Voronezh State University, Voronezh, 394893 Russia. Received May 24, 1994. AbstractâTheoretical prerequisites and possibilities for the application of the ...
' Palcontological Journal. Vol. 30. No. 1. 1996. pp. 75-80. Translated from Paleontologicheskii Zhurnal, No. 1, 1996, pp. 77-83. Original Russian Text Copyright © / 996 by Ralnikov English
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Copyright © /996
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МАИК Наука/Interperiodica Publishing (Russia).
Methods of Paleogeographic Reconstructions Based upon Fossil Remains of Amphibians and Reptiles of the Late Cenozoic of the East European Platform V. Yu. Ratnikov Voronezh State University, Voronezh, 394893 Russia Received May 24, 1994 Abstract—Theoretical prerequisites and possibilities for the application of the fossil remains of the Late Cen ozoic amphibians and reptiles to paleogeographic reconstructions are discussed.
trial cold-blooded v e r t e b r a t e s are a l m o s t restricted to the limits of forest-tundra a n d are c o m m o n l y located far to the south (areas of Salamandrella keyserlingii D y b o w s k i , Rana arvalis N i l s s o n , a n d Lacerta vivipara J a c q u i n only spread o v e r the d u m e t o s o u s and sedge t u n d r a zones) (see figure). So t h e o c c u r r e n c e of a m p h i b i a n s and/or r e p t i l e s even identified to the class level ( A m p h i b i a or R e p t i l i a ) in a locality, signifies that t h e locality is well off t h e ice cover.
R e m a i n s of a m p h i b i a n s and reptiles have c o m e into use, along with the r e m a i n s of m a m m a l s , in reconstruc tions of Cenozoic p a l e o g e o g r a p h i c situations. Thus, specialists w h o work on such reconstructions must be familiar with the peculiarities of these organisms and with the methodological aspects of herpetofauna analysis. An article on paleogeographic reconstruction based on anurans was earlier published [19]. However, it w e n t unnoticed a n d certain details of t h e analysis w e r e unclear in p a p e r s s u m m a r i z i n g p a l e o g e o g r a p h i c a l situ ations [21]. T h e p r e s e n t article discusses the theoretical prerequisites of such reconstructions.
Northern areal b o u n d a r i e s of Bombina bombina (L.), Pelobates fuscus (Laur.), Bufo viridis Laur., Rana lessonae C a m e r a n o , R. ridibunda Pall., Emys orbicularis (L.), a n d Coronella austriaca Laur. roughly c o i n c i d e with the transition from c o n i f e r o u s taiga to m i x e d forest.
A list of fossil herpetofauna p r o v i d e s a basis for analysis and we w o u l d like to pay particular attention to the form of the list. So far it is widely believed by both zoologists a n d paleontologists that l a n d s c a p e s of the past are evaluated by the species c o m p o s i t i o n , of a locality. T h e r e f o r e , species identified in t a p h o c o e n o s e s are the only o n e s used for p a l e o e n v i r o n m e n t recon struction [ 9 - 1 1 , 1 4 - 1 6 ] , but the analysis itself is restricted to a list of plausible habitats of t h e listed forms. It is o u r opinion that a p a l e o e n v i r o n m e n t recon struction should be m a i n t a i n e d using a quantitative ratio between fossil species that belong to different eco logical g r o u p s to p r o v i d e an idea about the particular biotope d o m i n a n c e and, therewith, t h e climatic z o n e . A similar p r o c e d u r e has long been used by s t u d e n t s of small m a m m a l s [13].
Southern areal boundaries of Salamandrella keyser lingii Dybowski, Triturus cristatus ( L a u r ) , T. vulgaris (L.), Bufo bufo (L.), Rana lessonae C a m e r a n o , Anguis fragilis L., Lacerta vivipara J a c q u i n , Vipera berus (L.), and n o r t h e r n areal b o u n d a r i e s of Eremias arguta (Pall.) and Vipera ursini ( B o n a p a r t e ) generally c o i n c i d e with the forest-steppe. Every species is a s s o c i a t e d with a certain type of b i o t o p e . B o t h density p o p u l a t i o n and t h e n u m b e r of individuals inhabiting t h e given territory display b i o t o p e distribution d e p e n d e n c e . S i n c e t h e adjacent cli m a t i c z o n e s can also i n c l u d e c o m m o n b i o t o p s , certain a m p h i b i a n and reptilian s p e c i e s turn out to inhabit two or m o r e z o n e s . On the o t h e r h a n d , e a c h z o n e is distinct for a specific set of s p e c i e s (table). T h a t is, environ m e n t a l c o n d i t i o n s in the vicinity of a locality can be reconstructed from a fossil a s s e m b l a g e .
Most of L a t e C e n o z o i c a m p h i b i a n s and reptilians of the East E u r o p e a n Platform have b e e n assigned to recent species, w h i c h allows us to reveal their habitat conditions by a n a l o g y with the R e c e n t representatives. Areas of the latter forms spread n o w over almost the entire East E u r o p e a n Platform, and their b o u n d a r i e s are determined by different factors: long standing s e a s o n s with positive t e m p e r a t u r e s , the degree to w h i c h the water w a r m s d u r i n g a m p h i b i a n larvae d e v e l o p m e n t , etc. It is observed as well, that the area b o u n d a r i e s strongly d e p e n d on landscape zone transition [2, 17]. The northern b o u n d a r i e s of the distribution of terres
A m p h i b i a n s and reptiles are c o n t r o l l e d to a variable d e g r e e by p o n d s , w h e r e a s a m p h i b i a n s are totally water d e p e n d e n t and do not go far from it ( m a x i m u m distance registered for a green t o a d is 10 k m ) [3]; reptiles have lost such a d e p e n d e n c e . T h a t is, fossil a m p h i b i a n fauna d e n o t e s the situation in valleys, and reptilian fauna basically indicates the situation on p l a c o r e s , and for 75
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Boundaries of natural zones (simplified) and boundaries of recent species areas: (A) amphibians; (B) reptiles. Legend: (1) former USSR boundaries; (2) natural zone boundaries; (3-13) amphibian areal boundaries: (3) Salamandrella keyserlingii, (4) Triturus vulgaris, (5) T. cristatus, (6) Bombina bombina, (7) Pelobates fuscus, (8) Bufo bufo, (9) B. viridis, (10) Rana ridibunda, (11) R. lessonae. (12) R. temporaria, (13) R. arvalis; (14—24) reptilian areal boundaries: (14) Emys orbicularis, (15) Anguis fragilis, (16) Eremias arguta, (17) Lacerta agilis, (18) L vivipara, (19) L viridis, (20) Natrix natrix, (21) N. tesselata, (22) Coronella austriaca, (23) Vipera ursini, (24) V. berus.
ases of joint o c c u r r e n c e they should be considered eparately as c o m p l e m e n t a r y elements. Species of enclosed biotopes characteristic of the forest zone can be discerned a m o n g recent species of amphibians and reptiles of temperate latitudes on the East European Platform: Siberian salamander Salamandrella keyserlingii D y b o w s k i , c o m m o n newt Triturus vulgaris (L.), crested newt T. cristatus (Laur.), gray toad Bufo bufo (L.), b r o w n frog Rana temporaria L., edible frog R. lessonae C a m e r a n o ; Anguis fragilis L., common lizard Lacerta vivipara, and c o m m o n viper Vipera berus (L.). Sharp-faced frog Rana arvalis N i l s son is most characteristic of the forest zone, but is also found in tall-grass wet m e a d o w s and, therefore, i n h a b its a very broad area, extending from steppes to foresttundra. The area of smooth snake Coronella austriaca Laur. also extends from forests to steppes, although the species prefers enclosed biotopes. Green toad Bufo viridis Laur., lake frog Rana ridibunda Pall., sand lizard Lacerta agilis L., green lizard L. viridis Laur., Eremias arguta (Pall.), and steppe viper Vipera ursini (Bonaparte) are typical inhabitants of open spaces, including deserts. They penetrate to s o m e extent into the forest zone. The distribution of fire-bellied toad
Bombina bombina (L.) is primarily related to the d y n a m i c s and heat m o d e of the ponds inhabited (it prefers small, well-warmed up p o n d s with lentic or slowly m o v i n g waters), and the distribution of spade-footed toad Pelobates fuscus (Laur.), to the availability of dry and sufficiently soft soils. Both species extend, but not too far, into the coniferous forest zone along the northern boundary of areas, although probably have an indirect connection to natural zones. Of the aquatic snakes, the grass snake Natrix natrix (L.) is the most characteristic of the enclosed biotopes, and water snake N. tesselata (Laur.), of the open biotopes, but fresh-water turtle Emys orbicularis L. does not expand to the north of the mixed forest zone [2, 3, 6, 18]. The forest-steppe zone is the most species-rich for it is inhabited by representatives of both forest and steppe biotopes. Forest-tundra is inhabited by w o o d l a n d forms due to its lack of typical tundra species. T h u s , we may evaluate a relative n u m b e r of fossils typical of open and enclosed biotops from the study of fossil assemblages consisting of Recent species. T h e resulting ratio allows us to reconstruct the e n v i r o n m e n tal conditions of the herpetofauna. T h e resulting q u a n titative ratios, however, can be inconsistent with past
METHODS OF PALEOGEOGRAPHIC RECONSTRUCTIONS
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Distribution of recent species of amphibians and reptiles through different zones: (++) species is common, (+) species is scarce Species
Tundra
Forest-tundra and coniferous forests
Salamandrella keyserlingii
+
Mixed and deciduous forest
Foreststeppe
++
++
+
Triturus vulgaris
+
++
+
T. cristatus
+
Bombina bombina Pelobates fuscus Bufo bufo
++
B. viridis Rana ridibunda
R. arvalis
+
Anguis fragilis
++
+
++
++
+ ++
++ ++
++
+
++
++
++
++
++
+
++
++
++
++
++
++
++
++
+
++
++
++
+
++
++
+
+
+
++
++
Emys orbicularis
++
++
++
++
++
++
+
++
++
+
+
++
++
++
+
++
++
Eremuas arguta Lacerta agilis L. vivipara
+
L. viridis ++
Natrix natrix N. tesselata Coronella austriaca
++
Vipera berus
++
V. ursini
ratios. So, the herpetofauna analysis requires the appropriate corrections. First of all, burial conditions, that is, the t a p h o n o m i c type of locality, affects the composition of the herpetofauna fossils. The greatest a m o u n t of localities is associated with alluvial c h a n n e l deposits. Fossil a m p h i b i a n s and reptiles from a significant part of a river basin are c o m monly a c c u m u l a t e d and, therefore, they s o m e w h a t adequately reflect the composition of herpetofauna that inhabited this territory in the past. T h i s allows us to reconstruct the paleogeographic situation that existed within the given basin with sufficient accuracy. Inundated, dead channel, and limnetic deposits are more favorable for the burial of a m p h i b i a n s , since those ponds supported concentrations of live amphibians. The bones of a n i m a l s that inhabit these ponds and the immediate vicinity, are buried here, a l o n g with r e m a i n s that were transported by overland flows. The c o m p o s i tion of the fossil herpetocomplex thus reflects the situation mostly in the pond vicinity. It is possible that the formation of p u r e autochthonous a n u r a n burials is in an inundated and dead channel, and in limnetic deposits. These are the burials of frogs that starved during hibernation, as in the U p p e r Pleistocene R u d n y i locality in Belgorod R e g i o n [20]. In such cases, most of the bones PALEONTOLOG1CAL JOURNAL
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Desert
++
++
R. lessonae R. temporaria
Steppe
++
++
+
+
belong to individuals of one genus and only partly reveal the composition of the fossil h e r p e t o c o m p l e x . The composition of herpetocomplexes in helobious deposits presumably agrees with the set of forms that inhabited the marsh and its i m m e d i a t e vicinity, that is, the immediate neighborhood of the locality. Diluvial, proluvial, and solifluctional deposits contain, at times, a great many bones. It turns out that the material was accumulated mostly by t e m p o r a l overland flows from a small area and thus d e n o t e s the situation in the i m m e d i a t e vicinity. Typical aquatic forms (such as green frogs) lack in oryctocoenosis. Burials in the cover overlying d e p o s i t s (classification of A.K. Agadzhanyan [1]) are generally associated with mole casts. They probably occur most c o m m o n l y after channel alluvium burials. B o r r o w e r s (such as spadefoots) may fall there more often, but rarely for animals using burrows as coverts (toads, snakes, etc.). Although other forms, even aquatic [ 2 0 ] , can be found in localities, a real quantitative relationship of species inhabiting a given territory in the past is severely w r o n g in value. Bones in karst crevice fillings w e r e a c c u m u l a t e d by underground waters that circulated in fractures. Fossil
78
RATNIKOV
herpetocomplexes in such localities contain forms that inhabited the vicinity of karst sinks and that served as collectors of dead bodies. Accumulations of fossil vertebrates in caves, different grottos, and niches, according to I.M. G r o m o v [8], a l o n g with accumulations in river alluvium deposits, constitute the major part of k n o w n localities. However, they are all associated with mountain regions and u n k n o w n on the East European Platform. Primary a c c u m u l a t i o n s of bones in localities discussed are formed as a result of the hunting activity of carnivorous birds and m a m m a l s . The composition of fossil animals association is inconsistent with the true ratio of animals and determined by the food choice of the carnivore. T h e rate of bone destruction also requires correction. Agadzhanyan [1] pointed out that the destruction rate of organic remains is higher in forest conditions than in steppes, due to the slower t e m p o of overland flows, abundance of scavengers, and the presence of h u m i d acids in soils. Therefore, the difficulty of locating even a few forest animal fossils testifies to the wide distribution of woodland and d u m e t o s o u s biotopes. An equal ratio of wood and steppe animal fossils is interpreted as signifying a significant p r e d o m i n a n c e of enclosed biotopes over open. W h e n analyzing faunas of small m a m m a l s , correction coefficients are primarily introduced to account for the quantity of skeletal elements of teeth [13], which is indicative of the species and thus a quantitative ratio of species is obtained which is closer to the real one. Contrary to rodents, the identification of amphibians and reptiles is based on bones. Having species with an equal a m o u n t of distinctive skeletal elements of both the enclosed and open biotopes within every recent genus of a m p h i b i a n s and reptiles, the coefficients need not be introduced for the reconstruction of paleogeographic conditions. Furthermore, the convection between osteologic features of anurans a n d their ecology permits one to distinguish paleogeographic conditions, in a n u m b e r of cases, based only on specific assemblages and groups, and even without a presice species identification. Representatives of the Bufo bufo assemblage and the group of frog species Rana ex gr. temporaria, as examples, are inhabitants of enclosed biotopes and representatives of the Bufo viridis assemblage are confined to open biotopes. In most localities of fossil herpetofauna, anurans are either the only group found, or they prevail over reptiles. This can probably be explained by the burial advantage of amphibians, because with all factors being equal, the overland flows are the major agent of b o n e accumulation, and the most known localities have aquatic origins. T h e rarely occurring salamander fossil is probably d u e to their small size and bone fragility. However, in s o m e occurrences, reptilian fossils exceed amphibian fossils in number. T h e highest percentage of reptilian fossils is comprised of snake vertebrae, the lowest, of lizard bones.
This can be explained by osteologic features: snakes have as many as a few hundred skeletal vertebrae. Fragments of turtle carapaces may constitute the majority of reptilian remains (although bad for identification). In temperate latitudes, such occurrences are rare. T h e quantity of amphibian and reptilian fossils in most occurrences is not abundant when c o m p a r e d to small m a m m a l remains. This is primarily e x p l a i n e d by the fact that rodents significantly o u t n u m b e r coldblooded vertebrates, and secondly, by the s u p e r i o r preservation of enameled m a m m a l teeth. H o w e v e r , the n u m b e r of species of a m p h i b i a n s and reptiles inhabiting the East European Platform is not big a n d , therefore, even with a small n u m b e r of identified species, the reconstruction of the landscape is adequately reliable. In s o m e occurrences, the n u m b e r of fossils of coldblooded terrestrial vertebrates exceeds the n u m b e r of m a m m a l s [20]. T h e reconstruction of the paleolandscape in a few localities will be considered as examples. T h e following taxa were identified from the H o l o c e n e t a p h o c oenosis in channel alluvium near Voroncha village, Korelichi District, G r o d n o Region (data from P.F. Kalinovskii): Amphibia: Bufo viridis Laur., 1; B. bufo c o m plex, 5; B. sp., 7; Rana temporaria L., 15; R. ex gr. temporaria, 3; R. temporaria c o m p l e x , 2; R. lessonae C a m e r a n o , 1; R. sp., 5 7 ; Anura fam. indet., 5 4 : Reptilia: Anguis fragilis L., 1; and Lacerta cf. agilis L., 2. T h e majority of fossils belongs to inhabitants of enclosed biotopes testifying to the existence of w o o d land in the river basin. A single find of green toad that spreads north to the m i x e d forest zone, as well as of edible frog and blind w o r m fossils, tells about the mixed or deciduous forest. F u r t h e r m o r e , one can s u g g e s t the existence of open w o o d l a n d s and clearings b a s e d on the presence of sand lizard fossils. The following amphibians from the L o w e r Pleistocene locality near Kuznetsovka village, U v a r o v o District, Tambov Region are associated with an inundated and dead channel, and limnetic deposits (reptiles have not been identified yet in the personal collection and partial material of Agadzhanyan): Bombina bombina (L.), 4; Pelobates fuscus (Laur.), 5; P. sp., 3 8 ; Pelobatidae gen. indet., 5; Bufo raddei Str., 2; B. viridis c o m p l e x , 8; B. bufo complex, 1; B. sp., 10; Rana arvalis Nilsson, 5; R. cf. arvalis Nilsson, 13; R. ex gr. temporaria L., 2; R. lessonae C a m e r a n o , 3; R. sp., 6 1 ; and A n u r a fam. indet., 4 2 . The n u m b e r of forms typical of open biotopes (B. raddei, B. viridis complex) is notably larger than that of enclosed biotopes (B. bufo c o m p l e x , R. ex gr. temporaria, R. lessonae), which indicates a roughly equal propagation of steppe and w o o d l a n d areas in the vicinity of the locality. A large n u m b e r of spade-footed toads is also associated with the w i d e d e v e l o p m e n t of steppe areas. T h e sharp-faced frog inhabits both w o o d l a n d s and wet tall-grass m e a d o w s and confirms the presence of these situations. Fire-bellied toad fossils suggests the availability of shallow
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METHODS OF PALEOGEOGRAPHIC RECONSTRUCTIONS well-warmed ponds, which agrees with a taphonomic type of locality. The following taxa, associated with mole casts, were identified in the Lower Pleistocene occurrence near Troitskoe village, Novokhopersk District, Voronezh Region (material was put by Agadzhanyan): Amphibia: Pelobates sp., 2; Bufo raddei St., 5; B. sp., 12; Anura. fam. indet., 9; Reptilia: Lacerta cf. agilis L., 2 3 ; L. sp., 8; Vipera ursini (Bonaparte), 1; and V. sp., 1. Both amphibians and reptiles depict open biotopes, which confirm the presence of steppe in the vicinity of the locality. An important feature of terrestrial vertebrates is their varying sizes over a stretch of area having varying habitat conditions [7, 22]. Theoretically, the determination of the sizes of buried individuals by their fossil bones will increase the scope of a paleoenvironment reconstruction. It is essential that the sizes that are determined for identified b o n e s are large enough, when compared to body sizes; otherwise, the error will be too great. A n u r a n s comprise the only group of terrestrial vertebrates that satisfies the outlined conditions. Their body length is easily derived from the following equation: L* = L x 1*/1, where L* is the length of the fossil body; L is the length of an individual of a corresponding species from the standard collection; 1* is the length of the fossil bone; and 1 is the length of a corresponding b o n e from the standard collection. Iliac bones of anurans are the most convenient for calculations: they are definable to a specific level and their length constitutes about one third of their body length. An attempt to establish the relationship between frog sizes and their habitat conditions has already been made [5]. T h e bone sizes of even-aged individuals from' three populations in Europe were used for the comparison. In our opinion, dimensional characteristics of populations, and not of single individuals, should be analyzed. The variations for every species are individual, and some display a trend. For example, the maximum sizes of brown frog individuals increase to the north along the western boundary of the former USSR [2]. Zoologists pointed to variations in three parameters: minimum, median, and m a x i m u m sizes of individuals in populations. After the determination of corresponding m e a s u r e m e n t s for a fossil population, one can conclude that past climatic conditions are similar to habitat conditions for recent populations with identical sizes. Unfortunately, data on m i n i m u m b o d y sizes are inoperable for fossil material, since this value is measured for mature animals. The remains of mature individuals are impossible to separate from juvenile ones, and, thus, the value of the m i n i m u m size will be undervalued when compared to real. By the s a m e token, the m e d i u m size does not suffice. Therefore, only the m a x i m u m sizes of individuals can be used for the analyses. The term " m a x i m u m sizes" is worthy of consideration. Very large individuals, that reached outstanding sizes, due to extremely favorable conditions or longer
79
lifespans, can be found in any population. H o w e v e r , by analogy, atypically sized individuals c a n n o t be p r e served as well d u e to their rarity [4]. That is, the m a x i m u m size is considered to be the d i m e n s i o n that m a n y individuals (or almost every) of a g e n e r a t i o n of amphibians achieves. It is this index that will be reflected by a b u n d a n t fossil material and s u c h individuals in Recent populations, if observed by zoologists, will be easily determined statistically. The above mentioned locality near R u d n y i can be used as an example. About 2 8 0 0 bones of b r o w n frogs were collected from this locality and m a x i m u m sizes approached as m u c h as 7 8 - 8 1 mm. Brown frogs of that size currently inhabit area between St. Petersburg and Moscow. One can suggest, based on this similarity, the existence of a past climatic situation in the past that was analogous to the present-day one south of St. Petersburg. Variations in the m a x i m u m size of individuals over areas are not alone unique to intraspecific p o p u l a t i o n s , but are also typical of h i g h e r taxa. T h u s , the largest anurans primarily inhabit tropical regions. T h e largest species of toads from the former U S S R (Bufo verrucosissimus Pall.) o c c u r s in the Caucasus. T h e r e f o r e , the finds of unusually large forms in a given territory can nowadays be interpreted as a credible indicator of a past w a r m e r and wetter climate. The L o w e r P l e i s t o c e n e Kholki locality of the Belgorod Region exemplifies a situation in which the r e m a i n s of individuals of toads were found with a body length reaching 1 1 0 - 1 1 5 m m , compared to 85 mm for recent representatives of that genus inhabiting the same region [2]. Extinct amphibian and reptilian forms are few in n u m b e r in Pleistocene localities and it is unlikely that neglecting them will adversely affect the a c c u r a c y of paleogeografical reconstructions in herpetofauna analysis. In the Pliocene deposits, extinct f o r m s o c c u p y a reasonably c o n s p i c u o u s , if not leading, position in extinct c o m m u n i t i e s and should be c o n s i d e r e d in their analyses. In summary, the following traits can be pointed out. (1) T h e n u m b e r of fossils of low terrestrial vertebrates in localities is c o m m o n l y less then that of m a m mals; nonetheless, they can be used for p a l e o e n v i r o n mental reconstruction. B e s i d e s , in s o m e c a s e s , they can o u t n u m b e r other vertebrates. (2) Identification of the systematic c o m p o s i t i o n of herpetofauna is carried out on skeletal b o n e s , and specific identifications are not alone used for d r a w i n g conclusions about past environments. (3) By virtue of their hematocryality, a m p h i b i a n s and reptiles react readily to climatic variations and are probably a more reliable climatic indicator than m a m mals. (4) Only anurans have bones that are distinguishable to a specific length and size, so that a n i m a l s can be determined with sufficient accuracy. This e n a b l e s one to make conclusions regarding the p a l e o c l i m a t e through the correlation of the m a x i m u m sizes of extinct
RATNIKOV
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population with R e c e n t representatives of t h e s a m e species. Unfortunately, d e s p i t e the fact that s o m e spe cies have notable variations in m a x i m u m sizes over an area, the quantitative characteristics and pattern of those variations are not sufficiently studied. S o m e experts even wholly d e n y the p r e s e n c e of a directional pattern. It would be a good idea to study this p r o b l e m in detail. For now, o u r c o m p a r i s o n can be b a s e d on the scant data of the b r o w n frog [2, 12]. (5) The rate of evolution of c o l d - b l o o d e d terrestrial vertebrates is slower than for m a m m a l s , which, of course, is p r o b l e m a t i c w h e n using data on h e r p e t o f a u n a for A n t h r o p o g e n e stratigraphy. However, t h e s a m e fac tor is advantageous for p a l e o g e o g r a p h i c reconstruc tions, since it allows us to d r a w c o n c l u s i o n s r e g a r d i n g p a l e o e n v i r o n m e n t s with R e c e n t a m p h i b i a n and reptile species for time intervals even t h o u g h R e c e n t taxa of rodents have not yet a p p e a r e d or are few in n u m b e r .
REFERENCES 1. Agadzhanyan, A.K., A Study of the History of Small Mammals, Chastnye metody izucheniya istorii sovremennykh ekosistem (Special Methods of the Historical Study of Recent Ecosystems), Moscow: Nauka, 1979, pp. 164-193. 2. Bannikov, A.G., Darevskii, I.S., Ishchenko, V.G., Rustamov, A.K., and Shcherbak, N.N., Opredelitel' zemnovodnykh i presmykayushchikhsya fauny SSSR (Hand book of Amphibians and Reptiles of the USSR), Mos cow: Prosveshchenie, 1977. 3. Bannikov, A . G and Denisova, M.N., Ocherki po biologii zemnovodnykh (Essays on Amphibian Biology), Mos cow: Uchpedgiz, 1956. 4. Efremov, I.A., Taphonomy and Paleontological Record. Book 1, Tr. Paleontol. Inst, Akad. Nauk SSSR, vol. 24, Moscow: Akad. Nauk SSSR, 1950. 5. Esteban, M. and Sanchiz, В., Paleoclimatic Inferences Based on Fossil Ranids, Studies in Herpetology: Proc. Eur. Herpet. Meet., Prague, 1986, pp. 379-382. 6. Garanin, V.I., Zemnovodnye i presmykayushchiesya Volzhsko-Kamskogo kraya (Amphibians and Reptiles of the Volga-Kama Region), Moscow: Nauka, 1983. 7. Geptner, V.G., Obshchaya zoogeografiya (General Zoo geography), Moscow, Leningrad: Biomedgiz, 1936, pp. 146-148. 8. Gromov, V.M., On Peculiarities of Osteal Remains Accumulation in Cave Localities, Byull. Кот. Izuch.
Chetvertichn. Perioda, Akad. Nauk SSSR, 1955, no. 20, pp. 88-92. 9. Hodrova, M., Plio-Pleistocene Frog Fauna from Hajnacka and Ivanovce, Czechoslovakia, Vestn. Ustredi ustavu Geol., 1981, vol. 56, no. 4, pp. 215-224. 10. Hodrova, M., Amphibia of Pliocene and Pleistocene Vcelar Localities (Slovakia), Cas. Mineral., Geol, 1985, vol. 30, no. 2, pp. 145-161. 11. Holman, J.A., Herpetofauna of the Egelholf Site (Miocene, Bastovian) of North-Central Nebraska, J. Vertebr. Paleontol., 1987, vol. 7. no. 2, pp. 109-120. 12. Ishchenko, V.G., Dinamicheskii polimorfizm burykh lyagushek (Dynamic Polymorphism of Brown Frogs), Mos cow: Nauka, 1978, p. 147. 13. Maleeva, A.G., On the Procedure of Paleoecological Analysis of the Late Cenozoic Teriofaunas, in Istoriya i evolutsiya sovremennoi fauny gryzunov (History and Evolution of Recent Rodent Fauna), Moscow: Nauka, 1983, pp. 146-178. 14. Mlinarski, M., Plazy (Amphibia) z pliocenu Polski. Cs. 15, Acta Paleontol. Polon., 1961, vol. 6, no. 3, pp. 261-282. 15. Mlinarski, M., Notes on the Amphibian and Reptilian Fauna of the Polish Pliocene and Early Pleistocene, Acta Tool. (Cracov), 1962, vol. 7, no. 1, pp. 177-197. 16. Mlinarski, M., New Notes on the Amphibian and Reptil ian fauna of the Polish Pliocene and Pleistocene, Acta Zool. (Cracov), 1977, vol. 22, no. 2, pp. 13-36. 17. Geograficheskii atlas SSSR dlya sed'mogo klassa (Geo graphical Atlas for Students of the 7th Grade), Nikolaeva, M., Ed., Moscow: GUGK, 1986. 18. Pikulik, M.M., Zemnovodnye Belorussii (Aphibians of Byelorussia), Minsk: Nauka Tekh., 1985, p. 191. 19. Ratnikov, V.Yu., О paleogeograficheskikh rekonstruktsiyakh po iskopaemym ostatkam sovremennykh vidov bezkhvostykh zemnovodnykh (On Paleogeographic Reconstructions Based on Fossil Remains of Recent Anurans), Available from VINITI, 1987, Voronezh, no. 8125-V87. 20. Ratnikov, V.Yu., Upper Quaternary Herpetofauna of Bel gorod Region, Paleontol. Zh., 1988, no. 3, pp. 119-122. 21. Ratnikov, V.Yu., Eopleistocene and Pleistocene Faunas of Anurans of East European Platform, Paleontol. Zh., 1992, no. l, pp. 89-110. 22. Terent'ev, P.V., Climatic Temperature Effect on Sizes of Snakes and Anurans, Byull. Mosk. O-va Ispyt. Prir. Otd. Biol., 1951, vol. 56, no. 2, pp. 14-23.
