“Missing perikymata”—fact or fiction? A study on chimpanzee (Pan troglodytes verus) canines

Abstract

21Recently, a lower than expected number of perikymata between repetitive furrow3type demonstrate that the enamel morphology described by them is not caused by a non3emergence of 30 striae of Retzius but can be attributed to structural variations in outer enamel that result in a 31 differential fracture behavior. While rejecting the presumed existence of non3emergent striae of 32 Retzius, our study provided evidence that, in furrow3type hypoplastic defects, a pronounced 33 tapering of Retzius increments can occur, with the striae of Retzius forming acute angles with the 34 outer enamel surface. We suggest that in such cases the outcrop of some striae of Retzius is 35 essentially unobservable at the enamel surface, causing too low perikymata counts. The 36 pronounced tapering of Retzius increments in outer enamel presumably reflects a mild to 37 moderate disturbance of the function of late secretory ameloblasts. The implications of these 38 findings for the reconstruction of crown growth patterns are discussed. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 (Boyde, 1989; Hillson, 2014). The outcrops of the long period growth layers at the enamel 46 surface are known as perikymata, with each perikyma consisting of a ridge, exhibiting a rather 47 smooth surface with only very shallow Tomes' process pits, and a groove characterized by deeper 48Tomes' process pits . Typically, a stria of Retzius reaches the outer enamel surface (OES) at the 49 bottom of a perikyma groove (Hillson, 2014). At the cervical margin of each perikyma groove, an 50 increment margin marks the transition to the cervically adjacent perikyma. Thus, the enamel 51 located between two consecutive increment margins at the OES corresponds to a Retzius 52 increment, that is, the stretch of enamel between two consecutive striae of Retzius. In teeth with a 53 known periodicity of the striae of Retzius (= repeat interval in days as evidenced by the number 54 of prism cross striations), crown formation times of lateral (imbricational) enamel can be 55 assessed based on perikymata counts. This approach has been widely used to reconstruct life 56 history traits in extant and fossil hominoids (e.g. Reid et al., 2008; Smith, 2008; Dean, 2010; 57 Hillson 2014) and to determine the timing of developmental stress events in great apes (Skinner 58 and Hopwood, 2004; Guatelli3Steinberg et al., 2012; Skinner and Pruetz, 2012; Skinner 2014). 59In a recent paper, Skinner and Pruetz (2012) reported the occurrence of a lower than 60 expected number of perikymata between repetitive furrow3type hypoplastic enamel defects 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 4 occur between consecutive furrow3t...

Developmental stress in South African hominins: Comparison of recurrent enamel hypoplasias in Australopithecus africanus and Homo naledi

“…6,7 By contrast, chimpanzees from Senegal, who experience only one wet season alternating with one very long dry season, show a reconstructed average interval between repetitive episodes of enamel hypoplasia of just under a year. 9,10 The assertion that repetitive linear enamel hypoplasia (rLEH) shows an average recurrence of 6 or 12 months, is not without challengers 11,12 , but see Smith et al 13 Furthermore, linking the recurrence with semi-annual moisture cycles, which are in turn linked to metabolic stressors such as seasonal food shortages, respiratory disease, malaria or intestinal worms 8 , remains speculative. With the discovery of Homo naledi, who lived in the same geographical area as Australopithecus africanus, it becomes possible to compare temporal ontogenetic patterns of enamel hypoplasia between low-and higher-latitude hominoids.…”

Quantifying linear enamel hypoplasia in Virunga Mountain gorillas and other great apes

“…Enamel geometry might also influence the morphology of LEH defects on the outer enamel surface. The angle at which striae of Retzius approach the outer enamel surface is related to the rate of enamel extension and secretion (Guatelli‐Steinberg et al, , 2017; Hillson & Bond, ; Kierdorf, Witzel, Kierdorf, Skinner, & Skinner, ). In modern humans, crown regions with more acute striae angles as they approach the outer enamel surface are associated with wider and shallower surface perikymata and LEH defects.…”

Characterization of short‐period and long‐period incremental markings in porcine enamel and dentine—Results of a fluorochrome labelling study in wild boar and domestic pigs

“…The time interval in days between two consecutively formed striae of Retzius, known as Retzius periodicity, Retzius interval or repeat interval (FitzGerald, 1998 ; Hogg, 2018 ; Kierdorf et al, 2013 ; McFarlane et al, 2014 , 2021 ; Smith et al, 2004 ), varies between species and among different individuals of the same species (FitzGerald & Rose, 2008 ; Hillson, 2005 , 2014 ). The long‐period increment between two successive striae of Retzius is also referred to as Retzius band (Tafforeau et al, 2007 ) or Retzius increment (Kierdorf et al, 2015 ). Retzius periodicity in enamel is established by counting daily prism cross‐striations between consecutive striae of Retzius (Hillson, 2014 ; Mahoney et al, 2018 ; O’Meara et al, 2018 ; Reid & Dean, 2006 ; Reid & Ferrell, 2006 ; Smith et al, 2004 ).…”

“…Along the crown flanks of teeth, the cyclic modulation of enamel growth is reflected by the presence of perikymata at the outer enamel surface (OES) that consist of regularly alternating horizontal grooves and ridges (Boyde, 1989 ; Hillson, 2014 ; Risnes, 1984 ). There is a clear correspondence between internal and external (surface) enamel incremental markings in that each stria of Retzius terminates in a perikyma groove at the OES (Boyde, 1989 ; Hillson, 2014 ; Kierdorf et al, 2015 ; Risnes, 1984 ). The increment margin or increment boundary present at the cervical edge of a perikyma groove marks the resumption of matrix secretion after the formation of a stria of Retzius, that is, the start of a new long‐period cycle of secretory ameloblast activity (Hillson, 2014 ).…”