skeletons of squalodelphinids closely related to Squalodon from the Chilcatay Formation, enhancing understanding of their distribution. In 2025, a comprehensive reassessment of European holotypes was published, including a detailed redescription of S. grateloupii's type material from and evaluations of multiple European species, clarifying historical confusions in the genus. Squalodon fossils typically consist of disarticulated skulls, jaws, and isolated teeth due to taphonomic biases in marine deposits, with complete or near-complete skeletons being exceptionally rare; one such example is the partial skeleton of S. whitmorei from strata in , , described in 2005.

Geographic and Stratigraphic Distribution

Fossils of Squalodon are known from marine deposits spanning the late to the middle , with the earliest records from the stage (approximately 27.8–23 million years ago) and the latest from the stage (approximately 13.8–11.6 million years ago). The genus exhibits peak abundance during the Early , particularly in the Aquitanian and stages (23–16 million years ago), when multiple species co-occurred in several regions. This temporal range reflects its presence in shallow to outer shelf environments across subtropical to temperate latitudes, with no verified occurrences in high-latitude polar settings such as . In , Squalodon fossils are widespread in the Tethys and seas, with key localities in (Saint-Paul-Trois-Châteaux Calcareous Molasse Formation, ), Italy (Libano Sandstone, Aquitanian; Salsomaggiore Formation, ), and (Doberg Formation, ; Upper Marine Molasse, ). Additional sites include (Antwerpen Sands Member, Langhian; Berchem Formation, ), (Linz Sands, ), (Maikop Group, ), (Middle Globigerina Limestone, Aquitanian), and . North American records are concentrated along the Atlantic and Pacific coasts during the , including and (Calvert Formation, ), (Pungo River Formation, ), (Astoria Formation, early ), and earlier sites in (Ashley Formation) and (near ). Asian occurrences are documented in from the Ashiya Group (late ) and the Mizunami Group (early ), indicating presence in the western Pacific realm. In , fossils of related squalodontids such as Phoberodon have been reported from (Gaiman Formation, early , ). Oceanic records include ( marine sands, such as those in the Waitaki region), representing the southernmost confirmed distribution. Recent taxonomic revisions limit the genus Squalodon primarily to the , with southern hemisphere records often reassigned to other archaic odontocetes. No reliable Squalodon fossils are known from , though related early odontocetes occur there in Eocene- strata. Taphonomic preservation of Squalodon remains typically involves disarticulated skulls, jaws, teeth, and postcranial elements in nearshore marine sediments, such as sandstones (e.g., Calvert and Libano formations) and diatomaceous deposits (e.g., associated with shelf environments in and ). These settings suggest rapid burial in coastal or deltaic systems, with common associations in phosphorite-rich beds indicating upwelling-influenced waters. The cosmopolitan biogeography of Squalodon, spanning the Tethys Sea, , and circum-equatorial margins, points to a preference for warm, epicontinental seas during a period of global greenhouse conditions.

Paleobiology

Diet and Feeding Ecology

Squalodon was a piscivorous and teuthophagous predator, primarily consuming and , with opportunistic predation on small marine mammals inferred from its dentition adapted for grasping and tearing prey. morphology, including serrated carinae on conical teeth and rugose enamel on posterior molars, facilitated cutting and processing of soft-bodied prey like squid and medium-sized , while procumbent incisors aided in initial capture. Minimal apical wear on many specimens suggests a feeding strategy involving rapid snaps rather than extensive mastication, consistent with tactics on evasive prey up to approximately 1 m in length given the predator's estimated body size of 2.5–3.5 m. Embrasure pits along the rostrum indicate a precise bite mechanism, enabling efficient prey seizure similar to that in basilosaurid archaeocetes, which supports a diet including varied marine vertebrates beyond solely . In some species, such as S. bellunensis, heavier tooth wear patterns hint at niche partitioning within Squalodontidae, potentially involving harder prey items or more abrasive feeding environments compared to lightly worn specimens like S. grateloupii. No direct evidence has been documented, but indirect support for this diet comes from analogous modern odontocete feeding ecologies and fossil assemblage associations with fish remains. Ecologically, Squalodon occupied a mid-to-upper in Miocene marine food webs, preying on primary and secondary consumers in productive coastal and offshore habitats. Its robust cranial features, including enlarged temporal fossae for powerful jaw adduction, positioned it as a competitor with early and contemporaneous odontocetes, such as smaller platanistoids, for shared resources in nearshore infralittoral settings. This role underscores Squalodon's contribution to trophic dynamics during the diversification of toothed whales, where body size and bite force enabled access to larger prey items relative to sympatric relatives.

Sensory Systems and Behavior

Squalodon exhibited cranial asymmetry in the naso-facial region, a feature linked to the early of echolocation in odontocetes, with the right and shifted anteriorly relative to the left side to facilitate sound focusing and production. This asymmetry, though less pronounced than in extant odontocetes, suggests precursor adaptations for biosonar, enabling and prey detection in marine environments. Such capabilities likely represented an intermediate stage between archaeocete-like hearing and the advanced high-frequency echolocation of modern toothed whales. Visual capabilities in Squalodon were supported by moderately large orbits, with an orbit ratio of approximately 23% relative to bizygomatic width, indicating functional suited to clear coastal waters where light penetration was sufficient for detecting movement or contrast. Unlike later odontocetes with reduced reliance on sight, Squalodon's anterolaterally directed orbits imply retained as a complementary , potentially aiding in shallow-water foraging or social interactions. Olfaction remained a viable sensory modality, as evidenced by well-developed olfactory recesses covering 5367 mm² and a perforated supporting olfactory nerve passages, allowing for chemosensory detection of environmental cues or prey scents in a manner more akin to semi-aquatic ancestors than modern anosmatic odontocetes. Behavioral inferences for Squalodon derive primarily from anatomical proxies, suggesting solitary or small-group living patterns typical of early odontocetes of similar body size (3–4 m), with no direct evidence of large pods but potential for in restricted coastal habitats. Locomotion was powered by a tail fluke and pectoral fins, enabling agile maneuvers for pursuit, with estimated cruising speeds of 20–30 km/h inferred from and vertebral counts comparable to those of modern delphinids, facilitating efficient travel and predatory chases in Oligo-Miocene seas.

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  21. https://www.jstage.jst.go.jp/article/bkmnh/8/0/8_75/_pdf
  22. https://www.researchgate.net/figure/Earliest-illustration-of-fossil-cetacean-Fragment-with-three-teeth-of-a-squalodontid_fig1_279286394
  23. https://www.sciencedirect.com/science/article/pii/S0960982222006789
  24. https://bmcbiol.biomedcentral.com/articles/10.1186/s12915-020-00805-4
  25. https://pmc.ncbi.nlm.nih.gov/articles/PMC8602015/
  26. https://www.sciencedirect.com/science/article/pii/S1631068313000468
  27. https://www.sciencedirect.com/science/article/pii/S0960982220308289
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