| Eosimias | |
|---|---|
 | |
| Restoration ofE. sinensis | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Primates |
| Suborder: | Haplorhini |
| Infraorder: | Simiiformes |
| Family: | †Eosimiidae |
| Genus: | †Eosimias Beard et al., 1994 |
| Species[1] | |
| |
Eosimias is a genus of earlyprimates, first discovered and identified in 1999 from fossils collected in the Shanghuang fissure-fillings of Liyang, the southern city ofJiangsu Province, China. It is a part of the familyEosimiidae, and includes three known species:Eosimias sinensis,Eosimias centennicus, andEosimias dawsonae.[3] It provides us with a glimpse of a primate skeleton similar to that of the common ancestor of theHaplorhini (including allsimians). The nameEosimias is designed to mean "dawn monkey", from Greekeos "dawn" and Latinsimius "monkey".[4]
Dating has proven this genus lived from 45 to 40 million years ago in the middleEocene.[4] The genusEosimias is unique because of the presence of primitive and derived traits. It provides new insight into thephylogenetic relationships between simians andprosimians (especially the phylogenetic position of the haplorhine prosimiantarsiers). It can best be described as a likely tree dweller that relied on a steady diet of insects and nectar.
Most eosimiid species are documented by unique or fragmentary specimens. This, as well as the strong belief that simians originated in Africa has made it difficult for many[who?] to accept the idea that Asia played a role in early primate evolution. Although some continue to challenge the anthropoid resemblances found in Eosiimidae, extensive anatomical evidence collected over the past decade substantiates its anthropoid status.[citation needed]
Eosimias sinensis (Chinese:中华曙猿,lit. 'dawn monkey of China') was first discovered inChina in 1992 by Christopher Beard. It was found in a mountain nearLiyang City,Jiangsu province,China.
The species is believed to have lived 45 million years before present, in theEocene epoch.[5]E. sinensis was tiny, as small as the smallest monkey presently, thepygmy marmoset (Cebuella pygmaea) ofSouth America, and could fit in the palm of a human's hand.[6] Its teeth are considered more primitive than those of early higher primates known from Africa, includingAlgeripithecus. Due to its highly primitive nature, some paleontologists considerE. sinensis to be evidence that higher primates may have originated inAsia rather thanAfrica.[5]
Christopher Beard was the lead member of the team that discoveredEosimias sinensis in 1994. Beard recovered a rightmandible, cataloged as IVPP V10591, which preserved P4–M2 and roots or alveoli for C1, P2–3, and M3. Although it retains primitive characters such as a small body size (mean estimates range from 67–137 grams (2.4–4.8 oz)) and an unfused mandibularsymphysis, it appears to be a primitive simian based on its dental characteristics, including a lowerdental formula of 2.1.3.3.[4]Eosimias sinensis has incisors which are vertical and spatulate. These creatures are known primarily from lower jaws and teeth, no cranial remains have been able to indicate whetherEosimias was diurnal or nocturnal.[7]
Eosimias centennicus was found in 1995 while doing fieldwork in theYuanqu Basin of the southernShanxi Province in China.[8] Among these recovered fossils is the first complete lower dentition ofEosimias, catalogued as IVPP V11000. All anatomical information yielded from these fossils confirms the anthropoid-like traits found inE. sinensis.Biostratigraphic evidence also suggests these fossils are younger thanE. sinensis, which is consistent with the anatomy of eosiimids because the dentition ofE. centennicus is slightly more derived than that ofE. sinensis.[8] This species was also found to be a very tiny primate, with mean estimates of body mass ranging from 91 to 179 grams (3.2 to 6.3 oz).E. sinesis was originally described on the basis of fragmentary fossils, but with the discovery ofE. centennicus and a complete lower dentition,Eosimias can more definitively be described as an earlyanthropoid.
Eosimias dawsonae is the newest of theEosimias species. It is categorized by the type specimen IVPP V11999, which includes a left dentary fragment and roots of the alveoli. It was collected by Christopher Beard in 1995.[9] Analysis of these remains has led to the conclusion it was the largest of the known species ofEosimias, yielding a body mass ranging from 107 to 276 grams (3.8 to 9.7 oz). Stratigraphic evidence also showsE. dawsonae is older thanE. centennicus.
Additionally, an expedition team discovered evidence of a new, small eosimiid fromMyanmar in 1999. The new specimen, represented by a right heel bone cataloged as NMMP 23, was found in wash residue in thePondaung Formation.[10] This specimen is very morphologically similar to theEosimias discovered in the Shanghuang region of China. The best estimate for NMMP 23 includes an overall mean weight of about 111 grams, which places it in the upper-sized end ofEosimias fossils discovered. The presence of eosimiid in Myanmar, as well as a high species diversity found in China leads to an apparent conclusion that they had a relatively wide distribution.[10]
A new species of eosimiid primate,Eosimias paukkaungensis, from the latest middle Eocene of Pondaung, central Myanmar, was discovered in the early 2000s. The specimen consists of left and right mandibular fragments preserving only the M3, so that its generic status is provisional. TheE. paukkaungensis fossil is much larger than homologues of the twoEosimias species from China.[2]
