Brachycephalus ephippium

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 : 773

Brachycephalus ephippium

Cranial ontogeny At TS13, the nasal region is almost fully formed; only inferior and superior laminae are still not developed. All ceratobranchials are reduced, and hyoid has an adult-like aspect. Serial sections show ossification in angulosplenials and squamosals ( Fig. 13a ), dentaries, maxillae, and premaxillae; also, a light staining is outlined in the lateral parts of the frontoparietal region. At TS15 ( Fig. 13b ), the general aspect of angulosplenial; cl, clavicle; ipc, inferior prenasal cartilage; mc, Meckel’ s cartilage; oc, otic capsule; pp, pterygoid process; pq, palatoquadrate; pts, postsacral vertebra; s, sacrum; sq, squamosal; tn, tectum nasi. The asterisks show the ceratobranchials I–IV still differentiated in the hyobranchial skeleton. Scale bars = 1 mm

the chondrocranium appears underdeveloped in comparison with the three former species. The palatoquadrates do not reach their perpendicular arrangement regarding the neurocranium axis, and the rostral region is very short, more similar to early stages of other species. The nasal region is comparatively robust and well developed. Ossification is still weak, and in whole-mount preparation, only a thin calcified line is seen as evidence of still developing dentaries, angulosplenials, and squamosals; histological sections show slight ossification in pterygoids, parasphenoid, prootics, and exoccipitals.

Postcranial ontogeny Developmental series is unfortunately not complete enough for a detailed description of postcranial ontogeny, but some comparisons are possible. Main differences regarding the former species concern autopodium development. In hands, all elements except for some phalanges are evident at TS13. Finger III apparently completes its development before the proximal phalanx of finger V is formed. Likewise, toe II development precedes the formation of a complete toe V. Ossification is evident in vertebrae, proximal elements of the pectoral girdle, pelvic girdle, and long bones of limbs. At TS15, almost all limb elements are differentiated (e.g., Fig. 13b ). Middle and terminal phalanges V and terminal phalanx II of the hand, plus terminal (and likely middle) phalange V and terminal phalanx I of the foot, never develop.

Figures

Fig. 13 Cranial and postcranial skeleton of Brachycephalus ephippium at late prehatching stages. a Embryo at TS13, showing a cross section of the lower jaw with ossified squamosals and angulosplenials investing the palatoquadrate and Meckel’s cartilage. b Embryo at TS15, showing a cross section through the otic capsule, showing the still slight ossification, and cleared and stained chondrocranium (anterolateral view) and left hand (dorsal view). Histological sections are colored with