Do cranial suture age and growth layer groups correlate in South American pinnipeds?

Abstract

Age is one of the most important life history parameters required to understand the dynamics of mammalian populations. Growth Layers Groups (GLGs) are incremental units of calcified tissue in the teeth (dentine and cementum), which represent a pattern of cyclical deposition that can be counted. However, the estimation of absolute age in GLGs demands a skull with teeth, the permission to destroy part of a tooth, equipment to cut the teeth, and experienced GLGs readers. In 1954 Sivertsen proposed an alternative method using cranial suture age (CSA) to establish age categories. However, there are no studies validating the CSA in relation to GLGs. Thus, this study examined whether there is a correlation between age categories proposed by the CSA and chronological age in years from GLGs of South American fur seals (Arctocephalus australis) (N = 52) and of South American sea lions (Otaria flavescens) (N = 37). 93% of the skulls of A. australis and 83.8% of O. flavescens corresponded accurately to the age in years estimated by each cranial suture age range. These results indicated the existence of high correspondence between the CSA and the GLGs age (r: 0.491 for A. australis and r: 0.675 for O. flavescens). However, an adaptation to Sivertsen's method is recommended: using only eight sutures (excluding the premaxillary-maxillary suture for CSA analysis, due to its late fusion), and updating the intervals for cranial sutures, that correspond to 16–32 = adults, 11–15 = young and 8–10 = pups.

Age estimation in the harbour seal (Phoca vitulina) based on the closure of skull sutures and synchondroses

“…Regarding the pattern of sutural/synchondrosal closure, the findings of the present study are similar to those of previous studies in other pinnipeds (Audibert et al, 2017; Doutt, 1942; Goswami et al, 2013; Stewardson et al, 2011a, 2011b). In the skulls studied by us, the sutures and synchondroses of the Calvaria ( S. lambdoidea , S. squamosa, S. sagittalis, S. coronalis ) and skull base ( Syn.…”

“…Following Doutt (1942) The scores for the studied sutures/synchondroses were then added up to provide a sum of closure level scores (SCS) (Oh et al, 2019) for each individual. Such sum scores have previously been used as an age indicator in pinnipeds by other authors, who referred to them as sutural (suture) age (Doutt, 1942;Sivertsen, 1954) cranial suture age (Audibert et al, 2017) or suture index (Stewardson et al, 2011a(Stewardson et al, , 2011b. Given that we used a system with four possible scores per suture/synchondrosis, the SCS for a skull could theoretically range from 12 (all sutures/synchondroses scoring 1) to 48 (all sutures/synchondroses scoring 4).…”

“…In addition to humans, the pattern and timing of sutural/synchondrosal closure has also been studied in various other mammal species (Bärmann & Sánchez‐Villagra, 2012; Cray et al, 2014; Goswami et al, 2013; Oh, Kim, et al, 2017; Oh, Oh, et al, 2017; Rager et al, 2014; Sánchez‐Villagra, 2010; Wilson & Sánchez‐Villagra, 2009). Ectocranial closure of sutures and synchondroses has been used as an age criterion in sika deer, Cervus nippon (Oh et al, 2019) and various species of pinnipeds (Audibert et al, 2017; Doutt, 1942; Sivertsen, 1954; Stewardson et al, 2011a, 2011b). Compared to the widely applied analysis of growth layer groups (GLGs) in dentin, cementum and bone (Hohn, 2009), the use of sutural/synchondrosal closure for estimation of age at death (also referred to as individual or chronological age) has the advantage of being a non‐destructive method that can be applied on skulls housed in museums without damage to teeth or bones.…”

“…Ectocranial closure of sutures and synchondroses has been used as an age criterion in sika deer, Cervus nippon (Oh et al, 2019) and various species of pinnipeds (Audibert et al, 2017;Doutt, 1942;Sivertsen, 1954;Stewardson et al, 2011aStewardson et al, , 2011b. Compared to the widely applied analysis of growth layer groups (GLGs) in dentin, cementum and bone (Hohn, 2009), the use of sutural/synchondrosal closure for estimation of age at death (also referred to as individual or chronological age) has the advantage of being a non-destructive method that can be applied on skulls housed in museums without damage to teeth or bones.…”

Age estimation and growth layer patterns in teeth of crabeater seals: A comparison of techniques

“…Knowing the ages of individuals can be useful to detect changes in growth rates due to climate change (Boyd & Roberts, 1993; Dellabianca et al, 2012; Knox, Stuart‐Williams, Warneke, Hoskinsv, & Arnould, 2013; Wittmann et al, 2016) or exposure to pollutants through tooth mineralization anomalies (Luque et al, 2013). Earlier studies relied on relative measures of age, such as the fusion of the cranial sutures (Audibert, Drehmer, Danilewicz, & de Oliveira, 2018), and changes in pelage or tooth wear (Hohn, 2018). Fortunately, the discovery of incremental layers deposited in teeth allowed more accurate and precise methods for estimating ages in mammals (Scheffer, 1950; Laws, 1953).…”