View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by American Museum of Natural History Scientific Publications AMERICAN MUSEUM Novitates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 2729, pp. 1-10, figs. 1-4 June 4, 1982 An Early Eocene Sirenian from Patagonia (Mammalia, Sirenia) PAUL C. SERENO' ABSTRACT Two mammalian maxillary fragments from the tition of Protosiren fraasi Abel (1904), a sirenian Lower Eocene ofArgentina were described as Flo- from the Middle Eocene of Egypt. These frag- rentinoameghinia mystica (Simpson, 1932) and mentary remains represent the earliest dental re- were designated as Mammalia, incertae sedis cord of fossil sirenians and extend the trans-At- (Simpson, 1945). These specimens are here re- lantic distribution of sirenians back to the Lower studied and reassigned to the order Sirenia. They Eocene. are shown to have many similarities with the den- INTRODUCTION Florentino Ameghino, premier South to determine the accuracy of his statement. American paleontologist and biostratigra- In the course of settling this issue, G. G. pher, is well known for his acute observations Simpson revisited all of Ameghino's locali- and trustworthy accounts, but his long and ties and amassed a large collection. Simp- productive career is remembered as well for son's thorough examination convincingly its sometimes spectacular unorthodoxy. In dispelled Ameghino's association, but also 1906 he announced to an unbelieving audi- brought to light fragmentary remains of un- ence the association of mammals of Tertiary certain affinity. Ironically, Simpson himself type with dinosaurs in beds he claimed were felt that these mammalian cheek-teeth were of Cretaceous age. His claim was often belit- possibly associated with a caniniform, "more tled in subsequent literature, but it was not or less dinosaur-like tooth" found in the same until the Scarritt Patagonian Expedition of block of matrix (Simpson, 1932). The cani- 1930-1931 that a serious attempt was made niform tooth (AMNH[R] 3162), of large size I Department of Geological Science, Columbia University; Department of Vertebrate Paleontology, American Museum of Natural History. Copyright C) American Museum of Natural History 1982 ISSN 0003-0082 / Price $1.05 2 AMERICAN MUSEUM NOVITATES NO. 2729 B - .. r . r -I _- .% )o ,,Ilk .%. -.. .--** FIG. 1. Forentinoameghinia mystica, AMNH 28402. A. Stereopair of occlusal view of upper pre- molar, anterior side at right, lingual side at bottom. B. Stereopair of lingual view of upper premolar, anterior side at right. relative to the cheek-teeth, has since been ACKNOWLEDGMENTS attributed to Sebecus along with many sim- I am indebted to Dr. Malcolm C. McKenna ilar crocodile teeth from the same beds. The for bringing the specimen to my attention maxillary fragments containing the cheek- and providing helpful comments. I also thank teeth suffered a more obscure fate-desig- Mr. Chester Tarka and Ms. Lorraine Meeker nated as Mammalia, incertae sedis, by Simp- for providing a thorough and painstaking cri- son (1945) and Marsupialia, incertae sedis, tique of early drafts of the illustrations. The by Romer (1966). Recently McKenna (1980) author was supported by an NSF Graduate has Fellowship and a Columbia Faculty Fellow- revived interest in this regard by sug- ship during preparation of this gesting a sirenian relationship. The present paper. paper redescribes and discusses the ABBREVIATIONS: possible AMNH, Fossil 'mammal collection, American affinities of these curious remains, quite ap- Museum of Natural History. propriately named Florentinoameghinia AMNH(R), Fossil reptile collection, American mystica Simpson, 1932. Museum of Natural History. 1982 SERENO: EOCENE SIRENIAN 3 paracone ,anterior cingulum posterior cingulum - paraconule - paracone . palate 1 cm I FIG. 2. Florentinoameghinia mystica, AMNH 28402. Labeled drawings of the premolar of figure 1 with the same orientation. SYSTEMATICS REVISED DESCRIPTION ORDER SIRENIA, INCERTAE SEDIS The remains of Florentinoameghinia con- FLORENTINOAMEGHINIA SIMPSON, 1932 sist oftwo right maxillary fragments (AMNH FLORENTINOAMEGHINIA MYSTICA 28402) containing three cheek-teeth and sev- eral small, indeterminate skull fragments, SPECIMENS: AMNH 28402, two maxillary emplaced in roughly a cubic decimeter -of fragments with three cheek-teeth. matrix (fide Simpson, 1932). There is no di- HORIZON AND LoCALITY: Notostylops Beds, rect contact between the maxillary fragments Oficina del Diablo, Cafiadon Vaca, near Paso but their association is implied by compa- Niemann ofthe Rio Chico del Chubut, Chu- rable size, similar texture and state of pres- but Territory, Argentina. ervation of the bone, and close proximity. 4 AMERICAN MUSEUM NOVITATES NO. 2729 1* p it 'PI, 1, .0. I . 15,:71- A --v... Z . i. J1 ~.r L1.X FIG. 3. Florentinoameghinia mystica, AMNH 28402. A. Stereopair ofocclusal view ofupper molars, anterior side at right, lingual side at bottom. B. Stereopair of lingual view of upper molars, anterior side at right. The single tooth of the first fragment (fig. the anterior surface. The metaconule is bro- 1A, B; fig. 2) is the most imperfect, missing ken away but must have been smaller, ifpres- a large portion of the central basin and ex- ent at all, for there is little space between the ternal margin. It is premolariform and tri- protocone and metacone. Well-developed angular in shape, measuring 10 mm. in length anterior and posterior cingula curve upward and 9 mm. in width. Although the apex of toward the paracone and metacone, respec- the protocone is absent, the truncated base tively. A moderate labial cingulum is also is sizable, already equaling the metacone in present. Except for a slight bulge in the pos- height. The subconical metacone is posi- terior cingulum, there is no development of tioned far to the interior ofthe tooth and has a hypocone. Three roots are positioned under anterolabial and posterolabial crests. Possi- the major cusps, the labial pair more robust ble missing material at the posterior surface than the lingual root. The tip of the latter is of the metacone, perhaps, has accentuated deflected labially, toward the posterolabial the posterolabial crest. The paracone is bro- root. ken away but would have been more labial It is probable that a diastema preceded this in position than the metacone, as indicated tooth; an anterior alveolar border, nearly 4 by the juncture of the anterior cingulum and mm. in length, is preserved with no indica- the base of this cusp. Closely allied with the tion of an adjacent tooth. This tooth, there- protocone is a small paraconule, damaged on fore, probably represents an anterior pre- 1982 SERENO: EOCENE SIRENIAN 5 anterior cingulum - metaconule posterior cingulum- hypocon par hypocone- I 1 cm FIG. 4. Florentinoameghinia mystica, AMNH 28402. Labeled drawings ofthe molars offigure 2 with the same orientation. molar, with several missing teeth between it The second tooth lacks most of the pro- and the other maxillary fragment. tocone and paracone, but its major features A strong hypocone is present in the re- are discernible. It is composed oftwo parallel maining teeth (fig. 3A, B; fig. 4). The most rows of cusps nearly equal in height, with anterior of these is trapezoidal in shape and connate bases. The well-developed hypocone sublophodont, with the metaconule shifted is clearly separated from the protocone, in behind the hypocone. A strong notch divides contrast to the condition in the preceding the paracone and metacone as well as the molar. There is noticeable development of weak labial cingulum. The damaged proto- the posterior cingulum, the crest of which cone and hypocone, on the other hand, re- arches from the metacone to the tip of the main closer and more connate than the para- hypocone, with a slight basin between itself cone and metacone. Closely applied to the protocone and hypocone are the paraconule and the adjoining row of cusps. The anterior and metaconule, respectively, which form cingulum is well-developed but remains low, incipient lophs. In addition, there are ante- and lingual and labial cingula are absent. The rior and posterior cingula of moderate de- second tooth measures 12 mm. in length and velopment. 11 mm. in width and is greater in overall 6 AMERICAN MUSEUM NOVITATES NO. 2729 dimensions than the first, which is approxi- Cuspidate cross lophs are the most dis- mately 10 mm. in length and width. tinctive feature of the specimen, best devel- About 15 mm. of the palate is preserved oped on what is probably M2. The metacon- lingual to the first, premolariform tooth. It ule has shifted entirely behind the hypocone is flat, not arched or grooved, and relatively and lost any former connections with the thin, thickening only near the alveolar bor- protocone. Thus there is an immediate re- der. The second maxillary fragment pre- semblance to other lophodont groups such serves a section of the wall of the choanal as macropodids, tapirs, some South Ameri- passage. The position and proportions of can ungulates, and some tethytheres (Pro- these maxillo-palatine fragments indicate a boscidea, Desmostylia, and Sirenia). rather lightly built palate and dental margin. A diverse fauna of diprotodonts was al- Above the two posterior teeth are two cav- ready present in Australia by the late Oli- ities separated by a thin partition. There is gocene (Tedford et al., 1975), the first known a sizable foramen at the bottom ofeach cavity macropodids occurring in as yet undescribed which, however, does not pierce the palate, faunas of medial Miocene age (Archer and as suggested by Simpson (1932). These cav- Bartholomai, 1978). In Dorcopsoides, per- ities could represent the crypts of succes- haps the most primitive member of the Ma- sional teeth positioned above what are per- cropodidae, conules are absent (Ride, 1971). haps deciduous molars. I concur with Stylar cusps, though reduced, are present and Simpson, however, in rejecting such an hy- the premolars are sectorialized.