Anura: Pelobatidae) MCZ by LIBRARY

Home , Megophryidae, Pelobatoidea, Scaphiopus, Spea

Scientific Papers

Natural History Museum The University of Kansas

18 July 2003 Number 30:1-13

Skeletal Development of Pelobates cultripes and a Comparison of the Osteogenesis of Pelobatid Frogs (Anura: Pelobatidae) MCZ By LIBRARY

Z008 Anne M. Magl.a' JUL 2 3

Division of Hcrpetologi/, Natural History Museiiui and Biodiversity Researcli Center, and Department ojEonbgi^gMSpY Evolutionary Biology, The University of Kansas, Laivreuce, Kansas 66045, USA CONTENTS

ABSTRACT 1 RESUMEN 2 INTRODUCTION 2 Acknowledgments 2 MATERIALS AND METHODS 2 RESULTS 3 Cranial Development 3 Hyobranchial Development 6 PosTCRANiAL Development 6 DISCUSSION 8 LITERATURE CITED 13

ABSTRACT The larval skeleton and osteogenesis of Pelobates cultripjes is described and compared to that of several pelobatoid and non-pelobatoid taxa. Several features of the larval skeleton are of interest, including: absence of a cartilaginous strip between the cornua trabeculae, type of articulation of cornua and suprarostrals, presence of adrostral tissues, and the condition of the otic process. By comparing sequence of ossification events across taxa, several patterns of skeletal development for Pelobates cultripes emerge, including: conserved timing of prootic ossification, delayed onset of mentomeckelian ossification, and early formation of vomerine teeth. Several other developmental features, including the absence of a palatine (= neopalatine) bone and the formation of the frontoparietal, also are discussed.

Key Words: Anura, Pelobatoidea, Pelobatidae, desarollo, osteologia, Pelobates, Scapliiopus, Spea.

^Current address: Department ofBiological Sciences, Uiiiversity ofMissouri-Rolla, Rolla, MO, 65409, USA; email: [email protected]

Natural History Museum, The University of Kansas 'SSN No. 1094-0782 © r v \i, I -^w.^. Ernst Mayr L!yrary -Museum of Cornparasfvc Zc-olcj^ flarvard Universiiy

Scientific Papers

Natural History Museum The University of Kansas

18 July 2003 Number 30:1-13

Skeletal Development of Pelobates cidtripes and a Comparison of the Osteogenesis of Pelobatid Frogs (Anura: Pelobatidae) MCZ By LIBRARY

2008 Anne M. Magl.a- JUL 2 3

Division of Herpetology, Nntiirnl Histon/ Museiiin and Biodiversity Research Center, and Department ofEcolo^^i/ and : - uji -<' — Evolutionan/ Biology, The Universitx/ of Kansas, Lawrence, Kansas 66045, USA • CONTENTS

ABSTRACT 1 RESUMEN 2 INTRODUCTION 2 Acknowledgments 2 MATERIALS AND METHODS 2 RESULTS 3 Cranial Development 3 Hyobranchial Development 6 PosTCRANiAL Development 6 DISCUSSION 8 LITERATURE CITED 13

ABSTRACT The larval skeleton and osteogenesis of Pelobates ciiltripes is described and compared to that of several pelobatoid and non-pelobatoid taxa. Several features of the larval skeleton are of inter-

est, including: absence of a cartilaginous strip between the cornua trabeculae, type of articulation of cornua and suprarostrals, presence of adrostral tissues, and the condition of the otic process. By comparing sequence of ossification events across taxa, several patterns of skeletal development for Pelobates cultripes emerge, including: conserved timing of prootic ossification, delayed onset of mentomeckelian ossification, and early formation of vomerine teeth. Several other developmental features, including the absence of a palatine (= neopalatine) bone and the formation of the frontoparietal, also are discussed.

Key Words: Anura, Pelobatoidea, Pelobatidae, desarollo, osteologia, Pelobates, Scaphiopus, Spea.

Current address: Dqmrtment ofBiological Sciences, Universiti/ ofMissoiiri-Rolla, Rolla, MO, 65409, USA; email: magliaa@unn:edu

Natural History Museum, The University of Kansas '^^"^ ^O- 1094-0782 © r-~^ »««,,, I •*.,^„. ^ ^ Ernst Mayr LJtsrary jyhweum of Cornpsra'fve Zoolo^ Harvard Universily Scientific Papers, Natural History Museum, The University of Kansas

RESUMEN Si bien la historia natural y ecologia de los pelobatidos son temas que comunmente se estudian, su osteologia y desarrollo son aspectos poco conocidos. En el presente trabajo se describen el esqueleto el larval y desarrollo de Pelobates ciiltripes , y se lo compara con varios taxones tanto pelobatoideos como no pelobatoideos. Varias caracteristicas del esqueleto larval son interesantes, tales como: la ausencia de una placa etmoidal entre los cuernos trabeculares, el tipo de articulacion de los cuernos con los suprarrostrales, la presencia de tejidos adrostrales y la condicion del proceso otico. Cuando se compara la secuencia de los eventos de osificacion en diferentes taxones, varios patrones resultan aparentes, incluyendo momento de osificacion del prootico conservativo, retardo en el inicio de osificacion del mentomekeliano y temprana formacion de los dientes del vomer. Otras caracteristicas del desarrollo, por ejemplo la ausencia de palatino (= neopalatino) y la formacion del frontoparietal, tambien se discuten.

Palabras Clnivs: Anura, Pelobatoidea, Pelobatidae, development, osteology, Pelobates, Scapliiopus, Syea. INTRODUCTION

The Pelobatoidea comprises about 95 extant frog spe- piinctntus. Wiens (1989) described the larval cranium and cies in three families (Pelobatidae, Megophryidae, and skeletal development of Spea bombifrons, and Hall and Pelodytidae; Frost, 1985; Lathrop et al., 1998), and are dis- Larsen (1998) described the osteogenesis of Scapliiopus (= tributed throughout the Holarctic and extend into the Old Spea) iiiteiiiioutana. Sokol (1981) described the larval cra- World tropics (Duellman and Trueb, 1986). Within Europe, nium of Pelodytes piuictatiis and mentioned several devel- pelobatoids are represented by at least seven species in opmental features of Scapliiopus (= Spea) bombifrons and two genera {Pelobates, Pelodi/tes) and range from southern Pelobates si/riacus (Sokol, 1975; 1981). Ramaswami (1943) de- Sweden and the Iberian Peninsula, east to the Ural Moun- scribed tlie chondrocranium of Megopluys parva and M. ro- tains (Frost, 2002). In North America, pelobatoids comprise busta based on serial sections. Within the genus Pelobates, the seven species in two genera (Scapliiopus, Spea) and range larval cranium and frontoparietal development of Pelobates in western North America from southern Canada to south- fuscus have been described (Plasota,1974; Rocek, 1980; 1988). ern Mexico (Frost, 2002). Pelobatoids have been the sub- Herein, I provide a detailed description of the larval ject of numerous life history and ecological studies (e.g.. skeleton and osteogenesis of Pelobates ciiltripes, a species

Driver, 1936; Axtell, 1958; Pfennig, 1990), and have been for which the development is poorly known, and compare studied often by morphologists and anatomists (e.g., its skeleton to those of several other frogs. Sewertzow, 1891; Smirnov, 1992). Unfortunately, most of Acknowledgments the works on the group are rarely considered by contem-

porary authors because they were published in the early I thank Linda Trueb and Chris Shell for their comments part of last century and /or were published in German or and Analia Pugener for comments and translation of the Russian. Therefore, works are disparate, and the adult Resumen. Miguel Lizana provided the ontogenetic series morphology and developmental anatomy of pelobatoids oi Pelobates cultripes and Jose E. Gonzalez, Museo Nacional remains poorly understood. de Ciencias Naturales (Madrid), allowed for the loan of

Only a limited number of works describe the morphol- adult P. cultripes. This work was supported by NSF Grant ogy of pelobatoids, and few of those have considered their # DEB 95-21691 (to Linda Trueb), the Natural History skeletal development. Rodriguez Talavera (1990) described Museum of The University of Kansas Panorama Society, the ossification sequence of Pelobates ciiltripes and Pelodytes and the Colorado Herpetological Society. MATERIALS AND METHODS

Twenty-one tadpoles of Pelobates cultripes from adult, two skeletons, and one formalin-preserved Pelobates Montalvo, Salamanca, Spain were staged according to the cultripes tadpole, as well as cleared-and-stained develop- developmental table of Gosner (1960), and were examined mental series of Spea niultiplicatn and Spea bouibifrous, were

for larval cranial and osteological development. These examined (Table 1). Osteological terminology is that of specimens were cleared and double-stained for bone and Pugener and Maglia (1997). Terminology of Rocek (1988) cartilage following the technique of Taylor and Van Dyke was followed for the frontoparietal complex (including the (1985), and were deposited in the herpetological collection median and lateral extrascapular bones). Descriptions and of The University of Kansas Natural History Museum illustrations were made with the aid of a stereo microscope (Table 1). The sample represents tadpoles between Gosner equipped with a camera lucida. Stages 28 and 46. Also, one cleared- and double-stained Skeletal Development of Pelobates cultripes

RESULTS Cranial Development

Larval cranium.—Description of the larval cranium is based on one Stage 30 specimen, the last stage before ossification of the cranium commences (Fig. 1). The cranium is relatively shallow, with the width (across the posterior margins of the palatociuadrates) about 80% of the length (midline), and the depth (at the level of the processus muscularis quadrati of the palatoquadrate) is only about one-third the length (Fig. 1). The floor of the braincase is formed by the basal plate (= basis cranii). At the level of the subocular fenestra, the basal plate is pierced by a pair of carotid foramina posteriorly and a pair of craniopalatine foramina anteriorly.

Posteroventrally, the notochord is present between the otic capsules. The otic capsules are about one-fourth the length of the cranium and each is pierced ventrolaterally by a large fenestra ovalis. Posteriorly, the jugular foramina exit the

Table 1 . Specimens examined. All specimens are deposited in the herpetological collections at the University of Kansas Natural History Museum, except adult Petobiitcs cultripes from the Museo Nacional de Ciencias Naturales, Madrid (MNCN). Stages are after Gosner (1960). '

Scientific Papers, Natural History Museum, The University of Kansas

- %Cx- — suprarostral c infrarostral c

ad rostral- # Meckel's c cornu trabeculum

commisura processus quadrato- - hyoquadrate p muscularis cranialis quadrat!

cranio- . palate- palatine f quadrate

carotid f ascending p prootic f _ larval otic p

>— tectum synoticum otic

-trochlear f capsule olfactory f foramen ? ad rostral

1 mm suprarostral c

fenestra ovalis infrarostral c

'- prootic f Meckel's c — oculomotor f—i

denotes Fig. 1. Larval cranium of Pelobntcs cultripcs (Stage 30; KU 288646) in dorsal (left), and ventral (right), and lateral (bottom) view. Gray cartilage; black denotes foramina; c = cartilage, f = foramen, p = process. dially from one another. Each suprarostral is composed of is crescentic, with the ventral surface being concave. Ven- a broad corpus and a laterally expanded ala; the corpus trally, each cornu bears a short triangular process for the fuses ventrolaterally to the ala and bears a processes for articulation of the quadratoethmoidal ligament. In the attachment to the cornu trabeculum. The suprarostrals are proximal lateral wall of each cornu is a large foramen for attached to the cornua medially by small ligaments and the lateral tiasal ramus of the opthalmic division of the laterally by what appears to be a synovial joint (similar to trigeminal nerve (Gaupp, 1896:131-138). that described by Sokol [1981] for Pelodytes punctatus). Each Ontogeny of larval cranjum.—Late in Stage 41, pri- suprarostral ala is directed dorsally and bears a ventral mordia of the alary cartilage, crista subnasalis, and oblique and a dorsal process. Attaching to the dorsal process is a cartilage appear anterior to the planum antorbitale. Meta- long, thin, dorsally projecting adrostral cartilage (= morphic climax begins around Stage 42, with the start of

Suprarostral 2; Hall and Larsen, 1998; epipraemandibular, erosion of the suprarostrals, as well as the commissura Rocek, 1980.) quadratocranialis anterior and the ascending process of The planum ethmoidale forms the anterior end of the the palatoquadrate cartilage. By Stage 43, the suprarostral braincase. Anteriorly, two rodlike cornua trabeculae ex- cartilages are absent and the cornua trabeculae are no tend to comprise about 40% the length of the cranium. longer distinct as paired cartilages; instead, they are in- Throughout their lengths, the cornua diverge from one corporated into the ethmoid plate and contribute to the another anterolaterally. In transverse section, each cornu solum nasi. Meckel's cartilages and the infrarostral Skeletal Development of Pelobates cultripes

Table 2. Sequence of skeletal ossification in Pelobates cultripes by Gosner (1960) stage at which they first appear. Scientific Papers, Natural History Museum, The University of Kansas

bone deposition lengthens the cultriform process; r- Copula 1 ceratohyal- forms alae, posterolaterally, ossification the ventral to the pars reuniens otic capsules. By Stage 33, the parasphenoid achieves its Copula 2 adult inverted T shape. 1 mm Vomers: These paired elements appear during Stage 43 as tiny centers of ossification anterior to the rostral tip of the parasphenoid; ossified primordia of vomerine teeth are present. By Stage 46, the anterior, prechoanal, also Cb1- postchoanal, and dentigerous processes are present. Premaxillne: The alary process is the first part to ossify, and appears concomitant with the nasals and septomaxillae during Stage 43. Each process forms as a thin, anteriorly directed sliver of bone on each side of the cornu trabeculum. The pars palatina and pars dentalis os- •—spicule sify at Stage 44, and premaxillary teeth are present by Stage L 45. Cb2-' Cb4 •— hypobranchial plate Maxillae: The pars facialis is the first portion of the •-CbS maxilla to ossify (Stage 43). Each maxilla is visible as an anteriorly directed sliver of bone, lying posterior, lateral, Fig. 2. Hyobranchial apparatus of Pelobates cultripcs larva (Stage 30; KU 288646) in ventral view; Cb I-IV = Ceratobranchials I-IV. and slightly ventral to the premaxillae. During Stage 44, the pars dentalis begins to ossify ventrally, and the palatine process appears lateral to the pars facialis. Primordia of lateral process. The posterior process unites with the teeth are present by Stage 45. hyobranchial plate via a cartilaginous bridge. Copula I is Mandibles: The infrarostral and Meckel's cartilages a well-developed, reniform cartilage. Anteriorly, Copula begin to elongate and form a horizontal articulation by II fuses to the pars reuniens; laterally it is fused to the hy-

Stage 43. By Stage 44, the paired angulosplenials ossify pobranchial plates. Ventrally, Copula II possesses an ovoid anteriorly from a center medial to Meckel's cartilage. Also urobranchial. Distally, the ceratobranchials articulate via by this stage, the dentaries are present as long, thin slivers the commissurae terminales and are continuous with the of bone; these ossify posteriorly, lateral to the infrarostral hypobranchial plates. Ceratobranchial 1 is the widest of cartilage and extend onto Meckel's cartilage. the ceratobranchials, but is not well chondrified;

Squamosals: Each sc^uamosal appears during Stage 43 Ceratobranchial IV is the most narrow and best chondri- as a thin sliver of bone on the medial side of the fied. Long spiculae arise dorsally from the proximal ends palatoquadrate cartilage. This center of ossification gives of the ceratobranchials and the commissurae terminales. rise to the ventral ramus of the adult squamosal. Zygo- Ontogeny of hyobranchium.—The hyobranchial ap- matic and otic rami are well developed by Stage 46. paratus begins to erode by Stage 43 when the ceratohyals Pterygoids: The posterior ramus is the first to ossify lengthen and the ceratobranchials begin to condense and early in Stage 44; it appears as a small, obliquely vertical fold over themselves. By Stage 44, the branchial arches are plate medial to the palatoquadrate cartilage. By Stage 46, absent and the ceratohyals form elongate hyalia. The the anterior ramus is present, but poorly ossified. The hypohyal plates condense at the midline and form rudi- medial ramus cioes not ossify until after Stage 46. mentary posteromedial processes by Stage 45. By Stage 46, Qtiiidratojugals: These elements appear by late Stage the laryngeal cartilages are present and well developed, 44 as two small centers of ossification on the lateral sur- and small posterolateral processes form on the lateral mar- face of the posterior end of each palatoquadrate cartilage. gin of the small hyoid plate. Also by this stage the posteromedial processes begin to ossify. Hyobranchial Development POSTCRANIAL DEVELOPMENT Larval hyobranchial skeleton.—At Stage 30, the vis-

ceral skeleton consists of Copulae 1 and II, two ceratohyals, Axial skeleton.—By Stage 28, the earliest stage in this and four pairs of ceratobranchials (Fig. 2). The ceratohyals series, neural arches of Vertebrae I-IX are present as small, are robust plates of cartilage connected medially by the cartilaginous semicircles lateral to the notochord (Fig. 3). pars reuniens to form an elongated transverse bar. Each Free ribs are absent. By Stage 31, the neural arches of the ceratohyal possesses a broad anterior process, a larger first seven vertebrae begin to ossify. Also during this stage

posterior process, a rhomboid hyoquadrate process (= ossification of the centrum of Vertebra I is faintly visible articularis process of de Sa, 1988), and a distally rounded as a small bifurcated plate dorsal to the notochord, form- Skeletal Development of Pelobates cultripes

28 44 «3

neural -U3 arch

1 mm 1 mm centrum

sacral hypochord diapophysis

Fig. 3. Development of the axial skeleton of Pelobates ciilliipes. Numbers refer to Gosner (1960) stage. White denotes ossification; gray denotes cartilage; transv p = transverse process. ing in a typical epichordal condition (Duellman and Trueb, scapula /suprascapula. The scapula and suprascapula 1986). are fused synchondrotically, constituting one cartilagi- The neural arches and centra develop steadily, and by nous unit (Fig. 4). Stage 35 the neural arches of Vertebrae I-X have begun to Ossification of the scapula /suprascapula begins by ossify. Also during this stage, most of the neural arches of Stage 35 as a small, barely visible narrowing between the the presacral vertebrae (= 1-VlIl) meet dorsally via a carti- elements. Also at this stage, dermal ossification of the laginous bridge. By Stage 38, the hypochord is present cleithrum begins. During Stage 38, the coracoid and clavicle ventral to the notochord; it begins to ossify by Stage 39 commence ossification and the epicoracoid cartilages ap-

(Fig. 3). The vertebral centra all show some ossification by pear. By Stage 39, the epicoracoids form well-developed Stage 39. medial cartilaginous bridges between the procoracoid During Stage 41, Vertebra IX (= sacrum) begins to form cartilages and the coracoids (Fig. 4). Ossification of all ele- small, lateral projecting cartilaginous diapophyses. By ments continues steadily, and by Stage 43, the two halves Stage 42, these sacral diapophyses begin to ossify (Fig. 3). of the pectoral girdle overlap at their ventromedial mar- Also during this stage, small cartilaginous processes form gins. Early in Stage 44 the sternum appears posterior to on the posterior margins of the neural arches of Vertebra the epicoracoid cartilages as an elongate piece of cartilage X. These small processes begin to ossify early during Stage (Fig. 4); by late Stage 44, the sternum begins to ossify. 43, and by late Stage 43, they detach from Vertebra X. Also Forelimb.—None of the forelimb elements are present during this stage. Vertebra X begins to fuse, via its ventro- by Stage 33, but by Stage 35, tlie humerus, radius, ulna, metac- lateral margins, to the sacrum. Because the neural arches arpals. Element Y, radiale, ulnare, Carpals 2-5, and several of this vertebra are not joined dorsally during this stage, phalanges appear in carhlage (Fig. 5). Also by this stage there and the centrum is not fully formed, the articulation of are small centers of ossification at the midpoint of the long Vertebra X and the sacrum appears to be a bicondylar ar- bones and metacarpals. By Stage 39, the radius and ulna fuse ticulation. at their medial margins, and Carpal 1, two prepollical ele- By Stage 44, the neural arches of Vertebra X join dor- ments, and the remaining phalanges appear (Fig. 5). At this sally and form the dorsal articulation with the sacrum (Fig. stage, all phalanges are present anci represent the adult for- 3). The urostyle is formed during Stage 46 when the mula of 2-2-3-3. By Stage 43, all metacarpals and phalanges hypochord fuses to both Vertebra X and its posterior pro- and Carpal 5 have begun to ossify. None of tlie remaining cesses. carpal elements is ossified by Stage 46 (Fig. 5). Pectoral girdle.—The earliest appearance of primor- Pelvic girdle.—By Stage 35, the ilium, ischium, and dia of the pectoral girdle is during Stage 35, in which pubis are present, although the pubis is thin and transpar- each half of the pectoral girdle is composed of carti- ent (Fig. 6); slight ossification of the ilium is apparent at laginous precursors of the procoracoid, coracoid, and the midpoint of the shaft. The ilium elongates anteriorly Scientific Papers, Natural History Museum, The University of Kansas

epicoracoid 39 cartilage

clavicle cleithrum

coracoid humerus

sternum

Fig. 4. Development of the pectoral girdle of Pchbatcs ciiltripes. Numbers refer to Gosner (1960) stage. Top illustrations are shown lateral view; bottom illustrations are shown in ventral view. White denotes ossification; gray denotes cartilage.

as the ventromedial borders of the ischia migrate toward prehallux (= spade) are present (Fig. 7). Also by Stage 35, one another. By Stage 42, the two sides of the pelvic girdle ossification of the long bones and metatarsals commences. fuse at the midline and the ilia attach to the developing By Stage 38, all of the elements of the adult skeleton are sacral diapophyses just anterior to the midpoint of the ilial present, with the phalangeal formula of 2-2-3-4-3. Also by

shaft (Fig. 6). During Stage 43, the ischium begins to os- this stage the prehallux begins to elongate and broaden

sify, ventral to the acetabulum. The pubis remains carti- into its adult spadelike form. By Stage 41, all of the pha- laginous through Stage 46. langes have begun to ossify (Fig. 7). The spade ossifies Hind limb.—No hind limb elements are evident be- during Stage 44. None of the tarsal elements is ossified by fore Stage 35. By this stage, the long bones. Tarsal 1, com- Stage 46.

bined Tarsal 2 + 3 + 4, most of the metatarsals, and the DISCUSSION

In comparing my results with published observations another at their bases (at the level of the planum

and the larval skeletons of other pelobatids, I found sev- antorbitale), and no cartilage is present between them. This

eral features of the larval skeleton and osteogenesis of is also the condition in Pelobntes fiiscus (Rocek, 1980) and Pelobates cidtripes that are of interest. These include: the Megoplin/s pnnm (Ramaswami, 1943). However, in other absence of a cartilaginous strip between the cornua trabe- pelobatoids, such as Spea inteniwntmia (Hall and Larsen,

cule, the type and position of the articulation of the cor- 1998), S. bombifivus (Wiens, 1989; pers. obs.), and Pelodi/tes nua trabeculae and suprarostral cartilages, the presence piiuctntiis (Sokol, 1981), the cornua are connected to one of adrostral tissues, the condition of the otic process, and another medially via a cartilaginous strip. the formation of the frontoparietal. There are also several The type and position of the suprarostral /cornu differences in the relative timing of ossification events that trabeculum articulation differ among pelobatoid groups. vary among pelobatoids and /or other frog taxa. In Pelobates ciitripes, the cornua articulate laterally with the Among pelobatoids, the cornua trabeculae may or may alae of the suprarostrals. This articulation is both syndes- not be joined to one another medially by a cartilaginous motic (via small ligaments at the medial portions of the strip. In Pelobates cultripes, the cornua diverge from one articulation) and synovial (laterally), but does not appear Skeletal Development of Pelobates cultripes

35 IV V " 3 Q ^ 40 ilium

ulnare "'^^%^:^ 44

sacral r\

~ diapophysisM prepollex-'/ i /// i pubis A ' ' / 1 mm

1 mm

1 mm 42

I I 1 mm

lum

Fig. 5. Development of the right manus of Pciohates culiripes. Num- (,; 1 mm bers refer to Gosner (1960) stage. White denotes ossification; gray de- Ischium notes cartilage. Digits are numbered (Roman numerals) according to Fabrezi (1992); 2-5 = Carpals 2-5; Y = Element Y; dist prep = distal prepollex. Fig. 6. Development of the pelvic girdle of PelolnitL'S cultripes. Num- bers refer to Gosner (1960) stage. Top left illustration is shown lateral to have a synchondrotic component. In Pdodytcs piiiictatus, view, bottom left illustration is shown in ventral view, right illustration is shown in dorsal view. White denotes ossification; gray denotes carti- the cornua articulate with the corpus of the suprarostrals lage. by joints that are synchondrotic medially, synovial laterally, and syndesmotic more laterally (Sokol, 1981). In Spea found these tissues in Spea. But, as pointed out by Hall intermoiitana, the cornua attach to the corpus of the and Larsen (1998), this may be an artifact of the methods suprarostrals by way of a synchondrotic articulation (Hall by which specimens were prepared. and Larsen, 1998). The articulation in Spea homhifrons There is considerable variation in the condition of the (Wiens, 1989; pers. obs.) and Spen tiiultiplicnta (pers. obs.) posterolateral portion of the palatoquadrate. In Pelobates is also via the suprarostral corpus, but it is syndesmotic in cultripes the palatoquadrate is posterolaterally flattened to these taxa. Although the type of articulation in Mcgophrys form a thin plate called the otic process (Sokol, 1981). Ex- paroa was not reported by Ramaswami (1943:plate I; fig. tending from the otic process, to articulate with the otic

1), it appears to include the suprarostral ala. capsule, is a chondrified otic ligament, which, when chon- The presence of adrostral cartilages (= Suprarostral 2; drified, is referred to as the larval otic process (Sokol, 1981). Hall and Larsen, 1998) or undifferentiated adrostral con- In Pelodytes puuctatus and Megophri/s parva, the otic pro- nective tissue masses varies among pelobatoids. In cesses resembles that in Pelobates cultripes (Sokol, 1981). Pelobates cultripes, there are well-c^eveloped, elongate However, with the exception of some species oi Mcgophn/s adrostral cartilages present at the posterolateral margins (Sokol, 1981), the otic ligament does not chondrify. In Spea of the suprarostrals. These also are present in Pelobates iutermontana (Hall and Larsen, 1998), Spea bombifrons fusciis (Sewertzow, 1891 :fig. 1; Rocek, 1980) and in (Wiens, 1989), and Spea multiplicata (pers. obs.), the otic Megoplm/s paroa (Ramaswami, 1941). Sokol (1981) sug- process is thick and rounded, and forms a cuplike struc- gested that these tissues were present, but unchondrified, ture (referred to as the "primitive" condition by [Sokol, in Pelodytes piinctatiis and Spea boinbifwns. However, nei- 1981:176] and Hall and Larsen [1998:219]). There is a ro- ther Hall and Larsen (1998; Spea iutcniioiitaiia), Wiens (1989; bust, unchondrified otic ligament connecting the otic pro-

S. boiubifw)is), nor myself (S. boiubifivus, S. niiilfiplicata) cess and the otic capsule. At the anterolateral margin of 10 Scientific Papers, Natural History Museum, The University of Kansas

IV was present in Spcn intermontana based on the existence of 35 J two centers of vomerine ossification. They suggest that the posterolateral ossification center, which subsequently fuses to the medial ossification center, is most likely the palatine V {} II r bone. Their argument is based primarily on topological U similarity. However, as was mentioned by Hall and Larsen ^-fiji,^.' (1998), two centers of ossification have been reported in Pseiidneris triseriata which also possesses a palatine bone (Stokely and List, 1954). Although topological similarity prehallux ....lit;; may help us recognize potentially homologous structures, 41 it is not a valid criterion for determining homology (del fibulare- tibiale Pinna, 1991 ). A test of congruence (Patterson, 1982), or the III ,v presence of both potentially homologous structures in the \ \ same organism, eaii be used to negate homology. There- '^ 1 V %. mm fore, it is inappropriate at this point to suggest that a pa- ii latine is present in pelobatoids. The sequence of ossification of cranial elements in '"'^cX I Pelobates cultripes resembles that of most other anurans (Tables 3, 4); however, a few differences warrant further ^prehallux discussion. In comparing my results with those of ^ Rodriguez Talavera (1990) on P. cultripes, I found few dif-

ferences (Table 3), most relating to the timing of ossification of the upper and lower jaw. These variations most

likely are the result of either interindividual / populational differences or the limited number of static stages in our respective ontogenetic series. Contrary to Rodriguez

Talavera (1990), in my sample, I found that the vomerine teeth begin forming at the same time (but from a separate

Fig. 7. Development of the right foot of Pclobiilcs ciiltripes. Num- ossification center) as the body of the vomer. I am not aware bers refer to Gosner stage. White denotes ossification; gray de- (1960) of the mention of early vomerine tooth development in notes cartilage. Digits are numbered I-V. Abbreviations: 1 = Tarsal 1; I find of this in 2+3+4 = combined Tarsal 2+3+4; Y = Element Y. any other pelobatoid, nor did evidence Spea boiubifroiis or S. luultiplicata.

the otic capsule there is a small cartilaginous process, the Compared to other taxa, the timing of ossification of larval crista parotica (Pusey, 1938; de Sa, 1988), for the at- the prootic seems to be similar among pelobatoids (or at tachment of the otic ligament. least pelobatids, sensu Ford and Cannatella, 1993). The In Pelobates cultripes, the element covering the fronto- prootic begins to ossify either immediately following the parietal fontanelle develops from five centers of ossifica- onset of ossification of the parasphenoid, frontoparietal, tion. Although a similar pattern of dermal roof formation and exoccipital (always the first three elements to ossify) (after has been reported for Pelobates fiisciis and the extinct or concomitant with the formation of the exoccipital fronto- fEopelobntes (Rocek, 1988), it has not been reported for any the onset of ossification of the parasphenoid and other extant taxon. Other authors (e.g., Cannatella, 1985; parietal). In the basal taxa considered {Bombina, Henrici, 1994) have referred to this roofing element as the Discoglossus), the prootic ossifies much later in develop- frontoparietal; however, based on topological position and ment (postmetamorphosis). timing of ossification, the medial and posterolateral ele- In Pelobates and Pelodytes, the mentomeckelian is one ments are not homologous with the frontoparietal of other of the last bones to ossify (postmetamorphosis). In other anurans. pelobatid taxa, the mentomeckelian ossifies before meta- The presence of a palatine bone (= neopalatine of morphosis. This may either be the result of precocial de- Duellman and Trueb, 1986) in pelobatoids has been a point velopment of the mentomeckelian in Spea or delayed ossi- of speculation and contention for many authors (e.g., fication in other taxa. Because of the presence of both pat- the Zweifel, 1956; Kluge, 1966; Rocek, 1980). It has been sug- terns in non-pelobatoid taxa, it is difficult to determine gested that the palatine has been lost or has been fused to evolution of this pattern within the pelobatoids. either the vomer or the maxilla (as discussed by Rocek, By comparing the relative timing of ossification of skel- 1980). Hall and Larsen (1998) suggested that the palatine etal regions (crai-iial, axial, forelimb, hind limb) among taxa Skeletal Development of Pelobates cultripes

Table 3. Comparison of cranial ossification sequences among pelobatoid taxa. Bars to the left indicate elements appearing simultaneously. Data for Spea inidtipUcnta were coded directly from specimens (Specimens Examined). Other data were collected from literature as follows: S. bombifrons,

Wiens (1989); S. intermontana. Hall and Larsen (1998); Pelobata cultripes and Pelodytcs puiictntiis. Rodriguez Talavera (1990).

Pchbntcs 12 Scientific Papers, Natural History Museum, The University of Kansas

Table 4. Comparison of cranial ossification sequences among non-pelobatoid taxa. Bars to the left indicate elements appearing simultaneously. Data were collected from literature as follows: Bombvw orientalis, Maglia and Pugener (1998); Diicoglosfus sanius, Piigener and Maglia (1997); Khiuophrynus donalif, Trueb (1985); Xenopus lacvis, Trueb and Hanken (1992); Clwcoplin/s picivtti. Wild, (1999); H\/la Inuciformis, de Sa (1988). Skeletal Development of Pelobates cultripes 13

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http: / / research.amnh.org / herpetology /amphibia / index. html Acta Universitatis Carolinae Biologica. 3:1-164. Gaupp, E. 1896. A. Ecker's und R. Wiedersheim's Anatomic des Frosches. Rocek, Z. 1988. Origin and evolution of the frontoparietal complex in 2 Vols. Braunschweg: Freidrich Vieweg Und Sohm. anurans. Amphibia-RepHlia 1988:385-403. Gosner, K. L. 1960. A simplified table for staging anuran embryos and Rodriguez Talavera, M. -R. 1990. Evolucion de peloditidos: morphologia larvae with notes on identification. Herpetologica 16:183-90. y desarollo del sistema esqueletico. Ph.D. Dissertation. Madrid:

Hall, J. A., and Larsen, ]. H. 1998. Postembryonic ontogeny of the Universidad Complutense de Madrid. spadefoot toad, Scopliiopu!^ iutennoutniius (Anura: Pelobatidea): Skel- Sewertzow, A. N. 1891. Ueber einige Eigenthiimlichkeiten in der etal morphology. Journal of Morphology 238:179-244. Entwickelung und im Bau des Schadels von Pchbtites fitscus. Bulletin

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