MAO Fang-Yuan, ZHENG Xiao-Ting, WANG Xiao-Li, WANG Yuan-Qing ,Bi Shun-Dong & MENG Jin (2018)
Evidence of diphyodonty and heterochrony for dental development in euharamiyidan mammals from Jurassic Yanliao Biota.
Vertebrata PalAsiatica (advance online publication)
DOI: 10.19615/j.cnki.1000-3118.180803
Free pdf:
Evidences for tooth replacement of known euharamiyidans are reported based on eight specimens of four species from the Jurassic Yanliao Biota, Liaoning Province, China. Tooth morphologies, eruptional and wear condition, and tooth germs are directly observed and/or revealed by Micro CT or slab CL scan. The euharamiyidan dentition has definite number of cheek teeth and monophyodont molars that are related to precise occlusion. Incisor germs are found in three specimens of Arboroharamiya but not in Shenshou lui and Xianshou linglong. The incisor germs in the upper jaw, presumably I2, have a large crown with two or three cusps; those in the lower jaw, interpreted as the permanent i2, are positioned dorsal to the root of the erupted incisor, interpreted as di2. Comparing dental development within various ontogenetic stages, the incisor tooth germs in Arboroharamiya and Vilevolodon would replace the deciduous incisors in a much later time than when ultimate molars became fully erupted and functional, if it did happen. The available evidence indicates presence of diphyodonty in the loci of the ultimate lower premolar and incisor, which are common mammalian features potentially related to lactation and parental care. The prolonged or delayed eruptions of incisors and ultimate molars in Arboroharamiya and Vilevolodon are probably associated with the specialization of dentition, with emphasis on the P4/p4 chewing function, which should be an autapomorphy and represent a heterochronic shift of tooth replacement in terms of ontogenetic timing comparing to other "haramiyidians". The heterochronic incisor replacement is probably owing to developmental suppression related to expansion of the premolars, and may have evolved independently multiple times within mammaliaforms. Â