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maximus- hoffmannii was the wording used in Russell (1967); this is in recognition of the belief of a close relationship between the two species. [38] Mike Taylor (June 8, 2010). " Notes on Early Mesozoic Theropods and the future of zoological nomenclature". Sauropod Vertebra Picture of the Week. Archived from the original on March 9, 2021. Mosasaurs were the ocean's most dominant predator at the end of the Cretaceous period and lived across the world's oceans. Large mosasaurs would have likely eaten almost any kind of prey they were able to catch, including fish, sharks, sea birds and even other mosasaurs, according to the U.S. National Park Service. These mosasaurs were apex predators and could be compared to modern orcas, while other mosasaur species were more specialized feeders and adapted to eat shellfish, like modern sea otters, Live Science previously reported. Mosasaurus lived alongside other large predatory mosasaurs also considered apex predators, most prominent among them being the tylosaurines and Prognathodon. [50] [61] Tylosaurus bernardi, the only surviving species of the genus during the Maastrichtian, measured up to 12.2 meters (40ft) in length [127] while the largest coexisting species of Prognathodon like P. saturator exceeded 12 meters (39ft). [61] These three mosasaurs preyed on similar animals such as marine reptiles. [9] [50] [61]
Currently, there is only one known example of a Mosasaurus preserved with stomach contents: a well-preserved partial skeleton of a small M. missouriensis dated about 75 million years old with dismembered and punctured remains of a 1 meter (3.3ft) long fish in its gut. This fish was much longer than the length of the mosasaur's skull, which measured 66 centimeters (26in) in length, confirming that M. missouriensis consumed prey larger than its head by dismembering and consuming bits at a time. Due to coexistence with other large mosasaurs like Prognathodon, which specialized in robust prey, M. missouriensis likely specialized more on prey best consumed using cutting-adapted teeth in an example of niche partitioning. [9]
The Formidable Jaws of the Mosasaurus
Mosasaurs probably evolved from an extinct group of aquatic lizards [1] known as aigialosaurs in the Earliest Late Cretaceous with 46 described genera. During the last 20 million years of the Cretaceous period ( Turonian– Maastrichtian ages), with the extinction of the ichthyosaurs and pliosaurs, mosasaurs became the dominant marine predators. They themselves became extinct as a result of the K-Pg event at the end of the Cretaceous period, about 66 million years ago. The type species, M. hoffmannii, is one of the largest marine reptiles known, [50] [46] though knowledge of its skeleton remains incomplete as it is mainly known from skulls. [7] Russell (1967) wrote that the length of the jaw equalled one tenth of the body length in the species. [38] Based on this ratio, Grigoriev (2014) used the largest lower jaw attributed to M. hoffmannii (CCMGE 10/2469, also known as the Penza specimen; measuring 171 centimeters (67in) in length) to estimate a maximum length of 17.1 meters (56ft). [46] Using a smaller partial jaw ( NHMM 009002) measuring 90 centimeters (35in) and "reliably estimated at" 160 centimeters (63in) when complete, Lingham-Soliar (1995) estimated a larger maximum length of 17.6 meters (58ft) via the same ratio. [d] [50] No explicit justification for the 1:10 ratio was provided in Russell (1967), [38] and it has been considered to be probably overestimated by Cleary et al. (2018). [51] In 2014, Federico Fanti and colleagues alternatively argued that the total length of M. hoffmannii was more likely closer to seven times the length of the skull, which was based on a near-complete skeleton of the related species Prognathodon overtoni. The study estimated that an M. hoffmannii individual with a skull measuring more than 145cm (57in) would have been up to or more than 11 meters (36ft) in length and weighed 10 metric tons (11 short tons) in body mass. [52] Mentioning the Penza specimen, Gregory S. Paul estimated in his 2022 book, The Princeton Field Guide to Mesozoic Sea Reptiles, a shorter maximum length for M. hoffmannii of 13 meters (43ft) and a body mass of 5.5 metric tons (6.1 short tons). [53] The Penza specimen, one of the largest known fossils of Mosasaurus [46]
T. Lynn Harrell Jr.; James E. Martin (2014). "A mosasaur from the Maastrichtian Fox Hills Formation of the northern Western Interior Seaway of the United States and the synonymy of Mosasaurus maximus with Mosasaurus hoffmanni (Reptilia: Mosasauridae)". Netherlands Journal of Geosciences. 94 (1): 23–37. doi: 10.1017/njg.2014.27. S2CID 131617632.Robert W. Meredith; James E. Martin; Paul N. Wegleitner (2007). The largest mosasaur (Squamata: Mosasauridae) from the Missouri River area (Late Cretaceous; Pierre Shale Group) of South Dakota and its relationship to Lewis and Clark (PDF). The Geological Society of America. pp.209–214. In 1997, Bell published the first cladistical study of North American mosasaurs. Incorporating the species M. missouriensis, M. conodon, M. maximus, and an indeterminate specimen ( UNSM 77040), some of his findings agreed with Russell (1967), such as Mosasaurus descending from an ancestral group containing Clidastes and M. conodon being the most basal of the genus. Contrary to Russell (1967), [38] Bell also recovered Mosasaurus in a sister relationship with another group which included Globidens and Prognathodon, and M. maximus as a sister species to Plotosaurus. The latter rendered Mosasaurus paraphyletic (an unnatural grouping), but Bell (1997) nevertheless recognized Plotosaurus as a distinct genus. [74]
Michael W. Caldwell (2007). "Ontogeny, anatomy and attachment of the dentition in mosasaurs (Mosasauridae: Squamata)". Zoological Journal of the Linnean Society. 149 (4): 687–700. doi: 10.1111/j.1096-3642.2007.00280.x.a b Tim T. Tokaryk; C. R. Harington (1992). " Baptornis sp. (Aves: Hesperornithiformes) from the Judith River Formation (Campanian) of Saskatchewan, Canada". Journal of Paleontology. 66 (6): 1010–1012. Bibcode: 1992JPal...66.1010T. doi: 10.1017/S002233600002093X. S2CID 130444236. M. maximus is a North American taxon Russell (1967) recognized as a distinct species. [38] It is now generally recognized as a junior synonym of M. hoffmannii, although some scientists maintain the taxon is a distinct species. [5] [7] It is likely that Mosasaurus was viviparous (giving live birth) like most modern mammals today. There is no evidence for live birth in Mosasaurus itself, but it is known in a number of other mosasaurs; [97] examples include a skeleton of a pregnant Carsosaurus, [97] a Plioplatecarpus fossil associated with fossils of two mosasaur embryos, [98] and fossils of newborn Clidastes from pelagic (open ocean) deposits. [97] Such fossil records, along with a total absence of any evidence suggesting external egg-based reproduction, indicates the likeliness of viviparity in Mosasaurus. [97] [98] Microanatomical studies on bones of juvenile Mosasaurus and related genera have found that their bone structures are comparable to adults. They do not exhibit the bone mass increase found in juvenile primitive mosasauroids to support buoyancy associated with a lifestyle in shallow water, implying that Mosasaurus was precocial: they were already efficient swimmers and lived fully functional lifestyles in open water at a very young age, and did not require nursery areas to raise their young. [99] [97] Some areas in Europe and South Dakota have yielded concentrated assemblages of juvenile M. hoffmannii, M. missouriensis and/or M. lemonnieri. These localities are all shallow ocean deposits, suggesting that juvenile Mosasaurus may still have lived in shallow waters. [100] Paleoecology [ edit ] Distribution, ecosystem, and ecological impact [ edit ] Mosasaurus inhabited the Western Interior Seaway of North America and Mediterranean Tethys of Europe and Africa.
Scientists during the early and mid-1800s initially imagined Mosasaurus as an amphibious marine reptile with webbed feet and limbs for walking. This was based on fossils like the M. missouriensis holotype, which indicated an elastic vertebral column that Goldfuss in 1845 saw as evidence of an ability to walk and interpretations of some phalanges as claws. [30] In 1854, Hermann Schlegel proved how Mosasaurus actually had fully aquatic flippers. He clarified that earlier interpretations of claws were erroneous and demonstrated how the phalanges show no indication of muscle or tendon attachment, which would make walking impossible. They are also broad, flat, and form a paddle. Schlegel's hypothesis was largely ignored by contemporary scientists but became widely accepted by the 1870s when Othniel Charles Marsh and Cope uncovered more complete mosasaur remains in North America. [16] [43] a b c Aaron R. H. LeBlanc; Michael W. Caldwell; Nathalie Bardet (2012). "A new mosasaurine from the Maastrichtian (Upper Cretaceous) phosphates of Morocco and its implications for mosasaurine systematics". Journal of Vertebrate Paleontology. 32 (1): 82–104. Bibcode: 2012JVPal..32...82L. doi: 10.1080/02724634.2012.624145. JSTOR 41407709. S2CID 130559113. Camille Arambourg (1952). Les vertébrés fossiles des gisements de phosphates (Maroc–Algérie–Tunisie) (PDF). Notes et Mémoires du Service Géologique (in French). Vol.92. Paris: Typographie Firmin-Didot. pp.1–372. Archived from the original (PDF) on November 27, 2022. a b Eric W. A. Mulder (1999). "Transatlantic latest Cretaceous mosasaurs (Reptilia, Lacertilia) from the Maastrichtian type area and New Jersey". Geologie en Mijnbouw. 78 (3/4): 281–300. doi: 10.1023/a:1003838929257. S2CID 126956543. Mosasaurus is a squamate like monitor lizards and snakes, but scientists still debate which of the two is its closest living relative.Mosasaurs had a body shape similar to that of modern-day monitor lizards (varanids), but were more elongated and streamlined for swimming. Their limb bones were reduced in length and their paddles were formed by webbing between their long finger and toe bones. Their tails were broad, and supplied their locomotive power. Mosasaurs had double-hinged jaws a Cyrus C. Greene (2018). Osteohistology And Skeletochronology Of an Ontogenetic Series Of Clidastes (Squamata: Mosasauridae): Growth And Metabolism In Basal Mosasaurids (MS). Fort Hays State University. Isolated bones suggest some M. hoffmannii may have exceeded the lengths of the Penza specimen. One such bone is a quadrate (NHMM 003892) which is 150% larger than the average size, which Everhart and colleagues in 2016 reported can be extrapolated to scale an individual around 18 meters (59ft) in length. It was not stated whether they applied Russell's 1967 ratio. [54]
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