Mammals have dominated almost all
terrestrial ecosystems for the last 65 million years, however fossil Mammals,
while not uncommon, are generally somewhat fragmentary, typically consisting of
bone fragments and teeth, with larger more intact skeletons forming less than
2% of all know Mammal remains, and the preservation of other tissues even
rarer. One location that does frequently produce more intact Mammal specimens
is the early Middle Eocene Messel Shale of southern Germany, where a large
number of Mammal specimens show exceptional preservation. Among the many
remarkable fossils from the Messel Shale have been found a large number of
specimens of the early Horse, Eurohippus
messelensis, including a total of thirteen described examples of female
Horses with preserved foetuses within their body cavities.
In a paper published in the
journal PLoS One on 7 October 2015, Jens Lorenz Franzen of the Department
Messelforschung at the Senckenberg Forschungsinstitut Frankfurt and the
Department Geowissenschaften at the Naturhistorisches Museum Basel, Christine Aurich of the Department Universitätsklinik für Kleintiere und Pferde at the
Veterinärmedizinische Universität Wien and Jörg Habersetzer, also of the
Department Messelforschung at the Senckenberg Forschungsinstitut Frankfurt,
describe a new specimen of Eurohippus
messelensis, also showing the presence of a preserved foetus.
Skeleton of a mare of Eurohippus
messelensis with foetus (white ellipse). The specimen was discovered and
excavated by a team of the Senckenberg Research Institute Frankfurt at the
Grube Messel, shoulder height ca. 30 cm, scale = 10 cm. Sven Tränkner in
Franzen et al. (2015).
The new specimen is about 2
million years older than any previously described example, but is nevertheless
considered to be the best preserved. It comprises a partially disarticulated
post-cranial skeleton and crushed and disarticulated cranium, encased within
what appears to be the preserved uterus of the adult, only the second such
specimen to preserve traces of the adult reproductive tract as well as the more
obvious bones of the foetus.
The foetus analyzed in detail by high-resolution micro-x-ray. Bones of
the mare are indicated by black lettering, bones and teeth of the foetus by white
lettering. L2-7 = lumbar vertebrae 2–7 of the mare. Scale = 10 cm. Jens Lorenz
Franzen & Jörg Habersetzer in Franzen et
al. (2015).
The reproductive biology of
extinct animals is notoriously hard to interpret. In Mammals length of
gestation is more closely tied to size than to phylogeny, however this is still
only a rough guide, for example modern Horses carry their foals for about
eleven months, compared to about nine months for Cows, which are approximately
the same size. The modern Blue Duiker, Philantomba
monticola, a small Antelope from the rainforests of Central and Southern
Africa, is generally considered an approximate ecological equivalent for Eurohippus messelensis, being
approximately the same size and living in a similar environment, and typically
carry their young for between 201 and 213 days, giving birth to one offspring
per year. The high proportion of pregnant female Eurohippus messelensis recovered from the Messel Shale suggests a
similar lifestyle, with females pregnant for much of the time, but only
carrying one foal per year.
Identification of the broad ligament (ligamentumlatum uteri). (a) The
broad ligament in the fossil mare from the Grube Messel. Sacrum and lumbar vertebrae
(L6-7) belong to the mare. Not to scale(b) Position and morphology of the broad
ligament (ligamentum latum uteri) attaching the uterine horn containing the
fetus to the lumbar vertebrae and the pelvis of a modern horse. Jörg
Habersetzer in Franzen et al. (2015).
See also…
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