page_title: Eolambia
section_title: Growth
hierarchical_section_title: Eolambia / Paleobiology / Growth
caption_attribution_description: English: Fig 13. Histology of FMNH PR 3847. (A) Composite micrograph of cross section of caudal dorsal rib of FMNH PR 3847 stitched from 42 individual micrographs. The boxed area is magnified in (B) under polarized light. Five definitive LAGs are marked with white arrows, while a sixth potential growth mark (grey arrow) may be present, but this is less certain as it is truncated by secondary osteons.
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: Being known from a variety of juvenile and adult specimens, the changes Eolambia underwent as it grew are well-documented. The number of teeth in the maxilla increased with age, from 23 in a juvenile to 33 in an adult. A similar increase occurred in the dentary teeth, from 18–22 in juveniles to 25–30 in adults. While juveniles lack secondary ridges on the crowns of their dentary teeth, faint secondary ridges are present in adults. The size of the "boot" of the ischium also increased with age, as documented by Kirkland. Changes may also have occurred in the straightness of the shaft of the ischium, as documented by specimens discovered by the FMNH.
  Results from a histological analysis performed on a rib from specimen FMNH PR 3847 were reported by McDonald and colleagues in 2017. Extensive bone remodeling has occurred in the internal matrix of the rib. The medullary cavity, which houses the marrow, is marked by the presence of many cavities, or lacunae. On the outer surface of the bone, osteons have almost completely replaced the interior of the bone; the layered growth of the bone is more visible on the interior of the bone, where five lines of arrested growth (LAGs) are visible. A sixth LAG is possibly present within the medullary region, but is relatively limited in extent, which makes this identification questionable.
  Since LAGs can be obliterated by bone remodeling, this represents an underestimate of the true number of LAGs that had actually developed; McDonald and colleagues estimated three or four missing LAGs by examining the spacing between the visible LAGs. This indicates that the animal was eight to nine years old when it died. The spacing between the LAGs decreases significantly towards the outer surface, indicating that growth was slowing, but the lack of the external fundamental system (a series of tightly-spaced LAGs) indicates that growth had not yet ceased. This is consistent with the unfused sutures between the centra and neural spines in the cervical and dorsal vertebrae, and the unfused sutures between the sacral centra and their corresponding ribs. 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.
caption: Cross section of a rib from specimen FMNH PR 3847; LAGs marked by arrows
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