page_title: Eolambia
section_title: Subsequent research
hierarchical_section_title: Eolambia / Classification / Subsequent research
caption_attribution_description: Lanzhousaurus (file name is incorrect). 中文: 半月金塔龍骨架
context_page_description: Eolambia is a genus of herbivorous hadrosauroid dinosaur from the early Late Cretaceous of the USA. 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 6 metres 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.
context_section_description: 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 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.
  In 2012, McDonald conducted a phylogenetic analysis of iguanodonts incorporating data from new Eolambia specimens. Contrary to previous authors, he found instead that Eolambia was the sister group of Probactrosaurus. This close relationship was based on two shared characteristics: the quadrate being straight save for the top end, which is curved backwards; and the top and bottom margins of the scapular blade being nearly parallel. 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). Using the 2012 version of the McDonald dataset, Francisco Verdú and colleagues independently recovered a similar result, with Eolambia being closely related to Protohadros and Jeyawati; however, McDonald and colleagues found the latter to be more derived in 2017.
  In 2018, Terry Gates and colleagues described the new iguanodotian genus Choyrodon, from the same locality as Altirhinus, considered in the past a relative of Eolambia. Their phylogenetic analysis based on the matrix of Norman (2015), and Choyrodon was found to be the sister group of Eolmabia. Commonly recovered relative Protohadros was not present in this matrix. Three characteristics supported this relationship: a trapezoidally-shaped occiput, and two shared traits of the teeth. The placement of these genera relative to other hadrosauriformes depended on whether the antorbital fenestra was coded as present or absent Choyrodon; the juvenile type specimen has one, but the possibility that adults would have a closed one couldn't be ruled out. The following two trees show the results with it coded as present and absent respectively, the former showing a large polytomy:
caption: Reconstruction of Jintasaurus, recovered by Zheng et al. as a sister group of Eolambia
exif: {"Image ImageDescription": "", "Image Make": "Canon", "Image Model": "Canon PowerShot SX230 HS", "Image Orientation": "Horizontal (normal)", "Image XResolution": "180", "Image YResolution": "180", "Image ResolutionUnit": "Pixels/Inch", "Image DateTime": "2013:05:31 13:29:18", "Image YCbCrPositioning": "Co-sited", "Image ExifOffset": "252", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "180", "Thumbnail YResolution": "180", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "5620", "Thumbnail JPEGInterchangeFormatLength": "4391", "EXIF ExposureTime": "1/30", "EXIF FNumber": "31/10", "EXIF ISOSpeedRatings": "1600", "EXIF SensitivityType": "Standard Output Sensitivity and Recommended Exposure Index", "EXIF ExifVersion": "0230", "EXIF DateTimeOriginal": "2013:05:31 13:29:18", "EXIF DateTimeDigitized": "2013:05:31 13:29:18", "EXIF ComponentsConfiguration": "YCbCr", "EXIF CompressedBitsPerPixel": "3", "EXIF ShutterSpeedValue": "157/32", "EXIF ApertureValue": "13/4", "EXIF ExposureBiasValue": "0", "EXIF MaxApertureValue": "13/4", "EXIF MeteringMode": "Pattern", "EXIF Flash": "Flash did not fire, compulsory flash mode", "EXIF FocalLength": "5", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "4000", "EXIF ExifImageLength": "3000", "Interoperability InteroperabilityIndex": "R98", "Interoperability InteroperabilityVersion": "[48, 49, 48, 48]", "Interoperability RelatedImageWidth": "4000", "Interoperability RelatedImageLength": "3000", "EXIF InteroperabilityOffset": "4822", "EXIF FocalPlaneXResolution": "1000000/61", "EXIF FocalPlaneYResolution": "1000000/61", "EXIF FocalPlaneResolutionUnit": "2", "EXIF SensingMethod": "One-chip color area", "EXIF FileSource": "Digital Camera", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF DigitalZoomRatio": "1", "EXIF SceneCaptureType": "Standard"}