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.

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.

[1] 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.

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.

[4] At the same time, the Oklahoma Museum of Natural History (OMNH) had recovered remains belonging to the same hadrosauroid from excavations in the southwestern region of the Swell.

[4] The Field Museum of Natural History (FMNH) also conducted excavations south of the town of Emery from 2009 to 2010, with permits from the Utah Geological Survey.

[3] A 1997 argon-argon dating of sanidine crystals recovered from a volcanic ash layer in the upper Cedar Mountain Formation by Cifelli and colleagues indicated an age of 97 ± 0.1 million years, which was then considered to be just after the boundary between the Albian and Cenomanian stages.

One of the characteristics used to distinguish Eolambia is the concave profile of the tooth row of the maxilla when viewed from the side, which is like Equijubus, Probactrosaurus, and several other hadrosauriforms but unlike Protohadros.

[4] Like Probactrosaurus and other hadrosauroids, the back of the maxilla connects to the jugal – which borders the bottom of the eye socket and infratemporal fenestra – through a finger-like projection that fits into a recess.

The bottom margin of the jugal bears a strong flange beneath the level of the infratemporal fenestra; this is also seen in Equijubus, Probactrosaurus, Protohadros, and several other hadrosauroids.

In the rearmost cervicals, there is also a deep depression separating the postzygapophyses, and the neural spines have steeply-angled front margins, which has the effect of creating prominent spike-like projections.

Furthermore, the neural spines transition from rectangular to strongly curved (concave in front and convex behind), the centra become more elongated, and the transverse processes disappear as well.

The fourth trochanter, located halfway down the femur, is vertically tall and triangular, similar to Probactrosaurus, Gongpoquansaurus, and other iguanodonts but dissimilar to more basal ornithopods.

Weishampel and colleagues used seven unifying characteristics to define the Hadrosauridae: the upward expansion of the ascending process of the maxilla; the absence of the paraquadrate foramen, which separates the quadrate and quadratojugal; the location of the angular on the inner surface of the lower jaw; the absence of the surangular foramen on the surangular; the narrow teeth of the maxilla; the presence of three or more teeth in each dentary tooth position; and the reduction of the top margin of the scapular blade.

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.

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[19][20] – albeit one convergently present in the Ankylosauria and Ceratopsia.

As demonstrated by Head, there is actually a foramen on the premaxilla; the premaxilla only borders the nostril on the bottom edge; there are two finger-like processes at the front of the maxilla in addition to the shelf; high neural spines of the caudal vertebrae also occur in the non-lambeosaurines Ouranosaurus and Bactrosaurus; and the expansion of the tip of the ischium also occurs in Camptosaurus, Iguanodon, Ouranosaurus, Gilmoreosaurus, and Bactrosaurus, indicating that the expansion is plesiomorphic for iguanodonts and was secondarily lost in hadrosaurines.

[4] Head further showed that Eolambia possessed seven sacral vertebrae, unlike eight or more in derived hadrosaurids, and that its antitrochanter was actually more poorly developed than those of Ouranosaurus and Altirhinus.

[25] 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.

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.

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.

[9] Iguanodon Mantellisaurus Ouranosaurus Altirhinus Morelladon Proa Batyrosaurus Sirindhorna Koshisaurus Jinzhousaurus Bolong Equijubus Xuwulong Gongpoquansaurus Probactrosaurus Jintasaurus Eolambia Protohadros Jeyawati Nanningosaurus Nanyangosaurus Yunganglong Gilmoreosaurus Levnesovia Bactrosaurus Tanius Huehuecanauhtlus Zhanghenglong Plesiohadros Shuangmiaosaurus Telmatosaurus Tethyshadros Claosaurus Hadrosauridae In 2018, Terry Gates and colleagues described the new iguanodontian genus Choyrodon, from the same locality as Altirhinus, considered in the past a relative of Eolambia.

The placement of these genera relative to other hadrosauriformes depended on whether the antorbital fenestra was coded as present or absent in Choyrodon; the juvenile type specimen has one, but the possibility that adults would have a closed one could not be ruled out.

The lakes fluctuated between high and low water levels in Milankovitch cycles of roughly 21,000 years, caused by the Earth's axial precession.

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.

Before burial, scavengers could have disrupted the skeletal material, which is evident in the severed Eolambia tibiae bearing tooth marks discovered in the Cifelli #2 quarry.

[9] A variety of smaller maniraptoran theropods are also present in the Mussentuchit, which would have functioned as scavengers; their remains include teeth attributed to the Dromaeosauridae, Paronychodon, and Richardoestesia.

They proposed that Eolambia was part of an influx of Asian dinosaurs into North America during the Cenomanian, which supplanted the earlier low-diversity native fauna.

[9][28][30][48] 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.