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Illustration Credit: Chuang Zhao |
New research details how a preserved fossil found in
China could be the oldest record of post-natal parental care from the Middle
Jurassic.
The specimen, found by a farmer in China, is of an
apparent family group with an adult, surrounded by six juveniles of the same
species. Given that the smaller individuals are of similar sizes, the group
interpreted this as indicating an adult with its offspring, apparently from the
same clutch.
A fossil specimen discovered by a farmer in China
represents the oldest record of post-natal parental care, dating back to the
Middle Jurassic.
The tendency for adults to care for their offspring
beyond birth is a key feature of the reproductive biology of living archosaurs
-- birds and crocodilians -- with the latter protecting their young from
potential predators and birds, not only providing protection but also provision
of food.
This behavior seems to have evolved numerous times in
vertebrates, with evidence of a long evolutionary history in diapsids -- a
group of amniotes which developed holes in each side of the skull about 300
million years ago and from which all existing lizards, snakes and birds are
descended
However, unequivocal evidence of post-natal parental
care is extremely rare in the fossil record and is only reported for two types
of dinosaurs and varanopid 'pelycosaurs' -- a reptile which resembled a monitor
lizard.
A new study by the Institute of Geology, Chinese
Academy of Geological Sciences, Beijing; the University of Lincoln, UK; and
Hokkaido University, Japan, presents new evidence of post-natal parental care
in Philydrosauras, a choristodere from the Yixian Formation of western Liaoning
Province, China. Choristoderes are a group of relatively small aquatic and
semi-aquatic diapsid reptiles which emerged in the Middle Jurassic Period more
than 160 million years ago.
The team reviewed the fossil record of reproduction in
this group using exceptionally preserved skeletons of the aquatic choristoderan
Philydrosauras. The specimen was donated to the Jinzhou Paleontological Museum
in Jinzhou City four years ago by a local farmer who discovered the skeleton.
The skeletons are of an apparent family group with an
adult, surrounded by six juveniles of the same species. Given that the smaller
individuals are of similar sizes, the group interpreted this as indicating an
adult with its offspring, apparently from the same clutch.
Dr Charles Deeming, from the School of Life Sciences,
University of Lincoln, UK, said: "That Philydrosauras shows parental care
of the young after hatching suggests protection by the adult, presumably
against predators. Their relatively small size would have meant that
choristoderes were probably exposed to high predation pressure and strategies,
such as live birth, and post-natal parental care may have improved survival of
the offspring. This specimen represents the oldest record of post-natal
parental care in diapsids to our knowledge and is the latest in an increasingly
detailed collection of choristoderes exhibiting different levels of
reproduction and parental care."
A test of whether post-natal parental care is an
ancestral behavior that has persisted in the evolutionary development of
amniotes will depend on future fossil discoveries.
Citation
Junchang Lü,
Yoshitsugu Kobayashi, D. Charles Deeming, Yongqing Liu. 2014. Post-natal parental care
in a Cretaceous diapsid from northeastern China.
Geosciences
Journal, 2014; DOI:
10.1007/s12303-014-0047-1