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108-604: Tylosaurus ( / ˌ t aɪ ˈ l oʊ ˈ s ɔːr ə s / ; "knob lizard") is a genus of russellosaurine mosasaur (an extinct group of predatory marine lizards ) that lived about 92 to 66 million years ago during the Turonian to Maastrichtian stages of the Late Cretaceous . Its fossils have been found primarily around North Atlantic Ocean including in North America , Europe , and Africa . Tylosaurus

216-637: A scapula that is significantly smaller than the coracoid and the absence of the anterior emargination of the coracoid, as well as the absence of a well-developed pubic tubercle. Tylosaurus limbs are primitive relative to other mosasaurs; their stylopodia (humeri and femora) lack both the complex muscle attachment sites and extreme proximodistal shortening present in other derived taxa. Both carpals and tarsals in tylosaurines are mostly unossified ; while other mosasaurs typically have between three and five carpals and tarsals, adult Tylosaurus never possess more than two ossified carpal bones (usually only

324-441: A 45° downward angle. A similar deflection appears in some juvenile T. nepaeolicus quadrates. Emerging from the posteroventral margin of the alar conch is the infrastapedial process. Its shape appears to changes ontogenetically in T. nepaeolicus and T. proriger ; in the former, the process is absent in juveniles but appears as a small bump in adults, while in T. proriger , it is present as a subtle point in juveniles of and becomes

432-516: A U-shaped curve. From top view, they are compressed at the lingual and labial (lip-facing) sides to form an oval-like shape. Teeth of immature T. proriger are initially compressed, but become conical in adulthood. Carinae (cutting edges) are finely serrated with small denticles except in juvenile T. nepaeolicus . In T. pembinensis , they are faint. The teeth generally have both anterior and posterior carinae, but some anterior teeth may have only anterior carinae. The placement of carinae, if paired,

540-433: A blunt, elongated "knob." The snout is heavily built, supported by a broad and robust internarial bar (comprising the posterodorsal process of the premaxilla, nasals, and anterior process of the frontal), which provided effective shock absorption and stress transfer. Because of this, it has been proposed that the tylosaurine rostrum was elongated for use in ramming prey or rivals, but recent research on Taniwhasaurus found

648-413: A complex neurovascular system in the snout, suggesting that the rostrum was extremely sensitive, and therefore it is unlikely that the rostrum was used as a ramming weapon. The snout holds the terminal branches for the trigeminal nerves through randomly scattered foramina on the rostrum and along the ventral margin of the maxilla, above the gum line . The premaxilla, maxilla, and frontal bones border

756-415: A decrease in polycotylid diversity. The study noted converging traits between Tylosaurus , pliosaurs, and some polycotylids in tooth morphology and body size. However, there was no evidence to suggest that Tylosaurus or its precursors evolved as a result of out-competing and/or driving to extinction the pliosaurs and polycotylids. Instead, Madiza and Cau proposed that Tylosaurus may have taken advantage of

864-405: A distinct downward curve, suggesting the presence of a tail fluke . Fossil evidence of the skin of Tylosaurus in the form of scales has been described since the late 1870s. These scales were small and diamond-shaped and were arranged in oblique rows, comparable to that found in modern rattlesnakes and other related reptiles. However, the scales in the mosasaur were much smaller in proportion to

972-399: A distinctively broad semicircle in adults. The process is small in T. bernardi, and in T. pembinensis and T. saskatchewanensis , it is rounded. In T. saskatchewanensis , the suprastapedial process almost touches the infrastapedial process. At the bottom of the shaft is the mandibular condyle, which forms the joint between the quadrate and the lower jaw. It is rounded in shape in adults. On

1080-640: A fragmentary skull measuring nearly 5 feet (1.5 m) in length and thirteen vertebrae lent to him by Louis Agassiz of the Harvard Museum of Comparative Zoology . The fossil, which remains in the same museum under the catalog number MCZ 4374, was recovered from a deposit of the Niobrara Formation located in the vicinity of Monument Rocks near the Union Pacific Railroad at Fort Hays , Kansas. Cope's first publication of

1188-407: A genus is determined by taxonomists . The standards for genus classification are not strictly codified, so different authorities often produce different classifications for genera. There are some general practices used, however, including the idea that a newly defined genus should fulfill these three criteria to be descriptively useful: Moreover, genera should be composed of phylogenetic units of

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1296-439: A gradual change in the development of the quadrate bone, and lived in the same locations. The means by which this lineage evolved has been hypothesized to be through one of two evolutionary mechanisms related to changes in ontogeny . First, Jiménez-Huidobro, Simões, and Caldwell proposed in 2016 that T. proriger evolved as a paedomorph of T. nepaeolicus , in which the descendant arose as a result of morphological changes through

1404-651: A later homonym of a validly published name is a nomen illegitimum or nom. illeg. ; for a full list refer to the International Code of Nomenclature for algae, fungi, and plants and the work cited above by Hawksworth, 2010. In place of the "valid taxon" in zoology, the nearest equivalent in botany is " correct name " or "current name" which can, again, differ or change with alternative taxonomic treatments or new information that results in previously accepted genera being combined or split. Prokaryote and virus codes of nomenclature also exist which serve as

1512-628: A long time and redescribed as new by a range of subsequent workers, or if a range of genera previously considered separate taxa have subsequently been consolidated into one. For example, the World Register of Marine Species presently lists 8 genus-level synonyms for the sperm whale genus Physeter Linnaeus, 1758, and 13 for the bivalve genus Pecten O.F. Müller, 1776. Within the same kingdom, one generic name can apply to one genus only. However, many names have been assigned (usually unintentionally) to two or more different genera. For example,

1620-497: A longer lifespan. Offsetting these advantages, larger organisms require more food and water, and shift from r to K-selection . Their longer generation time means a longer period of reliance on the mother, and on a macroevolutionary scale restricts the clade's ability to evolve rapidly in response to changing environments. Left unfettered, the trend of ever-larger size would produce organisms of gargantuan proportions. Therefore, some factors must limit this process. At one level, it

1728-441: A pair of faint buccal and lingual carinae, except in T. gaudryi , in which the teeth are mediolaterally compressed. Carinae are not serrated. The anterior surface tends to be either smooth of faintly faceted, while the posterior surface is striated. Both pectoral and pelvic girdles are unfused in adult Tylosaurus , in contrast to other taxa (e.g., Prognathodon overtoni ). Tylosaurus is also distinguished from other mosasaurs by

1836-409: A reference for designating currently accepted genus names as opposed to others which may be either reduced to synonymy, or, in the case of prokaryotes, relegated to a status of "names without standing in prokaryotic nomenclature". An available (zoological) or validly published (botanical) name that has been historically applied to a genus but is not regarded as the accepted (current/valid) name for

1944-587: A subsequent reanalysis of the same data suggested otherwise. An extensive study published in 2015 supports the presence of a trend toward larger body size in marine animals during the Phanerozoic . However, this trend was present mainly in the Paleozoic and Cenozoic ; the Mesozoic was a period of relative stasis. The trend is not attributable simply to neutral drift in body size from small ancestors, and

2052-427: A taxon; however, the names published in suppressed works are made unavailable via the relevant Opinion dealing with the work in question. In botany, similar concepts exist but with different labels. The botanical equivalent of zoology's "available name" is a validly published name . An invalidly published name is a nomen invalidum or nom. inval. ; a rejected name is a nomen rejiciendum or nom. rej. ;

2160-595: A third species based on a partial skeleton he collected near the southern portion of the Smoky Hill River that is now in the Yale Peabody Museum as YPM 1268, which Marsh named Rhinosaurus micromus . Cope responded by arguing that Rhinosaurus was already a preoccupied synonym of Liodon . He disagreed with Marsh's arguments but proposed that in case Marsh was indeed correct, the genus name Rhamphosaurus should be used. Marsh later discovered that

2268-455: A total of c. 520,000 published names (including synonyms) as at end 2019, increasing at some 2,500 published generic names per year. "Official" registers of taxon names at all ranks, including genera, exist for a few groups only such as viruses and prokaryotes, while for others there are compendia with no "official" standing such as Index Fungorum for fungi, Index Nominum Algarum and AlgaeBase for algae, Index Nominum Genericorum and

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2376-404: A trend towards larger size, although the first two are now extinct. Cope recognised that clades of Cenozoic mammals appeared to originate as small individuals, and that body mass increased through a clade's history. Discussing the case of canid evolution in North America , Blaire Van Valkenburgh of UCLA and coworkers state: Cope's rule, or the evolutionary trend toward larger body size,

2484-419: Is associated with increased fitness for a number of reasons, although there are also some disadvantages both on an individual and on a clade level: clades comprising larger individuals are more prone to extinction , which may act to limit the maximum size of organisms . Directional selection appears to act on organisms' size, whereas it exhibits a far smaller effect on other morphological traits, though it

2592-511: Is by no means universal. For example, among genera of Cretaceous molluscs, an increase in size is no more common than stasis or a decrease. In many cases, Cope's rule only operates at certain taxonomic levels (for example, an order may obey Cope's rule, while its constituent families do not), or more generally, it may apply to only some clades of a taxon. Giant dinosaurs appear to have evolved dozens of times, in response to local environmental conditions. Despite many counter-examples, Cope's rule

2700-613: Is classified within the family Mosasauridae in the superfamily Mosasauroidea . The genus is the type genus of its own subfamily, the Tylosaurinae . Other members of this group include Taniwhasaurus and possibly Kaikaifilu , and the subfamily is defined by a shared feature of an elongated premaxillary rostrum that does not bear teeth. The closest relatives of the Tylosaurinae include the Plioplatecarpinae and

2808-573: Is common among mammals. Large size enhances the ability to avoid predators and capture prey, enhances reproductive success, and improves thermal efficiency. Moreover, in large carnivores, interspecific competition for food tends to be relatively intense, and bigger species tend to dominate and kill smaller competitors. Progenitors of hypercarnivorous lineages may have started as relatively small-bodied scavengers of large carcasses, similar to foxes and coyotes, with selection favoring both larger size and enhanced craniodental adaptations for meat eating. Moreover,

2916-612: Is discouraged by both the International Code of Zoological Nomenclature and the International Code of Nomenclature for algae, fungi, and plants , there are some five thousand such names in use in more than one kingdom. For instance, A list of generic homonyms (with their authorities), including both available (validly published) and selected unavailable names, has been compiled by the Interim Register of Marine and Nonmarine Genera (IRMNG). The type genus forms

3024-422: Is flattened into multiple sides to form a prism-like geometry. Bardet et al. (2006) classified Tylosaurus species into two morphological groups based on marginal dentition. The North American ' proriger group ' includes T. proriger and T. nepaeolicus and is characterized by teeth with smooth or faint facets, less prominent carinae, and a vein-like network of primitive striations extending to near

3132-400: Is known of its teeth other than having striations and no facets. The distinction of an ' ivoensis group ' is contentious. Caldwell et al. (2008) argued that T. pembinensis cannot be compared with T. ivoensis as the former's teeth are not fluted, and that T. ivoensis is more allied with the distinctively fluted teeth of Taniwhasaurus . Jiménez-Huidobro and Caldwell (2019) listed

3240-442: Is not always equal; in at least T. proriger , T. ivoensis , T. gaudryi , and T. pembinensis , they are positioned such that the surface area of the tooth's lingual side is greater than the labial side. Both sides are always balanced in area in T. bernardi . The enamel surface is lined with thin fine ridges called striations that run vertically from the tooth's base. The surface is also either smooth or faintly faceted, in which it

3348-522: Is not consistent with previous phylogenetic analyses. In the Western Interior Seaway , two species— T. nepaeolicus and T. proriger —may represent a chronospecies , in which they make up a single lineage that continuously evolves without branching in a process known as anagenesis . This is evident by how the two species do not stratigraphically overlap, are sister species , share minor and intermediate morphological differences such as

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3456-446: Is possible that the clade's increased vulnerability to extinction, as its members become larger, means that no taxon survives long enough for individuals to reach huge sizes. There are probably also physically imposed limits to the size of some organisms; for instance, insects must be small enough for oxygen to diffuse to all parts of their bodies, flying birds must be light enough to fly, and the length of giraffes' necks may be limited by

3564-487: Is possible that this perception may be a result of sample bias. This selectional pressure can be explained by a number of advantages, both in terms of mating success and survival rate. For example, larger organisms find it easier to avoid or fight off predators and capture prey, to reproduce, to kill competitors, to survive temporary lean times, and to resist rapid climatic changes. They may also potentially benefit from better thermal efficiency , increased intelligence, and

3672-420: Is proportionally short in T. proriger (20-27% skull length) , T. bernardi (24% skull length) , and T. gaudryi (25-27% skull length), and long in T. pembinensis (28-31% skull length). The nasal bones were either free-floating or lightly articulated to the internarial bar, did not contact the frontal, and were not fused to each other as they are in extant varanid lizards . The nasals' loose association with

3780-460: Is somewhat arbitrary. Although all species within a genus are supposed to be "similar", there are no objective criteria for grouping species into genera. There is much debate among zoologists about whether enormous, species-rich genera should be maintained, as it is extremely difficult to come up with identification keys or even character sets that distinguish all species. Hence, many taxonomists argue in favor of breaking down large genera. For instance,

3888-481: Is still debate whether T. kansasensis is synonymous with T. nepaeolicus , and T. "borealis" has yet to be described in a formal publication. In 2020, Madzia and Cau performed a Bayesian analysis to better understand the evolutionary influence on early mosasaurs by contemporaneous pliosaurs and polycotylids by examining the rates of evolution in mosasauroids like Tylosaurus (specifically T. proriger , T. nepaeolicus , and T. bernardi ). A Bayesian analysis in

3996-559: Is supported in many instances. For example, all marine invertebrate phyla except the molluscs show a size increase between the Cambrian and Permian. Collectively, dinosaurs exhibit an increase in body length over their evolution. Cope's rule also appears to hold in clades where a constraint on size is expected. For instance, one may expect the size of birds to be constrained, as larger masses mean more energy must be expended in flight. Birds have been suggested to follow Cope's law, although

4104-474: Is the type species , and the generic name is permanently associated with the type specimen of its type species. Should the specimen turn out to be assignable to another genus, the generic name linked to it becomes a junior synonym and the remaining taxa in the former genus need to be reassessed. In zoological usage, taxonomic names, including those of genera, are classified as "available" or "unavailable". Available names are those published in accordance with

4212-448: Is unclear. Tylosaurus had 29 to 30 presacral vertebrae , 6 to 7 pygal vertebrae, and 89 to 112 caudal vertebrae; due to the lack of a bony articulation between the ilium and vertebral column, it is unclear whether any mosasaurs possessed true sacral vertebrae. In all tylosaurines, like in plioplatecarpines , the chevrons articulate to the caudal vertebrae, and are not fused to them, as they are in mosasaurines . The tail possesses

4320-436: Is usually a result of size varying pseudo-randomly rather than directed evolution. This does not fall into Cope's rule sensu stricto , but is considered by many workers to be an example of "Cope's rule sensu lato ". In other cases, an increase in size may in fact represent a transition to an optimal body size, and not imply that populations always develop to a larger size. However, many palaeobiologists are skeptical of

4428-621: The International Code of Zoological Nomenclature ; the earliest such name for any taxon (for example, a genus) should then be selected as the " valid " (i.e., current or accepted) name for the taxon in question. Consequently, there will be more available names than valid names at any point in time; which names are currently in use depending on the judgement of taxonomists in either combining taxa described under multiple names, or splitting taxa which may bring available names previously treated as synonyms back into use. "Unavailable" names in zoology comprise names that either were not published according to

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4536-824: The International Plant Names Index for plants in general, and ferns through angiosperms, respectively, and Nomenclator Zoologicus and the Index to Organism Names for zoological names. Totals for both "all names" and estimates for "accepted names" as held in the Interim Register of Marine and Nonmarine Genera (IRMNG) are broken down further in the publication by Rees et al., 2020 cited above. The accepted names estimates are as follows, broken down by kingdom: The cited ranges of uncertainty arise because IRMNG lists "uncertain" names (not researched therein) in addition to known "accepted" names;

4644-600: The Royal Saskatchewan Museum estimated a total length of over 9.75 meters (32.0 ft). A mounted skeleton of T. pembinensis, nicknamed "Bruce," at the Canadian Fossil Discovery Centre measures at 13.05 meters (42.8 ft) long and was awarded a Guinness World Records for "Largest mosasaur on display" in 2014. However, the skeleton was assembled for display prior to Bullard and Caldwell (2010)'s reassessment that found

4752-489: The Sternberg Museum of Natural History (FHSM VP-2496) may be from an even larger individual; Everhart estimated the specimen to come from a 14 meters (46 ft) individual compared to his 12 meters (39 ft) estimate for Bunker. The genus exhibits Cope's rule , in which its body size has been observed to generally increase over geologic time. In North America, the earliest representatives of Tylosaurus during

4860-843: The Turonian and Coniacian (90-86 mya), which included early T. nepaeolicus and its precursors, typically measured 5–7 meters (16–23 ft) long and weighed between 200–500 kilograms (440–1,100 lb). During the Santonian (86-83 mya), T. nepaeolicus and newly-appearing T. proriger were 8–9 meters (26–30 ft) long and weighed around 1,100 kilograms (2,400 lb). By the Early Campanian , T. proriger attained lengths of 13–14 meters (43–46 ft). Everhart speculated that because mosasaurs continuously grew throughout their lifetime, it would have been possible for some extremely old Tylosaurus individuals to reach 20 meters (66 ft) in absolute maximum length. However, he stressed

4968-557: The Tylosaurus specimen is anywhere between the first and sixth cervical vertebrae. In Platecarpus , the bronchi probably diverged below the sixth cervical into near-parallel pairs, while in Mosasaurus the organ is dislocated. A bifurcation point's position ahead of the forelimbs would be unlike terrestrial lizards, whose point is within the chest region, but similar to the short trachea and parallel bronchi of whales. Tylosaurus

5076-454: The external nares , or body nostril openings; unlike other mosasaurs, the prefrontal bones are excluded from the border of the nares by a long posterodorsal process of the maxilla. The nares open above the fourth maxillary tooth anteriorly in T. proriger and T. pembinensis, between the third and fourth tooth in T. nepaeolicus , and posterior to the fourth tooth in T. bernardi. Nare length relative to skull length varied between species: it

5184-419: The nomenclature codes , which allow each species a single unique name that, for animals (including protists ), plants (also including algae and fungi ) and prokaryotes ( bacteria and archaea ), is Latin and binomial in form; this contrasts with common or vernacular names , which are non-standardized, can be non-unique, and typically also vary by country and language of usage. Except for viruses ,

5292-404: The platypus belongs to the genus Ornithorhynchus although George Shaw named it Platypus in 1799 (these two names are thus synonyms ) . However, the name Platypus had already been given to a group of ambrosia beetles by Johann Friedrich Wilhelm Herbst in 1793. A name that means two different things is a homonym . Since beetles and platypuses are both members of the kingdom Animalia,

5400-583: The ulnare , sometimes the ulnare and distal carpal four) and two ossified tarsal bones (usually only the astragalus, sometimes the astragalus and distal tarsal four). Hyperphalangy (increased number of phalanges relative to the ancestral condition) is present in both fore- and hindlimbs, and the phalanges are spindle -shaped, unlike the short, blocky hourglass -shaped phalanges possessed by mosasaurines . The pisiform appears to be either unossified or absent in tylosaurines. The functional consequences of differences in limb anatomy across different mosasaur clades

5508-445: The absence of marginal fluting as a diagnostic (taxon-identifying) trait that differentiates Tylosaurus from Taniwhasaurus . The pterygoid teeth may have enabled ratchet feeding, in which the upper teeth held prey in place as the lower jaw slides back and forth via a streoptostylic jaw joint. The bases of the pterygoid teeth are nearly circular, and each tooth is divided into front and back-facing sides of near-equal surface area via

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5616-852: The analysis due to extensive missing data (i.e., lack of material with scoreable phylogenetic characters). Aigialosaurus Komensaurus carrolli Tethysaurus nopcsai Pannoniasaurus inexpectatus Yaguarasaurus columbianus Russellosaurus coheni Romeosaurus fumanensis Taniwhasaurus oweni Taniwhasaurus antarcticus Tylosaurus nepaeolicus [REDACTED] Tylosaurus proriger [REDACTED] Tylosaurus bernardi [REDACTED] Tylosaurus pembinensis [REDACTED] Tylosaurus saskatchewanensis [REDACTED] Angolasaurus bocagei Ectenosaurus clidastoides Selmasaurus johnsoni Plesioplatecarpus planifrons Latoplatecarpus willistoni Plioplatecarpus Platecarpus tympaniticus Halisaurinae Genus The composition of

5724-524: The animal to maintain elevated body temperatures in colder environments. Possession of this trait during infancy would in turn facilitate fast growth rates. Unreflective dark coloring and countershading would have provided the mosasaur with increased camouflage . Additional speculative functions includes increased tolerance to solar ultraviolet radiation , strengthened integuments. The study remarked that certain melanism -coding genes are pleiotropic for increased aggression . AMNH FR 221 preserves parts of

5832-448: The apex of the shaft into an incomplete loop, and it likely served as the attachment point for the depressor mandibulae muscles that opened the lower jaw. The process is slender and proportionally long in immature T. nepaeolicus and T. proriger , and thickened as the animals matured. The process is of similar length to T. proriger in T. saskatchwanensis and shorter in T. bernardi . In T. pembinensis , it abruptly turns medially at

5940-547: The atlas vertebra but is not preserved afterwards. The respiratory tract reappears below the fifth rib as a pair of bronchi and extends to just behind the as-preserved coracoids where preservation is lost. The pairing is suggestive of two functional lungs like modern limbed lizards but unlike snakes. Similar branching is also found in Platecarpus and putatively Mosasaurus , the only two other derived mosasaurs with their respiratory systems documented. The bifurcation point for

6048-442: The base for higher taxonomic ranks, such as the family name Canidae ("Canids") based on Canis . However, this does not typically ascend more than one or two levels: the order to which dogs and wolves belong is Carnivora ("Carnivores"). The numbers of either accepted, or all published genus names is not known precisely; Rees et al., 2020 estimate that approximately 310,000 accepted names (valid taxa) may exist, out of

6156-500: The blood pressure it is possible for their hearts to generate. Finally, there may be a competitive element, in that changes in size are necessarily accompanied by changes in ecological niche. For example, terrestrial carnivores over 21 kg almost always prey on organisms larger, not smaller, than themselves. If such a niche is already occupied, competitive pressure may oppose the directional selection. The three Canidae clades ( Hesperocyoninae , Borophaginae , and Caninae ) all show

6264-428: The cartilaginous respiratory system . This includes parts of the larynx (voice box), trachea (windpipe), and bronchi (lung airways). They were however only briefly described in the preserved position by Osborn (1899). The larynx is poorly preserved; a piece of its cartilage first appears below just between the pterygoid and quadrate and extends to behind the latter. This connects to the trachea, which appears below

6372-480: The dentary is between 56 and 60% of total length of the entire lower jaw in adult T. nepaeolicus and T. proriger , about 55% in T. pembinensis , and 62% in T. saskatchwanensis . The dentary is robust, though not as strongly built as it is in Mosasaurus , Prognathodon , or Plesiotylosaurus . The ventral margin of the dentary ranges from straight to slightly concave. A small dorsal ridge appears anterior to

6480-473: The evolution of predator size is likely to be influenced by changes in prey size, and a significant trend toward larger size has been documented for large North American mammals, including both herbivores and carnivores, in the Cenozoic. In some cases, the increase in body size may represent a passive, rather than an active, trend. In other words, the maximum size increases, but the minimum size does not; this

6588-510: The extinction of the pliosaurs and decline of polycotylids to quickly fill the ecological void they left behind. The Bayesian analysis also approximated a divergence of T. nepaeolicus from the rest of the genus around 86.88 million years ago and a divergence between T. proriger and T. bernardi around 83.16 million years ago. The analysis also generated a paraphyletic status of the genus, approximating Taniwhasaurus to have diverged from Tylosaurus around 84.65 million years ago, but this result

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6696-432: The first dentary tooth in mature individuals of T. proriger . The marginal dentition of most species is adapted for cutting large marine vertebrates, while those in T. ivoensis and T. gaudryi appear more optimized for piercing or smashing prey, and T. "borealis" in both piercing and cutting. Marginal teeth are triangular with a slight recurve towards the back of the jaws so that the lingual (tongue-facing) side forms

6804-446: The form "author, year" in zoology, and "standard abbreviated author name" in botany. Thus in the examples above, the genus Canis would be cited in full as " Canis Linnaeus, 1758" (zoological usage), while Hibiscus , also first established by Linnaeus but in 1753, is simply " Hibiscus L." (botanical usage). Each genus should have a designated type , although in practice there is a backlog of older names without one. In zoology, this

6912-475: The fossil was very brief and was named Macrosaurus proriger , the genus being a preexisting European mosasaur taxon. The specific epithet proriger means "prow-bearing", which is in reference to the specimen's unique prow-like elongated rostrum and is derived from the Latin word prōra (prow) and suffix -gero (I bear). In 1870, Cope published a more thorough description of MCZ 4374. Without explanation, he moved

7020-737: The generic name (or its abbreviated form) still forms the leading portion of the scientific name, for example, Canis lupus lupus for the Eurasian wolf subspecies, or as a botanical example, Hibiscus arnottianus ssp. immaculatus . Also, as visible in the above examples, the Latinised portions of the scientific names of genera and their included species (and infraspecies, where applicable) are, by convention, written in italics . The scientific names of virus species are descriptive, not binomial in form, and may or may not incorporate an indication of their containing genus; for example,

7128-528: The genus is a premaxilla ( TMM 40092-27) recovered from Middle Turonian deposits of the Arcadia Park Shale in Texas , which is dated between 92.1 and 91.4 million years old based on correlations with index fossils. Although formally referred to as Tylosaurinae incertae sedis during its first description, it was remarked to probably belong to T. kansasensis . The specimen was later listed within

7236-431: The incorporation of Hainosaurus as a synonym of Tylosaurus , this also makes the genus one of the last mosasaurs. Currently, eight species of Tylosaurus are recognized by scientists as taxonomically valid. They are as follow: T. proriger , T. nepaeolicus , T. bernardi , T. gaudryi , T. ivoensis , T. iembeensis , T. pembinensis , and T. saskatchewanensis . The validity of two additional taxa remain unsettled; there

7344-405: The lack of fossil evidence suggesting such sizes and the odds against any being preserved. Other Campanian- Maastrichtian species were similarly large. The most recent maximum estimate for T. bernardi is 12.2 meters (40 ft) by Lindgren (2005); historically the species was erroneously estimated at even larger sizes of 15–17 meters (49–56 ft). A reconstruction of T. saskatchewanensis by

7452-633: The largest component, with 23,236 ± 5,379 accepted genus names, of which 20,845 ± 4,494 are angiosperms (superclass Angiospermae). By comparison, the 2018 annual edition of the Catalogue of Life (estimated >90% complete, for extant species in the main) contains currently 175,363 "accepted" genus names for 1,744,204 living and 59,284 extinct species, also including genus names only (no species) for some groups. The number of species in genera varies considerably among taxonomic groups. For instance, among (non-avian) reptiles , which have about 1180 genera,

7560-461: The lateral sufrace of the bone within a bowl-like depression called the alar conch. The conch is shallow in T. nepaeolicus , T. proriger , and T. bernardi , and deep in T. pembinensis and T. saskatchewanensis . The alar rim is thin in T. nepaeolicus , T. proriger , and T. bernardi , and thick in T. bernardi , T. pembinensis , and T. saskatchewanensis . The suprastapedial process is a hook-like extension of bone that curves posteroventrally from

7668-412: The lingual and occasionally labial sides that do not reach the tooth's tip, and facets on the labial side. The facets are gentle in T. pembinensis , while in T. ivoensis they are slightly concave. The latter feature is also known as fluting. Marginal teeth in T. gaudryi are virtually indistinguishable from those in T. ivoensis . T. iembeensis was not placed within either group; no further description

7776-420: The lizard genus Anolis has been suggested to be broken down into 8 or so different genera which would bring its ~400 species to smaller, more manageable subsets. Cope%27s rule Cope's rule , named after American paleontologist Edward Drinker Cope , postulates that population lineages tend to increase in body size over evolutionary time. It was never actually stated by Cope, although he favoured

7884-433: The lower jaw to the cranium and holding the eardrums . The complex anatomy of the bone renders it extremely diagnostic, even to the species level. In lateral view, the quadrate resembles a hook in immature T. nepaeolicus and T. proriger individuals, but in adult forms for both species and in T. bernardi , T. pembinensis , and T. saskatchweanensis it takes on a robust oval-like shape. The eardrum (tympanum) attached to

7992-446: The marginal dentition, and the pterygoids house palatal dentition. On each side of the skull, Tylosaurus had 2 premaxillary teeth, 12 to 13 maxillary teeth, 13 dentary teeth, and 10 to 11 pterygoid teeth. The dentition is homodont , meaning that all teeth are nearly identical in size and shape, with the exception of the pterygoid teeth, which are smaller and more recurved than the marginal teeth. Tylosaurine dentaries were elongate;

8100-453: The medial surface of the bone, a thick, pillar-like vertical ridge often protrudes beyond the dorsal margin of the quadrate so that it is visible in lateral view. The upper jaws include the premaxilla and maxilla , and the lower jaws include the dentary , splenial , coronoid , angular , surangular , and prearticluar-articular (like other squamates , the prearticular is fused to the articular). The premaxilla, maxilla, and dentary house

8208-403: The most (>300) have only 1 species, ~360 have between 2 and 4 species, 260 have 5–10 species, ~200 have 11–50 species, and only 27 genera have more than 50 species. However, some insect genera such as the bee genera Lasioglossum and Andrena have over 1000 species each. The largest flowering plant genus, Astragalus , contains over 3,000 species. Which species are assigned to a genus

8316-428: The name could not be used for both. Johann Friedrich Blumenbach published the replacement name Ornithorhynchus in 1800. However, a genus in one kingdom is allowed to bear a scientific name that is in use as a generic name (or the name of a taxon in another rank) in a kingdom that is governed by a different nomenclature code. Names with the same form but applying to different taxa are called "homonyms". Although this

8424-505: The nostrils to the throat. In Tylosaurus , they are shaped like a compressed teardrop and bordered by the vomers , palatines , and the maxilla. Anterior to the choanae, each vomer borders the fenestra for the Jacobson's organ , which is involved in the tongue-based sense of smell . It begins opposite of the fourth maxillary tooth in Tylosaurus , and also ends immediately past the fifth maxillary tooth in T. bernardi . The exit point for

8532-535: The occurrence of linear evolutionary trends . It is sometimes also known as the Cope–Depéret rule , because Charles Depéret explicitly advocated the idea. Theodor Eimer had also done so earlier. The term "Cope's rule" was apparently coined by Bernhard Rensch , based on the fact that Depéret had "lionized Cope" in his book. While the rule has been demonstrated in many instances, it does not hold true at all taxonomic levels, or in all clades . Larger body size

8640-414: The posteroventral process. The vertical ramus is overlapped by the postorbitofrontal in most species, and the horizontal ramus overlaps the maxilla. In T. bernardi , the vertical ramus is not overlapped but joins with the postorbitofrontal by a suture, and is much thicker than the horizontal ramus. The quadrate bones (homologous to the incus in mammals) are located at the back of the skull, articulating

8748-427: The prefrontal, lacrimal, postorbitofrontal, and jugal bones . A diagnostic feature of Tylosaurus is that the prefrontals and postorbitofrontals overlap above the orbits, preventing contribution of the frontal. The jugal forms the bottom of the orbit; in Tylosaurus , it is L-shaped and has a distinctive serif-like extension at the lower back corner of the junction between the horizontal and vertical rami (arms) called

8856-447: The premaxilla in the latter. The frontal crest is present but poorly developed in most T. nepaeolicus skulls, and occasionally lost in some mature individuals. The frontal overlaps the prefrontals and postorbitofrontals above the orbits (eye sockets), and the parietal posteriorly. The position of the pineal eye on the parietal is variable, either appearing close to the frontoparietal suture or contacting it. The orbits are bordered by

8964-540: The primitive subfamilies Tethysaurinae and Yaguarasaurinae ; together they are members of one of three possible major lineages of mosasaurs (the others being the Mosasaurinae subfamily and Halisauromorpha group) that was first recognized in 1993. This clade was named the Russellosaurina by Polcyn and Bell in 2005. Tylosaurus was among the earliest derived mosasaurs. The oldest fossil attributable to

9072-541: The provisions of the ICZN Code, e.g., incorrect original or subsequent spellings, names published only in a thesis, and generic names published after 1930 with no type species indicated. According to "Glossary" section of the zoological Code, suppressed names (per published "Opinions" of the International Commission of Zoological Nomenclature) remain available but cannot be used as the valid name for

9180-407: The rest of the skull in Tylosaurus and other mosasaurs may be why the bones are frequently lost and therefore exceedingly rare; Tylosaurus is one of the only mosasaurs in which the nasal bones are clearly documented; the other is the holotype of Plotosaurus , although one of the bones is missing. The external nares lead to the choanae (internal nares) in the palate, which provide passage from

9288-448: The retention of juvenile features of the ancestor in adulthood. This was based on the presence of a frontal crest and convex borders of the parietal bone of the skull shared in both juvenile T. nepaeolicus and all T. proriger but lost in adult T. nepaeolicus . However, an ontogenetic study by Zietlow (2020) found that it was unclear whether this observation was a result of paedomorphosis, although this uncertainty may have been due that

9396-470: The same kind as other (analogous) genera. The term "genus" comes from Latin genus , a noun form cognate with gignere ('to bear; to give birth to'). The Swedish taxonomist Carl Linnaeus popularized its use in his 1753 Species Plantarum , but the French botanist Joseph Pitton de Tournefort (1656–1708) is considered "the founder of the modern concept of genera". The scientific name (or

9504-524: The sample size of mature T. nepaeolicus was too low to determine statistical significance. Second, the same study proposed an alternative hypothesis of peramorphosis , in which T. proriger evolved by developing traits found in mature T. nepaeolicus during immaturity. Based on results from a cladistical ontogram developed using data from 74 Tylosaurus specimens, the study identified a multitude of traits that were present in all T. proriger and mature T. nepaeolicus but absent in juvenile T. nepaeolicus :

9612-408: The scientific epithet) of a genus is also called the generic name ; in modern style guides and science, it is always capitalised. It plays a fundamental role in binomial nomenclature , the system of naming organisms , where it is combined with the scientific name of a species : see Botanical name and Specific name (zoology) . The rules for the scientific names of organisms are laid down in

9720-527: The skin. Microscopic analysis of scales in a T. nepaeolicus specimen by Lindgren et al. (2014) detected high traces of the pigment eumelanin indicative of a dark coloration similar to the leatherback sea turtle in life. This may have been complemented with countershading , present in many aquatic animals, though the distribution of dark and light pigments in the species remains unknown. A dark-colored form would have provided several evolutionary advantages. Dark coloration increases absorption of heat, allowing

9828-512: The skull size and depth are large, the length of the elongated rostrum exceeds 5% of the total skull length, the quadrate suprastapedial processes are thick, the overall quadrate shape converges, and the posteroventral process is fan-like. The following cladogram is modified from a phylogenetic analysis by Jiménez-Huidobro & Caldwell (2019) using Tylosaurus species with sufficiently known material to model accurate relationships; T. gaudryi , T. ivoensis , and T. iembeensis were excluded from

9936-409: The snout proportionally longer than most mosasaurs, with the exception of Ectenosaurus . The most recognizable characteristic of Tylosaurus is the elongated edentulous rostrum that protrudes from its snout, for which the genus is named. This is formed by the elongation of the front end of the premaxilla and dentary. The rostrum was small and acutely angled at birth, but rapidly developed into

10044-654: The species in a 2020 reexamination. A slightly younger specimen is of a skull (SGM-M1) of an indeterminate Tylosaurus species similar to T. kansasensis from the Ojinaga Formation in Chihuahua, Mexico , dated around ~90 million years old at earliest. A tooth from a Late Maastrichtian deposit in Nasiłów, Poland dating close to the Cretaceous–Paleogene boundary has been attributed to Hainosaurus sp. With

10152-598: The species into another European genus Liodon and declared his original Macrosaurus proriger a synonym. In 1872, Marsh argued that Liodon proriger is taxonomically distinct from the European genus and must be assigned a new one. For this, he erected the genus Rhinosaurus , which means "nose lizard" and is a portmanteau derived from the Ancient Greek words ῥίς ( rhī́s , meaning "nose") and σαῦρος ( saûros , meaning "lizard"). Marsh also described

10260-418: The species' number of vertebrae to be exaggerated. T. "borealis" is estimated at 6.5–8 meters (21–26 ft) in total length. The largest known skull of Tylosaurus is T. proriger KUVP 5033 (the "Bunker" specimen), estimated at 1.7 meters (5.6 ft) long. Depending on age and individual variation, Tylosaurus skulls were between 13 and 14% of the total skeleton length. The head was strongly conical and

10368-497: The specific name particular to the wolf. A botanical example would be Hibiscus arnottianus , a particular species of the genus Hibiscus native to Hawaii. The specific name is written in lower-case and may be followed by subspecies names in zoology or a variety of infraspecific names in botany . When the generic name is already known from context, it may be shortened to its initial letter, for example, C. lupus in place of Canis lupus . Where species are further subdivided,

10476-412: The standard format for a species name comprises the generic name, indicating the genus to which the species belongs, followed by the specific epithet, which (within that genus) is unique to the species. For example, the gray wolf 's scientific name is Canis lupus , with Canis ( Latin for 'dog') being the generic name shared by the wolf's close relatives and lupus (Latin for 'wolf') being

10584-482: The study's implementation can approximate numerically defined rates of morphological evolution and ages of divergence of clades. The Tylosaurinae was approximated to have diverged from the Plioplatecarpinae around 93 million years ago; the divergence was characterized by the highest rate of evolution among all mosasaurid lineages. This trend of rapid evolution coincided with the extinction of the pliosaurs and

10692-504: The taxon Rhamphosaurus was preoccupied as a genus of lizard named in 1843. As a result, he suggested a move to a newly erected genus named Tylosaurus . This name means "knob lizard" in another reference to the elongated rostrum characteristic of the genus. It is derived from the Latin tylos (knob) and Ancient Greek σαῦρος . Despite coining the new genus, Marsh never formally transferred the Rhinosaurus species to Tylosaurus ; this

10800-403: The taxon is termed a synonym ; some authors also include unavailable names in lists of synonyms as well as available names, such as misspellings, names previously published without fulfilling all of the requirements of the relevant nomenclatural code, and rejected or suppressed names. A particular genus name may have zero to many synonyms, the latter case generally if the genus has been known for

10908-613: The tip. The group was originally defined as having slender teeth, but subsequent research has since recognized that slenderness is an ontogenetic trait in T. proriger with robust teeth appearing in adult forms. Though not formally classified within a group, the marginal teeth of T. saskatchwanensis shares a comparable morphology with T. proriger . The second is the Euro-American ' ivoensis group ' and consists of T. ivoensis , T. gaudryi , and T. pembinensis . Their teeth are robust with prominent carinae with striations on

11016-434: The validity of Cope's rule, which may merely represent a statistical artefact. Purported examples of Cope's rule often assume that the stratigraphic age of fossils is proportional to their "clade rank", a measure of how derived they are from an ancestral state; this relationship is in fact quite weak. Counterexamples to Cope's rule are common throughout geological time; although size increase does occur more often than not, it

11124-576: The values quoted are the mean of "accepted" names alone (all "uncertain" names treated as unaccepted) and "accepted + uncertain" names (all "uncertain" names treated as accepted), with the associated range of uncertainty indicating these two extremes. Within Animalia, the largest phylum is Arthropoda , with 151,697 ± 33,160 accepted genus names, of which 114,387 ± 27,654 are insects (class Insecta). Within Plantae, Tracheophyta (vascular plants) make up

11232-476: The veins leading to sinuses inside the palatine occur right in front of the Jacobson's organ between the vomers and maxilla. This differs from living varanids, where the exit occurs behind the organ. The frontal bone in Tylosaurus usually, but not always, possesses a low midline crest. It is most prominent in T. proriger, and is moderately developed in T. saskatchewanensis and T. bernardi , extending onto

11340-429: The virus species " Salmonid herpesvirus 1 ", " Salmonid herpesvirus 2 " and " Salmonid herpesvirus 3 " are all within the genus Salmonivirus ; however, the genus to which the species with the formal names " Everglades virus " and " Ross River virus " are assigned is Alphavirus . As with scientific names at other ranks, in all groups other than viruses, names of genera may be cited with their authorities, typically in

11448-418: The whole body. An individual measuring 5 meters (16 ft) in total body length had dermal scales measuring 3.3 by 2.5 millimeters (0.130 in × 0.098 in), and in each square inch (2.54 cm) of the mosasaur's underside an average of ninety scales were present. Each scale was keeled in a form resembling that of a shark's denticles . This probably helped reduce underwater drag and reflection on

11556-587: Was first done in 1873 by Joseph Leidy by transferring Rhinosaurus proriger to Tylosaurus . Rhinosaurus micromus was formally transferred to the same genus in 1894 by John Campbell Merriam . Tylosaurus was one of the largest known mosasaurs. The largest well-known specimen, a skeleton of T. proriger from the University of Kansas Natural History Museum nicknamed "Bunker" (KUVP 5033), has been estimated to measure between 12–15.8 meters (39–52 ft) long. A fragmentary skeleton of another T. proriger from

11664-509: Was the third new genus of mosasaur to be described from North America behind Clidastes and Platecarpus and the first in Kansas . The early history of the genus as a taxon was subject to complications spurred by the infamous rivalry between American paleontologists Edward Drinker Cope and Othniel Charles Marsh during the Bone Wars . The type specimen was described by Cope in 1869 based on

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