Certain natural objects provoke a
deep response in me. Awe and wonder are too prosaic to describe the sensation
they engender. Something at the back of my mind screams “other!”..
That’s when the fascination with
finding out what this thing is, where it comes from and how it fits into our
world, begin, for me.
So it was when I saw my first
picture of this fossil, in a BBC news report
Adapted from the BBC (2020):
“Scientists in the US have uncovered the mystery of a giant egg discovered in
Antarctica almost a decade ago.
For years
researchers could not identify the fossil, which resembled a deflated football,
leading it to gain the sci-fi nickname "The Thing".
‘The Thing’ from forskning
(2020). Original caption reads: Legendre and his colleagues do not believe the
egg comes from a dinosaur, since the dinosaurs that lived in Antarctica at that
time were largely too small to lay such large eggs.
But now, scientists say the egg
probably belonged to a giant sea reptile that lived around 68 million years
ago. It is the believed to be the world's largest reptile egg.
The giant fossil egg from El Comercio (2020). Original
caption reads: Of almost 30 centimeters, it would correspond to a marine
reptile that lived more than 66 million years ago on the peninsula. (Photo:
Handout/Chilean National Museum of Natural History/AFP)
The fossil - which measures 11 by
7 inches (28cm by 18cm) - was found by researchers from Chile in 2011, but it
was only in 2018 that a scientist from the University of Texas at Austin
recognised it could be a deflated egg. While the size of the egg suggested it
belonged to an animal the size of a large dinosaur, its soft shell was
"completely unlike a dinosaur egg", Lucas Legendre, a postdoctoral
researcher at the University of Texas at Austin, said.
"It is most similar to the
eggs of lizards and snakes, but it is from a truly giant relative of these
animals," he said.
By comparing the size of hundreds
of reptiles alive today and their eggs, researchers say the animal that laid
the egg would have been at least seven metres long.
Other fossils found at the same
site suggest the egg could have belonged to a giant marine reptile called a
mosasaur, although it is unclear whether the egg was laid on land or at sea.
The media reports, I discovered
were based on a paper in the journal Nature by Legendre et al. (2020). Here is
the abstract:
“Egg size and structure reflect
important constraints on the reproductive and life-history characteristics of
vertebrates. More than two-thirds of all extant amniotes lay eggs. During the
Mesozoic era (around 250 million to 65 million years ago), body sizes reached
extremes; nevertheless, the largest known egg belongs to the only recently
extinct elephant bird, which was roughly 66 million years younger than the last
nonavian dinosaurs and giant marine reptiles. Here we report a new type of egg
discovered in nearshore marine deposits from the Late Cretaceous period
(roughly 68 million years ago) of Antarctica. It exceeds all nonavian dinosaur
eggs in volume and differs from them in structure. Although the elephant bird
egg is slightly larger, its eggshell is roughly five times thicker and shows a
substantial prismatic layer and complex pore structure. By contrast, the new
fossil, visibly collapsed and folded, presents a thin eggshell with a layered
structure that lacks a prismatic layer and distinct pores, and is similar to
that of most extant lizards and snakes (Lepidosauria). The identity of the
animal that laid the egg is unknown, but these preserved morphologies are
consistent with the skeletal remains of mosasaurs (large marine lepidosaurs)
found nearby. They are not consistent with described morphologies of dinosaur
eggs of a similar size class. Phylogenetic analyses of traits for 259
lepidosaur species plus outgroups suggest that the egg belonged to an
individual that was at least 7 metres long, hypothesized to be a giant marine
reptile, all clades of which have previously been proposed to show live birth.
Such a large egg with a relatively thin eggshell may reflect derived
constraints associated with body shape, reproductive investment linked with
gigantism, and lepidosaurian viviparity, in which a ‘vestigial’ egg is laid and
hatches immediately.”
Whether the identification of the
egg as being laid by a mosasaur is in the paper or was just suggested by Legendre
in interview, I am unsure as the paper is behind a paywall.
Good images of the mosasaur and
its hypothesised mode of giving birth are shown by Newsround (2020)
Mosasaur young hatching
underwater from Newsround (2020).
From media reports, several other
interesting facts can be gleaned:
- Chemical analysis, showed that the surface and sub-surface layer were different from the surrounding sediments and was originally living tissue, probably eggshell
- The egg contained no skeleton, hence all assignment to genus/species is supposition without supporting evidence
- The site did contain such evidence: fossils of mosasaur and young. However, plesiosaur fossils were also found too
- The fossil was found on the Antarctic peninsula island of Seymour
- The suggestion that the fossil could be a soft-shelled egg came from Julia Clarke, a professor in the University of Texas (Austin), Jackson School Department of Geological Sciences
The species that laid the egg
could therefore been a mosasaur or plesiosaur, or other species of suitable
size and age. A quick bit of research identified species of Ichthyosaur, Thalattosuchians
(marine crocodiles) and Palaeophis (marine snakes) that were of the correct
length [ca. 7m] and lived in the correct part of the cretaceous era.
But what of the site being in
Antarctica? I thought Dinosaurs liked hot climates? Well I had to find out what
position the continent was in, in the late Cretaceous. If we compare maps of
the disposition of the continents from 65mya and now, we see:
A comparison of the position of
the continents, as they were at the end of the Cretaceous and now.
Note how much further north the
Antarctic Peninsular is now – almost in contact with Argentina.
Additionally, according to
O’Herrle et al. (2015), the ocean temperatures averaged 350C.
Therefore, the ocean temperature near the poles would have been perfect for
marine reptiles.
Next, I wanted to know where
exactly, was Seymour Island and what the site was like. Consulting Reguero
(2019), I was quite surprised to find that a large number of palaeontological
surveys had taken place on the rocky
island over the last 30 years, and that it was at the tip of the Antarctic
Peninsular:
Map of Antarctica adapted to show
Seymour Island, from Maps of Antarctica (2001)
Reading around I found a paper by
Reguero (2019) that provides detail on the occurrence of marine reptiles on
Seymour Island:
“The López de Bertodano Formation
(LBF) contains a fully marine fauna indicative of open marine conditions. The
LBF has been the subject of extensive paleontological and stratigraphic studies
over the last 30 years and contains the best shallow marine record in the
Southern Hemisphere of the K/Pg mass extinction event.
Locality IAA 10/13 is very
productive and has a significant high geo-heritage value. Mesozoic marine
reptiles, mosasaurs and elasmosaurid plesiosaurs (Figure 9) are important
components of the Cretaceous marine deposits of Unit 9 of the López de
Bertodano Formation.”
Geological map of Seymour Island adapted from Reguero (2019)
and Montes et al. (2013). Original caption reads: “Figure 7 Schematic
geological maps (after Montes et al., 2013) of key fossil vertebrate sites in
Seymour Island, north eastern Antarctic Peninsula. Position of the Cretaceous
Paleogene boundary (K/Pg) is indicated.”
Reguero (2019), also provides a
nice panoramic showing the location of site IAA10/13, where many of the
mosasaur fossils originated:
Original caption reads: Figure 8.
General view of the uppermost horizons of the López de Bertodano Formation at
Seymour Island showing the K/Pg boundary between units 9 (Late Maastrichtian)
and 10 (Danian). Localities IAA 10/13 and 11/13 are indicated.
Having taken the time to research
the background of the picture of the giant egg that sparked my interest in this
topic, I have become aware of a hugely important palaeontological site. Again,
I feel the wonder of discovery, and although it is just a virtual and therefore
vicarious experience, it makes me proud to call myself a Scientist and
reaffirms my joy at seeking the interconnectedness of all things.
Scientists searching for fossil
locations on Seymour Island in 2011, from CBC News (2020). Original caption
reads: “People hike during an expedition on Seymour Island in Antarctica in
this picture taken in 2011, when the egg was found. (Rodrigo Otero/University
Of Chile/Handout”
Sadly, there is a the darker side
to the story. Reguero (2019), highlights the fragility of the site with respect
to international tourism. In particular, he raises concerns that Antarctic
cruises may be responsible for destruction of key samples through unauthorised
fossil collection on the island. Secondly, although we all understand that the
Antarctic environment is also under threat from global warming, I had not
realised how dire the situation is. Mehar (2020) reports that once again a new
Antarctic record high temperature of 20.750C was recorded
on Seymour Island on February 9th this year.
There is, however, a big caveat
to this story. In the same issue of Nature was a paper by Norell et al. (2020).
This provides evidence that early dinosaurs eggs such, as those laid by Protoceratops
and Mussaurus sp. were soft shelled. While this is a possibility, Legendre, did
point out that all the dinosaurs found in Antarctica so far have been too small
to produce the egg in question. I therefore, think that, the jury is still out
on the identity of the giant egg layer.
References:
BBC (2020) “Mystery egg likely belonged to giant sea
reptile, scientists say” at: https://www.bbc.co.uk/news/science-environment-53085318
accessed 24.06.20
CBC News (2020) “Mysterious Antarctic fossil identified as
giant egg” at: https://www.cbc.ca/news/technology/giant-egg-antarctica
accessed 26.06.20
Crame JA, Beu AG, Ineson JR, Francis JE, Whittle RJ, Bowman
VC (2014) The Early Origin of the Antarctic Marine Fauna and Its Evolutionary
Implications. PLoS ONE 9(12): e114743. https://doi.org/10.1371/journal.pone.0114743
El Comercio (2020) “Scientists reveal the mystery of a
famous fossil found in Antarctica” at: https://elcomercio.pe/tecnologia/ciencias/cientificos-revelan-el-misterio-de-un-famoso-fosil-hallado-en-la-antartica-noticia/?ref=ecr
accessed 24.06.20
forskning (2020). “Mysterious Antarctic fossils were huge
eggs” at: https://forskning.no/dinosaurer-ntb-paleontologi/mystisk-antarktis-fossil-var-enormt-egg/1702225
accessed 24.06.20
J. O. Herrle, C. J.
Schroder-Adams, W. Davis, A. T. Pugh, J. M. Galloway, J. Fath. Mid-Cretaceous High Arctic stratigraphy,
climate, and Oceanic Anoxic Events. Geology, 2015; 43 (5):
403 DOI: 10.1130/G36439.1
Live Science (2016) “Cretaceous Period: Animals, Plants
& Extinction Event” at: https://www.livescience.com/29231-cretaceous-period.html
accessed 25.06.20.
Legendre, L.J., Rubilar-Rogers, D., Musser, G.M., Davis S
N., Otero R.A., Vargas A.O., and J.A. Clarke. (2020) A giant soft-shelled egg
from the Late Cretaceous of Antarctica. Nature (2020). https://www.nature.com/articles/s41586-020-2377-7
Mehar, P. (2020) Tech Exploist, “Antarctica has recorded a
new record temperature yet again” at: https://www.techexplorist.com/antarctica-recorded-new-record-temperature/30077/
accessed 26.06.20
Montes M, Nozal F, Santillana S, Marenssi S, et al. (2013).
Mapa Geológico de la isla Marambio (Seymour) Escala 1:20.000 Primera Edición.
Serie Cartográfica Geocientífica Antártica. Madrid-Instituto Geológico y Minero
de España; Buenos Aires-Instituto Antártico Argentino.
Newsround (2020). “Fossil of giant egg belonged to
prehistoric sea reptile” at: https://www.bbc.co.uk/newsround/53090752
accessed 24.06.20
Norell, M.A., Wiemann, J., Fabbri, M. et al. The first
dinosaur egg was soft. Nature (2020). https://doi.org/10.1038/s41586-020-2412-8
accessed 25.06.20
Reguero, M. A. (2019). Antarctic
Paleontological Heritage: Late Cretaceous
Paleogene vertebrates from
Seymour (Marambio) Island, Antarctic Peninsula. Advances in Polar Science Vol.
30 No. 3: 328-355 doi: 10.13679/j.advps.2019.0015
No comments:
Post a Comment