In 1925
Raymond Dart announced the discovery of the first pre-Modern Human
Hominin remains in Africa, the Taung Child skull, from which the
first Australopithicine species, Australopithecus africanus,
was described. Since this time a wealth of Hominin species have been
described from Africa, and South Africa in particular, greatly
enhancing our understanding of the origin of our species, but no
further Hominin material was ever recovered from the Buxton Limeworks
site that produced the Taung Child. This site was originally
interpreted as a limestone cave system (early Man was expected to
live in caves, an expectation that has subsequently been vindicated
with many of South Africa's most productive Hominin sites found in
cave systems), with the skull recovered from a slitstone deposit
thought to have accumulated within the caves, but more recent
analysis of the limestone sediments has suggested that the presence
of root mats, Insect burrows and fragments of Bird's eggs in the
sediment, all of which suggest an in situ soil rather than a cave
deposit, as well as a microcalcitic crystalline structure to the
limestone matrix, which would be typical of a limestone concretion
formed within a soil.
In a
paper published in the journal PloS One on 28 September 2016,
Jennifer Parker of the Institute of Archaeology at University CollegeLondon and the Department of Earth and Planetary Sciences at Birkbeck College, University of London, Philip Hopley, also of the Department
of Earth and Planetary Sciences at Birkbeck College, and Brian Kuhn
of the Department of Geology at the University of Johannesburg,
describe an aggregation of fossil Bee's nests from the Buxton
Limeworks locality.
The
majority of Bee species are both solitary and ground nesting. They
favour fairly dry soils, as they seal their eggs into closed chambers
with a supply of food (pollen or nectar), and do not re-enter or move
the nests, which means that excess moisture can lead to Fungal
infections, destruction of the food source or even drowning of the
immature Bee (Bees living in particularly humid environments
generally do not nest on the ground). These burrows are typically
lined with a waxy substance secreted from an organ possessed by the
female Bees, called the Dufour’s gland, which helps to protect the
nest and juvenile from excess moisture.
The
aggregation examined by Parker et al.
comprises about 25 visible cells on a block of sediment 115 cm long
and 50 cm high. This block had been broken into a number of fragments
previously, enabling Parker et al.
to confirm the nests ran throughout the block. Previous studies of
similar material have relied on cutting serial thin sections of the
rock in order to determine the internal structure, a process which
destroys the samples, however Parker et al. were
able to examine the specimen using micro-CT (computed tomography)
facilities at the Natural History Museum in London, enabling the
construction of a three-dimensional model of the interior of the
block without destroying the specimen.
CT
Images of slice of Block 5 in shrink-wrapped form (above) and solid
form (below). Note the complex matrix of porosity, Cells (white
arrows) and tunnels made by unknown organism (blue arrows). Parker et
al. (2016).
This revealed that the cells were not connected by any form of tunnel
network, as would be expected in a nest built by communal Bees,
indicating this is an aggregation of solitary Bee's nests rather than
a single structure. This may be caused by the activity of a single
female Bee (some species construct over 30 individual nests close
together, each containing a single egg plus a food source), or a
group of Bees that nested in close proximity where favourable
conditions were found.
CT Image of Block 6D in shrink-wrapped form. Note the complex
matrix of porosity, Bee cell (white arrow) and tunnels made by
unknown organism (blue arrows). Parker et al. (2016).
The individual cells are approximately 14 mm in length and 7 mm in
width, and approximately flask shapes. All are at least partially
infilled with sediment. The cells were apparently lined, though this
lining has been replaced by calcite (limestone), making its exact
nature hard to judge, though as the cells themselves are infilled
with sediment rather than cacite, it is likely that the shape and
thickness of this lining has been preserved.
Three Different Individual Cells. (A) and (B) have been extracted
from the nest, and (C) (although broken in half laterally) remains in
the matrix. (A) displays a proximal view of a cell that has been
broken at the neck (the entrance); note the cell lining (arrow). (B)
displays a dorsal view of a cell, note the smooth cell wall; the
proximal end (at the left of the image) has been broken at the neck.
(C) shows a dorsal view of a cell that has been broken laterally; the
calcite lining (arrow) is clear, as is the cell shape (narrower and
blunter at the proximal (left) end, more rounded at the distal
(right)). Scale bar is 3mm. Parker et al. (2016).
The material that made up the cell lining has been replaced by
calcite (limestone), but this calcite still contains some trace of
the original material. Notably a large number of fibrous structures
160 to 350 μm, either unbranching of bifurcating (spiting in two)
are present within this matrix, these being apparently random in
their positioning and orientation, which Parker et al.
interpret as non-glandular plant trichomes (leaf hairs). The
selection of leaf hairs on their own as inclusions in a nest lining
seems unlikely, but several types of Bee do use leaf fragments or
pulped leaves to line their nests, and it is possible that the hairs
could have survived the destruction and diagenetic replacement of the
rest of the leaf material.
Petrographic Microscope Images of sections of a thin section of a
Cell. (A) shows the position of images (a), (b), and (c) in the whole
thin section. (a), (b), and (c) display sections of the cell lining
at a higher magnification to show the trichomes (arrows) and organic
lining structure (c; darker grey). (a), (b), and (c) are 1.5mm in
width (left to right). Parker et al. (2016).
If the lining of the nest had comprised leaf fragments it is likely
that the leaf hairs would be clumped into groups with similar
orientation. Since this is not the case, Parker et al. conclude
that the lining of the nest was almost certainly originally a leaf
pulp. Only one type of Bee makes such a nest today, Wood Carver Bees,
Anthidiini, and this is unlikely to have changed notably since the
Plio-Pleistocene deposits at Taung were laid down (about 2.8 million years ago). Wood Carder Bees
are numerous and diverse on every continent except Australia, and can
be expected to have been present in South Africa in the
Plio-Pleistocene.
These Bees favour dry soils in exposed sunny locations for nesting
sites, and are not known to nest in caves. This strongly supporting
the idea that Taung child was originally buried in soil deposits that
became calcified later rather than in a cave. The most likely
location for such a soil, given the Insect fauna, implied flora
(Carder Bees pollinate Herbaceous Flowering Plants) soil type (silt
particles) and later mineralization, would be a broad river
floodplain. The original (and subsequent) diggings at Taung found no
further Hominin remains, but these proceeded on the basis that the
site was an infilled cave, and that any remains would be found within
a very localized area. However a calcified palaeosol laid down on a
broad floodplain could potentially extend much further, forming beds
from hundreds of metres to tens of kilometres in extent, greatly
widening the area in which further Taung-associated material could be
found.
See also...
Nest cells of Leafcutter Bees from the Rancho La Brea Tar Pits. Leafcutter Bees (Megachilidae) cut their name from their habit of
cutting disk-shaped segments from leaves, from which they build their
nests. Each female...
The first photographs of the Taung Child. One of the most important breakthroughs in palaeoanthropology in the
twentieth century was the discovery of the fossil known as the Taung
Child, the first known specimen of Australopithecus, by Raymond Dart of
the University of the Witwatersrand
in South Africa in 1924. This discovery refocused efforts to find human
ancestors on the African continent, where...
Skull closure in the Taung Infant. The Taung Infant was discovered by workers at the Buxton Limeworks near Taung, South Africa in 1924 and described in a paper in the journal Nature
by palaeoanthropologist Raymond Dart in 1925. It is the partial skull
and endocast of the brain case of a three to four year old Australopithecus africanus, the first Australopithicine to be discovered, and the...
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