Eleutherodactylus Dumeril and Bibron 1841
Creators: name: Vallejo-Pareja, Maria Camila
name: Stanley, Edward L.
name: Bloch, Jonathan I.
name: Blackburn, David C.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Amphibia
Anura
Eleutherodactylidae
Eleutherodactylus

description: Eleutherodactylus Duméril and Bibron, 1841
Material: We refer to Eleutherodactylus 177 fossils from the Brooksville 2 and Live Oak (SB-1A) localities: 124 ilia, 37 humeri, three radioulnae, 12 sacra, and one urostyle (Figs 2, 3; Supporting Information, Table S3). Most of the fossils are from Brooksville 2 (174) where Eleutherodactylus is the dominant anuran taxon. Only three ilia attributed to Eleutherodactylus have been recovered from Live Oak (SB-1A) where scaphiopodids (spadefoot toads) are the dominant taxon. We note that there are undescribed fossils referable to Hylidae, Ranidae, and Rhinophrynidae in lower abundance at both localities (Fig. 2).
Description
Ilium: The fossil ilia have a wide and rounded acetabulum with an acetabular rim pronounced both ventrally and posterodistally and less pronounced from the middle to the dorsal end. When preserved, the dorsal acetabular expansion is posterodorsally narrow and slightly higher than the dorsal crest (UF-VP-501352; Fig. 2). The angle between the dorsal acetabular expansion and the dorsal prominence is large and greater than a right angle. The dorsal crest of the ilium is weakly to moderately developed and is convergent with the dorsal prominence (UF-VP-501352, UF-VP-494606; Fig. 2). The dorsal protuberance is well developed, and is significantly laterally extended from the dorsal prominence. The ventral acetabular expansion is short and wide with a small and narrow preacetabular region.
Sacrum: The morphology of the sacra, including the centrum, and ventral and dorsal regions, is well preserved (UF-VP-497977; UF-VP-497981; Fig. 2). The sacral transverse processes and the left side of the prezygapophyses are fractured in one specimen (UF-VP-497981). The sacrum of fossil Eleutherodactylus is shaped like an inverted ‘V’ in dorsal view due to the posterior projection of its long, thin, and straight sacral diapophyses that are weakly expanded distally. The centrum is procoelous and bicondylar posteriorly. Dorsally, the neural arch is narrow and less wide that the centrum length. The neural spine is not well developed; it is a small bump with the highest point in the middle of the dorsal arch. There are no crests posterior to the dorsal spine. The prezygapophyses are ovoid, longer than wider, their articular surfaces are oriented dorsomedially, and they are separated from each other by a distance greater than that of the maximum anterior cotyle width. The anterior cotyle is wider than long. The neural canal is also wider than longer, and dorsoventrally compressed. The posterior condyles are ovoid, dorsoventrally compressed, and narrower laterally with a small separation between them (Fig. 2).
Urostyle: The single fossil urostyle (UF-VP-501321; Fig. 2) is well preserved with the most diagnosable part complete. The distal portion of the shaft is broken, and the dorsal crest is incomplete behind the dorsal spine (Fig. 2). The fossil urostyle lacks transverse processes. Anteriorly the dorsal crest is tall and the dorsal tip is wide and blunt. In lateral view, the spine is slightly oriented anteriorly compared to the base of the crest in the urostyle shaft. The dorsal canal is triangular, with straight lateral walls that are slightly longer than the width of the base of the dorsal canal. Just anterior to the base of the dorsal canal, there is a noticeable protuberance that decreases in height posteriorly. The anterior end is bicondylar, with ovoid cotyles that are wider than high and slightly in contact medially (Fig. 2).
Humerus: The fossil humeri are well preserved, with most preserving the distal end and at least one-third of the shaft (UF- VP-501310; UF-VP-501314; Fig. 3). The humeri have a distal condyle with a large rounded humeral head that is the largest relative to the shaft among all extant taxa considered in our study. The radial epicondyle is not developed. The ulnar epicondyle has a flattened medial surface and is well developed, extending to, or beyond, the distal end of the humeral head. Posteriorly, the olecranon scar is centred on the shaft and oriented towards the proximal end. The humerus also lacks medial and lateral crests. The diaphysis of the bone is narrow and long, and has a ventral crest that is preserved in only one specimen (UF-VP-501312; Fig. 3).
Radioulna: The fossil radioulnae are well preserved except for the distal end that is broken (UF-VP-5013124; UF-VP-501323; Fig. 3). The radioulna is thin and long with the narrower portion of the diaphysis nearer to the olecranon than to the middle of the shaft. Laterally the diaphysis is somewhat angular. Considering the preserved portions of the bone, the widths are similar at the proximal and distal ends. The olecranon is wider in the ulnar section than in the radial section. The ventral portion of the olecranon in contact with the ulnar epicondyle of the humerus is not expanded and is slightly flat (Fig. 3).
Comparisons
We refer the fossils from Florida to the genus Eleutherodactylus based on shared morphological characteristics of the skeleton in comparison with other anuran taxa examined. The fossil ilia are assigned to Eleutherodactylus based on the combination of characteristics shared with the ilia of extant Eleutherodactylus (Fig. 4; Supporting Information, Fig. S4), especially a rounded acetabulum with an acetabular cup border that is more developed ventrally than dorsally. The extension and shape of the ventral acetabular expansion is small and short. Fossil and living Eleutherodactylus differ in the extension of the dorsal acetabular expansion in comparison to the dorsal crest. In the living species, Eleutherodactylus is characterized by its rounded acetabulum with a small or short dorsal acetabular expansion. The dorsal acetabular expansion of these ilia either does not surpass the level of the dorsal crest (as in E. planirostris UF-Herp-100175) or slightly extends beyond it (as in E. inoptatus UF-Herp-42264). A dorsal crest is present, but the degree of development varies from slightly (as in E. gryllus UF-Herp-279279) to well developed (as in E. planirostris UF-Herp-100175; Supporting Information, Fig. S4).
The fossil ilia that we refer to Eleutherodactylus are similar in size to those of extant spring peepers (Pseudacris crucifer, P. nigrita) and the eastern narrowmouth toad (Gastrophryne carolinensis; Fig. 4; Supporting Information, Fig. S2). In the fossil ilia (e.g. UF-VP-501355), the angle between the dorsal acetabular expansion and the dorsal prominence is greater than found in Rana clamitans (UF-Herp-76511), in which this angle is smaller and thus the dorsal acetabular expansion is steeper. The fossil ilia of Eleutherodactylus also differ from Rana in having a short dorsal prominence that does not surpass the level of the dorsal acetabular expansion (Fig. 4; Supporting Information, Fig. S2), a dorsal protuberance that is not dorsal, as in Rana, but laterally expanded, and a dorsal crest that is mainly developed beyond the dorsal prominence. In Rana, the crest is continuous with the dorsal prominence, increasing in height as it expands from the prominence. The fossil ilia of Eleutherodactylus differ from those of toads (Bufonidae: Anaxyrus), narrowmouth toads (Microhylidae: Gastrophryne), Mexican burrowing toads (Rhinophrynidae: Rhinophrynus), spadefoot toads (Scaphiopodidae: Scaphiopus), and treefrogs (Hylidae: Hyla and Pseudacris) in having a well-defined dorsal crest. They further differ from other treefrogs (Hylidae: Acris) in having a large, rounded acetabulum with a short preacetabular zone and a narrow ventral acetabular expansion (Fig. 4; Supporting Information, Fig. S2).
The fossil sacra from Florida are morphologically similar to those of living species of Eleutherodactylus. The sacrum of extant Eleutherodactylus (e.g. E. planirostris UF-Herp-100175; Fig. 2; Supporting Information, Fig. S4) has the same inverted V-shape and long narrow sacral diapophyses. Differences between the fossils and extant species are found in the shape of the neural canal, with some species (E. cundalii UF-Herp-3012) having a greater dorsoventral height and others being flatter (E. planirostris UF-Herp-100175). In fossil specimens (UF-VP-497981; UF-VP-497977), the neural arch has a similar height as observed in specimens of E. cundalii (UF-Herp-3012).
The fossil sacrum referred to Eleutherodactylus differs from Gastrophryne (Fig. 4; Supporting Information, Fig. S2) in that the latter has expanded sacral transverse processes that give a bowed shape to the sacrum. The anterior centrum of the sacrum of Gastrophryne is convex, forming a condyle. Rana also has an anterior condyle on the sacrum, as well as a neural arch with a well-developed crest (beginning at the dorsal spine and extending towards the sacral diapophyses) that is not enlarged, and which maintains a similar width from the base towards the distal end. The fossil sacrum differs from that of Anaxyrus and Incilius by lacking wide sacral diapophyses, and having both a neural arch that is wider than the centrum and a sharp dorsal crest that does not extend onto the diapophysis (Fig. 4; Supporting Information, Fig. S2). The prezygapophyses are oval, wider than long, and separated by a distance shorter than the maximum width of the anterior cotyle. Eleutherodactylus differs from hylids in the orientation and shape of the sacral diapophyses (Fig. 4; Supporting Information, Fig. S2). In Hyla, the sacral diapophyses are wide and oriented laterally and not posteriorly. In Acris, these are oriented posterolaterally, whereas in Pseudacris they are oriented posteriorly and the width of the diapophysis almost doubles from its base to distal end. The neural spine and dorsal crest are well developed in Hyla, Acris, and Pseudacris, and extend on to the diaphysis in the latter two. In Acris, there is a small ridge oriented anteroposteriorly that is posterior to the dorsal crest. The prezygapophyses are wider than long in Hyla and Pseudacris (Fig. 4; Supporting Information, Fig. S2), and in Acris are longer than wide and with the articular surface dorsally oriented. In Acris, the posterior condyles are rounded and widely separated.
The urostyle of extant Eleutherodactylus lacks transverse processes and has a tall dorsal crest that decreases in height posteriorly. As in the fossil from Florida (UF-VP-501321; Fig. 2), the dorsal canal in living species is triangular, has an anterior prominence, and the dorsal spine is wide and blunt (Supporting Information, Fig. S4). The fossil urostyle of Eleutherodactylus differs from that of hylids (Acris, Pseudacris, and Hyla) that either lack completely or have a small dorsal spine that projects posteriorly, not anteriorly, and has a smaller and narrower dorsal canal (Fig. 4; Supporting Information, Fig. S2). The urostyle of Gastrophryne also has a greatly reduced dorsal crest and has a small, rounded dorsal canal. The urostyle of Rana has a similarly oriented and tall dorsal spine, but it is projected posteriorly or nearly aligned with the base of the crest. In addition, in Rana the shape of the dorsal canal is also triangular with a wide base, but the lateral walls of the canal are rounded and not straight as in Eleutherodactylus (Fig. 4; Supporting Information, Fig. S2). The urostyle of Anaxyrus is easily distinguished from Eleutherodactylus by having anterior cotyles that are both rounded and completely in contact medially, as well as a small dorsal canal and a dorsal crest that is oriented posteriorly (Fig. 4; Supporting Information, Fig. S2).
The humeri of extant Eleutherodactylus can be diagnosed and differentiated from other taxa based on characteristics of the distal end (Figs 3, 4; Supporting Information, Figs S2, S 3; see also: Blackburn et al. (2020). Variation between extant species is found in the extension of the ventral crest in the diaphysis of the bone. This ventral crest can extend from half to one-third of the shaft length (Fig. 3; Supporting Information, Fig. S4). The humerus of Eleutherodactylus can be differentiated from that of small individuals of Rana because the shape of the humeral head is longer than wide in Rana, and the olecranon scar is oriented towards the radial epicondyle (Fig. 4; Supporting Information, Fig. S2). Eleutherodactylus can be differentiated from Gastrophryne (another taxon with small body size) because in the latter the shape of the distal condyle is wider than long, the ulnar epicondyle is wide, the olecranon scar is short and does not reach the ulnar epicondyle, and the diaphysis is wider relative to the distal condyle (Fig. 4; Supporting Information, Fig. S2). In small hylids (Acris, Pseudacris, and Hyla), the humeral head is relatively smaller and there are often medial or dorsal crests on the diaphysis (Fig. 4; Supporting Information, Fig. S2).
In extant Eleutherodactylus, the radioulna is long and thin with similar distal and proximal widths (Fig. 4; Supporting Information, Fig. S4). This is a feature seen in the fossil Eleutherodactylus but different from all other taxa that we considered here that have an expanded distal end or have a proximal end slightly wider than the distal end (Rhinophrynus) (Figs 3, 4; Supporting Information, Figs S2, S 3). Another characteristic that differentiates the radioulnae of fossil and extant Eleutherodactylus from other taxa is the lack of a widely expanded and flat surface for the articulation with the ulnar epicondyle of the humerus. This expanded surface can vary in shape across other taxa but is evident in Anaxyrus, Hyla, Pseudacris, Acris, Rana, and Gastrophryne. (Fig. 4; Supporting Information, Fig. S2).
Estimating body size of fossils
We used 3D meshes of individual bones from extant Eleutherodactylus (multiple species and several individuals of different ontogenetic stages of two species) to make 10 linear measurements that we then used to estimate the body size of the fossils (Fig. 5; Supporting Information, Figs S3–S 7). Based on the equations from our OLS regression analyses, the fossil specimens of Eleutherodactylus from the Oligocene of Florida range in SUL from 16.8–29.8 mm (Table 1). This is similar in size to the living greenhouse frog Eleutherodactylus planirostris (maximum female SVL 36 mm; size range include immature individuals, 12–32 mm; Schwartz and Henderson 1991, Krysko et al. 2019). Our regressions reveal strong significant relationships between each measurement and SUL, with coefficients of determination (R 2) of 0.803 or higher (Table 1). This indicates that these measurements are generally strong predictors of body size in Eleutherodactylus (Supporting Information, Fig. S7). Our results demonstrate that the best measurement to estimate body size, in both the interspecific and intraspecific datasets, is the pre-acetabular ilium width (Fig. 5A, B), though other measurements have similar R 2 values. The measurements with the lowest R 2 values are the length of the sacral centrum (0.838) for the interspecific dataset, and the width of the sacral anterior condyle (0.803) for the intraspecific dataset (Table 1; Supporting Information, Fig. S7).
We calculated the coefficient of variation (CV) of all measurements to determine which measurements or groups of individuals had the most variation. As expected from the R 2 values of the regressions, the measurements with the greatest coefficients of variation (Supporting Information, Table S5) are the width of the sacral centrum and width of the sacral anterior cotyle, for the interspecific and the intraspecific datasets, respectively. Based on the CVs, there is more variation in the interspecific dataset than in the intraspecific dataset. In the interspecific comparisons, there is more variation for each measurement among immature individuals as a group in comparison to mature individuals. In contrast, in the intraspecific comparisons, there is more variation among mature individuals. In general, E. glandulifer exhibits more variation than E. planirostris, and for the latter species only mature individuals were incorporated into the regression and geometric morphometric analyses.
Three-dimensional geometric morphometrics of the humerus
We performed a geometric morphometric analysis on the dataset that included the ontogenetic series of two species of Eleutherodactylus. The principal component (PC) analysis shows two groups in morphospace. The first includes only specimens of E. glandulifer and the other includes medium and large specimens of E. glandulifer and all individuals of E. planirostris (Fig. 5C; Supporting Information, Fig. S8). The variation represented by the two first PC axes is 47.8% and 10.7% for PC1 and PC2, respectively (Fig. 5C). This variation is driven by the distal condyle shape and the extension of the ulnar epicondyle. Juvenile and immature individuals form a group in morphospace and these have an ovoid condyle that lacks a developed ulnar epicondyle. The other group is represented by individuals with a rounded condyle and well-developed ulnar epicondyle, and these are all mature individuals with a completely ossified distal condyle (Supporting Information, Fig. S8). A non-parametric Procrustes’ ANOVA (Supporting Information, Table S6) indicates that the differences between mature and immature individuals is significant (P -value 0.001), as are the differences between the two species (P -value 0.002). When the Procrustes ANOVA is performed with only mature individuals, the difference between the two species is not significant (P -value 0.304; Supporting Information, Table S6; Fig. S8). When the fossils are included in the analysis, the difference between mature and immature individuals is significant (P -value 0.001) and the fossils fall in a group with the mature individuals (Fig. 5E). When immature specimens are removed from the analysis (Supporting Information, Fig. S8), there are no distinct groups among the mature individuals and the fossils are only weakly separated from the extant taxa.
The analysis of the interspecific dataset including 27 extant species of Eleutherodactylus shows two distinctive groups in morphospace, corresponding to immature individuals in one group and mature individuals in the other. Most variation is captured along PC1 (35.6%) and PC2 (20.4%) (Fig. 5D) and reflects the shape of the distal condyle, which is not completely ossified in immature individuals. A non-parametric Procrustes’ ANOVA (Supporting Information, Table S6) indicates that the difference between the mature and immature specimens is significant (P -value 0.001; Supporting Information, Table S6), whereas the difference between subgenera is not (P -value 0.113; Supporting Information, Table S6). The eight fossil specimens incorporated into the analysis share a similar shape and exhibit characteristics of mature individuals, regardless of their small size (Fig. 5F). In the PC analyses combining fossil and extant specimens, the variation explained by PC1 and PC2 is somewhat less than in the analysis of extant species alone (PC1, 33.3%; PC2, 18.1%), and the differences between the mature and immature individuals remains significant (P -value 0.001). However, when fossils are included in the analysis, the differences between subgenera also are significant (P -value 0.021), though this may be due to treating the fossils as a distinct additional group. A further analysis of only mature individuals does not reveal any clear groups in morphospace (Supporting Information, Fig. S8). All fossils from Florida are clustered together and there is not a significant difference between the subgenera (P -value 0.054; Supporting Information, Table S6).
description: Published as part of Vallejo-Pareja, Maria Camila, Stanley, Edward L., Bloch, Jonathan I. & Blackburn, David C., 2024, Fossil frogs (Eleutherodactylidae: Eleutherodactylus) from Florida suggest overwater dispersal from the Caribbean by the Late Oligocene, pp. 431-446 in Zoological Journal of the Linnean Society 201 (2) on pages 437-441, DOI: 10.1093/zoolinnean/zlad130, http://zenodo.org/record/13219918