Lufengpithecus lufengensis

^[1]

Lufengpithecus lufengensis is a prehistoric species of hominoid from the Late Miocene found in China,^[1] named after the Lufeng site^[1] and dated around 6.2 Ma.^[2] It is the latest Miocene fossil ape that has been discovered in the entire world. Some researchers believe that genus Lufengpithecus could be an ancestor to African apes and hominids.^[3]

Taxonomy

There are three known species of Lufengpithecus: keiyuanensis from near Kaiyuan in the Xiaolongtan Basin (10-11mya), hudienensis from Yuanmou Basin (7.1-8.2mya), and lufengensis from Shihuiba in the Lufeng Basin (6.2-6.9mya).^[4] Some argue that this taxa is a distinct clade of late Miocene East Asian hominoids that are not closely related to any extant taxa. In fact, compared to YV0999 (a cranium of L. hudienensis from Yuanmou), there may have been a high degree of local endemism of apes during this time, due to the wide differences between the two species.^[4] This fits with the topographic data of Southwest China at the time, which was subject to uplift and erosion, which created the complex topography of mountain ranges and basins that is still present in current day.

Discovery

Excavation

In the Lufeng region of China, a known miocine hominoid site, a series of excavations were done between 1975 and 1983 which recovered five skulls, tens of mandibles, hundreds of isolated teeth and some post-cranial bones of the species.^[3]

ZT 299

ZT299 is a relatively complete juvenile male cranium found in the Zhaotong Basin in Yunnan Province of Southeast China. While it was partly broken during recovery, it encountered almost no distortion beforehand. It has prominent, robust arching supraorbital costae, and eye orbits that are broader than they are tall, more so than any extant great apes. However, these still fall within the range of Pongo orbital height and width, although it does not have any of the key features of the genus or any of the African apes. It is only the second relatively complete cranium uncovered of this species.^[4]

PA 644

PA 644 is an adult crania discovered in 1987 that has been reconstructed, but is different in both age and development than ZT299.^[4]

PA 868

PA 868 is a juvenile mandible which was in process of sprouting its first molar of the Lufengpithecus lufengensis and was found in the Yunnan Province in southwestern China around the late 1950s.^[5]

PA 869

PA 869 is another juvenile mandible of Lufengpithecus lufengensis and was discovered in 1980 in Shihuiba Village, Lufeng County, Yunnan Province in China.^[6]

Morphology

Anatomy

Using an equation derived by Conroy (1987) based off the mesiodistal length of preserved teeth found, it is estimated that the species within the genus Lufengpithecus had a body mass between 55.4 and 67.6 kg.^[3]

Analysis from an excavated skull shows that a male L. Lufengensis possess supraorbital ridges which are ovoid and the transverse diameter is slightly longer than the vertical diameter; in females the supraorbital ridges are predicted to be quadrangularly shaped rather than ovoid. The glabellar region which is located between the eyebrows and above the nose along with the frontal triangle are both very depressed. The midsagittal line of the face is also concave.^[7]

Dentition

Postcanine records show that L. lufengensis was more dimorphic that modern ape species such as the orangutan. Therefore, at least dentally, there were large variations between males and females of the species. Researchers are unsure if L. lufengensis is the more dimorphic of extinct ape species, but is more dimorphic that all extant ape species. Due to the extremely high molar dimorphism found in L. lufengensis, there is no overlap between males and females in bivariate plots of mesiodistal and buccolingual dimensions. With respect to postcanines, L. lufengensis has expanded the known range of intraspecific sexual dimorphism.^[8] Dental Records also show that the L. lufengensis has molars with thick enamel, peripheralized cusp apices with expansive basin and a dense, complex pattern of occlusal crenulations. The pattern of compactness of the small transverse ridges in the enamel of permanent teeth of L. lufengensis' are very similar to that of modern humans.^[7] The L. lufengensis' upper central incisors are high-crowned and labiolingually thick in relation to mesiodistal length, with a distinct, high relief median lingual pillar. In contrast the lower incisors are high crowned and relatively narrow mesiodistal and moderately procumbent. Male L. lufengensis' lower-canines taper sharply toward the apex, appearing very glacial and are relatively very high-crowned. The mandibular symphysis has a moderate superior transverse torus and prominent robust inferior torus. The orbits are approximately square in outline and the interobital contains a wide region. The glabella appear to be broad and depressed. There is a superior margin of nasal aperture higher than inferior margin of orbits. The nasoalveolar clivus is also relatively short.^[9]

Relation To Other Species

Fossils from the genus Lufengpithecus from the late Miocene is crucial in understanding hominoid evolution in Asia. The fossil being studied may be a member of the Homininae and study wants to show estimate age of molars in Lufengpithecus lufengensis at time of death. The results of the paper will help understand “Life History” in Miocene and Plio-Pleistocene hominids and great apes and humans. “Life history refers to the timing or scheduling of events from conception to death” (Zhao & Qingwu & Wending 2007). The author uses fossil PA868 as baseline and the fossil is thought to be a juvenile. They use the right mandibular of the fossil which has right four premolar and permanent first molar (M1)and also has five right permanent tooth crown germs which are I1, I2, C, P3, and P4 and the author concludes that PA868 was most likely a female. Age at time of death of PA868 was estimated using the number of perikymata on the surface of the cusp to the developing cervix. Age was 2.4-4.5 years based on the central incisor germ and 2.5-4.7 years based on the canine germ. The author discovers that first molar emergence was younger than the age of death due to the emergence of symptoms resembling gingivitis. The age of molars in the PA868 was estimated 3.2-3.3 years. The age of the crown formation took about .25-.75 years for PA868. Cuspal enamel formed within .4–1 years. Lateral enamel formed in 686–1078 days .The age of first molar emergence for PA868 resembles that of extant great apes and is less in relation to modern humans. Lufengpithecus lufengensis is more similar to great apes and the hominoids and less related to monkeys and modern humans.^[10]

In the juvenile mandible of Lufengpithecus, the superior part of the anterior surface and the vertical implantation of the anterior teeth are a lot like the adults of the same species. Additionally, the juvenile and the adult species have these features in common with early Homo species and early great apes. The superior transverse torus is more prominent and developed in the adult species whereas the juvenile (PA869) has a less developed superior transverse torus. In the juvenile and the adult species the lateral prominences are separated into two branches which are only similar in a single orangutan species (based off the species discussed in the paper) and not related to humans. In the juvenile there are double mental foramina on the corpora whereas the adult species and every other species mentioned in the paper have single mental foramina. Results indicates that the corpus of juvenile mandible of Lufengpithecus possessed the basic structural framework of the adult mandible of same species and other species such as Sivapithecus, Australopithecus, early Homo, but possess a different framework from modern humans.^[6]

Habitat and Range

Before the hominoid lived, the vegetation in the area was dominated by subtropical evergreen broad-leaved taxa with a few temperate deciduous taxa. During the hominoid’s time, the landscape changed and evergreen broad-leaved forests and grasses began to take over. The dominant species at the times were Quercus E and Alnus. The vegetation was mostly angiosperms, followed by gymnosperms, and pteridophytes. Conifers began to decrease in this time, indicating a gradual warming of the climate during this time. The greater diversity and warm humid climate during the late Miocene would have favored this ape’s survival. Lake or wetland environments were also common during this time, and it is postulated that the ape lived in forests adjacent to open areas with grasses, which began expanding along with other C4 plants. These would have supplemented the diet of this ape.^[2] Other taxa found in this time would have been Sinocastor, Kowalskia, Pliopetaurista, Alilepus, and several proboscideans. Mammals found near the fossil include tapirs, insectivores, flying squirrels, bamboo rats, freshwater birds, fish, frogs, turtles, crocodiles, beavers, otters, terrestrial birds and waters, all which point to a swampy or lacustrine environment.^[2]

Diet

L. lufengensis had a diet that consisted of both hard and soft fruits based on the paleoenvironment. L. lefungensis had similarly developed molar shearing crests to other miocine hominids such as Proconsul nyanzae, Ouranopithecus macedoniensis, Dendropithecus macinnesis and a Yuanmou hominoid, indicating a possible preference for harder fruits. However, the Yuanmou hominoid differs from teeth of the genus Lufengpithecus in several aspects of the evidence studied such as tooth size proportions, M2 shearing crest development, tooth enamel thickness and body weight .When compared to hominoid species of similar regions such as a Yuanmou hominid, L. lufengensis has smaller front teeth indicating at least a partly more folivorous diet compared to other extinct hominoids. This means along with consuming some hard fruits, they would also consume berries and leaves.^[3]

An alternative theory that was developed about L. Lufengensis is that their diet was strictly leaves and berries. Research was done on a set of upper and lower molars and measurements of both the mesiodistal and buccolingual cusps were done and compared with other indigenous apes of the area in the time period. L. Lufengensis’s molars were much larger than all the other hominoids in size. The ratio of M1 to M3 shows a pattern and when there is a high M1 to M3 ratio it indicates a consumption of more fruits rather than leaves and berries. L. Lufengensis’s ratio was much lower than compared to the ratio of L. Hudienensis. Due to the shearing crest size of the teeth that belongs to L. Lufengensis researchers believe that L. Lufengensis’s consisted primarily of leaves and berries. Upon further inspection of the upper and lower molars researchers notice a pattern on the teeth that belong to L. Lufengensis. The enamel on the cusp of the molars is still relatively thick, this displays they were not worn down by tough foods. The crowns on their teeth tend to be less worn than those of other extinct apes that once inhabited the same area, such as L. Hudienensis. These four categories that researchers took in to account when examining the molars supports the hypothesis that they have proposed about L. Lufengensis’s diet.^[11]

References