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Journal of Paleontology, 89(5), 2015, p. 762–767 Copyright © 2016, The Paleontological Society 0022-3360/16/0088-0906 doi: 10.1017/jpa.2015.65


First fossil jacobsoniid beetle (Coleoptera): Derolathrus groehni n. sp. from Eocene Baltic amber


Chenyang Cai,1 Richard A. B. Leschen,2 Ye Liu,3 and Diying Huang4


1Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, Jiangsu 210008, China ⟨caichenyang1988@163.com⟩ 2Landcare Research, New Zealand Arthropod Collection, Private Bag 92170, Auckland, New Zealand ⟨leschenr@landcareresearch.co.nz⟩ 3Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China


liuye198282@126.com⟩ 4State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, Jiangsu 210008, China ⟨dyhuang@nigpas.ac.cn


Abstract.—Jacobsoniidae, comprising a small group of small-to-minute polyphagan beetles, is a family presently placed within Derodontiformia. No fossil jacobsoniid has been described to date. Here, we describe the first fossil jacobsoniid, Derolathrus groehni n. sp., based on two well-preserved individuals in middle Eocene Baltic amber. Micro–computed tomography (micro-CT) was used to reveal many diagnostic characters of the Recent genus Derolathrus Sharp. Derolathrus groehni is compared with modern Derolathrus species and is noteworthy for the well-developed eyes and elongate prothorax.


Introduction


With only 22 described species grouped in three genera (Háva and Löbl, 2005; Lawrence and Leschen, 2010; Peck, 2010), the family Jacobsoniidae is a small group of polyphagan beetles comprising small-to-minute species (0.65–2.5mm long). The family was provisionally included in Bostrichiformia by Lawrence and Newton (1995) and Philips et al. (2002) and is currently placed in Derodontiformia (Lawrence et al., 2010), although it shares characters with staphyliniforms (Crowson, 1959, 1960; Lawrence et al., 2011). Löbl andBurkhardt (1988) andHáva and Löbl (2005) catalogued all extant species of theworld and only one species has been described since then (Peck, 2010). Jacobsoniidae includes three extant genera: Saphophagus Sharpwithone species (S. minutus Sharp) restricted to New Zealand; Sarothrias Grouvelle with 13 species in the Indo-Australian region; and Derolathrus Sharp, with eight described species known from Sri Lanka, North America (Florida) and mainly tropical islands (e.g., Barbados, Canary Islands, Guadeloupe, Fiji, Hawai’i, Madeira, Mauritius, Virgin Islands). Derolathrus, like remaining jacobsoniid genera, are poorly


represented in collections and little about their biology is known (Háva and Löbl, 2005). There is unstudied material and unde- scribed species from Africa, Australia, the Neotropics, New Caledonia, and the Solomon Islands (Arnett et al., 2000; Lawrence and Leschen, 2010; Peck, 2006, 2010; Philips et al., 2002; Leschen, personal observation). Derolathrus species are tiny (from about 0.65mm to about 1.00mm) and require detailed study, especially of their cuticular microsculpture. Some species may be more widespread than thought; for example, Derolathrus atomus Sharp was described from Hawaii


and was recently recorded and considered accidentally intro- duced to the West Indies by Peck (2010). Derolathrus species have been collected by mass collecting techniques (in flight intercept traps and sifting leaf litter), and in in microhabitats (under bark, in rotten palm wood, from fungal fruiting bodies, in bat guano, and from bird nests; Lawrence and Leschen, 2010; Löbl and Burckhardt, 1988; Philips et al., 2002). To date, no fossils belonging to Jacobsoniidae have been recorded. Therefore, our discovery of a new Derolathrus species from the middle Eocene is of significance for understanding the origin and early evolution of the family.


Material and methods


The newly described species is known from two individuals preserved in two pieces of Baltic amber. The two specimens are in the collection of Carsten Gröhn (Glinde,Germany) and will be deposited at the Geologisch-Paläontologisches Institut und Museum der Universität Hamburg, Germany (GPIH). The pieces were not embedded in artificial resin. The precise age of Baltic amber is not determined (Weitschat andWichard, 2010). Due to transportation and extensive re-deposition, no amber-bearing deposits can be considered as the primary depositional site. We follow Ritzkowsky (1997) who considered Baltic amber to be of Bartonian-Lutetian-Ypresian (middle Eocene) age. Micro-CT was performed at the Zoological Institute and Museum of the Ernst-Moritz-Arndt University of Greifswald. The specimens were scanned using an XRadia XCT-200 (Carl Zeiss) equipped with switchable scintillator-objective lens units. Each amber piece was mounted on a holder and centered. A series of 1600 projections were performed using 10× magnification with the


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