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New Phylogenetic Analysis of the Family Elephantidae Based on Cranial-Dental Morphology.

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THE ANATOMICAL RECORD 293:74–90 (2010)
New Phylogenetic Analysis of the
Family Elephantidae Based on
Cranial-Dental Morphology
NANCY E. TODD*
Department of Biology, Manhattanville College, Purchase, New York
ABSTRACT
In 1973, Vincent Maglio published a seminal monograph on the evolution of the Elephantidae, in which he revised and condensed the 100þ
species named by Henry Fairfield Osborn in 1931. Michel Beden further
revised the African Elephantidae in 1979, but little systematic work has
been done on the family since this publication. With addition of new
specimens and species and revisions of chronology, a new analysis of the
phylogeny and systematics of this family is warranted. A new, descriptive
character dataset was generated from studies of modern elephants for
use with fossil species. Parallel evolution in cranial and dental characters
in all three lineages of elephants creates homoplastic noise in cladistic
analysis, but new inferences about evolutionary relationships are possible. In this analysis, early Loxodonta and early African Mammuthus are
virtually indistinguishable in dental morphology. The Elephas lineage is
not monophyletic, and results from this analysis suggest multiple migration events out of Africa into Eurasia, and possibly back into Africa. New
insight into the origin of the three lineages is also proposed, with Stegotetrabelodon leading to the Mammuthus lineage, and Primelephas as the
ancestor of Loxodonta and Elephas. These new results suggest a much
more complex picture of elephantid origins, evolution, and paleogeography.
C 2009 Wiley-Liss, Inc.
Anat Rec, 293:74–90, 2010. V
Key words: elephant; evolution; cladistics
In 1973, Vincent Maglio published a seminal monograph on the evolution of the Elephantidae. In his phylogeny, three lineages of elephants, Loxodonta, Elephas,
and Mammuthus, evolved from Primelephas in Africa,
6 ma. Not only did Maglio (1973) summarize the origin, evolution, and zoogeography of the entire family, he
also consolidated the 100þ species proposed by Henry
Fairfield Osborn in his two-volume Proboscidea into 25
valid species.
Beden (1979) expanded on Maglio’s (1973) work, but
focused on the African Elephantidae. He was responsible
for the identification and description of material from
East Lake Turkana, Kenya, the Omo Valley, Ethiopia,
Laetoli, Tanzania, and Hadar, Ethiopia. These collections represent the bulk of the elephant material from
Africa, and his collected works are a testimony to the
effort and required to identify such a large amount of
material in such a small amount of time.
In 1996, The Proboscidea, The Evolution and Palaeoecology of Elephants and Their Relatives (Shoshani and
Tassy, 1996) was published as an update of proboscidean
C 2009 WILEY-LISS, INC.
V
studies since Osborn’s 1936 and 1942 Proboscidea volumes. Seventeen other species have been added to the list
of taxa recognized by Maglio (1973). Some were considered to be junior synonyms by Maglio, but have now been
re-evaluated and reinstated. Others are completely new
species. Since 1996, three additional species have been
described and a number of subspecies are now formally
recognized. This brings the total number of elephantid
species to 43, though not all of these are included in the
cladistic analysis presented in this article (Table 1).
This article is dedicated in the memory of Dr. Jeheskel
Shoshani.
*Correspondence to: Nancy E. Todd, Department of Biology,
Manhattanville College, 2900 Purchase Street, Purchase, NY
10577. Fax: (914)323-5121. E-mail: toddn@mville.edu
Received 16 August 2008; Accepted 25 June 2009
DOI 10.1002/ar.21010
Published online in Wiley InterScience (www.interscience.wiley.
com).
75
PHYLOGENETIC ANALYSIS OF THE ELEPHANTIDAE
TABLE 1. Current classification of the family elephantidae [after Shoshani and Tassy (1996)]
Maglio (1970)
Shoshani and Tassy (1996)
Additional species/subspecies
Stegotetrabelodon syrticus
Stegotetrabelodon orbus
Stegotetrabelodon lybicus
Stegotetrabelodon exoletus
Stegodibelodon schneideri
Primelephas gomphotheroides
Primelephas korotorensis
Loxodonta adaurora
Loxodonta
Loxodonta
Loxodonta
Loxodonta
Loxodonta
Loxodonta
Loxodonta atlantica
Loxodonta africana
Loxodonta exoptataa
Elephas ekorensis
Elephas recki
Stages I-IV
Elephas iolensis
Elephas namadicusb
Elephas falconeric
Elephas
Elephas
Elephas
Elephas
Elephas
Elephas
Elephas
Elephas
Elephas
Elephas
Elephas
Elephas
Elephas
Elephas
Elephas
(Paleoloxodon)
(Paleoloxodon)
(Paleoloxodon)
(Paleoloxodon)
(Paleoloxodon)
? beyeri
(Paleoloxodon)
(Paleoloxodon)
meletensis
brumptia
shungurensisa
atavusa
ileretensisa
reckia
Elephas
Elephas
Elephas
Elephas
Elephas
recki
recki
recki
recki
recki
Elephas
Elephas
Elephas
Elephas
maximus maximus
maximus indicus
maximus sumatranus
nawatensis
antiquus
falconeri
mnaidriensis
creutzburgi
naumanni
creticus
cypriotes
planifrons
celebensis
platycephalus
hysudricus
hysudrindicus
maximus
Mammuthus subplanifrons
Mammuthus africanavus
Mammuthus meridionalis
Laiatico Stage,
Montavarchi Stage,
and Bacton Stage
Mammuthus armeniacusd
Mammuthus primigenius
Mammuthus colombie
Mammuthus imperator
adaurora adauroraa
adaurora kararaea
atlantica atlanticaa
atlantica zulu
africana africana
africana cyclotis
Mammuthus meridionalis gromovi
Mammuthus meridionalis meridionalis
Mammuthus meridionalis vestinus
Mammuthus trogontherii
Mammuthus? jeffersoni
Mammuthus exilus
Mammuthus hayi
Mammuthus lamarmorae
# Species 25
40
Mammuthus rumanus
43
a
Named by Michel Beden.
E. antiquus ¼ junior synonym.
c
Maglio felt that Elephas mnaidriensis (Adams, 1870), Elephas meletensis (Falconer and Cautley, 1862, 1868), Elephas
lamamorae (See Mammuthus) (Major, 1883), Elephas cypriotes (Bate, 1903), and Elephas creticus (Bate, 1907) were successive stages in dwarfing and perhaps did not warrant species designations.
d
M. trogontherii ¼ junior synonym.
e
M. jeffersoni ¼ junior synonym.
b
Both Maglio’s (1973) and Beden’s (1979) monographs
were primarily concerned with specimen and species
identification. Character evolution was determined by
identifying an ancestor from the older fossils from which
the evolution of more recent elephants could be deduced.
The material recovered from late Miocene and early
Pliocene African localities seemed to be the key to the
origin of the family. Preoccupation with an ancestral
morphotype, and the progressive development of characters from this morphotype to the extant elephants has
76
TODD
resulted in a preoccupation with anagenetic trends. Subsequent to Maglio (1973), species and subspecies have
been defined based on their position within these trends,
rather than based on the morphological characteristics
that they share or do not share with other species. As a
result, traditional systematic methods have been unable
to distinguish between homoplasies (which occur in parallel in all lineages of elephants), plesiomorphies, and
synapomorphies.
Unfortunately, this emphasis on identification led to
inconsistent use of terminology, character descriptions,
and measurement methods. Many of the similarities in
morphology among fossil elephants were based on plesiomorphic characters. Loxodonta has long been thought to
represent the ancestral condition for the family, and yet
many similarities have been observed between this genus and several late Pleistocene taxa in Europe (Todd,
1997). Unrelated species were grouped together based on
superficial resemblances that were the result of parallel
evolution or retention of ancestral characters (Maglio
1973). This is further complicated by the widespread
parallel evolution that has occurred in all three lineages,
Elephas, Mammuthus, and Loxodonta.
There have been few attempts to examine the relationships of species within the Elephantinae through character-based analysis. Tassy (1988, 1990), Tassy and Darlu
(1986, 1987), and Kalb and Mebrate (1993) have examined the Order Proboscidea and/or the Suborder Elephantoidea using cladistic methods. Tassy (1988, 1990)
and Tassy and Darlu (1986, 1987) have analyzed the
relationships within the Proboscidea, particularly the
relationships of tetralophodont-grade elephantoids to
each other and to the Elephantidae. In his discussion of
phylogeny and classification of the Proboscidea, Tassy
(1990) reviews previous classifications and examines the
relationships within the order using parsimony. His cladogram of the Proboscidea is resolved except for node 13
(the Elephantoidea defined as including the Mammutidae, Ambelodontidae, ‘‘gomphotheres,’’ Choerolophodon,
Stegodontidae, and the Elephantidae). This is the crucial
node for the origin of the elephantines (Stegodibelodon,
Primelephas, Loxodonta, Mammuthus, and Elephas),
and suggests that the origin of the Elephantidae is not
as simple as may have been previously thought.
Previous research has been aimed at determining the
probable ancestor of the family Elephantidae, the relationships of the sister groups Stegodontidae and Gomphotheriidae to the Elephantidae, and the status of the
paraphyletic ‘‘gomphothere’’ group. As a result, many of
the characters used in these analyses are too generalized
to distinguish between species within the Elephantidae.
The Elephantidae are included in these analyses at the
generic level only, and no study of the species relationships within the family has been done.
Kalb and Mebrate (1993) analyzed characters at the
generic level in African elephants, using proboscidean
specimens from the Middle Awash, Ethiopia. This is the
only recent study which focuses on dental characters of
African Elephantidae using character-based analysis.
They separate a ‘‘Loxodonta Group’’ from Loxodonta
adaurora and discuss the relationships of both Loxodonta clades to a Primelephas-Mammuthus-Elephas
clade. They grouped Primelephas with Mammuthus and
Elephas based on synapomorphies (concave-concave
enamel loops on lower molars, single posterior column).
Twin posterior columns in Loxodonta adaurora and
convex-concave enamel loops in the Loxodonta Group
separate these two groups from the Primelephas-Mammuthus-Elephas clade (Kalb and Mebrate, 1993). The
presence of a prominent posterior column which is completely isolated in unworn molars in these species
reflects the ancestral ‘‘trefoil’’ pattern from a gomphothere ancestor, and thus explains the direction of the development of the median loop (Kalb and Mebrate, 1993).
Study of the morphology of the extant species (Loxodonta africana and Elephas maximus) provides the basis
for a more rigorous analysis of the characters used to
define fossil species and subspecies of Elephas, Loxodonta and potentially Mammuthus (Todd, 2009). The
goal of this article is to present a cladistic analysis of
the Elephantidae based on a new, descriptive cranialdental character dataset, and to suggest a new phylogenetic scheme for the family.
MATERIALS AND METHODS
Species and Specimens
Because of the variability in specimens that have been
assigned to fossil taxa in the Elephantidae, and the variability in descriptions of such taxa in the literature,
characters were coded on the type specimens for each
species and subspecies only. The type specimen data is
proposed as the most accurate representation of the
‘‘true’’ morphology of each fossil and modern species.
Most of the type specimens consist of molars only, but
some do include the cranium and/or mandible. In a few
cases, only the mandible and mandibular teeth exist.
A few of the type specimens do not exist anymore, or
the specimen was inaccessible. The whereabouts of the
type for Loxodonta africana (originally named Elephas
africanus) is unknown. This specimen was examined
using a drawing from Osborn (1942:1197), and another
molar from the type locality (Cape Colony) located in the
British Museum of Natural History. The only designated
type for any of the subspecies of Loxodonta africana or
Elephas maximus is ‘‘Congo,’’ the type specimen for Loxodonta africana cyclotis. This specimen was located in the
American Museum of Natural History. An adult representative of each of the other extant subspecies was chosen as the specimen for use in coding character states.
The types for Loxodonta atlantica and Elephas iolensis
are housed in the Musée Nationale d’Histoire Naturelle
in Paris, but are listed without specimen numbers.
These are figured in Osborn (1942), however, and the
type localities for each are listed. The molars best matching both of these were examined during research in
Paris. An excellent cast of the type for Mammuthus subplanifrons was examined in the British Museum. Only
one specimen of Mammuthus meridionalis was studied,
and this was used as the example for this species.
The lectotype for Loxodonta exoptata is from Laetoli,
Tanzania, and is housed in the Humboldt Universität,
Berlin. This specimen is figured by Maglio (1969:18,
Plate I, Figs. 1 and 2), and the photograph was used in
addition to a specimen from East Turkana, Kenya. The
lectotype for Elephas recki (also Elephas recki recki) is
from Olduvai Gorge, Tanzania and is located in the
same museum. The specimen itself was not examined,
but a cast reconstruction matching the figure from
Osborn (1942) that was in the collections of the National
PHYLOGENETIC ANALYSIS OF THE ELEPHANTIDAE
Fig. 1. Ordered analysis of cranial, dental, and mandible characters
with successive weighting produced one cladogram in which the
Asian elephant groups with E. antiquus and the rest of the Eurasian
Elephas, while the African elephant occupies a position closer to the
basal African fossil species. A Nelson Consensus Tree of the 16 unordered trees remains largely unresolved. The genera are color coded,
with the African Elephas is in blue, and the Eurasian Elephas in light
blue. Stegotetrabelodon the outgroup.
Museum of Kenya was studied. The types for the subspecies Elephas recki brumpti, and Elephas recki shungurensis are from the Omo Valley, Ethiopia, and were
not available for study. Figures of these from Beden
(1979) and comparable specimens from other collections
were used as the example for each. The type for Elephas
recki atavus is on display in the Gallerie de Paléontologie in Paris. This is a very complete cranium with both
upper third molars still in place. The mandible for Elephas recki atavus was not found, and so KNM-ER 5711
was used for mandibular characters. This specimen consists of a cranium and mandible that is virtually identical to the type specimen. The type specimen for Elephas
ekorensis consists of upper right and left M3, and so cranial data was collected from KNM-EK 422, a partial cranium housed in the National Museums of Kenya. A list
of the type specimens and specimens used to code for
characters is included in Table 2.
Cladistic Analysis
Data sets were analyzed using Hennig86. With the
exception of one analysis, trees were obtained using the
mhennig command with branch swapping (mh*; bb*)
(trees were obtained for one dataset using ie*). For each
data set, trees were obtained from ordered, successively
weighted characters (cc; xsteps w) as well as unordered
and successively weighted characters (cc-; xsteps w).
Finally, multiple trees were condensed into a Nelsen
consensus tree (n; tplot).
Seventy-seven multistate characters were examined
on two species of extant elephants and 15 extinct species. This dataset includes a total of 77 multistate characters: 33 dental characters, 32 cranial characters, and
12 mandible characters defined based on the osteological
analysis of the extant elephants, as well as the extinct
species (Table 3) (Todd, 1997). Three general skeletal
characters and seven phenotypic characters were also
studied, but at the present time, these can only be used
77
Fig. 2. Unordered analysis of cranial, dental, and mandible characters with successive weighting produced 16 cladograms. A Nelson
Consensus Tree of the 16 unordered trees remains largely unresolved.
The genera are color coded. African Elephas is in blue, and the Eurasian Elephas in light blue.
to identify subspecies of the two living elephants and so
are not included in the cladistic analysis.
RESULTS
Once the character set was established, the literature
was surveyed in detail for comparison of character
descriptions. This was necessary to insure consistent terminology. Previous studies by Maglio (1973) and Beden
(1979, 1983, 1987) provided the groundwork for interpreting differing descriptions, but these descriptions are
often not used consistently across taxa. This has made it
difficult to compare species and specimens, and is the
principle reason for developing a new, well-defined character data set. Many of the new characters have a foundation in these previous studies, but all are new in
terms of their descriptions and states.
Two examples of the comparison process between previous studies and the new analysis are the dental characters involving folding of the enamel and the shape of the
enamel figure. Enamel folding is so variable in fossil elephants that it was necessary to separate this general
character into five separate characters. The basic trend in
dentition that has been proposed for all elephant lineages
is increased shearing efficiency of the molars. This was
accomplished in different ways in each lineage, but there
are allometric and functional changes in several features
which are intricately related. To increase plate spacing
while maintaining numbers of plates, the enamel thickness had to decrease. To compensate for thinner (and less
durable) enamel, the crown height increased. To compensate for thinner enamel, and maintain adequate surface
area, enamel became increasingly folded. Although the
degree and type of enamel folding varies among species,
there are very definite characteristics which can be isolated as characters with several states each.
Enamel folding is so complicated in fossil elephants,
that not only the pattern was coded but also four additional characters were created: placement of folds, amplitude of folds, spacing of enamel folds, and crenated
versus smooth enamel. Every specimen was coded for
these characters, and the results show a high degree of
78
TODD
TABLE 2. Type specimens and specimens substituted for types in this analysis
Species
Stegotetrabelodon orbus
Primelephas gomphotheroides
Loxodonta adaurora and
Loxodonta adaurora adaurora
Loxodonta adaurora kararae
Loxodonta atlantica
Loxodonta africana
Loxodonta africana oxyotis
Loxodonta africana cyclotis
Loxodonta exoptata
Elephas ekorensis
Elephas recki and E. r. recki
Elephas recki brumpti
Elephas recki shungurensis
Elephas recki atavus
Elephas recki ileretensis
Elephas iolensis
Elephas antiquus
Elephas namadicus
Elephas hysudricus
Elephas meletensis
Elephas mnaidriensis
Elephas maximus maximus
Elephas maximus indicus
Elephas maximus sumatranus
Mammuthus subplanifrons
Mammuthus meridionalis
Mammuthus armeniacus
Type specimen
Comments
KNM-LT 354
KNM-LT 351
KNM-KP 385
KNM-ER 347
MNHN
Location unknown, type locality
probably Cape Colony,
figured in Osborn (1942:1197)a
No type specimen
AMNH 90102 (?) ‘‘Congo’’
IPUB Z.94.96, figured in
Maglio (1969:18)a
KNM-EK 424
IPUB XVII 1382b
Omo L1.33, figured in Beden
(1979:387)a
Omo 148.72.1, figured in
Beden (1979:397)a
MNHN 1933.9.300
KNM-ER 1588
MNHN
BM M.2006
BM M.3092
BM M.3109
BM M.44312
BM M.44304
No type specimen
No type specimen
No type specimen
MMK 3020, cast in BMNHb
IGF 1054a
BM 32250, BM 32252
Partial mandible with LLM2-and LLM3
ULM3, URM3, LM3, and fragmentary palate
Almost complete adult skeleton, partial cranium
with UM3, and complete mandible with LM3
Partial cranium with UM3
Co-type, LRM2, 1 referred specimen-ULM3
LRM2, used URM3 from Cape Colony locality,
and NMNH 304615 for cranium and
mandible characters
Used NMNH 304615
Complete cranium and mandible M2 in wear
and M3 forming
LRM3, also used KNM-ER 3200 A-B
URM3, ULM3, also used KNM-EK 422 (cranium)
LLM2 in mandible fragment, examined cast of
this specimen
Mandible fragment with LLM2 and LLM3
Maxilla fragment with ULMa and ULM3
Complete cranium with URM3 and ULM3
Maxilla fragment with URMb and URMa
LLM3
LLM2
Partial cranium with frag. UM3
Cranium
ULMa(?)
LRM3
Used ROM 01.2.8.1
Used AMNH 30249
Used NMNH 282837
Type of ‘‘Archidiskodon subplanifrons’’
Used MNHN 1948-1-126
ULM3 and URM3, also referred to ‘‘M. trogontherii’’
a
A cast of this specimen was examined.
These specimens were not examined during the course of this study, but drawings and photographs were used to code for
characters, as well as other comparable specimens.
b
polymorphism within-species. Even when separated into
five different multistate characters, there is still a wide
range of variation.
A second example of comparisons with previous studies and the new analysis is the shape of the enamel figure. Again, the descriptions of this feature in the
literature are varied and too comprehensive for it to be a
single character. As described in the introduction, some
of this variation is due to developmental plasticity, but is
also related to shape changes in the molars, such as
overall width and allometric changes in enamel and
plate thickness. In this case, the original feature has
been divided into six multistate characters: presence of
anterior/posterior columns, general enamel figure shape,
shape of median area, lateral edges of enamel figure,
direction of lateral edges of enamel, and symmetry of
median loop. As with the first example, these characters
are still highly polymorphic.
Cladistic Analysis
The total data set includes 33 dental characters, 32 cranial characters, and 12 mandibular characters. The outgroup, Stegotetrabelodon orbus, and nine other species
are included in this analysis. When characters are or-
dered, one tree was obtained with a Length ¼ 176, CI ¼
65, and RI ¼ 51 (Fig. 1). When the characters are unordered, 16 equally parsimonious trees are obtained with
Length ¼ 153, CI ¼ 71, and RI ¼ 53. A Nelson Consensus
Tree is represented in Figure 2. The overall structure of
the two final trees is the same, though the relationship of
Eurasian Elephas to African Elephas is unresolved.
The dental data set contains 33 dental characters. The
outgroup is Stegodon kaisensis and includes 18 other
species. As this data set is based only on dentition, more
species can be included. Stegodon kaisensis (Stegodontidae) is a member of the sister group to the Elephantidae,
and provides a better outgroup than Stegotetrabelodon
when all genera of the Elephantidae are included in the
analysis. However, there is no cranial material for Stegodon kaisensis, so it cannot be used as an outgroup in the
total character analysis.
Nineteen equally parsimonious trees were obtained
with the characters ordered, Length ¼ 151, CI ¼ 43,
RI ¼ 58. One tree resulted with successive weighting of
characters (Fig. 3). In an unordered analysis, two
equally parsimonious trees were obtained with a Length
¼ 120, CI ¼ 50, and RI ¼ 60. The only difference
between the two trees is the position of S. orbus and
P. gomphotheroides (Fig. 4).
PHYLOGENETIC ANALYSIS OF THE ELEPHANTIDAE
TABLE 3. Cranial, dental, and mandible characters used
in the cladistic analysis
Dental characters
1. Molar shape
0 ¼ tapered at anterior end (ovate)
1 ¼ parallel-sided
2 ¼ widest in middle (elliptic)
3 ¼ tapered at posterior end (ovate)
2. Molar curvature
0 ¼ straight
1 ¼ curved at posterior end
(occlusal view)
(occlusal view)
3. Molar shape
0 ¼ height even at both ends
1 ¼ greatest height at posterior end
*Generally characterizes upper and lower teeth
(lateral view)
4. Greatest tooth width
0 ¼ base of crown
1 ¼ 1/4 up from base of crown
2 ¼ 1/2 up from base of crown
3 ¼ crown (posterior view)
5. Molar crown
0 ¼ ends at alveolar border
1 ¼ extends below alveolar border
(lateral view)
6. Cingulum
0 ¼ present
1 ¼ absent
(lateral view)
7. Occlusal surface
0 ¼ even
1 ¼ twisted
2 ¼ sagging in middle
(posterior
8. Inclination of plates to occlusal surface
0 ¼ weak
1 ¼ strong
(lateral
9. Valleys between plates
0 ¼ V-shaped
1 ¼ U-shaped
(lateral
10. Valley shape at base
0 ¼ compressed, diverge at apex
1 ¼ parallel
(lateral
11. Cement filling valleys
0 ¼ no
1 ¼ yes
view)
view)
view)
view)
(lateral view)
12. ‘‘S’’ curve to plates
0 ¼ no
1 ¼ yes
(lateral view)
13. Lateral edges of plate
0 ¼ low and rounded
1 ¼ straight, angled in toward apex
2 ¼ parallel-sided
3 ¼ high and bowed out slightly
14. Molar roots
0 ¼ strong or bifurcated
1 ¼ absent or open
(posterior view)
79
80
TODD
TABLE 3. Cranial, dental, and mandible characters used
in the cladistic analysis (continued)
Dental characters
15. Apical digitations
0 ¼ few (4 or less)
1 ¼ many (greater than 4)
(occlusal view)
16. Appearance of complete enamel loops
0 ¼ slow (within 6 worn plates)
1 ¼ quick (within 3 worn plates)
(occlusal view)
17. Single column at posterior end
0 ¼ present
1 ¼ small plate
*May be variable
(occlusal view)
18. Anterior/Posterior columns
0 ¼ strong anterior column
1 ¼ strong posterior column
2 ¼ strong anterior and posterior columns
3 ¼ no anterior/posterior columns
19. Median cleft
0 ¼ strong
1 ¼ weak
2 ¼ absent
20. Tusk shape
0 ¼ straight
1 ¼ curved or spiralled in front
2 ¼ straight spiral (twisted)
21. Tusk cross-section
0 ¼ rectangular or flattened
1 ¼ oval or ‘‘bean’’ shaped
2 ¼ round
22. Enamel height above cement
0 ¼ Low
1 ¼ High
*May be related to wear and amount of abrasion
23. Enamel figure shape
0 ¼ parallel-sided
1 ¼ true lozenge
2 ¼ parallel-sided with median loop
3 ¼ ‘‘pseudo-lozenge’’
4 ¼ ‘‘keyhole’’ shaped
5 ¼ rounded loops
24. Median area
0 ¼ loop
1 ¼ fold
2 ¼ absent or open
25. Lateral sides of enamel figure
0 ¼ pinched
1 ¼ rounded
2 ¼ intermediate
3 ¼ rectangular
26. Direction-lateral sides of enamel
0 ¼ turn anterior
1 ¼ turn posterior
2 ¼ even
*May be variable
27. Symmetry of enamel figure
0 ¼ symmetrical, in line with long axis of molar
1 ¼ asymmetrical, offset from long axis of molar
PHYLOGENETIC ANALYSIS OF THE ELEPHANTIDAE
TABLE 3. Cranial, dental, and mandible characters used
in the cladistic analysis (continued)
Dental characters
28. Medial edges of enamel figures
0 ¼ separated
1 ¼ in contact
29. Enamel folding
0 ¼ absent
1 ¼ regular
2 ¼ irregular
3 ¼ undulating
4 ¼ crinkled
30. Placement of folds
0 ¼ median area only
1 ¼ entire length of enamel figure
2 ¼ absent
31. Amplitude of enamel folding
0 ¼ absent
1 ¼ high
2 ¼ low
32. Spacing between enamel folds
0 ¼ absent
1 ¼ tight
2 ¼ loose
33. Crenated versus smooth enamel
0 ¼ Smooth
1 ¼ Crenated
*May be taphonomic
Cranial characters
34. Parietal/Occipital crest (¼nuchal ridge)
0 ¼ pronounced ridge
1 ¼ ridge
2 ¼ smooth
35. Shape of nares opening
0 ¼ ‘‘dumbell’’ shaped
1 ¼ turned down at lateral edges
2 ¼ rounded and turned up at lateral edges
*May be related to sexual dimorphism (frontal view)
36. Borders of nares opening
0 ¼ sharp and pronounced
1 ¼ smooth and rounded
37. Center of nuchal ridge
0 ¼ smooth and even
1 ¼ heart-shaped
2 ¼ concave
(frontal view)
38. Position of orbits relative to tooth row
0 ¼ anterior to tooth row
1 ¼ even with beginning of toothrow
2 ¼ posterior to beginning of tooth row
39. Slope of forehead and premaxillaries
0 ¼ premaxillaries steeper than forehead
1 ¼ in same plane
2 ¼ forehead steeper than premaxillaries
(lateral view)
40. Temporal line
0 ¼ smooth
1 ¼ line
2 ¼ ridge
41. Parietal depression
0 ¼ absent
1 ¼ muscle marking
2 ¼ furrow
81
82
TODD
TABLE 3. Cranial, dental, and mandible characters used
in the cladistic analysis (continued)
Dental characters
42. Occipitals
0 ¼ bulbous
1 ¼ flat
43. Slope of occipitals from condyles
0 ¼ anterior
1 ¼ vertical
2 ¼ posterior
(lateral view)
44. Position of supraoccipital relative to squamosal
0 ¼ directly superior
1 ¼ lateral
2 ¼ medial
(posterior view)
45. Alveolar border of premaxillaries
0 ¼ even
1 ¼ slopes down laterally
(inferior view)
46. Premaxillaries
0 ¼ parallel
1 ¼ flared
2 ¼ straight-sided but diverging
(inferior view)
*May be related to sexual dimorphism
47. Shape of occipital condyles
0 ¼ round or square
1 ¼ triangular, elongated triangle
2 ¼ ‘‘bean’’ shaped
48. Condylar fossa
0 ¼ flat and wide
1 ¼ flat and narrow
2 ¼ deep and wide
3 ¼ deep and narrow
49. Condylar facet
0 ¼ even with fossa
1 ¼ slopes posteriorly from fossa
2 ¼ slopes anteriorly from fossa
50. Basio-occipital
0 ¼ plate-like, with pronounced edges
1 ¼ smooth, completely fused
51. Basio-occipital and vomer
0 ¼ meet
1 ¼ separated
52. Position of exoccipital relative to condyles
0 ¼ lateral
1 ¼ anterior
(posterior view)
53. Forehead
0 ¼ rounded
1 ¼ flat
2 ¼ concave
(lateral view)
54. Tusk sheaths
0 ¼ rotated anteriorly
1 ¼ even
2 ¼ rotated posteriorly
(inferior view)
55. Ventral depression of palate
0 ¼ no
1 ¼ yes
56. Position of occipital condyles relative to tooth row
0 ¼ posterior
1 ¼ in line with end of tooth row
PHYLOGENETIC ANALYSIS OF THE ELEPHANTIDAE
TABLE 3. Cranial, dental, and mandible characters used
in the cladistic analysis (continued)
Dental characters
57. Opening of external nares
0 ¼ above orbit
1 ¼ even with orbit
2 ¼ below orbit
(lateral view)
58. Anterior portion of zygomatic
0 ¼ projecting anteriorly
1 ¼ receding
59. Premaxillaries
0 ¼ Directed out and forward
1 ¼ Directed out and downward
(lateral view)
60. Height of occipital condyles
0 ¼ low
1 ¼ elevated
61. Frontal bones
0 ¼ elongated
1 ¼ shortened
62. Skull shape
0 ¼ rounded
1 ¼ compressed parallel to facial plane
(lateral view)
63. Palate keel
0 ¼ absent
1 ¼ present
64. Nuchal fossa
0 ¼ deep
1 ¼ shallow
65. Occipital bosses
0 ¼ in facial plane
1 ¼ overhang forehead
(lateral view)
Mandible characters
66. Mandibular condyle shape
0 ¼ long anterio-posteriorly
1 ¼ oval
2 ¼ rectangular
67. Condyle surface
0 ¼ slopes medially
1 ¼ even
68. Ascending rami
0 ¼ diverging
1 ¼ curve in
2 ¼ parallel
69. Mandibular symphysis
0 ¼ directed forward
1 ¼ directed down
70. Length of mandibular symphysis
0 ¼ long
1 ¼ intermediate
2 ¼ short
*Relative character
71. Shape of symphyseal trough
0 ¼ horseshoe shaped
1 ¼ U-shaped
2 ¼ V-shaped
72. Mandibular corpus
0 ¼ swollen
1 ¼ gracile
(posterior view)
(frontal view)
83
84
TODD
TABLE 3. Cranial, dental, and mandible characters used
in the cladistic analysis (continued)
Dental characters
73. Position of coronoid process relative to
maximum length of corpus
0 ¼ posterior
1 ¼ half way
2 ¼ anterior
(lateral view)
74. Lateral side of ascending ramus
0 ¼ concave
1 ¼ flat
75. Angle of ascending ramus relative to corpus
0 ¼ 90 angle
1 ¼ acute angle
(lateral view)
76. Height of ascending ramus relative to
maximum length of corpus
0 ¼ ramus height < corpus length
1 ¼ ramus height ¼ corpus length
2 ¼ ramus height > corpus length
(lateral view)
77. Lower incisors
0 ¼ present
1 ¼ germ cavity
2 ¼ absent
Fig. 3. Ordered analysis of dental characters with successive
weighting produced one tree. The genera are color coded. African Elephas is in blue, and the Eurasian Elephas in light blue. Loxodonta is
paraphyletic, Elephas is polyphyletic. Stegodon kaisensis is the
outgroup.
DISCUSSION
Homoplasy is a persistent problem in this cladistic
analysis. All three lineages are undergoing similar
trends in character evolution, but at different rates and
times. As a result, each character appears on the tree
several times, resulting in low CI indices. In two clades
from an analysis of subspecies and species (Todd, 2006),
the dental similarities are clearly seen (Fig. 5,6). Some of
these similarities have phylogenetic significance, (Elephas iolensis and Elephas hysudricus), while others illus-
Fig. 4. Unordered analysis of dental characters with successive
weighting produced two trees. The only difference between the two
trees is the position of S. orbus and P. gomphotheroides. The genera
are color coded. African Elephas is in blue and the Eurasian Elephas
in light blue. In this cladogram, Loxodonta is polyphyletic, and Elephas
is paraphyletic.
trate the unique problems of parallel evolution, and the
difficulty in sorting out homoplasy resulting from convergence (Loxodonta atlantica and Elephas recki recki). This
creates a problem using parsimony, but it is possible to
make conclusions about phylogenetic relationships if this
complication due to parallel evolution is kept in consideration, and a new phylogeny is presented in Fig. 7.
Loxodonta is paraphyletic in both analyses of cranial
and dental characters. Elephas is polyphyletic in the ordered analysis but paraphyletic in the unordered analysis due to the inclusion of Mammuthus primigenius with
Fig. 5. In a previous cladistic analysis of subspecies within the elephantidae (Todd, 1997), the problem
of homoplasy is illustrated by the phenotypic similarities in several molar characters among African and
European Elephas and Loxodonta.
Fig. 6. In a previous cladistic analysis of subspecies within the elephantidae (Todd, 1997), all five subspecies of Elephas recki fail to group together, and some of these subspecies share similarities with Loxodonta and Eurasian Elephas.
86
TODD
Fig. 7. New phylogeny of the Elephantidae based on the cladistic
analysis. Loxodonta adaurora and Mammuthus are consolidated into
one lineage leading from Stegotetrabelodon and Elephas and the main
lineages of Loxodonta evolves from Primelephas. Age range and locality data obtained from: Asfaw et al. (1991), Andrews et al. (1981),
Aouadi (2001), Beden (1979, 1981, 1987), Behrensmeyer et al. (1995,
1997, 2002), Boaz et al. (1992), Brown (1985), Caloi et al. (1996), Cerling et al. (1999), Cooke (1993), Cooke and Coryndon (1970), Coppens
(1972), Coppens et al. (1978), Court (1995), Debruyne et al. (2003),
deBonis et al. (1988), Deino and Hill (2002), Gaziry (1987), Gheerbrant
et al. (1996, 1998, 2002), Harrison and Baker (1997), Hill (1995), Hill et
al. (2002), Jacobs et al. (1999), Kalb et al. (1982), Kalb and Mebrate
(1993), Kingston and Harrison (2003), Kingston et al. (2002), Klein
(1973-74), Labe and Guerin (2005), Leakey et al. (1995, 1996), Lister
(1996), Lister et al. (2005), Maglio (1970a, 1970b, 1972, 1973), Morgan
et al. (1994), Nanda (2002), Osborn (1931, 1936, 1942), Pickford
(1988), Plummer and Potts (1989), Poulakakis et al. (2002), Raynal et
al. (1990), Rogaev et al. (2006), Sanders (1990), Sanders et al. (2002),
Shipman et al. (1981), Shoshani (1996), Shoshani and Tassy (1996,
2005), Smart (1976), Tassy (1986, 2003), Tassy and Debryune (2001),
Tassy et al. (2003), Todd (1999, 2005, 2006), Todd and Roth (1996),
White et al. (1984), Wolde Gabriel et al. (1994).
the Eurasian Elephas species. In the analysis of dental
characters only, Loxodonta is paraphyletic in the ordered
analysis but polyphyletic in the unordered analysis.
Mammuthus is also paraphyletic in both analyses. There
are many other species of Mammuthus that could be
included in this analysis, but these are middle to late
Pleistocene forms that are highly derived. The three species included here are the older, more ancestral species.
Both Mammuthus meridionalis and Mammuthus armeniacus remain together as a clade, but do not group with
Mammuthus subplanifrons. Based on the results of previous metric analysis of the family elephantidae, M. sub-
planifrons is inseparable from Loxodonta adaurora, an
early loxodont species in Africa (Todd, 1997). Considering these results, and that M. subplanifrons consistently
groups with L. adaurora as a basal member of the Elephantidae in the cladistic analysis, it is highly likely
that these two species are the same species. This partially solves the homoplastic problem of Loxodonta, at
least in the unordered analysis. There are certain features of the skull of L. adaurora which are similar to
later mammoths including massive, flaring premaxillaries, twisted tusks (although straight), and a relatively
flat frontal. This suggests that L. adaurora does not
PHYLOGENETIC ANALYSIS OF THE ELEPHANTIDAE
87
Fig. 8. Beden’s (1979) phylogeny included Stegotetrabelodon as the potential ancestor for the family.
He also proposed several migrations of Elephas out of Africa into Eurasia. He also separated L. adaurora
from the main Loxodonta lineage. He also uses Elephas and Paleoloxodon as subgenera for the African
Elephas lineage.
belong in the Loxodonta lineage, and may, combined
with M. subplanifrons, represent the primitive mammoth condition.
The grouping of Stegotetrabelodon with L. adaurora
supports Beden’s (1979) phylogeny (Fig. 8). Both Maglio
and Beden proposed Primelephas as the ancestor of Elephas and Mammuthus (and Maglio included Loxodonta
as a descendant) and the position of Primelephas gomphotheroides as ancestral is supported in the cladistic
analysis. However, the cladistic analysis, and previous
metric analysis (Todd, 1997) suggests a closer relationship between Stegotetrabelodon and L. adaurora. Combined with the conclusion stated previously that M.
subplanifrons and L. adaurora are the same species;
this suggests that Stegotetrabelodon is ancestral to Loxodonta and Mammuthus. Primelephas is ancestral to Elephas only (Fig. 8). Both Maglio and Beden divided
Elephas recki into smaller taxonomic units, Stages 1–4
by Maglio, Elephas recki brumpti, E. r. shungurensis, E.
r. atavus, E. r. ileretensis, and E. r. recki by Beden. There
is still much variation even within these groups, and E.
recki as proposed is not a valid species (Todd, 2005).
There are specimens that belong to Loxodonta and Mammuthus, as well as Elephas and the Paleoloxodon group
that had been previously attributed to E. recki. Originally, a subgenus of Elephas, Paleoloxodon is resurrected
in this new phylogeny, and includes specimens previously attributed to E. recki from 2.5 to 4 ma in Africa.
Subspecies designations for E. recki are no longer considered valid (Fig. 7).
In Maglio’s (1973) phylogeny, he includes one migration out of Africa for Elephas, that subsequently underwent an adaptive radiation in Eurasia (Fig. 9). Beden
(1979) proposed two migrations of Elephas out of Africa;
an earlier wave that evolved into Elephas (Elephas), and
a second, younger wave that he designates Elephas
(Paleoloxodon) due to similarities of these species to the
African Elephas recki lineage. In this analysis, the Eurasian Elephas species, Elephas namadicus and Elephas
antiquus, group together with the extant Elephas
88
TODD
Fig. 9. In Maglio’s (1973) phylogeny, he includes Primelephas as the ancestor to the Elephantidae, and
only one migration event of Elephas out Africa into Eurasia, where the lineage subsequently underwent an
adaptive radiation.
maximus and with Elephas meletensis consistently in
both ordered and unordered cladograms. E. recki and
Elephas iolensis (African species) group consistently
with Elephas hysudricus (Eurasian) and Elephas mnaidriensis (Mediterranean dwarf). The cladistic analysis
presented here supports Beden’s phylogeny of two separate migrations out of Africa for Elephas, with potentially
two
separate
dwarfing
events
in
the
Mediterranean groups, although the allometric issues
involved with reduction in body size in elephants is
potentially generating homoplastic noise and this needs
further study.
Maglio (1973) and others firmly place E. hysudricus as
the ancestor to E. maximus. In this analysis, E. maximus
does not form a clade with E. hysudricus and E. iolensis.
However, previous metric data supports the relationship,
and it is retained here for now (Todd, 1997). The wide
range of metric variation in dentition in the African Elephas group, as well as the Eurasian species complicates
the situation, and much further work is needed. The
retention of a lozenge-like shape to the enamel figure in
E. recki, E. antiquus, and E. namadicus, as well as with
the dwarfed Mediterranean species, suggests an evolutionary relationship, as do various cranial similarities,
such as large parietal bosses that overhang the forehead.
There are recent data supporting the inclusion of some of
the Mediterranean dwarfs in Mammuthus (Poulakakis
et al., 2002), and this is an interesting possibility.
Elephas hysudricus, Elephas planifrons, Elephas maximus, and other Eurasian species have parallel-sided
enamel figures, much thinner enamel and more lamellae. Thus, there may be support here for two separate
genera within the Elephas group, an Elephas group that
migrates out of Africa 3.7 ma, and potentially back to
Africa with Elephas iolensis, and a Paleoloxodon group
that leaves Africa 2.5 ma (Fig. 7).
This cladistic study relies heavily on dentition, which
appears to be highly variable in fossil species and lineages, and again, more analysis is needed on cranial
characters
which
suggest
specific
evolutionary
PHYLOGENETIC ANALYSIS OF THE ELEPHANTIDAE
relationships between African and Eurasian species. In
addition, examination of postcranial elements potentially
adds further data for comparisons. This is the first cladistic analysis to focus specifically on the Elephantidae as
a whole, and the first new phylogenetic proposal in
many years. Much comparative study remains to be
done, as well as analysis of metric variation in fossil and
modern elephants in order to further elucidate the complicated evolutionary relationships within this family.
ACKNOWLEDGMENTS
This study would not have been possible without the
permission of the Directors and Curators at the following museums: American Museum of Natural History,
National Museum of Natural History, National Museums
of Kenya, Tanzanian Museum, Musée Nationale d’Histoire Naturelle, British Museum of Natural History, and
the Royal Ontario Museum. In addition, the author
thanks many who helped with comments and information along the way, particularly P. Tassy, W. Sanders, M.
Leakey, T. Harrison, J. Kalb, J. Kingston, A. Lister, L.
Agenbroad, E. Sargis, T. Plummer, R. Potts, K. Behresmeyer, A. Brooks and D. Lipscomb.
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