DIAGNOSTIC REVISION OF THE BRAZILIAN INTERTROPICAL PANOCHTHINI (CINGULATA: GLYPTODONTOIDEA) AND A CLADISTIC ANALYSIS OF THE TRIBE
KLEBERSON de O. PORPINO,1,2 JUAN C. FERNICOLA,2 and LÍLIAN P. BERGQVIST3
1
Departamento de Ciências Biológicas, Universidade do Estado do Rio Grande do Norte, Rua Antônio Campos s/n, Mossoró, 59610-090, Rio Grande do Norte, Brazil,
kleporpino@yahoo.com.br;
2
Sección Paleontología de Vertebrados, Museo Argentino de Ciencias Naturales ―Bernardino Rivadavia,‖ Av. Ángel Gallardo 470, C1405DJR, Buenos Aires, Argentina,
jctano@yahoo.com;
3
Departamento de Geologia/UFRJ, Av. Athos da Silveira Ramos, 274, CCMN, bloco G, Cidade Universitária, 21941-916, Rio de Janeiro/RJ,
Brazil, bergqvist@geologia.ufrj.br
ABSTRACT– The tribe Panochtini is a long time recognized as a group of glyptodonts characterized by a remarkable suit of exoskeletal characters. In the late Pleistocene of northeastern Brazil this tribe is represented by two species, Panochthus greslebini and
Parapanochthus jaguaribensis, not reported from high latitudes. In this paper we provide a
diagnostic revision of these species and carry out a cladistic analysis in order to test their positioning within Panochthini and to shed light on the relationships within this tribe.
Panochthus greslebini is a valid species which differs from other species of Panochthus by a
unique combination of characters including at least one caudal tube autapomorphy (presence of an apexian figure). Parapanochthus is a valid genus and differs from Panochthus in having main figures in the osteoderms from mediodorsal and lateral regions of carapace, which are primitive characters within Panochthini. The cladistic analysis based on 22 characters from carapace and caudal tube yielded a fully resolved tree. Within Panochthini Nopachthus
coagmentatus appears as the stem species followed by Propanochthus bullifer and Parapanochthus jaguaribensis, the sister group of Panochthus. Within Panochthus, Panochthus intermedius is the basalmost taxon followed by Panochthus subintermedius, as
traditionally proposed. The Brazilian species Panochthus greslebini is the sister-group to a clade formed by the Lujanian species (Panochthus tuberculatus (Panochthus
morenoi+Panochthus frenzelianus). However the support for the relationships within Panochthus is weak.
INTRODUCTION
The tribe Panochthini was erected by Castellanos (1927) as a subfamily (Panochthinae) within the family Doedicuridae, to encompass three related genera: Nopachtus,
Propanochthus and Panochthus. Later, Hoffstetter (1958) argued that the osteological
characters exhibited by the members of this group do not support a closer relationship with doedicurines and repositioned it as a tribe belonging to the large subfamily Hoplophorinae. Among Panochthini, Panochthus is the best known genus, comprising several species from the middle to late Pleistocene (Ensenadan-Lujanian) of Argentina, Uruguay, Paraguay and Brazil (Castellanos, 1941; Carlini and Scillato-Yané, 1999; Carlini and Tonni, 2000; Moreira, 1971, Porpino and Bergqvist, 2002), most of which were described on the basis of caudal tube and carapace morphology alone.
In northeastern Brazil two species of Panochthus has been recognized: Panochthus
greslebini reported from Rio Grande do Norte (Oliveira et al., 1984; Porpino and Bergqvist,
2002), Paraíba (Moreira, 1971; Bergqvist, 1993), Ceará (Castellanos, 1941; Paula Couto, 1954; Moreira, 1971), Piauí (Guerin et al., 1993), Bahia (Cartelle, 1992) and Pernambuco states (Rolim, 1972; Alves and Barreto, 1997) and Panochthus jaguaribensis reported only for Ceará (Moreira, 1965) and Rio Grande do Norte (Oliveira et al., 1982; Porpino and Bergqvist, 2002) (Fig. 1). Moreira (1971) argued that Panochthus jaguaribensis should be transferred to a distinct genus (Parapanochthus) due to its divergent caudal tube and carapace morphology relative to other species attributed to Panochthus, though this interpretation was challenged by Porpino and Bergqvist (2002). In addition to P. greslebini and P.
jaguaribensis, two other species were described for the same region, Panochthus rochai
(Paula Couto, 1954) and Panochthus oliveira-roxoi (Castellanos, 1941), but both were later considered as synonymies of P. greslebini respectively by Moreira (1971) and Porpino and Bergqvist (2002). Remains of P. greslebini and P. jaguaribensis are only known from the late
Pleistocene-Holecene of northeastern Brazil so far, and they were interpreted as endemic to the Brazilian intertropical area (sensu Cartelle, 1999). A literature review has convinced us that the Brazilian Panochthini is still poorly diagnosed, as the original diagnoses (Moreira, 1971) do not clearly differentiate them from the meridional species and also used doubtful characters. This is complicated by the lack of cladistic studies on Panochthini, which would improve the perspective on character distribution within the group.
In this paper we present a diagnostic revision of the Brazilian Panochthini based on the caudal tube and carapace osteoderm morphology. In addition, we carry out a cladistic analysis of Panochthini in order to shed light on the position of those species and on the internal relationships of this tribe.
MATERIAL AND METHODS
All studied material were collected in sediments deposited inside natural depressions in basement rocks which are widespread in northeastern Brazil and known locally as ―tanks‖ (Cartelle, 1999). These deposits are remarkable due to their rich mammalian remains which have been attributed to the late Pleistocene-early Holocene based on comparisons with better known southernmost mammalian faunas of Argentina and Uruguay (Paula Couto, 1980; Cartelle, 1999).
The exoskeletal morphology of glyptodonts is quite complex and the names applied to specific structures could vary significantly among authors. The caudal tube of Panochthini has a characteristically complicated morphology and in this paper we followed the terminology employed by Castellanos (1941) which is sufficiently detailed to account for the complexity observed and had been traditionally used in previous descriptive studies (Moreira, 1971; Porpino and Bergqvist, 2002). We also followed Castellanos (1941; see also Carlini et al., 2008) in denominations of carapace regions (Fig. 2). As the carapace and caudal tube
morphology of the Panochthini from northeastern Brazil were described thoroughly in previous works (Moreira, 1971; Porpino & Bergqvist, 2002) we focused here on the diagnostic characters only. Details on the methods and assumptions used in the cladistic analysis are given in the phylogenetic analysis section.
Institutional Abbreviations—DGM-M, Divisião de Geologia e Mineralogia, Fossil Mammal Collection, of Departamento Nacional da Produção Mineral, FC-DPV, Departamento de Paleontologia, Faculdad de Ciencias, Universidad de la República, Uruguay, MACN, Museo Argentino de Ciências Naturales ―Bernardino Rivadavia‖, Buenos Aires, Argentina; MCC, Museu Câmara Cascudo, Natal/RN, Brazil; MHN, Museu de História Natural e Jardin Botânico, Belo Horizonte/MG, Brazil. MLP, Museo de Ciencias Naturales de La Plata, La Plata, Argentina; MN-V¸ Museu Nacional, Vertebrate Paleontology Collection, Rio de Janeiro/RJ, Brazil.
SYSTEMATIC PALEONTOLOGY Suborder GLYPTODONTIA Ameghino, 1889 Superfamily GLYPTODONTOIDEA Gray, 1869
Family PANOCHTHIDAE Castellanos 1927 Subfamily PANOCHTHINAE Castellanos, 1927
Tribe PANOCHTHINI Castellanos, 1927
Panochthus greslebini Castellanos, 1941
= Panochthus oliveira-roxai Castellanos (1941)
=Panochthus rochai Paula Couto (1954)
Figure 3
Holotype – DGM 01M (originally cited as DNPM 1), a caudal tube.
Referred Material – MN 2760/1V, caudal tube and carapace fragments; MN 2136V, partial caudal tube; MN 5760/5V, MN 3612V, MN 3768V, MN 3733V, MN 3772V, MN 3774V,
MN 4221V, MN 4222/2V, MN 4223-4226V, MCC 1548-1551V, MCC 1554V, MCC 1558V, MCC 1562V, carapace osteoderms.
Revised diagnosis. Panochthus greslebini differs from all species of Panochthus (except P.
Intermedius for which the caudal tube is not known) in having caudal tube with an apexian
figure. Differs further from Panochthus tuberculatus, Panochthus morenoi and Pancohthus
frenzelianus in having a single apical figure in the dorsal side of the caudal tube. Differs
further from Panochthus tuberculatus and Panochthus morenoi in the absence of main figures in the lateral margin of carapace. Differs from Panochthus intermedius in lacking main figures in carapace osteoderms from posterodorsal and anterodorsal regions (except in the posteriormost row which forms the posterior border). Differs further from Panochthus
subintermedius in having more robust caudal tube, with wider apex and in having three lateral
figures posterior to the proximal annular figures series (instead of four). Differs further from
Panochthus frenzelianus in having caudal tube with more developed conical tubercles, one
single apical figure in the ventral side of caudal tube (instead of three) and three to four pairs of lateral figures posterior to the fused caudal rings (instead of only three). Differs also from
Panochthus tuberculatus in having caudal tube with a single distalmost central median figure
positioned between the dorsal ones at dorsal and ventral sides.
Remarks. When Castellanos (1941) erected Panochthus greslebini he not presented a formal diagnosis and based his original description on a single caudal tube collected in Ceará state. The diagnosis was provided by Moreira (Moreira, 1971) who in addition described a new nearly complete caudal tube from Paraíba state (MN 2760V), collected in association with osteoderms and carapace fragments. However, Moreira (1971) did not clarify which characters are exclusive of P. greslebini and which are shared with other species of
known species within Panochthus (e.g. hexagonal, pentagonal or quadrangular shaped osteoderm lacking main figures, caudal tube with triangular apex and terminal figures converging to a point distally) and consequently they are hardly diagnostic. Moreira (1971) also mentioned the lack of discernible delimitation between the osteoderms from mediodorsal region of carapace as diagnostic for P. greslebini. However, this fusion of osteoderms was interpreted as an ontogenetic feature of adult individuals in “Glyptodon” tuberculatus (=Panochthus tuberculatus; Burmeister, 1864, p. 85-86) as well as in other glyptodonts (e.g.
Glyptotherium, Gillette and Ray, 1981). Porpino and Bergqvist (2002) emphasized that P. greslebini close resembles Panochthus tuberculatus in the ornamentation of carapace and
caudal tube and is particularly similar to P. frenzelianus in the absence of main figures in the osteoderms of the lateral border of carapace, suggesting that a possible synonymy should not be discarded. Nevertheless, P. greslebini clear differs from P. frenzelianus in having caudal tube with more developed conical tubercles, a single apical figure on dorsal side of caudal tube (instead of three) and three to four lateral figures posterior to the fused caudal rings (instead of only three). Moreover, unlike P. greslebini, the median figures in the anterior half of ventral side of caudal tube of P. frenzelinus are arranged in transversal rows resembling the condition observed in genera outside Panochthini (e.g. Neosclerocalyptus, Hoplophorus). Ameghino (1889) and Castellanos (1941, p. 506) remarked that the carapace of P.
frenzelianus does not bear osteoderms with main figures in the lateral region, like in P. greslebini. Yet, in the figured holotype (Castellanos, 1941, fig 205), main figures can be
observed in up to two rows near the lateral border, as in P. tuberculatus, though, according to Castellanos (1941) this may be due to errors of reconstitution. Finally, P. greslebini clearly differ from all other species within Panochthus for which the caudal tube is known, by the presence of an apexian figure in the distalmost portion of caudal tube between the terminal figures.
The species Panochthus oliveira-roxoi was proposed in the same paper in which P.
greslebini was described (Castellanos, 1941) based on a caudal tube. Castellanos (1941)
pointed several distinctive characters present in the caudal tube of P. oliveira-roxoi, including terminal figures not converging to a point distally, lack of apical figures in dorsal and ventral sides and a truncated apex which undoubtedly represent robust diagnostic characters as they were not reported for other species within Panochthus. Unfortunately, as pointed out by Paula Couto (1954) and Moreira (1971), Castellanos (1941) based his descriptions on photographs while the actual type specimen is poorly restored, rendering several crucial anatomical details at least doubtful. The apex region, for instance, is completely restored. Moreira (1971) recognized this problem and presented a shortened diagnosis for this species based on a reassessment of the type specimen. Unfortunately, the characters he presented are not diagnostic as they are the same presented in the diagnosis of Panochthus greslebini (e.g. single apical figure on dorsal and ventral side) or are constant within Panochthus (e.g. carapace osteoderms without main figures; dorsoventrally flattened caudal tube).
The type of Panochthus rochai corresponds to a distal portion of caudal tube. Its preserved morphology is very close to that of MN 2760V, DGM 01M and MN 2136V, all attributed to P.greslebini. Paula Couto (1954) did not present a formal diagnosis for this taxon, but provided a detailed description of the caudal tube followed by a comparative discussion. Most of characters described by Paula Couto (1954) are common to all species assigned to Panochthus (e.g. presence of conical tubercules in lateral and terminal figures, length of lateral figures progressively decreasing anteriorly). By the other hand, other characters (e.g. the relative size of marginal figures at both ventral and dorsal sides and the development of the conical tubercles in terminal and lateral figures), agrees with the comparable features observed in the more complete specimens assigned to P. greslebini (MN 2760V and DGM 01M). In addition, the characters he used to differentiate P. rochai from
other species of Panochthus, in his comparative discussion (e.g. a single dorsal apical figure and an apexian figure in caudal tube), could be equally used to differentiate P. greslebini from those species. Consequently, the only features reported by Paula Couto (1954) which would distinguish P. rochai from P.greslebini are slight differences in the number and position of the marginal figures near the distalmost ventral figures and the number and distribution of central figures in the ventral side of caudal tube. These features, however, seems to vary considerably in specimens attributed to the same species (e.g. MN 2760V and DGM 01M) or in ventral and dorsal sides of the same specimen. Consequently, if they were considered as specific diagnostic characters virtually all single known caudal tube belonging to Panochthus should be assigned to a separated species. Therefore, we believe that this features would be best regarded as intraspecfic variation and, in our opinion, the available evidences support the recognition of P. rochai as a junior synonym of P. greslebini as proposed by Moreira (1971) and supported by Porpino and Bergqvist (2002).
GENUS Parapanochthus Moreira, 1971
Referred Material – MN 2759V, caudal tube; MN 2759/4V, carapace fragment from dorsal region; MN 2759/1V, MN 2759/5V, MN 2759/14-19V, MCC 1546, MCC 1563V, carapace osteoderms; MCC 1547V, carapace fragment from dorsal region
Revised diagnosis. Differs from Nopachthus coagmentatus in having less dorsally flat caudal tube, lateral and terminal figures with more rugose surface and terminal figures clearly separated dorsally. Differs from Propanochthus bullifer in having flat main figures in posterodorsal region of carapace (instead of convex) and caudal tube with apical figures, more transversally expanded apex at dorsal side, paired dorsoventral figures between the terminal and distalmost lateral figure (L1) at each side, more developed conical tubercles in lateral and terminal figures and a median single marginal figure in its distal portion. Differs from all
species within Panochthus in having thinner carapace osteoderms; large main figures in the osteoderms of mediodorsal region of carapace; smaller, more slender and cylindrical caudal tube, with less marked lateral figures margins, less developed conical tubercles and proportionally smaller and less depressed marginal figures on ventral side. Differs further from Panochthus greslebini and Panochthus subintermedius in having tree apical figures in dorsal side of caudal tube (instead of one).
Parapanochthus jaguaribensis (Moreira, 1965) =Panochthus jaguaribensis Moreira, 1965
Figure 4
Diagnosis: as for the genus by monotipy.
Remarks. Moreira (1965, 1971) diagnosed ―Panochthus” jaguaribensis as having the dorsal and lateral region of carapace entirely composed by osteoderms with large main figures, unlike all species assigned to Panochthus in which osteoderms bearing main figures are limited to few rows near the lateral and posterior borders of carapace (except for Panochthus
intermedius; Ameghino, 1889; Castellanos, 1941). This was an inference based on a limited
sample of carapace fragments collected in a tank deposit from Paraíba state (e.g. Fig. 4B). However, additional carapace fragments from Rio Grande do Norte state (e.g. MCC 1554V, Fig. 4A; see Porpino and Bergqvist, 2002) presenting identical morphology to those described by Moreira (1971) provided further support for this interpretation. Moreira (1971) relied on the presence of thinner osteoderms with large main figures in dorsal region of carapace and caudal tube characters, such as its more conical outline (instead of dorsoventrally flattened) and the presence of proportionally smaller lateral figures bearing slightly less developed central conical tubercle (Moreira, 1965, 1971), to propose the exclusion of Parapanochthus from Panochthus. This proposition was followed by latter authors (Paula Couto, 1979; Oliveira et al., 1982; McKenna and Bell, 1997). By contrast, Porpino and Bergqvist (2002)
stated that the diagnostic characters that Moreira (1971) listed for Parapanochthus
jaguaribensis do not support its exclusion from Panochthus. They remarked that the presence
of main figures in carapace osteoderms of Parapanochthus is not a distinctive character relative to Panochthus because at least one species within this latter genus present well- developed main figures (Panochthus intermedius; Lydekker, 1894; Castellanos, 1941). However, in P. intermedius these figures, though present in the posterodorsal and anterodorsal regions, are absent from the mediodorsal region unlike Propanochthus. Moreover, these figures, as observed in the holotype of P. intermedius (MLP 16.37), are smaller than in P.
jaguaribensis and absent in the lateral region of carapace, unlike this latter species. Therefore,
the presence of main figures in the mediodorsal region concur for distinguishing P.
jaguaribensis from all known species of Panochthus and, contrary to Porpino and Bergqvist
(2002), we believe that the distinctive characters proposed by Moreira (1971) for supporting the generic separation of P. jaguaribensis are robust and we reiterate here his taxonomic decision. This gain additional support from the results of the cladistic analysis we carried out in the present study (see bellow.)
DISCUSSION
Since its inclusion as a member of the paraphyletic superfamily Hoplophorinae (Fernicola, 2008) by Hoffstetter (1958), the tribe Panochthini has been accepted in major systematic works dealing with the classification of glyptodonts (Paula Couto, 1979; McKenna and Bell, 1997) and that it comprises a natural group has never been questioned. Most members of Panochthini share a strinking suite of caudal tube characters which allow differentiating them from most glyptodonts (Hoffstetter, 1958; Paula Couto, 1979). Besides caudal tube characters, the presence of carapace osteoderms uniformly ornamented by small
figures, comparable to the peripheral figures surrounding the main figures on osteoderms of other glyptodonts, has been recognized as a diagnostic character for this tribe (Hoffstetter, 1958; Cattoi, 1966). Nevertheless, with the exception of the type-genus Panochthus, this character is not observed in other genera assigned to this tribe (i.e. Nopachthus,
Propanochthus and Parapanochthus) which present main figures in all carapace osteoderms
(Paula Couto, 1979). In fact, even within Panochthus, some species present main figures (e.g.
P. intermedius), though, in most of them, they are restricted to few areas closer to the borders
of carapace. The genus Nopachtus was founded by Ameghino (1888) and originally included a single species: Nopachthus coagmentatus. It was originally interpreted as the direct ancestor of the remaining Panochthini (Ameghino, 1889), but later Castellanos (1941) reasoned that it may occupy a ―collateral‖ position (i.e. a sister-group position in current terminology) relative to other Panochthini. Ameghino (1889) remarked that Nopachtus resembles Plohophorus regarding its carapace morphology but also observed that it clearly differs from this genus in the morphology of caudal tube, which he considered similar to Panochthus. In fact, the caudal tube of N. coagmentatus presents large lateral and terminal figures bearing distinctive conical tubercles (Castellanos, 1941), as in other Panochthini (Panochthus, Parapanochthus). These caudal tube characters are also observed in non-Panochthini glyptodonts such as Hoplophorus (Paula Couto, 1957) and Neuryurus (Ameghino, 1889), however these genera, particularly the latter, present distinctive carapace morphology as compared to N. coagmentatus. The species
Nopachtus trouessarti was originally describe by Moreno (1888) as belonging to Panochthus
and was later transferred to Nopachtus by Castellanos (1925), but it strongly differs from
Nopachtus coagmentatus, as well as from the other known Panochthini (except, from Propanochthus) in having highly convex main figures in the osteoderms of posterior rows of
carapace. Cabrera (1944) founded the genus Phlyctaenopyga and the species Phlyctaenopyga
that of N. trouessarti. This similarity led Cabrera (1944) to hypothesize that P. ameghini and
N. trouessarti could be cogeneric, a suggestion which is hard to dismiss considering the
available evidence.
Propanochthus bullifer from the early (Castellanos, 1941; Paula Couto, 1979) or late
Pliocene (McKenna and Bell, 1997) of Argentina was originally described by Burmeister (1870-74) as belonging to Panochthus. The mediodorsal region of its carapace is not known while the known carapace fragments, corresponding to parts of the lateral and dorsolumbar regions, present osteoderms bearing main figures unlike Panochthus (Ameghino, 1889; Castellanos). These figures, particularly in posterior portion of the dorsolumbar region of carapace, are convex but less than in N. trouessarti and unlike this latter species, they show strongly excavated surface. The caudal tube is more slender than in Panochthus and show several distinctive character, such as median figures forming transversal rows, as in genera