References and Notes
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Coherent Structures (Oxford Univ. Press, Oxford, 1999).
2. A. Hasegawa, M. Matsumoto, Optical Solitons in Fi-
bers (Springer, Berlin, 2003).
3. G. I. Stegeman, M. Segev, Science 286, 1518 (1999).
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7. P. A. Cherenkov, Dokl. Akad. Nauk SSSR 2, 451 (1934).
8. S. Vavilov, Dokl. Akad. Nauk SSSR 2, 457 (1934).
9. I. Frank, I. Tamm, Dokl. Akad. Nauk SSSR 14, 109
10. Cherenkov radiation at speeds below the light thresh-
old has also been recently reported for a spatially
extended system of electric dipoles created by a
femtosecond optical pulse (26).
11. V. E. Zakharov, A.B. Shabat, Sov. Phys. JETP 34, 62 (1971).
12. N. Akhmediev, M. Karlsson, Phys. Rev. A 51, 2602 (1995).
13. For numerous reasons such as, e.g., Cherenkov radiation
or dissipation, most if not all solitons observed in nature
are not the “ideal” ones. To stress the importance of the
nonideal features of the solitons, the term “quasi-soli-
tons” has been introduced and widely used over the last
decade [see, e.g., (27)].
14. J. C. Knight, T. A. Birks, P. St. J. Russell, D. M. Atkin,
Opt. Lett. 21, 1547 (1996).
15. J. C. Knight, J. Broeng, T. A. Birks, P. St. J. Russell,
Science 282, 1476 (1998).
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17. J. C. Knight et al., IEEE Photon. Technol. Lett. 12, 807
18. W. H. Reeves et al., Nature 424, 511 (2003).
19. J. K. Ranka, R. S. Windeler, A. J. Stenz, Opt. Lett. 25,
20. W. J. Wadsworth et al., Electron. Lett. 36, 53 (2000).
21. J. Herrmann et al., Phys. Rev. Lett. 88, 173901 (2002).
22. A. L. Gaeta, Opt. Lett. 11, 924 (2002).
23. J. M. Dudley et al., J. Opt. Soc. Am. B 19, 765
24. Temporal proﬁle of the amplitude of an ideal ﬁber
soliton is given by secant hyperbolic: sech(t/) ⫽
). It is, however, not commonly
known that the Fourier transform of the sech-
function is again a sech-function. This can be
checked, e.g., using Mathematica 4.0 or in (28).
25. C. Luo, M. Ibanescu, S. G. Johnson, J. D. Joannopoulos,
Science 299, 368 (2003).
26. T. E. Stevens, J. K. Wahlstrand, J. Kuhl, R. Merlin,
Science 291, 627 (2001).
27. V. E. Zakharov, E. A. Kuznetsov, JETP 86, 1035
28. W. Feller, An Introduction to Probability Theory and
Its Applications (Wiley, New York, 1966), vol. 2, p.
Supporting Online Material
27 June 2003; accepted 13 August 2003
The Anatomy of the World’s
Largest Extinct Rodent
Marcelo R. Sa´nchez-Villagra,
* Orangel Aguilera,
Phoberomys is reported to be the largest rodent that ever existed, although it
has been known only from isolated teeth and fragmentary postcranial bones.
An exceptionally complete skeleton of Phoberomys pattersoni was discovered
in a rich locality of fossil vertebrates in the Upper Miocene of Venezuela.
Reliable body mass estimates yield ⬃700 kilograms, more than 10 times the
mass of the largest living rodent, the capybara. With Phoberomys, Rodentia
becomes one of the mammalian orders with the largest size range, second only
to diprotodontian marsupials. Several postcranial features support an evolu-
tionary relationship of Phoberomys with pakaranas from the South American
rodent radiation. The associated fossil fauna is diverse and suggests that
Phoberomys lived in marginal lagoons and wetlands.
Phoberomys belongs to the Caviomorpha, a di-
verse and endemic group of South American
rodents that includes arboreal, cursorial, and
fossorial forms and that ranges today in size
between ⬃200 g and ⬃50 kg (1). The evolution
of caviomorphs is recorded in a rich but geo-
graphically biased fossil record. The southern
portion of South America contains most of the
record (2); hence, discoveries in the northern
tropics are of special significance. The Urumaco
Formation in northwestern Venezuela contains
one of the few examples of a diverse fauna of
Upper Miocene vertebrates in the continent. Re-
cent explorations resulted in the discovery of
additional vertebrates in the upper and middle
members of this formation, including the rodent
reported here (table S1). Old and new discover-
ies make Urumaco one of the best-documented
tropical Miocene fossil fauna of vertebrates in
the world after La Venta in Colombia (3).
The Urumaco Formation is characterized
by diverse faunal associations in continental
(savannas), freshwater (swamps and rivers),
estuarine (brackish), and marine (coastal la-
goon, salt marsh, and sandy littoral) environ-
ments (table S1). Each assemblage can be
correlated with a distinctive sedimentary en-
vironment. The following facies are apparent:
shallow-water marine sediments rich in mol-
lusks and fishes; brackish water rich in ma-
rine catfish; and swampy paleoenvironments
rich in crocodilians and gavialids, in fresh-
water and marine turtles, and in freshwater
catfish. These general sequences repeat sev-
eral times in the outcrop (4). The skeleton
reported here was found in brown shales
interbedded with thin layers of coal.
Two specimens of Phoberomys pattersoni
Mones 1980 (5) provide the basis for this re-
port. One consists of an almost complete asso-
ciated skeleton (Fig. 1A). The skull is poorly
preserved and consists of a deformed palate
with the upper molariform series and most of
the dentaries, with molariform teeth and frag-
ments of the incisors. An additional shattered
partial skull, preserving most of the occipital
and portions of the basicranial region, was also
collected (Fig. 1B). Based on the degree of
tooth wear and sutural fusion, we estimate that
the specimens were adults at the time of death.
The proximal epiphysis of the tibia and the
distal epiphysis of the ulna are not fused to the
diaphysis. However, it is possible that the ani-
mal was an adult, because no sutures can be
recognized in the occipital region. In the pa-
karana Dinomys, probably the closest extant
relative of Phoberomys, the epiphyses of long
bones fuse late in ontogeny, some during adult-
hood (6). A description of the anatomy of the
postcranial skeleton of P. pattersoni is present-
ed in the supporting online material.
Allocation of the specimens to P. pattersoni
is secured based on two diagnostic features of
the last upper molar (5): the narrowing of the
posteriormost portion at the level of the last
three prisms, and the size (mesiodistal length: 41
mm; width: 20.7 mm) and relative proportions
of this tooth. Based solely on tooth dimensions,
P. pattersoni is slightly smaller than P. insolita
and P. lozanoi, which have a M3 with a mesio-
distal length of 47 and 48 mm, respectively.
Phoberomys, together with the genera Neo-
epiblema and Eusigmomys, belongs to the fossil
Family Neoepiblemidae, distributed in Argenti-
na, Chile, Brazil, and Venezuela (7). Of all other
species of Neoepiblemidae, cranial remains of
only Neoepiblema ambrosettianus have been
reported to date (7). This animal had a promi-
nent sagittal crest, absent in P. pattersoni. Based
on fragmentary dental remains, Phoberomys
(and therefore the neoepiblemids) has been clas-
sified either with the chinchillas and viscachas
(8), with the pakarana (9), or as the sister group
to both (10). We plotted a set of 13 postcranial
characters on a preexisting phylogenetic tree
based on molecular data and found that several
postcranial features support the association of
Phoberomys with the pakarana (Fig. 2). This
position for Phoberomys was the one that re-
quired the least number of steps.
P. pattersoni is reported to have been the
size of a rhinoceros (1, 11, 12). This rough
estimate, based on isolated teeth, can be
Universita¨t Tu¨bingen, Spezielle Zoologie, Auf der
Morgenstelle 28, D-72076 Tu¨bingen, Germany.
versidad Nacional Experimental Francisco de Miranda,
CICBA, Complejo Docente Los Perozos, Carretera
Variante Sur, Coro, 4101, Estado Falco´n, Venezuela.
Department of Organismic Biology, Ecology, and
Evolution, 621 Young Drive South, University of Cal-
ifornia, Los Angeles, CA 90095–1606, USA.
*To whom correspondence should be addressed. E-
19 SEPTEMBER 2003 VOL 301 SCIENCE www.sciencemag.org1708