Notes on Objects: Longhorn Beetle and Ammonite

I volunteer as an object-handler at Manchester Museum (I am there on Wednesdays from 11am to 1 pm, at the table near Nature's Library), which involves inviting people to handle certain objects from the museum's archives and talking to them about it. I often have a taxidermied fox, which is a good hook to bring people in, and they often have the slightly philosophical question, "Is it real?". It is real fox fur (and maybe claws?) but the insides and eyes aren't real, the insides are a polyurethane mold and the eyes are plastic. So it is a semi-real fox. Many people are very surprised that it feels so soft around the ears, a bit like a dog.
But my two favourite objects are the Giant African Longhorn Beetle and an unidentified ammonite, and I will give some further information about them here.

Giant African Longhorn Beetle (Petrognatha gigas)

This is a insect of the family Cerambycidae (the long-horn beetles), and the "horns" of it's name are it's antennae, which are used in insects for sensory purposes, including orientation, detecting sound and sensing chemicals. The Giant African Longhorn Beetle lives in dead acacia trees, and it is well suited to this, as it's long antennae and limbs look like the twigs of the acacia tree. The spikes on it's thorax (the "neck") and top of the abdomen look very like the prickles of the acacia tree.

Beetles are insects with “sheathed wings” according to the literal translation of their scientific name Coleoptera. All insects have two pairs of wings, the hardened forewing (elytra) and the hindwing, which is a fairly standard insect wing. The elytra protects the hindwing in flying species. In ground beetles, the elytra are fused together, therefore making them flightless and confined to the ground. All beetles have a hardened exoskeleton, which is made of sclerite plates separated by a rigid joint (suture) which provides both armour and flexibility. Not a lot is known about Giant African Longhorn Beetles as they have not been studied much, though they do have a particular way of breathing known as Bernoulli suction ventilation, see this article to learn more. 

  Cerambycidae is a large family of over 20,000 species. The largest member of this family is the Titan beetle (Titanus giganteus), which has a maximum body length of 16.7 cm. The longest beetle of all is the Hercules beetle (Dynastes hercules) which is up to 17.5 cm long and can lift up to 8kg over 850 times their own weight. Hercules beetles are rhinoceros beetles, so named because the male has two large horns on it's head, adding to it's length, which are used for fighting.  The larvae of this family are called roundhead borers, as they bore into living or recently felled wood, and are considered a pest by the logging industry, though the larva of the cactus longhorn beetle bore into prickly pears and chollas.

There are around 400,000 known species of beetles (25% of all know animal species), and there are probably over 1 million total known and unknown beetles in the world. 

Ammonite (of unknown classification)

 Ammonites were shelled, marine cephalopods (the same group which octopuses and squid belong to) which existed from the mid Devonian (400 million years ago) to the late Cretaceous (66 million years ago), in the KT (Cretaceous-Tertiary or Cretaceous- Paleocene) Mass Extinction which was probably caused by the effects of an asteroid impact and also caused the extinct of the non-avian dinosaurs. The ammonite I have on my handling table  is 160 million years old, placing it in the Late Jurassic (in the Oxfordian age), which is 95 million years older than T. rex. Ammonites as a group are much older than the oldest dinosaur (probably Eoraptor, which is 231.4 million years old), and even older than four-legged animals (Tetrapods) which evolved after 395 million years ago.  The white stuff in the sections of the shell is cacite crystals, which were formed when the shell was being fossilised. Water with dissolved salts in it got into some of the outermost sections of the shell, and as the shell was being compressed under the weight of sediment on the ocean floor, the water evapourated and left behind the salts, which grew into crystals. 

They are named ammonites due to their resemblance to the ram-like horns of the Egyptian God Ammon or Amun.

All regular ammonite shells grew out from the centre (the umbilicus) in a spiral in one plane, becoming gradually thicker as it grew. It grew by adding chambers on the shell from the umbilicus, and when it “moved” from an old chamber to a new one (the living chamber), it sealed off the old chamber except for the siphuncle, a “tube” which extended through the shell. The siphuncle could be used to change the air pressure in the sealed-off chambers (known as the phragomocone), so it could rise or descend, rather like a submarine does. The earliest phragomocene chambers tend to get less sediment in them, therefore it is common for crystals to grow in these sections. My ammonite has calcite crystals (which are a very common crystal) in a lot of the phragomocene chambers.

One of the largest ammonites found, Parauzosia seppenradensis

Ammonites would probably have had ten arms (all cephalpods have arms, not legs). It's arms may have surrounded hard aptychi, which may have been the jaw apparatus of the ammonite, similar to the beak in other cephalpods, or the aptychi could have been a sort of head shield, which is seen in living nautiloids. There is very little fossil evidence of the soft parts of ammonites, though it is likely that, in addition to the ten arms, they had an ink sack and a hyonome (see below).

Extant Nautilus shell

Ammonites are fairly distant relatives of the Nautiloids (which include the living Nautilus). The Ancestors of Ammonites branched off from the Nautiloid line (specifically straight-shelled Bactritid nautiloids) before 400 million years ago.

What is the difference between the Nautiloids and the Ammonites, then?

The basic difference is the difference in the sutures. These are the lines where the walls which separate each chamber (called the septa) meet the wall of the shell, which can be seen by looking at the outside of the shell. Nautiloid sutures are generally gentle curves, whereas Ammonite sutures are more wavy. The suture lines are determined by the shape of the septa when it meets the wall of the shell. The difference in the suture lines are caused by the different shapes of septa in Ammonites and Nautiloids. Ammonite septa are more wavy and to a varying extent convex from the front of the shell, whereas Nautiloid septa are smoother and more concave from the front. The shape of the septa can be observed when the ammonite shell is in cross-section. The wavy suture lines enabled ammonites to withstand high pressures whilst having a thinner shell than Nautiloids, though both subclasses were able to living at depth (Nautiloids at a deeper depth than Ammonites).

Ammonites and Nautiloids both have a siphuncle, but the siphuncle of Nautiloids is in the middle of the septa, whereas the ammonite siphuncle is on the outer edge of the shell. 

The evolution of the oocyte

A human egg cell, the corona radiata is on the outer surface, the zona pellucida is the clear ring behind it. 

Oocyte is the name for an immature egg cell (ova, in animals), an oocyte only becomes an egg cell finally when it is fertilized. 
The oocyte and the spermatozoa (sperm cell) are the sex cells of organisms which reproduce sexually, that is by combining the genetic material of two different organisms. Yet, the very earliest cellular organisms must have reproduced asexually, so why does the vast majority of complex organisms produce sexually exclusively? What caused this change, and why did it proliferate?

There is much speculation on why so many organisms switched from asexual to sexual reproduction. It is likely that sexual reproduction arose in an ancestor of the eukaryotes (organisms with more complex cells), deep in the Precambrian. But sexual reproduction has an immediate flaw, only half the population are capable of producing offspring physically, the females. An asexual population would quickly out-compete a sexual one purely by virtue of being able to grow at twice the rate of a sexual one. This is known as the “two-fold cost of sex”. However, this overlooks the role of the male. Males provide genetic diversity to a particular population, as when the sperm and ovum haploid genomes recombine in fertilization to form a zygote with a diploid genome, and therefore two copies of the same gene from each parent. In recombination, genetic “mistakes” in the sequence of base pairs should be corrected. Hybrids between two populations of the same species tend to be fitter genetically, a process known as heterosis (this is not always the case in all hybridizations, however). Therefore, an organism produced sexually may be more resistant to disease than asexually produced organisms. This is probably why almost all complex organisms (except very few, like the New Mexico whiptail lizard, which can also be created by hybridizing two other whiptail species) reproduce sexual, as they need to compete in a more dynamic ecology, so need the fast acquisition of advantageous traits in the whole population that only sexual reproduction. 

Isogamy and Anisogamy 

Some of the more primitive single-celled organisms reproduced by fission, which is regular cell division into genetically identical offspring cells. However, most single celled organisms swap genes, occasionally, through genetic recombination or the transfer of a nucleus mostly with organisms from a separate population, which has accumulated different genetic mutations to it's population. This is probably how sexual reproduction arose in the earliest organisms. Eventually specific cells began to specialize, by carrying the haploid genome of the organism, so it would combine with the haploid genome of another organism to create a diploid organism. This is this basis of sexual reproduction.

The gametes in these early sexual organisms would have appeared the same, only the haploid genome would be different between the two. This is known as isogamy, where each gamete has the same morphology. The gametes in some organisms began to specialize further, into anisogamy, where one gamete is larger than the other. One modern partially isogamous species is the green algae Volvox. In a study, colonies where all the gametes were small (isogamy) produced a smaller population, whereas anisogamous populations were larger. This shows that when there is one large gamete, which has a larger energy reserves (yolk granules in the cytoplasm) but is slower, and one small gamete, which can move faster but does not have large energy reserves, population sizes are larger. Anisogamy means that one gamete, the oocyte, can specialize in providing a larger energy supply for the zygote after fertilization and the other, the spermatozoa can specialize in being fast and numerous. This is a particular type of anisogamy known as oogamy. 

Due to the large tax on energy resources for the female there is a great difference between ovum and sperm number, there are around 400 ovum ovulated by a woman who has reached menopause compared to 200-500 million spermatozoa per ejaculate for human males, and up to 8 billion per million per ejaculate for domesticated pigs (who have been breed to be as fertile as possible).

Egg Laying 

The first vertebrates to have ova were reptiles, as when on land they could not reproduce by spawning. In reptiles, and later in birds, the ova once fertilized forms protective layers (the egg shell) and is passed out through the oviduct. In some of these species, the embryo is then kept warm (incubated) by mostly the mother (the father and mother Whooping Crane alternatively incubate the egg). This is known as ovipartity, and the embryo receives nutrition only from the nutritive yolk, meaning than in oviparous animals, more energy is needed to create the ovum than in viviparous animals (who have live young). But after fertilisation, there is less need for parental care, therefore enabling more offspring to be produced. The offspring, due to lack of long-duration parental care, have a higher mortality rate, but more are produced in relation to the amount of energy the parents lose in reproduction. Only a small number of mammalian species produce eggs (the monotremes) including the duck-billed platypus, which are descended from the some of the earliest mammals and hence having features common and almost unique to both mammals and reptiles.

The Zona Pellucida

The oocyte has multiple barrier to stop polyspermy (multiple sperm entering the oocyte, therefore producing a cytoplast with around double the normal number of chromosomes for the species, which would be unable to survive). Polyspermy may arise from having sperm that is too efficient at surviving and fertilising the oocyte, therefore a male with very efficient sperm may not pass on it's genes due to his offspring's inability to survive.

Sperm that is more efficient at fertilising an oocyte does not mean that it is beneficial to the female (for reasons as seen above) as this sperm may not have the best genetic material to pass onto successive generations. If mammals and reptiles evolved using spawning as a reproductive method, there would be all sorts of genetic problems as the only “screening process” would be that the sperm would be from an animal that had reached puberty. This gives rise to a very complex genital system in polygamous species, such as that seen in the Pekin Duck. The female Pekin Duck has a maze-like vagina to be able to “pick” the best sperm for reproduction. To counter this the male has a “corkscrew”-like penis and only the males with the precisely shaped penis for that one female's vagina will fertilise the oocyte. 

The first barrier to the sperm is the zona pellucida, then the plasma membrane, which also protect the fertilized ova on it's journey through the oviduct (or in the water in fish and amphibians). The zona pellucida is an essential feature, if it is not present the female will be infertile. It stops sperm from other, genetically incompatible species from binding and also emits chemicals that guide the sperm cells towards the oocyte. In ovipartial species, when the nucleus of the sperm and oocyte fuse, the zona pellucida signals for a release of calcium ions which eventually transform into the egg shell. For fertilization to occur the nucleus of the sperm needs to bind with the zona pellcida and “bore through” it, fusing in the oocyte's cytoplasm. After fertilisation the cortical reaction is triggered, which causes the plasma membrane to fuse and become impermeable to sperm. Without the zona pellucida, gametes from incompatible species can fuse, though the offspring are not viable.

Genes encoding on the surface of gametes are some of the most rapidly evolving genes, even faster than those responsible for immune responses, which have to adapt quickly due to microbe attacks. If the oocyte is "under pressure" to reduce polyspermy, the proteins on the surface of the oocyte will change, so that fewer sperm are compatible with the oocyte, meaning there is a smaller probability of polyspermy.

Bibliography

http://heart.sdsu.edu/~website/Biology_307/Lectures/pdfs/20_sperm.pdf

http://gbe.oxfordjournals.org/content/5/11/2073.full

http://www.britannica.com/EBchecked/topic/536936/sex/29380/The-origin-of-sex-and-sexuality

http://bioteaching.wordpress.com/2013/05/01/how-did-sperm-and-egg-evolve/

http://www.radiolab.org/story/91646-sperm/

the proper article (with paywall): http://www.americanscientist.org/issues/feature/2013/3/rapid-evolution-in-eggs-and-sperm

the (free) photocopy of the article: http://evotourism.files.wordpress.com/2013/05/evo-rapid-evolution-in-eggs-and-sperm.pdf

Genome- Matt Ridley (1999, Fourth Estate). 

Mutants- Armand Marie Leroi (2003, Harper Perennial). 

Mammoths: Ice Age Giants Exhibition

The preserved body of Lyuba from http://designyoutrust.com/2012/04/baby-mammoth-lyuba-goes-on-display/ originally from Reuters.

On the 3rd August 2014, I visited the Mammoths: Ice Age Giants exhibition at the Natural History Museum, London, which is open until the 7th September 2014. The exhibition was created by the Field Museum, Chicago, and features models of ancient Proboscideans, Pleistocene animals and, the gem of the exhibition, the preserved body of a 35 day old (at death) woolly mammoth, known as Lyuba or Люба, who died around 41,800 years ago on the modern day Yamal Peninsula.  I had read the accompanying book (by Adrian Lister with the same title as the exhibition) beforehand, as research for an essay on extinct Proboscideans, so I went here less for learning new information and more to see, to meet a woolly mammoth, in the flesh. I felt like a pilgrim, visiting the miraculous relics of a saint, in search of enlightenment. I suppose she could be a relic, is a way, for a secular age. A preservation almost as unlikely as the "miraculous" preservation of incorruptible saints, a visitor from an age and a land (in terms of habitat) long gone. I stood in front of her case for a long time. She is remarkable preserved, analogous to ancient Egyptian mummies, but instead of preservation in heat and salt she was preserved in mud and permafrost. She died by suffocation in mud, particles of which were found in her trunk and oesophagus, and you can tell. Her limbs are still in the position she was in when she suffocated, struggling through the mud and her eyes are shut to keep out the mud. It is less a preserved carcass and more of a crime scene, it looks as if she has only recently stopped moving and sunken into the mud. After death, she was rapidly covered in aoxic sediment, so post-mortem decay was negligent. There are some blooms of fungi on the skin; it is signs of the decay which occurred after she weathered out of the permafrost and before refrigerator and preservation by researchers. It is so strange that, around 4,000 years since the very last woolly mammoth died and decayed, mammoths put in "suspended animation" in permafrost still have enough biological material for fungi to grow upon, just as they grow upon a freshly dead elephant. Her trunk is different to that of modern elephants, it had two "fingers" on what would be the top of the nose and the upper lip (?) either side of the nostrils, which are very long and would have been very sensitive, used for the sort of fine motor movements that her feet could never manage. She is hairless, mostly, purely because of the conditions she was buried in, but there is some traces of hair and I saw some on the fold behind her knee. She shrunk after death, down to 50kg when she was found from about 100kg in life due to dehydration; her skin is wrinkled and loose, from one angle you can see her rib cage through the skin. I spent a long time circling her, and I almost felt like crying at the beauty and wonder of it, a visitor from a past age, a lost earth.
As you can see, I got rather too attached to a dead mammoth, but there was the rest of the exhibition to see too. I couldn't take pictures of Lyuba, but here are some pictures of the rest of it. It was very crowded, mostly with families with small children, and became a bit of an Ice Age "selfie safari", but when you could get close to the exhibits it was very good. It did such a good job of highlighting the importance of studying paleontology with a final exhibition on the efforts to prevent the extinction of modern elephants. In mammoths we have a very good model of the extinction which could (is?) facing their proboscidean cousins, the modern elephants. If we had no idea of the past, we can not prepare for and predict the future and this applies in all fields of biology, geography and geology.

The Proboscideans 

This is a model of Moertherium, one of the earliest Proboscideans. It was around the size of a large pig, and was probably largely aquatic, as was some of it's most recent ancestors. Small "tusks" are visible in the upper jaw. 

The fossilized jaw of this blogs name sake, Amebelodon. Amebelodon lived from around 15 to 5 million years ago and had two pairs of enlarged incisors (tusks). The tusks of the lower jaw became flattened and broad, until they nearly touched. These tusks were probably used to "mow" down tough grasses, by moving it's head from side to side like a scythe. 

Left Pygmy Mammoth jaw bone and Right Woolly Mammoth jaw bone. The Pygmy Mammoth is an example of island dwarfism, whereby animals stranded on an island speciate and become smaller, due to a lesser need for scarcer food and lack of predators which they need to be big to defend themselves against. The Pygmy Mammoths evolved after a population of Columbian Mammoths became isolated on the Californian Channel Islands, and was around 1.72m at the shoulder, in contrast to the Columbians at 4.3m at the shoulder. 

A life-sized model of a Pygmy Mammoth, with a mastodon at the front on the background.

A cast of the "Hyde Park Mastodon", an American Mastodon skeleton that was found in New York State and is a 95% complete skeleton. The teeth are clearly visible, which is what the Mastodon ("breast teeth") is named after.

A model of a Columbian Mammoth. Columbian Mammoths occupied some southerly regions of North America, including Mexico and was largely confined to grassland habitats. It existed at the same as the American Mastodon in North America, though as Mastodons probably stuck to swampy habitat they probably did not meet often.

Rest of the museum:

The Skull of a Stegodon, a fairly distant relative of the modern elephants, though due to similarities in habitat they resemble each other, an evolutionary process known as analogy. The tusks grew close to each other, so the trunk would not be able to go between the tusks, but rather hung down on either side of the tusks.

Gomphotherium skull. The Gomphotheriums had four pairs of long tusks, and is one of the earliest examples of sequential tooth development, whereby the cheek teeth of the animal erupt from the back throughout the animal's life to replace those which are worn out. Gomphotherium had a total of three molars in each side of each jaw at one time, and would have had six teeth "pass through" each side in it's lifetime. This became more extreme in mammoths and elephants, who have only one molar in each side of each jaw at one time.

Deinotherium skull, which had only had one pair of lower tusks, and these were probably used to scrap bark which they would have eaten. The trunk would have hung down in front of the lower tusks, and would only be visible when it raised it's trunk.  

Architecture 

The museum was built to house the Natural History Department of the British Museum, so it is laced with all sorts of natural historical details in the architecture. 

A carved ammonite centre, and what looks a bit like an Ediacaran animal, on the right (?), in the bird gallery. 

Carved sea-scorpion in the geology gallery. 

Carved lobed fish on a pillar in the geology gallery.