phylogenetic relationships and classification of didelphid marsupials ...

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22 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 322 ular morphology, Chironectes is unique among didelphids in lacking any trace of pedal plantar pads. The eleuthrodactylous hind foot of Dromiciops resembles the common didelphid morphotype in having a large opposable hallux, a grooming claw on dII, dIV . dIII, and dermatoglyph-bearing plantar pads (Hershkovitz, 1999: fig. 21). By contrast, the hind foot of peramelids is syndactylous (with fused dII and dIII; Hall, 1987; Weisbecker and Nilsson, 2008); the hallux is small and effectively nonopposable in caenolestids (Osgood, 1921: pl. 2, fig. 3), dasyurids (Thomas, 1888: pl. 23, fig. 8), and peramelids (Lyne, 1951: fig. 12); dIII and dIV are subequal in examined caenolestids and dasyurids, both of which groups also lack a grooming claw on dII; peramelids do not have distinct plantar pads; the plantar pads of caenolestids are smooth; and the plantar pads of some dasyurids are tubercular. The plantar epithelium of the heel is macroscopically naked in most of these outgroup taxa, but the underside of the heel is coarsely furred in some dasyurids (e.g., Sminthopsis crassicaudata). POUCH AND MAMMAE: Based on our firsthand examination of parous adult female specimens, pouchlike enclosures for nursing young are unequivocally present or absent among didelphids. Although our sample sizes were always small, we observed no intraspecific variation in this aspect of female reproductive morphology, nor did we observe any intermediate condition between absence and presence of a pouch. Despite the fact that several distinctly different pouch configurations can be recognized among opossums, we provisionally recognize all pouches as homologous in the absence of a priori evidence to the contrary. We found no trace of a pouch in suitable material (fluid-preserved specimens and carefully prepared skins) of parous adult female Cryptonanus, Glironia, Gracilinanus, Hyladelphys, Lestodelphys, Marmosa, Marmosops, Metachirus, Monodelphis, Thylamys, and Tlacuatzin. By contrast, well-developed pouches were consistently found to be present in suitably prepared parous adult females of Caluromys, Chironectes, Didelphis, and Philander. Although Lutreolina was described as pouchless by Thomas (1888), Cabrera (1919), and Marshall (1978a), two fluid-preserved parous females that we examined (UMMZ 166634, USNM 536827) had pouches exactly resembling the morphology illustrated and described by Krieg (1924: fig. 11). Caluromysiops is said to have a pouch (Izor and Pine, 1987; Reig et al., 1987), but no explicit description or illustration of the female reproductive anatomy of this genus is available, nor were we able to examine suitably preserved parous female specimens. The presence or absence of a pouch remains undocumented for many opossums, notably Chacodelphys. Contradictory literature accounts of a pouch as present or absent in Metachirus were discussed by Voss and Jansa (2003). The marsupium of Caluromys philander uniquely consists of deep lateral skin folds that enclose the nursing young and open in the midline (resembling the morphology that Tyndale-Biscoe and Renfree [1987: fig. 2.8] incorrectly attributed to didelphids in general). In Caluromys lanatus, Didelphis, and Philander, however, the lateral pockets are joined posteriorly, forming a more extensive enclosure that opens anteriorly (Enders, 1937: fig. 19). Yet another condition is exhibited by Chironectes and Lutreolina, in which the lateral pockets are connected anteriorly, forming a marsupium that opens posteriorly (Krieg, 1924: fig. 11A; Oliver, 1976: fig. 1B). In all marsupials that possess a pouch the mammae are contained within it, but the mammae of pouchless taxa are variously distributed (Tate, 1933: fig. 3). In most pouchless didelphids (e.g., Glironia, Marmosa, Metachirus) the mammae are confined to a more or less circular inguinal/abdominal array that occupies the same anatomical position as the pouch in taxa that possess a marsupium. However, other pouchless opossums (e.g., Cryptonanus guahybae, Marmosops incanus) have bilaterally paired mammae that extend anteriorly well beyond the pouch region. Although most of these anterior teats are not actually located on the upper chest, they are usually referred to as ‘‘pectoral’’ or ‘‘thoracic’’ mammae (e.g., by Tate, 1933; Reig et al., 1987). Most didelphids have, in addition to bilaterally paired mammae, an unpaired
2009 VOSS AND JANSA: DIDELPHID MARSUPIALS 23 median teat that occupies the ventral midline approximately in the center of the circular abdominal-inguinal array (fig. 5B). Mammary counts for didelphids are therefore usually odd-numbered, an allegedly diagnostic attribute previously noted by Bresslau (1920), Osgood (1921), and Tate (1933, 1947, 1948a). The only exceptions that we have encountered are Caluromys lanatus, Glironia venusta, 4 and Hyladelphys kalinowskii (fig. 5A), examined females of which have four mammae in two abdominal-inguinal pairs with no trace of a median teat. By convention, didelphid mammary complements are summarized by formulae representing the rightside (R), median (M), left-side (L), and total (T) teat counts in the format R–M–L 5 T. Thus, the mammary complement of the illustrated specimen of Marmosops parvidens could be written as 4–1–4 5 9, whereas that of Hyladelphys kalinowskii would be 2–0–2 5 4. Occasionally, lateral teats are unpaired, resulting in even-numbered totals for taxa that possess an unpaired median teat, but such anomalies are easily distinguished by formulae (e.g., 3–1–4 5 8 if the anteriormost right teat of AMNH 267344 were really missing in fig. 5B). Among other plesiomorphic marsupials that we examined, a marsupium is absent only in caenolestids and some dasyurids (e.g., Murexia). The pouch of Dromiciops consists of lateral skin folds opening medially (Hershkovitz, 1999: fig. 14), whereas the pouches of other dasyurids are variously configured (Woolley, 1974), and those of peramelids open posteriorly. Most nondidelphid marsupials lack an unpaired median teat, and therefore normally have even-numbered mammary counts, but an unpaired median teat is said to be present in Rhyncholestes (e.g., by Osgood, 1924; Patterson and Gallardo, 1987). CLOACA AND MALE GENITALIA: In most didelphids the openings of the urogenital and rectal ducts are inguinal, closely juxtaposed, 4 A parous adult female specimen with 2–0–2 5 4 mammae was recently collected near Iquitos, Peru, by M. Monica Díaz, whose observations confirm Marshall’s (1978c) report of four teats based on an old museum skin (FMNH 41440). The Iquitos specimen (with field number MMD 607) will be deposited in the Museo de Historia Natural de la Universidad Nacional Mayor de San Marcos (M.M. Díaz,personalcommun.). Fig. 5. Mammary morphology of adult female specimens of Hyladelphys kalinowskii (A, AMNH 267339) and Marmosops parvidens (B, AMNH 267344). Only two pairs of inguinal-abdominal teats are present in H. kalinowskii, which is unusual among didelphids in lacking an unpaired median teat; its mammary formula is 2–0–2 5 4. By contrast, the illustrated specimen of M. parvidens has four pairs of inguinal-abdominal teats plus an unpaired median teat (4–1–4 5 9).
Page 1 and 2: PHYLOGENETIC RELATIONSHIPS AND CLAS
Page 3 and 4: CONTENTS Abstract .................
Page 5 and 6: ABSTRACT This report summarizes a d
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