ISSN:
1573-7055
Keywords:
Dryolestidae
;
Eupantotheria
;
Jurassic
;
deciduous teeth
;
tooth replacement
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract The discovery of juvenile dentitions of late Jurassic (Kimmeridgian) Dryolestidae (Eupantotheria, Mammalia) from Guimarota, Portugal, yields for the first time information on the mode of tooth replacement in therian mammals prior to the dichotomy of placentals and marsupials. As in extant placentals, tooth replacement occurs at all antemolar positions [incisors (I1–I4), canine (C), premolars (P1–P4)]. P1 and P2 have premolariform milk predecessors, whereas the large premolariform third (P3) and fourth premolars (P4) are preceded by molariform deciduous premolars (dP3, dP4). Tooth replacement takes place in two waves, at least in the lower jaw, with I2, I4, P1, and P3 in the first series and I1, I3, C, P2, and P4 in the second. P4 is the last premolar to erupt, and it is present when the sixth molar (M6) starts to break through. The reduced tooth replacement pattern of marsupials (with only dP3 being replaced postnatally) evolved secondarily from the primitive or plesiomorphic mammalian condition, which was retained in Dryolestidae and Eutheria.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1027300726126
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