جستجوی مقالات مرتبط با کلیدواژه « perissodactyls » در نشریات گروه « زمین شناسی »

Fossil vertebrates from quaternary are little known in Iran. This is unfortunately the case for vertebrate fossils from other eras as well. Never the less, elephantidae fossil remains are among the first quaternary fossil vertebrates to be reported from Iran (Farchad and Sahabi 1961). In the recent years more remains of fossil mammals have been reported especially from cave deposits of Late Quaternary in different parts of country, mostly from the Zagros ranges (Biglari et al. 2009, Mashkour et al. 2009). Also, Pleistocene remains of mammals, including Rhinocerotidae, have been reported from eastern Iran (Hashemi and Darvish 2007). Here we report the first fossil mammals from mainly lake and alluvial deposits of Zavyeh area, north of Saveh in central Iran.
The Quaternary lake deposits in the study area have been recently studied in detail (Djamali et al. 2006). The former studies in this area failed to distinguish these deposits as an independent unit from the well known formations in the region. During the geological and sedimentological surveys by Djamali, the first vertebrate fossils were collected. Further investigations by authors lead to the discovery of several more remains.
This study is thus based on postcranial and dental remains of fossil Perissodactyla. These are parts of pelvis, including Ilium, pubis and sacrum of a large vertebrate resembling rhinos. Other fossils belongs to equids and consists of metapodials or leg and arm bones (metatarsus and metacarpus) and first phalanges (toe bones), as well as a few lower and upper dentitions. Provenance of equid remains is not as well known as the rhino material. Therefore, it is possible that they belong to different levels from the study area. The lower teeth belong to the molar row (m1-m3) and the upper tooth is a fourth premolar (P4). This material has been described and measured according to standard international protocols (Table 1). The measurements have been used in bivariate analysis and comparison of fossil material with extinct and extant similar species in order to identify the fossil material better (Fig. 6).
Based on the size and characteristics of the pelvis bones, they can be referred to rhinoceratidae. To better categorize these fossil remains, the length and width of acetabulum of Zavyeh has been compared with several fossils and extant species, including rhinos and other mammals (Table 2 and Fig. 6A). The graph of acetabulum dimensions clearly shows the association of Zavyeh fossil material with other rhinos, ruling out attribution of these specimens to other families. Zavyeh rhino is similar in size to present day species like the African rhinos as well as fossil material of Stephanorhinus genus. Since Stephanorhinus is the most abundant and prominent fossil rhino of the interglacial Quaternary, We believe that our fossil material is most likely belonging to this genus and an indefinable species.
The fossil equids are clearly belonging to Equus and based on the dental morphology they are better grouped within stenonid horses (Fig. 5). Their main characteristic is the V shaped entoflexid morphology on their lower teeth. To identify the species, we compared both dental and skeletal material with several extant and fossil equids. The dental comparisons show that the upper premolar tooth is close in size to stenonid species like present day grevyi zebras and hemiones like E. hemiones. However, the Zavyeh material is slightly larger than the mentioned species, reaching the lower size distribution of true horses. The Metapodial graphs show that these fossil materials are smaller than many caballoid horses. They are better suited among stenonids, like African zebras and E. hemionus from different areas (Fig. 6). Therefore, the equid fossils from Zavyeh are probably remains of E. hemionus This conclusion is mainly based on the wide distribution of this species in Quaternary and also their continuous presence in Iran during Holocene and present time. However, presence of other equid species cannot be excluded from this locality
In conclusion, presence of fossil rhinos, like Stephanorhinus, and equids, such as E. hemionus, are reported for the first time from Late Quaternary of Zavyeh, north of Saveh. The presence of rhinos in Late Quaternary of Iran, as was previously reported from eastern and central Iran (Hashemi and Darvish 2006, Biglari et al. 2009, Mashkour et al. 2009) is now documented to larger extent. This increases our data about presence of these peculiar animals in Iran. The equids should be investigated further to confirm their exact provenance and their possible relation with present day wild asses (E. hemionus onager) of the country. As far as the ancient environment is concerned, these fossils (along with other evidence) show the existence of favorable climatic conditions with more rain and less evaporation during the Late Quaternary of (north and west) Iran (Kehl 2009).