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An Example of How Our Monographic Series Recently Extinct Species Might Look:


RECENTLY EXTINCT SPECIES

No. 1, January 1999

Xenothrix mcgregori (Jamaican monkey)

By Ross D. E. MacPhee and Clare Flemming


Publication Datum: Williams and Koopman, 1952. Amer. Mus. Novitates 1546: 12.

Type Locality: Long Mile Cave, Trelawney Parish, Jamaica; location as reconstructed by MacPhee (1984).

Holotype: American Museum of Natural History Department of Mammalogy (AMNHM) 148198 (partial mandible).

Range: Jamaica, West Indies ( See fig. 1).

Map of Jamaica
FIG. 1: Map of Jamaica indicating sites where platyrrhine remains have been found.
1. Sheep Pen (Xenothrix)
2. Long Mile Cave (Xenothrix)
3. Coco Ree Cave (unnamed platyrrhine)
4. Jackson's Bay Caves (Xenothrix)

Distribution: Known only from the following cave sites: Long Mile Cave near Windsor, Trelawney Parish; Somerset Cave, Skeleton Cave, Lloyd’s Cave and "the new cave," all near Jackson’s Bay, Clarendon Parish (see Fincham [1998] for cave locations).

Estimated Extinction Date: After AD 1500, possibly after AD 1700 (MacPhee and Flemming, 1999).

Extinction Classification: A(1), 2 (for categories, see MacPhee and Flemming, 1999); " fossil" taxon (but see Remarks).

Current Classificatory Context: Xenothrix is a monotypic genus; subfamily Callicebinae, family Cebidae, superfamily Ceboidea, order Primates (See fig. 2).

Fig. 2
FIG. 2: Phylogenetic relationships of Xenothrix mcgregori (Horovitz and MacPhee, 1999). Box encloses the Antillean monkeys, which comprise a monophyletic group (with Callicebus). (Other phylogentic relationships indicated are not the focus of this paper.)

Phylogenetic Context: Most recent major source: Horovitz and MacPhee (in press a, b). Other key sources: Rosenberger (1977, 1981); Rosenberger et al., (1990); MacPhee and Fleagle (1991).

According to Horovitz and MacPhee (1999), among known platyrrhines Xenothrix is most closely related to the Antillean monkeys Paralouatta varonai (Cuba) and Antillothrix bernensis (Hispaniola) (fig. 2), both also extinct but not known to have survived into the modern era. Together these taxa comprise the Antillean monkey clade. The closest living relative of Antillean monkeys is probably the titi monkey, Callicebus, as originally proposed by Rosenberger (1977), although for Xenothrix only (see MacPhee et al., 1995).

Craniodental characters that are shared unambiguously by Xenothrix + other Antillean monkeys + Callicebus, according to Horovitz and MacPhee’s (1999) analysis, are: possession of two prominences on lateral wall of promontorium; ventral border of zygomatic arch extending below plane of alveolar border; mandibular canine root highly compressed; alveolus of maxillary canine smaller than that of maxillary distalmost premolar. Characters shared unambiguously by the three members of the Antillean monkey clade: nasal fossa wider than palate at level of first maxillary molar; alveolus of mandibular canine buccolingually smaller than those of maxillary distalmost premolar; protoconid of mandibular first molar with bulging buccal surface.

Systematic History: Xenothrix mcgregori has never been included in another co-ordinate taxon. Hershkovitz (1974) proposed that Xenothrix be placed in the monotypic family Xenotrichidae (emendation of Xenothricidae [Hershkovitz, 1970]). Szalay and Delson (1979, as tribe) and MacPhee and Fleagle (1991) agreed with this systematic manuever because it emphasized the distinctiveness of the Jamaican monkey. However, recent investigations (Horovitz and MacPhee, 1999, in prep.) strongly affirm that, not only is Xenothrix intimately related to Callicebus (cf. Rosenberger, 1977), but so are endemic Antillean platyrrhines generally, justifying their joint placement in Callicebinae. McKenna and Bell (1997) included X. mcgregori within Atelidae.

Diagnosis: A middle-sized monkey most closely related to other Antillean monkeys (Paralouatta, Antillothrix) and extant Callicebus, and distinguished by the following combination of characters: (1) femoral features convergent on non-leaping slow-climbing arborealists (unique among platyrrhines); (2) on lower molars, metastylid distal to metaconid and mesial to entoconid (unique among platyrrhines); (3) small, nearly incisiform canines (as judged from alveolar size; similar to Paralouatta varonai, extant callicebines, some pitheciines); (4) dental formula 2.1.3.2/2.1.3.2 (similar only to non-callimiconin callitrichines).

General Features: Szalay and Delson (1979) have drawn attention to the shortness of the dental row and mandible. This character can now be correlated with the unusual breadth of the facial skeleton (Horovitz and MacPhee, in press a).

Natural History and Ecology: As Xenothrix is known only as a fossil taxon from cave sites, aspects of its autecology have to be framed inferentially. Inferences based on skeletal remains are mainly concerned with interpreting dental function (e.g., Rosenberger, 1977; Szalay and Delson, 1979) and locomotor adaptations (MacPhee and Fleagle, 1991). Xenothrix has traditionally been regarded as a frugivore (e.g., Szalay and Delson, 1979). Hershkovitz (1974) drew attention to certain similarities in molar morphology between Xenothrix and Daubentonia, a Malagasy lemur that was once thought to feed primarily on insect larvae but is now known also to emphasize fruits, seeds, and plant parts in its diet (Sterling, 1993). As there is no evidence of any thoroughgoing convergence between the Jamaican monkey and the aye-aye (cf. Fleagle, 1999), such structural similarities as exist in the molars of these species are presumably correlated with reliance on softer foods. Fleagle (1999) has remarked on the apparent under-representation of medium-sized frugivores on Greater Antilles. This niche may have been filled by monkeys (and no doubt sloths and certain birds) on larger West Indian islands. Although Xenothrix possessed relatively large bunodont teeth and reduced canines, molar enamel is not thickened (L. Martin, pers. commun.) (fig. 3).

Fig. 3
FIG. 3 : Xenothrix mcgregori (AMNHM 268006), partial skull from Lloyd's Cave (Mantrap entrance) in Jackson's Bay area, recovered in 1996; distance between buccal surfaces of M1s, 26mm.

Although no skeletons of are known, it is clear from the isolated and mostly incomplete postcranials that have been assigned to this species that X. mcgregori was an unusual platyrrhine. Several features of the known limb skeleton suggest a slow quadrupedal locomotor style that has no evident counterpart among extant platyrrhines but was possibly somewhat convergent on sloths (MacPhee and Fleagle, 1991).

Using various indicators, MacPhee and Fleagle (1991) reconstructed the body weight of Xenothrix as lying between 2 and 4 kg (similar to size range found in the extant capuchin monkey, Cebus apella).

Hypodigm is insufficient to investigate sexual dimorphism or skeletal ontogenetic changes. No information on ontogeny and reproduction.

No sites in the interior of the island have yielded bones that are definitely attributable to Xenothrix (but see Remarks), but other aspects of its known occurrences indicate that it was probably able to live in a variety of habitats. For example, the area of Portland Ridge is occupied by dry tropical forest in which few species with large edible fruits occur.

Principal Collections: Holotype and entirety of the known hypodigm is housed in the Department of Mammalogy, American Museum of Natural History, New York, NY 10024 (212-769-5476). Skeletal remains only. Hypodigm content (all accession numbers are AMNHM): 1 partial skull with right and left P3-M2 (268006), 1 partial left maxilla (268007), 3 left mandibles (148198 [holotype], 268001, 268004), 2 proximal humeri (259901, 268005), 1 os coxae (259904), 2 femora (259900, 268003), 2 tibiae (259902, 259903).

Published Imagery: Holotype mandible (Williams and Koopman, 1952; Simons, 1972; Rosenberger, 1977; MacPhee, 1996a; Horovitz and MacPhee, in press a); skull and teeth (Williams and Koopman, 1952; Simons, 1972; Rosenberger, 1977; MacPhee, 1996a, 1996b, 1997; MacPhee and Flemming 1997; Horovitz and MacPhee, 1999, in press a; Weintraub, 1997); mandible (MacPhee 1997); postcranials (MacPhee and Fleagle, 1991; Horovitz and MacPhee, in press a).

Selectivity of Extinction within Major Group: Taxa within major group (Callicebinae) considered extant at beginning of modern era: 2 genera, 14 species (Groves’ [1993] list + Xenothrix following Horovitz and MacPhee [1999]). Taxa that became completely extinct in modern era: 1 genus, 1 species. Taxa listed as currently threatened (IUCN, 1996): 3 Vulnerable and 1 Data Deficient species (6 threatened subspecies also listed). Current distribution: Callicebus is continental and mostly distributed in Amazonian areas of South America (Fleagle, 1999). Notes: Fewer than 13 species of Callicebus are recognized by the majority of primate systematists. Late Quaternary continental diversity of major group is uninvestigated paleontologically. It is assumed to be same as modern, but this may be an oversimplification (cf. Hartwig, 1995). Antillothrix and Paralouatta should be counted as Quaternary callicebines, but as they are not known to have survived into the modern era they are not included in selectivity counts.

Xenothrix mcgregori is simultaneously the only genus-level and the only species-level taxon of anthropoid primates for which there is empirical evidence of complete extinction during the modern era.

History of Collection/Observation: Very rarely encountered in cave assemblages (MacPhee, 1997), doubtless because the Jamaican monkey was too large to be preyed upon by owls (MacPhee, 1996b). Principal collections of this species were made by Anthony in 1920 (mandible and several long bones found at Long Mile Cave) and McFarlane, Flemming, MacPhee and their colleagues between 1994 and 1996 (partial skull, partial palate, several long bones found at caves near Jackson’s Bay). The only additional confirmed material is a partial humerus from "New Cave," an unlocated cave also near Jackson’s Bay but probably on the other side of Portland Ridge (K. Koopman, pers. commun.)

The jaw in the Anthony collection was not recognized as that of an endemic primate until Williams and Koopman’s (1952) study. These authors noted the existence of, but did not describe, primatelike postcranials in the collection, which were analyzed by MacPhee and Fleagle (1991). The Jackson’s Bay finds increased the hypodigm substantially (Horovitz and MacPhee, 1999, in press a). At Lloyd’s Cave, a partial skull and palate of Xenothrix were found in surface debris together with remains of Rattus and domestic animals. The monkey fossils were unmineralized and unencrusted, in this regard appearing no different from the remains of definitely post-Contact introduced mammals. Published radiometric dates for sites yielding Xenothrix (e.g., MacPhee, 1984; McFarlane and MacPhee, 1995) are all much older than the Rattus associational evidence discovered in 1996, and therefore have no significance as "last occurrence" dates.

Unambiguous direct observations of this species do not exist. The closest approach is a passage in Sloane’s (1707, 1725) natural history of Jamaica that refers to monkeys " found wild in this island," but it is evident in context that Sloane was simply passing on reports about species of which he had no first-hand knowledge. Indeed, in context it cannot even be said that it was Xenothrix that was being referred to, as opposed to castaways that could have come from South America or Africa. Nevertheless, it still remains possible that Xenothrix survived as late as the early 18th century. This needs to be confirmed by radiometric dating.

Remarks: (1) A "fossil" taxon is here understood to be one that is (a) known only from its hard parts or other remains and (b) was never the subject of a direct observation or recording by a literate observer.

(2) Readers should be aware that intermediate hierarchical levels in Platyrrhini are diversely named and varied in taxic content (see Fleagle, 1998; Horovitz and Mayer, 1997). For sake of uniformity in data presentation, the relevant chapter (Groves, 1993) in Wilson and Reeder’s (1993) compendium is accepted as authority for current classificatory context.

(3) Isolated femurs, evidently platyrrhine, have been reported from Coco Ree Cave and Sheep Pen (Ford, 1990; Ford and Morgan, 1986). If these specimens are attributed correctly, Jamaica must have supported three monkey species in Quaternary, because the Coco Ree and Sheep Pen femora differ considerably from each other and from femora attributed to Xenothrix by MacPhee and Fleagle (1991) and Horovitz and MacPhee (in prep.). The Coco Ree specimen exhibits callitrichid characters according to Ford (1990), but it is much larger than femora of any extant marmosets. Sheep Pen is near Long Mile Cave; Coco Ree is located in Lluidas Vale in the interior of the island.

 

By Ross D. E. MacPhee and Clare Flemming, Department of Mammalogy, American Museum of Natural History, New York NY 10024 (macphee@amnh.org; flemming@amnh.org)

Published by CREO--Committee on Recently Extinct Species in January 1999.

 

References

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