Hyosciurus Archbold and Tate, 1935

Musser, Guy G., Durden, Lance A., Holden, Mary Ellen & Light, Jessica E., 2010, Systematic Review of Endemic Sulawesi Squirrels (Rodentia, Sciuridae), with Descriptions of New Species of Associated Sucking Lice (Insecta, Anoplura), and Phylogenetic and Zoogeographic Assessments of Sciurid Lice, Bulletin of the American Museum of Natural History 2010 (339), pp. 1-260 : 1-260

Hyosciurus Archbold and Tate, 1935

‘‘On the basis then of the extreme length of the nasals of old adults, the shortness of the tail, the long narrow foot, and the pronounced elongation of the claws,—this last perhaps in relation to a shift from arboreal to terrestrial or even semi-fossorial habits—it has seemed advisable to set up a separate genus, which may be named Hyosciurus ,’’ was Archbold and Tate’s (1935: 2) introduction to their description of this remarkable tropical ground squirrel:

A callosciurine genus of squirrel in which the nasal part of the skull reaches an extreme degree of lengthening in the adult (length of nasals exceeds length of frontals); the transverse suture between frontals and parietals forms an irregular, backwardly bowed arch …; nasals and premaxillae strongly produced in front of incisors; molar series carried forward so that the lacrimal is on a level with m2 instead of m1. Angular process of mandible strongly reflected. … Hind foot not typical of the normal sturdy tree-squirrel foot, but long and slender, the width at the base of the 5th metatarsal only 7 mm. (about 14 per cent of foot length, excluding the claws). Claws very long and but little curved; those of the forefoot about 8 mm. (or 80 per cent of length of 4th digit); those of hind foot 7 mm. (nearly 60 per cent of length of 4th digit). Tail very short, from 50 to 70 per cent of length of head and body. Mammary formula not determined.

The holotype and two other specimens were collected by G. Heinrich from Pegunungan Latimojong in central Sulawesi (see gazetteer), and the species was named in his honor, H. heinrichi . Heinrich had also collected two long-nosed squirrels from Gunung Ile-Ile in the northern peninsula of Sulawesi and these were also identified as H. heinrichi by Archbold and Tate (1935). A year later, however, Tate and Archbold (1936: 1) described the sample from Gunung Ile-Ile under the name ileile and arranged it as a subspecies of H. heinrichi . The perception of one species of Hyosciurus with a subspecies occurring on the northern peninsula and another in the central core of Sulawesi persisted ( Ellerman, 1940; Laurie and Hill, 1954) until Musser caught squirrels with both morphologies in the northern portion of central Sulawesi, heinrichi in the mountains and ileile in the lowlands with the two distributed parapatrically at middle elevations (Musser, 1987). Primary checklists of mammals published after 1987 have recognized the two species ( Corbet and Hill, 1992; Hoffmann et al., 1993; Thorington and Hoffmann, 2005).

Archbold and Tate (1935) thought Hyosciurus to be structurally similar to the long-nosed Rhinosciurus laticaudatus found on the Malaya Peninsula, Sumatra, Borneo, and some smaller islands on the Sunda Shelf ( Corbet and Hill, 1992: 302). Ellerman (1940: 398) also compared Hyosciurus with Rhinosciurus but at the same time signaled their trenchant cranial differences, and later, in his volume on additions and corrections to the 1940 treatise ( Ellerman, 1949: 14), noted that: Hyosciurus further differs from Rhinosciurus in having a much shorter proportionate orbit length, which in Hyosciurus is below a quarter of occipitonasal length, as in Nannosciurus . This is interesting because all the Squirrels from Celebes I have seen except the large Callosciurus rubriventer have a tendency to shortening of the orbit, and it suggests that Hyosciurus is not closely allied to Rhinosciurus , but is derived probably from one of the more primitive Celebes Squirrels and has acquired its lengthening of the rostrum quite independently of Rhinosciurus .

Ellerman’s view was supported by diagnostic cranial traits described by Moore (1959) that in his view consolidated the Sulawesian Hyosciurus , Prosciurillus , and Rubrisciurus into a natural group, the subtribe Hyosciurina of tribe Callosciurini ; Rhinosciurus was placed in subtribe Callosciurina , which contained most of the other Indomalayan genera. For Moore (1959: 175), ‘‘Ellerman … noted the important difference between Hyosciurus and Rhinosciurus and quite rightly inferred that they acquired their specializations of extremely long noses separately.’’

Other researchers disagreed. In the early 1940s, Zahn (1942: 116) promulgated the opinion, which was extreme at the time, that Sulawesian heinrichi was simply a species of Sundaic Rhinosciurus . In the 1990s, Zahn’s assessment was given a degree of legitimacy, for Corbet and Hill (1992: 301) allowed that ‘‘ Hyosciurus should perhaps be included’’ in Rhinosciurus and pointed out that both species of Hyosciurus (p. 302) ‘‘have the hair in the mid-line of the nape reversed, often followed by a median parting of hair, about 3–4 cm long, between the shoulders, a condition shared only by Rhinosciurus amongst Indomalayan squirrels.’’

Judged from analysis of molecular data, the shared protracted muzzle and reversed nape fur shared by Hyosciurus and Rhinosciurus do not signal close phylogenetic affinity—but instead, independently acquired morphologies associated with the evolution of long-nosed ground squirrels in tropical Asian rain forests. Analyses of the nuclear IRBP and mitochondrial 12S and 16S ribosomal DNA used by Mercer and Roth (2003) recovered a squirrel phylogeny that included a monophyletic group containing Rubrisciurus , Prosciurillus , and Hyosciurus separate from a cladistic cluster formed by Callosciurus , Rhinosciurus , and their relatives (see section on classification). Within the Sulawesian clade, Rubrisciurus is more closely related to the species of tree squirrels in Prosciurillus than to the morphologically divergent ground squirrels in Hyosciurus . The results from this molecular inquiry unambiguously support the hypotheses presented by Ellerman (1949) and Moore (1959) and not the assessments of Zahn (1942) or Corbet and Hill (1992).

Previously published descriptions defining Hyosciurus are incomplete or inaccurate so we provide here an emended generic diagnosis. The following combination of traits will distinguish Hyosciurus from other nannosciurine genera (see comparative measurements summarized in table 3, and compare skulls illustrated in figures 6, 12–14, 36, 37): (1) diurnal and terrestrial; (2) elongate muzzle; (3) dark brown upperparts flecked with buff and black, without ear tufts, nape patches, or dorsal stripes, but with hair reversed on nape followed by a median parting for 10–40 mm; (4) underparts completely white or cream, or with white or cream swath marked by dark brownish gray strips and patches, or broken into segments separated by brownish gray ventral fur; (5) tail short, slightly less than half the length of head and body; (6) hind feet long and slender; (7) claws very long relative to length of foot (25%–35% the length of the front foot) and only slightly shorter than the digits, thin, and slightly curved; (8) three pairs of teats (one abdominal and two inguinal); (9) rostrum elongate, nasals longer than width of interorbital region, as long as frontals in H. heinrichi but shorter than frontals in H. ileile (nasals 83%–86% of length of frontals), nasals and premaxillaries project well beyond anterior faces of upper incisors to form a short tube; (10) orbit short (indicated by lacrimal and posterior margin of zygomatic plate even with second upper molar); (11) posterior processes of the frontals about even with posterior wall of suborbit (the space between postorbital process and braincase); (12) jugal component of zygomatic arch low relative to size of skull; (13) low temporal ridges meet and fuse in adults 3–5 mm before occiput to form a short and wide sagittal crest (about 15% of parietal length); (14) anterior opening of the infraorbital canal lies far posterior to the premaxillary-maxillary suture (a reflection of the protracted rostrum), is not concealed by a bony flange of the ventral zygomatic root, the anteroventral lip of the canal is thick (almost forming a large tubercle), and the outer surface rough for insertion of the superficial masseter; (15) no transbullar septa (see Moore, 1959); (16) pterygoid fossa narrow and shallow in H. heinrichi , its lateral margin outlined by a low, inconspicuous ridge (the ‘‘ectopterygoid ridge’’ of Moore, 1959, which he thought was absent from skulls of Hyosciurus ); (17) posterior border of bony palate even or slightly posterior to caudal margins of third molars; (18) descending palatine vein typically transmitted through a foramen (posterior maxillary foramen) at the posterolateral margin of bony palate just caudad and slightly medial to end of tooth row; (19) braincase shorter relative to skull length (as measured by PPL/ONL: 40% for Rubrisciurus ; 38%–40% for species in the P. leucomus group; 37% and 35% for P. murinus and P. abstrusus , respectively; 32% and 33% for Hyosciurus heinrichi and H. ileile , respectively; computed from means listed in tables of measurements); (20) upper incisors orthodont in configuration relative to the rostrum (emerging from the rostrum at a right angle); (21) maxillary tooth rows parallel; (22) third upper premolar present, fourth premolar and first and second molars wider (labial-lingual distance) than long (anterior-posterior length), third molar nearly circular in coronal view (about as wide as it is long).

Hyosciurus shares number of teats with Prosciurillus (both have three pairs, including two inguinal pairs, but the anterior pair is postaxillary in position in Prosciurillus , not abdominal as in Hyosciurus ); a short orbit, parallel maxillary tooth rows, third upper premolar, and fourth premolar and first and second premolars that are wider than long with both Rubrisciurus and Prosciurillus ; the union of temporal ridges to form a sagittal crest anterior to the occiput with Rubrisciurus (but the temporal ridges are stronger, and the crest is longer in Rubrisciurus , forming one-third to three-fourths of the parietal length, depending upon age); and the position of the postorbital processes relative to the anterior margin of the braincase, and the relative size of the third molar with Prosciurillus . The combination of the other features in the diagnosis is unique to the Sulawesian ground squirrels.

Accounts of the two species of Hyosciurus are provided below. Qualitative morphological and quantitative morphometric comparisons between the two species are described and geographic and altitudinal distributions are outlined as derived from the collection localities of voucher specimens. The distinctiveness of the two species as defined by morphology and altitudinal distribution is supported by their sucking lice parasites. Each species of squirrel hosts a unique species of Hoplopleura (see the descriptions of sucking lice in the next section).

GAZETTEER AND SPECIMENS EXAMINED: Collection localities for the 53 specimens of H. heinrichi and the 14 examples of H. ileile studied are listed below. The number preceding each locality keys to a symbol on the map in figure 35.

Hyosciurus heinrichi

1. Gunung Kanino, 01 ° 179S, 120 ° 089E (estimated from Sheet SA 50-8), 4850 ft (1479 m): AMNH 225483, 225484.

2. Gunung Kanino, 5040 ft (1537 m), AMNH 225485; 5100 ft (1555 m), AMNH 225486.

3. Gunung Kanino, 5150 ft (1570 m): AMNH 225487.

4. Gunung Nokilalaki, 01 ° 139S, 120 ° 089E, 5700 ft (1738 m): AMNH 223541.

5. Gunung Nokilalaki, 5800 ft (1768 m): AMNH 223543, 223545, 225598.

6. Gunung Nokilalaki, 6500 ft (1982 m): AMNH 225465.

7. Gunung Nokilalaki, 6800 ft (2073 m): AMNH 225466, 225467; 6850 ft (2091 m), AMNH 225468.

8. Gunung Nokilalaki, 7000 ft (2134 m): AMNH 225469.

9. Gunung Nokilalaki, 7200 ft (2195 m): AMNH 225470.

10. Gunung Nokilalaki, 7300 ft (2226 m): AMNH 223542, 224544, 223548, 225471.

11. Gunung Nokilalaki, 7400 ft (2256 m): AMNH 225472, 225473; 7450 ft (2271 m), AMNH 223551.

12. Gunung Nokilalaki, 7500 ft (2287 m): AMNH 223546, 223547, 223549, 223550, 225474–82.

13. Pegunungan Takolekaju (‘‘Molengraff Range,’’ the old European name for the mountain range, is notated on the specimen tags; no more precise collection locality is available; P. Jenkins, in litt., 2008), an extensive mountainous region in the western portion of the central core with the north-south boundaries between approximately 01 ° and 02 ° 159S, and extending slightly diagonally from about 119 ° 459E in the north to 120 ° near its southern ramparts, 4000–4300 ft (1220–1312 m): BMNH 40.641 –40.652, 74.97.

14. Pegunungan Latimojong, 03 ° 309S, 121 ° 239E: 1600 m: AMNH 101311.

15. Pegunungan Latimojong, 2200 m: AMNH 101309; AMNH 101310 (holotype of Hyosciurus heinrichi ), 196506.

We also examined BMNH 40.691b, 40.691c, and 40.691d from Tamalanti in Central Sulawesi, a place not indicated on the distribution map. Tamalanti, visited by the collector W.J.C. Frost in 1938, is a ‘‘Plantation between Rantekaroa [02 ° 509S, 119 ° 509E] and Koelawi [01 ° 279S,119 ° 599E]’’ ( Laurie and Hill, 1954: 156), which was also the only information Musser and Paula Jenkins found when they searched through fieldnotes and other documents at BMNH. No elevation is notated on the specimen tags. Laurie and Hill (1954: 156) indicated that most of the animals collected by Frost at Tamalanti were recorded as coming from 3300–3800 ft (1006–1159 m), which seems too low for H. heinrichi .

Hyosciurus ileile

1. Gunung Ile-Ile, 00 ° 589N, 121 ° 489E (part of the larger Pegunungan Peleleh forming the mountainous backbone of the northwestern portion of the northern peninsula), 1700 m: AMNH 101308 (holotype of Hyosciurus heinrichi ileile ), 196507.

2. Tolai, Sungai Tolewonu, 01 ° 049S, 120 ° 279E (estimated from Sheet SA 50-8), 550 ft (168 m): AMNH 226497.

3. Tolai, Sungai Tolewonu: 950 ft (290 m), AMNH 226498; 1100 ft (335 m), AMNH 226499.

4. Valley of Sungai Miu, Sungai Sadaunta (also spelled ‘‘Sidaonta’’ or Sidaunta’’; tributary on right side of Sungai Miu), 01 ° 239S, 119 ° 589E (estimated from Sheet SA 50-8), 2900 ft (884 m): AMNH 224618.

5. Sungai Sadaunta, 3000 ft (915 m): AMNH 224619.

6. Sungai Sadaunta, 3150 ft (960 m): AMNH 224620.

7. Gunung Kanino, 01 ° 179S, 120 ° 089E (estimated from Sheet SA 50-8), 4600 ft (1402 m), AMNH 225459–62.

8. Gunung Kanino, 4800 ft (1463 m): AMNH 223540.

9. Gunung Kanino, 4960 ft (1512 m): AMNH 225463.