Insights about the rare occurrence of a small Paleohelcura tridactyla from the eolian Botucatu Formation (Cretaceous, Paraná Basin, Brazil)

Abstract

Paleohelcura tridactyla is a trackway characterized by up to three round tracks per series, typically arranged linearly or triangularly, often with a medial impression. This pattern is consistently found in several eolian deposits and has been described in the Botucatu Formation in Brazil, an eolian sandstone unit in the Paraná Basin deposited during the earliest Early Cretaceous under arid conditions. Here, we describe a new small morphotype of Paleohelcura tridactyla in the Botucatu Formation. This morphotype is smaller than previously described specimens of Paleohelcura tridactyla, and although it shares a similar size with Paleohelcura araraquarensis, it differs both in track morphology and series arrangement. We propose three hypotheses for the new morphotype: (1) The trackway may have been produced by the juvenile stage of the arthropod responsible for the larger Paleohelcura tridactyla tracks. (2) The size difference may indicate sexual dimorphism within the same species. (3) Alternatively, it could represent a different arthropod species, which is smaller in size but leaves similar track patterns. This discovery reinforces the ichnotaxonomical distinction between P. tridactyla and P. araraquarensis and raises the possibility that another arthropod species may have been present in the Botucatu Paleodesert fauna.

KEYWORDS:
Mesozoic; erg; Gondwana; South America; continental ichnology; arthropod

1. INTRODUCTION

Paleohelcura tridactyla is a trackway characterized by up to three round tracks per series, with linear or triangular arrangement, and often bearing a medial impression. The trackway consistently occurs in several eolian deposits, so being one of the main components of the Octopodichnus–Entradichnus ichnofacies model (Krapovickas et al., 2016). The Botucatu Formation sandstone (Paraná Basin) is an eolian deposit from the Early Cretaceous, and is the Brazilian part of a widespread eolian depositional system developed across the midland of Gondwana during the Late Jurassic to Early Cretaceous (Bertolini et al., 2023; Scherer et al., 2023; Peixoto et al., 2025). Two ichnospecies of Paleohelcura occur in the unit: P. tridactyla and P. araraquarensis (Peixoto et al., 2025). Here we describe the new occurrence of a new small morphotype of Paleohelcura tridactyla, discussing the ichnotaxonomical implications of this finding; And we explore the paleoecology of the producer; As well as the reasons behind its rarity.

2. GEOLOGICAL SETTING

The Botucatu Formation, an extensive eolian sandstone unit of the Paraná Basin (Figure 1A), was deposited under arid conditions during the Early Cretaceous. It represents a vast desert system that once covered midland Gondwana, with outcrops found across several Brazilian states and parts of South America and Africa (Bertolini et al., 2021, 2023; Scherer et al., 2023) (Figure 1B).

Figure 1
Map and stratigraphical context of Botucatu Formation in Paraná Basin. A – Paraná Basin location in South America. B – Paraná Basin and Botucatu Formation outcropping area. C – Botucatu Formation outcrop in the eastern border of Paraná Basin. D – Stratigraphic context of Botucatu Formation. Modified from Horn et al. (2022) and Peixoto et al. (2025). States names: SP = São Paulo, MG = Minas Gerais, RJ = Rio de Janeiro, SC = Santa Catarina, MS = Mato Grosso do Sul, Go = Goiás.

In São Paulo state (Figure 1C), the formation consists mainly of yellowish to reddish quartz-rich sandstones, ranging from very fine to coarse-grained (Wu & Caetano-Chang, 1992; Bertolini et al., 2021). Stratigraphically, the Botucatu Formation overlies the Jurassic fluvial-eolian Piramboia Formation in the north, and the Guará Formation in the south (Giannini et al., 2004; Silva Busso & Fernández Garrasino, 2004; Soares et al., 2008; Reis et al., 2019, 2022; Christofoletti et al., 2021) (Figure 1D). It is conformably overlain by the Serra Geral Group, associated with the Paraná-Etendeka Large Igneous Province (Fernandes et al., 2018; Gomes & Vasconcelos, 2021) (Figure 1D). The formation’s lower age is constrained by the Middle–Late Jurassic Pirambóia and Guará formations (Cabral, 2011), while its upper boundary is defined by the Serra Geral volcanism: The U–Pb dating of Chapecó-type dacites from Ourinhos (São Paulo state) indicates an age of ~134 Ma (Janasi et al., 2011), placing the Botucatu Formation’s deposition at the area in the Early Cretaceous, likely Valanginian.

2.1 Botucatu Formation Paleontology

Trace fossils have been documented at various sites within the extensive Botucatu Formation in Brazil (Francischini et al., 2020; Leonardi & Carvalho, 2021; Manes et al., 2021), as well as in its correlative unit, the Twyfelfontein Formation in Namibia (Porchetti & Wagensommer, 2015). Fossilized logs are restricted to specific locations, as Minas Gerais (Suguio & Coimbra, 1972; Pires et al., 2011; Malaquias et al., 2017), and in northernmost Argentina (Martínez et al., 2023). Most of the specimens came from Araraquara and São Carlos (Leonardi, 1979, 1980, 1981; Leonardi & Carvalho, 2002, 2021; Fernandes & Carvalho, 2008; Francischini et al., 2015, 2020; Porchetti et al., 2017; Peixoto et al., 2020, 2025; Buck et al., 2022; Leonardi et al., 2024).

3. MATERIAL AND METHODS

The three trackways described here are in a single slab collected when the São Bento Quarry, Araraquara County, São Paulo State, Brazil (Figure 1C) was still active (2005). The slab (CCLP-1820) is housed in the Laboratório de Paleontologia de Macroinvertebrados, in the campus Bauru of the Universidade Estadual Paulista “Júlio de Mesquita Filho” (UNESP). The original photos of the trackways are in Supplementary Material. The measurements were taken in the free and open-source software Inkscape (1.3.2), and are also in the Suppl. Mat.. To ensure reproducibility, beyond citing the original trace fossil descriptions, we also address the ichnotaxonomic approach, revision, or emendation we have followed using “sensu”, and explaining in the text (International Commission on Zoological Nomenclature, 1999, Article 51.2.1). The approach and theoretical referential we used: Trace fossil ichnotaxonomic approach (Rindsberg, 2018; Bertling et al., 2022). Trackway nomenclature and measurements (Trewin, 1994; Minter et al., 2007). For track measurements, we consider the largest axis of the track as the length, and the shortest is the width. We use internal width/external width to prevent producing fractions with zero as the divisor, as it is impossible to divide by zero (see Peixoto et al., 2020).

4. RESULTS

4.1 Ichnotaxonomy

Paleohelcura Gilmore, 1926; sensuPeixoto et al. (2020).

Type ichnospecies:Paleohelcura tridactyla Gilmore, 1926.

Remarks: Only Paleohelcura tridactyla and Paleohelcura araraquarensis are currently recognized as valid at the ichnospecies level (Minter & Braddy, 2009; Peixoto et al., 2020), both of which are found in the Botucatu Formation (Peixoto et al., 2025) (Figure 2). Paleohelcura tridactyla Gilmore, 1926 is morphologically similar to Stiaria intermedia Smith, 1909, and can be its junior synonymous (Clendenon & Brand, 2023). Until a systematic review is published, this work follows the working hypothesis of Minter & Braddy (2009). Further discussions on these ichnotaxa can be found in Minter & Braddy (2009), Peixoto et al. (2020, 2025), and Clendenon & Brand (2023).

Paleohelcura tridactyla primarily differs from Paleohelcura araraquarensis in the ratio of internal width to external width, which typically exceeds ¼. Regarding track series morphology, most Paleohelcura tridactyla specimens from the Botucatu Formation display only two tracks per series (Peixoto et al., 2025) (Figure 2C,D), making it difficult to determine whether they form a triangular or linear pattern. In contrast, Paleohelcura araraquarensis usually exhibits a triangular track series, with two anteriorly positioned tracks and a typically longer, more posteriorly and internally positioned track (Peixoto et al., 2020) (Figure 2A,B).

Figure 2
Paleohelcura occurring in Botucatu Formation. Paleohelcura araraquarensis (A and B), Paleohelcura tridactyla Large Morphotype (C and D). A – P. araraquarensis in convex hyporelief. B – P. araraquarensis in concave epirelief. Both scales are in mm. C – P. tridactyla in concave epirelief. Scale bar in cm. D – P. tridactyla in convex hyporelief with media impression. A and B were modified from Peixoto et al. (2020) and B and C from Peixoto et al. (2025).

Paleohelcura tridactyla Gilmore, 1926; sensuPeixoto et al. (2020).

Diagnosis: Trackways with external width greater than 20 mm, comprising two parallel track rows with series of commonly three tracks but there can be fewer or up to four tracks per series. Series have alternating to staggered symmetry. Tracks vary from slightly elliptical to tapered or circular and can be in a linear or triangular arrangement within series. A medial impression may be present (emended by Peixoto et al., 2020).

Ichnotaxonomic assignment: All three trackways in CCLP-1820 belong to Paleohelcura tridactyla based on the rounded tracks and an internal width/external width ratio larger than ¼. They also have an external width larger than 20 mm, but this is an arbitrary value, erected as a working hypothesis to differentiate Paleohelcura and Stiaria, and is being reviewed (see Clendenon & Brand, 2023).

Description: CCLP-1820 slab bears three trackways in convex hyporelief: Trackway 1, 2, and 3 (Figure 3A). All the measurements are in Suppl. Mat., and those useful for the comparisons in this work are in Table 1 and 2. The fact that in the same slab both morphotypes are present illustrate the size difference between them (Figure 3B). The trackways are composed of two parallel track rows with alternate series with two tracks per series. The tracks in both morphotypes are rounded. Trackway 1 and 3 (Figure 3B and D) bears a medial impression, which is absent in Trackway 2 (Figure 3C). The medial impression is commonly present in Paleohelcura tridactyla (Avanzini et al., 2011; Dunlop & Braddy, 2011; Clendenon, 2024) but is not a diagnostic characteristic. This characteristic is present in the Large Morphotype (Figure 3B), and in one trackway of the Small Morphotype (Figure 3D).

Figure 3
Paleohelcura tridactyla morphotypes. A – General view of the CCLP-1820 slab with the three specimens. B – Trackway 1, belonging to the Large Morphotype P. tridactyla. C – Trackway 2, belonging to the Small Morphotype P. tridactyla. D – Trackway 3, belonging to the Small Morphotype of P. tridactyla.

Table 1
Measurements of the trackway´s parameters in CCLP-1820. The values are the means of the several measurements in each trackway. I/E: internal width/external width. Raw measurements are in Supplementary Material 1.

	Trackway	External width means (mm)	Internal width means (mm)	I/E Mean	Pace means (mm)	Stride means (mm)
Large Morphotype	1 (Figure 3B)	44.67	20.58	0.46	26.34	51.76
Small Morphotype	2 (Figure 3C)	24.37	18.22	0.75	16.13	31.81
	3 (Figure 3D)

Table 2
Measurements of the tracks of the specimens in CCLP-1820. The values are the means of several measurements. See Suppl. Mat. 1.

		Track 1			Track 2
	Trackway	Length (mm)	Width (mm)	Length/Width	Length (mm)	Width (mm)	Length/Width
Large Morphotype	1 (Figure 3B)	6.19	5.35	1.16	6.37	5.34	1.19
Small Morphotype	2 (Figure 3C)	3.22	2.57	1.25	3.48	2.66	1.31
	3 (Figure 3D)

Remarks: We discriminate them into two morphotypes based on the external width size (Table 1). Trackway 1 belongs to the Larger Morphotype, with a mean external width of 44.67 mm, like the specimens described in Peixoto et al. (2025) (Figure 2C,D) The other two trackways (Trackway 2 and 3) belong to the Small Morphotype and have a mean external width of 24.37 mm. The external width of the Small Morphotype trackways is more similar to the external width of Paleohelcura araraquarensis (22.97 mm), than to the Large Morphotype of Paleohelcura tridactyla (44.67 mm). On the other hand, the mean internal width of the Small Morphotype trackways (18.22 mm) is larger than the internal width of Paleohelcura araraquarensis (2.21 mm). This results in a large internal width/external width ratio (0.75), larger than in Paleohelcura araraquarensis (0.09). This is one of the differences between Paleohelcura tridactyla and P. araraquarensis, and the Small Morphotype shows that this is consistent even in smaller P. tridactyla, reinforcing the difference between these two ichnospecies. Therefore, despite being similar in external width, the Small Morphotype of Paleohelcura tridactyla trackways differ in internal width/external width ratio, series arrangement, and track morphology in relation to Paleohelcura araraquarensis.

Regarding the difference between the trackways from the small and large morphotypes, the Large Morphotype is 83% wider than the Small Morphotype. The Small Morphotype has an I/E ratio of 0.75, and the Large Morphotype 0.46. It is important to note that since the tracemaker should have between three and four pairs of locomotor appendages, it is possible that some feet did not produce tracks, being this internally or externally in the trackway. The tracks in both morphotypes are rounded, but larger in the Larger Morphotype (Figure 4 and Table 2).

Figure 4
Track morphology of Paleohelcura tridactyla morphotypes. A – Large Morphotype (Figure 3B). B and C are tracks of the Small Morphotype (Figure 3C and D).

5. DISCUSSION

5.1 Tracemaker

The interpretation of Paleohelcura tridactyla as having been produced by scorpions has been challenged (Clendenon & Brand, 2023). Neoichnological experiments demonstrate that traces produced by scorpions and spiders bear some similarities with the fossil trackways Paleohelcura tridactyla and Octopodichnus, as previously attributed to these animals (Minter et al., 2007; Peixoto et al., 2020; Clendenon & Brand, 2023), but there are some differences. In contrast, experiments with Pterygota insects produces trackways consistently similar to the fossil trackways as Paleohelcura araraquarensis and Lithographus (and its synonyms, e.g., Hexapodichnus) (Davis et al., 2007; Peixoto et al., 2020).

At present, it is not possible to definitively assign a tracemaker to Paleohelcura tridactyla with the available data. However, among extant terrestrial arthropods, arachnids and some wingless insects (Zygentoma and Archaeognatha) remain the most probable candidates, as these groups produce trackways with rounded tracks (Davis et al., 2007; Getty et al., 2013; Peixoto et al., 2020; Clendenon & Brand, 2023). It is unlikely that P. tridactyla was produced by a pterygote insect, as these animals typically have long tarsi, resulting in linear to elliptical tracks, distinct from those of P. tridactyla. The differences between Paleohelcura tridactyla and P. araraquarensis also support this interpretation, as P. araraquarensis has been attributed to a pterygote insect (Peixoto et al., 2020). A pterygote insect large enough to produce the small morphotype of P. tridactyla would likely produce trackways similar to P. araraquarensis or Lithographus.

Therefore, it can be inferred that the animal producing both morphotypes of P. tridactyla likely had walking appendages distinct from Pterygota. The appendages and gaits would be more similar to those of arachnids and wingless insects (non-Pterygota) than to those of Pterygota.

5.2 Growth in terrestrial arthropods

Among terrestrial arthropods, arachnids and certain primitive groups of wingless insects (orders Archaeognatha and Zygentoma) exhibit ametabolous growth (Truman & Riddiford, 2019) (Figure 5). In this growth strategy, juveniles resemble adults but are smaller, and growth occurs through successive molts until reaching adulthood (Truman, 2019). In contrast, winged insects (Pterygota) undergo either hemimetabolous or holometabolous development, characterized by distinct growth stages.

Figure 5
An adult Brazilian yellow scorpion Tityus serrulatus with its offspring. Adults and juveniles are morphologically similar. The growth in arachnids and certain primitive groups of wingless insects occurs through successive molts, growing but without major morphological changes (ametabolous).

In hemimetabolous insects, there are three stages: egg, nymph, and adult. In holometabolous insects, development occurs in four stages: egg, larva, pupa, and adult. The defining feature of holometabolism is the profound morphological transformation during the pupal stage, where the insect undergoes metamorphosis, resulting in an adult that is drastically different from earlier stages (Truman, 2019; Truman & Riddiford, 2019). Holometabolous insects, belonging to the monophyletic group Holometabola, represent most of the insect diversity (Peters et al., 2014).

5.3 A juvenile or a dwarf?

The morphological similarities between both trackway morphotypes, aside from size, suggest that the animals producing them had similar walking appendages and gait. Three hypotheses could explain this:

1. Juvenile Hypothesis: The smaller Paleohelcura tridactyla trackway could have been made by a juvenile specimen of the same species that produced the larger morphotype. This species may follow an ametabolous growth strategy, where juveniles and adults share similar morphology (Truman, 2019) and gait, thus producing similar trackways.

2. Sexual Dimorphism Hypothesis: In some arthropods, males and females differ in body size and morphological traits (e.g., McLean et al., 2018). For instance, female scorpions and spiders are usually larger (McLean et al., 2018), and their trackways may reflect this size difference, while still being similar due to their comparable body morphology. However, it is important to note that other morphological differences, such as longer appendages in some male arachnids, could potentially lead to additional morphological variations in the trackway.

3. Smaller Species Hypothesis: Alternatively, the two morphotypes may have been produced by different species within the same higher phylogenetic group. These species would share similar body morphology and walking behavior. The larger morphotype would belong to a larger species, while the smaller morphotype could belong to a smaller species.

So far it is not possible to defend one hypothesis over another with the amount of data we have about ancient and modern desert fauna.

5.4 Why are these trackways so rare?

Three hypotheses might explain the rarity of these trackways:

1. Ecological Niche Hypothesis: The animal responsible for the smaller trackways, whether a smaller species, a juvenile, or represent a sexual dimorphism, may have spent most of its time in a habitat not represented in Botucatu Formation, such as interdune or dune slope environments. Thus, its trackways were only recorded when it crossed the slipface of the paleodune. A similar habitat preference is observed in modern desert arachnids and insects (Lawrence, 1959; Robinson & Seely, 1980). This would introduce a bias in the fossil record towards arthropods that spend more time on the slipface.

2. Taphonomic Bias Hypothesis: Besides being smaller, the animal producing the diminutive trackways would have been lighter than the producer of the larger morphotype. This lower body weight may have made it less capable of leaving discernible tracks in firmer substrates (Davis et al., 2007, p. 304). Consequently, there may be a taphonomic bias favoring the preservation of tracks from heavier arthropods.

3. Rapid growth bias: Growth strategies vary in different desert arthropods (Punzo, 2000). If the producer of the Large Morphotype of Paleohelcura tridactyla grows fast and spends most of its lifespan as an adult, there are fewer chances that the tracks of the juveniles of this species were recorded in comparison with those of adults. Therefore, each individual can produce more trackways as an adult than as a juvenile, so it is reasonable to find more adult trackways than juvenile ones.

6. CONCLUSIONS

In this study we describe the occurrence of a diminutive Paleohelcura tridactyla trackway from the Botucatu Formation. The specimen shares a similar external width with Paleohelcura araraquarensis but differs in internal width/external width ratio, series arrangement, and track morphology. The fact that these differences are present even in a small morphotype of P. tridactyla, with similar external width, reinforces the ichnotaxonomical separation between P. tridactyla and P. araraquarensis.

The tracemaker is possibly an arachnid or wingless insect (non-Pterygota). Three hypotheses are proposed for the potential tracemaker of the smaller forms: (1) The trackway may have been produced by the same arthropod responsible for the larger Paleohelcura tridactyla trackways found in the Botucatu Formation, but in its juvenile stage. (2) The two trackways’ size could represent the sexual dimorphism of the same arthropod species. (3) Alternatively, it could have been produced by a different arthropod species, in which the adults are naturally smaller, but similar to the larger species that produced the larger trackways. So far, it is not possible to definitively support one hypothesis over another based on our current understanding of ancient and modern desert fauna. However, exploring these hypotheses is an important first step toward better understanding the relationship between the ichnological record and the structure of populations and communities. Additionally, considering how neoichnological studies could help answer these questions—similar to how actualistic studies contribute to taphonomy (e.g., Behrensmeyer et al., 1979)—is crucial.

The rarity of these trackways, whether produced by juveniles, different sexes or different species, could be attributed to the low preservation potential of trackways produced by lighter animals; Or because they spend most of the time walking in facies not well captured in the eolian geological record; Or because they grow so fast that they spend short time as juveniles, decreasing the chances to be recorded as trace fossils.

The description of this new morphotype raises the possibility that another arthropod species may have been present in the Botucatu Paleodesert fauna, but the record is difficult to access, whether due to ecological issues or because their traces are subtle.

ACKNOWLEDGMENTS

We would like to thank Ismar Carvalho and Daniel Sedorko for their constructive comments on the text. This work was funded by: For BP grants #2023/10050-7 and #2023/01470-2 from the São Paulo Research Foundation (FAPESP), grant #151170/2023-1 from Brazilian Scientific and Technological Research Council – CNPq, and post-doctoral program grant (no. 88887.203738/2025-00) from Coordination of Superior Level Staff Improvement (CAPES). For MEMK FAPESP grant #2024/11124-7; For MBF FAPESP grant #2024/17495-7; For RPG FAPESP grant #2023/01470-2.

Supplementary Material

Supplementary material accompanies this paper.

Supplementary Material of Insights about the rare occurrence of a small Paleohelcura tridactyla from the eolian Botucatu Formation (Cretaceous, Paraná Basin, Brazil).

Supplementary_2_-_Table_raw_data

This material is available as part of the online article from https://doi.org/10.1590/2317-4889e20250018

• Manuscript ID: 20250018 BJGEO-2025-0018.R1.
• How to cite:
  Peixoto, B., Martins, H. B., Franco, M. B., Kono, M. E. M., & Ghilardi, R. P. Insights about the rare occurrence of a small Paleohelcura tridactyla from the eolian Botucatu Formation (Cretaceous, Paraná Basin, Brazil). Braz. J. Geol. (2025), 56: e20250018. https://doi.org/10.1590/2317-4889e20250018
• Financial support:
  For BP the grants #2023/10050-7 and #2023/01470-2 from the São Paulo Research Foundation (FAPESP). The grant #151170/2023-1 from Brazilian Scientific and Technological Research Council – CNPq. And the post-doctoral program grant (no. 88887.203738/2025-00) from Coordination of Superior Level Staff Improvement (CAPES). For MEMK FAPESP grant #2024/11124-7; For MBF FAPESP grant #2024/17495-7; For RPG FAPESP grant #2023/01470-2.
• Data availability statement:
  The original photos of the trackways and all the measurements are in Supplementary Material.

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Edited by

• SCIENTIFIC EDITOR:
  Carlos Henrique Grohmann http://orcid.org/0000-0001-5073-5572

• ASSOCIATE EDITOR:
  Ismar de Souza Carvalho https://orcid.org/0000-0002-1811-0588

Data availability

The original photos of the trackways and all the measurements are in Supplementary Material.

Publication Dates

• Publication in this collection
  06 Mar 2026
• Date of issue
  2026

History

• Received
  06 Mar 2025
• Accepted
  19 Aug 2025