脊椎动物头部及其头骨代表了一项重大创新,在脊椎动物的进化和生态成功中发挥了关键作用。为了全面了解头部骨骼的演变,在各种脊椎动物中,有关于软骨颅骨发育的可靠信息是至关重要的。因此,我们研究了Budgett青蛙幼虫的颅骨软骨形成,Lepidobatrachuslaevis(Ceratophryidae,Neobatrachia).我们使用几种方法研究了这种发展,包括软骨颅骨横切面的组织学准备,三种不同发育状态的形态学分析(间充质聚集,分化,和软骨化),和三维数字重建。因此,我们观察到Gosner阶段19的软骨颅骨的部位被横向压缩,也就是说,它最初高于宽。它逐渐变平,扩大,并分化,直到在Gosner阶段26达到非常宽和平坦的形状。此外,我们显示了L.laevis的软骨发育是以镶嵌模式进行的,这不同于非四足脊椎动物,其中观察到软骨形成的前后梯度。根据颅骨结构的软骨化状态,我们确定了莱维氏乳杆菌的19个发育阶段。达到分化为成软骨细胞阶段的第一个元素是支气管篮的下支气管板,软骨形成,也就是说,最终分化,同时发生在神经颅骨和内脏颅骨的几个结构中。我们假设Laevis\'软骨颅骨的快速软骨化是从其类型的局部适应半干旱气候条件,ElGranChaco在南美洲。由于仅暂时有合适的蓄水量,这种明显的加速发展对于确保t在水体消失时成为青蛙是有意义的。这里,我们提供了有关L.laevis软骨发育的新信息。我们将我们的结果与发育序列进行比较,以前从其他脊椎动物分类群已知,特别是在两栖动物系统发育中,试图了解脊椎动物头部骨骼的发育变异性和进化史。
The vertebrate head and its skull represent a significant innovation that has played a key role in the evolutionary and ecological success of vertebrates. For a global and integral understanding of the evolution of the head skeleton, it is essential to have reliable information on the development of chondrocranium in a wide range of vertebrate species. Therefore, we studied the cranial chondrogenesis of the larva of the Budgett frog, Lepidobatrachus laevis (Ceratophryidae, Neobatrachia). We studied the development using several methods, including histological preparation of transverse sections of the chondrocranium, morphological analysis of three different states of development (mesenchymal aggregation, differentiation, and chondrification), and three-dimensional digital reconstructions. As a result, we observed that the Anlage of the chondrocranium at Gosner stage 19 is laterally compressed, that is, it is initially higher than wide. It gradually flattens, enlarges, and differentiates until reaching a very wide and flat shape at Gosner stage 26. Furthermore, we show that the chondrocranial development of L. laevis takes place in a mosaic pattern, which differs to nontetrapod vertebrates in which an anterior to posterior gradient of chondrification is observed. We identified 19 developmental stages in L. laevis according to the chondrification state of its cranial structures. The first element reaching the differentiation-into-chondroblast stage is the hypobranchial plate of the branchial basket, and chondrification, that is, final differentiation, occurs simultaneously in several structures of the
neurocranium and viscerocranium. We hypothesize that the rapid chondrification of L. laevis\' chondrocranium is an adaptation to the semi-arid climate conditions from its type locality, El Gran Chaco in South America. Due to the only temporary availability of suitable water accumulations this apparent accelerated development would make sense to ensure the tadpoles are froglets by the time the water body disappears. Here, we provide novel information on chondrocranial development in L. laevis. We compare our results to the developmental sequences, previously known from other vertebrate taxa, particularly within the amphibian phylogeny, in an attempt to understand developmental variability and the evolutionary history of the vertebrate head skeleton.