Jelly beginning to Go

Weather in the northern part of the UK has been unseasonably cold with temperatures still dipping near to freezing during the night and an chilly wind blowing for the last couple of days.  There has not been a great deal of sign either, just showers and a very cloudy, grey sky with little breaks to permit the sunshine through.

This inclement whether has not seemed to have hindered the progress of the tadpoles, we think all those that are actually going to hatch have now hatched.  The first brave individuals have been spreading out across the pond, by Wednesday of this week they had ventured to the back of the pond and a few could be seen hanging from the pond sides a couple of inches under the surface.  By today, all parts of the pond have been conquered and some of the first of the tadpoles to hatch have spread themselves out amongst the pond weed and other hiding places.

Tadpoles

Incidentally, a large number of tadpoles seem content to remain in the projective jelly.  Perhaps these were amongst the last to emerge and therefore still have the remnants of the egg  yolk in their stomachs to sustain them.  They will have no need to leave the jelly until they have to seek food.  The jelly itself is now very discoloured and only a few of the spherical former eggs can be made out in this grey mass.

The Remnants of the Protective Jelly

Picture credit: Everything Dinosaur

The picture shows the grey, discoloured jelly in which a group of tadpoles can be clearly seen.  Other tadpoles, perhaps the first ones to hatch have now dispersed throughout the pond.  Perhaps those tadpoles remaining close to the jelly have still got the remnants of the egg yolk in their stomachs and so have not been forced to leave the protective jelly environment in order to find food.

Looking for Frogs

Members of the Everything Dinosaur team have not observed any frogs in the pond over the last week.  Even the small, male frog seems to have gone.  As far as we know adult Common Frogs tend not to feed in water, so the frogs may have left the pond to seek food.  Perhaps staying close to the pond or moving further out into the grassy area at the back of the yard.

Blackbird Feeding

Talking of food, we have worked out what has been happening to the Rams-horn snails that inhabit the pond.  A male blackbird was observed snatching up a snail from the shallows and attempting to fly off with it.  The snail was found in the middle of the yard in a battered and bloodied state.  It was returned to the water and seems to have survived its ordeal.

We wonder whether the blackbird is going to attempt to snatch a tadpole, they would certainly be more difficult to catch, but at least there is no hard shell to deal with.

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Nearly all Tadpoles Hatched

The weather over the last week or so has been unsettled, but fortunately we have not had any snow showers, just rain and sunny intervals.  The majority of the tadpoles have now hatched, although there are still several still within their transparent egg cases, but these are very active and we suspect that the remainder of the tadpoles will hatch in the next few days.

First Hatchlings

The first hatchlings emerged from the spawn that was in the middle and at the very top.  These animals hatched first perhaps due to the fact that the being at the top they received most sunlight and therefore were kept warmer, being in the middle of the spawn may have helped keep these embryos insulated and therefore protected better as the surface water cooled in the chilly nights.

Frogspawn is Hatching

By Thursday of this week some of the first hatched tadpoles had left the spawn and could be seen hanging vertically from pond weed and the fine fronds of algae, one of our team members remarked that they looked like little music notes hanging from the staves on a score sheet.  By today, Sunday,  a number of tadpoles have made the break from the spawn and are seeking shelter amongst the pond weed.  This might be as the yolk that nourished them once they had emerged, (the slightly brown bulge in the belly of the tadpole), has now been used up and the tadpoles are beginning to seek their own food.  Their black colouring whilst being effective in helping to absorb heat, does not provide them with a lot of camouflage in amongst the green Elodea.

Most of the Tadpoles have now Hatched

Picture credit: Everything Dinosaur

Tadpoles Have Hatched

The pictures shows that the majority of the tadpoles have now hatched.  They remain congregated around the spawn, especially on top of it where it is warmest.  Over the next few days it is likely that the tadpoles will disperse throughout the pond.

We noticed that during daylight hours the “clump” of hatched tadpoles spread out to form a rough doughnut shape, then as it grew darker and presumably colder the tadpoles seemed to gather together again, concentrating as a mass on top of the spawn again.  Whether this is an instinctive response to less daylight in order to keep warm so as to survive the colder night; or whether this is a strategy to avoid predation is unclear.

One adult frog has been spotted in the pond this week, the small adult male.  He has kept a low profile staying on the periphery of the pond away from the hatching tadpoles.  He has preferred to remain in cracks on crevices around the pond’s edge during daylight hours.

The Tadpoles have Started to Hatch

Great excitement this week in the pond as the tadpoles have begun to hatch.  The first signs of movement were detected on Wednesday morning.  This was on the 2nd of April, just 17 days after the spawn was laid.  Given the quite cold weather that we had been experiencing we were surprised how quickly the tadpoles developed.  However, it is worth noting that despite the cold weather and the chilly pond water, the spawn had been laid in a central position in the pond and this allowed the spawn to get what sun there was for most of the day.  Also, the jelly swells and becomes buoyant thus permitting the spawn to stay at the surface, again helping to warm the eggs.  Sat on their bed of pond-weed (Elodea) the spawn has been fairly quick to develop.

The Latest Picture of the Frog Spawn

Picture Credit: Everything Dinosaur

Tadpoles Starting to Hatch

By Wednesday lunchtime, team members were taking turns to watch the spawn, every now and then a little tadpole would move slightly, either curling or uncurling.  By Friday the movements had become stronger and more frequent.  The embryos had assumed a more tadpole-like shape and could be seen moving inside the egg membrane.

The first hatchlings were observed on Saturday afternoon (5th April).  The tadpoles have developed a definite head end (a round bulge) and a basic tail.  However, it will be a few days before they are swimming freely.

At this stage, the muscular and circulation systems are developing, the gill arches either side of the head are now forming.  The tadpoles hatch at around the time these gills are able to function.  The eyes and mouth are not fully developed and there is an adhesive organ present on the top of the head.  This permits the tadpole to attach itself to pond weed and remain there until further changes have taken place.

Spotting the External Gills

If you can get close enough and look very carefully at a tadpoles head from the top downwards (called a dorsal view by scientists), you should be able to see two small tiny bumps, one on each side of the head.  These are the external gills and they should be visible for about 12 days or so.  Over this period a fold of skin known as the operculum develops on the first branchial arch just in front of the external gills.  It grows backwards until the external gills are covered.  The eyes and mouth begin to develop.

The operculum does not close up completely, a single hole (called a spiracle) remains on the left side of the body.  Water is taken in through the newly formed mouth, passes over the internal gills and is expelled through this spiracle.  By this time the mouth should have developed definite jaws and the adhesive organ on top of the head should have almost completely disappeared.

The digestive system should have expanded (for the first few days after hatching the tadpoles live on the remains of the yolk from the egg – this can be seen as a bulge in their tummies).  Soon the tadpoles will have acquired the ability to swim and they will have started their journey towards becoming frogs – metamorphosis.

Frog Observed

Only one frog has been observed in the pond during daylight hours.  We think this is a male, it has been seen around the spawn and some of us have jokingly speculated that this might be the “expectant father” waiting for his babies to hatch.  We know that many species of amphibian demonstrate some care for their offspring.  For example, male Midwife toads (Alytes obstetricans) gather up the eggs once they have been fertilised and they carry them around on their back legs, but we are not aware of any paternal instinct being demonstrated by Common Frogs (R. temporaria).

Much of the country has been covered in a blanket of snow, this morning.  Typical of the British weather, no snow in winter and then on the 5th April we get some.  This picture was taken of the area behind the office this morning.

Oh to be in England now that April’s Here!

Picture credit: Everything Dinosaur

Frog Blog – Week 3 – Little Black Commas

Our frog spawn in the office pond is approximately 2 weeks old and despite the very bad weather we have experienced in the last few days there are signs that things are beginning to happen.  The weather has been quite cold, although it is hard to say that it has been unseasonal, with the early Easter it is easy to forget that we are still in March and on the whole the winter has been relatively mild.

Only one warm sunny day over the last week, we have had heavy rain and blustery showers but fortunately not too many bonfires from the construction workers nearby polluting the water with ash drifting into the pond.  The water temperature remains cold but a close examination of the frog spawn shows that the little black dots we started with inside their protective jelly are beginning to change.  The majority of them are showing some definition, we have a lot of “little black commas”, the eggs are showing signs of development and we can see the start of a defined head end and a tail.

A Close up of the Frog Spawn

Picture credit: Everything Dinosaur

Despite the cold weather the spawn is beginning to change, the picture shows that the embryos are developing, becoming more elongated and showing signs of progress.  We suspect that the water temperature will still be determining the rate of development, perhaps the warmer weather forecast for next week will help the spawn to hatch in the next 10 days or so.

Only one adult frog has been observed in the pond during office hours.  Ironically, it has taken to sitting next to the frog spawn using the surround pond week (Elodea) to support its weight.  We were a little concerned about this frog, normally frogs confine themselves to the margins of the pond, where there is more cover.  However, this frog, (we think it is a male), seemed quite happy to sit amongst the pond week in the centre of the pond.

Some of us started to speculate that this was the father, checking on his family to be, but this was probably a bit too fanciful for the more rational members of the team.  Amphibians do adopt many strategies when it comes to looking after and raising their young.  It is not just the so called higher forms of life, the mammals and birds that adopt a benevolent attitude to their offspring.

Frog Blog Week 2 – Tiny Black Dots – no movement yet

We have been keeping a careful watch on the frog spawn in the office pond.  The frogs spawned for the first time in our pond last Sunday, so we have decided to keep an observational record of how the tadpoles get on.  Four frogs were in the pond, we suspect one female and three males.  Identifying males and female frogs is not our strong suit, but we estimated the ratio of boys to girls based on the fact that one frog was bigger than all the rest, so we speculated that this was the female.

During the breeding season, the male frogs develop pronounced dark pads on their first digits of the hand.  These pads are present all year round but swell up in the breeding season and help permit males to grip the usually larger females during mating.

Also, the smaller frogs croaked and we think that only the males do this.  The sound does not carry very far, it is certainly not the loudest frog croaking we have heard, many tropical frogs would easier drown out the noise made by these Common Frogs as these animals lack a vocal sac to help the sound resonate.

By Monday the pond was empty and the adult frogs had left, perhaps to hunt in the surrounding rockery, we did not expect to see all four of them together again, but surprisingly on Wednesday all four frogs (one big one and three smaller ones) returned to the pond and there was a lot of activity again but no further spawning.

Frog Blog – Week 2

Picture credit: Everything Dinosaur

The weather in the north-west of England has been particularly cold over the last few days.  We have experienced strong gales, hail storms and even some snow.  This is the earliest Easter for 95 years, we suspect that the development of the eggs will be dependent on the water temperature, so it may take a while for the embryos to start to develop.  The jelly surrounding the tiny black dots (each no more than about 2mm across), has swollen and this helps the spawn stay afloat and close to the surface of the pond.  In this way the spawn can be warmed by sunlight to the greatest extent (surface water of ponds tends to be warmest).

We have been concerned this week, as there has been a lot building work going on around us and the construction teams have lit several bonfires.  This has led to large deposits of ash and other debris getting blown into the pond.  The silvery “scum” surrounding some of the spawn that can be seen in the picture, is ash that has drifted into the pond, we are not sure what effect this pollution will have on the spawn’s development.

We will have to keep you posted on the spawn’s progress…

Science Bit

Amphibians were the first truly semi-terrestrial animals, evolving in the late Devonian and becoming more numerous and diverse during the Carboniferous and Permian periods before suffering in the Late Permian mass extinction.  At the end of the Permian there were about 35 known families of amphibians, many of them considerably larger than their modern counterparts.  After the mass extinction event, at the beginning of the Triassic (248 million years ago), there were about 10 families remaining.

About 70 percent of all the types of amphibians around at the time of the Late Permian went extinct.  Today, there are about 4,300 species of amphibians in the world (mostly frogs), but the amphibian class has never fully recovered from the Permian mass extinction.  Amphibians were at their most diverse (in terms of families) and spectacular something like 50 million years before our ancestors (the first mammals) evolved.

Frog Blog – We have Frogspawn in the Office Pond!

Four years ago whilst some of us were away in Canada working on some palaeontology projects, arrangements were made to build a small pond behind the office.  We had managed to persuade one of the designers of the animal enclosures from Chester Zoo to undertake the work and to produce a water feature with a seating area so that we could take our breaks and watch any wildlife that might be attracted to the water.

The work took about a week and our designer friend built two small ponds in a corner of the paved area behind the offices.  He even cleverly cast some ammonite fossils and installed these in various places in the rockery to make us palaeontologists and fossil collectors feel at home.

Using his expertise, our designer chum shaped the pond so that there would be plenty of shallow areas and margins, important when wanting to create a natural pond.  In addition, he advised on the planting and even provided the oxygenating water plants, the marginals and the lilies.  His final touch was to provide us with a population of snails to help maintain the pond.  We have two species at the moment a small pond snail and rams-horns (Planorbis sp.)

The Pond when it was First Built and Landscaped

Picture credit: Everything Dinosaur

Over the last few years this water feature has proved popular with the local birds who use the shallows as a bird bath and we have been fortunate to have damsel fly larvae as well as water boatmen take up residence.  Although, frogs had been seen in the vicinity and team members were able to count 3-4 individuals at anytime in the summer, (we even had a particularly large one that was nicknamed “Freddie” after Andrew Flintoff the England cricketer who took up residence in 2005);  no breeding had taken place.

However, this morning, whilst returning to the office to sort out some Everything Dinosaur paperwork, a quick check of the pond and hey presto – our first ever frogspawn was spotted.  There had been a number of frogs seen in the pond over the last month or so and apparently last night (a particularly dark and wet night) the spawning took place.

From the amount of spawn produced, we estimate that it is from just one female.  A total of four frogs have been observed in the pond this morning (the back of one can be seen partially hidden by the spawn to the right of the picture).  We have speculated that it is the female with her three suitors.  The frogs are Common Frogs (Rana temporaria), one of three species of frog that are found in the UK (excluding any escaped exotics).  Like all native British amphibians and reptiles they are a protected species.  With much of their habitat destroyed, areas such as landscaped offices and gardens are becoming increasingly important to them.

It is nice to know that after nearly 5 years the frogs have felt comfortable enough with our pond to breed in it, we are playing a small role in the conservation of this species and amphibians need all the help they can get, as they are globally the most endangered and threatened of all the animal classes.

Frogs are special to many of the Everything Dinosaur team members, they are very specialised Lissamphibians (the group of amphibians that includes frogs, toads, newts, salamanders and the leg-less caecilians).  The Lissamphibians were present in the Palaeozoic and it is thought that frogs evolved sometime in the Triassic,  however, the fossil record for frogs is very patchy to say the least.  They were probably relatively abundant during the Age of Reptiles, but the lack of fossil evidence inhibits palaeontologists when it comes to working out Anura (frog) evolution.  Fossil bones have been recorded from a number of Mesozoic sites but they are usually isolated fragments, ilia, humeri (limb bones) and the more robust skull elements.

Occasionally, fossils are found that demonstrate that some of these amphibians would have been formidable hunters, even capable of eating baby dinosaurs and young crocodilians.  The discovery of a giant frog from Mesozoic deposits in Madagascar is evidence of this.

To read about the discovery of fossils of a giant Cretaceous frog: Giant Frog from Madagascar.