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Taxonomy of the Pleistocene giant beaver Castoroides (Rodentia: Castoridae) from the southeastern United States

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  • New Mexico Museum of Natural History and Science

Abstract and Figures

Two late Pleistocene skulls of Castoroides from Florida share a suite of morphologic features with two partial skulls from the early Pleistocene of Florida (including the holotype of Castoroides leiseyorum Morgan and White, 1995) and a late Pleistocene skull from South Carolina. These specimens are regarded as conspecific and can be readily distinguished from skulls of Castoroides ohioensis Foster, 1838 from the northeastern and midwestern United States by a number of characters including absence of a mesopterygoid fossa, shorter sagittal crest, lambdoidal crest strongly inflected anteriorly at midline of skull, larger postorbital process and incisive foramen, cheektooth rows less divergent posteriorly and located more anteriorly (relative to maxillary process of zygomatic arch), and a more massive premaxilla without an anterior protuberance. All Florida samples of Castoroides are now regarded as belonging to a single species that is not Castoroides ohioensis. The rule of nomenclatural priority requires raising Castoroides ohioensis dilophidus Martin, 1969 to the rank of species, Castoroides dilophidus, and regarding it as the senior synonym of Castoroides leiseyorum Morgan and White, 1995. The dental character which formed the basis for the subspecies name dilophidus is only known to occur in some late Pleistocene teeth from peninsular Florida and coastal Georgia, and is not present in all populations of the species C. dilophidus.
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BULLETIN
TAXONOMY OF THE PLEISTOCENE GIANT BEAVER
CASTOROIDES (RODENTIA: CASTORIDAE) FROM THE
SOUTHEASTERN UNITED STATES
Richard C. Hulbert Jr., Andreas Kerner, and Gary S. Morgan
Vol. 53, No. 2, pp. 26–43 November 10, 2014
ISSN 2373-9991
UNIVERSITY OF FLORIDA GAINESVILLE
TAXONOMY OF THE PLEISTOCENE GIANT BEAVER CASTOROIDES
(RODENTIA: CASTORIDAE) FROM THE SOUTHEASTERN UNITED STATES
Richard C. Hulbert Jr. 1, Andreas Kerner2, and Gary S. Morgan3
1Florida Museum of Natural History, University of Florida, Gainesville, Florida, USA 32611-7800; <rhulbert@mnh.u.edu>
2P.O. Box 336, Sparta, New Jersey, USA 07871 <intlfossils@msn.com>
3New Mexico Museum of Natural History and Science, 1801 Mountain Road NW, Albuquerque New Mexico, USA 87104
<gary.morgan1@state.nm.us>
Hulbert Jr., R. C., A. Kerner, and G. S. Morgan. 2014. Taxonomy of the Pleistocene giant beaver Castoroides (Rodentia: Castoridae) from the
southeastern United States, Fiji. Bulletin of the Florida Museum of Natural History 53(2):26–43. https://www.mnh.u.edu/bulletin/
publications/
ABSTRACT
Two late Pleistocene skulls of Castoroides from Florida share a suite of morphologic features with two
partial skulls from the early Pleistocene of Florida (including the holotype of Castoroides leiseyorum
Morgan and White, 1995) and a late Pleistocene skull from South Carolina. These specimens are regarded
as conspecic and can be readily distinguished from skulls of Castoroides ohioensis Foster, 1838 from the
northeastern and midwestern United States by a number of characters including absence of a mesopterygoid
fossa, shorter sagittal crest, lambdoidal crest strongly inected anteriorly at midline of skull, larger
postorbital process and incisive foramen, cheektooth rows less divergent posteriorly and located more
anteriorly (relative to maxillary process of zygomatic arch), and a more massive premaxilla without an
anterior protuberance. All Florida samples of Castoroides are now regarded as belonging to a single
species that is not Castoroides ohioensis. The rule of nomenclatural priority requires raising Castoroides
ohioensis dilophidus Martin, 1969 to the rank of species, Castoroides dilophidus, and regarding it as the
senior synonym of Castoroides leiseyorum Morgan and White, 1995. The dental character which formed
the basis for the subspecies name dilophidus is only known to occur in some late Pleistocene teeth from
peninsular Florida and coastal Georgia, and is not present in all populations of the species C. dilophidus.
Key words: Castoroides dilophidus; Rodentia; Pleistocene; synonymy; taxonomy; Florida.
TABLE OF CONTENTS
Introduction ............................................................................................................. 27
Materials and Methods ............................................................................................29
Systematic Paleontology ......................................................................................... 29
Discussion ............................................................................................................... 36
Acknowledgements ................................................................................................. 40
Literature Cited ....................................................................................................... 40
Appendix ................................................................................................................. 42
27 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL. 53(2)
INTRODUCTION
Along with the capybara Neochoerus, the giant
beaver Castoroides is one of two large-sized
rodents that is a member of the extinct Pleistocene
megafauna of North America, with a mass
currently estimated to have been about 60 to 100
kg (Reynolds, 2002; Hopkins, 2008). Historically,
the genus was best represented by fossils from the
northeastern and north-central United States (e.g.,
Wyman, 1846; Moore, 1890; Martin, 1912; Hay,
1914; Barbour, 1931; Engels, 1931; Erickson,
1962; Stirton, 1965), while its overall distribution
ranged from southern Canada to Alabama and
Florida in the east, to Oregon, the Yukon Territory,
and Alaska in the west (Cahn, 1932; Kurtén and
Anderson, 1980; Parmalee and Graham, 2002;
Harington, 2011). Although several species were
named in the nineteenth and very early twentieth
centuries, through most of the twentieth century
the general consensus was that the genus was
monotypic, with Castoroides ohioensis Foster,
1838 as the valid species name (Hay, 1914, 1923;
Stirton, 1965; Kurtén and Anderson, 1980; Martin,
1992).
In contrast to the skulls, mandibles, and
two skeletons known from the northern part of its
range, records of Castoroides from the southeastern
United States long consisted of only isolated
teeth and postcranial bones (Hay, 1923; Martin,
1969, 1975). Nevertheless, these specimens were
routinely assigned to Castoroides ohioensis. Martin
(1969) observed that some of the upper third molars
(M3s) and most of the lower fourth premolars (p4s)
of Castoroides from the Santa Fe River Basin in
northern peninsular Florida had a split or divided
loph/lophid, and used this character to diagnose the
subspecies Castoroides ohioensis dilophidus. This
subspecies name has been little used subsequently
in the scientic literature. Morgan and White (1995)
described the rst crania of Castoroides from the
Southeast, two early Pleistocene specimens from
Leisey Shell Pit 1 in central Florida (Site 3 in
Fig. 1). On the basis of several characters, most
notably the lack of the distinctive mesopterygoid
fossa that is present in C. ohioensis (Wyman, 1846;
Stirton, 1965), Morgan and White (1995) proposed
that the Leisey specimens belonged to a distinct
species that they named Castoroides leiseyorum.
Because of the older age of C. leiseyorum (early
Pleistocene) relative to all then known skulls of
C. ohioensis (middle or late Pleistocene), and
because the features of C. leiseyorum appeared to
be plesiomorphic relative to those of C. ohioensis,
the assumption was that the differences between
the two was primarily due to their different ages,
not their geographic distributions. Thus, after
the description of C. leiseyorum, late Pleistocene
specimens of Castoroides from Florida continued
to be referred to C. ohioensis and not C. leiseyorum
(e.g., Hulbert, 2001; Schubert et al., 2010).
Parmalee and Graham (2002) were the rst to
describe a skull of Castoroides of late Pleistocene
age from the southeastern United States; a specimen
from the Cooper River, South Carolina. This
specimen unexpectedly had the cranial features of
Castoroides leiseyorum instead of C. ohioensis,
which created a number of possible taxonomic
options. As discussed by Parmalee and Graham
(2002), these included: 1) a single, variable species,
with northern and southeastern populations possibly
distinguished as subspecies; and 2) two species,
one in the southeast and one for the remainder of
its range. Not discussed by Parmalee and Graham
(2002) is a three-species option, with a widespread
early Pleistocene species (i.e., C. leiseyorum) and
two late Pleistocene species, one for southeastern
North America and one for northern, midwestern,
and western North America. Parmalee and Graham
(2002) chose not select among these options, due to
the absence of late Pleistocene skulls from Florida
and lack of a link between crania with the features
of C. leiseyorum and teeth with the features of C.
ohioensis dilophidus. They recognized that the two
species-level names based on Florida specimens
of Castoroides might prove to be synonyms, with
Martin’s name having priority.
We report here two late Pleistocene crania of
Castoroides from Florida, the rst such specimens
to be described, and discuss their taxonomic
ramications. We also analyze a much larger
sample of teeth from Florida than were available
to Martin (1969), to better determine the range
HULBERT ET AL.: Castoroides from the southeastern United States 28
Figure 1. Locations of fossil sites in Florida containing specimens of Castoroides dilophidus. Numbers
correspond to those in the Appendix, which lists each site’s name and referred specimens. Squares are
early Pleistocene localities; triangles, middle Pleistocene; circles, late Pleistocene; and pentagons, undif-
ferentiated Pleistocene.
29 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL. 53(2)
of variation in the dental characters he used to
diagnose Castoroides ohioensis dilophidus and
their geographic and chronologic distributions. All
currently known fossil localities in Florida with
Castoroides are indicated in Figure 1 and listed in
the Appendix..
MATERIALS AND METHODS
Dental terminology and measurements follow
Woodburne (1961); terminology for cranial
features follows Stirton (1965). Standard dental
abbreviations are used (i, lower incisor; I, upper
incisor; m, lower molar; M, upper molar; p, lower
premolar; P, upper premolar; following numeral
indicates tooth position). All measurements in mm.
Chronologic boundaries for the Pleistocene Epoch
follow Gibbard et al. (2010).
Of the two skulls of Castoroides that
form the primary basis for this report, one was
collected by scuba divers from submerged deposits
in Lake Rousseau, a dammed reservoir of the
Withlacoochee River in north-central Florida
(Site 27 in Fig. 1). Fossils recovered from Lake
Rousseau were previously discussed by Schubert
et al. (2010), and include many of the common
late Pleistocene mammals found in Florida, such
as Holmesina septentrionalis, Tapirus veroensis,
and Palaeolama mirica. No taxa characteristic
of the early or middle Pleistocene (late Blancan or
Irvingtonian) have been found in Lake Rousseau.
The second new cranium of Castoroides was
collected in the lower Aucilla River in northern
Florida (Site 35 in Fig. 1), a region with numerous
latest Pleistocene deposits with abundant vertebrate
fossils (Mihlbachler et al., 2002; Webb and Simons,
2006). As was the case with Lake Rousseau, no
early or middle Pleistocene fossils are known from
this region. The Aucilla River skull is housed in
a private collection, but a high delity cast is in
the UF collection. Furthermore, the owner of the
original specimen has agreed to make it available
for study to other workers (contact RCH to make
arrangements).
The cranial morphology of Castoroides
ohioensis has been thoroughly described by Wyman
(1846), Martin (1912), Hay (1914), and especially
Stirton (1965). Their observations were conrmed
through direct examination of a very well preserved
specimen from Indiana, USNM 1634.
InstItutIonal abbrevIatIons
AMNH, American Museum of Natural
History, New York; SC, South Carolina State
Museum, Columbia; MMNS, Mississippi Museum
of Natural Science, Jackson; UF, Vertebrate Pale-
ontology Division, Florida Museum of Natural
History, University of Florida, Gainesville; UF/
FGS, Florida Geological Survey collection, now
housed at UF; UF/TRO, Timberlane Research
Organization collection, now housed at UF; USNM,
United States National Museum, Smithsonian
Institution, Washington, DC.
SYSTEMATIC PALEONTOLOGY
Order RODENTIA BOWDICH, 1821
Family CASTORIDAE HEMPRICH, 1820
Subfamily CASTOROIDINAE ALLEN, 1877
Genus CASTOROIDES FOSTER, 1838
CASTOROIDES DILOPHIDUS MARTIN, 1969
new rank
Castoroides ohioensis dilophidus Martin (1969); Martin
(1975).
Castoroides leiseyorum Morgan and White (1995);
Hulbert Jr. (2001); Parmalee and Graham (2002);
Hopkins (2008); Rinaldi et al. (2008); Samuels
(2009); Rinaldi et al. (2012).
Castoroides ohioensis Foster, Hulbert Jr. (2001), in
part; Schubert et al. (2010), in part.
Holotype.—UF 12404, a left p4 (Fig. 2A).
Type Locality.—Santa Fe River 2, on the
Columbia-Alachua county boundary, north-central
Florida, approximately 29.8° N; 82.7° W (Site
15 in Fig. 1). Fossils from Santa Fe River 2 are
predominantly late Pleistocene (Rancholabrean)
taxa, with a small percentage of early Pleistocene
(late Blancan) taxa. In this it differs from other
stretches on the Santa Fe River, such as Santa Fe
River 1, where Blancan mammals are abundant. A
late Pleistocene age is inferred for UF 12404 (and
all other Santa Fe River specimens of Castoroides)
not only because of the rarity of Blancan specimens
along Santa Fe River 2, but also because none
of the many purely late Blancan sites in Florida
HULBERT ET AL.: Castoroides from the southeastern United States 30
have produced a single specimen of Castoroides
(Morgan and Hulbert, 1995; Hulbert, 2010). Also,
two specimens of Castoroides from the Santa Fe
River were analyzed for rare earth isotopes (REE)
as part of the study by MacFadden and Hulbert
(2009) and they both had relative abundances of
REEs matching late Pleistocene species (e.g.,
Megalonyx jeffersoni, Bison sp., Mammuthus
columbi), and signicantly different from Blancan
taxa.
Chronologic and Geographic Range.—The
species is known from the early Pleistocene (early
Irvingtonian) to late Pleistocene (late Rancho-
labrean) of Florida and the late Pleistocene
of coastal South Carolina. Records from
geographically intermediate coastal Georgia are
assumed to represent Castoroides dilophidus, but
crania to conrm this are lacking (one p4 with a
divided second lophid is known from this region,
supporting referral to this species). Castoroides
dilophidus may have been more widespread in the
southeastern United States, but crania or lower
p4s are needed to distinguish it from Castoroides
ohioensis, so records from intervening regions such
as Tennessee, Mississippi, and Arkansas cannot
be condently referred to a species at this time.
Supposed very early Pleistocene (late Blancan)
records listed by Martin (1969) are actually late
Pleistocene (Morgan and White, 1995).
Referred Specimens.—UF 81736, braincase,
Leisey Shell Pit 1A, Hillsborough Co., FL
(holotype, Castoroides leiseyorum); UF 60868,
braincase, Leisey Shell Pit 1, Hillsborough Co.,
FL; UF 256059, braincase, Lake Rousseau, Marion
Co., FL; UF 258638, nearly complete skull with
broken portions of right and left incisors, Aucilla
River 1, Taylor Co., FL. (cast); SC75.33.1, nearly
complete skull with incisors (missing cheekteeth),
Cooper River, Charleston Co., SC. Additional
specimens listed in Appendix.
Revised diagnosis.—Member of Castoroides
that differs from Castoroides ohioensis in having
shorter sagittal crest; lambdoidal crest strongly
inected anteriorly at midline of skull; better
developed postorbital process; cheektooth rows
less divergent posteriorly and located more
anteriorly (relative to maxillary process of
zygomatic arch); larger incisive foramen; and more
massive premaxilla with greater distance between
the alveoli for incisors and the external nares. Also
differs from C. ohioensis in lacking mesopterygoid
fossa in basisphenoid and pronounced medial
protuberance on the premaxilla ventral to external
nares.
Description and comparison of new Florida
skulls.—Morgan and White (1995) and Parmalee
and Graham (2002) previously described crania
of Castoroides leiseyorum (= Castoroides diloph-
idus herein). Many aspects of the cranial and
dental morphology of Castoroides dilophidus
and Castoroides ohioensis are the same, so these
features will not be emphasized here. Differences
in the development of the internal choane between
the two species were noted by Rinaldi et al. (2012),
and will presumably be described in detail by those
authors in a future work. The two new Florida
crania of Castoroides, along with the two Leisey
braincases, are smaller than average specimens of
C. ohioensis and the Cooper River skull from South
Carolina (Table 1). Some of this can be attributed to
the relatively young age of UF 81736 and 256059,
based on open sutures between the major bones of
the two skulls, but the other specimens have closed
sutures and had apparently reached their nal adult
size. The two sagittal crests have completely fused
to form a single ridge only in UF 60868, while the
others have paired sagittal crests, suggesting they
were not fully mature. But the much larger South
Carolina skull also has paired sagittal crests, so
the difference in size between specimens from
peninsular Florida and more northern regions
appears to be real.
Viewed anteriorly, the external bone surface
of the premaxillae of Castoroides dilophidus is
extremely rugose (Fig. 3). Despite this, in lateral
view the anterior surface of the premaxilla overall
is relatively at (Fig. 4), without the prominent,
anteriorly protruding medial process found just
ventral to the external nares on the premaxillae of
Castoroides ohioensis (Engels, 1931:g. 3; Stirton,
1965:g. 1). The height of the premaxilla between
the external nares and the anterior border of the
31 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL. 53(2)
Figure 2. Cheekteeth of Castoroides dilophidus from the Pleistocene of Florida in occlusal view, anterior
to top of page in all images. A, UF 12404, right p4, Santa Fe River 2, holotype. B, UF 261933, left p4,
Withlacoochee River, C, UF/TRO 5, left p4, Waccasassa River. D, UF 166637, left p4, Santa Fe River
1. E, UF 261934, left p4, Lake Rousseau. F, UF 217396, right p4, Sun City Shell Pit. G, UF 12405, left
M3, Santa Fe River 2. H, UF/TRO 4, right M3, Peace River. I, UF/TRO 9, right M3, Waccasassa River.
Teeth in A–C and G–H have the anomalous ‘dilophid’ enamel pattern; others show the normal Castoroides
pattern. Scale bar is 1 cm.
HULBERT ET AL.: Castoroides from the southeastern United States 32
Figure 3. Anterior view of UF 258638, skull of Castoroides dilophidus from the late Pleistocene of
Florida, showing very rugose, tall premaxillae.
Figure 4. Right lateral view of UF 258638, skull of Castoroides dilophidus from the late Pleistocene of
Florida.
33 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL. 53(2)
incisor is 45–58 mm, compared to about 27 mm in
C. ohioensis.
In dorsal view (Figs. 5A,C; 6A), Castoroides
dilophidus has a relatively small but distinct
postorbital process formed on the squamosal, just
posterior to its suture with the frontal (postorbital
process absent or much weaker in Castoroides
ohioensis; Hay, 1914; Stirton, 1965). The
development of the sagittal crest in C. dilophidus
shows some variation. As in C. ohioensis, the
sagittal crest in C. dilophidus begins with the union
of the right and left frontoparietal crests at the
midline of the skull. In C. dilophidus this junction
occurs at a point even with or posterior to the
zygomatic process of the squamosal, posterior to
the parietal-frontal suture at the midline (Figs. 5C;
6A; also Parmalee and Graham, 2002:g. 4A). In
contrast, the sagittal crest in C. ohioensis begins
at the location of the parietal-frontal suture, well
anterior to the zygomatic process of the squamosal.
Figure 5. Partial skulls (braincases) of Castoroides dilophidus from the Pleistocene of Florida. A, dorsal,
and B, ventral views of UF 60868, Leisey Shell Pit 1, Hillsborough County, early Pleistocene. C, dorsal,
and D, ventral views of UF 256059, Lake Rousseau, Marion County, late Pleistocene.
HULBERT ET AL.: Castoroides from the southeastern United States 34
Figure 6. A, dorsal, and B, ventral views of UF 258638, skull of Castoroides dilophidus from the late
Pleistocene of Florida.
35 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL. 53(2)
Table 1. Measurements on crania of Castoroides dilophidus from Florida and South Carolina, with comparative values of Castoroides
ohioensis from the northern United States.
UF 258638 UF 256059 UF 81736 UF 60868 UF 258889 SC75.33.11C. ohioensis2
greatest length, tip of premaxilla to
post. end of occipital condyle 262 — — — — 289 242–2983
I1 to P4 diastema length 103.2 — — 112.9 98.5–118.5
width of postzygomatic constriction 63.9 71.7 77.7 79.9 72.5 81.6 71.5–88.2
width between outer edges of mastoid
processes 128.9 144.1 141.2 ~135 145.4 150.6 136.5–167.0
height of occiput from base of basi-
occipital to middle of lamboidal crest 59.2 55.3 59.8 62.5 63.6 68.5 62.2–68.0
height of rostrum above incisive
foramen 83.2 — — — — 98.0 78.5–100.0
angle of cheektooth row divergence 23° — — — — 22° 36–47°4
1after Parmalee and Graham (2002).
2range of 5 individuals from Stirton (1965) except where indicated.
3Stirton’s (1965) longest skull, UMMP 3110, is listed as having a length of 397.5 mm, about 100 mm more than the next longest skull. As
other dimensions of this specimen are only slightly larger or in some cases less than the other specimens in his sample, it is assumed that
the provided length is a typographic error and that 297.5 is the correct value.
4range of 5 individuals, USNM 1634 and crania gured by Wyman (1846), Martin (1912), Engels (1931), and Stirton (1965).
HULBERT ET AL.: Castoroides from the southeastern United States 36
As a result, the overall length of the sagittal crest
is greater in C. ohioensis. The lambdoidal crest
in C. dilophidus is deeply indented anteriorly
at the midline where it intersects the terminus
of the sagittal crest, whereas in C. ohioensis it is
relatively straight or only slightly indented. The
postzygomatic crest in C. dilophidus has a sharp
margin anteriorly, but fades near the middle of
the postzygomatic constriction; in C. ohioensis,
a sharp postzygomatic crest encircles nearly the
entire constriction.
In ventral view (Fig. 6B), Castoroides
dilophidus and Castoroides ohioensis differ in
the location of the toothrow in relation to the
zygomatic processes of the maxilla and squamosal.
The toothrow is located more anteriorly in C.
dilophidus, with the anterior border of the P4
alveolus even with the zygomatic process of the
maxilla, and the posterior border of the M3 is
anterior to the level of the zygomatic process of
the squamosal. The toothrow starts posterior to the
zygomatic process of the maxilla in C. ohioensis,
and the posterior border of the M3 is even with
the zygomatic process of the squamosal. In both
species the toothrows diverge posteriorly, such that
the distance between the right and left M3s is much
greater than the distances between the P4s (Fig. 6B).
However, the degree of divergence in C. dilophidus
is about half that observed in C. ohioensis (Table
1). In the two specimens in which it is preserved,
UF 258638 and SC75.33.1, the incisive foramen
is both wider and longer than in USNM 1634 and
other skulls referred to C. ohioensis (Wyman,
1846; Martin, 1912; Stirton, 1965). All skulls from
Florida lack the prominent mesopterygoid fossa on
the basisphenoid (Figs. 5B, 5D, 6B), resembling the
Cooper River skull, and differing from all known
skulls of C. ohioensis (Stirton, 1965; Parmalee and
Graham, 2002).
Another character used to distinguish Cas-
toroides dilophidus from Castoroides ohioensis
by Morgan and White (1995) and Parmalee and
Graham (2002) was a weaker or less developed
median ridge on the ventral surface of the
basioccipital. However, the two Rancholabrean
skulls for Florida, UF 256059 and 258638, have
moderately well-developed medial ridges on the
basiocciptial (Figs. 5D, 6B), within the observed
range of variation of C. ohioensis. Therefore this
character is not considered to be diagnostic for C.
dilophidus.
DISCUSSION
The original description of the subspecies
Castoroides ohioensis dilophidus was based on the
discovery of a high incidence of a dental anomaly
in p4s and M3s collected from the bed of the Santa
Fe River in north-central Florida (Martin, 1969).
The original sample consisted of only six p4s (of
which ve showed the anomaly) and seven M3s (of
which two showed the anomaly). Anomalous p4s
have a divided or split second anterior lophid (Fig.
2A–C; a single individual is known with a divided
rst anterior lophid, Table 2), while the M3s can
have either a divided rst (Fig. 2G) or second (Fig.
2H) posterior loph (or more rarely both). Such
teeth are referred to here as having the ‘dilophid’
pattern. In most such teeth, the divided loph/lophid
can be observed on both the occlusal surface and
at the base of the crown. In a few individuals
(e.g., UF 12405), the loph/lophid is pinched but
not completely divided on the occlusal surface,
but is fully divided at the base of the crown. In
others (e.g., UF 166634), the ‘pinched’ condition
remains consistent through the entire tooth. An M3
with a pinched rst posterior loph on the occlusal
surface and the dilophid pattern at the base of the
crown was described by Woodburne (1961) for a
Blancan specimen of Procastoroides sweeti from
Sand Draw, Nebraska. Woodburne (1961) gured
a second specimen in the same Blancan population
with a pinched anterior loph on a P4, something
we have not observed on any Florida Castoroides
P4. While it is tempting to interpret this as an
indication that the presence of the dilophid pattern
is a retained primitive character in Castoroides
samples from Florida, it is worth noting that all 13
p4s of P. sweeti observed by Woodburne (1961)
had the normal dental pattern, as do all known early
Pleistocene teeth of Castoroides from Florida.
We have greatly increased the size of the
known sample of p4s and M3s of Castoroides from
37 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL. 53(2)
Florida since the publication of Martin (1969), as
well as their geographic coverage through much
of peninsular region of the state (Fig. 1; Table 2;
Appendix). As observed by Martin (1969), the
dilophid pattern is more common in p4s (64%,
n=36) than in M3s (23%, n=39) throughout late
Pleistocene samples from Florida (Table 2). This
difference in frequency of the dilophid pattern
between p4s and M3s is highly signicant (p=
0.0012, Χ2=10.45, d.f.=1). This difference remains
signicant even if the four M3s with the incipient
dilophid pattern are grouped with the fully dilophid
individuals (p<0.01, Χ2=7.00, d.f.=1). The dilophid
pattern is now known to occur much more widely in
peninsular Florida than just the Santa Fe River basin,
including individuals from the Withlacoochee and
Rainbow rivers in west-central Florida, the Peace
River in southwestern Florida, and the Oklawaha
River in northeastern Florida (Fig. 1). Teeth with
the dilophid pattern have been found only in late
Pleistocene samples from Florida (Appendix)
and coastal Georgia. Irvingtonian sample sizes
for p4s and m3s are much smaller than for the
Rancholabrean, but all four known specimens (two
p4s, two M3s) are of ‘normal’ morphology (e.g.,
Fig. 2F). In a small sample of p4s of Castoroides
dilophidus from Andrews Island, Glynn County,
Georgia, one has the dilophid pattern (UF 277389),
while three do not (UF 265146–265148). To date,
none of the many known specimens of Castoroides
ohioensis from the northern and midwestern USA
display the dilophid pattern. Clearly, if dilophid
individuals do exist in C. ohioensis, they must be
very rare. There is no obvious selective advantage of
the dilophid pattern versus the normal one; indeed
it would seem to structurally weaken the tooth
and decrease the amount of functional enamel to
process food, albeit to a minor degree. A reasonable
explanation is that the unusual high frequency of
the dilophid condition in Rancholabrean samples is
the result of a population bottleneck caused when
high sea levels covered much of peninsular Florida
during Marine Isotope Stage 5 (and perhaps other
earlier high stands) resulting in a population crash,
followed by limited gene ow to and from more
continental areas of the USA. This may explain
Table 2. Enamel patterns observed in teeth of late Pleistocene (Rancholabrean) Castoroides dilophidus
from Florida.
lower fourth premolars upper third molars
normal pattern UF 14486, 36625, 46486, 166637,
261931, 261934, 261928, 266253,
276997, 277385, 278364; UF/TRO
28; MMNS VP-3587 [n = 13]
AMNH 94547, 97801a, 97801b; UF
12407–12410, 12463, 14912, 21016,
36622, 36634, 46670, 68339, 261930,
262201, 263661, 265076; 270850,
277386; 278367 UF/TRO 6–9; MMNS
VP-3659 [n = 26]
incipient dilophid
pattern1
UF 12411, 12412, 166634, 261951
[n = 4]
dilophid pattern UF 12404, 12406, 12417, 12427,
12440, 16177, 36628, 258889,
261932, 261933, 261938, 261939,
261949, 261967, 261983, 266321,
266322, 271213, 278363, 278365,
299668; UF/TRO 5, 10 [n = 23]
1st posterior loph divided: UF 14915,
261703, 265141; UF/TRO 4
2nd posterior loph divided: UF 261929,
261950, 262202, 278366
Both posterior lophs divided: UF
12405 [n = 9]
1Second posterior loph partially but not completely divided.
HULBERT ET AL.: Castoroides from the southeastern United States 38
why the dilophid pattern is rarer in late Pleistocene
samples from coastal Georgia than in those from
peninsular Florida.
The late Pleistocene crania of Castoroides
from Lake Rousseau and the Aucilla River
demonstrate that characters formerly believed to be
limited to the early Pleistocene species Castoroides
leiseyorum, and which differed in many ways
from those observed in Castoroides ohioensis,
persisted into the late Pleistocene in Florida.
This is in agreement with the morphology and
presumed late Pleistocene age of the Cooper River
skull from South Carolina described by Parmalee
and Graham (2002). There is no morphological
evidence separating the early Pleistocene Leisey
specimens of C. leiseyorum and the late Pleistocene
specimens of Castoroides from Florida and South
Carolina into separate species, although recovery
of more complete early Pleistocene material
will test this hypothesis. We do not consider the
presence or absence of the dilophid pattern by
itself a valid, diagnostic feature for distinguishing
species of Castoroides. Current fossil evidence
only supports the presence of a single species of
Castoroides in Florida with a chronologic range of
1 to 1.5 million years. Following the principal of
priority, Castoroides leiseyorum is here regarded as
the junior synonym of Castoroides dilophidus. If
more complete early Pleistocene skulls are found
in Florida that differ in the morphology of the
premaxilla and toothrow from the Cooper River
and Aucilla River skulls, then this synonymy could
be reversed and both species regarded as valid. If a
larger sample of early Pleistocene p4s and M3s from
Florida or the Southeast becomes available, and
they prove to completely lack the dilophid pattern,
or have it in a signicantly lower frequency than in
late Pleistocene samples, then the older population
could be recognized as a distinct subspecies.
The company Bone Clones© manufactures
and sells a reproduction of a skull and mandible
of Castoroides (their product number BC-
071). It is marketed under the name Castoroides
ohioensis, and as being “among the largest and
most complete” specimens known, but without
information regarding its place of origin (http://
www.boneclones.com/BC-071A.htm). A brief
discussion on this specimen is needed because copies
likely reside in a number of museum collections
and because it apparently displays a mixture of
cranial features of Castoroides ohioensis (widely
diverging tooth rows) and Castoroides dilophidus
(absence of mesopterygoid fossa, short sagittal
crest, tall premaxillae lacking anterior process,
etc.). The original specimen is now in a private
collection and not available for study. However,
we have had discussions with the collector of
the specimen, as well as the individual who did
the preparation and restoration of the specimen.
The collector revealed that it was found in Lake
Rousseau, Florida, and provided us with drawings
of the specimen made prior to its restoration.
Photocopies of these drawings are stored in the UF
collection along with a cast of the specimen under
the number UF 258889. The drawings reveal that
the cranium was originally recovered in two major
parts, the braincase and the premaxillae with the
incisors, but without the intervening section that
includes the orbits, zygomatic arches, maxillae,
and upper cheekteeth. The missing portions of
the skull, most notably the palate and orbits were
reconstructed based on those of Castor canadensis
and C. ohioensis. The real parts of the cranium have
the features described above for C. dilophidus. The
reconstruction also likely exaggerates the length of
the skull. Measurements taken on those portions of
the cast which are based on original fossil material
fall within the range of C. dilophidus and the lower
half of the range of C. ohioensis (Table 1). For
example, the width between the outer edges of the
mastoid processes on UF 258889 is 145.4 mm,
which is less than in the Cooper River specimen
SC75.33.1 (Parmalee and Graham, 2002).
According to the collector, the original fossils of the
right and left mandibles sold with Bone Clones©
skull BC-071 were found within a few meters of
the skull portions and almost certainly represent
the same individual. The cheekteeth were found
in the mandibles, and both p4s have the dilophid
pattern.
In published abstracts of an as yet unpub-
lished study, Rinaldi et al. (2008; 2012) also
39 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL. 53(2)
supported the separation of Castoroides into two
species, Castoroides ohioensis and what they
termed Castoroides leiseyorum. In addition to
unlisted differences in cranial features, Rinaldi et
al. (2008) concentrated on supposed differences in
the upper incisors between the two species. They
stated that the I1s of “C. leiseyorum” differed from
those of C. ohioensis by having a more pinnate
system of ridges on the anterior enamel and a more
sharply angled distal cutting edge. In addition to
SC75.33.1, we have ve available specimens from
Florida with the intact distal cutting edge of the
I1 (UF 1708, 13030, 17318, 46529, and 258889)
and 11 additional specimens preserving sections
of the I1 >70 mm long (UF 12872, 19412, 46411,
46412, 166631, 268283, 268284, 268285; UF/
FGS 7254; UF/FGS 4888; UF/TRO 25). The
enamel ridge pattern on the anterior face of these
16 specimens is highly variable (Fig. 7). Only
three individuals, UF 12872, 19412, and 46411
Figure 7. Upper incisors of Castoroides dilophidus from Florida in anterior view. A, UF 12872. B, UF
19412. C, UF 13030. D, 17318. E, UF 46529. F, UF/TRO 25. G, UF 166631. Distal cutting edge complete
in C, D, and E. A–B and E–G are rights; C and D are lefts, but are reversed so as to appear to be from the
right side. In all cases, lateral is to the left on the images, medial to the right, and distal to the bottom.
HULBERT ET AL.: Castoroides from the southeastern United States 40
have a highly pinnate ridge pattern (one or two
central ridges straight, medial and lateral ridges
slanted). In the other 12, some had predominantly
slanted medial ridges and straight lateral ridges
(e.g., UF 17318, 268284), some predominantly
straight medial ridges and slanted lateral ridges
(e.g., UF 13030, 46529, 268285), and some with
predominantly straight ridges on both sides of the
tooth (UF 46412, 166631, UF/TRO 25). Likewise,
the angle made by the distal cutting edge relative to
the long axis of the tooth is highly variable, ranging
from about 25 to 45°, and broadly overlapping the
range observed in C. ohioensis. The large range of
individual variation observed in these characters,
some between individuals from the same locality,
suggests that they are not suitable for distinguishing
between species. Also, the claim by Rinaldi et al.
(2008) that most of the enamel ridges meet the
distal cutting edge of the I1 at right angles in “C.
leiseyorum” is not observed in our specimens from
Florida (Fig. 7C–E).
Until diagnostic cranial specimens are
described from other regions of the southern US,
the geographic range of Castoroides dilophidus is
best considered to be limited to Florida and coastal
regions of Georgia and South Carolina. Likewise,
the range of Castoroides ohioensis should be
restricted to the area and chronologic interval
from which it is known from skulls, namely the
late Pleistocene of New York, the Great Lakes
region (Indiana, Ohio, Illinois, Minnesota, and
southern Michigan), and the northern Great Plains
(specically Kansas and Nebraska; Martin, 1912).
Fossils from other regions or different geologic
intervals are best referred to Castoroides sp.
ACKNOWLEDGEMENTS
We thank Robert Allen, Kent Ainsley, Steven
Alter, Mark Anderson, Robert Armistead, Eddie
Brawner, Pierce Brodkorb, Joseph Dumont,
Tony Estevez, William Faucher, Frank Garcia, T.
Goodwin, Richard Herr, Mitchell Hope, Bill Hunt,
Steve Hutchens, Cliff Jeremiah, Paul Karrow, Eric
Kendrew, Chet Kirby, Larry Lawson, P. Miniear,
Craig Nesbit, James Pendergraft, Norman Randall,
Mark Renz, Michael and Siena Searle, Don
Shaw, Robert Sinibaldi, Michael Stallings, Robert
Suarez, N. Thomas, Barbara and James Toomey,
John Waldrop, William Wallace, and Ben Waller
for donating specimens of Castoroides to the UF
collections. The curators and staff of the USNM,
MMNS, and AMNH allowed RCH to study
specimens in their care. Two anonymous reviewers
provided helpful comments and suggestions that
improved the manuscript. This is University of
Florida Contribution to Paleobiology 645.
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APPENDIX
Florida fossil localities with referred specimens of
Castoroides dilophidus. Site numbers match those
in Figure 1.
Early Pleistocene (early Irvingtonian Land
Mammal Age)
1. Tucker Borrow Pit, Brevard County. UF 137999,
phalanx.
2. Crystal River Power Plant, Citrus County. UF
17318, I1; UF 17319, M3; UF 17320, molar; UF
133904, axis vertebra.
3. Leisey Shell Pit 1, Hillsborough County. UF
60868, braincase; UF 80464, partial pelvis; UF
81736, braincase; UF 83119, 86862 astragali.
4. Leisey Shell Pit 2, Hillsborough County. UF
125214, partial cheektooth.
5. Leisey Shell Pit 3, Hillsborough County. UF
115965, mandible with i1, p4-m3 (Morgan and
White 1995:g. 2); UF 124563, lower molar; UF
132047, 219950, 241862 partial cheekteeth; UF
225740, M3; UF 160757, pelvis.
6. Sun City Shell Pit, Hillsborough County. UF
217395, M3; UF 217396, p4.
7. Fort Green Mine, Polk County. UF 24016, molar;
UF 95637, femur.
Middle Pleistocene (late Irvingtonian or early
Rancholabrean Land Mammal Ages)
8. Tri-Britton Site, Hendry County. UF 209380,
astragalus.
9. La Belle Highway Pit, Hendry County. UF
214399, astragalus.
10. Oldsmar 1, Pinellas County. UF 143695, distal
i1; UF 266757, lower molar.
11. Dickerson Coquina Pit, St. Lucie County. UF
266750, P4.
Late Pleistocene (late Rancholabrean Land
Mammal Age)
12. Paynes Prairie 1, Alachua County. UF 12457,
lot of 11 cheektooth and incisor fragments; UF
13030, I1; UF 265141, M3.
13. Ichetucknee River, Columbia County. UF 1708,
I1.
14. Santa Fe River 1, Columbia County. UF 10537,
166631–166633, 166648, 268284–268285, I1s; UF
166637, p4; UF 12410, 166634, M3s; UF 166638,
lower molar; UF 11871, 166634–166636, upper
molars; UF 10536, 10597, molars; UF 16782,
humerus; UF 244579, metacarpal 5; UF 10433,
10538, 10541, 157021, partial femora.
15. Santa Fe River 2, Columbia County. UF 12404,
12406, 12417, 12421, 12427, 12440, UF/TRO
28, p4s; UF 12405, 12407–12409, 12411, 12412
M3s; UF 12413, 12416, 12420, upper molars; UF
12419, 12422, 12423, 12442, 12450, 14925, lower
molars; UF 12414, 12415, 12418, 12424–12426,
12428, 12429, 12441, 12443–12449, 12451,
12452, 12453, 54351–54359, 54361, molars; UF
12430–12436, 268283, incisors; UF 12437–12439,
mandible fragments; UF 16782, distal humerus;
UF 12454–12455, partial femora; UF 54360, distal
tibia. UF 244580–244581, calcanea.
Santa Fe River 3, Columbia County. UF 277385,
p4; UF 277386, M3; UF 277389–277340, molars.
16. Santa Fe River 8, Columbia County. UF 12964,
partial incisor.
17. Santa Fe River 9, Columbia County. UF 16176,
incisor fragment; UF 16177, p4.
18. Santa Fe River (no specic locality), Columbia
County. UF/FGS 4888, I1; UF 261928, 266321,
266322, 278363, MMNS VP-3587 p4s; UF/FGS
4867, lower molar; UF 261929, 261930, 262201,
M3s; UF 11477, UF/FGS 4792, upper molars; UF
135779, i1.
19. Peace River, De Soto County. UF 266253, p4;
UF 265076, 263661, UF/TRO 4, M3s; UF 224037,
incisor fragment; UF 238549, astragalus.
43 BULLETIN FLORIDA MUSEUM NATURAL HISTORY VOL. 53(2)
20. Prairie Creek, De Soto County. UF 156797,
incisor fragment.
21. Peace River, Hardee County. UF 261703, M3.
22. Waccasassa River, Levy County. UF 19196,
299668, UF/TRO 5, UF/TRO 10, p4s; UF 14912,
14915, 270850, UF/TRO 6–9, M3s; UF 13978,
14911, 14913, upper molars; UF 46667–46669,
299669-299670 molars; UF 14909, 14910, 46663–
46666, 299667 I1s; UF 203815, i1.
23. Bradenton, Manatee County. AMNH 97801
lot of six cheekteeth including two M3s and eight
incisor fragments.
24. Eureka Lock, Marion County. UF/FGS 7258–
7261, upper molars; UF/FGS 7262, lower molar;
UF/FGS 7254, I1; UF/FGS 7255–7256, i1s.
25. Oklawaha River, Marion County. UF 68338,
mandible with m2-m3; UF 36625, 36628, 261949,
261967, 261983, p4s; UF 68340, 261958, 261968,
lower molars; UF 68341, 261952–261957, 261969,
261970, 261981, 261996, upper molars; UF 36622,
36634, 68339, 261950, 261951, M3s; UF 36623,
36624, 36626–36633, 68165, 68166 molars; UF
261959, 261960, I1s; UF 261961, i1; UF 68344,
261962, partial humeri; UF 68345, partial radius;
UF 36660, 261994, ulnae; UF 68346, partial
femur; UF 261965, partial tibiobula; UF 261995,
astragalus; UF 68347, 261966, calcanea; UF
261963, metatarsal; UF 36612, 36620, 68167,
68348, phalanges.
26. Withlacoochee River, Marion County. UF
14486, mandible with p4-m1; UF 46486, 261932,
261933, p4s; UF 12463, MMNS VP-3659, M3s;
UF 46528, lower molar; UF 46529, I1; UF 60847,
distal humerus.
27. Lake Rousseau, Marion County. UF 256059,
braincase; UF 261934, p4; UF 258889, cast of
associated braincase, premaxillae with I1s, and
mandibles with right and left i1, p4-m3.
28. Rainbow River, Marion County. UF 243542,
243543, partial incisors; UF 271213 p4.
29. North Fernandina Beach, Nassau County. UF
223127–223131, partial cheekteeth, UF 223123–
223126, partial incisors.
30. St. Johns Lock, Putnam County. UF/FGS 8732,
8837, upper molars; UF/FGS 8731, I1; UF/FGS
8734, four partial incisors; UF/FGS 8838, distal
tibiobula; UF/FGS 8733, astragalus.
31. Cross Florida Barge Canal near Rodman,
Putnam County. UF/FGS 10062, lower molar.
32. Venice Ditch, Sarasota County. AMNH 94547,
M3.
33. Coleman 3, Sumter County. UF 16647, lower
molar.
34. Branford 2A, Suwannee County. UF 261940,
partial i1; UF 261937, petrosal; UF 261938, partial
mandible with p4; UF 261939, p4; UF 261941,
lower molar; UF 261942, astragalus.
35. Aucilla River 1, Taylor/Jefferson counties. UF
258638 (cast), skull; UF 204915, 245044, partial
incisors.
36. Blue Springs, Volusia County. UF 276997, p4.
37. Cypress Spring Run, Washington County. UF/
FGS 4718, incisor.
38. Suwannee River, exact county unknown. UF
261931, 278364, 278365 p4; UF 262202, 278366,
278367 M3.
Pleistocene (Irvingtonian or Rancholabrean
Land Mammal Age)
39. Apollo Beach, Hillsborough County. UF 60860,
frontals and parietals; UF 61912, molar.
40. Rim Ditch Canal, St. Lucie County. USNM
244229, partial I1.
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Publication Date: November 10, 2014
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... The first appearance of Castoroides in the fossil record is in Florida and dates to the Irvingtonian I NALMA (1.9 mya to 900,000 BP) 2,77,78 . There is a more or less continuous record of Castoroides in the southeast, where the oldest known species of giant beaver, Castoroides leiseyorum, is assumed to have given rise to both Castoroides ohioensis and Castoroides dilophidus 79 . Unlike C. ohioensis, it appears that C. dilophidus remained confined to the southeast (Florida, Georgia, South Carolina, and Virginia) during the Rancholabrean NALMA (240,000 to 11,000 year BP) 79,80 . ...
... There is a more or less continuous record of Castoroides in the southeast, where the oldest known species of giant beaver, Castoroides leiseyorum, is assumed to have given rise to both Castoroides ohioensis and Castoroides dilophidus 79 . Unlike C. ohioensis, it appears that C. dilophidus remained confined to the southeast (Florida, Georgia, South Carolina, and Virginia) during the Rancholabrean NALMA (240,000 to 11,000 year BP) 79,80 . Virtually all specimens from Florida have been collected from river systems and many lack precise contextual information 80 . ...
Article
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This is a multi-individual (n = 11), stable carbon and nitrogen isotope study of bone collagen (δ13Ccol and δ15Ncol) from the giant beaver (genus Castoroides). The now-extinct giant beaver was once one of the most widespread Pleistocene megafauna in North America. We confirm that Castoroides consumed a diet of predominantly submerged aquatic macrophytes. These dietary preferences rendered the giant beaver highly dependent on wetland habitat for survival. Castoroides’ δ13Ccol and δ15Ncol do not support the hypothesis that the giant beaver consumed trees or woody plants, which suggests that it did not share the same behaviours as Castor (i.e., tree-cutting and harvesting). The onset of warmer, more arid conditions likely contributed to the extinction of Castoroides. Six new radiocarbon dates help establish the chronology of the northward dispersal of the giant beaver in Beringia, indicating a correlation with ice sheet retreat.
... Castoroides leiseyorum Morgan and White, 1995;Parmalee and Graham, 2002. Castoroides dilophidus (Martin, 1969 Hulbert et al. (2014) determined that C. leiseyorum is the junior synonym of C. dilophidus (Martin, 1969). This, in turn, resulted in their referral of the other known specimens of Castoroides from Florida, Georgia, and SC (the Southeastern Coastal Plain) to C. dilophidus, noting several characters that distinguish it from C. ohioensis, now putatively restricted to the northeastern and mid-continental USA and Canada. ...
... This, in turn, resulted in their referral of the other known specimens of Castoroides from Florida, Georgia, and SC (the Southeastern Coastal Plain) to C. dilophidus, noting several characters that distinguish it from C. ohioensis, now putatively restricted to the northeastern and mid-continental USA and Canada. Although SC2015.17.6, the right p4 from the Cooper River, does not have the "dilophid" pattern in which the second anterior lophid of the p4 is divided as do many of the specimens from Florida, Hulbert et al. (2014) do not consider this morphology as necessarily diagnostic or characteristic of C. dilophidus because of individual variation of this feature. ...
Article
Within this article we provide updated correlations of many of the lithostratigraphic units within the outer Coastal Plain of South Carolina to the most up-to-date marine oxygen isotope stages. We note the first viverravid from the Atlantic Coastal Plain (Didymictis proteus) and provide new information regarding the timing of certain Neotropical immigrant taxa into the southeastern USA. This includes the oldest record of Erethizon, capybara and, possibly, Allophaiomys plioceanicus in the USA. Numerous additional new taxonomic records for the state are documented.
... Because the subspecies C. o. dilophidus is based on a lower premolar tooth character that is not found in all specimens at the type locality and because the species C. leiseyorum is based on skull characters, a clear understanding of their taxonomic relationships, if any, cannot be determined with the material now in hand. Hulbert et al. (2014) suggest there may be, in fact, two distinct species of giant beaver from the Late Pleistocene of the eastern United States: one in the southeast (C. dilophidus), which would also include C. leisyorum, and one in the north (C. ...
... Interestingly, three Martin (1969) suggested this bilophid dental variation may be a trait characteristic of an Atlantic Coastal Plain subspecies ranging from Florida to at least Maryland. Hulbert et al. (2014) noted in their study of Castoroides that the dilophid pattern of the p4 was present in 36 specimens, or 64% of specimens from Florida; however, they did not conclude this character was of specific distinction but a population variable. ...
Article
A small but significant assemblage of Late Pleistocene mammals was recovered from an eroding shoreline at Paw Paw Cove, located on the Chesapeake Bay side of Tilghman Island, Talbot County, Maryland. Additionally, Clovis-age (11,050–10,800 radiocarbon [14C] years before present) artifacts were found in a lag deposit beneath a loess deposit at the site. An accelerator mass spectrometry date obtained from an organic stratum below the loess at the same location suggests that this small fossil assemblage is approximately 21,000 years old. Identifiable taxa include four extinct species, Castoroides sp. (giant beaver), Equus sp. (horse), Tapirus veroensis (Vero tapir), and Mammut americanum (American mastodon), along with Canis cf. C. latrans (coyote), and Cervus elaphus (wapiti). Significantly, the tapir and giant beaver are the first records for Maryland, and the tapir is the first record from the Coastal Plain of the Chesapeake region of Delaware, Maryland, and Virginia. The provisional identification of Canis cf. C. latrans may represent the first Late Pleistocene record from the Coastal Plain of the Chesapeake region of Delaware, Maryland, and Virginia.
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Modern beavers (Castor) are prolific ecosystem engineers and dramatically alter the landscape through tree harvesting and dam building. Little is known, however, about the evolutionary drivers of their woodcutting behaviour. Here we investigate if early woodcutting behaviour in Castoridae was driven by nutritional needs. We measured stable carbon and nitrogen isotopes (δ¹³C and δ¹⁵N) of coeval subfossil plants and beaver collagen (Dipoides sp.) from the Early Pliocene, High Arctic Beaver Pond fossil locality (Ellesmere Island), in order to reconstruct Dipoides sp. diet. Isotopic evidence indicates a diet of woody plants and freshwater macrophytes, supporting the hypothesis that this extinct semiaquatic beaver engaged in woodcutting behaviour for feeding purposes. In a phylogenetic context, the isotopic evidence implies that woodcutting and consumption of woody plants can be traced back to a small-bodied, semiaquatic Miocene castorid, suggesting that beavers have been consuming woody plants for over 20 million years. We propose that the behavioural complex (swimming, woodcutting, and consuming woody plants) preceded and facilitated the evolution of dam building. Dam building and food caching behaviours appear to be specializations for cold winter survival and may have evolved in response to late Neogene northern cooling.
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Mammoths provide a detailed example of species origins and dispersal, but understanding has been impeded by taxonomic confusion, especially in North America. The Columbian mammoth Mammuthus columbi was thought to have evolved in North America from a more primitive Eurasian immigrant. The earliest American mammoths (1.5 million years ago), however, resemble the advanced Eurasian M. trogontherii that crossed the Bering land bridge around that time, giving rise directly to M. columbi. Woolly mammoth M. primigenius later evolved in Beringia and spread into Europe and North America, leading to a diversity of morphologies as it encountered endemic M. trogontherii and M. columbi, respectively. In North America, this included intermediates (“M. jeffersonii”), suggesting introgression of M. primigenius with M. columbi. The lineage illustrates the dynamic interplay of local adaptation, dispersal, and gene flow in the evolution of a widely distributed species complex.
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the Subcommission on Quaternary Stratigraphy. 2010. Formal ratification of the Quaternary System/Period and the Pleistocene Series/Epoch with a base at 2.58 Ma.
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Fossils of the giant short-faced bear. Arctodus simus (Cope. 1879), have been recovered from over 100 localities in North America, extending from Mexico to Alaska and California to Virginia. Despite this large range, the species has never been recorded from the southeastern United States. The lesser short-faced bear, Arctodus pristinus Leidy, 1854 is well represented from this region, particularly Florida, but all known occurrences are late Pliocene - middle Pleistocene in age (about 2.5 to 0.3 Ma). Differentiating A. simus from A. pristinus can be difficult because large individuals of A. pristinus overlap in size with small individuals of A. simus, and there are few morphological differences. However, these two taxa can be clearly separated based on the relative proportions of their molars and premolars. Two Pleistocene records of A. sinus representing a minimum of three individuals from the Withlacoochee River drainage of central Florida are reported here, Substantially extending the distribution of this massive bear into southeastern North America. A late Pleistocene age for these occurrences is corroborated by an associated Rancholabrean fauna and rare earth elemental analyses. One of the reported individuals is quite large, supporting the hypothesis of extreme sexual dimorphism in A. simus and rejecting a hypothesis of two subspecies.
Article
Four previously unreported records of Castoroides provide sup-portive evidence that the giant beaver probably occurred through-out the southeastern United States, especially along the middle stretch of the Tennessee River. A distal section of an upper right incisor and an incisor fragment of the extinct Pleistocene giant beaver, Castoroides, were recovered from Bell Cave, Colbert County, Alabama. Cave ACb-3, also in Colbert County and con-taining an extensive deposit of late Pleistocene megafauna, yielded a single incisor enamel fragment. A fragment of a left ilium of this beaver was found in a dry stream bed in Ruby Falls Cave, Lookout Mountain, Hamilton County, Tennessee. These four specimens are referred to Castoroides sp. A relatively complete skull of Castoroides has been recovered from the Cooper River, near Strawberry Hill, Charleston County, South Carolina. The cranial characters of this specimen make it referable to Castoroides leiseyorum Morgan and White, 1995, which was described from the Irvingtonian Leisey Shell Pit, Hills-borough County, Florida. The taxonomy of Castoroides from the southeastern United States is uncertain, and at least two different interpretations are possible.
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A variety of estimators have been used by paleontologists for reconstructing body mass of fossil mammals. For rodents, the most commonly used proxy is ml area, although that value is known to overestimate masses in muroid rodents and is generally problematic in rodent taxa in which the ml is either enlarged (as in muroids) or reduced (as in extinct mylagaulids). This paper explores the potential utility of 2 alternative proxies, toothrow length and toothrow area; these measures are shown here to be very tightly correlated with body mass among rodents. Regression within certain clades of the Rodentia provides an even tighter fit. Applying these proxy measures to several fossil rodents provides an estimate of their masses. Comparison to published body masses of extinct rodents estimated from postcrania reveals that body masses for Castoroides and Palaeocastor estimated from femur length are consistent with those from dental proxies but that toothrow-based estimates for Phoberomys, the largest known fossil rodent, are discordant with the mass estimated from limb bone diameter. This difference may be explained by both allometric scaling of limbs and locomotor differences between Phoberomys and the caviomorph rodents on which the limb bone diameter regression was based.