Haddadus binotatus

Vera Candioti, Florencia, Goldberg, Javier, Akmentins, Mauricio S., Nogueira Costa, Paulo, Goulart Taucce, Pedro Paulo & Pombal, José, 2020, Skeleton in the closet: hidden diversity in patterns of cranial and postcranial ontogeny in Neotropical direct-developing frogs (Anura: Brachycephaloidea), Organisms Diversity & Evolution (New York, N. Y.) 20 (4), pp. 763-783 : 770-772

Haddadus binotatus

Cranial ontogeny At TS12, the cartilaginous cranial skeleton in this species is similar to that of Oreobates ( Fig. 6a ). Conversely, hyobranchial skeleton development is delayed, with the ceratohyals showing a metamorphosed hyale-like shape, but larval ceratobranchials I–IV still differentiated ( Fig. 6b ). The ceratobranchials I are the longest, stout, and slightly curved posteriorly, whereas ceratobranchials II–IV are thinner and oriented laterally. Unlike in Oreobates , angulosplenials and squamosals appear ossified both in histological and whole-mount preparations. At TS 13, palatoquadrate acquires a perpendicular disposition relative to the neurocranial axis, and further ossifications appear, i.e., the frontoparietals, parasphenoid, premaxillae, and maxillae, plus slightly outlined exoccipitals. The nasal region is comparatively more developed than in O. barituensis . Cranial at this stage are indicated. Abbreviations: ap, anterior process; as, angulosplenial; d, dentary; fp, frontoparietal; h, hyale; hp, hyoid plate; m, maxilla; n, nasal; pm, premaxilla; pp, posterior process; pt, pterygoid; sm, septomaxilla; sq, squamosal. Scale bars = 1 mm

hypochord; il, ilium; is, ischium; mc, metacarpalia; mt, metatarsalia; p, phalanges; pts, postsacral vertebra; pu, pubis; r, radius; s, sacrum; sc, scapula; ssc, suprascapula; ti, tibiale; u, ulna. Scale bars = 1 mm

skeleton at TS14 appears adult-like, with a longer snout and overall more robust ossifications. Dentaries, pterygoids, and small quadratojugals differentiate at this stage. At TS15 ( Fig. 7 ), the nasal region is prominent and developed, except for the lateral commissure between the oblique cartilage and the planum antorbitale which is still not completely formed. Further ossifications are the mentomeckelians ( Fig. 7a ), nasals and septomaxillae ( Fig. 6b ), vomers, prootics, and hyoid posterior processes. Maxillary teeth are present in the maxillae ( Fig. 7a ), and short zygomatic rami project rostrally in the squamosals ( Fig. 7c ). Serial sections of a hatched specimen show the neopalatines ossified.

Postcranial ontogeny The development of the axial skeleton is slightly faster than in Oreobates . Ossification of transverse processes begins at TS12 ( Fig. 6c ), and at TS13, all vertebrae appear well articulated and stronger. By TS14, the cartilaginous coccyx (postsacral elements 1 + 2) appears as a paired element and the hypochord begins to ossify. Finally, at TS15 ( Fig. 8a ), the prezygapophyses and postzygapophyses of all presacral vertebrae are cartilaginous but articulate with each other. The transverse processes are present in all presacral vertebrae, although larger in the anterior ones. The sacrum bears a pair of small, rounded diapophyses. The neural arch laminae of all vertebrae are fused at the midline and the regression of the notochord is visible caudally. In the pectoral girdle, clavicles begin to differentiate early at TS12 ( Fig. 6d ), and all bony elements, except the mineralized areas of the suprascapula, are already evident from TS13 ( Fig. 8b ). In turn, the pelvic girdle is more robust, with ischia slightly ossified and longer ilia with dorsal ridges already developed at TS14 ( Figs. 6e and 8c ). Limb chondrogenesis and ossification are faster than in Oreobates , with almost all elements ossified at TS14 ( Figs. 6f, g ; 8d, e ; and 9 ). Further differences involve the ulnare formed by a single condensation and the differentiation of the distal element of the prepollex before hatching. Other than the overall accelerated development, there are no significant variations in tarsal configuration and ontogeny.

Figures

Fig. 6 Skeletal morphology of Haddadus binotatus at TS12. a Skull in dorsal, ventral, and lateral views. b Hyobranchial apparatus, ventral view. Inset: detail of the suspensorium region, showing the arrangement of the palatoquadrate and ossifications developed. c Vertebral column, dorsal view. d Pectoral girdle, ventral view. e Pelvic girdle, lateral view. f Forelimb, dorsal view. g Hind limb, dorsal view. Abbreviations: as,

Fig. 7 Cranial skeleton of Haddadus binotatus at TS15. a Skull in dorsal and ventral views. b Detail of the rostral region, frontal view. c Detail of the suspensorium region, showing ossifications in lateral view. Abbreviations: as, angulosplenial; d, dentary; m, maxilla; mm, mentomeckelian; mt, maxillary teeth; n, nasal; oc, otic capsule; pm, premaxilla; qj, quadratojugal; sm, septomaxilla; sq, squamosal. Scale bars = 1 mm

Fig. 8 Postcranial skeleton of Haddadus binotatus at TS15. a Vertebral column, dorsal view. b Pectoral girdle, ventral view. c Pelvic girdle, lateral view. d Forelimb, dorsal view. e Hind limb, dorsal view. Abbreviations: c, coracoid; cl, clavicle; ct, cleithrum; fi, fibulare; il,

Fig. 9 Schematic representation of auto- and zeugopodium devel- opment in Haddadus binotatus. a Forelimb. b Hind limb. The adult configuration is shown at the left, and drawings at the right show the sequential ossification (black segments) of elements. Abbreviations: fi, fibulare; mc, metacarpalia; mt, metatarsalia; p, phalanges; ph, prehallux; pp, prepollex; r, radius; ra, radiale; ti, tibiale; u, ulna; ul, ulnare; Y, ele- ment Y; 1–5, distal carpalia and tarsalia; I–V, fingers and toes