Submitted: April 23th, 2020 – Accepted: June 26th, 2020 – Published online: June 28th, 2020 To link and cite this article: doi: 10.5710/AMGH.26.06.2020.3354 1 MITES (ACARI, ORIBATIDA, NANHERMANNIDAE) FROM THE EOCENE 2 OF PATAGONIA: FIRST SOUTHERN HEMISPHERE FOSSIL RECORD IN 3 MARINE SEDIMENTS 4 ÁCAROS (ACARI, ORIBATIDA, NANHERMANNIDAE) DEL EOCENO DE 5 PATAGONIA: PRIMER REGISTRO FÓSIL DEL HEMISFERIO SUR EN 6 SEDIMENTOS MARINOS 7 8 DAMIÁN A. FERNÁNDEZ1, PABLO A. MARTÍNEZ2, LUIS PALAZZESI3, 9 VIVIANA D. BARREDA3. 10 1 Laboratorio de Geomorfología y Cuaternario, CADIC-CONICET, Bernardo Houssay 11 200, V9410 Ushuaia, Argentina. [email protected] 12 2 Departamento de Biología, Facultad de Ciencias Exactas y Naturales, Universidad 13 Nacional de Mar del Plata, Deán Funes 3350, B7602AYL Mar del Plata, Argentina. 14 [email protected] 15 3 Sección Paleopalinología, División Paleobotánica, MACN-CONICET, Av. Ángel 16 Gallardo 470, C1405DJR Buenos Aires, Argentina. [email protected]; 17 [email protected] 18 19 14 pag. (text + references); 2 figs. 20 21 FERNÁNDEZ ET AL.: FOSSIL MITES FROM SW PATAGONIA 22 First record of a pre-Pleistocene fossil mite (Acari, Oribatida, Nanhermannidae) from 23 the Southern Hemisphere in marine sediments. 24 25 Corresponding author: Damián A. Fernández, [email protected] 1 26 Key words. Mites. Oribatida. Middle/Late Eocene.. Patagonia. Argentina. 27 Palabras clave. Ácaros. Oribatida. Eoceno Medio/Superior. Patagonia. Argentina. 28 2 29 COSMOPOLITAN, ABUNDANT, AND ADAPTED to nearly all terrestrial environments 30 today, mites are, however, uncommon in the fossil record. Extant diversity of mites 31 is second only to that of insects. With some 50,000 species described, of which 32 nearly 25% are oribatids, their past diversity is not well reflected in the fossil record 33 because of their rarity as fossils, especially in marine deposits and older strata 34 (Selden et al., 2008). Mites are more abundant in Quaternaries sites (e.g. Woolley, 35 1969; Elias, 1994; Heyne & Coetzee, 2001) and are being used in biostratigraphic 36 and palaeoclimatic studies of that period (e.g. Erickson, 1988; Schelvis, 1990; 37 Erickson et al., 2003; Krivolutsky & Sidorchuk, 2003; Mauquoy & van Geel, 2007; 38 Demske et al., 2013). A few are known from Cenozoic ambers (e.g. Selden et al., 39 2008 and references there in; Dunlop et al., 2013; Khaustov, 2014; Sidorchuk et al., 40 2019; Klimov et al., 2019; Poinar, 2019; Stilwell et al., 2020). Mites from 41 Cretaceous ambers are far fewer in number (e.g., Selden et al., 2008 and references 42 there in; Judson & Mąąkol, 2009; Sidorchuk et al., 2015b; Sidorchuk & Behan- 43 Pelletier, 2017; Arillo et al., 2018 and references there in). The only record from 44 South America until now is a large parasitengonid mite (Acari, Erythraeoidea) from 45 the continental Early Cretaceous Crato Formation of Brazil (Dunlop, 2007). There 46 are known three oribatids from the Jurassic (Krivolutsky & Krassilov, 1977; Sivhed 47 & Wallwork 1978; Selden et al., 2008), and only two species from Triassic amber, 48 north-eastern Italy (Sidorchuk et al., 2015a). The oldest known mite fossils come 49 from the Devonian localities of Gilboa, USA (Norton et al., 1988; Kethley et al., 50 1989) and Rhynie, Scotland (Hirst, 1923). 51 In this note we report the finding of a fossil remain belonging to an oribatid mite. It 52 is a leg, morphologically assignable to the family Nanhermannidae. It is the first 53 record of a pre-Pleistocene fossil mite from the Southern Hemisphere in marine 3 54 sediments. The specimen comes from the Río Turbio Formation (RTF), SW of Santa 55 Cruz province, Patagonia, Argentina (Fig. 1). The RTF represents sedimentation in a 56 transitional environment during the Middle Eocene, period when a global climate 57 event called Middle Eocene Climatic Optimum (MECO) is recorded (González 58 Estebenet et al., 2015). This finding supports the presence of these mites in the 59 southernmost tip of South America during the Eocene. Also provides a new record, 60 important from the phylogenetic and paleoecological point of view. 61 Institutional abbreviations. CADIC, Centro Austral de Investigaciones Científicas, 62 Ushuaia, Argentina; CONICET, Consejo Nacional de Investigaciones Cinetíficas y 63 Técnicas, Buenos Aires, Argentina; MACN, Museo Argentino de Ciencias Naturales 64 “Bernardino Rivadavia”, Buenos Aires, Argentina. 65 Anatomical abbreviations. Fe, femur; Ge, genu; Ta, tarsus; Ti, tibia; Tr, 66 trochanter. 67 MATERIALS AND METHODS 68 The fossil specimen was recognized from the analysis of palynological slides 69 deposited in the Museo Regional Provincial Padre Manuel Jesús Molina (Río 70 Gallegos, Santa Cruz), under the acronym MPM-PB, and catalog number 21662. The 71 sample analyzed corresponds to a dark shale that comes from an outcrop in the 72 surroundings of Río Turbio city (Fig. 1) and belongs to the upper member of the RTF 73 (Romero, 1977). The techniques for palynological processing comes from Wood et 74 al. (1996). The specimen was studied using a Leica DM2500 light microscope and 75 photographed using a Leica DFC450 C camera. The coordinate of the specimen 76 corresponds to the England Finder ruler. The morphological description follows the 77 terminology of Norton & Behan-Pelletier (2009). The fossil was drawn to obtain a 78 morphological detail by a compound microscope Olympus CX 31 with drawing 4 79 tube. For fossil identification Fujikawa (1990) and Ermilov (2009) were consulted. 80 SYSTEMATIC PALEONTOLOGY 81 Class ARACHNIDA Lamark, 1801 82 Subclass ACARI Leach, 1817 83 Order SARCOPTIFORMES Reuter, 1909 84 Suborder ORIBATIDA van der Hammen, 1968 85 Family NANHERMANNIDAE Sellnick, 1928 86 Referred material. Palynological slide MPM-PB 21662, O47–3. Museo Regional 87 Provincial Padre Manuel Jesús Molina, Río Gallegos, Santa Cruz, Argentina. 88 Geographic occurrence. Surroundings of Río Turbio city, 5 km northeast of the city, 89 beside National Route 40, Santa Cruz Province, Patagonia, Argentina (51° 30' 37.00" S 90 72° 15' 33.00" W) (Fig. 1). 91 Stratigraphic occurrence. Río Turbio Formation (Middle/Late Eocene, Priabonian, ca. 92 40 Myr) (González Estebenet et al., 2015). 93 Description. Tarsus almost complete, part of the genu, and complete femur and 94 trochanter. Tibia, in this group similar in size to the genu, covered by organic remains. 95 Length of each segment: Ta = 43 µm, Ti + Ge = 28 µm (where Ti is equal to or slightly 96 greater than Ge), Fe = 33 µm, Tr = 18 µm. In the tarsus, claw and numerous phaneres 97 are observed, but common setae and solenidia are indistinguishable. Some setae overlap 98 with their pair. Dorsal setae united in groups of two or more. Anterior ventral seta 99 stands out (probably s seta), apparent “holes” observed inside, possible eupathidium 100 (fanera that, unlike a normal seta that has a dense core of chitin, has a channel along its 101 axis). Two dorsal phaneres distinguished in the visible part of the genu, which would 102 correspond to a seta and a solenidium, and a ventral one. Dorsal and a lateral seta seen 103 on the femur. Small circles, possible insertions of phaneres or taphonomic artifacts. 5 104 Ventrolateral seta in the trochanter (Fig. 2). 105 Remarks. The leg has been completely preserved. The different segments can be 106 distinguished. In some areas there are overlapped organic matter remains. While the 107 cuticle of the leg has been altered becoming almost transparent (probably due to the 108 palynological processing), the setae remain in their position and are brown. Tarsus setae 109 are the darkest and more rigid part. Towards the base of the leg, they appear lighter and 110 somewhat collapsed (Fig. 2). 111 DISCUSSION AND CONCLUSIONS 112 The morphology and arrangement of the setae allow us to assign the mite remain here 113 described to the Nanhermannidae family. Although the description of the legs is not 114 frequent in representatives of Nanhermannidae, widened setae like those of the leg 115 described here are typical of Nanhermannia species (e.g. Fujikawa, 1990 Figs. 3, 4; 116 Ermilov, 2009 Fig. 4). This finding confirms the presence of mites related to that family 117 in the southern tip of South America during the Middle/Late Eocene. The most closely 118 related living clades to the RTF specimen are currently distributed in South America, 119 mainly in Venezuela, Ecuador, Peru, Chile, Brazil, Bolivia, Uruguay and Argentina. In 120 Patagonia, extant species have been cited for El Bolsón (Balogh & Csiszar, 1963), 121 Punta Bandera (Hammer, 1962b), Grand Malvina Island (Starý & Block, 1996) 122 (Argentina), Puerto Montt (Hammer, 1962a ), Punta Arenas and Puerto Natales 123 (Ermilov, 2016) (Chile). 124 Two main hypotheses can be raised about the living environment of the fossil mite: 1) 125 mite lived in a littoral environment 2) mite lived in leaf litter. 126 Hypothesis 1 is supported by the fact that the fossil bearing sediments were deposited in 127 a shallow marine environment according to sedimentological (Rodríguez Raising, 2015) 128 and paleontological studies (González Estebenet et al., 2012). While extant family 6 129 records mentioned above were made in terrestrial biotopes, Colloff (1983) cited the 130 presence of a species of Nanhermannia Berlese, 1913 in coastal lichens in the Islands of 131 the Clyde, Scotland. The leg shows signs of alteration as a result of the palynological 132 processing (see Remarks). The non-preserved mite body remains could have been lost 133 due to this process (and not due to transport). The leg is articulated and very well 134 preserved with the occurrence of delicate structures, hence we could assume that it has 135 not been transported far from the original habitat. 136 A continental origin of the fossil mite (Hypotheses 2) is supported by the fact that most 137 of the extant Nanhermannidae species live in leaf litter (Norton & Behan-Pelletier, 138 2009).