Open Paleo

Eolambia

Kirkland, 1998 EE-oh-LAM-bee-a

From Greek eos (dawn) + Lambeosaurinae: 'dawn lambeosaurine', indicating it is an early relative of lambeosaurine hadrosaurs.

100.5–93.9 million years ago Cenomanian, Late Cretaceous
Late Cretaceous stages

Eolambia 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.

Under dispute

Eolambia caroljonesa was originally described as a lambeosaurine hadrosaurid (Kirkland, 1998), but Head (2001) reidentified it as a basal hadrosauroid, and it is now consistently recovered as a basal hadrosauromorph well outside Hadrosauridae (McDonald and colleagues, 2012, 2017).

Diagnosis

  1. Sagittal crest formed by fused parietals extending above back of skull, visible in lateral view
  2. Squamosals meeting at midline in juvenile specimens with short paraoccipital processes
  3. Jugals long and low
  4. Maxilla lacking narial process and having 32 tooth positions in adult
  5. Lower jaw deepens rostrally with nearly no diastema; 30 tooth files with at least 3 teeth per file; teeth with single central carina
  6. Ischium long and stout with large, flaring, blade-like distal end

Species

Eolambia caroljonesa Kirkland, 1998

Type species

Named for Carole Jones, who discovered the type specimen in 1993 together with Ramal Jones, Carole's husband.

Holotype
CEUM 9758 , College of Eastern Utah Prehistoric Museum
Material
Disarticulated partial adult skeleton: paired frontals, partial parietals, braincase, right and left maxilla, right and left jugals, right postorbital, lower right quadrate, left dentary, atlas, cervical vertebra, anterior dorsal vertebra, proximal ischium, tibia fragment, right fibula
Horizon
Mussentuchit Member, Cedar Mountain Formation, Cenomanian, Late Cretaceous , 100.5–93.9 million years ago
Locality
Carol Site, Utah, United States Where the Carol Site sits in the member is disputed. Kirkland (1998) gives the holotype from the "basal Mussentuchit Member", and Carpenter and colleagues (1999) the Animantarx skeleton from the same site "just above the base", while Mori (2009) places the quarry "near the top of the Mussentuchit Member, only about 10 meters below the lowest Dakota Sandstone channel complex". The difference turns on a maroon smectitic layer below the quarry, which Mori includes in the Mussentuchit and Kirkland and Madsen (2007) place in the Ruby Ranch.

Synonyms of the genus

Name Type Reason
Eohadrosaurus nomen nudum Informal name ('Eohadrosaurus caroljonesi') used by Kirkland before the 1998 paper; replaced by the formal name Eolambia.

References

  1. Kirkland, J. I. (1998). A new hadrosaurid from the upper Cedar Mountain Formation (Albian-Cenomanian: Cretaceous) of eastern Utah - the oldest known hadrosaurid (lambeosaurine?). Lower and Middle Cretaceous Terrestrial Ecosystems (Lucas, S. G.; Kirkland, J. I.; Estep, J. W., eds.) 14: 283-295. kirkland1998a
  2. McDonald, A. T.; Bird, J.; Kirkland, J. I.; Dodson, P. (2012). Osteology of the basal hadrosauroid Eolambia caroljonesa (Dinosauria: Ornithopoda) from the Cedar Mountain Formation of Utah. PLoS ONE 7(10): e45712. doi:10.1371/journal.pone.0045712

    Redescribes the genus from the holotype, paratype and two juvenile bonebeds, giving the Mussentuchit Member without a position within it.

    mcdonald2012c
  3. Mori, H. (2009). Dinosaurian faunas of the Cedar Mountain Formation and LA-ICP-MS detrital zircon ages for three stratigraphic sections. Masters thesis, Brigham Young University.

    Places the Carol Site quarries near the top of the Mussentuchit Member, against Kirkland and Madsen (2007).

    mori2009a
  4. Carpenter, K.; Kirkland, J. I.; Burge, D.; Bird, J. (1999). Ankylosaurs (Dinosauria: Ornithischia) of the Cedar Mountain Formation, Utah, and their stratigraphic distribution. Vertebrate Paleontology in Utah (Gillette, D. D., ed.) 99-1: 243-251.

    Gives the Animantarx holotype, from the same site, as "just above the base of the Mussentuchit Member".

    carpenter1999a
  5. Kirkland, J. I.; Madsen, S. K. (2007). The Lower Cretaceous Cedar Mountain Formation, eastern Utah: the view up an always interesting learning curve. Field Guide to Geological Excursions in Southern Utah (Geological Society of America Rocky Mountain Section 2007 Annual Meeting) 35: 1-108.

    Records that the Ruby Ranch–Mussentuchit contact, elsewhere a chert-pebble lag, "appears gradational" along the north end of the San Rafael Swell.

    kirkland2007a
  6. Paul, G. S. (2024). The Princeton Field Guide to Dinosaurs (3rd ed.). Princeton University Press.

    Source of the appearance features.

    paul2024a
  7. Head, J. J. (2001). A reanalysis of the phylogenetic position of Eolambia caroljonesa (Dinosauria, Iguanodontia). Journal of Vertebrate Paleontology 21(2): 392-396. doi:10.1671/0272-4634(2001)021[0392:AROTPP]2.0.CO;2

    Reidentified Eolambia as a basal hadrosauroid outside Hadrosauridae, overturning the original lambeosaurine assignment.

    head2001a
  8. McDonald, A. T.; Gates, T. A.; Zanno, L. E.; Makovicky, P. J. (2017). Anatomy, taphonomy, and phylogenetic implications of a new specimen of Eolambia caroljonesa (Dinosauria: Ornithopoda) from the Cedar Mountain Formation, Utah, USA. PLOS ONE 12(5). doi:10.1371/journal.pone.0176896

    Recovered Eolambia caroljonesa as basal hadrosauromorph well outside Hadrosauridae.

    mcdonald2017a
  9. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

    Treats Eolambia as a basal hadrosauromorph.

    jones2026a