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Article

Review of Tridactyl Avian Footprints (Ichnofamily Avipedidae) with Emphasis on Type Material from the Miocene of the Carpathians (Ukraine, Hungary and Romania)

by
Ricardo Melchor
1,2,*,
Viktória Káposztás
3 and
Yaryna Tuzyak
4
1
Instituto de Ciencias de la Tierra y Ambientales de La Pampa, Consejo Nacional de Investigaciones Científicas y Técnicas-Universidad Nacional de La Pampa, Rivadavia 236, Santa Rosa 6300, La Pampa, Argentina
2
Departamento de Geología, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de La Pampa, Av. Uruguay 151, Santa Rosa 6300, La Pampa, Argentina
3
Department of Collections, Geological Survey, Supervisory Authority for Regulatory Activities, Stefánia út 14, H-1143 Budapest, Hungary
4
Paleontological Museum, Ivan Franko National University of Lviv, 79005 Lviv, Ukraine
*
Author to whom correspondence should be addressed.
Foss. Stud. 2026, 4(2), 13; https://doi.org/10.3390/fossils4020013
Submission received: 20 March 2026 / Revised: 27 April 2026 / Accepted: 28 April 2026 / Published: 26 May 2026
(This article belongs to the Special Issue New Directions in the Study of Vertebrate Trace Fossils)
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Abstract

Numerous ichnotaxa (about 21 ichnogenera and 39 ichnospecies) have been proposed for fossil tridactyl avian footprints. The purpose of this contribution is to analyze type material from Ukraine of the first proposed tridactyl avian ichnogenus, Avipeda, and related ichnogenera from the Carpathians of Hungary and Romania (Aviadactyla, Ornithotarnocia, Passeripedia, and Carpathipeda). The criteria for erection of ichnofamilies, ichnogenera and ichnospecies of avian footprints are discussed. It is proposed that trackway features only be used for ichnospecies. The ichnofamily Avipedidae comprises essentially small leptodactylous avian footprints showing three digits directed forward, with digits united or separate proximally, and lacking web imprint. The type material of Avipeda is represented by small footprints (less than 30 mm in length) that are wider than they are long, showing large total divarication and near symmetry with respect to digit III. Examined material from the type series of Avipeda from the Miocene of Ukraine also contains tetradactyl bird footprints that are better compared with Gruipeda. Aviadactyla and Ornithotarnocia (from the Lower Miocene of Ipolytarnóc, Hungary) are considered potentially available, whereas Passeripedia is deemed unavailable. Carpathipeda (erected for material from the Miocene of Romania) is indistinguishable from Avipeda. Additional comparisons are necessary to evaluate the status of other tridactyl avian ichnotaxa.

1. Introduction

A recent revision of the ichnotaxonomy of avian footprints suggest that at least 36 ichnogenera and 77 ichnospecies have been recognized from the Paleogene and Neogene [1] and 17 ichnogenera and 26 ichnospecies from the Cretaceous [2]. Several factors influenced the proliferation of ichnotaxa including the lack of uniform ichnotaxonomic criteria, distinctions based on the age of the hosting rocks, inferences about the presumed producer and, in the past century, poor communication of research results. Difficulty for accessing publications due to language barriers also played a role. In particular, the age of the hosting sequence and the presumed producers played an important role, although these criteria are commonly not recommended as ichnotaxobases [3].
The first formally named bird tracks were tetradactyl footprints and included the ichnogenera Ignotornis Mehl, 1931 [4] from the Early Cretaceous of Colorado (USA), and Iranipeda (Urmiornis) Lambrecht, 1938 [5] from the Pliocene of Iran. Works by Panin and Avram [6] and Vyalov [7,8] were particularly influential in applying a biological nomenclature to fossil footprints. Some later works that expanded this scheme were those of Sarjeant and colleagues [9,10] and also Lockley et al. [11]. Although ichnotaxonomy should be based essentially on morphological grounds [3,12], until recently, there were an implicit convention that Cretaceous and Paleogene/Neogene bird ichnotaxa should be compared and treated separately (e.g., [9,10,11,13]). In the last two decades or so, some authors beginning with de Valais and Melchor [14], and later replicated by other authors [15,16,17,18,19], started to make morphological comparisons of bird ichnotaxa that were independent from the age or presumed producers. Ichnotaxonomy should be based as much as possible on repetitive morphological features that are essentially linked to the anatomy of the producer [20]. New ichnotaxa should be based preferentially on a large sample size—to appreciate variability—and on specimens with a good to excellent degree of preservation [20]. It is not always easy to assess variability for a group of bird footprints from a lithostratigraphic unit, however, observations on modern bird footprints are commonly very useful [21].
Tridactyl avian footprints represent a very common and simple bird footprint morphology in modern and fossil examples. At least 21 ichnogenera and 39 ichnospecies have been proposed to date, which are mostly grouped into four ichnofamilies (Table 1).
Vyalov [7,8] envisaged the ichnogenus Avipeda as comprising all avian fossil footprints, as this author observed very little variability in the Miocene assemblages he studied from the Carpathians of Ukraine. Although Sarjeant and Langston Jr. [10] tried to restrict the morphological variability of Avipeda, the ichnogenus has become a sort of wastebasket and is in need of revision and comparison with several similar ichnotaxa. Kordos [25] already recognized the need for wider comparisons of bird ichnogenera using the type material and unified nomenclatural principles (i.e., ichnotaxobases). In this paper, the type material of Avipeda from Ukraine described by Vyalov [7,8] or belonging to the type series, as well as related ichnogenera described by Kordos [24,25] from Hungary and Romania, is compared to assess the morphological variability and to analyze the taxonomical status. The ichnotaxobases used for avian footprints are also reviewed.

2. Materials and Methods

We follow the general conventions used by Leonardi [44] and Buckley et al. [45] for measurements on individual footprints and trackways. Measurements on individual footprints include footprint length (FL), footprint width (FW), width of digit III (DWIII), and divarication of digits II and IV (II–IV), II and III (II–III), and III and IV (III–IV). To estimate the projection of digit III beyond the length of the lateral digits, the anterior triangle (AT) was measured after Weems [46] and Lockley [47]. The maximum height of the anterior triangle (ATl) was measured perpendicular to the base of the triangle (ATw). The anterior triangle height/width ratio (AT l/ATw) is considered a measure of the degree of mesaxony (e.g., [46,47]). The ratio DWIII/FL is taken as indicative of leptodactylous vs pachydactylous footprints [48]. Leptodactylous or slender-toed footprints are narrow and rarely show phalangeal pads and claw traces, although digits are pointed. Pachydactylous or thick-toed footprints display digit imprints that are wide in comparison with their length with distinct claw traces and phalangeal pads [48]. The degree of preservation of footprints is evaluated following the scale proposed by Marchetti et al. [20].
For trackways (i.e., at least three consecutive footprints for bipedal animals) the pace length (PL), pace angulation (PA), stride length (SL), rotation with respect to the midline (FR) and the trackway external width (TWo) can be measured [44]. The meaning of the ratio pace length to footprint length (PL/FL) is objective and can be used as an ichnotaxobase [11]; however, there is no direct relationship to leg length. Instead, the relationship involves the inference of height at hip and speed [49,50].
Photogrammetric three-dimensional (3D) models were created from the analyzed type specimens. For the specimens hosted at the Supervisory Authority of Regulatory Affairs, Department of Collections (Budapest, Hungary) a total of 70 to 233 photographs were taken for each specimen. These photographs were taken using a Nikon Z 7II camera and a Nikkor Z 24–70 mm f/4 S lens, at 24 mm, 35 mm and 70 mm focal length, in NEF (Nikon’s RAW) file format using DX sensor settings, each with a file size ranging from 23 to 27 MB. The 3D models from these photographs were created using RealityScan 2.0.1 software.
For the remaining specimens, three-dimensional and digital elevation models (DEMs) were generated using digital photographs processed with the photogrammetric software Agisoft Photo Scan Professional Edition 1.7.3 (www.agisoft.com). Resultant models were scaled and oriented using the free software Meshlab 2021.07 (www.meshlab.net). Depth-color images of the 3-D models were generated using the free software Paraview 5.10 (www.paraview.org), relative to a horizontal plane which was defined by markers set onto the surface of the model in Agisoft Photoscan.
Acronyms include: SARA: Supervisory Authority for Regulatory Affairs, Department Collections, Budapest, Hungary. PM-IFNUL: Paleontological Museum of the Ivan Franko National University of Lviv, Ukraine.

3. Ichnotaxobases for Avian Footprints

There is not a general agreement on what are the more adequate ichnotaxobases to distinguish ichnofamilies, ichnogenera and ichnospecies of avian footprints [1,13,14,51]. Panin and Avram [6] and Vyalov [7,8] first consistently applied binomial nomenclature in Latin to fossil footprints (see also a review in [1]). Panin and Avram [6] already considered that the nomenclature they proposed was parataxonomic and recognized the utility of comparing fossil footprints with those of extant groups. These authors were also aware of the limitations and potential contributions of paleoichnology to the knowledge of the evolution of different animal groups. For the Miocene, Panin and Avram [6] proposed the naming of the different categories for fossil footprints using a “root” related to the taxonomic category of the extant producers of similar tracks, and the suffix -ipedae for families. These authors recognized four families for avian footprints: Ardeipedae, Anatipedae, Charadriipedae and Gruipedae. However, they failed to provide a definition for each of them and the names should be adapted to the current guidelines of the ICZN [52] to include the suffix-idea [10].
The currently proposed avian ichnofamilies includes Trisauropodiscidae Lockley et al., 1992 [11]; Ignotornidae Lockley et al., 1992 [11]; Avipedidae Sarjeant and Langston Jr., 1994 [10]; Anatipedidae (Sarjeant and Langston Jr., 1994) Sarjeant and Reynolds, 2001 [9]; Gruipedidae Sarjeant and Langston Jr., 1994 [10]; Culcitapedidae Sarjeant and Reynolds, 2001 [9]; Jindongornipodidae Lockley et al., 2006 [53]; Koreanornipodidae Lockley et al., 2006 [53]; Shandongornipodidae Lockley et al., 2007 [54]; Limiavipedidae McCrea et al., 2014 [33]; Paxavipedidae McCrea et al., 2015 [35].
The ichnotaxobases for avian ichnofamilies should be very broad and follow the categories of bird foot types: for example, tridactyl, anisodactyl, palmate, semipalmated and zygodactyl. This is in line with the proposal by Panin and Avram [6], and was best developed by Sarjeant and Langston Jr. [10] and Sarjeant and Reynolds [9]. However, some subsequent proposals commonly used ichnotaxobases that represent a subset of features or even inferences about the length of legs of the presumed producer (e.g., [33,35]). In the diagnosis or description of Limiavipedidae and Paxavipedidae, proposed for Cretaceous avian footprints, an underlying aspect is the biological affinity of the presumed producer. However, ichnotaxa should be based on morphology and not on inferences about the producer [3].
The most used ichnotaxobases for erection of ichnofamilies are (in relative order): number of digits, overall shape, presence/absence of interdigital web, position of hallux with respect to digit III, footprint rotation with respect to the midline (FR) and total divarication (II–IV). These features are related to footprint morphology, although some authors also include features related to trackway parameters (for example, stride length, footprint rotation, external trackway width see Figure 1). It is recommended that ichnofamilies and ichnogenera be based primarily on footprint features and trackway features be used for ichnospecies in combination with other minor footprint features. This is in line with the idea that footprint morphology reflects the autopodium of the producer and that behavioral variants (speed, gait, foraging vs. walking, etc.) that are commonly reflected in the footprint arrangement in a trackway be preferentially related to ichnospecies [14]. A further family ichnotaxobase that is not commonly used is the relative digit width (DWIII/FL) implying a producer with leptodactylous or pachydactylous feet. This criterion was proposed qualitatively (e.g., “slender digits”) in selected examples [11,53].
When comparing the criteria used by different specialists to identify avian ichnofamilies with those used to distinguish ichnogenera and ichnospecies, there is a marked overlap (Figure 1). The compilation by Abbassi et al. [1] suggested that avian ichnogenera were mainly diagnosed considering the number of digits, total digit divarication, relative digit length, and presence/absence of webbing, whereas ichnospecies are mainly distinguished by digit divarication, footprint size, and relative digit length, with other relevant features being digit shape, presence/absence of claw traces, and shape of metatarsal pads.
We especially emphasize that trackways features are better applied to the ichnospecies level and do not recommend their usage to define ichnofamilies.

4. Ichnofamilies Proposed for Avian Tridactyl Footprints

There are four ichnofamilies proposed for tridactyl avian footprints: Trisauropodiscidae, Avipedidae, Limiavipedidae and Paxavipedidae (Table 1). In addition, there are currently five tridactyl avian ichnogenera that have not been included in an ichnofamily: Ornithoformipes Patterson and Lockley, 2004 [40], Rivavipes Mustoe et al., 2012 [42], Tatarornipes Lockley et al., 2012 [43], Aramayoichnus Aramayo et al., 2015 [39]; and Rionegrina Melchor et al., 2023 [41] (the latter is functionally didactyl).
Trisauropodiscidae was proposed to embrace tridactyl and tetradactyl slender-toed aviform tracks from southern Africa recognized under the ichnogenus Trisauropodiscus Ellemberger, 1972 [37]. The occurrence of this ichnogenus from Upper Triassic to Lower Jurassic units were reviewed by Abrahams and Bordy [38], and findings additional to those reported by Elenberger [37,71] from the type series were documented by Abrahams et al. [72]. Abrahams and Bordy [38] concluded that there are two morphotypes within the material described under Trisauropodiscus by Ellenberger [37,71], and no clear hallux imprint was noticed in the field or cast material. In particular, morphotype II of Abrahams and Bordy [38], comparable with Trisauropodiscus aviforma Ellenberger, 1972 [37], displays a clear bird-like morphology (including slender digits and wide divarication). However, a detailed ichnotaxonomic revision of this material is pending. Trisauropodiscus isp. documented from the Middle Jurassic of Morocco [73] displays a hallux imprint and thus assignation to the ichnogenus is doubtful. Trisauropodiscidae embraces footprints that are similar to those included under Avipedidae and may have priority over the latter, however, considering the extended use of Avipedidae, it is probably advisable to keep the latter as a distinctive and valid ichnofamily. The use of Trisauropodiscidae is strongly related to the uncertainties about the producer with no known candidate in Late Triassic-Early (or Middle) Jurassic sequences.
Avipedidae was proposed using three simple and broad features: tridactyl character, digits joined or not in a metatarsal pad and absence of web imprint [10]. Avipedidae originally included Avipeda Vyalov, 1965 [8] (the type ichnogenus), Aquatilavipes Currie, 1981 [21], Aviadactyla Kordos, 1985 [24], Ludicharadripodiscus Ellenberger, 1980 [28], Fuscinapeda Sarjeant and Langston Jr., 1994 [10] and Ornithotarnocia Kordos, 1985 [24]. We can also add [1] Carpathipeda Kordos in Kordos and Prakfalvi, 1990 [25] (synonymized under Aviadactyla by [10]) and Passeripedia Kordos in Kordos and Prakfalvi, 1990 (synonymized under Avipeda by Sarjeant and Langston Jr., 1994 [10]). Reyesichnus Alonso et al. 1980 [29], Yacoraitichnus Alonso and Marquillas, 1986 [31], and Uvaichnites Díaz- Martínez et al., 2012 [30] can be added to the list of ichnogenera (Table 1). In this way, at least 11 ichnogenera and 29 ichnospecies can be considered under Avipedidae. In a recent review [1], Passeripedia and Ludicharadripodiscus were considered nomina dubia, Fuscinapeda was considered a nomen nudum, Aviadactyla a junior synonym of Ornithotarnocia and Carpathipeda a junior synonym of Avipeda.
The two remaining ichnofamilies are related to small (Paxavipedidae) and large tridacyl footprints (Limiavipedidae) and were defined using specimens from the Cretaceous. Paxavipedidae was proposed for small (FL = 20–40 mm) tridactyl footprints lacking hallux and web imprint, which render them very similar to Avipedidae, although the authors argued that the distinctive features were the footprint asymmetry (II–III > III–IV) and inward rotation of footprints, and that they represented short-legged producers [35]. The asymmetry of footprint is a highly variable feature that is not commonly used as ichnotaxobase (Figure 1), the inward rotation of footprint is a common feature in bird trackways, and the implications of short-legged producers are difficult to demonstrate objectively, requiring an assumption about the height at hip of the producer. The ichnofamily Paxavipedidae includes Paxavipes and Barrosopus. McCrea et al. [35] considered that Paxavipedidae is distinct enough from Avipedidae; however, these authors used only Cretaceous specimens of Aquatilavipes, as representative of Avipedidae. The multivariate analysis performed by McCrea et al. [35] included footprint length, footprint width, digit length and digit divarication of Cretaceous ichnospecies including Paxavipes babcockensis, Barrosopus slobodai, Aquatilavipes izumiensis and Aquatilavipes swilboldae. A similar footprint asymmetry (II–III > III–IV) found in Paxavipes is also verified in the type material of Avipeda, including Avipeda phoenix and Avipeda sirin from the Miocene of the Carpathians (Table 8.3 in [1]). The ratio PL/FL is similar for both ichnospecies within Paxavipedidae and reaches 3.2, whereas the average for Avipedidae is 4.0. This underscores the doubtful implications regarding the length of legs of the producer, as discussed above.
Limiavipedidae includes the type ichnogenus Limiavipes McCrea et al., 2014 [33] and Wupus Xing et al., 2007 [34] (Table 1), recorded from Lower to Upper Cretaceous beds [2]. The diagnosis of Limiavipedidae emphasizes trackway features, inferences pointing to a long-legged producer and the size of the footprints. The essential features are a large size (FL = 60–137 mm), linked to long legs as expected for the size of the presumed producer (e.g., [49,50]). However, the ratio pace length to footprint length (PL/FL = 2.6 to 3.0) is slightly smaller than in Paxavipedidae (PL/FL = 3.2) and smaller than in Avipedidae (PL/FL = 4.0). The erection of this ichnofamily is also related to the age of the hosting beds and the discussion about the morphological distinction between avian and non-avian theropod footprints [74].

5. Type Material of Avipeda Vyalov, 1965 [8]

Four slabs belonging to the Paleontological Museum of the Ivan Franko National University of Lviv, Ukraine were examined for this study. The slabs came from the Prut River Valley, near Deliatyn city, from the Ukranian Carpathians. They belong to the lower part of the Stebnyk or the underlying Dobrotiv formations (Lower to Middle Miocene) [75,76]. Vyalov [7,8] indicated that the holotype of A. phoenix came from the Dobrotiv Formation and those of A. sirin from the Stebnyk Formation. The examined specimens belong to Avipeda phoenix (specimen PM-IFNUL 8659 and 8678) and Avipeda sirin (specimens PM-IFNUL 8643 and 8756).

5.1. Avipeda phoenix

Specimen PM-IFNUL 8659 is shown in Figure 2. This specimen was illustrated in Vyalov [8] as plate XIII and in Vyalov [7] as plates XXVII and XXVIII. The specimen is a slab with flat-topped wave ripples, several small bird footprints (FL = 14–22 mm), and poorly preserved artiodactyl footprints (Pecoripeda amalphea Vyalov, 1965 [8]) (Figure 2a). The bird footprints preserved as negative epirelief display thin digits and wide divarication (II–IV= 130–174°), thus suggesting deeply set footprints in a muddy substrate. Some digit imprints are pointed, although no clear claw traces were observed. Preservation degree is about 1.5 and the footprints are preferentially preserved on the ripple crests. The slab contains at least three trackways, the longest contains at least seven consecutive footprints, and the remaining three and four footprints. The artiodactyl footprints apparently cut the bird footprints and are transmitted footprints (from overlying laminae).
Specimen PM-IFNUL 8678 is displayed in Figure 3. The bottom of this slab exhibits sole marks in the form of subparallel groove casts up to 1–2 cm wide. Sparse bird footprints including three composing a trackway are preserved in positive hyporelief (Figure 3a). A more or less continuous ridge arranged at a high angle with the groove casts and associated almond-shaped positive hyporeliefs that are very close to a bird footprint with thick digits, are probably related to bivalve trace fossils (Lockeia or Ptychoplasma) (Figure 3a), although the specimen label indicates mudcracks. The bird footprints are also small (FL = 16–19 mm) and include some that are tridactyl and others that display a spur-like hallux imprint (footprints #3, #5 and #7) (Figure 3b). The digit imprints are not generally joined proximally, and in some cases display a metatarsal pad imprint. Some footprints display digital pads and claw traces. The preservation of bird footprints associated with sole marks is unusual, as sole marks imply eroding turbulent flows that would erase delicate avian footprints. A possible explanation is that the footprints postdate the groove casts.

5.2. Avipeda sirin

Specimen PM-IFNUL 8643 is shown in Figure 4. This specimen was figured by Vyalov [7] as A. phoenix (plate LIII, Figure 1), but is currently cataloged as A. sirin. It is considered that assignation to the latter ichnospecies is concordant with the size range applied by Vyalov to distinguish both ichnospecies. The specimen is a sole surface of slab with at least ten complete bird footprints, and several incomplete ones, preserved in positive hyporelief (Figure 4a,b). As with specimen 8678, the surface is covered with groove casts that are a few millimeters wide, as well as wider blunt ridges (about 1 cm wide) oriented at a high angle to the groove casts (possible mudcrack fill). Most of the footprints are tridactyl with wide total divarication (II–IV = 91–146°) and claw traces, including three that compose a trackway (footprints #1 to #3), whereas a single footprint (#4) exhibits a possible hallux trace. There are also some tridactyl footprints (e.g., #9) that exhibit a lower total divarication (II–IV = 47–80°). Bird footprints generally lack the metatarsal pad impression.
Specimen PM-IFNUL 8756 is displayed in Figure 5. The specimen consists of a slab with sole surface covered by numerous incomplete bird footprints preserved in positive hyporelief (Figure 5a). Most of the surface is covered with partial footprints of reduced relief, and only three are nearly complete to allow for measurements. The density of the bird footprints is similar to those observed in the shoreline of a lake or a small pond [77]. This agrees with a sole surface that is convex downward (Figure 5b), suggesting a local depression in the depositional surface. The footprints are tridactyl and commonly have metatarsal and phalangeal pads, as well as claw traces. There is no evidence of mudcracks and/or groove casts.

5.3. Comparison of Avipeda Ichnospecies

Vyalov [7,8] proposed three ichnospecies for Avipeda: A. phoenix, A. sirin, and A. filiportatis. Avipeda filiportatis is tetradactyl and was correctly reassigned to Gruipeda by Sarjeant and Langston Jr. [10]. Vyalov [7] diagnosed A. phoenix as the smaller species, having an obtuse divarication angle between digits (II–IV), whereas A. sirin was slightly larger and showed higher divarication. Our analysis of the described material and detailed measurements suggest that the sample from the type series of Avipeda strongly overlaps in size and divarication angle (Figure 6a,b).
For this reason, the most conservative approach would be to consider Avipeda sirin as a junior synonym of Avipeda phoenix, as proposed by Abbassi et al. [1]. The occasional presence of hallux imprints, and contrasting divarication angles in some specimens may imply that some of the footprints from the type series can be assigned to other ichnotaxa. (i.e., Gruipeda).

6. Type Material of Tridactyl Footprints from Ipolytarnóc

Kordos [25] proposed three new ichnogenera and ichnospecies for tridactyl footprints from Lower Miocene deposits from Ipolytarnóc, Hungary: Aviadactyla media, Ornithotarnocia lambrechti and Passeripedia ipolyensis (Table 1). Below, the holotype specimens of these ichnospecies are described.

6.1. Aviadactyla media

Specimen SARA V.12729, Vt.104 is a sandstone slab with undulate top containing at least 13 nearly complete tridactyl bird footprints and several incomplete ones, preserved as negative epirelief (Figure 7a,b). The degree of preservation is 1.5–2. The prints are shallower in the depressed areas. Three pairs of footprints (#1–2, #4–5 and #6–7) are considered consecutive, although no trackway was identified (Figure 7c). In most of the footprints, the digits do not unite proximally, although some display a metatarsal pad, and claw traces are common. Kordos [24] designated two footprints from this slab as the holotype, but they were not identified during this study. The footprints range from 17 to 27 mm in length and total divarication (II-IV) is 81–106°.

6.2. Ornithotarnocia lambrechti

Specimen SARA V.12721, Vt.103 is a sandstone slab with at least six nearly complete tridactyl bird footprints and several artiodactyl footprints (Pecoripeda cf. amalphea), preserved as negative epirelief (Figure 8a,b). The degree of preservation is about two, with thick digits lacking of claw traces, commonly joined in the metatarsal area. Footprints # 12-9-8 (original designation by Kordos) compose a trackway. The holotype is represented by two consecutive prints from the trackway (#12 and #9) (Figure 8c). The footprints are larger than those of Aviadactyla media (FL = 32–40 mm) and the total divarication angle (II–IV = 93–118°) overlaps.

6.3. Passeripedia ipolyensis

The specimen SARA V.12718, Vt.107 is a slab with irregular surface and multiple subrounded and millimetric pits, some of which are aligned (Figure 9a,b). Similar structures were illustrated in plate II by Kordos [24]. The holotype in this slab is footprint #12, after the original designation. Two other specimens (footprints #34 and #96 after Kordos [24]) were assigned to this ichnospecies (Figure 9c,d). Our interpretation of the material is that footprint #12 (the holotype) is an inorganic structure related with the fortuitous alignment of millimetric pits (lateral “digits”) and the edge of a broken laminae (“digit” III) (Figure 9a,b). These pits may be raindrop imprints, although the margin is very sharp and deep to be compatible with these structures. Considering that the footprint bearing levels in Ipolytarnóc are covered by pyroclastic deposits [78], the most likely alternative is that the millimetric pits represent impact structures related to accretionary lapilli. Alternatively, they can represent hail imprints. The remaining specimens (footprints #34 and #96), represent partial prints of probable bird origin, although only two digits are imprinted in each specimen.

7. Type Material of Carpathipeda

Kordos [25] described four plaster casts originally deposited in the Palaeovertebrate Collection of the Hungarian Geological Institute (now SARA Geological Survey), which contained bird and artiodactyl footprints. They were obtained from Miocene strata of the Tara-Vrancea area in Romania, one of the sites that was studied by Panin and Avram [6] when proposing several mammal and bird ichnotaxa. The material was used to propose the bird ichnogenus Carpathipeda, including the type ichnospecies Carpathipeda panini and Carpathipeda vialovi.

7.1. Carpathipeda panini

The specimen SARA V.15274, Vt.141 is a cast that contains at least 13 complete and several incomplete bird footprints that appear as negative epirelief (Figure 10a,b). The footprints exhibit slender and pointed digits that commonly do not join in the metatarsal area and lack phalangeal pads. Two pairs of footprints (#4 and #15, #16 and A) are considered consecutive. The holotype is footprint #2. A single complete specimen is also found in specimen V.15276, Vt.142 (#5 in Figure 10c,d). The footprints are small (FL = 17–27 mm) and display a large divarication angle (II-IV = 93–141°).

7.2. Carpathipeda vialovi

The specimen V.15276, Vt.142 is a cast of the holotype that is shown in Figure 10c,d. The ichnospecies is represented by a single footprint preserved in negative epirelief. The footprint exhibits well-defined digit imprints with claw traces that do not unite in the metatarsal area. The specimen is only slightly larger (FL = 29 mm) than the material of C. panini (FL = 17–27 mm) with a total divarication very close to the upper range of the latter ichnospecies (II–IV = 143°). The original description indicates that C. vialovi is 50–70% larger than C. panini; however, this was not verified.

8. Discussion and Conclusions

It is proposed that ichnotaxobases for avian footprints accord with the following rationale. Familiar ichnotaxobases should be broad and roughly conform to major bird footprint types. Generic ichnotaxobases should include a subset of properties especially focused on footprint morphology. Specific ichnotaxobases can refer to behavioral variants including trackway features or minor morphological differences. Both ichnofamilies and ichnogenera should rely essentially on footprint morphology as a reflection of the autopodium of the producer [20].
Among the proposed ichnofamilies for tridactyl avian footprints, Paxavipedidae can be synonymized with Avipedidae. Avipedidae is best described as comprising small leptodactylous avian footprints showing three digits directed forward, with digits united or separated proximally, and lacking web imprint. The status of Triasuropodiscidae is pending upon an ichnotaxonomical re-evaluation of the type material from South Africa.
Analysis of the published images of Avipeda holotypes and material of the type series from Ukraine (Figure 2, Figure 3, Figure 4 and Figure 5) is used to propose that the ichnogenus should be limited to small footprints (FL ≤ 30 mm) that are wider than they are long, showing large total divarication and near symmetrical with respect to digit III (II–III ≅ III–IV) (Table 2). This proposal is pending upon examination of the holotype specimens. We also document that the type material from the Miocene of the Carpathians include some tetradactyl footprints (Figure 3b,c and Figure 4a) that should be treated under a separate ichnotaxon (i.e., Gruipeda).
Avipeda sirin is considered a junior synonym of Avipeda phoenix as the material displays a continuous and overlapping variation in footprint length and total divarication (Figure 6a,b), the two key features considered to distinguish these ichnospecies by Vyalov [7,8].
Among the type material from Ipolytarnóc, Hungary, both Aviadactyla media (Figure 7) and Ornithotarnocia lambrechti (Figure 8) are considered potentially available, although a detailed comparison with the type material of Aqualitavipes swiboldae and A. phoenix is pending (Table 2). The holotype of Passeripedia ipolyensis (Figure 9a,b) is considered an inorganic structure, whereas the additional material of the ichnospecies includes incomplete or poorly preserved avian footprints (Figure 9c,d). For these reasons, P. ipolyensis is considered not available.
The ichnospecies Carpathipeda panini (Figure 10a,b) and Carpathipeda vialovi (Figure 10c,d) are indistinguishable from Avipeda phoenix (Table 2) and are thus considered subjective junior synonyms.
Further comparisons of the type material of tridactyl avian footprints are necessary to clarify the availability of several ichnogenera (e.g., Fuscinapeda, Reyesichnus, Yacoraitichnus, see Table 1) and even ichnospecies within Avipeda (e.g., Avipeda adunca, Avipeda thrinax, Avipeda gryponyx, Avipeda circumontis).

Author Contributions

Conceptualization, R.M. and Y.T.; methodology, R.M., V.K. and Y.T.; software, V.K.; formal analysis, R.M.; investigation, R.M., V.K. and Y.T.; resources, R.M.; data curation, R.M., V.K. and Y.T.; writing—original draft preparation, R.M.; writing—review and editing, V.K. and Y.T.; funding acquisition, R.M. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by projects PICT2019-114 from the Agencia Nacional de Promoción Científica y Tecnológica of Argentina, PIP2021-2023-146 from CONICET, and project G22 from Universidad Nacional de La Pampa to RNM. The work was also supported by the GINOP-2.3.3-15-2017-00043 grant.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

Three-dimensional models and digital elevation models of footprints from Ivan Franko National University of Lviv were produced by Victor Emanuel Castillo from INCITAP, Argentina. Rodolfo Coria (Museo Carmen Funes, Plaza Huincul, Neuquén, Argentina) is thanked for providing images of the type material of Barrosopus slobodai. The comments by two anonymous reviewers improved the original version of the manuscript.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Figure 1. Histogram of the relative frequency of use by different authors of criteria for distinction of ichnofamilies, ichnogenera and ichnospecies. DW: digit width, FL: footprint length, FW: footprint width, P/A: presence/absence, II–IV: angle between digits II–IV, SL: stride length, TWo: trackway external width, FR: footprint rotation from the midline, PL: pace length. The numbers in the columns represent the case studies using this feature as an ichnotaxobase. Compiled from [5,6,7,9,10,11,14,18,21,23,24,27,28,30,31,33,35,39,42,51,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70].
Figure 1. Histogram of the relative frequency of use by different authors of criteria for distinction of ichnofamilies, ichnogenera and ichnospecies. DW: digit width, FL: footprint length, FW: footprint width, P/A: presence/absence, II–IV: angle between digits II–IV, SL: stride length, TWo: trackway external width, FR: footprint rotation from the midline, PL: pace length. The numbers in the columns represent the case studies using this feature as an ichnotaxobase. Compiled from [5,6,7,9,10,11,14,18,21,23,24,27,28,30,31,33,35,39,42,51,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70].
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Figure 2. Type material of Avipeda phoenix (PM-IFNUL 8659). (a) General view of the slab showing the measured bird footprints (numbers), artiodactyl footprints (some arrowed) and ripples. (b) Detail of the longest A. phoenix trackway.
Figure 2. Type material of Avipeda phoenix (PM-IFNUL 8659). (a) General view of the slab showing the measured bird footprints (numbers), artiodactyl footprints (some arrowed) and ripples. (b) Detail of the longest A. phoenix trackway.
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Figure 3. Material of the type series of Avipeda phoenix (PM-IFNUL 8678). (a) View of the sole of the slab with bird footprints (numbered), groove casts and probable bivalve trace fossils (black arrows). (b,c) Detail of footprints #3 and #5 showing possible hallux imprint (white arrows).
Figure 3. Material of the type series of Avipeda phoenix (PM-IFNUL 8678). (a) View of the sole of the slab with bird footprints (numbered), groove casts and probable bivalve trace fossils (black arrows). (b,c) Detail of footprints #3 and #5 showing possible hallux imprint (white arrows).
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Figure 4. Type material of Avipeda sirin (PM-IFNUL 8643). (a) View of the sole of the slab with bird footprints (numbered) and groove casts. Possible hallux print in footprint #4 arrowed. (b) Digital elevation model of the specimen.
Figure 4. Type material of Avipeda sirin (PM-IFNUL 8643). (a) View of the sole of the slab with bird footprints (numbered) and groove casts. Possible hallux print in footprint #4 arrowed. (b) Digital elevation model of the specimen.
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Figure 5. Type material of Avipeda sirin (PM-IFNUL 8756). (a) View of the sole of the slab with a dense array of bird footprints. Measured footprints are numbered. (b) Digital elevation model of the specimen. Note phalangeal pads in footprint #1 (arrowed). II–IV: digits II to IV.
Figure 5. Type material of Avipeda sirin (PM-IFNUL 8756). (a) View of the sole of the slab with a dense array of bird footprints. Measured footprints are numbered. (b) Digital elevation model of the specimen. Note phalangeal pads in footprint #1 (arrowed). II–IV: digits II to IV.
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Figure 6. Histograms show (a) the variation of footprint length (FL) and (b) total divarication angle (II–IV) of the type series of Avipeda phoenix and Avipeda sirin.
Figure 6. Histograms show (a) the variation of footprint length (FL) and (b) total divarication angle (II–IV) of the type series of Avipeda phoenix and Avipeda sirin.
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Figure 7. Type material of Aviadactyla media (SARA V.12729, Vt.104). (a,b) Orthomosaic and digital elevation model of the specimen. Measured footprints are numbered. (c) Detail of some of the best-preserved footprints, including two considered consecutive (#4 and #5).
Figure 7. Type material of Aviadactyla media (SARA V.12729, Vt.104). (a,b) Orthomosaic and digital elevation model of the specimen. Measured footprints are numbered. (c) Detail of some of the best-preserved footprints, including two considered consecutive (#4 and #5).
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Figure 8. Type material of Ornithotarnocia lambrechti (SARA V.12721, Vt.103). (a,b) Orthomosaic and digital elevation model of the specimen. Measured footprints are numbered. Arrows point to some of the artiodactyl footprints. (c) Detail of the best-preserved footprints, that are interpreted as a trackway. Footprints #12 and #9 are the holotype.
Figure 8. Type material of Ornithotarnocia lambrechti (SARA V.12721, Vt.103). (a,b) Orthomosaic and digital elevation model of the specimen. Measured footprints are numbered. Arrows point to some of the artiodactyl footprints. (c) Detail of the best-preserved footprints, that are interpreted as a trackway. Footprints #12 and #9 are the holotype.
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Figure 9. Type material of Passeripedia ipolyensis (SARA V.12718, Vt.107). (a,b) Orthomosaic and digital elevation model of the holotype. Arrows point to equivalent features in the images. The inset in b is the original diagram by Kordos [24]. Scale divisions in (a) are 1 mm. (c,d) Photographs of the paratype material corresponding to footprints #34 and #96 by Kordos [24] (arrowed). The insets also show the corresponding original diagrams. Note profusion of subcircular pits and that some areas of the surface have been repaired.
Figure 9. Type material of Passeripedia ipolyensis (SARA V.12718, Vt.107). (a,b) Orthomosaic and digital elevation model of the holotype. Arrows point to equivalent features in the images. The inset in b is the original diagram by Kordos [24]. Scale divisions in (a) are 1 mm. (c,d) Photographs of the paratype material corresponding to footprints #34 and #96 by Kordos [24] (arrowed). The insets also show the corresponding original diagrams. Note profusion of subcircular pits and that some areas of the surface have been repaired.
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Figure 10. Type material of Carpathipeda panini (SARA V.15274, Vt.141) (a,b) and Carpathipeda vialovi (SARA V.15276, Vt.142) (c,d). (a,b) Orthomosaic and digital elevation model. The numbers refers to the original designation by Kordos and Prakfalvi [25], and A refers to a footprint not identified previously. The holotype is #2. (c,d) Orthomosaic and digital elevation model. Footprint #1 is the holotype and unique specimen of C. vialovi, whereas footprint #5 belongs to C. panini. Numbering after Kordos and Prakfalvi [25].
Figure 10. Type material of Carpathipeda panini (SARA V.15274, Vt.141) (a,b) and Carpathipeda vialovi (SARA V.15276, Vt.142) (c,d). (a,b) Orthomosaic and digital elevation model. The numbers refers to the original designation by Kordos and Prakfalvi [25], and A refers to a footprint not identified previously. The holotype is #2. (c,d) Orthomosaic and digital elevation model. Footprint #1 is the holotype and unique specimen of C. vialovi, whereas footprint #5 belongs to C. panini. Numbering after Kordos and Prakfalvi [25].
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Table 1. Compilation of ichnotaxa proposed for tridactyl avian footprints, grouped by ichnofamily and modified from the compilation by Abbassi et al. [1].
Table 1. Compilation of ichnotaxa proposed for tridactyl avian footprints, grouped by ichnofamily and modified from the compilation by Abbassi et al. [1].
IchnofamilyIncluded IchnogeneraIncluded Ichnospecies
Avipedidae Sarjeant and Langston Jr., 1994 [10]Aquatilavipes Currie, 1981 [21]Aquatilavipes swiboldae Currie, 1981 [21]
Aquatilavipes izumiensis Azuma et al., 2002 [22]
Aquatilavipes wallacei Zonneveld et al., 2011 [15]
Aquatilavipes curriei McCrea and Sarjeant, 2001 [23]
Aviadactyla Kordos, 1985 [24]Aviadactyla media Kordos, 1985 [24]
Aviadactyla panini (Kordos in Kordos and Prakfalvi, 1990 [25]) Sarjeant and Reynolds, 2001 [9]; comb. nov.
Aviadactyla vialovi (Kordos in Kordos and Prakfalvi, 1990 [25]) Sarjeant and Reynolds, 2001 [9]; comb. nov.
Avipeda (Vyalov, 1965 [8]) Sarjeant and Langston Jr., 1994Avipeda phoenix (Vyalov, 1965 [8]) Sarjeant and Langston Jr., 1994
Avipeda sirin Vyalov, 1965 [8]
Avipeda filiportatis Vyalov, 1965 [8] (=Gruipeda filiportatis Sarjeant and Langston Jr., 1994 [10])
Avipeda adunca Sarjeant and Langston Jr., 1994 [10]
Avipeda ipolyensis (Kordos, 1985) Sarjeant and Langston Jr., 1994 [10] (=Passeripedia ipolyensis Kordos, 1985 [24]).
Avipeda thrinax Sarjeant and Reynolds, 2001 [9]
Avipeda gryponyx Sarjeant and Reynolds, 2001 [9]
Avipeda circumontis Lockley et al., 2022 [26]
Gruipeda disjuncta (Panin and Avram, 1962 [6])
Gruipeda minor (Panin, 1965 [27])
Gruipeda vegrandiunus Fiorillo et al., 2011 [16]
Carpathipeda Kordos in Kordos and Prakfalvi, 1990 [25] Carpathipeda panini Kordos in Kordos and Prakfalvi, 1990 [25]
Carpathipeda vialovi Kordos in Kordos and Prakfalvi, 1990 [25]
Fuscinapeda Sarjeant and Langston Jr., 1994 Fuscinapeda sirin (Vyalov, 1965 [8]) Sarjeant and Langston Jr., 1994 [10]
Fuscinapeda meunieri Sarjeant and Langston Jr., 1994 [10]
Fuscinapeda texana Sarjeant and Langston Jr.,1994 [10]
Ludicharadripodiscus Ellenberger, 1980 [28] Ludicharadripodiscus edax Ellenberger, 1980 [28]
Ornithotarnocia Kordos, 1985 [24]Ornithotarnocia lambrechti Kordos, 1985 [24]
Passeripedia Kordos, 1985 [24] Passeripedia ipolyensis Kordos, 1985 [24]
Reyesichnus Alonso et al., 1980 [29]Reyesichnus punensis Alonso et al., 1980 [29]
Uvaichnites Díaz-Martínez et al., 2012 [30]Uvaichnites riojana Díaz-Martínez et al., 2012 [30]
Yacoraitichnus Alonso and Marquillas, 1986 [31]Yacoraitichnus avis Alonso and Marquillas, 1986 [31] (=Gruipeda filiportatis de Valais and Cónsole-Gonella, 2019 [32])
Limiavipedidae McCrea et al. 2014 [33]Limiavipes (McCrea and Sarjeant, 2001 [23]) McCrea et al. 2014 [33]Limiavipes curriei (McCrea and Sarjeant, 2001 [23]) McCrea et al., 2014 [33]
Wupus Xing et al., 2007 [34]Wupus agilis Xing et al., 2007 [34]
Paxavipedidae McCrea et al. 2015 [35]Barrosopus Coria et al. 2002 [36]Barrosopus slobodai Coria et al. 2002 [36]
Paxavipes McCrea et al., 2015 [35]Paxavipes babcockensis McCrea et al., 2015 [35]
Trisauropodiscidae Lockley et al., 1992 [11]Trisauropodiscus Ellenberger, 1972 [37]Trisauropodiscus aviforma Ellenberger, 1972 [37] (=morphotype II Abrahams and Bordy, 2023 [38])
UnknownAramayoichnus Aramayo et al., 2015 [39]Aramayoichnus rheae Aramayo et al., 2015 [39]
Ornithoformipes Patterson and Lockley, 2004 [40]Ornithoformipes controversus Patterson and Lockley, 2004 [40]
Rionegrina Melchor et al., 2023 [41]Rionegrina pozosaladensis Melchor et al., 2023 [41]
Rivavipes Mustoe et al., 2012 [42]Rivavipes giganteus Mustoe et al., 2012 [42]
Tatarornipes Lockley et al., 2012 [43]Tatarornipes chabuensis Lockley et al., 2012 [43]
Table 2. Summary of measurements on Avipedidae ichnospecies analyzed in this paper. Data in millimeters for linear measurements and degrees for angles, when available both range and average values (between parentheses) are indicated. n: number of footprints, DP: degree of preservation [20], FL: footprint length, FW: footprint width, DWIII: width of digit III, ATl/ATw: anterior triangle length/anterior triangle width ratio, II–IV: total divarication, II–III: angle between digits II and III, III–IV: angle between digits III–IV, PL: pace length, SL: stride length; PA: pace angulation, FR: footprint rotation, nd: no data.
Table 2. Summary of measurements on Avipedidae ichnospecies analyzed in this paper. Data in millimeters for linear measurements and degrees for angles, when available both range and average values (between parentheses) are indicated. n: number of footprints, DP: degree of preservation [20], FL: footprint length, FW: footprint width, DWIII: width of digit III, ATl/ATw: anterior triangle length/anterior triangle width ratio, II–IV: total divarication, II–III: angle between digits II and III, III–IV: angle between digits III–IV, PL: pace length, SL: stride length; PA: pace angulation, FR: footprint rotation, nd: no data.
Avipeda
phoenix		Aquatilavipes swilboldaeAviadactyla mediaOrnithotarnocia lambrechti*2 Carpathipeda paniniBarrosopus slobodai*1 Paxavipes babcockensis
n36413614821
DP1–1.52–31.51.5–21–21.5–22
FL14.1–30.8 (20.3)19.8–43.7 (35)17–27.3 (23.2)31.8–40.3 (35)17–29 (24.0)27.7–40 (31.7)20.5–33.6 (27.8)
FW18–47.5 (25.1)(44)20–32.6 (27.2)40.2–47.1 (43.5)20–35.8 (32.1)31–44 (36.7)21–38.6 (30.9)
FL/FW0.55–1.23 (0.82)0.7–1 (0.81)0.65–1.12 (0.86)0.67–0.86 (0.78)0.67–0.84 (0.75)0.74–0.97 (0.87)0.74–1.14 (0.92)
DWIII(2.6)(2.8)(2.8)(4)(2.4)(5)(4.1)
DWIII/FL(0.13)(0.08)(0.11)(0.12)(0.09)(0.16)(0.15)
ATl/ATw0.13–0.67 (0.39)0.5–0.5 (0.43)0.33–0.47 (0.41)0.29–0.51 (0.4)0.31–0.58 (0.47)0.45–0.58 (0.52)0.4–0.54 (0.48)
II–IV47–174 (119)87–130 (113)81–109 (94)93.8–118 (106)93–140 (128)100–130 (117)76–119 (99)
II–III(61)(46)(49)(57)(61)(60)(57)
III–IV(59)(59)(45)(47)(64)(56)(43)
PL34–92(80)38–60nd42–7030–135 (100)74.2–100.1
SL93–180(140)ndndnd135–235154–190
PA100–169(155)ndndnd153–168153–173
FRinwardndinwardsubparallelinwardinward (15–25)inward (17)
*1 Data from McCrea et al. [35]. *2 Includes C. vialovi.
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Melchor, R.; Káposztás, V.; Tuzyak, Y. Review of Tridactyl Avian Footprints (Ichnofamily Avipedidae) with Emphasis on Type Material from the Miocene of the Carpathians (Ukraine, Hungary and Romania). Foss. Stud. 2026, 4, 13. https://doi.org/10.3390/fossils4020013

AMA Style

Melchor R, Káposztás V, Tuzyak Y. Review of Tridactyl Avian Footprints (Ichnofamily Avipedidae) with Emphasis on Type Material from the Miocene of the Carpathians (Ukraine, Hungary and Romania). Fossil Studies. 2026; 4(2):13. https://doi.org/10.3390/fossils4020013

Chicago/Turabian Style

Melchor, Ricardo, Viktória Káposztás, and Yaryna Tuzyak. 2026. "Review of Tridactyl Avian Footprints (Ichnofamily Avipedidae) with Emphasis on Type Material from the Miocene of the Carpathians (Ukraine, Hungary and Romania)" Fossil Studies 4, no. 2: 13. https://doi.org/10.3390/fossils4020013

APA Style

Melchor, R., Káposztás, V., & Tuzyak, Y. (2026). Review of Tridactyl Avian Footprints (Ichnofamily Avipedidae) with Emphasis on Type Material from the Miocene of the Carpathians (Ukraine, Hungary and Romania). Fossil Studies, 4(2), 13. https://doi.org/10.3390/fossils4020013

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