Bandringa
Name: Bandringa.
Phonetic: Ban-dring-ah.
Named By: R. Zangerl - 1969.
Synonyms: Bandringa herdinae.
Classification: Chordata, Gnathostomata,
Chondrichthyes, Elasmobranchii, Ctenacanthiformes.
Species: B. rayi (type).
Diet: Carnivore.
Size: Adults up to about 3 meters long.
Known locations: USA, Illinois - Carbondale
Formation. Pennsylvania. Ohio.
Time period: Moscovian of the Carboniferous.
Fossil representation: Numerous individuals, some
almost complete. Adults and juveniles both known.
Many
prehistoric sharks
look just plain weird, and Bandringa
is certainly
no exception. The immediate stand out feature of this shark is the
long spoonbill shaped snout that accounts for a good portion of the
sharks total length. Some fish we know today do have such a snout,
and they use it for digging out small aquatic animals that are
otherwise buried in soft sediment. With this comparison in mind it is
easy to envision Bandringa sharks hunting in a
similar manner.
Indeed, the mouth of Bandringa is orientated to
face more downwards
as opposed to forwards like in most other sharks.
Bandringa
was first named in 1969 by R. Zangerl with the type species as
B. rayi. Then ten years later Zangerl named a
second species,
B. herdinae. What stood out about these species
was that at up to
three meters in length the type species B. rayi
was much larger and
living in freshwater. B. herdinae however was
tiny in comparison,
only about ten to fifteen centimetres in length and living in
saltwater. Then in 2012 a new study by Lauren Cole Sallan and
Michael I Coates was penned and later published online in 2014, and
this would change a great deal about what we thought we knew about the
Bandringa genus.
The
main focus of the study by Sallan and Coates was the marine (salt
water) specimens of B. herdinae. For them the
problem with the
species was not the small size of the individuals, but the simple
observation that all known specimens of B. herdinae
were either
juveniles or egg cases, there were no known adults. Then in looking
at B. rayi, only adults had been attributed to
the type species.
Then by charting the known geographical locations for fossils, the
result was quite simple, Both B. rayi and B.
herdinae are in fact
one and the same species. Immediately this means that Bandringa
herdinae is now a synonym to Bandringa rayi,
but this also reveals a
very interesting and startling theory about this shark.
Adults
of Bandringa have so far always been found in
freshwater deposits. In
itself this is not unusual, many prehistoric sharks lived in
freshwater, and even today some cartilaginous fish, including the
bull shark (Carcharhinus leucas) and some
stingrays are known to
enter and swim up freshwater river systems. But then why are the
juveniles only found in freshwater? The simple answer is that this is
one of the earliest confirmed cases of sharks actually migrating to a
nursery ground.
It
is not unknown for sharks to migrate to specific areas in order to lay
eggs or give birth to live young, it is after all behaviour that is
well documented. Even the fossil record supports this behaviour with
juvenile teeth of the giant shark C.
megalodon being much more
common than adult teeth in some shallow water environments such as
around central America and off the coast of Maryland, USA. What is
unusual here though is that the adults that are living in freshwater
are choosing to migrate from freshwater into saltwater.
Freshwater
to saltwater migration is known in some fish, best known of which is
the European eel (Anguilla anguilla) which
starts out life in the
Sargasso Sea before migrating into freshwater rivers and lakes where
they live for about five to twenty years before finally returning to
the Sargasso Sea to spawn. However up until the study by Sallan and
Coates such migration was completely unknown for sharks. Eels are
known to die in the Sargasso after spawning, but this may not have
been the case for Bandringa. Firstly sharks are
not known for dying
en masse after laying eggs, and the lack of adult fossils in with
the juveniles would indicate that adults would return to freshwater
ecosystems after egg laying.
One
question to be asked is why would Bandringa choose
to establish nursery
grounds in saltwater? Well so far all juveniles of Bandringa
were in
shallow coastal waters which would provide a number of benefits for
rearing young sharks. Shallow coastal waters usually have a
proportionately broad abundance of life with an almost unlimited number
of small aquatic animals, from worms, to shrimp and even some kinds
of fish buried in the soft sandy sediments. When an animal like a
shark is young large amounts of small animals is exactly what you need
to grow large fast. Coastal waters also restrict the movements of
larger predators enabling a greater chance of survival for small
juveniles. Coastal waters also tend to be much warmer, being more
easily heated by the sun and perhaps even being warmed by oceanic
currents, raising metabolic rates and increasing the rate of growth
than what would have been experienced in colder rivers systems.
The
same soft sediments that would have contained large amounts of prey
animals for juvenile Bandringa have also offered a
high level of
preservation in some of these juveniles with even soft tissues being
preserved. These have helped confirm the presence of some features
such as the downward facing mouth, as well as revealing new ones not
preserved in adults due to different fossilisation factors not
preserving them. These include small needle-like spines on the head
and cheeks, but also the presence of a vast array of electro
receptors that are on the snout. This confirms that like in other
sharks with long snouts, the snout of Bandringa
primarily served as a
sensory organ detecting buried prey, before then being used to dig
them out.
The
fact that we now know that one genus of shark migrated from freshwater
to saltwater to raise young in a nursery ground now raises the
question, how many other ‘freshwater’ sharks migrated to salt
water nursery grounds?
Further reading
- Bandringa rayi: A New Ctenacanthoid Shark
form the Pennsylvanian
Essex Fauna of Illinois. - Fieldiana Geology 12:157-169. -
R. Zangerl - 1969.
- New Chondrichthyes from the Mazon Creek fauna (Pennsylvanian)
of Illinois. - Mazon Creek Fossils 449-500. - R. Zangerl
- 1979.
- The long-rostrumed elasmobranch Bandringa Zangerl, 1969, and
taphonomy within a Carboniferous shark nursery. - Journal of
Vertebrate Paleontology vol 34, issue 1 - Lauren Cole Sallan
& Michael I Coates - 2014.
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