Staatliches Museum für Naturkunde, Rosenstein 1, D-70191 Stuttgart and Institut für Biologie, Universität Hohenheim, Stuttgart, Germany.
Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Invalidenstraße 43, Berlin, 10115, Germany.
Biol Rev Camb Philos Soc. 2024 Oct;99(5):1613-1637. doi: 10.1111/brv.13084. Epub 2024 Apr 10.
The question of what the ancient life cycle of tetrapods was like forms a key component in understanding the origin of land vertebrates. The existence of distinct larval forms, as exemplified by many lissamphibians, and their transformation into adults is an important aspect in this field. The temnospondyls, the largest clade of Palaeozoic-Mesozoic non-amniote tetrapods, covered a wide ecomorphological range from fully aquatic to terrestrial taxa. In various species, rich ontogenetic data have accumulated over the past 130 years, permitting the study of early phases of temnospondyl development. In temnospondyls, eight ontogenetic phases have been identified in which the skeleton formed. In branchiosaurids and the eryopiform Sclerocephalus, large parts of the ossification sequence are now known. Most taxa in which small specimens are preserved had aquatic larvae with external gills that superficially resemble larval salamanders. In the edopoids, dvinosaurs, and eryopiforms, the larvae developed slowly, with incompletely ossified axial and appendicular skeletons, but possessed a fast-developing dermal skull with strong teeth. Irrespective of adult terrestriality or a fully aquatic life, there was no drastic transformation during later ontogeny, but a slow and steady acquisition of adult features. In dissorophoids, the limbs developed at a much faster pace, whereas skull formation was slowed down, especially in the amphibamiforms, and culminating in the neotenic Branchiosauridae. In the zatracheid Acanthostomatops, slow but profound transformation led to a fully terrestrial adult. The basal dissorophoid Stegops retained rapid development of dermal skull bones and established a fully dentigerous, strongly ossified palate early. In Micromelerpeton, formation of the last skull bones was slightly delayed and metamorphosis remained a long and steady phase of morphological transformations. In amphibamiforms, metamorphosis became more drastic, with an increasing number of events packed into a short phase of ontogeny. This is exemplified by Apateon, Platyrhinops, and Amphibamus in which this condensation was maximised. We distinguish three different types of metamorphosis (morphological, ecological and drastic) that evolved cumulatively in early tetrapods and within temnospondyls.
古代四足动物的生命周期是怎样的，这个问题是理解陆地脊椎动物起源的关键组成部分。许多有尾两栖动物都具有明显的幼虫形态，并且它们会经历从幼虫到成体的转变，这是该领域的一个重要方面。盾皮鱼类是古生代-中生代最大的非羊膜四足动物类群，其生态形态范围广泛，从完全水生到陆生。在各种物种中，过去 130 年来积累了丰富的个体发育数据，使得对盾皮鱼类早期发育阶段的研究成为可能。在盾皮鱼类中，已经确定了骨骼形成的 8 个个体发育阶段。在宽甲鱼和始螈类的 Sclerocephalus 中，现在已经知道了大部分的骨化序列。大多数保存了小型标本的类群，其幼虫都具有外部鳃，这些鳃在外观上与幼体蝾螈相似。在 edopoids、dvinosaurs 和始螈类中，幼虫发育缓慢，其轴性和附肢骨骼没有完全骨化，但具有快速发育的真皮头骨和强壮的牙齿。无论成年后是否为陆生或完全水生，后期的个体发育过程中没有剧烈的转变，而是缓慢而稳定地获得成年特征。在泥螈类中，四肢的发育速度要快得多，而头骨的形成速度则减慢，尤其是在两栖螈类中，最终形成了幼态的宽甲鱼科。在棘螈类 Acanthostomatops 中，缓慢但深刻的转变导致了完全的陆生成年个体。基干泥螈类 Stegops 保留了真皮头骨骨骼的快速发育，并很早就建立了一个完全有齿的、强烈骨化的腭。在小鲵螈属 Micromelerpeton 中，最后头骨骨骼的形成略有延迟，变态成为一个漫长而稳定的形态转变阶段。在两栖螈类中，变态变得更加剧烈，更多的事件在短时间的个体发育中发生。这在 Apateon、Platyrhinops 和 Amphibamus 中得到了体现，这些物种的这种浓缩达到了最大值。我们区分了三种不同类型的变态（形态、生态和剧烈），这些变态在早期四足动物和盾皮鱼类中逐渐进化。
