The marine lizard genus Ectenosaurus, which belonged to the mosasaur family, is extinct. It is categorized with taxa such as Angolasaurus and Platecarpus in the Plioplatecarpinae subfamily. From the Santonian and Campanian of Kansas, Alabama, and Texas, Ectenosaurus is known. The term "drawn-out lizard" refers to the extended muzzle and is derived from the Greek words "ectenes" ("drawn-out") and "sauros" ("lizard").
Description
Ectenosaurus is thought to have reached a length of 5–6 m (16–20 ft), with the surviving head measuring around 64.5 cm (2.12 ft) in length. It was an uncommon genus of mosasaur that stands out from other mosasaur genera thanks to a number of distinctive traits. Its elongated jaws, which resemble those of other mosasaurs with extended jaws, such Plotosaurus and Pluridens, are the most noticeable of these traits. According to Russell (1967), there is proof of a close relationship between Ectenosaurus and Platecarpus in the form of the teeth, the frontal morphology, and the enormous suprastapedial projection of the quadrate. Based on the longer snout, the prefrontals' omission from the narial boundaries, and the combination of the supra- and infrastepedial processes, he distinguished between Ectenosaurus and Platecarpus.
Scales and Locomotion
Conclusions concerning the mosasaur integument as a whole as well as movement and propulsion may be made thanks to the specimen FHSM VP-401, which preserves very thorough skin impressions from Ectenosaurus. Despite the creatures' comparable proportions, the scales are significantly smaller (2.7×2.0 mm) than those of the well-known LACM 128319 specimen of Platecarpus (3.8×4.4 mm). The intricate network of alternating crossed-helical and longitudinal fiber bundles, together with tiny, firmly attached body scales, indicates that the front torso of Ectenosaurus was rather rigid. This also suggests that, contrary to the previously widely held belief about mosasaur locomotion, the entire body could not move by undulating like snakes do. Instead, the main means of propulsion would have had to be the tail, which most likely had a tail fin like other mosasaur species.
History of Discovery
In 1894, Ectenosaurus was first identified as a species of Platecarpus, P. clidastoides. The type specimen was obtained from Logan County, Kansas, by either C.H. Sternberg or G. Bauer. It was kept in the Munich-based Bayerische Staatssammlung für Palaontologie, where it was probably destroyed in the Second World War. In 1953, George Sternberg found another specimen, this one considerably better preserved; he first recognized it as a Clidastes velox. The specimen, which was once included in the catalogue under the number GFS 109-53, was around 3 meters (9.8 feet) in length and was mostly articulated, although erosion had destroyed its tail and back limbs. After then, this item remained on display at the Fort Hays State University Sternberg Memorial institution until 1999, when the institution was relocated and closed. The specimen has been stored since the museum relocated, and its catalog number is FHSM VP-401. Dale A. Russell investigated it in 1963 and concluded that it was, in fact, a Platecarpus clidastoides and not a Clidastes velox. The species was reclassified as belonging to the new genus Ectenosaurus by him in his 1967 book Systematics and Morphology of American Mosasaurs. Russell also identified YPM 4671, 4672, 4673, and 4674 in the Yale Peabody Museum as examples of Ectenosaurus clidastoides. To replace the type specimen of E. clidastoides, Alexander Willman, Takuya Konishi, and Michael Caldwell selected FHSM VP-401 as the neotype in 2021. They also designated Ectenosaurus everhartorum, a new species of Ectenosaurus, from another specimen of the species that was found in Logan County in the 1970s and cataloged as FHSM VP-5515. Mike and Pamela Everhart, two marine reptile researchers, are honored in the name of this species. Willman and colleagues withdrew the YPM specimens from E. clidastoides and classified them as Ectenosaurus sp. since they could not be distinguished from one another. Two new species of the genus, E. tlemonectes from the Kansas Niobrara and E. shannoni from the Alabama Mooreville Chalk, were named by Caitlín R. Kiernan and Jun A. Ebersole in 2023.
Classification
Due in part to its lengthy classification as a species of Platecarpus, Ectenosaurus has been seen as a plioplatecarpine throughout the most of the period since it was discovered. Nonetheless, other assessments identify it as a mosasaurine that is closely related to Prognathodon. The cladogram with Ectenosaurus positioned in relation to other plioplatecarpines is based on Simões et al. (2017) and condensed to solely showcase the Plioplatecarpinae.
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A reconstruction of E. clidastoides by Gasmasque.
Partial skeleton of E. clidastoides.
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