Table 1.

This is not an exhaustive list of terms used or definitions given. Age classes are given as used in the original sources and the definitions or reasoning for the assignment to this age class are direct quotes from the text. Additional details are often provided in the respective sources for assigning age classes, but these quotes are intended to be representative and not overarching. EFS, external fundamental system.

age classdefinitionsource
embryothese occur both in situ and inside fragments of eggs exposed on erosional surfaces[3]
perinatewe use the term ‘perinate’ (‘around birth’)[4]
small nestlingthe bone tissue that forms the shafts of the longer limb bones is … composed of vascular canals surrounded by an undifferentiated mineralized bone matrix[5]
large nestlingin cross section, the shafts of the long bones generally have a cortex that is well differentiated from the marrow cavity[5]
younganumerous differences in cranial and postcranial morphology given between ‘young’ and ‘adult’ Protoceratops[6]
juvenilea bone that is less than one-half the size of that of a typical adult specimen[7]
juvenileall vertebrae in embryonic and neonate ornithischian material, unsurprisingly, preserve open neurocentral sutures[8]
juvenilehistological section of the tibia shows well-vascularized, woven and parallel-fibred primary cortical bone typical of juvenile ornithopods[4]
subadultthe frontoparietal fontanelle is open in late-stage subadults[9]
subadultindividuals of adult or virtually adult size, with additional characters indicating pre-adult status … but individuals lack several adult characters[10]
subadulta bone between one-half and two-thirds the size of that of a typical adult specimen[7]
subadultthe individuals in this stage have both ‘young’ and ‘adult’ characters[11]
subadult or young adultaneurocentral sutures have closed, partial fusion of scapula and coracoid and of the ilium and ischium, fusion of some cranial elements[12]
adultfully grown individuals with full expression of adult characters, often including fusion of skull elements[10]
adulta bone that is approximately the size of that of a typical adult specimen[7]
adultthis histology is typical of an EFS and indicates that the individual was fully grown[13]
old adultnearly all of the cranial sutures are obliterated by co-ossification[14]
  • aThe quotations have been compressed for brevity.