The Anatomy of the World's Largest Extinct Rodent

Article (PDF Available)inScience 301(5640):1708-10 · October 2003with 683 Reads
DOI: 10.1126/science.1089332 · Source: PubMed
Abstract
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 evolutionary 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.
Figures - uploaded by Orangel Aguilera
Author content
All content in this area was uploaded by Orangel Aguilera
Phylogenetic position of Phoberomys superimposed on a phylogeny of caviomorph rodents (23) compared in this study. Thirteen characters and 29 character states were examined in 13 caviomorphs. Relationships among taxa were based on a parsimony analysis of molecular data (23, 24), and Phoberomys was added to that tree in several alternative positions, using the scaffold approach (25). The morphological characters were optimized in these different topologies. The most parsimonious placement for Phoberomys was as sister group of Dinomys (47 steps), three steps shorter than the hypothesis of sister group relationship with chinchillas and viscachas and indeed at least three steps shorter than any other hypothesis. Based only on dental traits, Phoberomys has been classified together with the chinchillas and viscachas, with the pakaranas (Dinomys), or as sister group to both. Several postcranial traits support the pakarana hypothesis, represented in this tree: Rectus femoris muscle attachment in pelvis forms an elongated crest; medial and lateral ridges of femoral trochlea convergent proximally; medial condyle wider than lateral condyle in posterior view of femur; medial ridge of astragalar trochlea protrudes posteriorly further than lateral one; anconeal process of ulna extends further cranially than coronoid process. Some of these shared-derived character states of Dinomys and Phoberomys evolved convergently in other caviomorphs. See supplementary information for a complete list of characters, the character matrix, and a list of specimens examined.
… 
References and Notes
1. A. Scott, Nonlinear Science: Emergence and Dynamics of
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).
4. L. F. Mollenauer, R. H. Stolen, J. P. Gordon, Phys. Rev.
Lett. 45, 1095 (1980).
5. E. M. Dianov et al., JETP Lett. 41, 294 (1985).
6. F. M. Mitschke, L. F. Mollenauer, Opt. Lett. 11, 659
(1986).
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
(1937).
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).
16. R. F. Cregan et al., Science 285, 1537 (1999).
17. J. C. Knight et al., IEEE Photon. Technol. Lett. 12, 807
(2000).
18. W. H. Reeves et al., Nature 424, 511 (2003).
19. J. K. Ranka, R. S. Windeler, A. J. Stenz, Opt. Lett. 25,
25 (2000).
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
(2002).
24. Temporal profile of the amplitude of an ideal fiber
soliton is given by secant hyperbolic: sech(t/)
2/(e
t/
e
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
(1998).
28. W. Feller, An Introduction to Probability Theory and
Its Applications (Wiley, New York, 1966), vol. 2, p.
503.
Supporting Online Material
www.sciencemag.org/cgi/content/full/301/5640/1705/
DC1
Fig. S1
27 June 2003; accepted 13 August 2003
The Anatomy of the World’s
Largest Extinct Rodent
Marcelo R. Sa´nchez-Villagra,
1
* Orangel Aguilera,
2
Ine´s Horovitz
3
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
1
Universita¨t Tu¨bingen, Spezielle Zoologie, Auf der
Morgenstelle 28, D-72076 Tu¨bingen, Germany.
2
Uni-
versidad Nacional Experimental Francisco de Miranda,
CICBA, Complejo Docente Los Perozos, Carretera
Variante Sur, Coro, 4101, Estado Falco´n, Venezuela.
3
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-
mail: marcelo.sanchez@uni-tuebingen.de
R EPORTS
19 SEPTEMBER 2003 VOL 301 SCIENCE www.sciencemag.org1708
checked using the new postcranial material.
Estimation of body mass in Phoberomys has
two main limitations: We do not know what
kind of locomotion the animal performed (13),
and its body size was obviously an order of
magnitude larger than that of the largest extant
representatives of its group (14 ). Despite these
caveats, having available both femora and hu-
meri of the same specimen permits the calcu-
lation of a range of body mass. Femora and
humeri provide the most reliable estimates be-
cause they do not share weight-bearing func-
tions with other bones in their limb segments
(15). The body mass is estimated using predic-
tive equations based on anteroposterior diame-
ters of humeral and femoral diaphyses. The
equations are provided on the basis of data for
53 specimens representing 16 species of cavi-
omorphs showing different locomotor habits
(15). The anteroposterior diameter was mea-
sured at 35 and 65% from the distal end for the
humeral and femoral shafts, respectively. The
analysis yields body mass estimates of 436 kg
using the humerus and of 741 kg using the
femur (16 ).
Among caviomorphs and many other mam-
mals, femoral sections tend to have greater an-
teroposterior diameters than do humeral sections
of the same animal (15, 17). Phoberomys had a
gracile forelimb and a disproportionately robust
hindlimb. Tibia and femur are particularly ro-
bust—much more so in Phoberomys in relation
to the rest of the skeleton than is the case in most
extant caviomorphs (18). It is likely that the
hindlimbs of Phoberomys played a more impor-
Fig. 1. Phoberomys
pattersoni.(A) Entire
array of elements of
skeleton (Universidad
Nacional Experimental
Francisco de Miranda,
UNEFM-VF-020) in dif-
ferent views, collected
at ´o Gregorio (11°
1452N, 70°1818W),
in the northern part of
the town of Urumaco.
Most of the skeleton is
preserved with the ex-
ception of several
bones from the hands
and feet, the scapulae,
and the ribs. Thirteen
vertebrae are pre-
served, including the
atlas. (B) Additional
shattered partial skull
in ventral view
(UNEFM-VF-021), pre-
serving most of the
occipital and portions
of the basicranial re-
gion. Collected in El
Hatillo, sector Taparito
(11°1431N/70°1444
W).(C) Lingual and (D)
occlusal view of the left
dentary of UNEFM-VF-
020. (E to L) Miscella-
neous bones of UNEFM-
VF-020. (E) Left innom-
inate, lateral view; (F)
right femur, anterior
view; (G) right femur,
distal view; (H) astraga-
lus, dorsal view; (I) as-
tragalus, ventral view;
(J) humerus, flexor as-
pect; (K) radius; (L) right
ulna, anterior view. Ab-
breviations: an, astraga-
lar neck; ap, anconeal
process; cp, coronoid
process; dc, deltoid
crest; ef, ectal facet;
fm, foramen magnum;
gf, glenoid fossa; gt,
greater tubercle; mc,
medial condyle; mt, medial trochlea; mtr, medial trochlear ridge; p, palate; Rfm, Rectus femoris
muscle attachment; s, mandibular symphysis; sf, sustentacular facet. Bars: (A), 10 cm; (B) to (D), 5
cm; (E) to (L), 5 cm.
Fig. 2. Phylogenetic position of Phoberomys super-
imposed on a phylogeny of caviomorph rodents
(23) compared in this study. Thirteen characters and
29 character states were examined in 13 cavi-
omorphs. Relationships among taxa were based on
a parsimony analysis of molecular data (23, 24), and
Phoberomys was added to that tree in several alter-
native positions, using the scaffold approach (25).
The morphological characters were optimized in
these different topologies. The most parsimonious
placement for Phoberomys was as sister group of
Dinomys (47 steps), three steps shorter than the
hypothesis of sister group relationship with chinchil-
las and viscachas and indeed at least three steps
shorter than any other hypothesis. Based only on
dental traits, Phoberomys has been classified to-
gether with the chinchillas and viscachas, with the
pakaranas (Dinomys), or as sister group to both.
Several postcranial traits support the pakarana hy-
pothesis, represented in this tree: Rectus femoris
muscle attachment in pelvis forms an elongated
crest; medial and lateral ridges of femoral trochlea
convergent proximally; medial condyle wider than
lateral condyle in posterior view of femur; medial
ridge of astragalar trochlea protrudes posteriorly
further than lateral one; anconeal process of ulna
extends further cranially than coronoid process.
Some of these shared-derived character states of
Dinomys and Phoberomys evolved convergently in
other caviomorphs. See supplementary information
for a complete list of characters, the character ma-
trix, and a list of specimens examined.
R EPORTS
www.sciencemag.org SCIENCE VOL 301 19 SEPTEMBER 2003 1709
tant role in locomotor propulsion than the fore-
limbs, which were probably important in food
manipulation. Because of this, the body mass
estimation based on the femur is more reliable:
P. pattersoni probably weighed 700 kg. With
Phoberomys, the size range of the order is in-
creased and Rodentia becomes one of the mam-
malian orders with the widest size variation,
second only to the Diprotodontia (kangaroos,
koalas, wombats, and possums) (fig. S1).
The fossil record of Caviomorpha is exten-
sive, with 140 fossil genera recognized in a
recent review (8), but no form competes with
Phoberomys in terms of size. Artigasia magna
from the upper Pliocene of Uruguay is reported
to be gigantic, but its lower teeth are only
60% the size of those of P. pattersoni (19).
Artigasia, like most fossil rodents, is known
based only on dental and mandibular parts.
The paleoenvironment in which P. patter-
soni was found and the associated fauna indi-
cate that this rodent was either semiaquatic or
foraged in or near water, as capybaras do. P.
pattersoni had a deep and massive horizontal
ramus of the mandible, correlated with a high
degree of hypsodonty. Phoberomys clearly had
an abrasive diet, perhaps consisting of sea-
grasses. Potential predators could have been the
many crocodiles reported from Urumaco, in-
cluding some of the largest forms that ever
existed, such as Purussaurus spp. Contempo-
raries included Stupendemys geographicus, the
worlds largest turtle (20).
References and Notes
1. D. Starck, Lehrbuch der Speziellen Zoologie. Wirbelt-
iere. Teil 5: Sa¨ugetiere (Gustav Fischer Verlag, Jena,
Germany, 1995).
2. J. J. Flynn, A. R. Wyss, Trends Ecol. Evol. 13, 449
(1998).
3. R. F. Kay, R. H. Madden, R. L. Cifelli, J. J. Flynn, Eds.,
Vertebrate Paleontology in the Neotropics. The Mio-
cene Fauna of La Venta, Colombia (Smithsonian In-
stitution, Washington, DC, 1997).
4. Le´xico Estratigra´fico de Venezuela (Ministerio de En-
ergı´a y Minas, Boletı´n de Geologı´a, Caracas, ed. 3,
1997).
5. A. Mones, Ameghiniana 17, 277 (1980).
6. A. Mones, Comun. Paleontol. Mus. Hist. Nat. Montev.
2, 1 (1997).
7. F. R. Negri, J. Ferigolo, Bolet. Mus. Pare. Emı´lio Goeldi
11, 1 (1999).
8. M. C. McKenna, S. K. Bell, Classification of Mammals
Above the Species Level (Columbia Univ. Press, New
York, 1997).
9. S. O. Landry, Univ. Calif. Pub. Zool. 56, 1 (1957).
10. M. G. Vucetich, D. H. Verzi, J.-L. Hartenberger, C. R.
Acad. Sci. Ser. II Sci. Terre Planetes 329, 763 (1999).
11. L. Kraglievich, An. Soc. Cient. Argent. 114, 155
(1932).
12. C. de Paula Couto, Tratado de Paleomastozoologia
(Academia Brasileira de Ciencias, ´o de Janeiro,
1979).
13. B. Demes, W. L. Jungers, Folia Primatol. 52,58
(1989).
14. J. Bertram, A. A. Biewener, J. Morphol. 204, 157
(1990).
15. A. R. Biknevicius , D. A. McFarlane, R. D. E. MacPhee,
Am. Mus. Novit. 3079, 1 (1993).
16. Predictive equations for body size (15): log W log
a b (log AP), where W is body mass (in kilograms),
log a is intercept, b is slope, and AP is the antero-
posterior diameter of the bone examined. Anteropos-
terior proximal femur diameter (APF): log W
1.678 2.518 (1.80618), W 741.1; anteropos-
terior distal humerus diameter (APH): log W
1.467 2.484 (1.6532), W 436.1 kg.
17. A. R. Biknevicius, J. Mammal. 74, 95 (1993).
18. The humerus/femur length ratio (H/F) and the (humer-
us radius)/(femur tibia) length ratio [(H R)/(F
T)] in P. pattersoni (0.76 and 0.78, respectively) are
average compared with those of other caviomorphs. For
a sample of 17 extant caviomorphs, the mean values
SD were H/F 0.80 0.08 and (H R)/(F T)
0.74 0.09. In the sample, there are no marked trends
associated with growth or phylogeny (21). On the other
hand, the ratios between femur versus humerus cross-
sectional diameters (APF/APH) (15) show that the hind-
limbs of P. pattersoni are robust. APF/APH is 1.42,
whereas the average SD for a sample of 19 cavi-
omorph species (21) is 1.27 0.18. Robust hindlimbs in
comparison to forelimbs characterizes also the clade
composed of Dinomys, Chinchilla, and Lagostomus
(mean SD 1.40 0.26), the closest relatives to
Phoberomys among extant caviomorphs.
19. J. C. Francis, A. Mones, Kraglieviana 1, 89 (1966).
20. R. C. Wood, Breviora 436, 1 (1976).
21. M. R. Sa´nchez-Villagra, O. Aguilera, I. Horovitz, un-
published data.
22. R. M. Nowak, Walker’s Mammals of the World ( John
Hopkins Univ. Press, Baltimore, ed. 6, 1999).
23. D. Huchon, J. P. Douzery, Mol. Phylogenet. Evol. 20,
238 (2001).
24. We added Lagostomus to the tree to increase the
relevant sampling in our scaffold analysis. All rel-
evant treatments of caviomorph taxonomy and
phylogeny place Lagostomus together with Chin-
chilla (22).
25. M. S. Springer et al., Proc. Natl. Acad. Sci. U.S.A. 98,
6241 (2001).
26. We thank J. Bocquentin, A. Ranci, A. Rinco´n, J. Reyes,
D. Rodrigues de Aguilera, and R. Sa´nchez for help with
fieldwork; J. Reyes and E. Weston for laboratory work;
E. Weston and three anonymous reviewers for com-
ments on the manuscript; O. Aguilera Jr. for assist-
ance with digital imaging; S. Melendrez for recon-
struction of the skeleton of Phoberomys in Fig. 2; D.
Mo¨rike (Stuttgart) and E. Weber ( Tu¨bingen) for ac-
cess to collections; and J. Bocquentin and A. Ranci for
preliminary work on the identification of the giant
rodent. Work in Venezuela by M.R.S.-V. was partially
supported by the National Geographic Society and
the University of Tu¨bingen. The Smithsonian Tropical
Research Institute and the Universidad Nacional Ex-
perimental Francisco de Miranda (UNEFM) supported
the field and laboratory work of O.A. O.A. is a Re-
search Associate of the Smithsonian Tropical Re-
search Institute.
Supporting Online Material
www.sciencemag.org/cgi/content/full/301/5640/1708/
DC1
SOM Text
Fig. S1
Tables S1 to S3
References
6 May 2003; accepted 6 August 2003
Amazonia 1492: Pristine Forest
or Cultural Parkland?
Michael J. Heckenberger,
1
* Afukaka Kuikuro,
4
Urissapa´ Tabata Kuikuro,
4
J. Christian Russell,
2
Morgan Schmidt,
3
Carlos Fausto,
5
Bruna Franchetto
5
Archaeology and indigenous history of Native Amazonian peoples in the Upper
Xingu region of Brazil reveal unexpectedly complex regional settlement pat-
terns and large-scale transformations of local landscapes over the past mil-
lennium. Mapping and excavation of archaeological structures document pro-
nounced human-induced alteration of the forest cover, particularly in relation
to large, dense late-prehistoric settlements (circa 1200 to 1600 A.D.). The
findings contribute to debates on human carrying capacity, population size and
settlement patterns, anthropogenic impacts on the environment, and the im-
portance of indigenous knowledge, as well as contributing to the pride of place
of the native peoples in this part of the Amazon.
Was the Amazon a natural forest in 1492,
sparsely populated and essentially pristine, as
has been traditionally thought? Or, instead,
were parts of it densely settled and better
viewed as cultural forests, including large
agricultural areas, open parklands, and work-
ing forests associated with large, regional
polities (13). Despite growing popularity for
the latter view (46), entrenched debates re-
garding pre-Columbian cultural and ecologi-
cal variation in the region remain unresolved
due to a lack of well-documented case studies
(7, 8). Here, we present clear evidence of
large, regional social formations [circa (c.)
1250 to 1600 A.D.] and their substantial in-
fluence on the landscape, where they have
altered much of the local forest cover. Spe-
cifically, archaeological research in the Up-
per Xingu (Mato Grosso, Brazil), including
detailed mapping and excavations of exten-
sive earthen features (such as moats, roads,
and bridges) in and around ancient settle-
ments, reveals unexpectedly complex region-
al settlement patterns that created areas of
acute forest alteration.
The Upper Xingu is unique in the south-
ern peripheries of the Amazon as the larg-
est contiguous tract of tropical forest still
1
Department of Anthropology,
2
Land-Use and En-
vironmental Change Institute,
3
Department of Ge-
ography, University of Florida, Gainesville, FL
32611, USA.
4
Associac¸a˜o Indı´gena Kuikuro do Alto
Xingu, Parque Indı´gena do Xingu, Mato Grosso,
Brazil.
5
Department of Anthropology, Museu Nacio-
nal, Universidade Federal do Rio de Janeiro, Quinta
da Boa Vista, Rio de Janeiro 20940 040, Brazil.
*To whom correspondence should be addressed. E-
mail: mheckenb@anthro.ufl.edu
R EPORTS
19 SEPTEMBER 2003 VOL 301 SCIENCE www.sciencemag.org1710
  • Article
    Full-text available
    Neoepiblemidae (Caviomorpha) includes South American hystricognath rodents that together with Chinchillidae and Dinomyidae compose the clade Chinchilloidea. Despite the considerable advance in knowledge of the past decades, these extinct rodents are still poorly studied. To contribute to the taxonomy, systematics, and ontogeny of this group, in this paper we study the cheek tooth morphology of the genus Neoepiblema Ameghino, 1889, from upper Miocene deposits through qualitative and quantitative analyses. For this purpose, we describe the anatomical variation, perform a quantitative analysis using linear measurements, and provide comments on the dental replacement. Based on the cheek tooth morphology, our interpretations indicate that there are two species of Neoepiblema that can be differentiated from each other. Neoepiblema ambrosettianus is not a valid name, and N. horridula, the first described Neoepiblema species, is the senior synonym. Hence, N. acreensis is a valid name for the second species of the genus. In neoepiblemids, the premolar is replaced during the early postnatal period, similar to euhypsodont dinomyids and in contrast to some other euhypsodont caviomorphs (e.g., cavioids), which replace the premolar during the intrauterine stage. These data on dental replacement in neoepiblemids contribute to knowledge about the ontogeny of this extinct rodent group.
  • Chapter
    Full-text available
    Los roedores caviomorfos se encuentran en una gran variedad de hábitats, tienen hábitos diversos, y una gran disparidad en el tamaño corporal. Como consumidores primarios, constituyen una oferta de alimento importante para los predadores. Revisamos 127 trabajos que incluyeron 249 dietas de mamíferos carnívoros con el fin de detectar la presencia de caviomorfos en sus dietas. Identificamos cuales fueron las especies más consumidas y exploramos los posibles patrones de predación a escala biogeográfica. Para esto exploramos la relación entre la frecuencia de ocurrencia (FO) de caviomorfos en la dieta de carnívoros con el peso corporal de éstos y el de sus presas (caviomorfos); con la riqueza específica de las dietas y con posibles variaciones geográficas (latitud y longitud). Por otro lado exploramos la relación entre aspectos de sociabilidad de caviomorfos con la predación por carnívoros, así como la superposición en el tiempo de actividad de predadores y presas (caviomorfos). Finalmente presentamos un estudio que resalta la importancia de dos especies de cavimomorfos como estructurantes de un ensamble de aves rapaces en la estepa Patagónica.
  • Article
    Full-text available
    South America was isolated during most of the Cenozoic, and it was home to an endemic fauna. The South American Native Ungulates (SANUs) exhibited high taxonomical, morphological, and ecological diversity and were widely distributed on the continent. However, most SANU fossil records come from high latitudes. This sampling bias challenges the study of their diversity dynamics and biogeography during important tectonic and biotic events, such as the Great American Biotic Interchange, the faunal exchange between North and South America after the formation of the Isthmus of Panama. We describe new SANU remains from the Neogene of the Cocinetas (northern Colombia) and Falcón (northwestern Venezuela) Basins. In the Cocinetas Basin, the middle Miocene fauna of the Castilletes Formation includes Hilarcotherium miyou sp. nov. (Astrapotheriidae), cf. Huilatherium (Leontiniidae), and Lambdaconus cf. L. colombianus (Proterotheriidae). The late Pliocene fauna of the Ware Formation includes a Toxodontinae indet. and the putative oldest record of Camelidae in South America. In the Falcón Basin, the Pliocene/Pleistocene faunas of the Codore and San Gregorio Formations include Falcontoxodon aguilerai gen. et sp. nov. and Proterotheriidae indet. We provide a phylogenetic analysis for Astrapotheriidae and Toxodontidae. The new data document a low-latitude provinciality within some SANU clades (e.g., Astrapotheriidae, Leontiniidae) during the middle Miocene. This contrasts with the wide latitudinal distribution of clades of other mammals recorded in the fauna, including the sparassodont Lycopsis padillai, the sloth Hyperleptus?, and the proterotheriid Lambdaconus cf. L. colombianus. The Pliocene/Pleistocene tropical faunas from northern South America are characterized by the predominance of native taxa despite their proximity to the Isthmus of Panama (fully emerged by that time). Only one North American ungulate herbivore immigrant is present, a cf. Camelidae indet. The Pliocene and early Pleistocene faunas suggest that environmental changes and biotic interactions affected the diversity dynamics and biogeographic patterns of SANUs during the Great American Biotic Interchange. Cover image: Detail from Figure 34, life reconstruction of the Ware Formation faunal assemblage, Cocinetas Basin, Colombia, by Stjepan Lukac.
  • Article
    Full-text available
    In rodents, and other vertebrates in general, the morphology of tarsal bones, especially the astragalus and calcaneus, has been shown to be tightly linked to locomotor movements. As a result, it has been used to infer locomotor behaviors in extinct species. Recent expeditions in Peruvian Amazonia have led to the discovery of the oldest caviomorph rodent fossils in South America, including two calcanei and one astragalus. The morphologies of these three tarsal bones are described in detail and compared with other extant and extinct caviomorphs. In order to assess and infer the locomotor behaviors of these rodents, linear measurements were taken on these tarsal bones and analyzed via multivariate analyses based on a previously assembled large data set. Both qualitative and quantitative analyses consistently suggest that the osteological adaptations of the astragalus enhance movements for climbing, those of one calcaneus rather enhance movements indicating terrestrial and partly fossorial lifestyle, whereas the other calcaneus may have belonged to a generalist form with a tendency toward a semiaquatic lifestyle. These results fit well with the associated paleoenvironments and hint at ecological diversity early in caviomorph history.
  • Chapter
    The first rodents did not arrive in South America until the mid-Eocene, at about 41 million years ago. This recent discovery makes the history of the caviomorphs extremely interesting, since the earliest known rodents are now known to be from tropical forest and not from dry, savanna-like habitats as previously believed. The group is ancient and is clearly related to the African phiomorph rodents. In this chapter and in Chap. 8, I enjoy describing the probable mode of dispersion of caviomorphs and primates from Africa to South America, since so many have difficulties accepting rafting over the Atlantic Ocean. The history of caviomorphs in South America also includes giant species that appeared during the latter part of the Neogene, culminating in the 1000 kg Josephoartigasia of the Río Plata (Plate River). This chapter also has some original illustrations by Roman Uchytel and by others.
  • Chapter
    Body mass is a fundamental ecological parameter of mammals with implications for a variety of other ecological characteristics. While it cannot be directly measured in fossil taxa, it can be inferred using allometric relationships between skeletal dimensions and mass derived from extant species. Many such relationships have been described, primarily for dental and limb dimensions. Methods of statistical analysis vary widely, however, in ways with substantial implications for the inferred masses of fossil species. The subset of extant species from which the relationship is derived must be representative of the evolutionary and ecological scope of the fossil taxa for which mass is to be estimated. Increasing computing power and an explosion of phylogenetic comparative methods offer the opportunity to gain an understanding of the processes driving these important empirical relationships.
  • Article
    Bats are atypical small mammals. Size is crucial for bats because it affects most aerodynamic variables and several key echolocation parameters. In turn, scaling relationships of both flight and echolocation have been suggested to constrain bat body size evolution. Previous studies have found a large phylogenetic effect and the inclusion of early Eocene fossil bats contributed to recovering idiosyncratic body size change patterns in bats. Here, we test these previous hypotheses of bat body size evolution using a large, comprehensive supermatrix phylogeny (+800 taxa) to optimize body size and examine changes reconstructed along branches. Our analysis provides evidence of rapid stem phyletic nanism, an ancestral value stabilized at 12 g for crown-clade Chiroptera followed by backbone stasis, low-magnitude changes inside established families, and massive body size increase at accelerated rate in pteropodid subclades. Total variation amount explained by pteropodid subclades was 86.3%, with most changes reconstructed as phyletic increases but also apomorphic decreases. We evaluate these macroevolutionary patterns in light of the constraints hypothesis, and in terms of both neutral and adaptive evolutionary models. The reconstructed macroevolution of bat body size led us to propose that echolocation and flight work as successive, nested constraints limiting bat evolution along the body size scale.
  • Article
    We demonstrate the amplification of a wavelength-shifting soliton in an active photonic crystal fiber (PCF). When a redshifting soliton experiences optical gain in a certain spectral range in the active PCF, in addition to its amplification, the redshifting speed of the soliton is increased dramatically and the corresponding pulse width of the soliton can also be reduced down dramatically. The dramatical increase in the redshifting speed is due to the amplification and large pulse compression. Large pulse compression arises because of the self-reinforcing feature of the fundamental soliton during amplification. Furthermore, gain-induced deceleration of the optical soliton causes the collision between the soliton and its corresponding dispersive wave and the generation of the temporal analog of reflection of optical beams. Our experimental results coincided with the simulated results partly.
  • Article
    Full-text available
    South America was isolated from other continents during most of the Cenozoic and it was home of an endemic mammalian fauna. Among the most characteristic faunal elements are the South American native ungulates (SANUs), a group of ungulate-grade mammals that were widespread and highly diverse in the continent. Despite of significant advances, the phylogenetic interrelationships of SANUs are not fully resolved, and remain a major challenge in palaeomammalogy. The evolutionary history of SANUs and other endemic mammals is recorded mostly in higher latitudes; however, most of the mammal diversity today is found in lower latitudes, and there is a need to increase the record of Neotropical fossils in order to better understand the evolution of diversity gradients in mammals. The aim of this dissertation is to study exceptional new fossils that serve to address the phylogenetic relationships of one of the main SANU clades (Notoungulata) with other placentals, and review the systematics and diversity of Neogene mammals based on the documentation of new fossil assemblages from northern South America. Chapter one presents the description of the oldest notoungulate skeleton with associated dental and postcranial remains: Thomashuxleya externa (Isotemnidae, Notoungulata) from the middle Eocene of Patagonia, Argentina. The exceptionally complete specimen is the basis of an estimate of body size of approximately 235 kg; the fossil is integrated in an examination of the phylogenetic hypotheses for the relationships of Notoungulata with other placentals. An analysis combining morphological and molecular data favours a limited number of hypothetical trees, but it cannot definitely arbitrate between affinities of Thomashuxleya with Afrotheria or Laurasiatheria. When constrained as monophyletic with the Pleistocene notoungulate Toxodon (known for collagen sequences), Thomashuxleya is reconstructed on the stem to Euungulata (Perissodactyla + Artiodactyla) or as sister to Perissodactyla. The isolation of South America finished with the formation of the Isthmus of Panama, which established a land connection with North America and facilitated the faunal exchange between the two continents, a biotic event known as the Great American Biotic Interchange (GABI). Chapter two presents a biogeographic analysis of the mammalian faunas in South America from the Miocene to the Pliocene, and a revision of the temporal and geographic distribution of mammals during the GABI. It shows that the tropical and temperate faunas can be clearly differentiated since at least the middle Miocene, and documents a strong sampling bias in the fossil record towards higher latitudes and younger localities, which represents a challenge to paleontological studies of the GABI. Chapter three and four represent contributions towards filling this temporal and geographic gap in the Neotropical fossil record based on the description of new material from the Cocinetas (northern Colombia) and Falcó (northwestern Venezuela) basins Chapter three describes new remains of giant rodents (Neoepiblemidae, Caviomorpha) from the Urumaco Formation (late Miocene), in the Falcón basin. It documents the presence of at least two taxa of neoepiblemids in the assemblage, Phoberomys and Neoepiblema. Furthermore, the dental variation observed suggests that several of the Phoberomys species previously described represent different ontogenetic stages of only few taxa. Chapter four describes Neogene SANU material from the Cocinetas and Falcón basins, and it provides a phylogenetic analysis for Astrapotheriidae and Toxodontidae. In the Cocinetas basin, the middle Miocene fauna of the Castilletes Formation includes Hilarcotherium sp. nov. (Astrapotheriidae), cf. Huilatherium (Leontiniidae), and Neodolodus cf. colombianus (Proterotheriidae). The late Pliocene fauna of the Ware Formation includes Toxodontinae indet. and the oldest record of Camelidae indet. (Artiodactyla) in South America. In the Falcón basin, the Pliocene faunas of the Codore and San Gregorio Formations include Toxodontidae gen. et sp. nov. and Protherotheriidae indet. These new data add evidence to the tropical provinciality documented for Astrapotheria, Leontiniidae during the middle Miocene. The Pliocene faunas from the Ware and San Gregorio formations are characterized by the predominance of native South American taxa, despite their proximity to the Isthmus of Panama. Only one North American ungulate herbivore immigrant is present (Camelidae indet.). The Pliocene faunas also document an important landscape change in the region and suggest that ecological processes. Key words Mammalia, Notoungulata, Litopterna, Astrapotheria, Caviomorpha, Neotropics, Patagonia, Argentina, Colombia, Venezuela, Phylogeny, Biogeography, Eocene, Miocene, Pliocene, Great American Biotic Interchange and biotic interactions could have affected the diversity dynamics and biogeographic patterns of SANUs during the GABI
  • Article
    Full-text available
    The extinct clade of caviomorph rodents Neoepiblemidae includes forms that lived in South America from the early Miocene to Pliocene. Among them is Perimys. The exceptional preservation of ear ossicles in this rodent is described and analyzed in a study of the phylogenetic transformations of these structures in caviomorphs including 21 extant and two extinct genera. Caviomorphs exhibit a conserved malleoincudal complex, with synostosis of the malleus and incus, Bbullet-shaped^ mallear head, and absence of orbicular apophysis. They also show a reduction of the mallear anterior process, in some cases even lacking this structure. The malleoincudal complex of Perimys shows an elongation of the head, but not as marked as in Chinchillinae. The incudal long process of Perimys is slightly more prolonged than the short process, as in chinchillids. In contrast, dinomyids have the incudal long process disproportionally more prolonged than in most caviomorphs. Concerning the disparity of caviomorph middle ear ossicles, Perimys shares the morphospace with chinchillids and other small forms. Within chinchilloids, Perimys is closer to chinchillids than to neoepiblemids.
  • Article
    Full-text available
    Molecular and morphological data have important roles in illuminating evolutionary history. DNA data often yield well resolved phylogenies for living taxa, but are generally unattainable for fossils. A distinct advantage of morphology is that some types of morphological data may be collected for extinct and extant taxa. Fossils provide a unique window on evolutionary history and may preserve combinations of primitive and derived characters that are not found in extant taxa. Given their unique character complexes, fossils are critical in documenting sequences of character transformation over geologic time and may elucidate otherwise ambiguous patterns of evolution that are not revealed by molecular data alone. Here, we employ a methodological approach that allows for the integration of molecular and paleontological data in deciphering one of the most innovative features in the evolutionary history of mammals—laryngeal echolocation in bats. Molecular data alone, including an expanded data set that includes new sequences for the A2AB gene, suggest that microbats are paraphyletic but do not resolve whether laryngeal echolocation evolved independently in different microbat lineages or evolved in the common ancestor of bats and was subsequently lost in megabats. When scaffolds from molecular phylogenies are incorporated into parsimony analyses of morphological characters, including morphological characters for the Eocene taxa Icaronycteris, Archaeonycteris, Hassianycteris, and Palaeochiropteryx, the resulting trees suggest that laryngeal echolocation evolved in the common ancestor of fossil and extant bats and was subsequently lost in megabats. Molecular dating suggests that crown-group bats last shared a common ancestor 52 to 54 million years ago.
  • Article
    Recently discovered deposits containing terrestrial mammal fossils, together with multidisciplinary studies of classical sequences, have yielded dramatic insights into the biotic and environmental history of South America. Notable advances include several new fossil primate taxa, an improved chronology of two major immigration events (caviomorph rodents and new world monkeys), documentation of the oldest mammalian faunas dominated by grazing taxa (which suggests that grasslands appeared at least 15 million years earlier than on other continents), evidence of early biogeographical provinciality within South America, and improved sampling of the best known Cenozoic tropical South American paleofauna.
  • Article
    Full-text available
    We measured the lengths and diameters of four long bones from 118 terrestrial carnivoran species using museum specimens. Though intrafamilial regressions scaled linearly, nearly all intraordinal regressions scaled non-linearly. The observed non-linear scaling of bone dimensions within this order results from a systematic decrease in intrafamilial allometric slope with increasing body size. A change in limb posture (more upright in larger species) to maintain similar peak bone stresses may allow the nearly isometric scaling of skeletal dimensions observed in smaller sized mammals (below about 100 kg). However, strong positive allometry is consistently observed in a number of large terrestrial mammals (the largest Carnivora, the large Bovidae, and the Ceratomorpha). This suggests that the capacity to compensate for size increases through alteration of limb posture is limited in extremely large-sized mammals, such that radical changes in bone shape are required to maintain similar levels of peak bone stress.
  • Article
    The external dimensions of the limb bones and the geometry of their midshaft cross-sections were determined for Loris tardigradus and Nycticebus coucang. Relative cortical thickness, cortical area, and second moment of area were calculated and contrasted with locomotor stresses. The difference in shape-related strength of the bones between the smaller- and the larger-bodied species is more pronounced than can be expected from stresses acting during normal locomotion. The Nycticebus skeleton has a much higher safety margin overall and seems to be dimensioned for infrequent but critical stresses of high magnitude. Lorisine gaits in general are characterized by low ground reaction forces, great mobility in all joints, and a nearly equal share in propulsion and weight-bearing by the fore- and hindlimb. Accordingly, the long bones of lorises (especially those of L. tardigradus) tend to be less rigid than those of other mammalian species (including other primates), they lack a preferential plane of higher bending strength, and femur and humerus do not differ markedly in their capacity to withstand mechanical stresses. External dimensions of the humerus and femur of the two African lorisine species parallel and corroborate these results. Some more general implications for the relationships between bone shape and locomotor stresses are also discussed.