characterizing dental development in fossil hominins is important for distinguishing between them and for establishing where and when the slow overall growth and development of modern humans appeared. Dental development of australopiths and early Homo was faster than modern humans. The Atapuerca fossils (Spain) fill a barely known gap in human evolution, spanning ~1.2 to ~0.4 million years (Ma), during which H. sapiens and Neandertal dental growth characteristics may have developed. We report here perikymata counts, perikymata distributions and periodicities of all teeth belonging to the TE9 level of Sima del Elefante, level TD6.2 of Gran Dolina (H. antecessor) and Sima de los Huesos. We found some components of dental growth in the Atapuerca fossils resembled more recent H. sapiens. Mosaic evolution of perikymata counts and distribution generate three distinct clusters: H. antecessor, Sima de los Huesos and H. sapiens. Dental enamel microstructure provides a timescale for dental development in the past. It also has the power to resolve taxonomic attribution when morphological character complexes and the timing of tooth formation are combined. Studies on dental enamel growth and relative dental development have been carried out in different hominin populations, from australopiths 1-4 , to early Homo 5 , H. naledi 6 , a Chinese specimen of the early Late Pleistocene 7,8 , Neandertals 9-12 , and archaic/modern H. sapiens 13-16. However, some of these works focused exclusively on the anterior dentition 1,2,5,6,10 while others employed crude estimates to reconstruct missing portions of the worn crown 17. These studies suggest that australopiths and early Homo shared dental development that was faster than in modern humans, with suggestions that the shift toward fully modern human dental development appeared some time after H. erectus or relatively late in human evolution 5. This potential shift was observed from a relatively reduced number of teeth, as KNM-ER 15000 and Sangiran S7-37. However, caution is claimed because substantial intraspecific variation in aspects of dental development (such as long-period line periodicity) within early hominin taxa has subsequently been demonstrated 4. Later Neandertals appear not to have an identical dental development with H. sapiens, as some aspects of their dental development tend to be more advanced 9,10,12. However, a recent study of a single Neandertal from El Sidrón (Spain) suggests that this hominin, with some