Did extinct lemurs wean their offspring earlier than likesized diurnal anthropoids

Teeth contain an internal chronometer of their own growth in the form of short-term (i.e., daily) and long-term incremental lines. By making thin sections through the crowns and roots and by counting daily incremental lines throughout all of crown and root formation, one can determine prenatal and postnatal crown formation time as well as root extension rates. These can be used to study the pace of dental development within the context of other aspects of cranial and skeletal growth and development. Using this technique, we have been able to infer not merely overall molar crown formation time but dental precocity at birth, age at molar crown completion, and likely age at M1 gingival eruption for three extinct lemurs: Megaladapis edwardsi, Palaeopropithecus ingens, and Archaeolemur majori (Godfrey et al., 2005a, in press b; Schwartz et al., 2002, 2005). Table 4 documents these data alongside data for like-sized anthropoids and much smaller-bodied extant lemurs. Megaladapis and Palaeopropithecus have short crown formation times, early initiation of molar crowns (well before birth),

Table 4. Reconstructing extinct lemur life-history parameters®

A. Crown Formation Time (CFT) and inferred Ml eruption in extinct lemurs

A. Crown Formation Time (CFT) and inferred Ml eruption in extinct lemurs

Table 4. Reconstructing extinct lemur life-history parameters®

Taxon

Ml CFT

Prenatal CFT

Age at M1 crown completion

Likely age at M1 gingival emergence

Palaeopropithecus ingens Megaladapis edwardsi Archaeolemur majori

221 days 380 days 522 days

187 days 132 days 85 days

34 days (1.1 mo) 248 days (8.3 mo) 437 days (14.6 mo)

~ 0.2-0.5 year ~0.75-1.1 year ~1.25-1.6 year

B. Crown Formation Time (CFT) and observed Ml eruption in extant lemurs and other primates

Taxon

Ml CFT

Prenatal CFT

Age at M1 crown completion

Age at M1 gingival emergence

Propithecus verreauxi Lemur catta Varecia variegata Pongo pygmaeus Gorilla gorilla Papio hamadyras

191 days l95 days 220 days 993 days 1237 days 529 days

94 days 67 days 55 days

24 days

25 days 36 days

97 days 128 days 165 days 969 days 1212 days 493 days

~0.25-0.33 year ~0.4-0.5 year ~0.5-0.6 year ~4.6 years ~3.5 years ~1.7 years

a Data on extinct and extant lemurs are taken from Schwartz et al. (2002, 2005, in press) and Godfrey et al. (2005a, in press b). Data on Pongo are taken from Kelley and Schwartz (2005), on Gorilla from Willoughby (1978) and D. Reid (unpublished), and on Papio from Dirks (2003), Dirks et al. (2002), and Smith et al. (1994). We assume that weaning occurred in giant lemurs at around the age of Ml gingival emergence. Some living lemurs wean their offspring before the first molar erupts, while others wean them shortly thereafter.

a Data on extinct and extant lemurs are taken from Schwartz et al. (2002, 2005, in press) and Godfrey et al. (2005a, in press b). Data on Pongo are taken from Kelley and Schwartz (2005), on Gorilla from Willoughby (1978) and D. Reid (unpublished), and on Papio from Dirks (2003), Dirks et al. (2002), and Smith et al. (1994). We assume that weaning occurred in giant lemurs at around the age of Ml gingival emergence. Some living lemurs wean their offspring before the first molar erupts, while others wean them shortly thereafter.

and rapid root extension rates (and thus short root formation times). Likely behavioral correlates of this accelerated pace of dental development and eruption include early processing of fibrous foods. In contrast, crown formation begins and finishes later (relative to birth) in the smaller-bodied Archaeolemur.

Our projected ages at weaning are much earlier in Palaeopropithecus and Megaladapis than in like-sized anthropoids (Pongo and Gorilla), and slightly earlier in Archaeolemur than in baboons (Papio). In light of our data on dental development, we believe that weaning occurred at a very young age (probably before 6 months) in Palaeopropithecus, at around 1 year in Megaladapis, and later yet in Archaeolemur. By studying microwear across an ontogenetic series, Flanagan (2004) found evidence of a juvenile foraging phase—i.e., prolonged acquisition of foraging skills—in Archaeolemur, similar to that exhibited by Macaca fascicu-laris (a full adult foraging microwear signal is not manifested until after the emergence of the second molar; Godfrey et al., 2005a). Preliminary data suggest very prolonged molar crown formation time and late weaning in Hadropithecus; unfortunately, our data here are limited to the second molar (Godfrey et al., 2005a, in press a). Preliminary microwear data across ontogenetic series also suggest early acquisition of full-adult foraging skills in Palaeopropithecus and Megaladapis (Godfrey et al., in press b).

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