AMERICAN MUSEUM Novitates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 2877, pp. 1-1.8, figs. 1-10 April 28, 1987 Auditory Features and Affinities of the Eocene Bats Icaronycteris and Palaeochiropteryx (Microchiroptera, incertae sedis) MICHAEL J. NOVACEKI ABSTRACT The earliest known bats are skeletons of Icaro- ly, there is no reason to recognize a "primitive- nycteris index from the early Eocene of western ancestral" group, Eochiroptera, that is excluded Wyoming and a few less well-represented species from Microchiroptera or Megachiroptera. The re- from the early Eocene of France. Also known are lationships ofIcaronycteris and Palaeochiropteryx Palaeochiropteryx tupaiodon and several other within Microchiroptera remain uncertain. Asso- species from the middle Eocene of western Ger- ciation ofthese taxa and several other Eocene forms many. These taxa have been regarded as primitive within the microchiropteran superfamily Palaeo- forms, either "ancestral" to echolocating micro- chiropterygoidea fails to clarify these relation- chiropterans or "ancestral" to both micro- and ships. Palaeochiropterygoidea has not been de- megachiropterans. Details ofbasicranial structure fined by derived characters, and Icaronycteris and suggest that these Eocene forms were, however, Palaeochiropteryx are more accurately designated specialized echolocators comparable to Recent Microchiroptera incertae sedis. Several primitive microchiropterans. Moreover, quantitative anal- features shown by Icaronycteris suggest that the ysis reveals that the Eocene bats have a more pro- development of a sophisticated system for echo- nounced expansion of the cochlea than many Re- 'location within Microchiroptera occurred earlier cent microchiropteran species. There is clear than certain modifications ofthe postcranial skel- justification for reference ofIcaronycteris and Pa- eton. laeochiropteryx to the Microchiroptera. Converse- INTRODUCTION The oldest bats in the fossil record are early scribed by Jepsen (1966) from an exquisite, Eocene in age. Icaronycteris index was de- nearly complete skeleton found in the Green I Chairman and Associate Curator, Department ofVertebrate Paleontology, American Museum ofNatural History. Copyright © American Museum of Natural History 1987 ISSN 0003-0082 / Price $2.00 2 AMERICAN MUSEUM NOVITATES NO. 2877 River Formation of Fossil Lake, Wyoming. The above classification is, however, in Later found were two other skeletons of this conflict with certain other studies. Segall genus (Novacek, 1985a). Also known from (1971) argued that Icaronycteris index shared early Eocene faunas are Icaronycteris? menui, a more general basicranial structure with er- Archaeonycteris brailloni, andAgeina tobieni, inaceid insectivorans and megachiropterans, all described by Russell et al. (1973) from the and lacked many of the morphological cor- Mutigny and Avenay quarries in northeast relates with ultrasonic echolocation found in Epemay, Maine, France. These latter three microchiropterans. Furthermore, Jepsen species are known only from partial denti- (1966, 1970) had also emphasized the large tions. number of primitive traits in the skeleton of The middle Eocene bat Palaeochiropteryx Icaronycteris. Accordingly, Van Valen (1979) tupaiodon was first described by Revilliod recognized Icaronycteris and other palaeo- (1917) from the famous "Grube Messel" near chiropterygoideans as members of the sub- Darmstadt, Hessen, West Germany. A large order Eochiroptera, a group either more re- number of skeletons (more than 54 individ- motely divergent than or "ancestral" to the uals) of this bat have been recovered from Microchiroptera and Megachiroptera (Van the site (see Smith and Storch, 1981). Other Valen, 1979, fig. 1). bats from the Messel pit include Archeonyc- Study of described and undescribed ma- teris trigonodon Revilliod, 1917; "Archaeo- terial representing Icaronycteris contradicts nycteris" revilliodi Russell and Sige, 1970; Segall's (1971) description of the auditory Hassianycteris messelensis Smith and Storch, system of this bat as "non-microchiropter- 1981; and Hassianycteris magna Smith and an." Icaronycteris and Palaeochiropteryx both Storch, 1981. All of these forms are repre- clearly show several features that correlate sented by nearly complete skeletons. In ad- with the presence of ultrasonic echolocation dition, several species of middle Eocene bats in Recent microchiropterans. This point was (Cecilionycteris prisca Heller, 1935; Mat- the subject ofa briefreport (Novacek, 1985a). thesia germanica Sige and Russell, 1980; and The purpose of this paper is to provide a Matthesia? insolita Sige and Russell, 1980) more thorough description of these traits, are known from the "Grube Cecilie," Gei- better reproductions of the relevant illustra- seltal, near Halle a. S., East Germany. tions, and a discussion on the systematic im- The affinities ofthese fossil forms are prob- plications of the auditory morphology and lematic. Winge (1923, p. 304) regarded Pa- other cranioskeletal features in these fossil laeochiropteryx as essentially a primitive ves- bats. pertilionid of the suborder Microchiroptera. In a recent review, Smith and Storch (1981) ACKNOWLEDGMENTS endorsed some ofWinge's views, but did not refer Palaeochiropteryx to the Vespertilion- I thank Karl Koopman, Malcolm C. idae. They grouped the above-cited species McKenna, Andre Wyss (AMNH), Elizabeth (except for Hassianycteris which they loosely Pierson (University of California, Berkeley), allied with emballonurids or rhinolophids and Thomas A. Griffiths (Illinois Wesleyan Uni- recognized as Microchiroptera incertae sedis) versity), and Gary S. Morgan (Florida State within the Palaeochiropterygoidea Revilliod Museum) for criticisms of the manuscript. I 1917, suborder Microchiroptera. From this am especially appreciative to Dr. Griffiths for group they removed Archaeopteropus tran- his detailed comments and for sharing with siens Meschinelli, 1903 (locality: Monteviele, me his insights on the hyoid apparatus in northeast Italy, early Oligocene), and referred bats. For loan of specimens I am grateful to this species to the Megachiroptera. In this J. A. Lillegraven (University of Wyoming), action they claimed that Palaeochiroptery- D. Baird (Princeton University collections goidea was ". less paraphyletic" (Smith and now transferred to Yale University), and J. Storch, 1981, p. 163). Their grouping also Franzen (Senckenberg Museum, Frankfurt, endorses Jepsen's (1966) original description West Germany). of Icaronycteris, wherein this taxon was as- Figures 1, 3, 7, 8, and 9 are stereophotos, signed in the Microchiroptera. radiographs, and drawings from G. L. Jep- 1987 NOVACEK: EOCENE BAT EARS 3 Fig. 1. Stereophotograph of ventral skull of Icaronycteris index; type, PU (Princeton University) 18150. Note this specimen is now deposited in the Yale Peabody Museum Collection. Figure from Jepsen (1970). Symbols are: An, angular process ofdentary; Ax, axis; C, upper right canine; Cp, coronoid process of left dentary; Fp, postglenoid foramen; GI, glenoid fossa; i3, third lower left incisor; L, locator bristles; Ld, labial surface of left dentary; M3, third upper right molar; m3, third lower left molar; Oc, occipital condyles; P4, fourth upper right premolar; p3, third lower left premolar; SI, left stylohyal; Vc, vertebroarterial canal of atlas; Vd, ventral border of right dentary; Z, zygomatic arch. sen's collection of figures of Icaronycteris in- University] 18150) did not show marked en- dex. These were loaned by D. Baird at Prince- largement of the cochlea, although he ac- ton and are now maintained, along with the knowledged that only a small part of this type specimen, by the Yale Peabody Mu- structure was preserved. He based his as- seum. Dr. H. Tuengerthal made the radio- sessment on the observation that in Icaro- graphs shown in figure 4; Chester Tarka pre- nycteris the basioccipital is rather broad and pared figure 2; Barbara Pilarzk made figure straight along its boundaries with the tym- 5; and Lisa Lomauro prepared figures 6 and panic cavity and diverges only in its posterior 10 as well as the final layouts for all figures. region. Segall (1971) contrasted this condi- This paper was supported by the Frick Lab- tion, which is characteristic of many mam- oratory Endowment Fund in Vertebrate Pa- mals including megachiropterans, with the leontology at the American Museum ofNat- typically narrow, strongly biconcave basioc- ural History. cipital of microchiropterans. Whereas some microchiropterans do show a very reduced, AUDITORY STRUCTURES biconcave basioccipital (particularly natal- COCHLEA: Segall (1971) remarked that the ids, some rhinolophids, and vespertilionids), type of Icaronycteris index (PU [Princeton in several other microchiropterans (many 4 AMERICAN MUSEUM NOVITATES NO. 2877 Fig. 2. Ventral view ofbasicranium andjaws ofIcaronycteris cf. index; UW (University ofWyoming) 2244. Modified from Novacek (1985a). Symbols are: Co, cochlea; Ect, ectotympanic; Oa, orbicular apophysis of the malleus. For other symbols, see fig. 1. phyllostomids, some mormoopids [e.g., larger in modern microchiropterans than in Pteronotus macleayii] and some emballo- megachiropterans (Pye, 1966; Henson, 1970; nurids) the basioccipital is nearly as broad Novacek, 1980, 1 985a). In Icaronycteris only between the cochleae as is typically found in a rough estimate of cochlear dimensions can megachiropterans. Nevertheless, the basioc- be made