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Machimosaurus

Machimosaurus is an extinct genus of teleosaurid crocodylomorphs within the clade Thalattosuchia, comprising large-bodied marine reptiles that inhabited shallow coastal, estuarine, and lagoonal environments during the Late Jurassic (Oxfordian to Tithonian stages) and into the Early Cretaceous (Hauterivian stage).^[1] Fossils of the genus, first described from isolated teeth in 1837, have been recovered primarily from Europe (including England, France, Germany, Portugal, Spain, and Switzerland) and Africa (Ethiopia and Tunisia), revealing several valid species adapted as durophagous ambush predators with robust, foreshortened snouts, enlarged supratemporal fenestrae, and blunt-crowned teeth suited for crushing hard-shelled prey such as turtles, armored fish, and possibly other marine reptiles.^[1]^[2] The genus includes at least five recognized species, with M. hugii as the type species from the upper Kimmeridgian–lower Tithonian of Switzerland and the Iberian Peninsula, reaching body lengths of up to 7 meters; M. mosae from the uppermost Kimmeridgian–lowermost Tithonian of northeastern France, estimated at approximately 6 meters; M. buffetauti from the lower Kimmeridgian of France and Germany, around 5 meters; M. nowackianus from the Oxfordian or Kimmeridgian of Ethiopia; and M. rex from the Early Cretaceous of Tunisia, the largest known thalattosuchian at up to 7.2 meters in length.^[1]^[2]^[3] These species exhibit variations in robustness and habitat preferences, from open-sea adaptations in M. hugii (with reduced skull ornamentation for diving) to more coastal, high-energy environments favored by M. mosae (featuring thick osteoderms and robust ribs).^[1] The discovery of M. rex notably demonstrates teleosaurid survival across the Jurassic–Cretaceous boundary, challenging earlier assumptions of their extinction at the end of the Jurassic.^[2] Paleobiological reconstructions indicate that Machimosaurus species were semi-aquatic generalists, capable of tolerating brackish to fully marine conditions and possibly even freshwater incursions, filling top-predator niches in Mesozoic coastal ecosystems alongside dinosaurs and other marine reptiles.^[1] Their durophagous dentition and strong bite force enabled a diet focused on shelled invertebrates and vertebrates, distinguishing them from more piscivorous teleosaurids, while their body plans—supported by keeled osteoderms and powerful limbs—facilitated ambush hunting in shallow waters.^[1]^[2] Ongoing taxonomic revisions continue to refine species distinctions based on cranial and postcranial morphology, underscoring Machimosaurus as a key taxon for understanding thalattosuchian diversity and adaptation in the Mesozoic.^[1]

Description

Size and proportions

Machimosaurus species displayed a range of adult body sizes, with estimated total lengths varying from approximately 4.8 meters for smaller specimens of M. buffetauti to 7.15 meters for the largest individuals of M. rex, based on regression equations derived from skull and femoral measurements compared to more complete teleosaurid skeletons.^[4] These estimates reflect revisions to earlier projections, which had overstated lengths for some taxa by using inappropriate scaling from modern crocodylians.^[4] Size estimates for M. nowackianus are unavailable due to fragmentary remains (anterior dentary only).^[1] The overall body plan of Machimosaurus was characterized by an elongated snout that could reach up to 1.55 meters in length in the largest skulls, contributing significantly to the anterior portion of the body, alongside a robust torso reinforced by thick ribs and extensive osteoderm coverage for protection in marine environments.^[4] The tail formed the majority of the posterior body, comprising over 50% of total length in reconstructed specimens, enabling strong lateral undulations for propulsion in aquatic habitats.^[5] Limb-to-body ratios, with relatively short femora compared to extant crocodylians, further supported a semi-aquatic lifestyle, emphasizing swimming efficiency over terrestrial mobility.^[4]

Skull morphology

The skull of Machimosaurus is characterized by an elongated yet robust structure, featuring a broad, mesorostrine rostrum that constitutes less than 60% of the basicranial length, indicative of adaptations for a durophagous lifestyle involving the crushing of hard-shelled prey.^[5] The posterior region of the skull is notably widened, with enlarged, parallelogram-shaped supratemporal fenestrae exceeding 27% of the basicranial length, which enhance the attachment area for jaw adductor muscles and support increased mechanical stress during feeding.^[5] Sutures along the snout are generally poorly ornamented with low-relief ridges in species like M. hugii, though stronger sculpturing appears in M. buffetauti and M. mosae, reflecting subtle variations in cranial reinforcement across taxa.^[5] Dentition in Machimosaurus is heterodont and specialized for puncturing and grinding, with 17–22 conical, blunt-crowned teeth per maxilla, the posterior ones often bulbous and low-crowned to facilitate the processing of shelled prey such as turtles.^[5] Enamel surfaces bear prominent apicobasal ridges, particularly closely packed on both labial and lingual sides in M. hugii, transitioning to anastomosed patterns apically; these striations, along with false denticles or "pseudo-denticles" in some species, increase surface friction for gripping and abrading tough food items.^[6] The palate exhibits modifications such as uniform, narrow inter-alveolar spaces in M. hugii, aiding in the distribution of crushing forces, while the quadrates are robust, with species-specific features like a dorsal depression in M. buffetauti absent in others.^[5] Interspecific variations highlight adaptive diversity; for instance, M. hugii possesses sub-globidont teeth and sub-rectangular orbits, whereas M. buffetauti has circular orbits and stronger cranial ornamentation, and M. mosae features transverse ellipsoidal orbits with 17–18 maxillary alveoli.^[5] M. rex, the largest species, exhibits a platyrostral snout with similar blunt-crowned dentition and dense longitudinal ridges on the skull surface, though its exceptionally large cranium (up to 160 cm long) underscores enhanced durophagous capabilities in coastal environments.^[7] These cranial traits collectively emphasize Machimosaurus' specialization for bone-crushing predation within thalattosuchian crocodylomorphs.^[5]

Postcranial skeleton

The postcranial skeleton of Machimosaurus is known from incomplete but informative specimens, revealing adaptations consistent with a semi-aquatic lifestyle among teleosaurids. The vertebral column consists of amphicoelous centra with fused neural arches in adults, supporting flexibility and stability in coastal environments.^[5]^[8] Preserved vertebral series vary by specimen; for example, the neotype of M. mosae includes 22 vertebrae encompassing approximately half of the cervical series, all dorsal and sacral vertebrae, and about one-third of the caudal series, suggesting a total presacral count in the range of 20–25 based on comparisons with related teleosaurids.^[5] Cervical vertebrae feature hourglass-shaped centra with thick margins and rectangular neural spines nearly as tall as the centra themselves, providing dorsal elevation for buoyancy and stability in water.^[8] Dorsal vertebrae are taller than wide, with concave ventral margins and robust transverse processes that articulate with ribs for thoracic reinforcement.^[8] Sacral vertebrae, typically numbering three, exhibit robust, ventrally bent ribs fused to the centrum for pelvic anchorage and enhanced stability in dynamic aquatic settings.^[5] Caudal vertebrae show elongated centra and tall neural arches bent posteriorly, with zygapophyseal articulations suited for lateral undulations that enable efficient tail propulsion during swimming; partial series indicate at least 40 caudals overall, though distal portions are often unpreserved.^[5]^[8] Ribs are numerous and robust, with up to 19 preserved in some specimens (seven cervical and twelve thoracic); cervical ribs are T-shaped with ovoid capitula and tubercla, while thoracic ribs are strongly curved to form a protective basket around the viscera.^[8] Appendicular elements are fragmentary but include coracoids (with short or elongate glenoid processes varying by species), pubes, ilia, ischia, femora, tibiae, and fibulae; forelimbs appear shortened relative to body length, as indicated by proportionally short femora in teleosaurid regressions, supporting paddling motions without full flipper modification.^[5]^[4] The tail features partial caudal series with associated chevrons and transverse process exostoses for muscular attachment, contributing to a propulsive structure adapted for rapid aquatic locomotion via lateral flexure.^[5] Dermal armor comprises extensive osteoderms covering the body and tail, with up to 22 preserved in a single specimen; dorsal osteoderms are rectangular to sub-square, ornamented with large subcircular pits and anastomosed grooves for vascularization, arranged in paired longitudinal rows for streamlined protection.^[5]^[8] Ventral osteoderms are keeled and thicker, forming multiple rows in the thoracic region with smoother pits and anterior facet bars, providing flexible shielding without impeding ventral undulation; this armor is denser dorsally, aiding thermoregulation and defense while maintaining body flexibility.^[5]^[9]

Discovery history

Initial discoveries

The genus Machimosaurus was established in 1837 by the German paleontologist Christian Erich Hermann von Meyer, who named the type species M. hugii based on isolated, blunt, conical tooth crowns exhibiting numerous longitudinal ridges. These specimens originated from the Upper Kimmeridgian Reuchenette Formation at Solothurn in Switzerland and the Kahlenberg near Hannover in Germany, with the lectotype designated as a single tooth crown (NMS 8342) from the Swiss locality.^[5] Initially, von Meyer misspelled the genus as Madrimosaurus due to a transcription error, which he corrected to Machimosaurus in 1838.^[5] During the early 19th century, additional isolated teeth attributable to Machimosaurus were reported from the Kimmeridge Clay Formation in England, including a single incomplete crown from Smallmouth Sands in Dorset, though such finds were sparse and often overlooked. In Germany, beyond the Kahlenberg material, fragmentary remains from northern localities were initially misclassified as belonging to the teleosaurid genus Teleosaurus or even the ichthyosaur Ichthyosaurus, reflecting the limited understanding of thalattosuchian diversity at the time. These early European discoveries, primarily from Kimmeridgian marine deposits, highlighted Machimosaurus as a distinct durophagous crocodylomorph but were hampered by their isolated nature.^[5]^[10] Further species were described in the late 19th and early 20th centuries, expanding the known geographic scope. In 1879, Émile Sauvage and François Liénard formally described M. mosae (based on Liénard's unpublished manuscript) from a partial skeleton recovered from the uppermost Kimmeridgian to lowermost Tithonian Argiles de Châtillon Formation near Ambleteuse in the Boulonnais region of northeastern France. In 1938, Friedrich von Huene named M. nowackianus (initially as cf. Simolestes nowackianus) based on the rostral portion of a mandible from the Oxfordian–Kimmeridgian strata at Harrar in Ethiopia, marking the first African record and underscoring a broader Eurasian-African distribution. These additions relied heavily on cranial fragments, as postcranial elements were rarely associated with diagnostic teeth or jaws.^[5] Early taxonomy of Machimosaurus faced significant challenges due to the predominance of fragmentary, isolated remains, which led to frequent synonymies, misidentifications, and debates over ontogenetic variation versus species differences. The absence of complete skeletons or associated postcrania further complicated distinctions from contemporaneous teleosaurids like Steneosaurus, delaying a comprehensive understanding of the genus until later revisions.^[5]

Recent revisions and new species

In the mid-2010s, significant taxonomic revisions refined the understanding of Machimosaurus, addressing longstanding issues with species synonymies and diagnostic criteria. Young et al. (2014) conducted a comprehensive review of the genus, synonymizing several historically recognized taxa—such as Steneosaurus obtusidens and Steneosaurus durobrivensis—into the senior synonym Machimosaurus hugii, while validating three European species: M. hugii, M. mosae, and M. nowackianus. They emphasized the durophagous adaptations of the genus, including robust, blunt teeth suited for crushing hard-shelled prey, based on detailed examinations of cranial and dental material from Late Jurassic deposits. An addendum in 2015 by the same team formally described a new species, M. buffetauti, from a nearly complete skull (SMNS 91415) discovered in the Kimmeridgian of southeastern France, highlighting its distinct short, broad rostrum and confirming its placement within the genus through comparative morphology.^[11]^[12] A major expansion of the genus occurred in 2016 with the description of Machimosaurus rex by Fanti et al., based on an articulated partial skeleton from the Early Cretaceous Douiret Formation in southern Tunisia—the first unequivocal Machimosaurus specimen from Africa. This discovery extended the geographic range of the genus beyond Europe and underscored its survival across the Jurassic-Cretaceous boundary, with the holotype's 155 cm skull initially suggesting a total body length of approximately 9.5 m, making it the largest known thalattosuchian at the time. The species exhibits pronounced durophagous features, such as low-crowned, multicusped teeth and a reinforced skull, indicative of a diet focused on mollusks and crustaceans in shallow marine environments. Subsequent analyses revised these estimates and deepened insights into M. rex. Young et al. (2016) recalibrated body length proportions using comparative data from other teleosaurids, reducing the estimate for M. rex to about 7.15 m and cautioning against direct analogies with extant crocodylians for large-headed marine forms, as such proxies can overestimate sizes by up to 30%. Further refinement came in a 2020 phylogenetic study by Johnson et al., which incorporated M. rex into a broader analysis of Teleosauroidea, confirming its durophagous niche through reassessment of cranial metrics and ecological modeling, while noting the specimen's partial preservation limits precise volumetric reconstructions.^[13] Ongoing taxonomic debates center on species validity within Machimosaurus, particularly the distinction between M. nowackianus (from the Kimmeridgian of Ethiopia) and M. hugii. Although Young et al. (2014) upheld M. nowackianus as distinct based on rostral proportions and dental ornamentation, subsequent morphometric comparisons have questioned this separation, suggesting possible overlap or synonymy due to intraspecific variation in isolated Ethiopian material; however, no consensus has emerged without additional complete specimens. These revisions collectively highlight Machimosaurus as a diverse, durophagous lineage with a wider paleobiogeographic footprint, including North African sites that bridge European and Gondwanan faunas.^[11]

Classification

Taxonomic history

Machimosaurus was first described and named by Hermann von Meyer in 1837, based on isolated tooth crowns from the Late Jurassic of Switzerland and Germany, and initially placed within the family Teleosauridae due to its characteristic blunt, crushing dentition indicative of a durophagous lifestyle.^[5] This early classification emphasized its affinities with other semi-aquatic thalattosuchians adapted to coastal marine environments. However, subsequent discoveries led to taxonomic debates, particularly in the late 19th and early 20th centuries, where some larger specimens were initially considered potential metriorhynchids owing to their marine adaptations and robust build, though these were later reattributed or excluded from the genus.^[5]^[11] By the mid-20th century, Machimosaurus was firmly recognized as a teleosaurid, with detailed revisions by Bernhard Krebs in 1967 and 1968 confirming its placement based on Portuguese material and emphasizing its distinction from more pelagic forms.^[5] Further refinements occurred in the late 20th century, including Stéphane Hua's 1999 rediagnosis of key European specimens, which solidified its teleosaurid status while highlighting intraspecific variation.^[14] In 2012, Mark T. Young and colleagues erected the subfamily Machimosaurinae to accommodate Machimosaurus and related durophagous teleosaurids, recognizing their specialized crushing adaptations as a derived trait within Teleosauridae.^[15] A pivotal revision came in 2014 (published 2015) by Young, Hua, Steel, and colleagues, who re-evaluated the genus across European and African material, validating multiple species and distinguishing Machimosaurus from misidentified metriorhynchid specimens, such as a large Kimmeridge Clay skull reclassified as Plesiosuchus manselii.^[5] This work established Machimosaurinae more robustly within Teleosauridae. In 2020, Johnson et al. elevated Machimosaurinae to the family Machimosauridae, recognizing it as morphologically and biogeographically distinct from Teleosauridae within Teleosauroidea.^[13] Current consensus (as of 2024) positions Machimosaurus within the family Machimosauridae of Teleosauroidea, a basal thalattosuchian clade sister to the more derived, fully pelagic Metriorhynchoidea, supported by phylogenetic analyses emphasizing its semi-aquatic, coastal niche.^[14]^[13]^[5]

Phylogenetic position

Machimosaurus is positioned within the clade Thalattosuchia, specifically as a member of Teleosauroidea, a group of semi-aquatic crocodylomorphs adapted to marine environments during the Jurassic. Within Teleosauroidea, the genus belongs to the family Machimosauridae, which includes the former subfamily Machimosaurinae (or tribe Machimosaurini in some classifications) and is recovered alongside Teleosauridae in comprehensive cladistic analyses. This placement positions Machimosauridae as part of the basal Teleosauroidea, sister to the more derived Metriorhynchoidea clade, highlighting its intermediate role in the transition toward fully pelagic lifestyles seen in metriorhynchids.^[13] Key synapomorphies supporting the inclusion of Machimosaurus in Machimosauridae include robust dentition characterized by large, blunt conical teeth with anastomosing enamel patterns suited for durophagous feeding, as well as palatal thickening involving exposure of the basisphenoid and associated structural reinforcements. These features are shared with closely related machimosaurs such as Lemmysuchus obtusidens, forming a polytomy including Machimosaurini in recent phylogenies. Additional cranial traits, such as dorsally oriented external nares and the absence of antorbital fenestrae (except in some outgroup taxa), further define this group.^[13]^[1] Phylogenetic analyses from 2015 to 2024, incorporating datasets with 140–153 operational taxonomic units and 456–502 morphological characters, consistently recover Machimosaurus as part of a monophyletic Teleosauroidea, with Machimosauridae as a distinct family; the genus itself forms polytomies rather than strict monophyly in maximum parsimony and Bayesian trees, with sensitivity to character selection in resolving intra-teleosauroid relationships, such as proximity to Steneosaurus or Lemmysuchus. These studies utilize software like TNT and MrBayes to generate strict consensus trees.^[13]^[16]^[1] Relative to outgroups, Machimosaurus is more derived than the basal thalattosuchian Pelagosaurus typus, which lacks the specialized dentition and palatal adaptations, but less specialized than geosaurs (e.g., Geosaurus spp.) within Metriorhynchidae, which exhibit greater marine adaptations such as reduced limbs and fully aquatic tail propulsion. This intermediate position reflects Machimosaurus's role as a coastal generalist within the broader diversification of Thalattosuchia.^[13]^[1]

Distribution

Temporal range

Machimosaurus is known from the Middle Jurassic to Early Cretaceous, spanning the Oxfordian to Hauterivian stages, approximately 163 to 130 million years ago.^[1]^[2] This temporal range encompasses deposits primarily from lagoonal environments in Europe, where the genus achieved its greatest abundance.^[1] Fossils of M. sp. occur in Middle to Upper Oxfordian strata (ca. 160–152 Ma), while M. buffetauti is from Lower Kimmeridgian strata (ca. 157–152 Ma); M. hugii and M. mosae are recorded from Upper Kimmeridgian to Lower Tithonian levels (ca. 157–145 Ma).^[1] The genus reached peak diversity during the Kimmeridgian stage (157.3–152.1 Ma), with at least three non-sympatric species in Europe (M. buffetauti, M. hugii, M. mosae) alongside M. nowackianus in Africa, reflecting a broad distribution across the northern Tethyan margins.^[1] Stratigraphically, these occurrences correlate with formations like the Lacunosamergel (Lower Kimmeridgian, Germany), Solothurn Turtle Limestone in the Reuchenette Formation (Upper Kimmeridgian, Switzerland), and Argiles de Châtillon (Uppermost Kimmeridgian–lowermost Tithonian, France).^[1] The Jurassic occurrences for the genus span approximately 15–20 million years, centered on these European and African lagoonal units, with an additional Early Cretaceous record in Tunisia extending the total duration.^[1]^[2] Isolated teeth from Spain, possibly of Berriasian age (145–139.4 Ma), have been tentatively attributed to Machimosaurus, but this remains unconfirmed as the specimens are lost.^[1] The youngest confirmed records come from North Africa, where M. rex is documented from the Hauterivian Douiret Formation in Tunisia (ca. 133–129 Ma), correlating with early Cretaceous coastal deposits and representing the last known occurrence of the genus.^[2]

Geographic distribution and paleoenvironments

Fossils of Machimosaurus are primarily known from Late Jurassic deposits across western Europe, reflecting a predominantly Laurasian distribution with extensions into northern Africa, facilitated by connectivity through the Tethys Sea and its marginal currents.^[5] Recent discoveries include machimosaurid remains from the Oxfordian of south-central Poland, further extending the European distribution.^[17] In Europe, key occurrences include Switzerland, where specimens such as the type species M. hugii derive from the Reuchenette Formation (Solothurn Turtle Limestone) in the Jura Mountains, deposited in shallow protected lagoons with depths of approximately 5–20 m and periodic salinity fluctuations due to restricted circulation.^[1] German sites encompass the Solnhofen Limestone in Bavaria, an evaporite sequence formed in hypersaline lagoons within the Tethyan archipelago, as well as the Langenberg Formation near Oker (Lower Saxony), representing a shallow-water bay or lagoon environment.^[1]^[18] In France, Machimosaurus remains have been reported from the Calcaires Coquilliers Formation in Normandy, indicative of a homoclinal mid-ramp setting with storm-wave reworking in shallow marine conditions, and from lagoonal deposits in the Ain department during the Lower Kimmeridgian.^[1] Portuguese localities include the Alcobaça Beds (Guimarota mine near Leiria), preserving fossils in lagoonal settings with freshwater influx from nearby wooded swamps, and the Lourinhã Formation (Praia Azul Member), associated with brackish to coastal platform environments.^[1] Additional European finds occur in the Kimmeridge Clay Formation of England (shallow water depths of 10–30 m), the Tereñes and Lastres Formations of Spain (shallow tide-less seas and fluvial-dominated deltaic systems), and isolated teeth from Poland's Lower Kimmeridgian strata.^[1]^[1]^[1] The genus extends southward into Africa, with records from Ethiopia near Harrar in sandy clay deposits of probable Oxfordian–Kimmeridgian age, suggesting deltaic or coastal plain paleoenvironments along the southern Tethyan margin.^[1] In Tunisia, M. rex is documented from coastal carbonate sequences in the Tataouine Basin (Douiret Formation), representing shallow marine lagoons with low-energy conditions during the Early Cretaceous, highlighting a biogeographic persistence influenced by Tethyan marine pathways.^[2] Overall, Machimosaurus inhabited a range of shallow marine to brackish settings, including lagoons, reefs, and deltaic systems characterized by variable salinities and depths typically under 20 m, underscoring its adaptation to dynamic coastal ecosystems across the Tethys realm.^[1]

Paleobiology

Diet and feeding

Machimosaurus exhibited a durophagous diet, primarily chelonivorous, targeting hard-shelled marine turtles such as Solnhofia parsonsi from the Solnhofen Limestone, with supplementary consumption of fish, crustaceans, and mollusks.^[19]^[20] This specialization is evidenced by bite marks and embedded teeth on turtle carapaces, including healed punctures on Solnhofia specimens up to approximately 25 cm in carapace length, indicating predation on prey sized 20–30 cm.^[19] Tooth wear patterns on robust, blunt, conical teeth with apicobasal ridges and microscopic denticles further support shell-crushing capabilities, allowing processing of armored invertebrates over soft-bodied vertebrates.^[19]^[20] Biomechanical adaptations enhanced its feeding efficiency, including a shortened mandibular symphysis for increased jaw leverage, enlarged jaw adductor musculature, and overall cranial robustness to withstand high-stress crushing.^[20] Finite element models of machimosaurin skulls demonstrate elevated bite forces suitable for durophagy, with stress distribution optimized for hard prey penetration, distinguishing Machimosaurus from piscivorous teleosaurids.^[21] Although direct coprolites containing turtle fragments are rare, associated teleosaurid gastric residues and bite trace fossils from lagoonal deposits corroborate this diet.^[20] In lagoonal paleoenvironments, Machimosaurus occupied an apex or mesopredator trophic level, exploiting heavily armored benthic prey in coastal food webs and contributing to the ecological diversification of Teleosauroidea during the Late Jurassic.^[20] Its preference for durophagous feeding reflects convergent evolution with other shallow-marine crocodyliforms, emphasizing niche partitioning through specialized hard-prey exploitation.^[21]

Locomotion and adaptations

Machimosaurus, as a semi-aquatic teleosaurid crocodylomorph, relied on tail-driven propulsion for movement in aquatic environments, involving lateral undulation of the body and tail to generate thrust, akin to the swimming mechanics observed in modern crocodilians.^[22] This method allowed efficient navigation through coastal and lagoonal waters, though teleosauroids like Machimosaurus were not as hydrodynamically optimized as more pelagic marine reptiles, resulting in relatively modest swimming speeds.^[22] Burst speeds were likely comparable to those of extant crocodilians, reaching up to 15–24 km/h during short pursuits or escapes.^[23] The genus exhibited adaptations for shallow diving, supported by robust cervical vertebrae and enlarged basioccipital tubera that anchored strong neck-depressing musculature, enabling head-down maneuvers to depths of around 10-15 meters.^[5] These features, combined with a vertebral column showing increased flexibility in lateral flexion toward the tail, facilitated ambush predation and foraging in nearshore habitats without the need for deep submergence.^[24] However, thalattosuchians including Machimosaurus were structurally limited for prolonged or deep dives due to expansive cranial sinuses that could not withstand high pressures.^[25] On land, Machimosaurus adopted a sprawling quadrupedal gait typical of semi-aquatic crocodylomorphs, with limb proportions and osteology indicating capability for short-distance travel but reduced endurance compared to fully terrestrial reptiles.^[5] The robust but relatively short limbs, suited more for paddling in water than sustained walking, suggest that terrestrial movement was primarily used for basking or accessing nesting sites rather than long migrations.^[5] Physiological adaptations to brackish and marine conditions included potential cephalic salt glands, inferred from endocranial evidence in thalattosuchian relatives, which aided osmoregulation by excreting excess salt acquired from ingested seawater or prey.^[26] These glands were small and primitive compared to those in fully pelagic metriorhynchids, reflecting Machimosaurus's lifestyle in coastal rather than open-ocean settings.^[26]

Ecological interactions

Machimosaurus occupied a specialized niche within Late Jurassic marine ecosystems, characterized by niche partitioning that minimized competition with sympatric crocodylomorphs. Its larger body size, reaching up to 9.5 meters in length, enabled the exploitation of larger prey items, such as sizable fish and shelled invertebrates, compared to the smaller Steneosaurus, which targeted smaller, more agile aquatic organisms. This size-based differentiation reduced dietary overlap in coastal lagoon and shallow marine environments of the Jurassic Sub-Boreal Seaway, allowing multiple teleosaurids to coexist.^[27] As a mid- to upper-level predator, Machimosaurus engaged in predatory interactions both as hunter and potential prey. Fossil evidence, including bite marks on plesiochelyid turtle shells from Swiss Kimmeridgian deposits, directly attributes predation on hard-shelled reptiles to Machimosaurus, with embedded teeth and crushed carapaces indicating its durophagous capabilities. Conversely, in formations like the Kimmeridge Clay, Machimosaurus coexisted with larger apex predators such as the pliosaurid Pliosaurus, which, at over 10 meters long, likely preyed upon juvenile or subadult Machimosaurus individuals, highlighting a complex trophic web.^[5]^[28] Machimosaurus shared its habitats with other teleosaurids, such as Sericodon, and diverse marine vertebrates including ichthyosaurs and early seabirds, implying partitioned foraging zones to avoid direct competition—Machimosaurus likely focused on nearshore, lagoonal areas while others exploited open-water niches. As a durophage with a high trophic position, evidenced by its assignment to the macrophagous feeding guild in tooth morphology analyses, Machimosaurus exerted significant community impact by preying on shellfish and turtle populations, potentially regulating their abundances in coastal ecosystems.^[28]

References

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Comparative functional morphology indicates niche partitioning ...
May 15, 2024 · We created a functional dataset of continuous craniomandibular and dental characters known from neontological studies to be functionally significant in modern ...
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The long-term ecology and evolution of marine reptiles in a Jurassic seaway - Nature Ecology & Evolution
### Summary of Machimosaurus and Related Marine Reptiles in the Jurassic Sub-Boreal Seaway