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Number 3461, 16 pp., 4 figures, 1 table December 30, 2004
Propalaeocastor (Rodentia, Mammalia) from the
Early Oligocene of Burqin Basin, Xinjiang
WENYU WU,! JIN MENG,’ JIE YE,! AND XIJUN NI
ABSTRACT
A new species of castorids, Propalaeocastor irtyshensis, n.sp., from the Burgin Basin of
Xinjiang Uygur Autonomous Region, China, is described. The new species, represented by a
right maxilla with well-preserved P4—M3, is the earliest and northernmost occurrence of cas-
torids in China. It is characterized mainly by the cheek tooth crown being higher than that of
P. butselensis but lower than that of Steneofiber aff. dehmi (probably a new species of Pro-
palaeocastor), and by lingual confluence of the mesoflexus to the lingual fossette of the pre-
mesoflexus. Comparison with known species previously assigned to Steneofiber from Europe
and Kazakhstan leads to the conclusion that the early Oligocene forms previously assigned to
the genus, such as “‘S. butselensis”’ and “‘S. kazachstanicus’’, differ significantly from those
represented by S. eseri from the Late Oligocene and Early Miocene of Europe. We consider
Propalaeocastor a valid genus, provide an emended diagnosis for it, and discuss its evolu-
tionary trend in relation to Steneofiber. Preliminary analysis of Burgin fauna suggests an age
of early Early Oligocene. Faunal transformations across the Eocene—Oligocene boundary in
the Burgin region are comparable to those of Europe and the Mongolian Plateau and suggest
linkage of faunal turnovers and global climate changes.
INTRODUCTION sive in Eurasia and North America (Stirton,
1935; Korth, 2001) and date back to the lat-
The beavers are represented by two living
est Eocene (McKenna and Bell, 1997). Ste-
species of a single genus, Castor fiber and neofiber, known from Europe and Asia, is
C. canadensis, which are members of the one of the earliest castorids. This genus is
family Castoridae and distributed in Eurasia considered either a member of Castoroidinae
and North America, respectively (Nowak, (McKenna and Bell, 1997) or a member of
1999). Fossil species of castorids are exten- Castorinae (Korth, 2001). According to
‘Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, PR.
China.
? Division of Paleontology, American Museum of Natural History ([email protected]).
Copyright © American Museum of Natural History 2004 ISSN 0003-0082
a AMERICAN MUSEUM NOVITATES NO. 3461
Korth (2001), the early Oligocene Steneofi- previously referred to Steneofiber and discuss
ber is the earliest castorine in Europe and has the taxonomic validities of Propalaeocastor
unspecialized cheek teeth in which flexi are and Steneofiber. We also examine the com-
closed to form fossettes at relatively early position of Propalaeocastor, the relation-
stages of wear. Species of Steneofiber are ships between Propalaeocastor and Steneo-
well studied in Europe since Stirton’s work fiber, and the biostratigraphic and biogeo-
(1935), but are less so for those more re- graphic implications of the new species and
cently found in Asia. Several species referred its associated fauna.
to Steneofiber are known from the Oligocene The terminology used for the upper cheek
of Kazakhstan in Central Asia and are rep- teeth of the early castorids is adapted from
resented by fragmentary specimens (Lytshev, Hugueney (1975, 1999) and Lytshev and
1970, 1978; Lytshev and Shevyreva, 1994; Shevyreva (1994), and is illustrated in figure
Emry et al., 1998). 1. Measurements are made under the Wild
Taxonomy of Steneofiber has been unsta- M7A stereomicroscope, with each tooth di-
ble and confusing. Most notable is the pro- mension measured twice from opposite sides;
posal of Asteneofiber Kretzoi (1974: 426— the average values of measurements are pre-
427), a genus based on S. butselensis, which sented in table 1.
has not been recognized until recently (Hu-
gueney and Escuillié, 1995, 1996; Hugueney, SYSTEMATIC PALEONTOLOGY
1999). In other studies Asteneofiber is usu-
CASTORIDAE HEMPRICH, 1920
ally synonymized with Steneofiber (McKen-
na and Bell, 1997), a view probably followed CASTORINAE HEMPRICH, 1920
by Korth (2001), who did not recognize the
Propalaeocastor Borissoglebskaya, 1967
name of Asteneofiber.
Another relevant genus is Propalaeocastor SYNONYM: Asteneofiber Kretzoi, 1974:
Borissoglebskaya, 1967. The type species P. 427.
kazachstanicus is from the Early Oligocene TYPE SPECIES: Propalaeocastor kazachs-
of Central Kazakhstan. The genus was later tanicus Borissoglebskaya, 1967.
synonymized to Steneofiber (Lytschev and TypPE LOCALITY AND AGE: Kyzylkak, 70
Shevyreva, 1994). Recently, Korth (2001) re- km southwest to City Dzhezkazgan in central
sumed the name Propalaeocastor and placed Kazakhstan, Early Oligocene.
it, together with Anchitheriomys and Oligoth- EMENDED DIAGNOSIS: Primitive, small cas-
eriomys, to Tribe Anchitheriomyini under the torids with brachyodont to mesodont cheek
subfamily Agnotocastorinae. teeth having folded enamel but lacking ce-
We report here a new early Oligocene spe- ment filling; P3 absent; P4 subquadrate;
cies, Propalaeocastor irtyshensis, which is cheek teeth decreasing in size posteriorly; in
the earliest and northernmost occurrence of addition to the five main lophs (anteroloph,
castorids in China. The new species is rep- protoloph, mesoloph, metaloph, and poster-
resented by a right maxilla with well-pre- oloph), the metastyle crest, protolophule I
served P4—M3 discovered during the field and II, and metalophule I and II also present
season of 2002. The specimen was found at (figs. 1, 3); the paraflexus, mesoflexus, me-
the 115.5 m horizon of the section on the taflexus, hypoflexus, premesoflexus (or fos-
northern bank of the Irtysh River near Burgin sette), and postmesoflexus (or fossette) de-
City, Xinjiang. This level is 26 m above the veloped; the protolophule II dividing the pre-
Late Eocene locality (XJ1999027 = 99027 mesoflexus into the labial flexus (or fossette)
in our previous publication) in the same sec- and lingual fossette; the short paraflexus
tion that has been reported elsewhere (Ye et about one-third to one-half of the tooth
al., 2002). Screenwashing of sediments from crown width and positioned anterior to the
the castorid bed generated isolated teeth rep- hypoflexus; the hypoflexus about two-fifths
resenting 14 additional rodent species. The of the tooth crown width with its labial end
assemblage of small mammals suggests an being opposite to the lingual fossette of the
age of early Early Oligocene. premesoflexus; lower teeth having five main
We compare the new species with those lophids (anterolophid, metalophid, mesolo-
2004 WU ET AL.: PROPALAEOCASTOR FROM CHINA 3
mesostria
mesostyle
premesostria metastyle crest
mesoloph metacone
patasinia Eas x oh postmesoflexus(or postmesofossette)
paracone yi metastria
protoloph a i
premesoflexus(premesofossette) ‘ metaflexus (or metafossette)
anteroloph a metaloph
paraflexus(or parafossette) 1 \ posteroloph
lingual premesofossette 4 metalophule II
protolophule I Wa
metalophule I
protolophule II 4
endoloph iS mesoflexus(or mesofossette)
hypocone
protocone
hypoflexus
hypostria
Fig. 1. Terminology of the upper cheek tooth of Propalaeocastor.
phid, hypolophid, and posterolophid), a me- with size and dental morphology similar to
tastylid crest, and an endostylid crest; the those of Propalaeocastor butselensis. Differ-
preparafossettid, premesofossettid, and post- ing from Propalaeocastor butselensis in hav-
mesofossettid present in addition to the par- ing higher tooth crown, much longer meso-
aflexid, mesoflexid, metaflexid, and hypo- flexus that bends posteriorly, more developed
flexid; all main lophs and lophids on the anteroloph, posteroloph, metastyle crest, and
cheek teeth transversely or nearly transverse- paraflexus, more folded enamel, and the lin-
ly extended. gual end of the mesoflexus connected the lin-
INCLUDED SPECIES: Propalaeocastor but- gual premesofossette. Differing from ‘‘Ste-
selensis (Misonne, 1957), P. shevyrevae neofiber aff. dehmi” in having lower tooth
(Lytshev and Shevyreva, 1994), P. aff. shev- crown, smaller size, shorter mesoflexus and
yrevae (Lytshev and Shevyreva, 1994), P. more transversely extended main lophs and
zaissanensis (Lytshev and Shevyreva, 1994), flexus. Differing from P. kazachstanicus, P.
and P. irtyshensis, n.sp. Steneofiber aff. deh- shevyrevae, and P. aff. shevyrevae mainly in
mi Freudenberg, 1941 is probably a species having lower tooth crown. In contrast, P. ka-
of Propalaeocastor (see below). zachstanicus possesses longer and anteropos-
GEOLOGICAL RANGE: Early Oligocene. teriorly more stretched mesoflexus; P. shev-
yrevae has a postmesofossette on the P4 and
Propalaeocastor irtyshensis, new species closed metaflexus to form fossette at all stag-
Figures 1—4, table 1 es of wear on M1-2; P. aff. shevyrevae has
the mesoflexus being confluent with the la-
HoLotyPe: A right maxilla with P4—M3,
bial premesofossette and has a postmesofos-
IVPP (Institute of Vertebrate Paleontology
sette on P4 and the labially always closed
and Paleoanthropology, Chinese Academy of
paraflexus on M1-2.
Sciences) V13690.
TYPE LOCALITY AND AGE: Locality
DESCRIPTION
XJ200203 (=200203 [Ye et al., 2002],
47°50.454'N, 86°40.883’E), 20 km northwest The root of the zygomatic arch is pre-
to Burgin City, Xinjiang. Early Oligocene. served on the fragmentary maxilla and is an-
EtyMo_ocy: After the name of the Irtysh terolateral to the P4. A distinct posterior pal-
River. atine foramen is medial to the position be-
DIAGNOsIs: Brachyodont Propalaeocastor tween M1 and M2 at the maxillary—palatine
- AMERICAN MUSEUM NOVITATES NO. 3461
maxillary-palatine suture
2mm
Fig. 2. Sketch showing the maxillary—palatine suture, the posterior palatine foramen, and the groove
leading anteriorly from the foramen on the palate of Propalaeocastor irtyshensis, n.sp. IVPP V13690).
suture on the palate. A groove leads anteri- metastria are distinctly present on all four
orly from the foramen. cheek teeth. The hypostria is the deepest
Measurements of individual tooth are pre- stria, and deepest on P4, about three-fourths
sented in table 1. The total length of P4—M3 of the crown height, while it is about a half
is 11.75 mm along the occlusal surface or of the crown height on the other teeth. The
12.15 mm along the crown base. The teeth mesostria is also deepest on P4, around a half
are moderately or slightly worn so that all the labial crown height; it is most shallow on
lophs and fossettes are clear. Cheek teeth are M1, about one-fifth of the crown height. The
brachyodont with the lingual side being high- metastria is deepest on M3, about three-fifths
er than the labial. The length of each tooth of the crown height and decreased in depth
is greater than its lingual crown height (the from M2 to P4. The parastria is the shallow-
teeth are only lightly or at the most moder- est stria; it is deepest on P4 and absent on
ately worn). The occlusal surface of the M1 and M3. In addition, a shallow “‘pre-
cheek tooth is slightly arched, with the labial mesostria”’ is present on M2 and M3. The
side being more ventral. The enamel—dentine measurements of each stria are presented in
boundary is distinct on all teeth. All cheek table 1.
teeth are wider than long. Cheek tooth enam- Although broken, the preserved maxilla
el is folded. The enamel folds are more com- shows no sign of P3. There is no contact fac-
plicated on the labial half than the lingual et on the anterior surface of P4. In addition,
side of the tooth, whereas the enamel around unlike molars in which the enamel along the
the protocone and hypocone is much thicker anterior edge thins at the area contacting the
than that distributed on the labial half of the anterior tooth, the enamel along the anterior
tooth. Cement filling is absent. edge of P4 is thick and even. Thus, we con-
Four main striae are present on each upper sider that the individual does not have a P3
cheek tooth: parastria, mesostria, metastria, in life.
and hypostria. The hypostria, mesostria, and P4 is subquadrate, molariform, and the
2004 WU ET AL.: PROPALAEOCASTOR FROM CHINA ,
|
2mm
Fig. 3. Line drawing of right P4¢—M3 of Propalaeocastor irtyshensis, n.sp. IVWPP V13690). A, Labial
view; B, occlusal view; C, lingual view.
largest cheek tooth. It is supported by three narrow paraflexus which opens labially and
thick roots: one lingual and two labial. As in extends about two-fifths of the crown surface
molars, the P4 protocone is the largest cusp width at the current stage of tooth wear. The
of the tooth and has a rounded lingual con- paracone is located at the labial end of the
tour; its lingual side is the highest region of protoloph and is confluent with the mesostyle
the tooth crown. In contrast, the hypocone is through a strong crest that closes the pre-
angular lingually. The protocone and hypo- mesoflexus labially. The protolophule I is
cone are separated by a deep hypoflexus that connected lingually with the anterior arm of
extends anterolaterally. On the lingual sur- the protocone or the anteroloph. The proto-
face the hypostria between the protocone and lophule IH, which is more labial than in mo-
hypocone is about three-fourths of the crown lars, connects the protoloph and mesoloph
height, the deepest of all cheek teeth. The and thus separates the premesoflexus from
protocone and hypocone are connected by a the lingual premesoflexus. The labial pre-
curved endoloph. mesoflxus is a circular, shallow lake, whereas
The transverse anteroloph and protoloph the lingual premesoflexus is transversely
on P4 are complete and between them is a elongate and very deep. Because the enamel
6 AMERICAN MUSEUM NOVITATES NO. 3461
E
Fig. 4. Right upper jaw with P4—M3 (IVPP V13690) of Propalaeocastor irtyshensis, n.sp. A, Oc-
clusal view of right P4—M3 (stereograph); B, occlusal view of right P4—M3 (inverse); C, anterior view
of P4, showing unihypsodonty; D, lingual view; E, labial (buccal) view. All scale bars = 5 mm.
2004 WU ET AL.: PROPALAEOCASTOR FROM CHINA 7
TABLE 1
Measurements (in mm) of Upper Cheek Teeth of Propalaeocastor irtyshensis, n.sp. (IVPP V13690)
P4 M1 M2 M3
Length x Width
at surface 3.42 x 3.33 2.95 X 3.50 2.93 x 3.23 2.45 X 2.93
at base 3.62 x 4.74 2.95 x 4.50 2.93 x 4.30 2.45 x 3.62
Height
labial 1.96 1.47 1.50 1.27
lingual 2.93 2.35 2.55 2.30
Parastria 0.38 — 0.175 —
Premesostria — — 0.175 0.16
Mesostria 0.88 0.22 0.38 0.28
Metastria 0.05 0.28 0.35 0.75
Hypostria ES 1.13 1.16 0.598
Maximum height/
maximum length indices 0.81 0.80 0.87 0.94
aEstimated.
ridge of the endoloph does not merge with metacone to close the metaflexus labially; a
that of the mesoloph, the lingual premeso- shallow metastria is present at the joint.
flexus is therefore not closed, but has a nar- The molars decrease in size posteriorly.
row gap at its posterior side, confluent with M1 is the most worn cheek tooth and has the
the mesoflexus. There seems no sign of clos- lowest crown but highest root exposed on the
ing of the lingual premesoflexus with the in- lingual side. It is shorter but wider than P4
creased wear of this tooth. This condition is and differs from P4 in several aspects. The
similar to that of M3 but differs from M1 paraflexus is a small, enclosed fossette at the
and M2 in which the mesoflexus and lingual anterolabial corner. The premesofossette is
premesoflexus are completely separated. The narrow and transverse, and is labially en-
mesoflexus of P4 is deep and opens labially. closed. The lingual premesofossette is com-
On the labial side of the crown, the mesostria plete and deep. The mesoloph is as narrow
is about half of the crown height. The mid- as the metastyle crest, lies within the anterior
portion of the mesoflexus is nearly closed by half of the tooth, and completely joins the
an enamel spike extending posterolingually endoloph. The mesoflexus is divided by a
from the mesoloph and an enamel loop ridge that connects the mesoloph and the me-
growing out of the metaloph. The enamel tastyle crest into a lingual, kidney-shaped
loop originates at the same place as the me- fossette and a labial, transverse trench that
tastyle crest would have joined, but it ex- partially opens labially. The metastyle crest
tends anteromedially rather than labially. The and metaloph are complete and nearly par-
postmesoflexus is a small fold confluent with allel; they confine respectively a narrow
the mesoflexus. The metalophule I and me- postmesoflexus anteriorly and posteriorly. In
taloph form a continuous, transverse crest ex- addition to the metalophule II, there is an-
tending from the hypocone to the metacone. other lophule, here not termed, that connects
The metalophule II extends from the metal- the metaloph and the posteroloph. Thus there
oph posteriorly to join the posteroloph and are two lingual metafossettes on M1.
divides the metaflexus into a lingual, circular Probably because of the lower degree of
fossette and a labial, elongate fossette. The wear, M2 differs from M1 in having a trans-
metalophule II is notched so that the lingual versely longer paraflexus and premesoflexus
and labial portions of the metaflexus are par- and more labially open mesoflexus and me-
tially confluent. The posteroloph joins the taflexus. However, other differences of struc-
8 AMERICAN MUSEUM NOVITATES NO. 3461
tures are not wear related, including an in- tyshensis 1s most similar to those from Eu-
complete metastyle crest, an incomplete me- rope and Kazakhstan that have usually been
talophule II, and a continuous mesoflexus referred to Steneofiber, such as P. butselensis
(lack of the ridge connecting the metastyle (= Steneofiber butselensis; see below for dis-
crest and mesoloph). cussion) from the earliest Oligocene (MP21)
M3 differs from M1 and M2 mainly in be- of Belgium, P. kazachstanicus (= S. ka-
ing reduced posteriorly, with a rounded pos- zachstanicus), P. shevyrevae (= S. shevyre-
terior contour. Unlike M1 and M2, the lin- vae), P. aff. shevyrevae (= S. aff. shevyre-
gual side of the hypocone is rounded, rather vae), and P. zaissanensis (= S. zaissanensis)
than angular. The paraflexus becomes beaded from the Early Oligocene of Kazakhstan.
fossettes. The mesoflexus is L-shaped, with These species share the following characters:
the turning apex narrowly confluent with the (1) The cheek teeth are brachyodont to me-
lingual premesofossette. The postmesofosset- sodont. (2) In addition to the five main lophs
te is complete and circular. The metalophule (anteroloph, protoloph, mesoloph, metaloph,
II is incomplete. The metaflexus is about a and posteroloph), minor ridges are also pre-
half of the tooth width and is more open than sent, including the metastyle crest, protolo-
that of M1 and M2. The hypoflexus is some- phule I and IH, and metalophule I and II. (3)
what constricted at its midpoint. All main lophs and the metastyle crest extend
transversely. (4) The paraflexus is transverse-
COMPARISONS ly short. (5) The premesoflexus is divided
into the labial premesoflexus (or premesofos-
Korth (2001) has recently divided Casto- sette) and the lingual premesofossette. (6)
ridae into four families, Agnotocastorinae, The labial end of the hypoflexus is opposite
Palaeocastorinae, Castoroidinae, and Casto- to the lingual premesofossette. (7) The tooth
rinae, and placed Steneofiber in Castorinae. enamel is folded. Given these similarities,
According to Korth (2001), Agnotocastori- our comparison will focus on the species of
nae possesses several primitive characters, Propalaeocastor and those we consider to be
such as presence of P3 or dP3, P4 subequal Steneofiber, including S. kumbulakensis, S.
in size to molars, the posterior palatine fo- dehmi, and S. eseri.
ramen within the palatine bone, and smooth Based on the study by Hugueney (1975)
palatal surface. In contrast, Castorinae, Cas- and our observation on a cast of Propalaeo-
toroidinae, and Palaeocastorinae share the castor butselensis (a fragmentary right max-
derived conditions of these features, includ- Ula with worn M1-—M2, a courtesy from
ing loss of dP3 and P3, P4 the largest upper Wang Ban-Yue) from the earliest Oligocene
cheek tooth, the posterior palatine foramina of Hoogbutsel of Belgium, it is clear that P.
within the palatine—maxillary suture, and the irtyshensis is comparable to P. butselensis in
palatal surface grooved. The new species we size. The measurements of the cast are: M1,
described here has all the derived conditions. 3.08 X 3.62, 4.50 (length xX width at the
Although McKenna and Bell (1997, electron- crown surface, width at the crown base); la-
ic version) place Steneofiber in Castoroidinae bial height 1.12; lingual height 2.00; the in-
and Korth (2001) distinguishes the three non- dex of maximum height/ maximum length
agnotocastorine subfamilies based on post- 0.65; M2, 2.90 X 3.23, 3.96; labial height
cranial characters, we consider Propalaeo- 1.17; lingual height 1.86; index of maximum
castor irtyshensis to belong to Castorinae for height/maximum length 0.64. P. irtyshensis
the following reasons: (1) Steneofiber is differs from P. butselensis in having higher
probably derived from ‘“‘Asteneofiber’ but- tooth crown, much longer mesoflexus that
selensis (Hugueney, 1999), (2) Asteneofiber bends posteriorly, more developed antero-
is here considered synonymous with Propa- loph, posteroloph, metastyle crest, and para-
laeocastor, and (3) Xu (1995) suggested that flexus, more folded enamel, and the lingual
Steneofiber should be placed in Castorinae end of the mesoflexus confluent with the lin-
because Steneofiber and Castor were shown gual premesofossette. Although M1 and M2
to form a clade in his phylogenetic analysis. on the cast of P. butselensis are worn at a
Among early castorines, Propalaeocastor ir- greater degree than those of P. irtyshensis,
2004 WU ET AL.: PROPALAEOCASTOR FROM CHINA 9
the mesostria extends to the half way point well developed and the paraflexus opens la-
of the crown height and the metastria is al- bially on the less worn P4 and M2.
most absent. In contrast, the mesostria is The Propapaeocastor zaissanensis from
short and the metastria on molars of P. ir- Talagay of Zaissan Basin is represented by
tyshensis is well developed. one moderately worn P4, two deeply worn
Propalaeocastor kazachstanicus from M1 and/or M2, and one moderately worn
Zaissan Basin and Central Kazakhstan is also M3. The description, figures, and measure-
similar to P. irtyshensis in size, but has high- ments provided by Lytshev and Shevyreva
er tooth crown. The maximum height/maxi- (1994: figs. 5, 6; tables 1, 4) show that P.
mum length indices of moderately worn zaissanensis is similar to P. irtyshensis in
size and crown height. Its maximum height/
cheek teeth of P. kazachstanicus are M1/2:
maximum length index is 0.88 for P4 and
1.46, M3: 1.20 (Lytshev and Shevyreva,
1994: 85), which are apparently greater than 0.92 for M3. In addition, the two species are
those of P. irtyshensis (P4: 0.81; M1/2: similar in some dental morphology, includ-
ing the shape of the mesoflexus and hypo-
0.80—0.87; M3: 0.94). Moreover, the meso-
flexus, the depth of mesostria and hypostria,
flexus of P. kazachstanicus is longer and an-
the position of the mesoflexus, hypoflexus,
teroposteriorly more stretched; the parastria,
premesofossette, and postmesoflexus, the
mesostria, and metastria either disappear or
depth of the hypostria, and the relative po-
are shallow. On moderately worn cheek teeth
sition of the two fossettes of the mesoflexus
of P. irtyshensis, however, the mesoflexus is
on worn M1/2. Moreover, on M3 of both
shorter and the mesostria, metastria, and
species the mesoflexus is confluent with the
sometimes parastria remain open.
lingual premesofossette and a postmesofos-
Compared to P. irtyshensis, P. shevyrevae
sette is present. P. zaissanensis differs from
from Talagay of Zaissan Basin also has
P. irtyshensis in the following aspects: The
greater maximum height/maximum length
premesoflexus on worn P4 of P. zaissanensis
indices: P4: 0.81—0.92; M1/2: 1.21-—1.32
is displayed as two isolated circles whereas
(Lytshev and Shevyreva, 1994: 91). P4 of P.
the lingual premesoflexus is connected with
shevyrevae possesses a postmesofossette and
the mesoflexus on P4 of P. irtyshensis; the
the metaflexus on M1 and M2 is closed to
lingual premesoflexus on the P4 of P. irtysh-
form a fossette at all stages of wear. In con-
ensis does not seem to become an isolated
trast, the metaflexus remains open labially as
lake after further wear, as it is on M1 and
the metastria with various depths on the mo-
M2. In P. zaissanensis the labial premeso-
lars and the postmesofossette is absent on P4
fossette and lingual metafossette on P4 are
of P. irtyshensis.
larger; the hypoflexus on M1 and M2 is lon-
Propalaeocastor aff. shevyrevae from Po-
ger, and the M3 hypoflexus is confluent with
dorozhnik and Novei Podorozhnik of the
the mesoflexus (Lytshev and Shevyreva,
Zaissan Basin is similar to P. irtyshensis in 1994: fig. 6). The absence of the postmeso-
size, but differs from the latter in having
fossette on M1 and M2 of P. zaissanensis
higher tooth crown. The maximum height/ probably resulted from deep wear of the
maximum length index of P. aff. shevyrevae
teeth.
is 1.04 for nearly unworn P4, 1.00 for mod- Recently, “‘Steneofiber cf. S. butselensis”’
erately worn P4, and 1.53 for moderately was reported from the Buran Svita of Podo-
worn M1/M2. On the P4 of P. aff. shevyre- rozhnik, locality K15, south of Lake Zaissan
vae the mesoflexus is confluent with the la- (Emry et al., 1998: 307, fig. 8I-K). This oc-
bial premesofossette, the postmesofossette currence is represented by a right P4, a right
present, and the metastria absent. The para- p4, and a left m1/2. Judging from the figures
flexus on M1/M2 is always closed labially. (no description is provided in the original
On the P4 of P. irtyshensis the mesoflexus is study), we think those specimens belong to
confluent with the lingual premesofossette, Propalaeocastor for the reason given above,
the postmesofossette is absent, and the me- and may belong to P. aff. shevyrevae from
tastria, although shallow, is present. The me- the same locality (Lytshev and Shevyreva,
tastria on the MI—M3 of P. irtyshensis is 1994). These teeth appear more derived than
10 AMERICAN MUSEUM NOVITATES NO. 3461
those of P. butselensis because the metastyle (MP29, Late Oligocene) of Germany (Freu-
crest is better developed and the mesoloph is denberg, 1941); therefore it is difficult to
complete on P4. compare the type specimens with that of P.
P. irtyshensis is also similar to the Early irtyshensis. Specimens of S. dehmi are now
Oligocene “‘Steneofiber aff. dehmi’ from discovered from several Late Oligocene lo-
Saint-Martin-de-Castillon of France (Hugue- calities of Germany, Switzerland (Engesser
ney, 1975; MP24) in dental pattern. In both et al., 1984, 1993), France, and Turkey
species the metastyle crest is present, the pre- (Unay, 1989). Hugueney (1975) noted that
mesoflexus is divided into the labial preme- unworn M1—2 and M3 of S. dehmi from
soflexus (or fossette) and lingual premeso- Heute-Provence retain double connections of
fossette by the protolophule II, the labial end the protoloph and metaloph with lingual
of the hypoflexus is opposite to the lingual cusps. It implies that primitive characters re-
premesofossette, and finally the tooth enamel main only on unworn teeth. However the up-
is folded. However “‘S. aff. dehmi’’ differs per and lower cheek teeth rows from Mine
from P. irtyshensis in having higher tooth de Rochette of Switzerland (Engesser et al.,
crown (based on Hygueney’s [1975] figures; 1984: 14, fig. 5) display a larger size, higher
height measurements were not provided), crown, and simpler dental pattern in which
larger size, longer mesoflexus, and main the metastyle crest, the premesoflexus, and
lophs and flexus extended slightly posterolin- the postmesoflexus are absent, the paraflexus
gually. Given its similarities to the species of and the hypoflexus are longer, the labial end
the Early Oligocene forms, “‘Steneofiber aff. of the hypoflexus is opposite to the lingual
dehmi’’ may prove to be another species of end of the paraflexus, and the main lophs ex-
Propalaeocastor, but we choose not to syn- tend more obliquely.
onymize it in this study. Steneofiber eseri (Von Meyer, 1846) from
Among the species of Propalaeocastor, it the Early Miocene (MN2) of Orlinger Tal
is difficult to make a thorough comparison near Ulm in Germany is the type species of
between P. irtyshensis and P. zaissanensis the genus. In McKenna and Bell (1997, elec-
and, to some degree, the other species from tronic version) a note, based on Stirton
Kazakhstan because of the originally variable (1935), indicates that the type species of Ste-
dental morphology of castorids and the iso- neofiber is S. castorinus Pomel, 1846, from
lated teeth with various degrees of wear. Aquitanian Saint-Gerand le Puy. According
Nonetheless, the differences that we recog- to Stefen (1997: 5) and Hugueney (1999:
nized above are sufficient to justify the es- 284), however, Pomel’s paper appeared in
tablishment of the new species. 1847 and S. eseri has priority over S. cas-
The Late Oligocene Steneofiber kumbulak- torinus. In addition to the type specimens,
ensis from Agypse of the Aral region differs Hugueney (1975) and Stefen (1997) made
from P. irtyshensis in being larger and hav- further investigations of Steneofiber eseri
ing higher tooth crown (Lytshev, 1970: table from Poncenat and Orlinger Tal, respectively.
1; the maximum length/maximum height in- Based on their work, we found that the dental
dices: are, 25: for. P4, ol. 32orINi, 1.36.for pattern of lightly worn upper cheek teeth of
M2, and 1.22 for M3), longer paraflexus S. eseri is similar to that of P. irtyshensis in
(about two-thirds of the tooth width on all having five main lophs, a vestigial metastyle
upper cheek teeth), longer mesoflexus which crest, a premesofossette, and a postmesofos-
curves backwards and joins to the metaflexus sette. In S. eseri, however, the protoloph and
on P4 to form a U shape, and more folded mesoloph merge into one, and the metastyle
enamel. More importantly, Steneofiber kum- crest, premesofossette, and postmesofossette
bulakensis lacks the lingual premesofossette, disappear soon after wear of the tooth so that
the labial end of the hypoflexus is opposite the cheek tooth has only four lophs. S. eseri
to the lingual end of the paraflexus, and lophs differs from P. irtyshensis considerably in
extend obliquely. having a much larger size, much higher tooth
Steneofiber dehmi was based on a juvenile crown, and longer paraflexus. In addition, the
mandible with dentition and two other iso- labial end of the hypoflexus in S. eseri is
lated lower cheek teeth from Gaimersheim opposite to the lingual end of the paraflexus,
