Online Supplementary Materials for:

Evolutionary novelty in a rat with no molars

Jacob A. Esselstyn, Anang Setiawan Achmadi, and Kevin C. Rowe S1. SUPPLEMENTARY MATERIALS AND METHODS We collected 15 standard measurements [1] from the skulls of Sulawesi shrew-rats and from Rhynchomys soricoides, an ecologically similar species endemic to Luzon Island, Philippines: greatest length of skull (GLS), zygomatic breadth (ZB), interorbital breadth (IB), length of the rostrum (LOR), breadth of the rostrum (BOR), breadth of the zygomatic plate (BZP), breadth of the braincase (BBC), height of the braincase (HBC), post-palatal length (PPL), length of incisive foramina (LIF), breadth of incisive foramina (BIF), length of bony palate (LBP), breadth of mesopterygoid fossa (BMF), length of auditory bulla (LB), and length of nasal (LON). We also report standard external measurements collected from freshly caught specimens, including total length (TTL), tail length (Tail), hind-foot length including the claws (HF), ear length (Ear), and mass (Mass) in grams. Measurements were taken from only adult specimens, as judged by complete eruption of the molars and/or fully fused cranial sutures. Cranial measurements were taken with digital calipers precise to the nearest 0.01 mm. External measurements were gathered from specimen tags and field notes. Museum acronyms are as follows: AMNH (American Museum of Natural History, New York, USA), FMNH (Field Museum of Natural History, Chicago, USA), and MZB (Museum Zoologicum Bogoriense, Bogor, Indonesia). S2. SUPPLEMENTARY RESULTS Paucidentomys vermidax has a soft pelage, as is the case with Melasmothrix, Rhynchomys, Sommeromys, and Tateomys; Echiothrix, however, has a very spiny pelage. In Paucidentomys, the dorsal fur is soft, long (ca. 9 mm at mid-dorsum), and dark grey at the base, while the distal ca. 2 mm are brown. Soft black guard hairs extend ca. 3 mm beyond the underfur, giving the animal a grey-brown appearance. The ventral pelage is soft with a grey base (ca. 6 mm) and brown tips (ca. 3 mm). The pelage is paler on the venter than on the dorsum, especially on the chest and in the groin area. Rhynchomys soricoides is more distinctly bicolored, with a darker dorsum and lighter venter. Overall, the pelage of Paucidentomys is paler than in Melasmothrix and Tateomys, but slightly darker than in Echiothrix.

Paucidentomys has relatively large ears (21–22 mm, ca. 13% of head and body length) that are ovate and dark brown with sparse, short, brown hairs that are too small to be seen with the naked eye; the ears of the other species are either covered with a sparse coat of short brown and silver hairs (Echiothrix, Melasmothrix, Sommeromys, and Tateomys), or are lightly covered with long white hairs on the interior surface and short dark hairs around the margin (R. soricoides). The mystacial vibrissae of Paucidentomys are black at the base and white at the tip. They are longer (up to ca. 60 mm long, extending beyond the ears when adpressed) than those of Echiothrix, Melasmothrix, Tateomys, and R. soricoides, but similar in relative length to those of Sommeromys.

The tail is longer than head and body in Paucidentomys (ca. 20% longer), Echiothrix, Sommeromys, and both species of Tateomys, but shorter in Melasmothrix and Rhynchomys (table S1). It is bicolored, with a dark grey dorsal surface, and dirty white ventral surface in Paucidentomys. The transition between the dorsal and ventral tail colors is less stark than in Echiothrix. The tail is only very weakly dorso-ventrally bicolored in Tateomys and uniformly dark in Melasmothrix; species of Rhynchomys vary in the distribution of tail pigmentation [2]. In Paucidentomys, the tail is covered in short (ca. 1 mm) hairs that increase in length and apparent density distally; the tail is hairier than in Echiothrix, Melasmothrix, Sommeromys, and Tateomys, but similar to that of R. soricoides. Hairs on

the tail of Paucidentomys are black on the dorsal surface, but on the venter they are either entirely white or black at the base and white at the tip, as in R. soricoides.

The hind feet are somewhat long (37–38 mm, ca. 23% head and body length; table S1) and narrow. The skin on the upper surfaces of the fore and hind feet is dark brown and covered with pale brown, silver, and black hairs, with black hairs becoming less abundant distally, such that the terminal 50% of the fingers and toes are paler than the more proximate dorsal surfaces. On the hind feet, digits 2–4 have relatively long (ca. 5 mm), pale brown hairs emerging from the base of each claw. The dorsal surfaces of the feet of Echiothrix are paler in overall color, while those of Melasmothrix and Tateomys are darker. Rhynchomys tend to have dark fur on the dorsal surfaces of the fore feet, but pale fur over the hind feet. The claws of Paucidentomys are long, sharp, and opaque, except that the pollex has a short, fused nail. Echiothrix, Melasmothrix, Rhynchomys, Sommeromys, and T. macrocercus also have long sharp claws; T. rhinogradoides has especially long, broad nails on the fore feet. The palmar surface in Paucidentomys, which is pale brown, possesses two large metacarpal pads and three smaller interdigital pads; together, they cover most of the palmar surface. The plantar surface is darker and holds a long, thin thenar, a small hypothenar, and four prominent interdigital pads. The thenar is longer and narrower than that of Echiothrix, much longer than those of Melasmothrix, Sommeromys, and Tateomys, and narrower and straighter than that of R. soricoides.

The skull of Paucidentomys is more elongate than those of any other Sulawesi shrew-rat, but similar in general conformation to that of Rhynchomys. The braincase presents a smooth, semi-translucent surface, lacking the relatively square shape with subtle temporal and occipital ridges found in Echiothrix (figure S2). Like the new taxon, Melasmothrix, Sommeromys, and Tateomys have smoothly rounded braincases without prominent ridges. The braincase of Rhynchomys is slightly more angular, but also lacks prominent ridging. The elongate rostrum of the new species is straight and the nasal bones terminate above the upper incisors, curving upward very slightly near their terminus. In the other genera, the nasals extend slightly (Echiothrix, Melasmothrix, Rhynchomys, and Tateomys) to greatly (Sommeromys) beyond the upper incisors and also flare upward near their anterior terminus, especially in Melasmothrix (figure S2). When the skull is viewed laterally, its dorsal margin forms a very slight concave arc from the highest point of the braincase to the terminus of the nasal bones in Paucidentomys and Sommeromys. In Paucidentomys, the cranium is inflated above the orbit, interrupting this concave arc. In Rhynchomys and Tateomys the profile of the dorsal margin of the skull forms a nearly straight line, whereas it is a slightly convex arc in Echiothrix (figure S2). In Melasmothrix this view presents a convex ark to the point where the nasals begin to rise, just posterior of the upper incisors (figure S2).

The zygomatic arches of Paucidentomys form nearly straight lines from their squamosal to maxillary attachments and are more delicate than in the other genera. In Sommeromys the zygomatic arches curve slightly inward. In all other genera examined, the zygomatic arches have a slightly greater lateral bow than in Paucidentomys. Thus the zygomatic breadth is greater than the braincase breadth in Echiothrix and R. soricoides, but roughly equivalent or slightly narrower in Paucidentomys, Melasmothrix, Sommeromys, and Tateomys (table S1). The infraorbital foramina are more ovate in Paucidentomys and Melasmothrix than in the other genera, where they are more triangular.

The palate of the new animal is so long that the vestigial molar alveoli are under the anterior zygomatic plate. This position is slightly more anterior than in Rhynchomys, but far more so than in any of the Sulawesi shrew-rats. The incisive foramina are somewhat long, narrow (table S1), and well anterior of the infraorbital foramen and zygomatic process of the maxillary bone in Paucidentomys, as they are in Melasmothrix, Rhynchomys, and Tateomys (figure S2). However, in Echiothrix and Sommeromys, the infraorbital foramen and zygomatic process of the maxillary overlap with the incisive foramina (figure S2).

In Paucidentomys, Echiothrix, and Rhynchomys, the pterygoid plate, which normally lies just anterior to the auditory bulla, has been lost (figure S2). All other Sulawesi shrew-rats possess

pterygoid plates. The pterygoid processes are small and inconspicuous in Paucidentomys, forming a thin, rounded ridge projecting slightly medial of ventral, narrowing the apparent breadth of the mesopterygoid fossa when viewed from a ventral aspect. The pterygoid processes form posterior-projecting points that flare laterally in Echiothrix, Melasmothrix, Sommeromys, and Tateomys. In R. soricoides, the pterygoid processes are more prominent, but terminate in a blunt point, nearly contacting the bony Eustachian tube. The pterygoid foramen of Paucidentomys is much more posterior than in R. soricoides, lying just anterior to the Eustachian tube and posterior to the sphenopterygoid canal. The sphenopterygoid canal of Paucidentomys is inconspicuous and provides an anteriorly directed passage approaching the palate. However, in Melasmothrix and Tateomys, it is a simple hole, rather than a true canal. In Paucidentomys, the middle lacerate foramen is isolated from the post-glenoid foramen by a partial to complete bridge of bone; these fossae are continuous in Echiothrix, Melasmothrix, Rhynchomys, and Tateomys, whereas they are obscured by the auditory bullae in Sommeromys. In Paucidentomys, a small stapedial foramen and a groove just anterior to the mesopterygoid fossa are present. This groove holds the infraorbital artery, indicating the common pattern of carotid arterial circulation noted in most murids [3]. The same pattern is present in the other shrew-rats. However, Sommeromys possesses a unique carotid circulation pattern, in which the stapedial artery serves only the periotic region [3].

In Paucidentomys, the mandible is long and delicate with little evidence of muscle attachments (figure S2). The coronoid process is a small, inconspicuous protrusion, as in Echiothrix, not an elongate, curved process as in many murids. Melasmothrix and Tateomys have slightly more prominent coronoids, while those of Rhynchomys and Sommeromys are still more robust and more typical of murids (figure S2). The condyle of the dentary in Paucidentomys is very narrow, providing little articular surface, similar to that of Rhynchomys; it is thinner than in any of the Sulawesi shrew-rats. The angular process is thin and of moderate length; it is shorter and blunter in Echiothrix and T. macrocercus, thinner in Melasmothrix, more prominent in Sommeromys, and more triangular in Rhynchomys and T. rhinogradoides (figure S2). The shelf that normally holds the lower molars is very narrow in Paucidentomys, but slight depressions representing vestigial molar alveoli are visible (figure S2). The other genera have broad shelves on the dorsal surface of the dentary body, in which the molars are rooted (figure S2). Overall, the mandible of the new species looks like an extremely stretched, wispy version of the Echiothrix mandible, minus the molars and supporting structures.

The new animal has a dental formula of 1/1 0/0 0/0 0/0 (figure S2). The lack of molars distinguishes it from all other rodents. On the palate there are three very slight depressions on each side, representing the vestigial molar alveoli. Each depression is covered by a thin layer of semi-translucent bone. In MZB 35001, one of the depressions is not completely covered by bone, and a minuscule hole is present. All other Sulawesi shrew-rats have three molars with complex cusps in each quadrant; Rhynchomys has 2 (rarely 3) small, simple molars per quadrant [2]. The bony palate over the position of the alveolus of the third molar appears to be thicker in Rhynchomys and is not translucent like in Paucidentomys. Although the only two known specimens of Paucidentomys lack molars, it is conceivable that some individuals possess very small, rudimentary molars.

The upper incisors of Paucidentomys are bicuspid, sharp, and short (figure S3); all other rodents have unicuspid incisors, but some lineages (e.g. Mus and Musseromys) have a small shelf behind the cutting edge of the incisors. However, these shelves are the product of wear, while the posterior cusp of the incisor in Paucidentomys is the result of developmental processes. The posterior cusp of the incisor varies in stature, being inferior to (FMNH 213102) or approximately equal in prominence (MZB 35001) to the anterior cusp. Both the anterior and posterior cusps terminate in sharp, laterally compressed, triangular points. These projections are connected by a sharp, concave cutting edge at the lateral margin of the tooth. The upper incisors of Paucidentomys and Rhynchomys are rooted shallowly, relative to those in Echiothrix, Melasmothrix, Sommeromys, and Tateomys, giving the appearance that extreme elongation of the rostrum limits rooting depth.

In Paucidentomys and Echiothrix, the lower incisors are separated from each other by a gap of 1–2 mm in preserved specimens. Live Echiothrix, and perhaps Paucidentomys, are capable of separating their lower incisors by 7–10 mm and using them as a pair of forceps to manipulate earthworms (Musser in litt). Most other murids, including the other Sulawesi shrew rats, have lower incisors that are close to each other, with a nearly fixed position (Musser in litt.). In Paucidentomys the lower incisors are also rooted shallowly, with the alveolus terminating below the vestigial molar alveoli. In Echiothrix, the lower incisive alveolus extends beyond the coronoid process, while in Melasmothrix, Sommeromys, and Tateomys the alveolus terminates below the third molar. S3. SUPPLEMENTARY REFERENCES 1 Musser, G. G. & Heaney, L. R. 1992 Philippine rodents: Definitions of Tarsomys and Limnomys

plus a preliminary assessment of phylogenetic patterns among native Philippine murines (Murinae, Muridae). Bull. Amer. Mus. Nat. Hist. 211, 1–138.

2 Balete, D. S., Rickart, E. A., Rosell-Ambal, R. G., Jansa, S. & Heaney, L. R., 2007 Descriptions of two new species of Rhynchomys Thomas (Rodentia: Muridae: Murinae) from Luzon Island, Philippines. J. Mammal. 88, 287–301.

3 Musser, G. G. & Durden, L. A. 2002 Sulawesi rodents: Description of a new genus and species of Murinae (Muridae, Rodentia) and its parasitic new species of sucking louse (Insecta, Anoplura). Amer. Mus. Nov. 3368, 1–50.

S4. SUPPLEMENTARY FIGURES

Figure S1. Maps of (a) Southeast Asia, showing the position of Sulawesi Island and (b) Sulawesi, showing the two localities from which Paucidentomys vermidax has been collected (Mt. Latimojong [circle] and Mt. Gandangdewata [diamond]).

118ºE

1.5ºN

0º

1.5ºS

0–1000 m

>2000 m1000–2000 m

4.5ºS

3ºS

6ºS

120ºE 122ºE 124ºEChina

VietnamPhilippines

Malaysia

Indonesia

500 km

(a) (b)

Figure S2. Images of the crania and mandibles of (a) Paucidentomys vermidax, (b) Echiothrix centrosa, (c) Melasmothrix naso, (d) Rhynchomys soricoides, (e) Tateomys rhinogradoides, and (f) T. macrocercus.

Figure S3. Images of the upper incisors of the holotype of Paucidentomys vermidax, showing (a) oblique (antero-lateral), (b) anterior, and (c) ventral views.

S5. SUPPLEMENTARY TABLES Table S1. Summary of morphometric data from Sulawesi shrew-rats and Rhynchomys soricoides. Presented are the mean (top), standard deviation (middle), and sample size (bottom). Abbreviated variables are defined in the Supplementary Materials and Methods. Species GLS ZB IB LR BR BZP BBC HBC PPL LIF BIF LBP BMF LB LON TTL Tail HF Ear Mass Paucidentomys vermidax

43.28 0.06

2

15.24 0.40

2

5.96 0.32

2

17.55 0.00

2

4.98 0.11

2

1.27 0.12

2

15.36 0.76

2

11.09 0.32

2

17.85 0.50

2

5.64 0.53

2

1.91 0.05

2

9.85 0.12

2

1.63 0.00

2

5.65 0.28

2

16.24 0.05

2

362.5 7.78

2

199.0 1.41

2

37.5 0.71

2

21.5 0.71

2

103.5 6.36

2 Echiothrix centrosa

52.5 1.98

3

22.87 0.97

3

7.04 0.46

3

21.19 1.19

3

7.19 0.50

3

3.52 0.35

3

18.6 0.17

3

14.05 0.40

3

18.1 0.79

3

9.78 0.88

3

3.39 0.17

3

10.08 0.44

3

2.57 0.18

3

5.74 0.16

3

22.16 1.20

3

452.7 15.31

3

240.3 5.03

3

51.67 1.53

3

34.0 1.00

3

257.0 52.0

2 Melasmothrix naso

32.68 0.25

2

14.07 0.12

2

6.19 0.08

3

12.48 0.24

2

5.16 0.31

3

1.28 0.03

3

14.34 0.16

3

8.79 0.28

3

12.26 0.14

3

4.75 0.33

3

1.84 0.11

3

6.09 0.17

3

1.81 0.16

3

5.24 0.23

3

11.25 0.25

2

207.0 7.77

3

88.0 5.0 3

28.0 0.0 3

18.0 1.0 3

48.0 5.0 3

Rhynchomys soricoides

49.53 0.57

4

17.77 0.77

4

6.68 0.36

4

22.45 0.45

4

6.86 0.44

4

1.71 0.17

4

16.94 0.42

4

12.05 0.33

4

16.60 0.32

4

6.73 0.25

4

1.98 0.09

4

14.77 0.39

4

2.18 0.12

4

5.31 0.19

4

19.74 0.19

4

350.7 14.86

4

145.7 9.43

4

41.7 1.71

4

24.5 1.00

4

185.0 8.66

3 Sommeromys macrorhinos

31.80 0.52

4

13.09 0.24

4

5.61 0.16

4

12.02 0.54

4

4.90 0.21

4

1.43 0.03

4

13.24 0.36

4

10.43 0.39

4

9.58 0.37

4

2.90 0.36

3

1.92 0.19

3

6.02 0.26

4

2.01 0.15

4

4.28 0.22

4

11.80 0.37

4

282.5 13.80

4

182.5 8.81

4

30.0 0.82

4

18.3 1.71

4

26.83 3.00

3 Tateomys macrocercus

30.99 - 1

13.73 - 1

6.14 - 1

12.05 - 1

4.97 - 1

1.04 - 1

14.17 - 1

9.41 - 1

11.02 - 1

3.71 - 1

1.95 - 1

6.48 - 1

1.89 - 1

4.19 - 1

11.04 - 1

278 - 1

164 - 1

30 - 1

19 - 1

39 - 1

Tateomys rhinogradoides

39.91 0.31

2

15.31 0.16

2

6.97 0.18

2

14.35 0.01

2

4.89 0.18

2

1.48 0.22

2

15.83 0.52

2

9.90 0.11

2

16.41 0.21

2

5.81 0.06

2

1.99 0.04

2

7.84 0.30

2

2.34 0.10

2

5.46 0.08

2

13.81 0.30

2

319 - 1

175 - 1

38.5 2.12

2

23.0 1.41

2

92.0 0.00

2

S6. SPECIMENS EXAMINED Echiothrix centrosa: AMNH 153013, 225680, 225685 Melasmothrix naso: FMNH 213284, 213447, 213448 Paucidentomys vermidax: FMNH 213102, MZB 35001 Rhynchomys soricoides: FMNH 198883, 198885–198887 Sommeromys macrorhinos: AMNH 226956, MZB 34758, 34759, 34903 Tateomys macrocercus: FMNH 213450 Tateomys rhinogradoides: FMNH 213338, 213434