Prenatal development in crocodilians represents a very interesting model for comparative studies. As the speed of prenatal development of crocodilians varies depending on incubation conditions, the staging of embryos and fetuses is a very important prerequisite for data correlation. To establish a background for future developmental studies on Crocodylus niloticus, we characterized its prenatal development in a collection comprising 169 animals during embryonic/incubation days 9-70. The characteristics included external morphology, head morphometry, and wet body weight determined before fixation. We documented the external morphology of prenatal Nile crocodiles in a large collection of photographs and described landmarks during the morphogenesis of the head, face and limbs. In the development of the facial processes (medial nasal, lateral nasal, maxillary), three phases could be distinguished: union, separation, reunion. At the free jaw margin, a regular series of prominences was present. The outer aspect of a prominence gave rise to a labial scale, the inner aspect to a tooth. In contrast to mammals (humans and mice), the hindlimbs of C. niloticus developed faster than the forelimbs. We also determined changes in basic measures of the head and of the wet body weight. Both morphological and morphometric characteristics showed an apparent inter-individual variability among animals of the same age. This variability decreased among animals of a similar body weight (irrespective of their age). Body weight can be considered as the most representative and complex parameter for crocodile staging reflecting the overall growth of a whole embryo/fetus.

• MeSH
• aligátoři a krokodýli anatomie a histologie   embryologie   genetika   MeSH
• hlava anatomie a histologie   MeSH
• tělesná hmotnost MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Mammals and birds have a specialized cardiac atrioventricular conduction system enabling rapid activation of both ventricles. This system may have evolved together with high heart rates to support their endothermic state (warm-bloodedness) and is seemingly lacking in ectothermic vertebrates from which first mammals then birds independently evolved. Here, we studied the conduction system in crocodiles (Alligator mississippiensis), the only ectothermic vertebrates with a full ventricular septum. We identified homologues of mammalian conduction system markers (Tbx3-Tbx5, Scn5a, Gja5, Nppa-Nppb) and show the presence of a functional atrioventricular bundle. The ventricular Purkinje network, however, was absent and slow ventricular conduction relied on trabecular myocardium, as it does in other ectothermic vertebrates. We propose the evolution of the atrioventricular bundle followed full ventricular septum formation prior to the development of high heart rates and endothermy. In contrast, the evolution of the ventricular Purkinje network is strongly associated with high heart rates and endothermy.

• MeSH
• aligátoři a krokodýli embryologie   genetika   fyziologie   MeSH
• embryo nesavčí metabolismus   MeSH
• Hisův svazek embryologie   metabolismus   fyziologie   MeSH
• hybridizace in situ MeSH
• mezikomorová přepážka embryologie   metabolismus   fyziologie   MeSH
• modely kardiovaskulární MeSH
• převodní systém srdeční embryologie   fyziologie   MeSH
• proteiny T-boxu genetika   metabolismus   MeSH
• Purkyňova vlákna embryologie   metabolismus   fyziologie   MeSH
• srdce embryologie   fyziologie   MeSH
• srdeční frekvence genetika   fyziologie   MeSH
• srdeční komory embryologie   metabolismus   MeSH
• vývojová regulace genové exprese MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Understanding complex situations and planning difficult actions require a brain of appropriate size. Animal encephalisation provides an indirect information about these abilities. The brain is entirely composed of soft tissue and, as such, rarely fossilises. As a consequence, the brain proportions and morphology of some extinct vertebrates are usually only inferred from their neurocranial endocasts. However, because the morphological configuration of the brain is not fully reflected in the endocast, knowledge of the brain/endocast relationship is essential (especially the ratio of brain volume to endocast volume or the equivalent proportion of interstitial tissue) for studying the endocasts of extinct animals. Here we assess the encephalic volume and structure of modern crocodilians. The results we obtained using ex vivo magnetic resonance imaging reveal how the endoneurocranial cavity and brain compartments of crocodilians change configuration during ontogeny. We conclude that the endocasts of adult crocodilians are elongated and expanded while their brains are more linearly organised. The highest proportion of brain tissue to endocast volume is in the prosencephalon at over 50% in all but the largest animals, whereas the proportion in other brain segments is under 50% in all but the smallest animals and embryos. Our results may enrich the field of palaeontological study by offering more precise phylogenetic interpretations of the neuroanatomic characteristics of extinct vertebrates at various ontogenetic stages.

• MeSH
• aligátoři a krokodýli anatomie a histologie   růst a vývoj   MeSH
• biologická evoluce MeSH
• fylogeneze MeSH
• lebka anatomie a histologie   růst a vývoj   MeSH
• magnetická rezonanční tomografie MeSH
• mozek anatomie a histologie   růst a vývoj   MeSH
• zkameněliny MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH

• Klíčová slova
• věda - aplikace - sborníky prací, Rolex cena - práce vědecké - laureáti pro rok 1987 - sborníky prací,

• Konspekt
• Biologické vědy
• NLK Obory
• biologie
• věda a výzkum
• environmentální vědy