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A new Eocaiman (Alligatoridae, Crocodylia) from the
Itaboraí Basin, Paleogene of Rio de Janeiro, Brazil
André E.P. Pinheiro a , Daniel C. Fortier b c , Diego Pol d , Diógenes A. Campos e & Lílian P.
Bergqvist a
a Laboratório de Macrofósseis, Departamento de Geologia , Universidade Federal do Rio de
Janeiro , Ilha do Fundão, Av. Athos da Silveira Ramos s.n, Rio de Janeiro , Brazil
b Departamento de Paleontologia e Estratigrafia , Universidade Federal do Rio Grande do
Sul , Campus do Vale, Av. Bento Gonçalves 9500, Cx.P. 15001, 91501-970 , Porto Alegre ,
Brazil
c Intituto de Geociências, Universidade Federal de Minas Gerais , Av. Antônio Carlos 6627,
Pampulha, Belo Horizonte , Brazil
d CONICET - Museo Paleontológico Egidio Feruglio , Avenida Fontana 140, Trelew , 9100 ,
Argentina
e Museu de Ciências da Terra, Departamento Nacional de Produção Mineral , Av. Pasteur 404,
Rio de Janeiro , Brazil
Published online: 17 Dec 2012.
To cite this article: André E.P. Pinheiro , Daniel C. Fortier , Diego Pol , Diógenes A. Campos & Lílian P. Bergqvist (2013): A
new Eocaiman (Alligatoridae, Crocodylia) from the Itaboraí Basin, Paleogene of Rio de Janeiro, Brazil, Historical Biology: An
International Journal of Paleobiology, 25:3, 327-337
To link to this article: http://dx.doi.org/10.1080/08912963.2012.705838
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A new Eocaiman (Alligatoridae, Crocodylia) from the Itaboraı
´Basin,
Paleogene of Rio de Janeiro, Brazil
Andre
´E.P. Pinheiro
a
*, Daniel C. Fortier
b,c1
, Diego Pol
d2
,Dio
´genes A. Campos
e3
and Lı
´lian P. Bergqvist
a4
a
Laborato
´rio de Macrofo
´sseis, Departamento de Geologia, Universidade Federal do Rio de Janeiro, Ilha do Funda
˜o, Av. Athos da
Silveira Ramos s.n, Rio de Janeiro, Brazil;
b
Departamento de Paleontologia e Estratigrafia, Universidade Federal do Rio Grande do Sul,
Campus do Vale, Av. Bento Gonc¸alves 9500, Cx.P. 15001, 91501-970, Porto Alegre, Brazil;
c
Intituto de Geocie
ˆncias, Universidade
Federal de Minas Gerais, Av. Anto
ˆnio Carlos 6627, Pampulha, Belo Horizonte, Brazil;
d
CONICET - Museo Paleontolo
´gico Egidio
Feruglio, Avenida Fontana 140, Trelew 9100, Argentina;
e
Museu de Cie
ˆncias da Terra, Departamento Nacional de Produc¸a
˜o Mineral,
Av. Pasteur 404, Rio de Janeiro, Brazil
(Received 17 April 2012; final version received 20 June 2012; first published online 17 December 2012)
A new small species of Eocaiman is described on the basis of three anterior left mandibular rami and one isolated tooth.
The specimens came from the middle-upper Paleocene Itaboraı
´Basin (Rio de Janeiro State, Brazil; Itaboraian South
American Land Mammal Age). The new taxon differs from the other two Eocaiman species, such as its small size, likely
participation of the splenial in the mandibular symphysis, a reduced angle between the longitudinal axis of the symphysis
and the mandibular ramus, and enlarged ninth and tenth dentary teeth (in addition to the large first and fourth dentary teeth).
The participation of the splenial in the mandibular symphysis is a unique character among caimanines (with the only
possible exception being Tsoabichi greenriverensis). The new taxon provides new information on the taxonomic and
anatomical diversity of the genus Eocaiman, a taxon of prime importance to understand the evolutionary origins of caimans
given its position as the basalmost member of Caimaninae. Furthermore, the new taxon has a relatively small body size in
comparison with other species of Eocaiman, a case paralleled by other Itaboraian reptilian groups (e.g. snakes), suggesting
that this ecosystem provides critical data to test the relationship between reptilian body size and climate.
http://zoobank.org/83636F22-D121-4A77-9141-BE68987B6CBF
Keywords: Crocodyliformes; Alligatoroidea; Caimaninae; Eocaiman; Itaborai; Paleogene
1. Introduction
Crocodylomorph archosaurs are an important and diverse
group of reptiles that first appeared in the Late Triassic.
Extant diversity is relatively low, consisting of 24 –30
species (Martin 2008; Hekkala et al. 2011; Densmore III
et al. 2011) with a worldwide distribution in tropical and
subtropical regions. Extant species belong to Crocodylia
(Gmelin 1789, sensu Benton and Clark 1988), a crown
group that first appears in the Late Cretaceous (Benton and
Clark 1988; Brochu 2003; Pue
´rtolas et al. 2011). The
crocodylian body plan was established during the
Mesozoic (Gasparini 1981), but it was during the Cenozoic
that crown crocodylians likely achieved a worldwide
distribution, replacing other crocodylomorph lineages that
thrived during the Mesozoic (Buscalioni et al. 2003;
Salisbury et al. 2006; Pue
´rtolas et al. 2011). As Brochu
(2003) noted, the basal most members of Brevirostres
(Crocodyloidea þAlligatoroidea) already have the stereo-
typical aspect of extant crocodiles, with long and
dorsoventrally flattened snouts outwardly resembling the
modern American alligator or the Nile crocodile. The
crown-group Alligatoridae, first appears in the earliest
Paleocene and includes two major stem-based clades –
Alligatorinae and Caimaninae (Brochu 1999).
Alligatorinae has a rich fossil record, especially in the
Paleocene and Eocene of North America and Europe, but
the group is currently restricted to only two living species of
Alligator that inhabit the southeastern United States
(A. mississippiensis) and eastern China (A. sinensis).
The Paleogene fossil record of Caimaninae is, in contrast,
much more incomplete (Brochu 2011) but is more speciose
today, ranging from five to seven species depending on the
division of some species complexes (Brochu 2010). The
caimanine fossil record in the Paleogene of South America
is discontinuous but indicates this clade was established
very early in the Cenozoic (Brochu 2010, 2011). The oldest
caimans, Necrosuchus ionensis,Eocaiman palaeocenicus
and Notocaiman stromeri, are all known from the Paleocene
of Patagonia (Simpson 1937; Bona 2007; Brochu 2011).
The genus Eocaiman, erected by Simpson (1933), was
one of the first lineages that radiated in South America
(Simpson 1933; Brochu 1999; Bona 2007). Eocaiman
cavernensis was the first species described and the only
one known from substantial cranial material found in
q2013 Taylor & Francis
*Corresponding author. Email: paleolones@yahoo.com.br
Historical Biology, 2013
Vol. 25, No. 3, 327–337, http://dx.doi.org/10.1080/08912963.2012.705838
Downloaded by [American Museum of Natural History] at 07:07 06 June 2013
Colhue
´-Huapı
´Lake (middle Eocene of Chubut [Re
´et al.
2010], Argentina; Casamayoran South American Land
Mammal Age [SALMA]). Langston (1965) referred
materials to this genus from La Venta (middle Miocene
of La Venta, Colombia; Laventan SALMA). The first
material tentatively referred to Eocaiman from the
Paleocene was described by Gasparini (1981) from the
lower Paleocene of Salamanca Formation (Chubut,
Argentina; Peligran SALMA). More recently, the Sala-
manca Formation has yielded a more complete specimen,
described as E. palaeocenicus (Bona 2007). Several
authors have mentioned the presence of Caiman sp. in the
paleofaunal lists of the mid–late Paleocene Itaboraı
´Basin
for over 60 years (e.g. Price and Paula-Couto 1946, 1950;
Price and Campos 1970; Palma and Brito 1974). This
material is here described and recognised as a new species
of the genus Eocaiman based on a phylogenetic analysis,
constituting the smallest known species of the genus.
1.1. Institutional abbreviations
AMNH, American Museum of Natural History, New York,
United States; DGM, Departamento de Geologia e
Mineralogia, now designated as MCT; MACN, Museo
Argentino de Ciencias Naturales Bernardino Rivadavia,
Buenos Aires, Argentina; MCT, Museu de Cie
ˆncias da
Terra; CPRM, Companhia de Pesquisas e Recursos
Minerais; DNPM, Departamento Nacional de Produc¸a
˜o
Mineral, Rio de Janeiro; Brazil; MLP, Museo de La Plata,
Argentina; MPEF, Museo de Paleontologı
´a Egidio
Feruglio, Trelew, Argentina; UCPM, University of
California Paleontological Museum, California, United
States; UFRJ-DG, Universidade Federal do Rio de Janeiro,
Departamento de Geologia, Rio de Janeiro, Brazil.
1.2. Anatomical abbreviations
d3, third dentary tooth; d3–d10, dentary teeth from third
to tenth; d3–d13, dentary teeth from third to thirteenth
positions; d4, fourth dentary tooth; d4 a, fourth dentary
tooth alveolus; d4a–d12a, dentary teeth alveoli from
fourth to twelfth positions; d9, ninth dentary tooth; d10,
tenth dentary tooth; d13, thirteenth dentary tooth; mc,
meckelian channel; ms, mandibular symphysis; sl,
posterior end of mandibular symphysis; sp ds, splenial
dorsal scar; sp vs, splenial ventral scar.
2. Itaboraı
´Basin: geology, paleontological context
and age
The depressional margins of eastern of Brazil are related to
the breakup of Western Gondwana: the separation of South
America from Africa and the opening of the South Atlantic
Ocean, a geologic structural process known locally as the
‘Continental Rift of Southeastern Brazil’ – CRSB (Medeiros
and Bergqvist 1999a; Sant’Anna and Ricomini 2001;
Sant’Anna et al. 2004). The Itaboraı
´Basin holds the major
fossiliferous deposits of Rio de Janeiro State (southeastern
Brazil) and represents the only ones that preserve vertebrates
and macroinvertebrates. These fossils record one of the
earliest phases of the radiation of the endemic mammalian
lineages of South America after the Cretaceous–Paleogene
biotic crisis (e.g. Bergqvist and Ribeiro 1998; Klein and
Bergqvist 2002; Bergqvist et al. 2009).
The basin is a small depression lying over the crystalline
basement of the Paraı
´ba do Sul Group (Medeiros and
Bergqvist 1999a, 1999b). The Itaboraı
´Basin is a small half-
graben, having a rhombohedral shape with a NE–SW major
axis 1.400º
¯m, and a NW –S E directed minor axis 500º
¯mwide.
The sedimentary sequence reaches a maximum thickness of
125º
¯m (Rodrigues-Francisco et al. 1985). Lithologically, the
calcareous sediments of the Itaboraı
´Basin mostly comprise
limestones deposited during a hydrothermal phase (S1 layer
by Medeiros and Bergqvist 1999b [Rodrı
´gues-Francisco et al.
1985; Sant’Anna et al. 2004]). A second sedimentary cycle
was deposited in fissures and is composed of lacustrine marls,
karstic marls and breccias formed by freshwater and clastic
flows containing plant and animal remains from the margins
of the basin (S2 layer by Medeiros and Bergqvist 1999b;
Figure 1). Due to strong CRSB tectonic activity, some NE-
directed faults were generated in the basin (with the Sa
˜o Jose
´
Fault being the most significant) and include an extrusive
ankaramitic magmatic event that crosscut the S1 and S2
sedimentary sequences (Ferrari 2001). These extrusive rocks
are absolutely K/Ar dated to 52.6 ^2.4 Ma (early Eocene
sensu Riccomini and Rodrigues-Francisco 1992).
The occurrence of fossils in the Itaboraı
´Basin has been
known since the 1930s when the Portland Maua
´National
Company began the extraction of calcareous sediments for
industrial cement production (Leinz 1938). According to
Bergqvist et al. (2005, 2008), the relative fossil diversity of
the Itaboraı
´Basin at family level consists of 44%
mammals, 23% mollusks, 14% reptiles (lizards, chelo-
nians, crocodyliforms), 7% birds, 5% amphibians and 7%
plants. The crocodyliform fauna from Itaboraı
´includes at
least four undescribed taxa. One of them has been listed as
Caiman sp. (e.g. Price and Paula-Couto 1950; Price and
Campos 1970) and is the focus of the present contribution.
The other three taxa have been identified as members of
Sebecidae and are much larger in body size. These include
a large skull referred as a bretesuchid (Gasparini et al.
1993; Pinheiro et al. 2011a), an isolated maxilla identified
as Sebecus indet. (Price and Paula-Couto 1946), and
premaxillary–maxillary remains of a gracile form
identified as Sebecus cf. huilensis (Pinheiro et al. 2011b).
The age of the Itaboraı
´sediments has been inferred based
on biostratigraphic information of different taxonomic
groups, but these inferences differ markedly depending on
the group being analysed (Bergqvist et al. 2005, 2009). Early
A.E.P. Pinheiro et al.328
Downloaded by [American Museum of Natural History] at 07:07 06 June 2013
inferences were based on gastropods, plants and polyno-
morphs, and the age varied between the lower Paleocene and
Pliocene (e.g. Maury 1935; .Mezzalira 1946; Magalha
˜es
1950; Trindade 1956; Parodiz 1969; Cunha et al. 1984a,
1984b; Lima and Cunha 1986; Mussa et al. 1987). Post-
Cretaceous isolation of South America generated a strongly
endemic resident mammalian fauna, complicating faunal
correlation with other continents (Flynn and Swisher 1995).
However, this endemism facilitated correlations within
South America, and allowed the establishment of approxi-
mately 20 mammal-based ages (SALMAs) for this continent
(Bergqvist et al. 2005). The inferred age of the Itaboraı
´Basin
based on themammalian fauna hasbeen the matter of a recent
debate, ranging from the early Paleocene (Muizon and Brito
1993) to earliest Eocene (Gelfo et al. 2009). According to
Rage (1998), there may be an important problem in the
‘Itaboraı
´’s S2 paleofauna’, which may include, at least to
some extent, a mixture of fossils of slightly different ages, a
possibility given fossiliferous sediments found in multiple
fissure infillings. Gayet et al. (1991) noted that deposition of
S2 does not comprise a unique continuous sedimentary
process; some deposits possibly formed during the middle
Paleocene, while other shorter depositional events occurred
during late Paleocene or even early Eocene.
Because of its paleontological importance, the Itaboraı
´
Basin area was designated as a paleontological park in
1995 (Figure 1): ‘Parque Paleontolo
´gico de Sa
˜o Jose
´de
Itaboraı
´’ (‘Sa
˜o Jose
´de Itaboraı
´Paleontogical Park’,
municipal law no. 1.346 [Beltra
˜o et al. 2001]).
3. Systematic paleontology
Order: Crocodylia Gmelin 1789 (sensu Benton & Clark
1988)
Suborder: Brevirostres von Zittel 1890 (sensu Brochu
1997)
Superfamily: Alligatoroidea Gray 1844
Family: Alligatoridae Cuvier 1807 (sensu Norell et al.
1994)
Subfamily: Caimaninae Brochu 1999 (following Norell
1988)
Genus: Eocaiman Simpson 1933
Type species
Eocaiman cavernensis Simpson 1933
Taxonomic content
The genus comprises 3 species based on 20 specimens:
Eocaiman cavernensis (AMNH 3158); E. palaeocenicus
Figure 1. Location of the Itaboraı
´Basin and Paleontological Park with basin litostratigraphic chart on the right (modified from Bergqvist
et al. 2005).
Historical Biology 329
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(MPEF-PV 1933, 1935, 1936; MLP 90-II-12 –117, 90-II-
12–124, 93-XII-10 – 11, 93-XII-10–13, 95-XII-10 –20,
95-XII-10–27; MACN-PV CH 1914, 1915, 1916, 1627);
E. itaboraiensis sp. nov. (MCT 1791-R, 1792-R, 1793-R,
1794-R). Additionally, fragmentary materials (UCPM
38,878, 39,023) from the middle Miocene of Colombia
(Villavieja Formation, La Venta) were also referred to
Eocaiman sp. by Langston (1965), but a detailed study of
these materials remain to be conducted to test their
phylogenetic affinities.
Temporal range and distribution
Lower Paleocene to middle Miocene: Eocaiman palaeo-
cenicus represents the most ancient record from the lower
Paleocene of Chubut Province, Argentina (El Gauchito
locality, Salamanca Formation; see Bona 2007). Eocaiman
cavernensis comes from the middle Eocene of Chubut
Province, Argentina (Sarmiento Formation). The geologi-
cally youngest material referred to this genus would be
from the Miocene of Colombia (‘La Venta fauna’ of
Honda Group) if the affinities of the above-mentioned
undescribed material is confirmed.
Emended diagnosis
Caimaninae with following unique combination of
characters; mandibular symphyseal region broad and
shallow (with a width/height ratio of at least 1.6 at the
level of the fourth dentary teeth), and extending to fifth or
sixth dentary alveolus; first and fourth dentary teeth
enlarged, with tenth –eleventh or twelfth–thirteenth teeth
enlarged at mid-posterior region of the toothrow; dentary
height at first and fourth dentary teeth lower than the height
at the level of eleventh –twelfth dentary teeth; alveolar
margin of dentary concave between fourth and tenth –
thirteen teeth (where alveolar margin arises markedly).
Eocaiman itaboraiensis sp. nov
(Figures 2–5)
Holotype
MCT 1791-R, a well-preserved small left anterior dentary
fragment, broken at the level of the eleventh alveolus and
bearing four fully preserved teeth (d3,d5,d9 and d10).
Referred specimens
MCT 1792-R, a small left anterior dentary fragment with
no teeth preserved (the material lacks part of the first
alveolus), is broken at the level of the thirteenth alveolus,
and lack the mesial dentary portion from the seventh
alveolus. MCT 1793-R, is a small left anterior dentary
fragment with no preserved teeth; broken at ninth to tenth
alveoli level and with the alveoli filled by sediment. All
specimens comprise only the anterior left dentary rami and
missing the splenials. An isolated small blunt tooth (root
and crown), MCT 1794-R, was deposited together with the
holotype and paratypes in the MCT collections. This tooth
has diagnostic features of a caimanine and is clearly
distinct from all other crocodyliforms known form the
Itaboraı
´Basin; therefore, we tentatively refer this tooth to
E. itaboraiensis.
Etymology
The species name, itaboraiensis, refers to the provenance
of the material from the Itaboraı
´Basin.
Locality
Itaboraı
´Basin, 2285002000 S and 4285203000 W. Sa
˜o Jose
´
Farm, Sa
˜o Jose
´de Itaboraı
´neighbourhood, ENE of the Rio
de Janeiro metropolitan area (SE Brazil): 34º
¯km NE of Rio
de Janeiro City; 25º
¯km ENE of Nitero
´i City; 15.5 SE of
Itaboraı
´City.
Figure 2. Left dentaries of Eocaiman itaboraiensis sp. nov. in
left lateral view. A, MCT 1791-R; B, MCT 1792-R; C, MCT
1793-R. Scale bars equal 5º
¯mm.
A.E.P. Pinheiro et al.330
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Horizon and age
From the fissure infilling S2 sequence of the Itaboraı
´Basin
(Medeiros and Bergqvist 1999b), composed of marls and
collapsed breccia formed by the dissolution and opening of
fissures in the S1 sequence. These materials lack more
precise data on the horizon or the exact fissure infilling in
which it was found. Itaboraian SALMA (58 –56.5 Ma,
middle–upper Paleocene [Marshall 1985]).
Diagnosis
Eocaiman itaboraiensis is a caimanine that differs from all
other species in the following set of characters
(autapomorphies marked with *): dentary with slightly
elevated region along symphyseal suture; reduced angle
between longitudinal axes of symphysis and mandibular
ramus (approximately 68)*; sutural facets on medial
surface of dentary for splenial reaching mandibular
symphysis, ventral and dorsal to Meckelian groove; first
tooth procumbent; tenth and eleventh mandibular teeth
enlarged*; concave alveolar margin of dentary short and
poorly developed, comprising region of d6–d8; dentary
tooth row mesially deflected posterior to d5 in dorsal
view*.
Remarks
The specimens referred to E. itaboraiensis sp. nov. have
been kept associated in the MCT collection but lack
information regarding their precise provenance. However,
the different colouration of these fossils and the carbonate
matrix (varying from yellowish to greyish-white) suggests
these specimens were recovered from different S2 fissures
infills.
4. Description
4.1. General features
The specimens of E. itaboraiensis are notably small, with
the dentary fragment of all three specimens not exceeding
30º
¯mm in length: MCT 1791-R measures 25º
¯mm from the
first to the tenth alveolus; 1792-R measures 29º
¯mm from
the first to the twelfth alveolus; 1793-R measures 25.5º
¯mm
Figure 5. Select teeth of Eocaiman itaboraiensis sp. nov. A,
crown surface detail of MCT 1791-R in lingual view; B, MCT
1794-R labial view in left, lingual view in right; C, MCT 1794-R
labial crown surface detail; D, MCT 1794-R lingual crown
surface detail. Abbreviations:d9, ninth dentary tooth; d10, tenth
dentary tooth. Scales: A, equals 1º
¯mm; B, equals 2º
¯mm, Cand D,
equal 1º
¯mm.
Figure 4. Left dentaries of Eocaiman itaboraiensis sp. nov. in
occlusal (dorsal) view. A, MCT 1791-R; B, MCT 1792-R; C,
MCT 1793-R. Scale bars equal 5º
¯mm.
Figure 3. Left dentaries of Eocaiman itaboraiensis sp. nov. in
medial view. A, MCT 1791-R; B, MCT 1792-R; C, MCT 1793-
R. Scale bars equal 5º
¯mm.
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from the first to the ninth alveolus (Figures 2–4). The
similar size of the three specimens and the ornamentation
of their external surfaces suggest E. itaboraiensis was a
small-bodied taxon, and if these specimens indeed
represent adult individuals it would represent the smallest
caimanine taxon known to date.
The dentary of E. itaboraiensis is intermediate in
robustness between the markedly robust dentary of
E. palaeocenicus (MPEF-PV 1933) and the more gracile
and low dentary of E. cavernensis (AMNH 3158). The
holotype (MCT 1791-R) is 12% longer than the two
referred specimens (as measured from the length of the
second to the ninth alveoli) and 35.3% broader (as
measured by the maximum lateromedial width of the
symphyseal region), suggesting a difference in their
ontogenetic stages (Figure 4). Other characters that vary
among these specimens are consistent with an ontogenetic
explanation, such as ornamentation and the degree of
development of the enlarged dentary teeth.
The ornamentation of the holotype (MCT 1791-R) is
more strongly developed than in the other specimens, with
more numerous and deeper circular pits located mainly in
the anteriormost portion of the dentary and more
developed but irregularly shaped depressions along the
posterior region of the preserved dentary (Figure 2). The
ornamentation of MCT 1792-R and 1793-R is poorly
developed and consists of small and well-spaced pits
and shallow grooves, resembling the condition of
E. cavernensis (AMNH 3158). The holotype (MCT
1791-R) bears seven neurovascular foramina on the lingual
surface of alveolar region, whereas in MCT 1792-R there
are nine neurovascular foramina located at level of d1 and
d7, and in MCT 1793-R there are nine foramina between
d1 and d9 (Figures 3 and 4).
4.2. Mandibular symphysis
The length of the mandibular symphysis in E. itabor-
aiensis resembles the condition of other species of
Eocaiman, extending posteriorly to the sixth mandibular
alveolus (Figures 4 and 6). In the holotype, the posterior
end of the symphysis reaches the final two-third of d6,
whereas in the MCT 1792-R and 1793-R symphysis
reaches the posterior margin of the d6 (Figure 4). The
dorsal surface of the dentary at the symphyseal region is
wide and low, but bears a slightly elevated area along the
sutural margin of the symphysis. The low and spatulated
morphology of the symphyseal region of E. itaboraiensis
is more similar to that of E. cavernensis (AMNH 3158)
than the rounded and ‘U’-shaped condition of
E. palaeocenicus (MPEF-PV 1933 [Figure 6]).
The angle formed between the longitudinal axis of the
mandibular symphysis and the longitudinal axis of the
mandibular ramus of E. itaboraiensis is the smallest
among known species of Eocaiman, forming an angle of
approximately 68(E. cavernensis, 11.78;E. palaeocenicus,
22.58[Figure 6]).
The splenials are not preserved in E. itaboraiensis but
the sutural facets on the dentary indicate that the splenials
reached the mandibular symphysis, especially dorsally.
The medial surface of the dentary bears a well-marked
lineation dorsal to the Meckelian groove and along its
ventromedial margin; both lineations end at the mandib-
ular symphysis (Figure 3). The sutural surface of the
mandibular symphysis is dorsal to the Meckelian groove,
and the posterior surface of the symphysis has an irregular
outline with the ventral portion more developed, also
suggesting that the splenial may cover the posterodorsal
region of the symphysis. However, as the splenials are not
preserved in any of the specimens of E. itaboraiensis, we
can only determine that the splenial reached the
mandibular symphysis but we cannot determine the details
of its participation. In caimanines (and derived alligator-
ines), the splenial extends anteriorly dorsal to the
Meckelian groove but does not reach the symphysis
(Brochu 1999; Bona and Desojo 2011). The only possible
exception has been noted for Tsoabichi greenriverensis,a
caimanine from the Lower Eocene of Wyoming, which
possibly possesses a splenial participation of the
mandibular symphysis although its condition cannot be
determined with certainty (Brochu 2010). Splenial
participation in the mandibular symphysis is a plesio-
Figure 6. Outline drawings of the anterior dentaries of
Eocaiman species in left lateral and occlusal views. Aand B,
E. itaboraiensis sp. nov. MCT 1791-R; Cand D,E. itaboraiensis
sp. nov. MCT 1792-R; Eand F,E. itaboraiensis sp. nov. MCT
1793-R; Gand H,E. cavernensis AMNH 3158; Iand J,E.
palaeocenicus MPEF-PV 1933. Vertical dashed lines represent
the transversal axis at the level of the posterior end of the
mandibular symphysis. Scale bars equal 1º
¯cm.
A.E.P. Pinheiro et al.332
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morphic condition for Brevirostres (Brochu 1999, 2010),
maintained in basal forms of Alligatoroidea (e.g.
Leidyosuchus,Stangerochampsa [Brochu 1999]) and
Alligatorinae (e.g. Navajosuchus mooki).
4.3. Tooth row morphology
The alveolar concavity at the anterior region of the dentary
extending from d5 to d10 is only slightly developed in
E. itaboraiensis (being more marked in MCT 1791-R than
1792-R and 1793-R [Figure 2]). This resembles the
condition of E. cavernensis (AMNH 3158), although in
the latter species it extends from d6 to d11. The anterior
alveolar concavity in E. palaeocenicus (MPEF-PV 1933)
and Eocaiman sp. (UCPM 39,023) extends from d6 to d10
and is much more developed, especially in UCPM 39,023.
Posterior to this region, the alveolar margin of the dentary
ascends and at the level of d10 –d11 this margin is much
higher than at the level of d4 (Figure 5), a condition shared
with other species of Eocaiman (Simpson 1933; Bona
2007). This contrasts with the condition of other members
of Caimaninae (e.g. Caiman DGM 301-RR, 157-RR, 148-
RR, and 156-RR), Melanosuchus (DGM 154-RR and 305-
RR) and Paleosuchus (DGM 268-RR, 291-RR, 292-RR
and 293-RR), in which the alveolar margin at the twelfth or
thirteenth tooth is almost at the same level of the alveolar
margin of d4.
The tooth row of E. itaboraiensis is medially deflected
in dorsal view posterior to d6 (Figure 4), as in
E. cavernensis (AMNH 3158) but not in E. palaeocenicus
(MPEF-PV 1933). The first twelve teeth of E. itabor-
aiensis are known – MCT 1791-R preserves the first ten
alveoli, with teeth in d3,d5,d9 and d10; 1792-R preserves
the first thirteen alveoli and the base and root of the first
seven; 1793-R preserves the ten first alveoli. The first,
fourth, tenth, and probably the eleventh alveoli of MCT
1791-R are enlarged relative to the other alveoli (Figures 4
and 7). The tooth size variation is similar in pattern to the
holotype but with slightly different sizes in the two smaller
referred specimens (MCT 1792-R and 1793-R), which
show less enlargement of d4,d10 and d11 (Figures 4
and 7). However, in MCT 1792-R the partially preserved
twelfth and thirteenth alveoli (Figure 3) are anteroposter-
iorly longer than the tenth and eleventh alveoli, indicating
that the largest dentary teeth of E. itaboraiensis had not
been preserved in the available specimens. This pattern of
alveolar variation in the other two species of Eocaiman is
slightly different but shares the presence of enlarged teeth
in the first, fourth, twelfth and thirteenth alveoli (in E.
cavernensis [AMNH 5158] the d10 is also enlarged, while
in E. palaeocenicus [MPEF-PV 1933] not the d10, but the
d11 is enlarged [Figure 7]).
The first dentary tooth of E. itaboraiensis is anteriorly
procumbent, a feature shared with E. cavernensis (AMNH
3158) and Eocaiman sp. (UCPM 38,878 and 39,023); an
unusual feature among crocodylians (Figure 5). Eocaiman
palaeocenicus (MPEF-PV 1933) clearly has the general-
ised morphology of crocodylians with anterodorsally
facing anterior alveoli. The first five dentary teeth of
E. itaboraiensis are set in evenly spaced alveoli that are
completely divided by interalveolar septa, whereas all
dentary teeth posterior to d5 or d6 are set in a continuous
alveolar groove. This condition is only present in the
posteriormost teeth of the upper and lower toothrow of
mature living caimanine species, although the alveolar
groove is more anteriorly extensive in juvenile specimens
Figure 7. Comparisons of the anteroposterior length of anterior alveoli of the dentary. The left toothrow was measured for all taxa
except for E. cavernensis (AMNH 3158) where measurements for d3–d13 were measured from the better-preserved right mandibular
ramus.
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(e.g. Caiman, Melanosuchus; AEPP pers. obs). The
presence of an anterior alveolar groove (between d8 and
d11) is also present in the large (almost 30º
¯cm estimated
mandibular length) and presumably adult holotype of E.
palaeocenicus (MPEF-PV 1933).
Preserved teeth posses a marked neck between the root
and crown and are slightly buccolingually compressed
(Figures 2, 3 and 5). They are pointed, cordiform in shape,
have a slight lingual curvature, and bear many low,
irregular apicobasal carinae on the outer enamel surface on
both crown surfaces (Figure 5). The distal and mesial
carinae are well developed in all preserved teeth and lack
serrations. The tenth tooth has an extensive apicobasal wear
facet (Figure 5). The isolated tooth MCT 1794-R tentatively
referred to E. itaboraiensis is small and blunt but preserves
most of the features observed in the holotype (e.g. many
irregular and low apicobasal carinae on its lingual and labial
surface). The distal and mesial carinae are well developed
and have modestly developed enamel wrinkles but not true
denticles (sensu Prasad and Broin 2002). In MCT 1794-R,
the labial surface of the root and the base of the crown bears
a slightly marked apicobasal sulcus. The sulcus divides the
labial surface of the root into two lateral bulges, conferring
a cordiform inverted crown shape. This condition is similar
to that of posterior teeth of some extant crocodylians (e.g.
Melanosuchus niger [DGM 154-RR, 286-RR, 305-RR])
and therefore MCT 1794-R is interpreted as a posterior
tooth of E. itaboraiensis (Figure 5).
5. Phylogenetic affinities of Eocaiman itaboraiensis
To analyse the phylogenetic affinities of the new taxon, a
cladistic analysis was conducted based on the dataset of
Brochu (2010), with the addition of one character
(modified from Bona 2007) and one character from
Brochu (1999) (Supplementary Data). The dataset
includes 3 non-alligatorid alligatoroids as successive
outgroups, and 16 alligatorids in the ingroup, including all
the caimanine species used by Brochu (2010) and
E. palaeocenicus. A total of 29 taxa and 125 characters
were analysed (see 1.1 and 1.2 in Supplementary data
available online). Multistate characters were treated as
unordered (following the original analysis of Brochu
2010) and all characters were equally weighted. The
parsimony analysis was conducted using TNT version 1.1
(Goloboff et al. 2008). An exhaustive branch-and-bound
search strategy was conducted performing the ‘implicit
enumeration’ option to recover the most parsimonious
trees (MPTs). Also, to avoid changes in the definition of
the character states, we coded E. itaboraiensis and
Tsoabichi as ‘?’ for character 40, and ‘2’ for the other
caimanines.
The phylogenetic analysis recovered nine MPTs
(length ¼187, CI ¼0.642, RI ¼0.801). The number
of MPTs is due to different positions for N. ionensis,asin
the original analysis of Brochu (2010). The reduced
consensus excluding Necrosuchus shows that the topology
recovered is the same as the one obtained by Brochu
(2010) with a monophyletic Caimaninae and Eocaiman
placed as the most basal member of this clade (Figure 8).
The two added taxa, E. itaboraiensis and E. palaeoceni-
cus, form a monophyletic group with E. cavernensis
(Figure 8), with the following internal topology:
(E. palaeocenicus þ(E. itaboraiensis þE. cavernensis)).
The Eocaiman clade is supported by a single
unambiguous synapomorphy: dentary at level of first and
fourth teeth lower than at level of eleventh –twelfth teeth
(character 124 [1]); a feature retrieved as a synapomorphy
of this genus in the analysis of Bona (2007). The presence
of only one synapomorphy is due to the fragmentary nature
of the specimens of E. palaeocenicus and E. itaboraiensis.
Nevertheless, this feature distinguishes Eocaiman from
other caimanines.
Eocaiman cavernensis and E. itaboraiensis are
recovered as sister taxa given the presence of a single
unambiguous synapomorphy: the presence of procumbent
first dentary teeth (character 125). The anterior end of the
mandibular symphysis of these two forms is dorsoventrally
low and has a subhorizontal ventral margin at its anterior
end. This condition contrasts with the condition of most
caimanines (including E. palaeocenicus) in which the
anterior dentary teeth project anterodorsally and the
anterior margin of the dentaries is anteriorly convex and
elevated.
Both E. cavernensis and E. palaeocenicus share an
anteroposteriorly long symphysis with no splenial
Figure 8. Phylogenetic relationships of Eocaiman itaboraiensis
sp. nov. Reduced strict consensus of nine most parsimonious trees
excluding Necrosuchus ionensis (solid black circles show the
alternative positions of this taxon within Caimaninae clade
among most parsimonious trees).
A.E.P. Pinheiro et al.334
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participation, while E. itaboraiensis may have a short
participation of the splenial in the symphysis, a
plesiomorphic condition for Alligatoridae (in which the
splenials are sutured under and below the Meckelian
groove [Brochu 2004]). Caimanines lack splenial partici-
pation in the mandibular symphysis, with the possible
exception of Tsoabichi (Brochu 2010), but project an
anterior process dorsal to the Meckelian groove (Brochu
1999, 2010). The possible presence of the plesiomorphic
participation of the splenial in the symphysis could suggest
that E. itaboraiensis is the basalmost known caimanine,
but this hypothesis requires two additional steps in the data
set used here, because of the synapomorphic features of
Eocaiman noted above, and therefore is rejected.
Alternatively, if the splenial participation in E. itabor-
aiensis and Tsoabichi are indeed confirmed, the evol-
utionary history of this character in Caimaninae (and
among alligatoroids in general) may have been more
complex than previously thought.
6. Discussion
Eocaiman is diagnosed by a single synapomorphy, the
relative level of the mandible in the anterior (first and
fourth alveoli) and mid-portion (eleventh and twelfth) of
the tooth row. However, species of this genus also share a
set of other common features that may diagnose Eocaiman
(see Diagnosis), but have not been included in a
phylogenetic analysis because they vary continuously in
alligatorids. These include the broad and shallow
mandibular symphysis that extends to the fifth–sixth
dentary alveoli and the marked concavity of the alveolar
margin between the fourth and tenth –thirteen teeth (where
the alveolar margin arises markedly).
Extant caimans have a strictly tropical distribution
(Ross 1998), and as stated by Brochu (2010, 2011), the
origin of Caimaninae suggests a dispersal event of basal
alligatoroids from North America to southern South
America early in the Cenozoic, with a minimum
divergence time of at least 60 Ma for the two groups.
This hypothesis, however, requires a dispersal event across
a salt-water environment (alligatorids are generally
intolerant of salt water [Taplin et al. 1982]), as there is
no strong evidence on the existence of terrestrial bridges
between the Americas during the early Cenozoic.
However, the fossil record of basal alligatoroids (Brochu
1999) and basal caimanines (Bona 2007; Brochu 2010,
2011) is not sufficiently complete to allow a thorough
understanding of this dispersal.
Eocaiman itaboraiensis and the recently described E.
palaeocenicus provides some information on the diversi-
fication pattern of Caimaninae during the Paleogene of
South America, which so far is restricted to three species
of Eocaiman,N. ionensis (Brochu 2011) and an additional
taxon from the Paleocene of Patagonia of uncertain
phylogenetic affinities (N. stromeri). Despite the lack of
current knowledge on the affinities of some of these forms
(Figure 8; see also Brochu 2011), the Paleogene diversity
of caimanines from South America appears to be restricted
to basal lineages of this clade. Eocaiman is the basalmost
Caimaninae (as suggested by Simpson [1933] and later
corroborated by phylogenetic analyses [Brochu 1999,
2010, 2011; Bona 2007]). In our analysis, Necrosuchus is
recovered in multiple positions but always basally within
the lineages leading to extant caimanines (i.e. Paleosuchus
and Caiman þMelanosuchus). The Oligocene –Miocene
fossil record of Caimaninae in South America, in contrast,
is dominated by more derived forms, representing early
members of extant lineages (e.g. Caiman tremembensis,
from the Oligocene of Brazil) or bizarre endemic clades
such as the gigantic Purusaurus (Brochu 2003).
Paleoenvironmental interpretations of the Itaboraı
´
Basin during the Paleocene suggest a semi-arid climate
based on the presence of plant remains (e.g. Psidium
[Myrtaceae], Celtis [Ulmaceae]) with periods of high
humidity (infilling fissure karst [Mussa et al. 1987;
Medeiros and Bergqvist 1999b; Bergqvist et al. 2005]).
The deposition of the Itaboraı
´sediments likely occurred
during the Paleocene–Eocene Thermal Maximum
(PETM), an event of increased global mean temperature
from 5 to 88C (McInerney and Wing 2011). The presence
of crown-crocodylians implies a mean annual temperature
equal to or higher than 14.28C. Increasing aridity and
thermal seasonality at mid-latitudes during the Cenozoic
likely restricted crocodyliforms to lower latitudes
(Markwick 1998).
The notably small body size of the three specimens of
E. itaboraiensis, in comparison with other species of
Eocaiman from the Paleocene and Eocene of Patagonia,
during the PETM appears to contradict the general
relationship of reptilian body size and temperature (i.e.
reptilian paleothermometer [Head et al. 2009]). Several
factors could explain this apparent conflict. One of them is
that the Itaboraı
´deposits have a systematic bias favouring
the fossilisation of only small-sized specimens. We found
this hypothesis untenable, as there are large-bodied
specimens of sebecid crocodyliforms, birds (e.g. Diogen-
ornis fragilis) and mammals (e.g. Epidolops ameghinoi
and Carodnia vieirai) known from these beds. Other
possible explanations could be related either to some of the
problems noted for this method (Denny et al. 2009;
Makarieva et al. 2009; Sniderman 2009) or to physiologi-
cal particularities of E. itaboraiensis that lived in the
presumably warm and dry environment of the Itaboraı
´
Basin. For instance, the small body size of E. itaboraiensis
might be related to a dry climate, since miniaturisation is
sometimes an evolutionary adaptation in stressful
environments (Hanken and Wake 1993). An interesting
parallel exists in the reduced body size of the boiid snakes
Historical Biology 335
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known from these sediments (Rage 2001), suggesting that
the Itaboraı
´herpetofauna may represent an interesting case
of study for testing the reptilian paleothermometer
hypothesis.
Acknowledgements
For access to and assistance with collections, we thank
C. Mehling (AMNH), R. Machado (CPRM/DNPM), A. Resetar
and K. Lawson (FMNH), J. Cundiff (MCZ), P. Holroyd (UCMP),
A. Hasting, K. Krysko and R. Hulbert (UF), and A. Wynn and
J. Jacobs (USNM). The Florida Museum of the Natural History,
the University of California Museum of Paleontology and the
Brazilian agencies CAPES and CNPq funded collection visits by
DF while FONCyT PICT 0736 provided support to D. Pol. C.A.
Brochu (UI) kindly provided photos of E. cavernensis and
critical comments. Thanks to F.S. Silva and C.W. Gabriel (LAFO
and LAGESED of DEGEO/CCMN/UFRJ) for microscopic
photos of Figure 5. Thanks also to C. Martinez (ULA) for
suggestions. TNT is a free program made available by the Willi
Hennig Society.
Notes
1. Email: danielcfortier@yahoo.com.br
2. Email: dpol@mef.org.ar
3. Email: dac@abc.org.br
4. Email: bergqvist@geologia.ufrj.br
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