Two marsupial species ( Monodelphis domestica, Macropus eugenii ) and four eutherian species (Mesocricetus auratus, Suncus murinus, Tupaia belangeri and Cavia aperea ) were examined to compare and contrast the timing of lung and metabolic development during the postnatal maturation of the mammalian respiratory apparatus. Using light, scanning and transmission electron microscopy, the lung structural changes were correlated with indirect calorimetry to track the metabolic development. Marsupial and eutherian species followed the same pattern of mammalian lung development, but differed in the developmental pace. In the two newborn marsupial species, the lung parenchyma was at the early terminal sac stage, with large terminal air sacs, and the lung developed slowly. In contrast, the newborn eutherian species had more advanced lungs at the late terminal sac stage in altricial species ( M. auratus, S. murinus ) and at the alveolar stage in precocial species ( T. belangeri, C. aperea ). Postnatal lung development proceeded rapidly in eutherian species. The marsupial species had a low metabolic rate at birth and achieved adult metabolism late in postnatal development. In contrast, newborn eutherian species had high metabolic rates and reached adult metabolism during the first week of life. The time course of the metabolic development is thus tightly linked to the structural differentiation of the lungs and the timing of postnatal lung development. These differences in the neonatal lung structure and the timing of postnatal lung maturation between marsupial and eutherian species reflect their differing reproductive strategies.

Marsupials represent only 6% of all living mammals. Marsupialia and Placentalia are distinguished mainly by their modes of reproduction. In particular, the differences in the stage of development of the neonates may be one explanation for the divergent evolutionary success. In this respect one important question is whether the survivability of the neonate depends on the degree of maturation of the respiratory system relative to the metabolic capacity at the time of birth. Therefore, this review highlights the differences in lung morphology and metabolic development of extant Marsupialia and Placentalia. The Marsupial neonate is born with a low birth weight and is highly immature. The neonatal lung is characterized by large terminal sacs, a poorly developed bronchial system and late formation of alveoli. Marsupialia have a low metabolic rate at birth and attain adult metabolic rate and thermoregulatory capacity late in postnatal development. In contrast, the eutherian neonate is born with a relative high birth weight and is always more mature than marsupial neonates. The neonatal lung has small terminal sacs, the bronchial system is well developed and the formation of alveoli begins few days after birth. Placentalia have a high metabolic rate at birth and attain adult metabolic rate and thermoregulatory capacity early in postnatal development. The differences in the developmental degree of the newborn lung between Marsupialia and Placentalia have consequences for their metabolic and thermoregulatory capacity. These differences could be advantageous for Placentalia in the changing environments in which they evolved.

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Reproduction of African elephants Loxodonta africana and Asian elephants Elephas maximus has in the past been poor in European zoos and juvenile survival has been low. A range of potential complications, such as stillbirths or maternal aggression towards the calf, makes it imperative that the date of parturition is predicted as accurately as possible. Behavioural, endocrinological and physiological data were collected from three pregnant elephants for up to 3 months prior to parturition in order to assess their value for predicting the date of birth. Behavioural observations indicated that activity, particularly the frequency of stereotypic behaviour, increased prior to parturition. Pregnant cows grew restless and exhibited frequent excretion, tail beating against the vulva and excessive throwing of hay or sand against the belly. Our results suggest that observations of prepartal behavioural changes are a useful indicator for predicting parturition, particularly for veterinarians and keepers who are familiar with the usual behaviour patterns of the animals in their care. Measurement of luteal activity indicated that luteo‐lysis occurred 2‐3 days prior to parturition in both elephant species. Thus, endocrinological analysis provides an excellent and accurate prediction of the timing of parturition.