Құрып кеткен динозаврлар туысы - Eolambia

Extinct genus of dinosaurs

Eolambia (meaning "dawn lambeosaurine") is a genus of herbivorous hadrosauroid dinosaur from the early Late Cretaceous of the United States. It contains a single species, E. caroljonesa, named by paleontologist James Kirkland in 1998. The type specimen of Eolambia was discovered by Carole and Ramal Jones in 1993; the species name honors Carole. Since then, hundreds of bones have been discovered from both adults and juveniles, representing nearly every element of the skeleton. All of the specimens have thus far been found in Emery County, Utah, in a layer of rock known as the Mussentuchit Member of the Cedar Mountain Formation. Measuring up to long, Eolambia is a large member of its group. While it closely approaches the Asian hadrosauroids Equijubus, Probactrosaurus, and Choyrodon, in traits of the skull, vertebrae, and limbs, it may actually be more closely related to the North American Protohadros. This grouping, based on the straightness of the quadrate bone and scapula, would represent an isolated, endemic radiation of hadrosauroids. Despite resembling hadrosaurids – lambeosaurine hadrosaurids in particular – in several features, leading to its initial identification as one of them, these similarities have been rejected as either entirely convergent or misinterpreted. Eolambia would have lived in a forested environment at the edge of lakes in a humid floodplain environment, feeding on gymnosperms, ferns, and flowering plants. The water levels in the lakes changed over time with cyclical wet and dry spells caused by the precession of the Earth, reflected by alternating bands in the sediments of the Mussentuchit Member. As a juvenile, Eolambia would have been preyed upon by large crocodylomorphs residing in the lake waters. With increasing age, however, they became impervious to the crocodylomorphs, and mature individuals (at least eight to nine years in age) were preyed on by large theropods such as the neovenatorid Siats.

In 1979 Peter Galton and James A. Jensen described a fragmentary right femur, BYU 2000, belonging to a hadrosaurian dinosaur discovered in sediments belonging to the Cedar Mountain Formation in Arches National Park, Utah. Though poor material, it was important for it (alongside a second North American femur described in the paper) was the first hadrosaur specimen from the Lower Cretaceous anywhere in the world. Galton and Jensen hypothesized more complete remains of a hadrosaur may be found from the formation in the future. Various hadrosauroid teeth had also been found in quarries of small vertebrates in the western region of the San Rafael Swell, near Castle Dale in Emery County, Utah; they were described in 1991 by J. Michael Parrish. Subsequently, in 1993, Carole Jones and her husband Ramal Jones discovered fragmentary bones in a fossil site located in the northwestern region of the Swell. They brought the site to the attention of Donald Burge, director of the institution then called the College of Eastern Utah Prehistoric Museum (CEUM). The site, which is formally known as CEUM Locality 42em366v, would subsequently be named Carol's Site (sic) in her honour. The fossils, stored under the specimen number CEUM 9758, represent the partial remains of an adult hadrosauroid, including parts of the skull, vertebrae, ischium, and leg. CEUM 5212, a partial skull and forelimb from an adult, was found nearby in CEUM Locality 42em369v. In a 1998 paper published in the bulletin of the New Mexico Museum of Natural History and Science, Kirkland formally named the specimens as a new genus, Eolambia, with the type and only species being Eolambia caroljonesa. The generic name combines the Greek prefix eos/ἠώς ("dawn", "morning", implying "early") with the suffix lambia (derived from Lambeosaurus, which is in turn named after Canadian paleontologist Lawrence Lambe). In all, the genus name means "dawn (or early) lambeosaurine", in reference to its supposed position as the most basal lambeosaurine. Meanwhile, the specific name honors Carole Jones. The name Eolambia was suggested by paleoartist Michael Skrepnick; it replaced the informal name "Eohadrosaurus caroljonesi", which was used by Kirkland before the 1998 paper. However, the epithet caroljonesa, following the ICZN, is incorrect and in this case the correct spelling would be caroljonesae.

Additional excavations since 1998 have revealed additional skeletal elements belonging to Eolambia. It is now the most completely known iguanodont from between the Cenomanian and Santonian stages. Nearly every single skeletal element belonging to the taxon is represented by multiple fossils across existing collections. At least twelve individuals, including at least eight juveniles, Bentonite is also present within the sandstone itself throughout the Mussentuchit. as well as studies of fossil megaflora and invertebrates, had initially suggested that the uppermost Cedar Mountain Formation – including the Mussentuchit – dated to the Albian stage. Subsequently, in 2007, James Garrison and colleagues dated the volcanic ash layer passing through the Cifelli #2 Quarry – which is likely the same layer dated previously by Cifelli and colleagues – to 96.7 ± 0.5 million years ago. At an approximate level, the Cifelli and Garrison estimates agree with each other, thus indicating a Cenomanian age for Eolambia. Garrison and colleagues also re analyzed the pollen assemblage from localities throughout the Mussentuchit, concluding that the assemblage spans the Albian Cenomanian boundary. which agrees with a prior body length estimate of by Thomas R. Holtz Jr. in 2012. Earlier, in 2008, an adult specimen was estimated as having a length of and a height at the hip of
The first few dorsal vertebrae are similar to the cervical vertebrae, but have taller and more prong like neural spines. The rest are amphiplatyan, meaning that they are flat at both ends. They also have postzygapophyses which are less elongate and more pedestal like, in addition to taller and more rectangular neural spines. The parapophyses, which are depressions instead of projections, have moved off from the transverse processes to the neural arch, between the transverse processes and the articular processes known as the prezygapophyses at the front of the vertebrae. However, they move back onto the base of the transverse processes in the last few dorsals. The first, fifth, sixth, and seventh of these traits were recognized in Eolambia, with the rest being unknown due to missing material. Kirkland further assigned Eolambia to the Euhadrosauria, defined by Weishampel and colleagues to include the common ancestor of Hadrosaurinae (now the Saurolophinae) and Lambeosaurinae – the two primary branches of hadrosaurids – and all of its descendants. the absence of a foramen on the premaxilla; the (at least partial) enclosure of the nostril by the premaxilla; the development of a shelf on the maxilla; the very tall neural spines of the caudal vertebrae; the robustness of the humerus; and the large "boot" of the ischium in adults. Kirkland found that two additional traits separated the crestless Eolambia from other, crested lambeosaurines, which were considered as being related to the development of the crest: the elevation of the nasal cavity above the eye socket, and the shortening of the parietal. If Eolambia were to be recognized as a lambeosaurine, then the Lambeosaurinae would have to be redefined to exclude those two traits. Alternatively, if Eolambia was instead the sister group of the Lambeosaurinae, then it would represent a morphology in hadrosaurids that is close to the divergence between hadrosaurines and lambeosaurines. This possibility is supported by the presence of a groove on the bottom of the sacrum of Eolambia, which was recognized by Kirkland as a defining trait of hadrosaurines He thus remarked that adult Eolambia specimens would resolve this issue. Head argued that Corythosaurus and Lambeosaurus have ischial tips no more expanded than those of Mantellisaurus or Ouranosaurus. Head also demonstrated that the teeth of Eolambia were broader and more asymmetrical than Kirkland had assumed; he also noted that subadults only possessed two teeth per tooth position, unlike hadrosaurids, Examination of the OMNH specimens further demonstrated that the postacetabular region of the ilium did not form a distinct process, and the articulations at the bottom of the femur are not very prominent, both of which separate Eolambia from more derived iguanodonts such as hadrosaurids. Thus, Head concluded that Eolambia was a basal member of the Hadrosauroidea, outside of the Hadrosauridae, a conclusion supported by a phylogenetic analysis finding it to be a non hadrosaurid hadrosauroid closely related to Probactrosaurus.

In 2004, Norman included Eolambia for the first time in a comprehensive phylogenetic analysis of iguanodonts, as part of a chapter focusing on iguanodonts in the second edition of The Dinosauria. He found that Eolambia was the sister group to Altirhinus, with both of them being more basal than Protohadros, Probactrosaurus, or the Hadrosauridae. Within the same volume, Horner, Weishampel, and Catherine Forster conducted a separate phylogenetic analysis of hadrosaurids, likewise including Eolambia. They found Eolambia again as a non hadrosaurid hadrosauroid, albeit as the sister group to Protohadros. Although Head had specifically redefined the Hadrosauridae, based on shared characteristics, to include Protohadros, Horner and colleagues adapted a taxon based definition that excluded Protohadros and thus Eolambia. They also identified additional characteristics differentiating Eolambia from hadrosaurids: there are coarse denticles on the teeth of the dentary, and the coronoid process is weakly expanded. Variance in recovered phylogenetic positions for Eolambia persisted in the following years. In the 2009 description of Levnesovia, Hans Dieter Sues and Alexander Averianov found that Protohadros occupied an intermediate position relative to Altirhinus and Probactrosaurus, being the sister group of Fukuisaurus. Meanwhile, in accordance with the results of Horner and colleagues, Albert Prieto Márquez and Mark Norell found in 2010 that Eolambia was instead the sister group of Protohadros. He also noted features of Eolambia that were convergent upon hadrosaurids: the presence of a single tooth carina; the nearly square outer corner of the predentary; and the midpoint of the quadratojugal notch (which articulates with the quadratojugal) being located roughly halfway up the surface of the quadrate (being located less than 60% of the bone's height down from the top). In 2012, Holtz classified Eolambia as a primitive member of the Styracosterna along with Altirhinus. Wenjie Zheng and colleagues added Jintasaurus to the group in 2014, while José Gasca and colleagues recovered the original group in 2015. However, McDonald extensively revised his phylogenetic dataset further in preparation for the 2017 description of the FMNH specimens. As with Horner and colleagues, as well as Prieto Márquez and Norell, McDonald and colleagues found that Eolambia was the sister group of Protohadros, with both of them being placed as basal hadrosauromorphs (results reproduced below). with Eolambia being closely related to Protohadros and Jeyawati; however, McDonald and colleagues found the latter to be more derived in 2017. Topology A: Antorbital fenestra coded as present in Choyrodon Overall, the growth rate of Eolambia appears to have been comparable to that of Hypacrosaurus and Maiasaura, which reached maturity after seven or eight years.

Sedimentological data from the Mussentuchit Member indicates that Eolambia lived on a poorly drained floodplain, around a system of large, perennial lakes. The lakes fluctuated between high and low water levels in Milankovitch cycles of roughly 21,000 years, caused by the Earth's axial precession. These cycles is reflected by the alternating layers of muddy sandstone and mudstone in present day rock deposits. During dry periods, the exposed lakebed formed a broad beach devoid of plants. The cracked mud of the lakebed produced mud clasts, while organic debris and scavenged carcasses were scattered around the water's edge as the lake progressively retreated. Meanwhile, during periods in which the sea level rose, small rivers invaded the floodplain, which reworked and displaced the debris that had been deposited during the dry season. With a paleolatitude of 46° N, the Mussentuchit would have had a warm mean surface temperature of , about warmer than the present day, according to general circulation models.

Crocodylomorphs are abundant in the Mussentuchit deposits, being represented largely by teeth. The largest known teeth have been referred to the Pholidosauridae;efn|name=n1|Given that these classifications are based solely upon teeth, they are unreliable. McDonald and colleagues elected to recognize these morphotypes as indeterminate neosuchians in 2017. However, given the uniform small size of these teeth, and the co occurrence of these morphotypes in some crocodilians, which was discovered by expeditions from the FMNH. Teeth belonging to more basal ornithopods have also been discovered, with similar teeth having been referred to the Pachycephalosauria or to toothed birds by Cifelli in 1999. A giant oviraptorosaur has also been discovered, alongside teeth from ceratopsians and sauropods. These plants would have provided an abundant source of food for Eolambia. This alternative interpretation suggests that the common ancestor of Eolambia, Protohadros, and more derived hadrosauroids was not exclusively Asian, but instead distributed across Asia and North America. McDonald and colleagues further suggested that Eolambia and Protohadros represent a localized group of hadrosauroids endemic to North America, much like other groups of styracosternans throughout the Cretaceous. Such contemporary groups included a central Asian group of Shuangmiaosaurus, Zhanghenglong, and Plesiohadros.