Redescription of the Middle Eocene frog ...

Michael Wuttke

Redescription of the Middle Eocene frog Lutetiobatrachus gracilis WUTTKE in SANCHIZ, 1998 (Lower Geiseltalian, »Grube Messel«, near Darmstadt, southern Hesse, Germany) Author’s Address: Dr. Michael Wuttke, Generaldirektion Kulturelles Erbe RLP, Direktion Landesarchäologie, Referat Erdgeschichte, Große Langgasse 29, D-55116 Mainz, [email protected]

Abstract An isolated find from the Middle Eocene of »Grube Messel«, near Darmstadt, here is extensively described after a first nomenclatural relevant description by Wuttke in Sanchiz (1998). Because of the poor state of preservation, this species is an incertae sedis anuran. The find comes from the Tetraedron-facies of the Messel oil-shale. The species was probably semiterrestrial.

Kurzfassung

29 kaupia | Darmstädter Beiträge zur Naturgeschichte | Heft 18 | 29–41 | Darmstadt, 18. Dezember 2012 |

Aus dem Mittel-Eozän der Grube Messel bei Darmstadt wird anhand eines Einzelfundes die von Wuttke (in Sanchiz 1998) definierte Anurengattung und –art Lutetiobtrachus tobieni ausführlich beschrieben, deren Familienzugehörigkeit aufgrund mangelnder Erhaltung offen bleiben muss. Der Fund stammt aus der Tetraedron Fazies des Messeler Ölschiefers, die Art dürfte eine semiterrestrische Lebensweise gehabt haben.

Introduction

Materials and methods

From the black pelite of the Messel Formation (Weber & Hofmann 1982), anurans were early described (Weitzel 1938) that have now been assigned to the Palaeobatrachidae and Pelobatidae families (Wuttke 1988 a+b, 1996, 2012, this issue; Wuttke et al. 2012). The view of the origin of the former Messel Lake has changed radically in recent years, especially by the investigations of Pirrung et al. (2001), Felder & Harms (2004), Mertz & Renne (2005), and Micklich (2002, 2012). The specimen described here is so far, after some fourty years of intensive fossil excavations, the only one of its kind. It comes from the Tetraedron facies (sensu Goth 1990; formerly facies type 3, sensu Franzen et al. 1982), which was formed by the massive development of the alga Tetraedron and the simultaneous reduction of the clayey background sedimentation (Goth, 1990, Clausing 2001). The Tetraedron facies has yielded a number of other singular finds, though exclusively aquatic vertebrates, including the only tadpoles of Palaeobatrachus tobieni (emend. Wuttke et al. 2012), another, undescribed palaeobatrachid species (Wuttke & Schaal, in prep.), the eel Anguilla ignota (Micklich 1983), and the ?terrestrial salamander Chelotriton robustus (Westphal 1980). The causes of the reduction in the background sedimentation in the Tetraedron facies, a general sedimentation that may have lasted for about 640.000 years (Lenz et al. 2011), have yet to be determined; climatic factors possibly played of role.

Available for study was a single find from the collections of the Forschungsinstitut Senckenberg, SMF 476, Frankfurt am Main (Germany). All the bones of the ventral side are missing, therefore, in the author’s opinion, there must have been a counter slab, but it seems to be lost. Abbreviations of the measurements used, arranged by morphological units are: Body lengths: Head/torso length (HL); Skull: Medial skull length (MSL); Lateral skull length (LSL); Greatest skull width (SW); Skull width measured over the premaxillae (SWP); Length of squamosum (LS) Total length of rami of squamosum (LRS); Length of ramus zygomaticus (RZ); Length of ramus oticus (RO); Vertebral column: Length of vertebral column, incl. urostyl (VCL); Width of transverse processes of presacral vertebrae II–VIII (PW 2–8); Width of sacral diapophyses (SDW); Distal length of left transverse process of presacral vertebra III ((PDL 3); Proximal length of left transverse process of presacral vertebra III (PPL 3); Urostyl length (UL); Anterior angle of transverse processes of presacral vertebrae II–VIII (PAA 2–8); Anterior angle of right/left/ sacral diapophysis (SDAAR/SDAAL); Posterior angle of right/left sacral diapophysis (SDPAR/SDPAL); Angle between anterior and posterior border of right/left sacral diapophysis (SDAR/SDAL); Pectoral girdle: Greatest length of right and left clavicula (CLR 1/ CLL 1); Greatest width of right and left clavicula (CWR 2 / CWL2); Greatest distal length of right coracoid (CLR1); Greatest distal width of right and left coracoid (CDWR 2 / CDWL2; Greatest medial width of right and left coracoid (CMWR 3/CMWL 3); Greatest length of right and left scapula (SLR 1/SLL 1); Greatest distal width of right and left scapula (SDWR 2 / SDWL 2); Greatest medial width of left scapula (SMWL 3); Pelvis: 1.Total length of pelvis (PL); Ilium length (IL); Acetabulum height (AH); Interilial width (IIW); Forelimbs: Humerus length (HL); Antebrachium length (AL); Length of 3rd metacarpale (MCL 3); Hind limbs: Femur length (FL); Crus length (CL); Calcaneus length (CCL); Length of 4th metatarsale (MTL 4).

The genus Lutetiobatrachus is monotypic and comprises the species Lutetiobatrachus gracilis. Its nomenclatural history is a little bit confusing. The taxon was extensively described by Wuttke (1988 a: 184–203) in thesis format, and mentioned again by Wuttke (1988 b, 1996). These papers did not fulfil the criteria of an original nomenclatural work, as either the description, in case of the thesis, was not published, or in the other cases no diagnostic characters were provided. Therefore the taxon name was considered a nomen nudum by Morlo et al. (2004). In fact, the name Lutetiobatrachus gracilis became nomenclaturally available through a review monograph on fossil anurans published by Sanchiz (1998). This work provided the full name, a descriptive diagnosis and holotype reference for this fossil. Herein, Sanchiz (1998: 97) did explicitly credit Wuttke as the author of the taxon name by combining the species name with Wuttke’s name as author for taxonomic reference, and by referring to the unpublished work of Wuttke (1988 a) for diagnostic characters. Consequently, the proper name and authorship for this monotypic genus and single species is Lutetiobatrachus Wuttke in Sanchiz, 1998. (see also Martin et al. 2012). This species is an incertae sedis anuran from the Middle Eocene of Messel. However, given that the information connected with this taxon is scattered among various publications, I here provide a first complete description, summarizing the available data.

Systematics

Description

Class: Amphibia Linné, 1758; Subclass: Lissamphibia

Body measurements/Proportions [in cm]: Body length: 2.92; Skull: MSL 1.13; SW 1.25; SWP 0.37; LS 0.35; RO 0.05; Vertebral column: VCL 1.60; PW20.63; PW30.7; PW 60.33; PW70.33; PW 80.3; SDW 0.36; UL 0.53; PAA 640°; PAA7 33°; PAA8 25°; SDAAR 23°; SDPAR 43°; SDAR1 20°; Pelvis: IL 1.24; IIB0.54; Forelimbs: HL 0.96; AL 0.56; Hind limbs: FL 1.2 6; CL at least 1.44.

Order: Salienta Laurenti, 1768 Suborder: Archaeobatrachia Reig, 1958 Family: incertae sedis Genus: Lutetiobatrachus Wuttke in Sanchiz, 1998 Species: Lutetiobatrachus gracilis Wuttke in Sanchiz, 1998 Lutetiobatrachus Wuttke in Sanchiz, 1998

Type species: Lutetiobatrachus gracilis Wuttke in Sanchiz, 1998

Derivatio nominis: from Lutetian, the stratigraphic designation for the marine Middle Eocene, and βℵ⎮∫〈⎠⎪⎟ (Greek) = ›frog‹ Diagnosis: Frontoparietale long, not sculptured, broader rostrally than caudally; a sutura medialis extends to the level of the posterior orbital rim; the frontoparietale is fused caudally. Margo posterior straight; temporal ridges extend lateroventrally from its posteriolateral edges. Premaxilla and maxilla dentated; maxilla with a small processus posterior maxillae and a long processus quadratojugalis. Large, smooth triangular nasalia, which contact each other medially. Quadratojugale fully developed. Vertebral column with eight presacral imbricate vertebrae; transversal processes of the fifth vertebra shortened and extended laterally, and those of vertebrae six to eight long and strongly oriented anteriorly. Sacral vertebrae with large, wing-shaped (broadly dilated) diapophyses. Coccyx broad and long (reaching the symphysis of the pelvis) with (?)remains of the 10th and 11th vertebrae. Ilia strongly bowed, not fused with the ischium. Femur shorter than the crus. Lutetiobatrachus gracilis Wuttke in Sanchiz, 1998 Plate 1, Figs. 1 + 2; Plate 2, Figs. 1 + 2; Figs. 1–8 Derivatio nominis: gracilis (Lat.) = ›slender, delicate‹ Holotype: SMF-Me 476, incomplete skeleton of an adult animal in the collection of the Forschungsinstitut Senckenberg, Frankfurt am Main, Germany. Plate 1, Figs. 1 + 2; Plate 2, Figs. 1 + 2; and Figs. 1–8. The skeleton is visible dorsally; the ventral impression of the skeleton was lost during recovery and/or preparation. Locus typicus: »Grube Messel« (Messel Pit Fossil Site) near Darmstadt, southern Hesse, Germany. Stratum typicum: Lower Geiseltalian (Franzen & Haubold 1986), Oil-Shale Formation (sensu Weber & Hofmann 1982) of the Oil-Shale Messel Pit, near Darmstadt, Hesse, Germany. Diagnosis: Same as the genus diagnosis.

Skull The compact skull is only slightly broader than long; its elements are strongly ossified. The nasal capsule is completely covered by the nasalia, which contact each other medially. The skull is reinforced on the margins by the complete maxillary arch (maxillae, quadratojugalia), as is characteristic of members of primitive anuran families. The pars dentalis of the maxilla is significantly higher anteriorly than that of the premaxilla. The otoccipitale is plainly covered by the frontoparietale; the temporal processes of the frontoparietale are not developed. Frontoparietale (Fig. 1) The frontoparietale is longer than broad; its lateral sides broaden caudally, attaining their greatest width at the prooticum (lateral processes sensu Spinar 1972). From there, they probably narrow quickly (the entire temporal region is strongly deformed and shattered, destroyed?) to merge with the straightextending margo posterior frontoparietalis [posterior margin] at the caudal margin. Narrow ridges extend lateroventrally from the posterior lateral edges. The frontoparietale diverges in a slight V-shape anteriorly. From the crest of the emargination, a longitudinal suture (sutura medialis) extends caudally about twothirds of the total length of the frontoparietale. Only the right side of the anterior surface of the frontoparietale is preserved. On this surface is a series of fine, orocaudally oriented grooves, which are probably the impressions of former blood vessels. The caudal regions are smooth. Nasale (Fig. 1) In specimen the nasalia are very likely triangular; their exact form is not reconstructable, as their medioanterior parts are only incompletely preserved. Their facies externa is completely smooth. The nasalia very likely contact each other along their medial margins. The anterior edge of the nasalia is not entirely clear; it presumably extends in a short curve to the maxilla. Each nasale extends from its anteriolateral point of articulation caudally, in constant contact with the maxilla, up to the processus nasalis maxillae, that is, to the anteriolateral end of the orbit. Their more curved caudal rims form the anterior limit of the orbits.

31 Michael Wuttke | Redescription of the Middle Eocene frog Lutetiobatrachus gracilis WUTTKE in SANCHIZ, 1998 |

Haeckel, 1866

Fig. 1: Lutetiobatrachus gracilis. Skull in dorsal view. Holotype, SMF-Me 476. Scale bar = 1 mm. 1 = left premaxilla, pars dentalis; 2 = maxilla; 3 = palatinum; 4 = left mandibula; 5 = ramus lateralis squamosi; 6 = margo scapularis of the cleithrum; 7 = ramus oticus squamosi; 8 = paired processes, suspected; 9 = right temporal ridge of the frontoparietale; 10 = quadratum; 11 = quadratojugale; 12 = processus quadratojugalis maxillae; 13 = suspected border of the proc. posterior maxillae; 14 = medial suture of the frontoparietale; 15 = frontoparietale; 16 = proc. nasalis maxillae; 17 = nasalia. Dashed line = suspected element borders.

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2 17

3 16

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14 13

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Premaxilla (Fig. 1) Only the external sides of the premaxillae are visible. The pars dentalis, possesses (probably) 12 densely packed teeth of the same length (externally measured length = 0.25 mm). It reaches its greatest height in the region of the nasal process, and then quickly tapers laterally. A palatine process (processus palatinalis) is only very weakly developed, if at all. A nasal process (sensu Spinar 1972) ca. 1.5 mm long arises dorsocaudally from the pars dentalis. The process of the right premaxilla (which appears to be less deformed) has a rounded cross-section narrowing caudally; it is slightly curved laterocaudally. Maxillare (Fig. 1) The maxillaria are robust, each nearly reaching posteriorly the caudal end of the skull. The dorsal side is not sculptured. From the reconstruction, the pars dentalis possesses 47 curved, densely packed, similarly shaped teeth about 0.5 mm in length. From the pars facialis maxillae arises preorbitally a short nasal process, whose exact form cannot be reconstructed. The pars facialis extends further caudally at a constant width; at the point of articulation of the quadratojugal process, it probably (it is deformed by the mandibles underneath) merges with a short processus maxillaris posterior (»caudal projection« sensu Spinar 1972: 200). A relatively smooth, stretched-out quadratojugal process arises posteroventrally from the pars dentalis.

Quadratojugale (Fig. 1) The quadratojugale is awl-shaped; its posterior, spherically thickened, but caudally flattened end borders freely on the quadratum. Anteriorly it is broad; its pointed anterior section to a great extent lies behind much of the labial side of the processus quadratojugalis maxillae. Vomer The vomera were lost entirely during recovery and/or preparation, such that even in X-ray images they are not recognizable. But as evidenced by the particular bulging in the nasalia, it is likely that they were toothed. In the compaction of the skeleton, their teeth sockets were compressed dorsally through the overlying bone. Palatinum (Fig. 1) At the anterior rim of the orbit there are two lateromedially extending structures, which are interpreted as being the remains of the palatinum. These dorsally flattened and smooth elements begin relatively narrow directly underneath the processus nasalis maxillae but then gradually broaden medially. Their exact form is not reconstructable. Pterygoid (Figs 1, 2) The form of the A-shaped pterygoidia is only partly reconstructable from direct observation and through X-ray imaging, as they are partially covered by the rami of the squamosa and were partly destroyed during recovery. The following description, especially for the posterior ramus, is therefore based on analogue structures in living species. The maxillary ramus is slim and rounded, and it articulates with the pars dentalis of the maxilla about in

1 2

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Fig. 2: Lutetiobatrachus gracilis. Pterygoid. Holotype, SMF-Me 476. Scale bar = 1 mm. 1 = ramus maxillaris; 2 = ramus posterior; 3 = ramus medialis. Dashed line = suspected element borders. Fig. 3: Lutetiobatrachus gracilis. Left squamosum from laterodorsal. Holotype, SMF-Me 476. Scale bar = 1 mm. 1 = ramus lateralis; 2 = ramus zygomaticus; 3 = ramus oticus; 4 = dorsal expansion of ramus oticus.

1 3 2

Quadratum (Fig. 1) The quadratum is a small rounded bone that appears to be lightly flattened rostrally. The posterior process of the pterygoid, the lateral process of the squamosum, and the caudal end of the quadratojugale meet at the quadratum. Squamosum (Fig. 3) The paired squamosa are only incompletely preserved. From a lateral perspective, they have a T-shape. The ramus zygomaticus and ramus oticus exhibit a weak sculpturing dorsolaterally; the ramus lateralis is smooth. The ramus zygomaticus begins broadly at the ramus lateralis and extends rostrally in a constant width. Its anterior border is not preserved. The otic ramus also begins broad, but then narrows quickly (from a strictly lateral perspective); it caudal margin is hemispherical. From dorsolateral (Fig. 2), the otic ramus is broad (because of compaction, its medial borders are not recognizable) before it merges with the narrow, keel-shaped ramus zygomaticus. The ramus oticus is similar to that of Eopelobates wagneri (Wuttke 2012, this issue), which is connected to an »otic plate« (sensu Lynch 1971: 47). Because of the state of preservation, such a plate cannot be ruled out in Lutetiobatrachus. In contrast to both of the rami described above, the ramus lateralis squamosi has a more triangular crosssection; its starts broad at the dorsal ramus and then narrows quickly to ultimately approach, now at constant thickness, the again broadening ventral articulation base. Its terminal end is free: it is not fused with the quadratum or the quadratojugale.

Otoccipitale The otoccipitale is completely broken and deformed, so little can be said about its form. Its anteroposterior shape likely was long medially while quickly becoming shortened laterally. It probably nearly reached the quadratum. Vertebral column The vertebral column consists of eight imbricate presacral vertebrae and a wing-shaped, broadened sacral vertebra. The vertebral column is incompletely preserved: during recovery and preparation some centra were lost, such that even in X-ray imaging the vertebral type is not recognizable; and the neural regions have been strongly deformed by compaction. Atlas Only barely identifiable remains exist of the atlas. Vertebrae two and three The second and third vertebrae possess long transverse processes that are slightly broadened at their lateral ends. The transverse processes of V2, somewhat shorter than those of V3, are slightly curved anteriorly, while those of V3 curve laterally. Their surface is smooth. The spinous processes and zygapophyses of each are only slightly prominent. A medial neural ridge is lacking in these (and all other) vertebrae. Vertebra four The relatively broad transverse processes of V 4 are slightly curved anteriorly and are somewhat shorter than those of V 3. Vertebra five The transverse processes of V 5 are shortened and curved laterally, and do not extend over those of V 6– V8.


the middle of the orbit. It is weakly curved. The posterior ramus, somewhat thicker than the anterior ramus, branches off from this with a kink. The posterior ramus of the right pterygoid extends so far that it descends under the right mandible. Because in extant taxa the posterior ramus articulates in the region of the quadratum, it must here likewise be quite long and weakly curved (Fig. 2). Of the medial ramus, only the thin, rounded terminal part of the right pterygoid has been preserved. It articulates with the prooticum anteromedially (Fig. 1)

Fig. 4: Lutetiobatrachus gracilis. Vertebral column. Holotype, SMF-Me 476. Scale bar = 1 mm. 1 = atlas; 2 = right transverse process of V2; 3 = right transverse process of V3; 4 = right transverse process of V4; 5 = right transverse process of V5, reduced; 6 = right transverse process of V6; 7 = right transverse process of V7; 8 = right transverse process of V8; 9 = right sacral diapophysis; 10 = possible V10; 11 = possible V11; 12 = coccyx. Dotted line = suspected internal structures; dashed line = suspected element borders.

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Fig. 5: Lutetiobatrachus gracilis. Left cleithrum. Holotype, SMFMe 476. Scale bar = 1 mm. 1 = ramus cranialis; 2 = margo scapularis; 3 = ramus caudalis.

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Fig. 6: Lutetiobatrachus gracilis. Pelvis. Holotype, SMF-Me 476. Scale bar = 1 mm. Number key: 1 = left ilium; 2 = acetabular zone from within.

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Vertebrae six to eight V6, V7, and V8 have strongly anteriorly curved and relatively long and thin transverse processes.

Pectoral Girdle Of the pectoral girdle, only the cleithra are preserved, and these in a very poor condition.

Sacral Vertebra The sacral diapophyses are broadly wing-shaped; their anterior extent reaches the base of the transverse processes of V8. Their anterior and posterior regions of equally strongly developed.

Cleithrum (Fig. 5) Only the dorsal sides of the cleithra are visible. Only parts of the corpus, the cranial and caudal rami, and the margo scapularis can be recognized. The scapular margin is clearly concave. A central bulge along the slightly curved cranial margin (margo cranialis) indicates that there was a spina acromoidea on the internal side, which was impressed during compaction. The caudal margin is clearly concave. The extent of the cranial and caudal rami is not reconstructable.

Coccyx (Fig. 4) The coccyx is very deformed and shattered. It is connected broadly onto the sacral vertebra and narrows only gradually caudally. Its end, still relatively broad, certainly covered parts of the symphysis when the frog was alive. Whether there was a joint between the coccyx and the sacral vertebra or whether these two were fused cannot be determined by X-ray imaging. In its proximal region there are a number of strongly broken and deformed structures, which are most probably incompletely fused postsacral vertebrae. Two laterosinistrally and laterodextrally projecting rounded structures are recognizable, which through X-ray imaging can be considered the postzygapophyses of an 11th vertebra. The somewhat further caudally situated right-sided thickening of the coccyx could indicate this as well. This is not conclusive, however.

Pelvic girdle Ilium (Fig. 6) Only the medial sides of the two ilia are available for reconstruction, which is also made difficult by the incomplete preservation and the strong compaction. The strongly curved shaft of the ilium extends anteriorly somewhat over the pars rostralis of the sacral wing. Both, the pars ascendens and (in fragments) the pars descendens, are preserved in the acetabular zone of the left ilium. The pars descendens is relatively broad and short; the pars ascendens, in contrast, is somewhat longer, and ends relatively pointed. In the dorsal preacetabular zone (sensu Trueb 1977: 172) of the left ilium is a thickening that cannot, however, be attributed to a tuber superius sensu stric-

Fig. 7: Lutetiobatrachus gracilis. Holotype, SMF-Me 476. Arm. Scale bar = 1 mm. 1 = humerus; 2 = antebrachium; 3 = metacarpal II; 4 = metacarpal III; 5 = metacarpal IV; 6 = metacarpal V. Dashed line = suspected element borders. 1 4 5

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Ischium The ischium is not preserved.

Extremities Forelimbs Humerus (Fig. 7) Both humeri are visible from ventrolateral. The left humerus is the better preserved, so the following description is primarily based on it. The proximal epiphysis is broad and slightly flattened on top. The humerus shaft gradually narrows distally, reaching its narrowest about half way. Neither a crista ventralis nor a crista lateralis is present. The distal epiphysis has about the same dimensions as the proximal. The eminentia capitata, which is not very strongly developed, is broken; it is still in place in the articular cavity of the antebrachium. The rest of the pieces of the distal epiphysis are so strongly deformed that nothing can be said about the degree of development of a fossa cubiti ventralis. Antebrachium (Fig. 7) The antebrachium, formed from the fusion of the radius and ulna, still shows in front a definite sulcus intermedius, evidence of their formerly distinct ontogenesis. Both bones are equally robust. The length of the antebrachium is about 4/5 that of the humerus. The collum is narrow at its proximal end, broadening gradually towards its anterior. The olecranon and the radial process have nearly the same posterior dimensions; they are not especially prominent.

Carpus (Fig. 7) About the carpals cannot be told something, as what remains is merely a dark, more or less formless mass. Metacarpus (Fig. 7) Four metacarpalia have been preserved in an ossified state: metacarpalia II–V of the left hand and metacarpalia II and III of the right one. Based on the length relationship of the antebrachium to metacarpale III, the metacarpalia are not as much developed in length as in Palaeobatrachus tobieni (Wuttke et al. 2012). Their proximal and distal epiphyses are slightly broadened; the narrowest point of each is about mid-length (for precise measurements, see Tab. 1) Phalangia (Fig. 7) Only the phalangia of the fifth ray of the left hand and the first and second rays of the right hand are preserved. The first and middle phalangia do not possess any special characteristics. The terminal phalangia are slightly broadened laterally.


to (it is possible that this is a diagenetic phenomenon, that is, particular parts have not been so strongly affected by compaction). A crista dorsalis is not present.

Fig. 8: Overall reconstruction of Lutetiobatrachus gracilis.

spawning, in any case during the time period of the deposition of the Tetraedron facies (sensu Goth 1990).

Discussion

Hind Limbs Femur (Fig. 8) Only the proximal and medial parts of the femora are preserved in an ossified state; the distal end of the right femur is indicated merely by an impression. They appear to be at most very slightly S-shaped. Crus (Fig. 8) Only the anterior and medial parts of the right crus are preserved; both epiphyses are missing. The crus was probably perfectly straight. As far as can be reconstructed from original bony material and impressions, the cruri were longer than the femora (at least 1.9: 1.3 mm). Soft-part preservation In L. gracilis, there are flattened, slightly oval black shapes in the orbits (»eye pigments« sensu Spinar 1972: 96). For the interpretation of their genesis, see Wuttke (1983) and Liebig (1998) as fossilized bacteria’s and the revised and well founded interpretation by, e.g. Vinther (2009) as melanosomes.

Body form and lifestyle The incomplete preservation of the pectoral girdle and hind limbs makes a reconstruction of the lifestyle of L. gracilis quite difficult. However, a fully aquatic lifestyle can be ruled out by the complete maxillary arch, the greater length of the crus, and the incompletely fused frontoparietal, as well as the lack of expansion of the otic capsule. Evidence against a purely terrestrial lifestyle is the weakly developed spinous processes of the vertebral column – even though in small terrestrial species these are naturally less developed. Overall, L. gracilis was likely a semiterrestrial species that dwelled near the lake during

This specimen, the only one of Lutetiobatrachus gracilis found thus far, is visible in dorsal view. During recovery and/or preparation, nearly all of the ventral parts of the skull, all the vertebral centra, the ventral parts of the pectoral girdle, and parts of the extremities were lost. Moreover, the remaining parts of the skeleton have been somewhat affected by sediment compaction and diagenesis, such that particular important characteristics are not recognizable with the necessary certainty. In spite of the comprehensible characters it merely can be said that the plesiomorphies speak against an assignment into the more strongly apomorphic bufonid, ranid, or hylid families. In the skull region, this is seen in the complete maxillary arch (maxillae with posterior and quadratojugal processes, and a non-reduced quadratojugale), the simple, not differentiated triradiate pterygoid, and the not further differentiated squamosum. These traits can be seen as evidence for coming from one of the more archaic anuran families. This holds true as well for the frontoparietale, whose suture does not reach the caudal rim. Not evitably, however, is that this is primarily a frontoparietale with a retained azygous ossification center that is still clearly recognizable in the embryo. A posterior fusion of a primary paired frontoparietale cannot be ruled out. As for the post-cranial skeleton, the strongly broadened (expanded) sacral diapophyses, the relatively short posterior transverse processes that are strongly oriented anteriorly, and the coccyx with its remains of (?)transverse processes also support this possibility. Further, what is unusual is the strong lateral form of the transverse processes of the anterior vertebrae II– IV, which is found particularly in groups whose ribs are fused with the transverse processes. Such a fusion is found in the discoglossids (e.g., Bombina, Lynch 1973: 168) pipids (Trueb 1973) and palaeobatrachids. It should be emphasized, however, that the evidence for such processes in Lutetiobatrachus is found neither by direct observation nor through X-ray imaging. Clarke (by letter) in his investigation of various species of extant discoglossids found some species in which there is a complete fusion of one rib pair, and one species with two fused rib pairs with the third pair »fused onto their transverse processes.« Comparative studies using X-ray imaging have shown that in various specimens of Bombina the fusion of particular rib pairs occurs to various degrees of completeness. In incomplete fusion, images reveal a fine suture (an ankylosis seam or juncture), which in complete fusion no longer exists. There is recognizable, however, a thickening of the area of the process at the place of contact, a characteristic lacking in Lutetiobatrachus (neither are such thickenings recognizable in the pipids). Neither fossil nor extant discoglossids have thus far been found that have a complete, unrecognizable fusion of all pairs of ribs (all fossil species found thus far have three free rib pairs). This seems as an evidence against an assignment of Lutetiobatrachus to

Evidence against assigning to the discoglossids: a) The formation of the frontoparietal: all fossil and living discoglossids known to me have a paired frontoparietale (with the exception of the Latonia, a terrestrial group placed by Spinar (1976) in its own family – in any case in which the primarily paired frontoparietal is fused secondarily. b) The form of the ilium. According to Estes & Sanchiz (1982: 11), »the presence in the iliumia of a long ischiatic process of the supra-acetabular expansion« is characteristic of all discoglossids, a trait that is found as well in the fossil forms Paradiscoglossus americanus (Estes & Sanchiz 1982: figs. 1 + 2), Latonia seyfriedii (Meyer 1845: pl. 4), Opistocoelellus hessi (Spinar 1976: 59, fig. 3), Discoglossus giganteus (Wettstein-Westersheimb 1955: pl. 1).

In spite of the poor state of preservation of the ilia, the existence of such a processus ischiaticus in Lutetiobatrachus can be ruled out. The significance of particular characteristics of Lutetiobatrachus (a posteriorly fused frontoparietale, no free ribs, no supra-acetabular expansion) clearly points against a classification into Discoglossidae. At most, this could be a representative of an earlier branching from the stem group of the discoglossids, having modified these three plesiomorphic characters of that family. With Discoglossidae being ruled out, the only possible candidate family of anurans known in Europe thus far is Pelobatidae. The oldest representative thus far of the pelobatids in Europe is Eopelobates wagneri from the Middle Eocene of Messel (for the problematics of Eopelobates systematics see Wuttke 2012, this issue) and a Pelobates-like, yet to be described form from the Upper Eocene of Belgium (Rocek in Böhme et al. 1984). In view of the combination of characteristics of Eopelobates, this specimen can be in any case eliminated from such a classification. Based on the criteria provided by Rocek (1981, 1988), the Pelobates line of the Pelobatidae originated at a stem species with an azygous third frontoparietal element (see above). This characteristic might possibly apply to Lutetiobatrachus. Also, the other trait combinations of vertebral column, cleithrum, pelvis, and skull are not contrary to its assignment into the Pelobatidae. Though the Pelobatidae-typical sculpturing of the maxilla, squamosal, and frontoparietal is lacking, this could be a case of apomorphic traits that are structurally related to a terrestrial lifestyle. The squamosum can be used only conditionally for a systematic diagnosis of Lutetiobatrachus, because the evidence of its existence as well as a proof for the lack of an »otic plate« cannot be presented. The development of these traits was likely functionally the result of a change in diet of the phylogenetic predecessors, which required a structural improvement of the jawarticulation complex. This additional support of the squamosum resulted in an added abutment for the control of the lower-jaw joints, which at the same

time made possible the development of a more powerful »chewing« musculature. Without a clarification of this question, a classification into the Pelobates stem-line is thus not possible; too little is known about the phylogenetic development of the pelobatid squamosum. In an overall evaluation, the characteristics of Lutetiobatrachus are not sufficient for allocating this Messel species to the Pelobatidae. Lutetiobatrachus possesses some traits that would be expected of an earlier representative of the Pelobates stem line (maxillary arch complete; large nasals that fully cover the nasal capsule; posteriorly fused frontoparietale; large, wing-shaped sacral diapophyses), but their relevance can be determined only by the investigation of further fossil material. Sanchiz (1998: 98) considers it possible that Lutetiobatrachus can be assigned to the palaeobatrachids. Against this, in my opinion, is its incompletely fused frontoparietale (which in the palaeobatrachids moreover extends far anteriorly), prominent nasalia that extend further posteriorly, and the complete maxillary arch with connected quadratojugaia. A systematic classification of Lutetiobatrachus into one of the known anuran families will not be made until better-preserved material is recovered at Messel.

Acknowledgements This project firstly was carried on in the context of a dissertation. The author cordially thanks Professor J. Boy of Mainz for providing me with this topic, his constant interest in the progress of the project, and help in obtaining the research material. Gratefully is thanked to Drs. J. L. Franzen and S. Schaal (Forschungsinstitut Senckenberg, Frankfurt am Main) for their loan of the fossil material. J. Hogan (Munich) translated most parts of the manuscript. Dr. B. Sanchiz, Madrid, clarified nomenclatural problems. Dr.s. G. Gruber, N. Micklich and J. Köhler (Hessisches Landesmuseum, Darmstadt) gave valuable comments from which the manuscript benefitted. For help with scanning and processing the author thanks T. Bizer, of Mainz. Special thanks appertain to J. Köhler (Hessisches Landesmuseum Darmstadt) for his engagement in clearing up nomenclatural questions and to Deutsche Forschungsgemeinschaft for its financial support (Projects Bo 553/4–1 and Bo 553/4–2).


Discoglossidae. Clarke (by letter) stands up an other position: because the occurrence of free ribs is a plesiomorphic character, it cannot be ruled out that forms existed in which all the ribs were fused and that were derived from a species with only one free pair.

Plate 1: Fig. 1–2 Lutetiobatrachus gracilis WUTTKE in SANCHIZ 1998 Salientia, Archaeobatrachia, Fam. incertae sedis. »Grube Messel« near Darmstadt (S-Hesse, Germany); Lower Geiseltalium, Middle Messel Formation. Fig. 1: Holotype, dorsal side, SMF-Me 476; vaporized with ammonium chloride, ca. x 3.4. Fig. 2: Holotype, radiography, ca. 5.3; © S. Tuengerthal

1

2

Plate 2: Fig. 1–2 Lutetiobatrachus gracilis WUTTKE in SANCHIZ 1998 Salientia, Archaeobatrachia, Fam. incertae sedis »Grube Messel« near Darmstadt (SHesse, Germany); Lower Geiseltalium, Middle Messel Formation. Fig. 1: Holotype, SMF-Me 476, skull; vaporized with ammonium chloride, ca. x 8.8. Caption key:1= left maxillare; 2 = Proc. maxillaris of the pterygoid; 3= Proc. quadratojugalis maxillae; 4= Pars lateralis of the squamosum; 5 = quadratum; 6 = quadratojugale; 7 = Ramus zygomaticus of the squamosum; 8 = Sutura medialis of the frotoparietale; 9 = gouges on the frontoparietale; 11 = nasale; 12 = premaxillare.

1

2

Caption key: 1= left stinted Proc. transversus of the 5th vertebra; 2 = Facies interna of the acetabular zone; 3= Apex alae ossis ilii of the right ilium; 4 = ?apophysis of an 11th vertebra at the coccyx; ?apophysis of an 10th vertebra at the coccyx; 6= right sacral diapohysis; 7 = right Proc. transversus of the 8th vertebra; 8 = right Proc. transversus of the 7th vertebra; 9 = right Proc. transversus of the 6th vertebra; 10 = right Proc. transversus of the 5th vertebra; 11 = right Proc. transversus of the 4th vertebra; 12 = right Proc. transversus of the 3rd vertebra; 13 = right Proc. transversus of the 2nd vertebra; 14 = temporal region of the frontoparietale


Fig. 2: Holotype SMF-Me 476, vertebrate column and pelvis from dorsal; vaporized with ammonium chloride, ca. x 8.9.

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