Part 95

Comparison and remarks.--The type specimen was the only individual referred by Brown (1908) to this species. The remaining material of weasels from this deposit was referred by Brown to his Putorius cicognanii angustidens. Examination of the original materials convinces the writer, too, that the specimens, except no. 12431, are of the species erminea [= cicognanii of Brown]. No. 12431 itself may possibly be erminea but is far more probably of the species frenata. The uncertainty is due to the fact that an occasional skull alone of a subadult male erminea is extremely difficult certainly to distinguish from a skull alone of an adult female frenata. This is true among Recent specimens in the northern Mississippi Valley today; more exactly in Iowa and southern Minnesota the females of frenata, oftentimes intergrades between the subspecies Mustela frenata longicauda, M. f. noveboracensis and M. f. primulina, by only the skulls are next to indistinguishable from certain, unusually slender skulls of male erminea. At other places where the ranges of the two species meet, this difficulty is not so often encountered. Also, the type of gracilis has the skull broken in such a way that the postglenoid length in relation to the length of the skull as a whole could not be accurately determined in this particular skull.

The type specimen of gracilis surely is an adult and because of its small size is thought to be a female. Of known long-tailed weasels of the species frenata, gracilis is structurally nearest to M. f. primulina which occurs in the same region today and to M. f. noveboracensis, the long-tailed weasel of the eastern United States. M. gracilis differs from noveboracensis and agrees with primulina in possessing well-marked temporal ridges which fuse to form a low sagittal crest, in having the mastoid processes projecting farther, laterally, beyond the braincase, in having the anterior ends of the tympanic bullae produced below the squamosal rather than on the same plane with the squamosal, and in having the bullae more inflated anteromedially. M. gracilis differs from both noveboracensis (97 and 56 with skulls of comparable age) and primulina (64 and 24 with skulls of comparable age) in that the zygomatic breadth amounts to less than 58 per cent of the basilar length. Another difference from any one of the skulls of females of primulina is the longer rostrum, which, when measured from the posterior base of the postorbital process of the frontal to the anterior end of the nasal on the same side, amounts to more than 35 per cent of the basilar length. As pointed out by Brown (1908:182) this specimen represents the extreme of slender skull among known kinds of American weasels.

Selected measurements of no. 12431, the type specimen of Mustela gracilis, are as follows: Basilar length of Hensel, 38.1 mm.; length of upper tooth-rows, 14.3 to 14.4; breadth of rostrum, 11.0; interorbital breadth, 8.5; orbitonasal length, 13.6; mastoid breadth, 18.2; length of tympanic bulla, 13.0; breadth of tympanic bulla, 6.3; depth of tympanic bulla, 3.25; outside length of P4, 4.5; inside length of P4, 4.7; breadth of M1, 3.4; length of inner moiety of M1, 1.8; depth of skull at anterior margin of basioccipital, 12.2; depth of skull at posterior borders of last upper molars, 11.3; distance from foramen ovale to tympanic bulla, 3.6 mm.

=MUSTELA AFRICANA= Desmarest

Tropical Weasel

(Synonymy under subspecies)

Type.--Mustela africana Desmarest, Nouv. Dict. d'Hist. Nat., vol. 19, p. 376. 1818.

Range.--Known from the headwaters of the Amazon in eastern Perú and from near the mouth of the same river, on its southern side in Brazil, all within the Tropical Life-zone. See figure 29 on page 221.

Characters for ready recognition.--Differs from Mustela frenata, the only geographically adjacent species of the genus, by: presence of thenar pad on forefoot; presence of a longitudinal, median, abdominal stripe of same color as upper parts; upper lips being broadly edged, entirely round, with color of underparts; failure of longest facial vibrissae to reach posterior margin of ear; absence of p2; relative flatness (see pl. 29, fig. i and pl. 39, fig. h) of tympanic bullae.

Characters of the species.--Size large (total length of adults approximately 500 mm.); foot-soles naked; thenar pad present on forefoot; length of claws, measured on concave sides, less than one and one-fourth times depth of claws measured at bases; longest facial vibrissae not reaching posterior margin of ear; tail relatively long haired; tail at all ages terminating in point as is characteristic of only juveniles and very young of Mustela frenata and M. erminea; tip of tail, and muzzle, only slightly darker than remainder of upper parts; upper lips broadly edged with color of underparts; pelage coarse, harsh and sparse; longitudinal, median, abdominal stripe of same color as upper parts present; skull broad and deep; braincase large, rounded, and much inflated anteriorly; palatal region wide; tympanic bullae less inflated than in any other American species of the subgenus; angle of lower jaw reduced; dental formula

3 1 2-3 1 -, -, ---, -; teeth heavy; medial lobe of M1 but slightly larger than 3 1 2 2

lateral lobe. See plates 28, 29, 30, 39 and cranial measurements.

Geographic variation.--The reddish versus chocolate color of the upper parts constitutes the only variation of a geographic nature so far detected.

Remarks.--One of the most noteworthy of the several unique characters of this large, tropical weasel is the longitudinal, median, abdominal band. The species exhibits the minimum degree of development of certain features that become progressively less apparent as one proceeds southward from Central America. The relative uniformity of the coloration of the upper parts (reduction in intensity of black color on the muzzle and tip of the tail) and the reduction of the tympanic bullae are two cases in point. Viewed dorsally the general outline of the skull is most nearly matched by that of the skull of Mustela frenata meridana from Venezuela or that of M. f. helleri from Perú. However, the resemblance is not close. The tympanic bullae, although unique among American weasels, are more like those of M. f. meridana from Venezuela than like those of any other kind. The great postorbital width (relatively less in M. africana than in several South American subspecies of Mustela frenata) and small angular process of the mandible are characters, in varying degrees, also common to all South American weasels. Structurally M. africana clearly is more nearly like other subspecies of M. frenata from South America than it is like any species or subspecies from North America.

Mustela africana is the most primitive of the American weasels. The distinctive cranial and dental characters, excepting the reduction in number of premolars, are of a primitive nature. For example, the relatively wide postorbital region, the large braincase that is inflated anteriorly, and the flattened, tympanic bullae, are points of resemblance to the holarctic Mustela erminea, which species is regarded as nearest the original stem form; also the mentioned characters correspond to ontogenetic stages passed through by other weasels. Mostly on these accounts, one is led to look upon M. africana as a migrant from North America. It may have become isolated from its original stock, by a water barrier in the Central American region, for a length of time sufficient to permit of a degree of differentiation to develop between it and the North American weasels which prevented crossbreeding with the frenata stock when that stock, at a later time, reached South America. This assumption is suggested only by evidence from the Recent specimens. No remains of true weasels (subgenus Mustela) have been recorded from deposits in South America older than the Recent period. The alternate possibility, that M. africana intergrades with some race of M. frenata in western or northern South America, has been considered and regarded as highly improbable.

Cabrera (1940:15) has made the distinctive structural characters of Mustela africana basis of the generic name Grammogale to include the one species africana. I am inclined to accord Grammogale only subgeneric rank.

It is possibly significant that Mustela africana is intermediate in several respects between Lyncodon and typical Mustela. The median, longitudinal, abdominal band of the same color as the upper parts in M. africana and the relative uniformity of the coloration of its upper parts might be considered as an intermediate stage between the dark, bicolored (black muzzle and tail tip and brown body) upper parts and light-colored underparts of the North American weasels on the one hand and the light, unicolored upper parts and dark-colored underparts of the Patagonian weasel (Lyncodon) on the other hand. The number of premolars,

2-3 ---, is also intermediate between the numbers 2

3 2 - and - of the North American Mustela and the Patagonian 3 2

Lyncodon, respectively. The American Mustela and the Patagonian Lyncodon, respectively. The more medially, as opposed to anteriorly, directed medial cusp of P4 (characteristic of approximately half of the specimens examined), and the structure of the skull in general of M. africana also seem to be morphologically intermediate between those parts of Mustela and Lyncodon.

On the chance that Lyncodon is closely enough related to Mustela, to be included in a group with Mustela rather than in a group with Grisonella, it is worth noting that Lyncodon lujanensis Ameghino (1889:324, 325), from the villa of Lujan and at the city of Córdoba, at each place in the Pampean [= Pleistocene] formation of Argentine (see also Cabrera, 1928:263) is the first and only fossil form of this group recorded from the whole of South America. Actually, however, Lyncodon seems to me to be as nearly related to Grisonella, if not more so, than to Mustela. If Lyncodon is more closely related to Grisonella and Grison than to Mustela, then the above remarked intermediacy in characters of M. africana has more of interest as a tendency to parallelism than it has of phylogenetic import. Appraisal of phylogenetic relationships would require appraisal of the ancestral stem forms of the Grison stock and the Mustela stock. None of either is known from deposits of the Pliocene, the period of time immediately preceding the Pleistocene.

None of the skulls of Mustela africana seen or figured has the nasomaxillary sutures entirely obliterated and the specimens would, judged on this character alone and by analogy with North American species, be regarded as young and subadult. However, the sutures close at what seems to be a later age than in M. frenata and M. erminea. The condition of the mammae in the type specimen of M. stolzmanni and in the specimen from Moyobamba, indicate that they have borne young. North American weasels old enough to bear young lack visible traces of the nasomaxillary sutures. I have examined no skulls of africana with greatly worn teeth and hence cannot say if the sutures are obliterated in advanced age.

If available data be correct, this species is unique within the genus in that the two sexes are of approximately the same actual size and of the same relative proportions in the body and in the skull. There was no difference between individuals said to be of different sexes from Pará, described and figured by Goeldi (1904:61-62, pls. 1, 2). The undoubted female, type specimen of Mustela africana stolzmanni, is as large as the undoubted male, no. 37475, of the same species, but of a different subspecies, from Pará, Brazil. All the specimens of M. a. africana that I have handled are labeled male and those of M. a. stolzmanni female. More material may show that the female is smaller than the male, as is the case in all near relatives of M. africana.

Little has been recorded concerning the habits of this species. Tate (1931:254) states that a live individual which he saw in a cage at Pará had been captured "swimming in the salt water of the estuary about half a mile away from the shore." On the label of the specimen from Moyobamba, there appears: "caught in Willow tree."

Subspecies examined.--All described forms, of which there are two.

=Mustela africana africana= Desmarest

Tropical Weasel

Plates 28, 29, 30 and 41