Bessoecetor Simpson, 1936

S. Scott, Craig, C. Fox, Richard & P. Youzwyshyn, Gordon, 2002, New earliest Tiffanian (late Paleocene) mammals from Cochrane 2, southwestern Alberta, Canada, Acta Palaeontologica Polonica 47 (4), pp. 691-704 : 700-701

Genus Bessoecetor Simpson, 1936

Propalaeosinopa Simpson, 1927: 2 , figs. 2, 3.

Thylacodon ( Matthew and Granger, 1921) (in part); Russell in Rutherford 1927: 41.

Palaeosinopa Matthew, 1901 (in part); Simpson 1935a: 230.

Palaeictops Matthew, 1899 (in part); Van Valen 1967: 232.

Remarks.—Simpson erected “ Propalaeosinopa ” in 1927 for “ Propalaeosinopa albertensis ” from the middle Tiffanian Erickson’s Landing locality, Alberta. Van Valen (1967) and Dorr (1977) suggested that “ Propalaeosinopa diluculi ” and “ Propalaeosinopa thomsoni ” (both previously placed in the genus Bessoecetor by Simpson [1936, 1937]) were junior synonyms of “ P. albertensis ”.This hypothesis was followed by Holtzman (1978), but has been rejected by most other workers.There is now general agreement that “ P. thomsoni ” is conspecific with “ P.diluculi ”, a view we accept here, with the holotype of “ P. albertensis ” being too poorly preserved for assessment (see Rose 1981a, and Krause and Gingerich 1983).Indeed, we conclude that AMNH 15543B, an incomplete left dentary containing a severely worn p4, retains no diagnostic characters, and that “ Propalaeosinopa albertensis ”, the genotypic species, is therefore a nomendubium, with the generic name “ Propalaeosinopa ” having no status.As such, “ P. diluculi ” and “ P. thomsoni ” are here returned to Bessoecetor Simpson, 1936 , with B.septentrionalis ( Russell, 1929) as the genotypic species (see below).

Bessoecetorseptentrionalis comb.nov. ( Russell, 1929) Fig. 3D–I .

Thylacodon sp. nov. Russell in Rutherford, 1927: 41.

Diacodon septentrionalis Russell, 1929: 173 .

Palaeosinopa diluculi Simpson, 1935a: 230 .

Bessoecetor thomsoni Simpson, 1936: 9 , figs. 3, 4.

Bessoecetor diluculi Simpson, 1937: 122 , figs. 20, 21.

Propalaeosinopa albertensis Simpson, 1927 ; Van Valen 1967: 226.

Propalaeosinopa thomsoni ( Simpson, 1936) ; Rose 1981a: 150.

Propalaeosinopa diluculi ( Simpson, 1935a) ; Rose 1981a: 150.

Propalaeosinopa septentrionalis Fox, 1990: 58 .

Holotype: UALVP 126 , incomplete left dentary with m3, Fig. 3I 1 –I 3 .

Type horizon and locality: Cochrane 1, Paskapoo Formation, southwestern Alberta (see Fox [1990] for description and history of the Cochrane 1 locality).

Age and distribution: Late Torrejonian of Alberta (type locality [ Fox 1990]), Montana (Gidley Quarry, upper Lebo Formation, Crazy Mountain Field, Sweetgrass County [ Simpson 1937]; Silberling Quarry, upper Lebo Formation, Crazy Mountain Basin, Sweetgrass County [ Simpson 1937]), and Wyoming (Cedar Mountain localities [UW V−82004, 82006, 82015, 82040], Polecat Bench Formation, southern Bighorn Basin, Hot Springs/Washakie counties [ Hartman 1986]; Swain Quarry, Fort Union Formation, Washakie Basin, Carbon County [ Szalay 1968; Rigby 1980]); earliest Tiffanian of Alberta (Cochrane 2, Paskapoo Formation, Alberta Basin [ Youzwyshyn 1988; Fox 1990]) and Montana (Douglass Quarry, Crazy Mountain Basin, Sweetgrass County [ Krause and Maas 1990]); early Tiffanian of Montana (Scarritt Quarry, Melville Formation, eastern Crazy Mountain Basin, Sweetgrass County [ Krause and Maas 1990]); middle Tiffanian of Alberta (Burbank locality, Paskapoo Formation, Alberta Basin, confluence of Red Deer and Blindman rivers [ Fox 1990]; Hand Hills West Upper Level, Paskapoo Formation, Alberta Basin [ Fox 1990]; Joffre Bridge Roadcut Lower Level, Paskapoo Formation, Alberta Basin, near Red Deer [ Fox 1990]; DW−2 locality, Paskapoo Formation, Alberta Basin, near Blackfalds [ Fox 1990]), Wyoming (Cedar Point Quarry, Polecat Bench Formation, Bighorn Basin, Big Horn County [ Rose 1981a]; Chappo Type locality, Chappo Member, Wasatch Formation, Lincoln County [ Gunnell 1994]; Hallelujah Hill [locality UW V−77005], Fort Union Formation, east flank Rock Springs Uplift, Sweetwater County [ Winterfeld 1982]), and North Dakota (Brisbane locality, Slope Formation, Grant County [ Holtzman 1978]; Judson locality, Tongue River Formation, Morton County [ Holtzman 1978]).

Material.— UALVP 25119, 28413, P4s; UALVP 18408, 28423, 28425, M1s; UALVP 28427, 28429, 28430, 28432, 28433, 28439, 28551, M1s or M2s (total: 7); UALVP 28411, 28412, 28416, 28420, 28421, M2s (total: 5); UALVP 28422, M3; UALVP 28415, incomplete dentary with p2–3; UALVP 28435, 28437, p2s; UALVP 28428, p3; UALVP 28546–28549, 28552, dp4s (total: 5); UALVP 28434, 28438, 28440, 28441, p4s; UALVP 25092, 28417, 45130, 45131, m1s; UALVP 28414, 28444, 45132, m2s; UALVP 28445, 28450, 45129, m3s.

Remarks.—Russell (in Rutherford 1927) identified an incomplete dentary containing m3 from the Torrejonian Cochrane 1 locality, Alberta, as a new species of Thylacodon ( Marsupialia , Didelphidae ).He subsequently designated the specimen, UALVP 126, as the holotype of a new species of the leptictid Diacodon Cope, 1875 , which he named Diacodon septentrionalis ( Russell, 1929) .Russell also desig − nated two additional lower molars, catalogued together as UALVP 333, from Cochrane 2, as paratypes; subsequently, he (1932) tentatively referred three complete upper molars from Cochrane 2 to this same species. Van Valen (1966) re − ferred one of these upper molars ( UALVP 428, thought by Russell to possibly be a P4) to his new palaeoryctid, Pararyctespattersoni.Soon after, Van Valen (1967) included “ D.” septentrionalis in the leptictid Palaeictops Matthew, 1899 . Novacek (1977) in his review of North American early Tertiary leptictids consigned all Paleocene species (with the exception of Myrmecoboides Gidley, 1915 ) to Prodiacodon Matthew, 1929 .He did not recognize “ Palaeictops ” septentrionalis (fide Van Valen 1967) because of the fragmentary nature of the material, and noted the difficulty in determining if the teeth were better referred to a leptictid or pantolestid taxon.

Comparisons made by Youzwyshyn (1988) imply that Russell’s “ D.” septentrionalis , even when UALVP 428 is removed, is a composite taxon.If compared to teeth of “ Propalaeosinopa diluculi ” from the late Paleocene of Canada and the United States, as well as with the original material of “ P. diluculi ” from Gidley Quarry ( Simpson 1937), the holotype of “ Diacodon ” septentrionalis ( UALVP 126) is found to be virtually identical with the m3s of this pantolestid taxon. Russell’s “ Diacodon ” septentrionalis , then, has priority over Simpson’s “ P. diluculi ”.As noted above, the genus Propalaeosinopa has no taxonomic status; we therefore refer UALVP 126 to Bessoector septentrionalis comb.nov., and designate it as the holotype.“ P. diluculi ” and “ P. thomsoni ” are here considered junior synonyms of B. septentrionalis .

Russell’s (1929) paratypes of “ Diacodon ” septentrionalis ( UALVP 333) from Cochrane 2 do not belong to the same species as the holotype, but instead are lower molars of an unidentified genus and species of palaeoryctid.The upper molars ten − tatively referred in 1932 by Russell and illustrated in his figs.8 and 9 pertain to two different species of Prodiacodon, Prodiacodonfuror and Prodiacodon sp. , cf. P.puercensis , respectively.Accordingly, the only specimen of B. septentrionalis from Russell’s 1932 hypodigm is the holotype.

The dentition of B.septentrionalis from Cochrane 2 is virtually identical to that described by Simpson in 1936 (as Bessoecetor thomsoni ) and in 1937 (as Bessoecetor diluculi ), differing only in minor respects: the protocone of P4 is larger and the metastylar area more pronounced, the ectoflexus of M1 and M2 is shallow, and the parastylar lobe less prominent. Additionally, the talonid of p4 is somewhat reduced, and the m2 paraconid more internal.The Cochrane 2 specimens are well within the size ranges for other samples of Bessoecetor septentrionalis from the Torrejonian and Tiffanian of western North America, and provide no supplemental descriptive information to that provided by Simpson and others.

Figures

Fig.3. A–C. Pararyctes rutherfordi sp.nov., Cochrane 2 locality, Alberta. A.Holotype, incomplete right maxilla with P4, M2–3, UALVP 45094 in occlusal view (A1, A2). B.Left M2, UALVP 25180 in occlusal view. C.Left m1 or m2, UALVP 45095 in labial (C 1), lingual (C2), and occlusal (C3) views. D–I. Bessoecetor septentrionalis comb.nov., Cochrane 2 locality, Alberta. D.Right P4, UALVP 25119 in occlusal view. E.Left M1, UALVP 28423 in occlusal view. F.Left M2, UALVP 28412 in occlusal view. G.Right p4, UALVP 28438 in labial (G 1), lingual (G2), and occlusal (G3) views. H. Left m2, UALVP 28414 in labial (H1), lingual (H2), and occlusal (H3) views. I.Holotype, left m3, UALVP 126 in labial (I 1), lingual (I2), and occlusal (I3) views.Scale bars 1 mm.

Fig.1. A–C. Ptilodus gnomus sp.nov., Cochrane 2 locality, Alberta. A.Holotype, right P4, UALVP 45145 in labial (A 1), lingual (A2), and occlusal (A3) views. B.Left p4, UALVP 45148 in labial (B 1), lingual (B2), and anterior (B3) views. C.Incomplete left dentary having i1, p3–4, UALVP 18670 in labial (C1) and lingual (C2) views. D. Baiotomeusrusselli sp.nov., Cochrane 2 locality, Alberta.Holotype, left P4, UALVP 18787 in labial (D 1), lingual (D2), and occlusal (D3) views. E–H. Thryptacodonorthogonius, comb.nov., Cochrane 2 locality, Alberta. E.Left M1, UALVP 45099 in occlusal view. F.Holotype, left M2, UALVP 124 in occlusal view. G.Left M3, UALVP 24993 in occlusal view. H.Right m1, UALVP 42872 in labial (H 1), lingual (H2), and occlusal (H3) views. Scale bars 1 mm.