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

This study is the first report of the terrestrial mammalian vertebrate fossils from the south of Ardabil. Terrestrial vertebrate fossil beds have great importance in paleontology studies. The role of these types of fossil groups is crucial in understanding paleoenvironments. In this study, extraction and identification of terrestrial vertebrate fossils families such as Bovidae, Equidae, Giraffidae, and Elephantidae are discussed.

Study area in Northwest of Iran, South of Ardebil and is in Kiwi city. The fossil layer studied in a railway trench at a height of 9 meters from the axial plane. After constructing a drilling platform at the trench and reticulation of platform fossil part extraction operations were done. Then, complete removal of parts from sediments and repair of damaged specimens and measurement of the required parameters was done. Systematic studies were also done based on information from fossil samples. The displacement of pieces of fossil specimens was completely evident before being fossilized by paleo fractures and also by separation from the main part. It should be noted that unfortunately before the fossil layer was found, some fossil parts were destroyed by road construction machinery. Components and identifiable parts included: premolar, Radial bone, Ulna, the top of the metatarsals of Family Giraffidae, Maxillary first molar to third (M1-M3) of Family Bovidae, metatarsals and incisors tooth of Family Equidae, Part of the femoral head Family Elephantidae.

Fossil parts of this study have the ability to reflect the characteristics of their paleoenvironment. Discussing these features from dental samples is more comprehensible and defensible. The exact study of dental Feature of different species of mammalian fossils with a vegetarian diet in Maragheh fauna and the study area was limited to the domain of fodder diets (family of Bovidae and Equidae) and leaf diets (family of Giraffidae), There is also the presence of various species of fossils such as Giraffidae, Bovidae, Equidae and even Elephantidae that exhibit these diets, which confirmed this type of nutrition at the time of its existence (Late Miocene). Therefore, using the study of the hypsodont tooth in the family of Bovidae and species of Equidae, as well as the presence of brachyodont type teeth in Giraffidae species, It can be said that the paleoenvironment of the studied area and Maragheh should be rich in grassland cover (hypsodont type), and in terms of tree cover to the extent that the leaf (brachyodont type) is used to feed it. Therefore, it is possible to compare the paleoenvironment of the studied area and Maraghe with some of the Savannah environments of today's Africa. As a result, the paleoenvironment Northwest of Iran (with a stronger probability of the southern provinces of Ardebil and Tabriz) in the Late Miocene could have been in the form of a vegetation plain with grasses, among which there were low shrubs. The study area is comparable to that of Maragheh fauna in terms of conditions the paleoenvironment and paleogeography and placing in the upper Miocene migration belt (Fortelius et al., 2003).

Different groups in the fossil layer including the family of Bovidae, Equidae, Giraffidae, and Elephantidae were extracted and identified. Initial field and laboratory studies indicate the transport of fossil parts before fossilization. Evidence of these displacements is the pre-fossil fractures, as well as the discovery of teeth from the jawbone. Fossil parts are oriented which specifies the direction of the paleo-currents. The sedimentary sequence of the fossiliferous layer contained sandy and clay layers. Regarding the importance of systematically studying these types of fossil groups, the finding of these fossils contributes greatly to recognizing the paleoenvironment for understanding the type of environment, biodiversity, and so on. This fauna can be compared to the co-eval fauna of the Maragheh representing a similar paleoenvironmental and paleogeographical character. The relative age of fauna can be assigned the late upper Miocene to earliest Pliocene.

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).

Vertebrate fossil fauna of Late Miocene age in Maragheh contains various mammals preserved in pyroclastic deposits of southern Sahand volcano. This study has been conducted on Gazella capricornis (a perfect skull). Since no other sample with such a good perfectness was found before at other localities (previous ones were isolated horns or tooth rows), it can be proposed as a complemental to the samples type. Gazella capricornis was found not only in Maragheh but also in Samos and Pikermi (Greece), Akkaşdaği (Turkey), Bulgaria, … (east of Europe and west of Asia); which indicates similarities in Late Miocene-Early Pliocene fossil fauna, paleogeography, relative ages, sediments and paleoecology between these regions.