Early Paleogene insectivore mammals of Asia and establishment of the major groups of Insectivora

Abstract

Early Paleogene insectivore mammal associations of Asia include true insectivores (superorder Insectivora: order Lipotyphla: suborders Erinaceomorpha and Soricomorpha; orders Didymoconida and Leptictida) and insectivore-like placentals (superorder Ferae: order Cimolesta: suborders Didelphodonta, Palaeoryctida, and Pantolesta). The associations from Mongolia are the most taxonomically diverse. The Late Paleocene association from the Zhigden Member of the Naran-Bulak Formation of the Tsagan-Khushu and Naran-Bulak localities includes the following soricomorph insectivores: the micropternodontid Sarcodon pygmaeus Matthew et Granger and Hyracolestes ermineus Matthew et Granger (Sarcodontinae), the geolabidid Gobigeolabis verigranum Lopatin, the nyctitheriid Praolestes nanus Matthew, Granger et Simpson, P. maximus Kondrashov, Lopatin et Lucas (Praolestinae subfam. nov.), Jarveia erronea Kondrashov, Lopatin et Lucas (Asionyctiinae). Moreover, the Zhigden association includes the didymoconid Archaeoryctes euryalis Lopatin (Ardynictinae), the palaeoryctid Pinoryctes collector gen. et sp. nov., and the pantolestid Zhigdenia nemegetica gen. et sp. nov. (Pantolestinae). The Early Eocene association from the Bumban Member of the Naran-Bulak Formation of the Tsagan-Khushu locality includes the micropternodontid Prosarcodon maturus Lopatin et Kondrashov (Sarcodontinae); the nyctitheriids Bumbanius rarus Russell et Dashzeveg (Praolestinae), Oedolius perexiguus Russell et Dashzeveg, Edzenius lus gen. et sp. nov. (Asionyctiinae), and Eosoricodon terrigena Lopatin (Eosoricodontinae); the plesiosoricid Ordolestes ordinatus gen. et sp. nov. (Butseliinae); and the cimolestids Naranius infrequens Russell et Dashzeveg, Tsaganius ambiguus Russell et Dashzeveg, and Bagalestes trofimovi gen. et sp. nov. (Cimolestidae). The Middle Eocene association from the Khaychin Formation of the Khaychin-Ula 2 and Khaychin-Ula 3 localities includes the erinaceomorphs Eogalericius butleri Lopatin and Microgalericulus esuriens gen. et sp. nov. (Erinaceidae, Galericinae), the soricomorphs Metasarcodon reshetovi Lopatin et Kondrashov (Micropternodontidae, Sarcodontinae), Soricolestes soricavus Lopatin (Soricidae, Soricolestinae), and Asiapternodus mackennai Lopatin (Apternodontidae, Asiapternodontinae subfam. nov.); the didymoconids Ardynictis captor Lopatin (Ardynictinae), Khaichinula lupula gen. et sp. nov. (Didymoconinae), Kennatherium shirense Mellett et Szalay, and Erlikotherium edentatum gen. et sp. nov. (Kennatheriinae subfam. nov.); and the palaeoryctid Nuryctes gobiensis Lopatin et Averianov (Palaeoryctidae). Late Paleocene insectivores from the Dzhilga 1a locality (Kazakhstan) comprise the nyctitheriids Voltaia minuta Nessov and Jarveia minuscula Nessov (Asionyctiinae). The faunal assemblage dated terminal Early Eocene from the Andarak 2 locality (Kyrgyzstan) includes the micropternodontid Metasarcodon udovichenkoi (Averianov), the erinaceid Protogalericius averianovi gen. et sp. nov. (Galericinae), and the palaeoryctids Nuryctes alayensis Lopatin et Averianov and Palaeoryctidae gen. et sp. indet. From the end of the Paleocene to the onset of the Middle Eocene, the taxonomic composition and ecological structure of insectivore communities of Central Asia gradually changed, insectivore-like placentals and primitive soricomorph groups were replaced by the Recent families of Lipotyphla. The morphological and evolutionary study of Early Paleogene Asian insectivores has provided important data on phylogenetic relationships of the Insectivora. The family Micropternodontidae is divided into the subfamilies Sarcodontinae and Micropternodontinae. The earliest insectivore family Geolabididae is recorded in the Paleogene of Asia. A new classification of the family Nyctitheriidae, dividing it into the subfamilies Nyctitheriinae, Amphidozotheriinae, Asionyctiinae, Eosoricodontinae, and Praolestinae subfam. nov., is proposed. Based on the morphological continuity between Eosoricodontinae (Nyctitheriidae) and Soricolestinae (Soricidae), the family Soricidae is proposed to originate from eosoricodontine nyctitheriids. The family Plesiosoricidae is divided into the subfamilies Butseliinae and Plesiosoricinae. A new subfamily, Asiapternodontinae subfam. nov., is established in the family Apternodontidae. The analysis of evolutionary transformations of the dental system suggests the continuity of molar types in the suborder Soricomorpha, which supports the validity of the infraorders Tenrecomorpha and Soricota (the latter includes the superfamilies Micropternodontoidea, Nesophontoidea, Soricoidea, Talpoidea, and Solenodontoidea). The subfamily Galericinae (Erinaceidae) is recorded in Asia at the Early-Middle Eocene boundary. The family Didymoconidae is divided into the subfamilies Ardynictinae, Didymoconinae, and Kennatheriinae subfam. nov. Some members of the subfamily Kennatheriinae display a clear edentate functional pattern, which is atypical for insectivores and is interpreted as an adaptation for feeding on colonial insects. The following scenario of insectivore evolution, describing the major stages of their history, is proposed: (1) in the first half of the Late Cretaceous, the first occurrence of Insectivora (probably in North America); (2) in the second half of the Late Cretaceous, the primary radiation of Insectivora, establishment of Leptictida, Didymoconida, and Lipotyphla; detachment of Erinaceomorpha and Soricomorpha; (3) at the Cretaceous-Paleocene boundary, the primary radiation of Soricomorpha and establishment of Tenrecomorpha (Africa) and Soricota (North America); (4) in the Paleocene, expansion of Soricota in the Northern Hemisphere, the primary radiation of Erinaceomorpha, and emergence of Erinaceidae (North America); (5) at the Paleocene-Eocene boundary, radiation of Soricota and Erinaceidae; (6) at the Early-Middle Eocene boundary, appearance of Soricidae, Talpidae, and Galericinae; (7) in the Middle Eocene-Oligocene, replacement of primitive groups by Recent families and related groups and the formation of the Recent subfamilial diversity of the families Soricidae, Talpidae, Erinaceidae, and Tenrecidae; (8) in the Miocene-Pliocene, disappearance of primitive groups of the Recent families, a decrease in the diversity of Erinaceomorpha, extensive radiation of Soricidae and the formation of the Recent generic diversity of insectivores.