Rattus rattus species group. A distinctive species known only by four specimens in the original series (NMW B26, B27, 21497, and 27027; Musser and Heaney, 1985; Musser and Newcomb, 1983). Because Zelebor (1869) provided no exact collection site, Musser and Heaney (1985) stated that the island was unknown where the rats were obtained. In response, Dr. K. Bauer wrote Musser the following: "It is true, that Zelebor (1869) gave no more exact information. But K. Scherzer, the ‘Historiographer’ of the expedition did. In his detailed three volume report ‘Reise der Österreichischen Fregatte Novara um die Erde in den Jahren 1857, 1858, 1859 unter den Befehlen des Commodore R. von Wüllerstort-Urbair,’ published in Vienna 1861/62 (and later in Italian and English translations), he summarized the scientific results. And in connection with a sketch of the fauna found on the Nicobar Islands (vol. 2:71/72) he states (in translation): ‘In mammals, all islands of the group are poor. We only found 8 species . . . and two different murids (Mus). One of these, nearly as big as the Norway Rat, we saw only on Car-Nicobar and Sambelong (= Great Nicobar); . . . always in the crowns of cocos palms, very fast, difficult to see and shoot, doing heavy damage to cocos plantations. . . . A second, in size like our Black Rat, lives on Car-Nicobar in holes in the ground that it shares in total peace with a (terrestrial) crab (Gecarcinus).’ . . . This history gives detailed information on spots visited and time spent there. . . . Careful study of this text might well give further hints, but already from a hurried overview it seems quite certain, that the palmarum sample came from Car-Nicobar."

Rattus palmarum is large (head and body length for three adults = 225-240 mm, greatest skull length = 49.0-54.0 mm) and has a moderately long tail (220-231 mm); brownish, dense, and rough dorsal coat with long guard hairs; white underparts; ten pairs of mammae, and a large, robust cranium with thick and high dorsolateral ridges. The skull is a larger, more robust version of that seen in R. burrus from the other Nicobar Isls, R. simalurensis from the Simalur Group and R. lugens from the Mentawai Arch. It may be most closely related to R. burrus, which occurs on Trinkat, Little Nicobar, and also Great Nicobar Isls but not Car Nicobar, and it may be R. palmarum and R. burrus that Scherzer saw on Great Nicobar. Rattus andamanensis occurs on Car Nicobar (see that account). It is about the same body size as Scherzer’s "Black Rat," and the larger-bodied R. palmarum, which also occurs on that island, matches the "Norway Rat" in body size.