ZT 299 is a 6.0 to 6.5 million-year-old juvenile male Lufengpithecus lufengensis cranium from the terminal Miocene period of Yunnan, China. An international team of scientists discovered the cranium in 2013 in an open-pit lignite mine in the Zhaotong Basin in northeastern Yunnan province. ZT 299 is only the second juvenile ape crania recovered from the Miocene of Eurasia and is provisionally assigned to the species Lufengpithecus lufengensis. ZT 299 reinforces the view that Lufengpithecus represents a distinct, late surviving lineage of East Asian Miocene apes, apes that appeared about 25 million years ago during the Miocene period.
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Analysis
During the Miocene, much of Asia and Africa was covered by expanses of forest and damp woodland. It was here that Miocene Apes thrived, and dozens of genera with many species of early apes lived during this time. Miocene Apes originated in Africa during the early Miocene, but dispersed into Europe and Asia during the middle to late Miocene, about 15 to 5 million years ago. When the world began to get cooler and drier, Miocene apes died off, leaving animals behind who were more easily able to adapt to new environments.
ZT 299 sheds light on the morphology of late Miocene apes. Although ZT 299 was partially broken during extraction, it shows almost no distortion, and scientists have accurately repositioned all portions of the cranium except for a section comprising the upper lip and left cheek, and the facial skeleton is mostly intact. There is a well-preserved brain endocast corresponding to the preserved portion of the brain case.
Scientists dated ZT 299, which is 6.0 to 6.5 million years old, by comparing recovered fauna, specifically the time-constrained rodent species Sinocastor, Kowalskia, and Pliopetaurista. All three rodent species indicate an age no older than the latest Miocene, about five million years ago, and no younger than the early Pliocene. Scientists also used paleomagnetic dating to determine the age of the sediment layer from which the cranium was recovered.
The cranium shares the dental morphology expressed by two other species of Lufengpithecus, L. lufengensis and L. hudienensis. Only the first molars of ZT 299 are erupted, and judging by the amount of wear, they had been in use for some time. Most of the remaining permanent teeth are preserved in their crypts. ZT 299’s sex was determined by observing the beginnings of a deep mesial groove in the canine crowns.
Interpretation
It is possible that ZT 299 represents a new species of Lufengpithecus due to differences between ZT 299 and the reconstructed adult cranium of L. lufengensis (PA 644) and the juvenile cranium of L. hudienensis (YV0999), however, its juvenile status complicates assessment. ZT 299 is more similar to L. lufengensis than to either L. keiyuanensis or L. hudienensis. While some argue that a case exists for a new species, different developmental stages of comparable crania and uncertainty concerning reconstruction of other samples makes the naming of a new species unjustified. Instead, ZT 299 is assigned to Lufengpithecus cf. lufengensis.