if you went onto a MSc degree after your BSc in Zoology here – the attached job at Chester Zoo might be of interest
if you went onto a MSc degree after your BSc in Zoology here – the attached job at Chester Zoo might be of interest
You should all know that velociraptors weren’t really like they were portrayed in ‘Jurassic Park’. They were an awful lot smaller, they had feathers, and they probably weren’t quite so smart. But they *were* nasty predators. Or were they? This BBC article describes a recent fossil suggesting that Velociraptor was also a scavenger, because of bite marks on a Protoceratops skeleton.
Original article in Palaeogeography, Palaeoclimatology, Palaeoecology (University needed to get past abstract):
2007 Science article showing the presence of quill knobs in velociraptors (open access); 2011 Science article showing dino feathers in amber (Uni needed to get past abstract); great blog post on the feathers in amber article at WhyEvolutionIsTrue. More on velociraptors, including gratuitous but potentially correct picture:
Great amateur video of phantom crane flies, which have very cool black and white legs. Phantom crane flies – Bittacomorphids of the Family Ptychopteridae – are found in North America; their maggot has an amazing extensible respiratory siphon, which means it can breathe under water (they generally live in mud or on the edges of streams). And the adults don’t have ocelli.
Here you can find out all you wanted to know about Ptychopteridae.
This article shows that 700 species of crane fly link S America and Australasia, revealing origins going back to the Permian.
The most dramatic early eyes known up to now have been, not surprisingly, the calcite eyes of trilobites. These mineral lenses, formed into a compound eye, lend themselves to fossilisation, plus there are millions of fossilised trilobites lying around in rocks. In the latest issue of Nature, there is a dramatic description of an incredibly tiny fossil from Australia that reveals that at least one organism from the early Cambrian – 515 MY ago – had eyes that were incredibly complex and modern.
The work was carried out by a group from Australia (with help from the Natural History Museum in London), led by Michael Lee and John Paterson. They studied rocks from the Emu Shale in Kangaroo Island in South Australia. This is a famous layer of shale which contains some exceptionally preserved organisms, and is a useful comparison with the Burgess Shale in Canada and Chenjiang in China.
The researchers found a number of isolated fossilised eyes that had apparently come from some kind of arthropod. They are about 7 mm long, are curved, and are composed of up to 3,000 individual lenses or ‘ommatidia’. They are not made of calcite, and they are not from a trilobite. They are incredibly beautiful. The eye of the robber fly is included for comparison. These were NOT from a fly! They are from a marine organism!
The fossilised eyes were all about the same size, suggesting they had all come from adults. Sadly, there are no clear animal remains associated with them. They presumably became separated from the body either because the animals were predated in some odd way (predators spitting out the eyes?) or because they are in fact the cast of the organism as it grew in size. They say:
“One possibility is that the fossils reported here are of previously shed corneas. The corneal surfaces of living arthropods detach during ecdysis and remain loosely connected to the rest of the exuvia; moulted corneas might be more prone to decay and thus more susceptible to early diagenetic mineralization (in this case phosphatization) than complete eyes attached to intact organisms.”
The fine detail of the fossils made it possible to calculate the precise distance between the ommatidia. Note that the lenses are hexagonal, just as in modern arthropods:
The authors then go on to look at the optics of these eyes, in terms of the density of the ommaditidia. And report that this kind of complexity and density has previously been found only in the the Ordovician, around 40 MY later.
So – what animal do they belong to? They are too small to be from everyone’s favourite Cambrian predator, Anomalocaris. The authors reckon that they could be from a bivalve arthropod found in the Emu Bay shale called Tuzoia:
The large, unnamed Tuzoia species from the Emu Bay Shale has stalked compound eyes that are ovoid to round and 6–9 mm in diameter: very similar to the fossil eyes described here. However, no detailed structure of the visual surface is preserved in the articulated eyes of Emu Bay Shale or Burgess Shale Tuzoia specimens.
Here’s a picture of Tuzoia:
The authors conclude:
The specimens described here represent the first microanatomical evidence confirming the view that highly developed vision in the Early Cambrian was not restricted to trilobites. Furthermore, in possessing more and larger lenses, plus a distinct bright zone, they are substantially more complex than contemporaneous trilobite eyes, which are often assumed to be among the most powerful visual organs of their time. The new fossils reveal that some of the earliest arthropods had already acquired visual systems similar to those of living forms, underscoring the speed and magnitude of the evolutionary innovation that occurred during the Cambrian explosion.
How do we know what to accept as fact? This perpetual epistemological issue is only heightened by the internet and CGI. Here’s another enigma. A seagull picks up a video camera and zooms round night-time Nice. But is it real? How could we know?
Context is everything. We know how being very small alters the ways physical factors are felt – eg through small insects being stuck in water tension, the power of Brownian motion, or the scaling effects of falling from a height. But what about temporal context? What are the effects of temporal factors on the way that physical effects are perceived? Here’s a great mechanical example – a cymbal being struck. But what happens if you perceive that movement at 1000 frames per second? You realise that something rather amazing has happened. How might this affect our understanding of biological processes?
Spotted on Lucas Brouwers’ Twitter feed (@lucasbrouwers), this great video of a Powelliphanta snail from New Zealand snarfing an earthworm. Keep your eye on the video – it all happens incredibly quickly! Odd thing to say about a snail, but true.
According to this PDF from the NZ Department of Conservation, Powelliphanta snails can grow up to 9 cm across and are nocturnal. They are also endangered, primarily because of human activity, although a recent survey suggested they were making a slight recovery. According to Wikipedia, “There are 21 species and 51 subspecies within the genus. The relationship between the species is complex, and it has been suggested that the group Powelliphanta gilliesi-traversi-hochstetteri-rossiana-lignaria-superba forms a ring species.”
There are other carnivorous snails on NZ, including the Rhytididae, which seem to be particularly vicious, according the NZ Dept of Conservation:
“They can eat other snails by biting their heads off and then they carry them to a quiet spot on the back of their foot where they insert their tails up into the prey’s shell. The tail secretes a liquid that slowly dissolves the prey’s flesh and the calcium from its shell. The Rhytida snail then absorbs the dissolved nutrients. It can take the snail several days to actually complete such a meal.”
One rhytidid snail, Wainuia urnula urnula, seems to use a similar rapid action to that seen in Powelliphanta and probably has the same basis. According to Murray Efford in The Journal of Molluscan Studies, “In the laboratory, W. urnula urnula captured landhoppers by rapidly everting the TVU-section odontophore beneath the prey and immediately drawing it into the mouth in a single action.”
So that’s how they (probably) do it. No sucking, just incredibly rapid movement, using that odontophore…
Anomalocaris – literally “unusual shrimp” – was first identified in 1892 by Joseph Frederick Whiteaves from mid-Cambrian deposits in British Columbia. It looked pretty much like this fossil, and was thought to look something like the drawing below.
One of the many things that was odd about this “shrimp” is that it never seemed to have a body or a head. All they ever found was the “tail”. There are plenty of these fossils about, and you can pick them up on eBay for a few hundred dollars (not recommended unless you are certain of provenance, that appropriate permission has been obtained, etc).
As is now well known, in 1985 Harry Whittington in Cambridge and Derek Briggs solved the mystery of the missing head of Anomalocaris, and at the same time also clarified the nature of Laggania, which was thought to be a non-descript sponge, and Peytoia, which was seen as a pineapple ring-like jellyfish thing:
They all turned out to be part of the same animal – a vicious predator which is now thought to be related to the arthropods. It still bears the name Anomalocaris, but what was thought to be the body of the “strange shrimp” is in fact a predatorial claw, while the “legs” are thorny projections. Peytoia is the mouth of Anomalocaris, while Laggania turned out to be its body:
This was part of the Whittington/Briggs/Conway Morris redescription of the Burgess Shale animals which led Stephen Jay Gould to write Wonderful Life, and which is still the source of much debate today. At up to 60 centimetres long, Anomalocaris, and related members of the “great appendage” group are thought to have been the top predators in the Cambrian seas, spearing passing prey with their raptorial claws.
Here’s a nice model of Anomalocaris, from the Manchester Museum:
Here’s a close-up (annoyingly, I couldn’t get to see its mouth) – you can see a Burgess Shale fossil of Waptia below it:
Indeed, these predators are now known to have extended their domination of the seas into the Devonian, as shown by this recently discovered fossil of Schinderhannes bartelsi from 407 MY ago (Kühl et al. 2009):
Many reconstructions of great appendage predators – and in particular of Anomalocaris – show them munching away on trilobites. This video from Phleschbubble is particularly striking (Anomalocaris turns up at around 50 seconds. NB the file is pretty large so may take some time to download)
And this great drawing by Sam Gon III shows:
“two Anomalocaris canadensis converging on an Olenoides trilobite. This doesn’t necessarily imply that they engaged in cooperative hunting. The second Anomalocaris could have merely been attracted to the commotion caused by the activities of the other. It would be interesting to consider what kinds of agonistic behaviors occurred between individuals, and whether they engaged in any specialized territorial or courtship behaviors.”
This video (sorry about the music!) not only shows one eating what looks like a trilobite, it also has a pair engaging in either mating or intra-sexual conflict. This is cool but, of course, entirely gratuitous! NB the “streamers” seen on these reconstructions are typical of both Anomalocaris saron and a related anomalocaridid, Amplectobelua symbrachiata.
So, if you believe the videos (and you shouldn’t), the main diet of anomalocaridids would appear to be trilobites. But for the last couple of years Professor “Whitey” Hagadorn of Amherst College has been arguing that the evidence just isn’t there. In 2009 he presented a paper to “Walcott 2009”, a conference to mark the centenary of the discovery of the Burgess Shale deposits, and then three weeks ago he presented more data to the Geological Society of America’s annual meeting.
In an interview with Wired magazine, Hagadorn points out that there’s no direct evidence (e.g. trilobite traces in anomalocaridid guts, or clear anomalocaridid coprolites containing trilobite bits for example), and, as he explains in his 2009 abstract, while the teeth in the mouthparts look pretty sharp (see the picture above):
“Anomalocaridid mouth plates and their tips are never broken, nor are tips worn. If plates were hard, and were used to manipulate, puncture, crush, or masticate biomineralized prey, they would be expected to show evidence of abrasion or breakage. Absence of this evidence is striking given the frequency (0.01-1%) of healed malformations in extant marine arthropods, most of which are due to prey manipulation or feeding. Moreover, anomalocaridid plates and their biting tips are commonly wrinkled, exhibit preburial shearing and tearing, and mantle or are deformed by biomineralized fossils such as brachiopods, trilobites, and Scenella. Plates are preserved as organic carbon and exhibit fracture patterns typical of desiccating arthropod cuticle. Thus anomalocaridid plates, including their tips, were unmineralized and pliable in life.”
Furthermore, in his latest presentation, Hagadorn has made a 3-D reconstruction of the mouth of Anomalocaris and found that not only was the mouth soft, it also couldn’t completely close. So – says Whitey – Anomalocaris and its fellows could do no more than suck nastily on stuff.
I’m neither a paleontologist nor do I do biomechanics, so will find it hard to judge when the data are eventually published (it may be in review, though there’s no trace of it on his website). On the basis of Hagadorn’s talks, opinion for the moment seems to be divided as to whether he is right. That may change when his work is published.
However, let’s assume he is right, and anomalocaridids didn’t eat trilobites. That simply begs the question – who did eat them? Because one thing is certain – those trilobites did get munched by something. There are apparent coprolites (= fossilised turds) that contain trilobite bits, as seen in this picture by Vannier & Chen (2005):
Furthermore, there are plenty of trilobite fossils that have chunks taken out of them, as seen here in this reference to the work of Babcock & Robinson (1989 – taken from my next Evolution of Invertebrates lecture):
The final answer will come, I suppose, when someone finds a clear association between a predator and a consumed trilobite. Until then, studies like that of Whitey Hagardorn are the best we can do.
h/t: Ray Moscow
References and links:
Babcock, L.E. and Robinson, R.A. 1989. Preferences of Palaeozoic predators. Nature, 337, 695-696.
Kühl, G., Briggs D E. G. & Rust J (2009) A great-appendage arthropod with a radial mouth from the Lower Devonian Hunsrück Slate, Germany. Science 323:771-773
Vannier J. & Chen J. (2005) Early Cambrian food chain: New evidence from fossil aggregates in the Maotianshan Shale Biota, SW China. Palaios 20:3-26.
Anomalocaris homepage by Sam Gon III – this contains loads of anatomical and taxonomic information, as well as references, links and reconstructions – a goldmine! This is contained within an excellent website devoted to their apparent prey: trilobites.info
I work with maggots. Not big fat maggots you use for fishing, but Drosophila maggots. They are incredibly simple, but are capable of performing most of the behaviours shown by the adult fly (with the obvious exceptions of mating and flying). The tiny fly Drosophila was chosen by Thomas Hunt Morgan at the beginning of the last century when he decided to study evolution. After a few years, his attempt to make Drosophila evolve was coming to nothing, when he found a white-eyed mutant fly. The rest, as they say, is history, as Morgan and his students revealed the laws of genetics that had been sketched out half a century earlier by Mendel.
Throughout the 20th century, Drosophila was studied by geneticists, and it was the first multicellular organism to have its genome sequenced, just as the new millenium dawned. Now there are hundreds of laboratories around the world studying the genetics and neurobiology of Drosophila. It would be fair enough to imagine that we knew almost everything there is to know about which cells do what in the fly, and even more so in its juvenile, more simple form, the maggot. How wrong that would be!
An article soon to be published by Nature from the world-famous laboratory of Lily and Yuh Jan describes the astonishing finding that Drosophila maggots – and, you can be pretty sure, virtually every other kind of fly maggot – is covered with tiny “eyes”. Nobody had any idea that this was the case.
Up until today, the maggot’s “eyes” were thought to be a group of 12 cells called Bolwig’s organ. They are named after the Danish scientist Niels Bolwig, who did his doctoral thesis on vision in fly maggots, and later went on to pioneer studies of primates in the wild; he died in 2004. There are two Bolwig’s organs, which you might imagine are the dome-shaped things on the front of the maggot’s face below. These structures are in fact the maggot’s “nose” or dorsal organ (my favourite bit of a maggot).
Bolwig’s organs, as shown in this lovely image by Bala Iyengar, are not at the front of the face, but instead deep inside the maggot’s body:
The Jan lab show that if the Bolwig’s organs are killed, maggots would still avoid light – (b) below – just like normal maggots (a) below:
There’s a great video on the Nature website showing a Bolwig-less maggot squiggling away from the light.
This proves that there must be some other cells in the maggot that can detect light (there was no change in temperature when the maggots had a light shone on them). Furthermore, Bolwig-less maggots did not respond to green or red light, but did avoid short-wavelength light at high intensities.
The paper reports that a particular set of cells in the maggot’s body wall, called class IV dendritic arborization neurons, responded to light – even when they were grown, isolated, in culture. These cells cover the whole of the maggot, as seen in this dramatic image – all the green cells are class IV neurons, and every one is an “eye”!
Amazingly, it turns out that these cells also express a taste receptor, Gr28b, which may be directly involved in sensing light, although this has yet to be demonstrated. This isn’t quite so surprising in that in the nematode worm C. elegans, a similar gene is also involved in responses to light. Another protein, TrpA1, which is involved in responses to light in the adult fly, is necessary for these class IV neurons to respond.
The authors conclude:
Our study has uncovered unexpected light-sensing machinery, which could be critical for foraging larvae to avoid harmful sunlight, desiccation and predation. By providing precedence for photoreceptors strategically placed away from the eyes, our finding of an array of class IV dendritic arborization neurons with elaborate dendrites tiling the entire body wall, and acting as light-sensing antennae, raises the question of whether other animals with eyes might also possess extra-ocular photoreceptors for more thorough light detection and behavioural response.
Even more importantly, this surprising result shows quite how much we have yet to discover about this animal about which, many people might have thought, we knew virtually everything. We know so much, but so little!
Yang Xiang, Quan Yuan, Nina Vogt, Loren L. Looger, Lily Yeh Jan & Yuh Nung Jan (2010). Light-avoidance-mediating photoreceptors tile the Drosophila larval body wall. Nature. doi:10.1038/nature09576