# Penghu 1

Penghu 1 is a fossil jaw (mandible) belonging to an extinct hominin species of the genus Homo. It was collected from seafloor sediments of the Penghu Channel off the coast of Taiwan, dating to sometime in the Middle Pleistocene or Late Pleistocene. The precise classification of the mandible is disputed. Some believe it to be the fossil of a H. erectus, an archaic Human or possibly a Denisovan.

## History and discovery

The fossil was recovered sometime before 2008 by fishermen working in the Penghu Channel between the Penghu Islands and mainland Taiwan and acquired by Tainan citizen Kun-Yu Tsai. The fossil was found 60–120 meters below the water's surface and about 25 kilometers off the western coast of Taiwan in an area which was once part of the mainland. Sea levels have risen since the last ice age and in consequence have submerged the area where the fossil was recovered. After Tsai donated the fossil to the National Museum of Natural Science, it was described in 2015 by an international team of Japanese, Taiwanese, and Australian scientists.
Penghu 1 is currently housed at the National Museum of Natural Science in Taichung.
The fossil is stratigraphically dated to younger than 450 kya, based on prehistoric sea-level lowering to either between 190 and 130 kya, or to between 70 and 10 kya.

## Fossil morphology

The fossil consists of a nearly complete right lower jaw with four teeth, including worn molars and premolars. The mandible has a high index of robustness, a robust lateral torus, large molars, and with the help of 3D reconstruction it was revealed to have a large bicondylar breadth. These features help confirm that the fossil was from the middle-late Pleistocene era. The alveoli of its four incisors and right canine have been preserved as well showing their great length. The specimen was assigned to the genus Homo based on its jaw and tooth morphology. The mandible shows a receding anterior surface and lacks a pronounced chin which has helped distinguish it from the species Homo sapiens. However, the fossil exhibited derived traits similar to early Homo habilis including the shortness and width of its jaw. These and other characteristics such as the agenesis of the M3 molar have been sufficient evidence to classify the specimen of the genus Homo.

## Classification

Although the genus of the Penghu 1 has been widely accepted, there is much discussion on the potential species of the specimen. The Penghu 1 mandible has been described as most similar to Hexian fossils of Homo erectus. Both Penghu 1 and the Hexian mandible share a similar crown size, mandibular prominence, and general robustness. As a result of these similarities and their late presence in Eastern Asia, the authors of "The first Archaic Homo of Taiwan" proposed several models for their existence. The features the mandibles' shared could be explained by either the retention of primitive characteristics of early Asian Homo erectus, a migration of Homo with robust jaws from Africa, inclusion in the species Homo heidelbergensis, or they could have been an adapted form of Homo erectus. However, the species identity or taxonomic relationships lack consensus due to limited material. Co-author Yousuke Kaifu cautioned that additional skeletal parts are needed before species evaluation. In 2015, paleontologist Mark McMenamin argued that unique dental characteristics of the jaw were sufficient to establish a separate species, which he dubbed Homo tsaichangensis. In a 2015 paper, Lelo Suvad accepted the validity of the new species H. tsaichangensis. Chinese anthropologists Xinzhi Wu and Haowen Tong did not agree with the naming of a new species, tentatively assigning the mandible to archaic Homo sapiens, leaving open the possibility of elevating it to a distinct species should more fossils be discovered.
In 2019, Chen Fahu along with a group of co-authors presented a piece suspecting the Penghu 1 mandible to belong to a Denisovan. This conclusion has been supported through its comparison with the Denisovan Xiahe mandible. The Xiahe mandible was discovered on the Tibetan Plateau and is dated to be around 160,000 years old. The Xiahe specimen has similar dental morphology compared to Penghu 1. They share 4 distinct characteristics: their M2's are close in mesiodistal width, they both show the agenesis of the M3 molar, they have a similar unique M2 root structure which relates to modern Asian populations, and the P3 displays Tomes' root, which is rarely found in other fossil hominins.
Wu & Bae (2024) assigned Penghu 1 to the new species Homo juluensis, as Xujiayao hominin, Xiahe mandible and Denisovans.