Non-technical Summary
Tropidoleptus was a genus of brachiopods that had a very peculiar morphology and occurred in the Devonian period (about 419–358 million years ago) throughout the world. Although there have been reports of the presence of this genus in the Paraná Basin (Brazil) since the nineteenth century, its actual occurrence has been the subject of much debate. The objective of this work was to clarify this situation. For that, dozens of specimens from the Brazilian state of Mato Grosso were analyzed. The studied samples have typical characteristics of Tropidoleptus, therefore this genus actually also occurred in the Paraná Basin. Tropidoleptus possibly arrived in the Paraná Basin 385 million years ago, at the moment when there was a marine connection among the Brazilian Paraná, Parnaíba, and Amazonas basins. The occurrence of Tropidoleptus can be used as a marker of shallower marine environments, and in the Paraná Basin in particular, it can indicate that the rocks, where they are present, are less than 390 million years old.
Introduction
The brachiopod Tropidoleptus underwent several morphological changes throughout its existence in the Devonian (Isaacson and Perry, Reference Isaacson and Perry1977) and is considered a cosmopolitan genus (Harper, Reference Harper2007). This genus has unique characteristics that make its classification into a distinct order challenging. It previously has been assigned to the orders Strophomenida, Terebratulida, and Orthida (see Hall and Clarke, Reference Hall and Clarke1894; Schuchert, Reference Schuchert and Pompeckj1929; Schuchert and Cooper, Reference Schuchert and Cooper1932; Williams and Wright, Reference Williams and Wright1961; Wright, Reference Wright and Moore1965). Jaanusson (Reference Jaanusson and Dutro1971) included Tropidoleptus in the order Telotremata, which would encompass spiriferids and terebratulids. On the other hand, Harper et al. (Reference Harper, Alvarez, Boucot, Gourvennec, Williams and Wright2003) and Harper (Reference Harper2007) suggested that this genus belong to an undefined order. More recently, Harper et al. (Reference Harper, Alvarez, Boucot, Williams, Wright and Schemm-Gregory2010) proposed elevating the family Tropidoleptidae to the order Tropidoleptida.
In Brazil, the presence of this taxon in the Amazonas and Parnaíba basins is indisputably recorded (e.g., Rathbun, Reference Rathbun1874, Reference Rathbun1878; Carvalho, Reference Carvalho1972; Fonseca and Melo, Reference Fonseca and Melo1987; Melo, Reference Melo, McMillan, Embry and Glass1988; Gama Junior, Reference Gama Junior2008; Queiroz et al., Reference Queiroz, Gama Júnior and Pires2013; Santos et al., Reference Santos, Rezende and Ponciano2021). However, its occurrence in the Paraná Basin is still a matter of debate (see Ribeiro, Reference Ribeiro2020). Although Derby (Reference Derby1895) documented the occurrence of Tropidoleptus in the Paraná Basin (Chapada dos Guimarães, Mato Grosso), he relied on a single poorly preserved specimen. Subsequently, Orville Derby himself issued a note in Clarke's (Reference Clarke1913) monograph correcting his identification and stating that it was actually Leptocoelia sp. (= Australocoelia sp.). The specimen studied by Derby (Reference Derby1895) was not illustrated in his work, but Kunzler (Reference Kunzler2012) found it in the paleoinvertebrate collection of the Museu Nacional/UFRJ (MN 3323-I) and provided the first illustration of it. Upon review, Kunzler (Reference Kunzler2012) concluded that it was indeed Tropidoleptus, but due to the poor state of preservation of the specimen, its identification remains open to discussion (e.g., Ribeiro, Reference Ribeiro2020). Clarke (Reference Clarke1895) reported the occurrence of Tropidoleptus? in samples from Jaguariaíva, Paraná state.
Caster (Reference Caster1947) reported the presence of specimens of Tropidoleptus in the Paraná Basin, specifically in the state of Mato Grosso, but neither described nor illustrated them. Almeida (Reference Almeida1954) mentioned the occurrence of Tropidoleptus in the region of Chapada dos Guimarães. Suárez-Riglos (Reference Suárez-Riglos1967) mentioned that Caster's material included specimens of Tropidoleptus. Additionally, Lange and Petri (Reference Lange and Petri1967) noted that Tropidoleptus carinatus (Conrad, Reference Conrad1839) was the most common macrofossil of the São Domingos “member”, clearly referring to the Middle Devonian layers of Mato Grosso, as evident from the subsequent fossil listing. Finally, Quadros and Melo (Reference Quadros and Melo1989) claimed to have found Tropidoleptus in the locality of Monjolo (dos Padres?) (Chapada dos Guimarães), but they did not provide descriptions or illustrations of the specimens.
As can be seen, the occurrence of Tropidoleptus in the Paraná Basin has been supported primarily by citations, with only one poorly preserved specimen illustrated and partially described (Kunzler, Reference Kunzler2012). Therefore, the purpose of this paper is to definitively establish the presence of Tropidoleptus in the Paraná Basin by analyzing numerous samples from the state of Mato Grosso. Resolving this question is crucial because Tropidoleptus is a significant taxon for paleobiogeographic discussions concerning the connections between the main Brazilian intracratonic basins (Amazonas, Parnaíba, and Paraná) and other basins in South America, the Old World, and Laurasia during the Devonian (see Isaacson and Perry, Reference Isaacson and Perry1977; Harper et al., Reference Harper, Alvarez, Boucot, Williams, Wright and Schemm-Gregory2010).
Geological setting
The Paraná Basin, covering an area of about 1,500,000 km2, is among the largest intracratonic basins in South America. It extends across parts of Brazil, Argentina, Paraguay, and Uruguay (Melo, Reference Melo, McMillan, Embry and Glass1988; Grahn, Reference Grahn1992; Milani et al., Reference Milani, Melo, Souza, Fernandes and França2007; Fig. 1). Devonian outcrops are found along the borders of this basin, specifically in the Brazilian states of Paraná (eastern border), Mato Grosso, Mato Grosso do Sul, and Goiás (northwestern border) (Melo, Reference Melo, McMillan, Embry and Glass1988). Although there are different proposals to divide the Devonian in the Paraná Basin into various different units (e.g., Bergamaschi, Reference Bergamaschi1999; Milani et al., Reference Milani, Melo, Souza, Fernandes and França2007; Grahn et al., Reference Grahn, Mauller, Pereira and Loboziak2010; Sedorko et al., Reference Sedorko, Netto and Savrda2018), this paper adopts the lithostratigraphic framework presented by Grahn et al. (Reference Grahn, Mauller, Bergamaschi and Bosetti2013) for the entire basin. In their classification, Grahn et al. (Reference Grahn, Mauller, Bergamaschi and Bosetti2013) divided the Devonian strata in the Paraná Basin into the Furnas Formation (Lochkovian), Ponta Grossa Formation (late Pragian–early Emsian), and São Domingos Formation (late Emsian–Frasnian).
Figure 1. Map of the Paraná Basin highlighting the Devonian outcrops. The red square indicates the region of the Juscimeira and Monjolo dos Padres outcrops, northwest–northwestern border of Paraná Basin, east–eastern border of Paraná Basin. Brazilian states: SC = Santa Catarina, PR = Paraná, SP = São Paulo, MG = Minas Gerais, MS = Mato Grosso do Sul, MT = Mato Grosso, GO = Goiás (adapted from Borghi and Fernandes, Reference Borghi and Fernandes2001; Scheffler et al., Reference Scheffler, Silva and Sedorko2020).
São Domingos Formation
The specimens examined in this formation were collected from the Monjolo dos Padres and Juscimeira outcrops, both located in the state of Mato Grosso (Fig. 1). Due to the friable sandstone lithology of these outcrops, dating them through palynology is not possible. However, based on the macrofaunal content, it is likely that these specimens are of Givetian age (see Quadros and Melo, Reference Quadros and Melo1989; Sedorko et al., Reference Sedorko, Netto, Scheffler, Horodyski and Bosetti2021), suggesting their affiliation with the São Domingos Formation (Figs. 1–3). The São Domingos Formation is stratigraphically situated above the Ponta Grossa Formation and below the Itararé Group (Carboniferous) on the eastern border, and below the Aquidauana Formation (Carboniferous) on the northwest border. It represents a marine deposit that encompasses foreshore to offshore environments, with deltaic facies observed at some localities (Sedorko et al., Reference Sedorko, Netto and Savrda2018, Ribeiro et al., Reference Ribeiro, Ghilardi and Caminha2019). Lithologically, the São Domingos Formation is composed of poorly sorted conglomeratic sandstones, sporadically bituminous shales, and micaceous siltstones containing abundant plant fragments (Grahn et al., Reference Grahn, Mauller, Bergamaschi and Bosetti2013). In the lower part of the São Domingos Formation (late Emsian–Eifelian), elements of the depleted Malvinokaffric fauna (or Malvinoxhosan, sensu Penn-Clarke and Harper, Reference Penn-Clarke and Harper2021) are present, while after the Givetian, organisms of the typical Malvinokaffric fauna become scarce or disappear (Bosetti et al., Reference Bosetti, Grahn, Horodyski, Mauller, Breuer and Zabini2010, Reference Bosetti, Grahn, Horodyski and Mauller2012).
Figure 2. Location of the outcrops: (1) Simplified geological map of the Juscimeira outcrop region (Lacerda Filho, Reference Lacerda Filho, Abreu Filho, Valente, Oliveira and Albuquerque2004). (2) Simplified geological map of the Monjolo dos Padres outcrop region (Grahn et al., Reference Grahn, Mauller, Pereira and Loboziak2010).
Figure 3. Sedimentological profile of the Juscimeira outcrop (adapted from personal correspondence, Henrique Z. Tomassi, 2021).
Materials and methods
The specimens examined in this study are housed in the paleoinvertebrate collection of the Museu Nacional/Universidade Federal do Rio de Janeiro (MN-I) and the Universidade Federal de Mato Grosso (MP, CD). The Museu Nacional specimens are the same ones previously analyzed by Caster (Reference Caster1947) and are part of the Caster Collection. Initially, these specimens were sent to the University of Cincinnati and later repatriated to the Museu Nacional collection in 2016 (see Scheffler et al., Reference Scheffler, Fernandes, Silva, Videira-Santos and Sousa2021). The specimens that were not affected by the tragic fire in 2018 because they were not inside the palace are MN 12002-I, MN 12003-I, MN 12004-I, MN 12005-I, MN 12006-I, MN 12007-I, MN 12008-I, MN 12009-I, MN 12010-I, MN 12011-I, MN 12012-I, MN 12013-I, MN 12014-I, MN 12015-I, MN 12016-I, MN 12017-I, MN 12018-I, MN 12019-I, MN 12020-I, MN 12021-I, MN 12022-I, MN 12023-I, MN 12024-I, MN12025-I, MN12026-I, and MN 12035-I. The specimens that were inside the palace and were later rescued are MN 10674-I, MN 10675-I, MN 10676-I, MN 10680-I, MN 10681-I, MN 10686-I, MN 10687-I, MN 10688, and MN 10690-I. Unfortunately, specimen MN 3323-I, which was previously studied by Derby (Reference Derby1895), was lost in the fire and is no longer available for examination.
The original accession numbers of specimens MN 10674-I, MN 10675-I, MN 10676-I, MN 10680-I, MN 10681-I, MN 10686-I, MN 10687-I, MN 10688-I, and MN 10690-I were inferred based on the positions of specimens in the collection before the fire. However, it is not possible to relate these individual specimens to their individual numbers. Because all of these specimens originated from the Monjolo dos Padres outcrop, we have designated the specimen in Figure 5.6 as MN 10674-I.
The samples deposited in the Universidade Federal de Mato Grosso collection include MP 533, MP 522a, b, MP 506, MP 507, MP 508 (part and counterpart), MP 510, and CD 310a–c.
We conducted a comparison of the material from the Paraná Basin with the hypotypes of Tropidoleptus carinatus (Conrad, Reference Conrad1839) studied by Williams (Reference Williams1913) from the Devonian of New York, United States of America. Currently, these samples are housed in the National Museum of Natural History/Smithsonian Institution collection with accession number USNM 59603 (1–88), originating from the Portage Formation. Additionally, Devonian specimens from the Amazonas Basin (Maecuru and Ererê formations) and Parnaíba Basin (Pimenteira and Cabeças formations) in Brazil were also analyzed. These samples are preserved in the collection of the Museu de Ciências da Terra/CPRM (DGM 2845-Ia–d; DGM 2902-I; DGM 2903-I), Instituto de Geociências/Universidade Federal do Rio de Janeiro (UFRJ 432-Bq, UFRJ 428-Bq), and Museu Nacional/UFRJ (MN 6379-I, MN 6382-I, MN 6391-I, MN 6398-I, MN 6400-I, MN 6402-I (not recovered after the fire).
For taxonomic identification, we consulted the Treatise on Invertebrate Paleontology (Harper, Reference Harper2007) and various articles on Tropidoleptus taxonomy across different Devonian regions worldwide.
Repositories and institutional abbreviations
MN/UFRJ (MN-I), Museu Nacional of Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil; IGEO/UFRJ (UFRJ-Bq), Instituto de Geociências of Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil; UFMT (MP, CD), Universidade Federal de Mato Grosso, Cuiabá, Brazil; MCT/CPRM (DGM-I), Museu de Ciências da Terra of Serviço Geológico do Brasil, Rio de Janeiro, Brazil; NMNH/SI (USNM), National Museum of Natural History/Smithsonian Institution, Washington D.C., United States of America.
Systematic paleontology
Class Rhynchonellata Williams et al., Reference Williams, Carlson, Brunton, Holmer and Popov1996
Order Tropidoleptida Schuchert, Reference Schuchert, Zittel and Eastman1896
Superfamily Tropidoleptoidea Schuchert, Reference Schuchert, Zittel and Eastman1896
Family Tropidoleptidae Schuchert, Reference Schuchert, Zittel and Eastman1896
Genus Tropidoleptus Hall, Reference Hall1857
Type species
Strophomena carinata Conrad, Reference Conrad1839.
Tropidoleptus carinatus (Conrad, Reference Conrad1839)
Figures 4, 5
- Reference Conrad1839
Strophomena carinata Conrad p. 64.
- Reference Hall1857
Tropidoleptus carinatus (Conrad); Hall, p. 151.
- Reference Derby1895
Tropidoleptus? sp. Derby, p. 76.
- Reference Frech1897
Tropidoleptus rhenana Frech, p. 143, note 1, pl. 23a, fig. 9.
- Reference Drevermann1902
Tropidoleptus carinatus var. rhenana (Frech); Drevermann, p. 99, pl. 12, figs. 11, 12.
- Reference Katzer1933
Tropidoleptus carinatus var. maecurensis Katzer; Clarke, p. 181, pl. 10, fig. 7a, b.
- Reference Caster1947
Tropidoleptus sp. Caster, p. 126.
- Reference Suárez-Riglos1967
Tropidoleptus carinatus (Conrad); Suárez-Riglos, p. 33, pl. 1, figs. 1–11.
- Reference Carvalho1972
Tropidoleptus carinatus (Conrad); Carvalho, p. 25, pl. 2, figs. 1–14, pl. 3, fig. 1–3.
- Reference Isaacson1977
Tropidoleptus carinatus (Conrad); Isaacson, pl. 1, figs. 20–37, pl. 2, figs. 1–3.
- Reference Isaacson and Perry1977
Tropidoleptus carinatus (Conrad); Isaacson and Perry, p. 1115.
- Reference Isaacson and Perry1977
Tropidoleptus carinatus rhenana (Frech); Isaacson and Perry, pl. 2, figs. 1–17.
- Reference Cooper and Dutro1982
Tropidoleptus platys Cooper and Dutro, p. 43, pl. 4, figs. 13–21.
- Reference Fonseca and Melo1987
Tropidoleptus carinatus (Conrad); Fonseca and Melo, pl. 1, figs. 1–9, pl. 2, figs. 1–12.
- Reference Racheboeuf, Gourvennec, Deynoux and Brice2004
Tropidoleptus sp. Racheboeuf et al., p. 104, fig. 4.10.
- Reference Harper, Alvarez, Boucot, Williams, Wright and Schemm-Gregory2010
Tropidoleptus carinatus (Conrad); Harper et al., figs. 1–6.
Figure 4. Tropidoleptus carinatus (Conrad, Reference Conrad1839): (1) exterior, ventral valve, MN 12003-I; (2) interior, ventral valve, MN 12005-I; (3) exterior, ventral valve, MN 12011-Ia; (4) interior, dorsal valve, MN 12012-I; (5) interior, dorsal valve, MN 12016-I; (6) interior, dorsal valve, MN 12014-I; (7) exterior ventral valve, MN 12015-Ib; (8) interior, ventral valve, MN 12015-Ia. All scale bars represent 5 mm.
Figure 5. Tropidoleptus carinatus (Conrad, Reference Conrad1839): (1) exterior, ventral valve, MP 533; (2) exterior, dorsal valve, MP 522a; (3) exterior, ventral valve, MP 522b; (4) exterior, dorsal valve, CD 310b; (5) interior, ventral valve, MP 507; (6) interior, dorsal valve, MN 12017-I; (7) interior, MN 12004-Ia; (8) interior, dorsal valve, MN 12022-I. All scale bars represent 5 mm.
Holotype
Undesignated holotype; type-series likely deposited in the American Museum of Natural History, United States of America (Gama Júnior, Reference Gama Junior2008; Queiroz et al., Reference Queiroz, Gama Júnior and Pires2013).
Occurrence
?Antarctica, unknown geological unit, Givetian (Harper et al., Reference Harper, Alvarez, Boucot, Williams, Wright and Schemm-Gregory2010); South Africa, Witterberg Group, Givetian–Frasnian (Boucot et al., Reference Boucot, Brunton and Theron1983a; Penn-Clarke et al., Reference Penn-Clarke, Rubidge and Jinnah2018; Penn-Clarke, Reference Penn-Clarke2019); Germany, Lower Dark and Neichnerberg formations, Pragian–Emsian (Fuchs, Reference Fuchs1982; Ubelacker et al., Reference Ubelacker, Jansen and De Baets2016); ?Australia, Cocktatoo Formation, Frasnian (Roberts, Reference Roberts1971); Belgium, unknown formation, Pragian–Emsian (Boucot et al., Reference Boucot, Bahlburg, Breitkreuz, Isaacson, Niemeyer and Urzúa1995); Bolivia, Huamampampa, Belén, and Sicasica formations, late Eifelian–?Frasnian (Isaacson, Reference Isaacson1977, Reference Isaacson1993; for age see Blieck et al., Reference Blieck, Gagnier, Bigey, Edgecombe, Janvier, Loboziak, Racheboeuf, Sempere and Steemans1996; Troth et al., Reference Troth, Marshall, Racey and Becker2011); Brazil, São Domingos, Maecuru, Ererê, Pimenteira, and Cabeças formations, middle/late Eifelian–Givetian (Suárez-Riglos, Reference Suárez-Riglos1967; Fonseca and Melo, Reference Fonseca and Melo1987; Melo, Reference Melo, McMillan, Embry and Glass1988; this paper); Canada, Torbrook Formation, Lochkovian (Boucot, Reference Boucot, Boucot and Lawson1999); Colombia, Floresta and Gutierrez formations, ?Emsian–Frasnian (Caster, Reference Caster1939; Morales, Reference Morales1965; Barrett, Reference Barrett1986); Chile, Zorritas Formation, Eifelian or Givetian (Isaacson et al., Reference Isaacson, Fisher and Davidson1985; Isaacson, Reference Isaacson1993; Boucot et al., Reference Boucot, Bahlburg, Breitkreuz, Isaacson, Niemeyer and Urzúa1995, Reference Boucot, Racheboeuf and Niemeyer2008); England, unknown formation, Pragian–Emsian (Boucot et al., Reference Boucot, Bahlburg, Breitkreuz, Isaacson, Niemeyer and Urzúa1995); Morocco, unknown formation, Pragian–Givetian (Jansen, Reference Jansen2001; Harper et al., Reference Harper, Alvarez, Boucot, Williams, Wright and Schemm-Gregory2010; Halamski and Balinski, Reference Halamski and Balinski2013); France, unknown formation, Givetian (Rachebouef in Boucot et al., Reference Boucot, Bahlburg, Breitkreuz, Isaacson, Niemeyer and Urzúa1995); Central Sahara (Algeria and Niger), Tamesna Basin, Pragian–Givetian (Mergl and Massa, Reference Mergl and Massa2004); United States of America, Beechwood Limestone Member, Silica, ”Beers Hill”, Portage, Ludlowville and Mahantango formations, Givetian–Frasnian (Williams, Reference Williams1913; Ellison, Reference Ellison1965; Kesling and Chilman, Reference Kesling and Chilman1975; McGhee and Sutton, Reference McGhee and Sutton1985); Spain, Salobral Formation, Givetian (Carls, Reference Carls1988; Carls and Valenzuela-Ríos, Reference Carls and Valenzuela-Rios2002); Libya, Aouinet Ouenine II and Idri formations, ?Pragian–Frasnian (Freulon, Reference Freulon1964; Havlicek and Rohlich, Reference Havlicek and Rohlich1987; Mergl and Massa, Reference Mergl and Massa1992); Mauritania, Aratane Formation, ?Pragian–Givetian (LeMaître, Reference LeMaître1952; Sougy, Reference Sougy1964; Rachebouef et al., Reference Racheboeuf, Gourvennec, Deynoux and Brice2004); Czech Republic, Drakov Quartzite, Pragian (Isaacson and Chlupac, Reference Isaacson and Chlupac1984); Peru, Cabanillas Formation, ?Eifelian (Newell, Reference Newell1949; for age see Laubacher et al., Reference Laubacher, Boucot and Gray1982); Venezuela, Caño Grande and Caño del Oeste formations, ?Early Devonian–Givetian (Sanchez and Benedetto, Reference Sanchez and Benedetto1983).
Description
Length 10.5–25.2 mm, width 12.1–26.3 mm (Table 1, Fig. 6). The width is greater than the length, with the maximum width of valve found in median region; endopunctate; ~20 ribs arising at beak, ribs wider than the interspaces, relatively thick, and sparsely spaced, rarely multiplying by bifurcation; presence of concentric growth lines; contour of valves is subquadrate, semielliptical to semicircular, slightly concavo-convex to plano-convex. The beak is small, extending slightly beyond the hinge line, while the shell margins are rounded. Strophic, with a non-crenulate hinge line. The dorsal valve is almost planar, while the ventral valve is more concave; the median rib on ventral valve is slightly larger than others and extends to the anterior commissure.
Table 1. Measurements of the analyzed specimens.
Figure 6. Plots of measurements of length versus width of analyzed Tropidoleptus carinatus (Conrad, Reference Conrad1839); n = 27.
Ventral interior
Open delthyrium with a triangular shape, where height is smaller than the base size, and absence of deltidial plates; prominent teeth are present and diverge anterolaterally; muscular field broad, long, and weakly imprinted, with an inflated umbonal region; presence of delicate myophragm.
Dorsal interior
Well-excavated dental pits are delimited by lateral lobes of the notothyrial platform, poorly preserved cardinal process projects above the hinge line. Crura extend anterolaterally as descending lamellae from the lateral lobes of the notothyrial platform. A thin myophragm starts from the anteromedial region of the notothyrial platform and extends over more than half of the valve, thinning anteriorly.
Material
MN 10674-I, MN 10675-I, MN 10676-I, MN 10680-I, MN 10681-I, MN 10686-I, MN 10687-I, MN 10688-I, MN 12002-Ia,b, MN 12003-Ia, b, MN 12004-Ia, b, MN 12005-I, MN 12006-I, MN 12007-I, MN 12008-I, MN 12009-I, MN 12010-I, MN 12011-I, MN 12012-I, MN 12013-I, MN 12014-I, MN 12015-Ia, b, MN 12016-I, MN 12017-I, MN 12018-I, MN 12019-I, MN 12020-I, MN 12021-Ia, b, MN 12022-I, MN 12023-Ia, b, MN 12024-I, MN 12025-I, MN 12026-Ia–e, MN 12035-Ia–c, MP 533, MP 522a, b, MP 506, MP 507, MP 508 (part and counterpart), MP 510, CD 310a–c (55 samples).
Provenance
Outcrops Monjolo dos Padres and Juscimeira, São Domingos Formation (possibly Givetian).
Observation
Tropidoleptus reported by Kayser (Reference Kayser1897) from the Los Espejos Formation in Argentina was synonymized as Castellaroina (see Boucot in Amos, Reference Amos1972; Harper and Boucot, Reference Harper and Boucot1978; and Benedetto and Montoya, Reference Benedetto and Montoya2015). Tropidoleptus cited by Thomas (Reference Thomas1905) in Argentina may not belong to the genus either.
Remarks
The specimens analyzed in this study exhibit the main morphological features of Tropidoleptus, as described by Conrad (Reference Conrad1839), Isaacson and Perry (Reference Isaacson and Perry1977), Harper (Reference Harper2007), and Harper et al. (Reference Harper, Alvarez, Boucot, Williams, Wright and Schemm-Gregory2010). These features include: (1) endopunctate shell surface; (2) subquadrate, semielliptical to semicircular contour of valves, slightly concavo-convex to plano-convex; (3) slightly larger median rib on ventral valve compared to other ribs; (4) ribs originating at the beak, wider than interspaces, relatively thick, and sparsely spaced, rarely multiplying by bifurcation; (5) presence of concentric growth lines; and (6) crura extending anterolaterally as descending lamellae.
Based on these observations, there is no doubt that Tropidoleptus was present in the Devonian of the Paraná Basin. We concur with the inclusion of Tropidoleptus in the order Tropidoleptida, as discussed by Harper et al. (Reference Harper, Alvarez, Boucot, Williams, Wright and Schemm-Gregory2010).
Several species have been proposed within the genus Tropidoleptus. Other than the type species, at least four additional species can be recognized: T. occidens (Hall, Reference Hall1860); T. platys Cooper and Dutro, Reference Cooper and Dutro1982; T. fascifer Kayser, Reference Kayser1897; and T. rhenanus (Frech, Reference Frech1897).
Tropidoleptus fascifer was proposed by Kayser (Reference Kayser1897) from Argentina. However, it was subsequently designated as the type species of the subgenus Castellaroina by Boucot in Amos (Reference Amos1972), which was later elevated to genus rank by Harper and Boucot (Reference Harper and Boucot1978). Benedetto and Montoya (Reference Benedetto and Montoya2015) proposed an emended diagnosis for the genus Castellaroina and provided a detailed description of the species Castellaroina fascifer (Kayser, Reference Kayser1897). As a result, T. fascifer is no longer considered a valid species of Tropidoleptus.
Tropidoleptus rhenanus (= rhenana) was proposed by Frech (Reference Frech1897) based on species from the Devonian of Germany. However, Drevermann (Reference Drevermann1902) conducted a comprehensive analysis of extensive German, American, and Bolivian material and concluded that T. rhenana could not be considered a separate species from T. carinatus. The external morphological characteristics (e.g., the number of ribs, length/width ratio, and median rib) are similar among these specimens. Drevermann (Reference Drevermann1902) suggested a possible distinction based on the extent of the muscular field, which extends beyond half of the valve. However, it has been shown in figures by Isaacson and Perry (Reference Isaacson and Perry1977) that T. carinatus also can exhibit these features. Upon careful comparison, it is apparent that “T. rhenanus” has slightly more angular ribs compared to T. carinatus (see Isaacson and Perry, Reference Isaacson and Perry1977; Harper et al., Reference Harper, Alvarez, Boucot, Williams, Wright and Schemm-Gregory2010; Schemm-Gregory and Henriques, Reference Schemm-Gregory and Henriques2013). This suggests that “T. rhenanus” can be classified as a subspecies (Tropidoleptus carinatus rhenanus), rather than a distinct species, which aligns with the findings of Drevermann (Reference Drevermann1902) and Isaacson and Perry (Reference Isaacson and Perry1977).
Tropidoleptus occidens was proposed by Hall (Reference Hall1860) for specimens from the Devonian of Iowa, United States of America. However, the limited number of described specimens and their poor preservation make it challenging to conduct a thorough comparison with T. carinatus. One notable difference is the presence of two enlarged median ribs on the ventral valve, as described by Hall (Reference Hall1860), which is not a typical characteristic of Tropidoleptus. It should be noted that the illustrations by Hall and Clarke (Reference Hall and Clarke1894) do not provide a clear characterization of these two enlarged median ribs. In contrast, Tropidoleptus typically possesses only one enlarged median rib (see Harper, Reference Harper2007; Harper et al., Reference Harper, Alvarez, Boucot, Williams, Wright and Schemm-Gregory2010). Stainbrook (Reference Stainbrook1938) synonymized T. occidens as Stropheodonta occidens (Hall, Reference Hall1860).
Tropidoleptus platys was proposed by Cooper and Dutro (Reference Cooper and Dutro1982) based on specimens from the Devonian of New Mexico, United States of America. However, the characteristics identified by these authors are not sufficiently robust to designate T. platys as a distinct species for the following reasons. (1) The obsolescence of ribs on the anterior margin noted in T. platys may be attributed to taphonomic factors rather than being a consistent characteristic across all specimens (some specimens of T. carinatus also exhibit this feature, as indicated by Cooper and Dutro, Reference Cooper and Dutro1982; see also Isaacson and Perry, Reference Isaacson and Perry1977, for an example. (2) Cooper and Dutro (Reference Cooper and Dutro1982) mentioned that specimens of T. carinatus from the Kashong Shale are larger than T. platys, while T. carinatus specimens from the Tully Limestone are smaller than T. platys. Hence, size cannot be considered a diagnostic feature in this case. The samples of T. carinatus described by Isaacson and Perry (Reference Isaacson and Perry1977) exhibit lengths of 15–30 mm, while Isaacson (Reference Isaacson1977) recognized a length range of 3.4–20.4 mm in Bolivian specimens. The specimens described by Cooper and Dutro (Reference Cooper and Dutro1982) have a lengths of 13.9–16.7 mm, which is within the size range expected for T. carinatus (3) The supposed smaller concavity and less-pronounced costate in T. platys compared to T. carinatus are not evident when comparing the illustrations by Cooper and Dutro (Reference Cooper and Dutro1982) with the specimens described by us and in other papers (e.g., Williams, Reference Williams1913; Isaacson, Reference Isaacson1977; Isaacson and Perry, Reference Isaacson and Perry1977; Fonseca and Melo, Reference Fonseca and Melo1987; Harper et al., Reference Harper, Alvarez, Boucot, Williams, Wright and Schemm-Gregory2010). (4) The more transverse shell of T. rhenanus (here considered synonymous with T. carinatus) compared to T. platys is not a robust diagnostic character because it is highly susceptible to taphonomic influences. Therefore, based on the characteristics presented here, T. platys is considered synonymous with T. carinatus.
A comparison of T. carinatus specimens from the Paraná, Parnaíba, and Amazonas basins, as well as the hypotypes from New York (hypotypes of Williams, Reference Williams1913), revealed no significant differences among them. The observed variations were consistent with intraspecific variations, as discussed by Isaacson and Perry (Reference Isaacson and Perry1977), confirming the presence of the same species across these regions (Fig. 7). Nevertheless, two subtle main differences were identified in the analyzed Brazilian specimens compared to those described by Isaacson and Perry (Reference Isaacson and Perry1977): (1) the ventral myophragm appears to be less vigorous, and (2) the median septum (referred to as the myophragm here) is less developed. These differences also were recognized by Fonseca and Melo (Reference Fonseca and Melo1987) in Devonian specimens from the Parnaíba Basin.
Figure 7. Tropidoleptus carinatus (Conrad, Reference Conrad1839). (1) Exterior, ventral valve, Harford Mills, New York, USA, Portage Formation, USNM 59603 (21); (2) exterior, dorsal valve, Harford Mills, New York, USA, Portage Formation, USNM 59603 (88); (3) interior, ventral valve, BR-020, Itainópolis, Piauí, Brazil, Pimenteira Formation, MN 6391-I; (4) exterior, ventral valve, BR-020, Itainópolis, Piauí, Brazil, Pimenteira Formation, MN 6400-I; (5) interior, dorsal valve, Serra de Ererê, Monte Alegre, Pará, Brazil, Ererê Formation, DGM 2845-Ia; (6) exterior, ventral valve, Maecuru River, Monte Alegre, Pará, Brazil, Maecuru Formation, DGM 2902-I. All scale bars represent 5 mm.
Finally, in the existing literature, several subspecies of Tropidoleptus carinatus have been proposed, including T. carinatus freuloni Boucot, Massa, and Perry, Reference Boucot, Massa and Perry1983b; T. carinatus nigeriensis Boucot, Massa, and Perry, Reference Boucot, Massa and Perry1983b; and T. carinatus titanius Mergl and Massa, Reference Mergl and Massa2004. The specimens studied here can be clearly distinguished from T. carinatus titanius by their smaller size (with a maximum width of ~33 mm, compared to 56 mm in T. carinatus titanius). However, in order to reliably differentiate the T. carinatus specimens studied here from T. carinatus freuloni and T. carinatus nigeriensis, it would be necessary to examine specimens the latter two subspecies. Analysis of the photos presented by Boucot et al. (Reference Boucot, Massa and Perry1983b) was inconclusive for this purpose.
Paleoenvironmental and paleobiogeographic considerations
Paleoenvironment
Tropidoleptus carinatus (Conrad, Reference Conrad1839) is a species commonly associated with shoreface environments worldwide, although it also could occur in shallower areas of the transitional offshore (see Isaacson and Perry, Reference Isaacson and Perry1977; Boucot et al., Reference Boucot, Bahlburg, Breitkreuz, Isaacson, Niemeyer and Urzúa1995; Harper et al., Reference Harper, Alvarez, Boucot, Williams, Wright and Schemm-Gregory2010). The Paraná Basin specimens of Tropidoleptus carinatus are found in friable, well-sorted sandstones. In the Juscimeira outcrop, the level containing Tropidoleptus is characterized by massive medium-grained sandstone (personal correspondence, Henrique Z. Tomassi, 2021). Specimens in the Monjolo dos Padres outcrop were found in sandstones with hummocky cross-stratification (tempestites), interbedded with shales (Quadros and Melo, Reference Quadros and Melo1989). Most specimens are disarticulated, and some show signs of abrasion, all of which may be a result of the naturally abrasive nature of the lithology (friable sandstone) and the high-energy paleoenvironment, rather than indicating long-distance transport. Tropidoleptus carinatus was not found in thinner facies such as argillite, siltstone, or shale, suggesting that this species was also restricted to shallower environments in the Paraná Basin, likely between the distal shoreface and proximal offshore. Further taphonomic studies are required to provide additional support for this interpretation.
Paleobiogeography
Tropidoleptus is another extra-Malvinokaffric brachiopod genus found in the Devonian deposits of the Paraná Basin, alongside other genera such as Chonostrophia?, Cryptonella, Plicoplasia?, Pustulatia?, and Schellwienella (Clarke, Reference Clarke1913; Cerri, Reference Cerri2013; Penn-Clarke and Harper, Reference Penn-Clarke and Harper2021; Rezende and Isaacson, Reference Rezende and Isaacson2021; Sedorko et al., Reference Sedorko, Netto, Scheffler, Horodyski and Bosetti2021; Videira-Santos et al., Reference Videira-Santos, Scheffler and Fernandes2022).
The genus Tropidoleptus originated in the Lochkovian of Nova Scotia (Canada), part of the ancient Avalonia/Baltica region (see Boucot, Reference Boucot, Boucot and Lawson1999; Robardet, Reference Robardet2003), belonging to the “Old World Realm” (Dowding and Ebach, Reference Dowding and Ebach2018; Dowding et al., Reference Dowding, Ebach and Mavrodiev2022). From its origin, Tropidoleptus dispersed to different parts of the world, including Europe, North Africa, and South America, the central portion of North America, South Africa, and possibly Antarctica, indicating its cosmopolitan distribution (Isaacson and Perry, Reference Isaacson and Perry1977; Harper, Reference Harper2007; Harper et al., Reference Harper, Alvarez, Boucot, Williams, Wright and Schemm-Gregory2010) (Fig. 8). However, the genus eventually became extinct during the Late Devonian extinction event, as noted by Harper et al. (Reference Harper, Alvarez, Boucot, Williams, Wright and Schemm-Gregory2010).
Figure 8. Occurrence of Tropidoleptus carinatus (Conrad, Reference Conrad1839) throughout the Devonian. SP = South Pole, NP = North Pole; 1 = Canada, 2 = England, 3 = Belgium, 4 = Germany, 5 = Czech Republic, 6 = Morocco, 7 = Libya, 8 = Central Sahara (Algeria/Niger), 9 = Mauritania, 10 = Venezuela, 11 = Colombia, 12 = Amazonas Basin (Brazil), 13 = Parnaiba Basin (Brazil), 14 = Peru, 15 = Bolivia, 16 = Chile, 17 = South Africa, 18 = Paraná Basin (Brazil), 19 = France, 20 = United States of America, 21 = Antarctica, 22 = Australia, 23 = Spain. Dotted arrow = migration with doubts (adapted from Habicht, Reference Habicht1979; Raymond, Reference Raymond1987; Melo, Reference Melo, McMillan, Embry and Glass1988; Golonka, Reference Golonka, Ross and Scotese1994; Scotese et al., Reference Scotese, Boucot and McKerrow1999; di Pasquo et al., Reference di Pasquo, Amenabar and Noetinger2009; Boucot et al., Reference Boucot, Xu, Scotese and Morley2013; Ribeiro, Reference Ribeiro2020). *There are doubts about the Pragian age for Venezuela and the Emsian age for Colombia; Tropidoleptus carinatus possibly entered these locations later.
According to paleogeographical reconstructions, Avalonia/Baltica and the rest of Europe were closely positioned during the Early Devonian, with only a narrow Rheic Ocean separating them (Robardet, Reference Robardet2003). Additionally, southeastern Europe, including the Armorican Massif, the Iberian Peninsula, and possibly central Europe (Bohemia) and perhaps the Moesian Terrane, were positioned adjacent to the Gondwana plate, forming its northern border (Plusquellec et al., Reference Plusquellec, Boumendjel, Morzadec and Paris1997; Robardet, Reference Robardet2003; Vaida et al., Reference Vaida, Seghedi and Verniers2005). This paleogeographic context suggests a potential pathway for the rapid migration of Tropidoleptus from Avalonia/Baltica to Bohemia and northern Gondwana during the Early Devonian (Fig. 8).
During the Eifelian global transgression (see Haq and Schutter, Reference Haq and Schutter2008), the sea advanced into the Amazonas and Parnaíba basins, which are part of the Amazonian sub-region, as defined by Penn-Clarke and Harper (Reference Penn-Clarke and Harper2021). Tropidoleptus along with other brachiopods, echinoderms, trilobites, and various taxa, migrated from regions such as Armorica, Bohemia, and North Africa towards the northern (Amazonas Basin) and northeastern (Parnaíba Basin) parts of Brazil between the Emsian and Eifelian (Fonseca and Melo, Reference Fonseca and Melo1987; Díaz-Martínez et al., Reference Díaz-Martínez, Isaacson and Sablock1993; Scheffler et al., Reference Scheffler, Dias-da-Silva, Gama, Fonseca and Fernandes2011; Carvalho and Ponciano, Reference Carvalho and Ponciano2015; Fonseca, Reference Fonseca2015; Scheffler, Reference Scheffler2015). This migration route highlights the dispersal of organisms during this period of time.
Penn-Clarke and Harper (Reference Penn-Clarke and Harper2021) reached the conclusion, based solely on brachiopods, that the Amazon Basin predominantly hosted taxa from the eastern Americas, including Malvinokaffric elements, while the Parnaíba Basin exhibited a combination of eastern Americas and Malvinokaffric taxa. Nevertheless, as mentioned earlier, it is important to recognize that the faunal composition of these basins also was influenced by elements of the Old World.
During the Eifelian, Tropidoleptus also extended its distribution to various other regions of present-day South America (e.g., Bolivia, ?Chile, and ?Peru). The influence of the Northern Gondwana fauna, as noted earlier during the Middle Devonian in South America, has been documented by several studies (e.g., Isaacson and Sablock, Reference Isaacson and Sablock1988; Díaz Martínez et al., Reference Díaz-Martínez, Isaacson and Sablock1993; Racheboeuf et al., Reference Racheboeuf, Le Hérissé, Paris, Babin, Guillocheau and Truyols-Massoni1993; Blieck et al., Reference Blieck, Gagnier, Bigey, Edgecombe, Janvier, Loboziak, Racheboeuf, Sempere and Steemans1996; Tourneur et al., Reference Tourneur, Plusquellec, Fernández-Martínez and Martínez2000). The evidence presented in this study suggests that the faunal distribution in southwest Gondwana was influenced by sea-level events and facilitated dispersal, which in turn influenced the distribution and mixing patterns between various paleobiogeographic sub-regions, as previously postulated by several authors (e.g., Melo, Reference Melo, McMillan, Embry and Glass1988; Dowding et al., Reference Dowding, Ebach and Mavrodiev2022). Additionally, differences in latitudes have an effect on taxonomic distribution and bioregionalization, as supported by the findings of Penn-Clarke and Harper (Reference Penn-Clarke and Harper2021).
According to Penn-Clarke and Harper (Reference Penn-Clarke and Harper2021) and Dowding et al. (Reference Dowding, Ebach and Mavrodiev2022), further biogeographic studies are necessary to reassess the status of sub-regions within the Malvinokaffric Realm. However, these studies should not rely solely on one phylum of organisms. In the case of southwest Gondwana, the similarity between taxa from different Malvinokaffric basins appears to vary depending on the phylum being considered. For instance, the work of Scheffler et al. (Reference Scheffler, Fernandes and Fonseca2013) highlights the lack of similarity between crinoids from the Paraná Basin and those from other basins in South America and South Africa, illustrating the need for a comprehensive examination across multiple phyla.
Tropidoleptus, known for inhabiting warmer waters, traditionally has been regarded as an end marker of the typical endemic fauna of certain Devonian paleobiogeographic realms (Dowding et al., Reference Dowding, Ebach and Mavrodiev2022). However, its presence has been documented in these areas even prior to the collapse of the aforementioned paleobiogeographic realms (Isaacson, Reference Isaacson1977; Penn-Clarke et al., Reference Penn-Clarke, Rubidge and Jinnah2018; Penn-Clarke, Reference Penn-Clarke2019). For instance, the Malvinokaffric Realm is thought to have ceased to exist by the Givetian (Boucot, Reference Boucot1988; Li, Reference Li2010; Dowding and Ebach, Reference Dowding and Ebach2018; Penn-Clarke and Harper, Reference Penn-Clarke and Harper2021; Rezende et al., Reference Rezende, Figueroa, Ponciano and Gallo2021). Nonetheless, there are records of Tropidoleptus in Malvinokaffric regions (Bolivia and South Africa) in older deposits (e.g., Isaacson, Reference Isaacson1977; Harper et al., Reference Harper, Alvarez, Boucot, Williams, Wright and Schemm-Gregory2010; Troth et al., Reference Troth, Marshall, Racey and Becker2011; Penn-Clarke et al., Reference Penn-Clarke, Rubidge and Jinnah2018; Penn-Clarke, Reference Penn-Clarke2019).
The arrival of Tropidoleptus in the Paraná Basin during the Givetian coincides with the decline of the typical Malvinokaffric fauna that had previously inhabited the basin, as well as with the occurrence of a “Lilliput effect” in the relict fauna (Bosetti et al., Reference Bosetti, Grahn, Horodyski, Mauller, Breuer and Zabini2010; Grahn et al., Reference Grahn, Horodyski, Mauller, Bosetti, Ghilardi and Carbonaro2016). The occurrence of T. carinatus in strata of presumed Givetian age in the Paraná Basin supports the idea that the Parnaíba, Amazonas, and Paraná basins had been interconnected since the early Givetian, and that warm waters entered the Paraná Basin, which was located near the south pole at that time (Grahn et al., Reference Grahn, Horodyski, Mauller, Bosetti, Ghilardi and Carbonaro2016). This coincided with the Acadian orogeny and the circulation of warm water counterclockwise currents associated with a transgression and the northward movement of western Gondwana, facilitating the influx of these warm currents (Isaacson and Sablock, Reference Isaacson and Sablock1990; Grahn et al., Reference Grahn, Horodyski, Mauller, Bosetti, Ghilardi and Carbonaro2016).
It is likely that Tropidoleptus migrated to the Paraná Basin from the Parnaíba and/or Amazonas basins during this transgression episode, supporting the idea that elements of the boreal fauna could colonize southern environments during the Devonian. This migration of invertebrates from the Parnaíba and Amazonas basins to the Paraná Basin in the Eifelian/Givetian transition, associated with the transgression of warmer waters, also is observed in echinoderms (e.g., Scheffler et al., Reference Scheffler, Dias-da-Silva, Gama, Fonseca and Fernandes2011, Reference Scheffler, Francisco and Bosetti2017; Scheffler, Reference Scheffler2015).
Conclusions
In this study, we have provided confirmation of the presence of Tropidoleptus carinatus (Conrad, Reference Conrad1839) in Devonian strata of the Paraná Basin. The morphological characteristics of the specimens analyzed align with the accepted variations for this species that have been described in the literature. The migration of T. carinatus is thought to have occurred during a late Eifelian/early Givetian marine transgression, which facilitated the influx of warmer waters from the Amazonas and Parnaíba basins into the Paraná Basin.
The presence of T. carinatus can serve as an indicator of shoreface and shallower portions of the transitional offshore environments, when found in situ. In the context of the Paraná Basin, its occurrence can be used to suggest that the associated strata are not older than the late Eifelian. However, in order to provide further support to these interpretations, it is essential to conduct a taphonomic study and utilize dating methods other than fossil composition to accurately determine the age of the outcrop where T. carinatus is found. Such comprehensive investigations can provide valuable insights into the paleoenvironmental context and temporal distribution of this species within the basin.
Acknowledgments
The authors would like to express their gratitude to the following curators for granting access to the collections under their care: S. Caminha (Universidade Federal de Mato Grosso), R. Silva (Museu de Ciências da Terra/CPRM), I. Carvalho (Universidade Federal do Rio de Janeiro), M. Florence (National Museum of Natural History/Smithsonian Institution), K. Hollis (National Museum of Natural History/Smithsonian Institution), and D. Erwin (National Museum of Natural History/Smithsonian Institution). The authors also would like to extend their appreciation to H.Z. Tomassi (NASOR) for collecting the fossils and providing the stratigraphic information from the Juscimeira outcrop; F. Alvarez (Universidad de Oviedo) and B. Mascarenhas (Universidade de São Paulo) for providing bibliography; C. Santos for sharing photos of the specimens from the Parnaíba Basin; M.I. Manes (Universidade Federal do Rio de Janeiro) and J. Smith for the revision of the English language. RVS acknowledges financial support from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (process 141382/2021-0) and the Comissão Fullbright Brasil. SMS acknowledges support from CNPq grants (process 409209/2021-0).
Declaration of competing interests
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
