PALAIOS, 2010, v. 25, p. 730–741 Research Article DOI: 10.2110/palo.2010.p10-057r FEEDING TRACES ASSOCIATED WITH BIRD TRACKS FROM THE LOWER CRETACEOUS HAMAN FORMATION, REPUBLIC OF KOREA AMANDA R. FALK, 1 * STEPHEN T. HASIOTIS, 1 and LARRY D. MARTIN 2 1 University of Kansas, Department of Geology, Lawrence, Kansas 66049, USA; 2 University of Kansas, Department of Ecology and Evolutionary Biology, Lawrence, Kansas 66049, USA e-mail: afalk @ ku.edu ABSTRACT The bird track localities of the Republic of Korea are among the richest and most diverse avian tracksites in the world; however, no behavioral studies have been conducted with them. This paper examines the association of invertebrate traces, avian footprints, and small, enigmatic elongate and double-oval traces from silicone casts (KS001 and KS064) taken from two specimens from the Haman Formation near Jinju. Two distinct types of bird tracks are present: a larger type with a well-defined hallux impression on the majority of the tracks, Koreanaornis isp., and a smaller type without a clear hallux impression, K. hamanensis. Elongate traces interpreted to be peck marks and double-oval traces interpreted to be probe marks were found on KS001. The peck marks range from 4.0 to 11.2 mm long and average 7.6 mm in width. There are two distinct morphologies of probe marks which may represent different species or genera of birds. The large probe mark is 6.9 mm long and 2.9 mm wide, whereas the smaller probe marks are 4.5 mm long by 2.2 mm wide and 5.7 mm long by 3.0 mm wide, respectively. Invertebrate traces associated with the bird tracks and feeding traces include Cochlichnus, Steinichnus, and Arenicolites. This represents the first report of peck marks from a fossil bird track locality. INTRODUCTION Early Cretaceous bird tracks from Asia are well known from China (Lockley et al., 2006b; Zhang et al., 2006; Lockley et al., 2007), the Republic of Korea (Baek and Yang, 1997; Lim et al., 2000, 2002; Lockley et al., 2006a; Lockley and Harris, 2010), and Japan (Azuma et al., 2002). Both the Haman and Jindong Formations of the Republic of Korea are important because of the large number of well-preserved tracks and the geographic distribution of these track-bearing localities. Thousands of bird tracks are exposed in one locality in the Haman Formation, making it one of the largest bird tracksites in the world. Despite the expanse and number of tracks, no extensive behavioral studies have been conducted with them. Bird tracks from the Haman Formation consist of palmate (webbed), anisodactyl (non-webbed tracks with toes II, III, and IV pointing forward and a reflexed hallux), and incumbent anisodactyl (reduced to nonexistent hallux) tracks (Lim et al., 2002). The web-footed tracks are interpreted as being similar to avocets (Charadriiformes), with the webbing restricted to the proximal portion of digits II–IV. These, along with other sites in the Republic of Korea (Kim et al., 2006), are the oldest webbed-footed bird tracks known (Lim et al., 2000, 2002). The Haman Formation contains the most diverse avian ichnofauna currently known with six ichnospecies, including the anisodactylous Koreanaornis and Jindongornipes, which have been interpreted as shorebirds, and the webbed Uhangrichnus and Ignotornis (Lockley et al., 1992; Baek and Yang, 1997; Kim et al., 2006; Lockley and Harris, 2010). Herein the term shorebird refers to an avian morphotype rather than the order Charadriiformes. Modern avian genera do not appear in the fossil record until the Eocene (Feduccia, 1996) and shorebirds present in the Early Cretaceous are unlikely to be the same taxonomically as extant Charadriiformes (Lockley and Harris, 2010). Studies on the feeding behavior of modern shorebirds and other water-margin birds are common, especially from an ecological standpoint (e.g. Holmes, 1966; Brooks, 1967; Quammen, 1982, 1984; Prakash et al., 2008), although published, detailed accounts of feeding traces are rare. An example of a study on sediment-beak interaction (Lane, 1987) produced a figure cited in several secondary sources as an example of morphological variation in shorebird bills and its effect on the method of feeding (i.e., Gill, 2006). The morphology and length of a bird’s beak indicates the depth to which it probes and can act as a proxy for the type of prey on which it feeds (Lane, 1987). Beak morphology will also affect the shape of the probe mark and how often the bird probes into the sediment; for example, a longer- and curved-billed bird will probe much more slowly than a short- and straight-billed bird, as the latter is easier to draw in and out of the sediment. Feeding behavior in shorebirds is extremely varied; some feeding patterns depend on light schedules and tides, whereas other patterns appear independent of natural phenomena (Lane, 1987). Many birds do not directly interact with the sediment using their beaks, but rather pry open shells or crustaceans (i.e., oystercatchers, gulls), or turn over * Corresponding author. FIGURE 1—Map showing the location of Jinju, near the track-bearing locality of the Haman Formation, Republic of Korea. Star 5 Gyeongsangnamdo Institute of Science Education (GISE); DPRK 5 Democratic People’s Republic of Korea; ROK 5 Republic of Korea. Copyright g 2010, SEPM (Society for Sedimentary Geology) 0883-1351/10/0025-0730/$3.00