MAOTUNIA FROM NORTHERN CHINA

This lovely is Maotunia sp. from the Drumian Changhia Formation of China. You can see the 3D phosphatized gut glands still stuck to the underside of the dorsal carapace. 

Wang et al. published a paper in December 2018 on the fossilized gut of the trilobite Lioparia bassleri and the distribution of exceptional preservation in the Cambrian Stage 4-Drumian Manto Formation of northern China. 

Photo: Rudy Lerosey-Aubril

SOLAR WINDS: THE MAGNETOSPHERE

The Earth has a magnetic field with north and south poles. The magnetic field of the Earth is surrounded by the magnetosphere that keeps most of the particles from the Sun from hitting the Earth.

Some of these particles from the solar wind enter the atmosphere at one million miles per hour. 

We see them as one of the most beautiful of all-natural phenomena — Earth's polar lights, the aurora borealis in the north and the aurora australis, near the south pole. The auroras occur when highly charged electrons from the solar wind interact with elements in the Earth's atmosphere and become trapped in the Earth's magnetic field. We see them as an undulating visual field of red, yellow, green, blue and purple dancing high in the Earth's atmosphere — about 100 to 400 kilometres above us.

This image shows the parts of the magnetosphere. 1. Bow shock. 2. Magnetosheath. 3. Magnetopause. 4. Magnetosphere. 5. Northern tail lobe. 6. Southern tail lobe. 7. Plasmasphere.

Photo credit: Magnetosphere_Levels.jpg: Dennis Gallagherderivative work: Frédéric MICHEL - Magnetosphere_Levels.jpg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=9608059

HOPLOSCAPHITES NEBRASCENSIS

This sweet beauty with lovely oil in water colouring is a Hoploscaphites nebrascensis (Owen, 1852) macroconch. This is the female form of the ammonite, her larger body perfect for egg production by the smaller males, or microconchs of the species.

Hoploscaphites nebrascensis is an upper Maastrichtian species and index fossil. It marks the top of ammonite zonation for the Western Interior. 

This species has been recorded from Fox Hills Formation in North and South Dakota as well as the Pierre Shale in southeastern South Dakota and northeastern Nebraska.

It is unknown from Montana, Wyoming, and Colorado due to the deposition of coeval terrestrial units. 

It has possibly been recorded in glacial deposits in Saskatchewan and northern North Dakota, but so far this is just hearsay.

Outside the Western Interior, this species has been found in Maryland and possibly Texas in the Discoscaphites Conrad zone. This lovely one is in the collection of the deeply awesome (and enviable) José Juárez Ruiz. A big thank you to Joshua Slattery for his insights on the distribution of this species.

SHELTER POINT FOSSIL CRAB SITE

This lovely fossil crab is Longusorbis cuniculosus from the Upper Cretaceous ) Late Campanian, Northumberland Formation near Campbell River, British Columbia. This photo was featured in the 2004 BCPA Calendar.

Shelter Point on northern Vancouver Island is a lovely beach site where clastic strata are exposed in the intertidal platform of Oyster Bay. 

The site is located just off the Island Highway, about 10 km south of downtown Campbell River and 4 km farther south along the lower Oyster River. Haggart et al. presented an abstract on this locality at the 12th British Columbia Paleontological Symposium, 2018, Courtenay, abstracts; 2018 p. 28-30. I'll pop a link below if you'd like to give it a read. 

Shelter Point has been collected since the 1970s. No pre-glacial strata were recognized in this area by Muller and Jeletzky (1970). Richards (1975) described an abundant fauna in the beds at Shelter Point, approximately 2 km north of the Oyster Bay exposures, including the crab Longusorbis and associated ammonites and inoceramid bivalves, and he assigned these beds to the Spray Formation of the Nanaimo Group. This information, combined with the very low dip of the Oyster Bay strata and their general lithological similarity with the coarse clastic strata found commonly in the Nanaimo Group, suggested a Late Cretaceous (Campanian) age of the Oyster Bay strata.

Beginning in the 1980s, fossil collectors from the Vancouver Island Palaeontological Society began amassing significant collections of fossils from the strata of southern Oyster Bay that are found several hundred metres southeast of the local road called Appian Way, thus providing the informal moniker Appian Way Beds for these localized exposures. 

While these collections included a great diversity of gastropod, bivalve, nautiloid, scaphopod, echinoderm, and coral specimens, as well as impressive collections of plant materials, much previously undescribed, no taxa found commonly in Campanian strata of the Nanaimo Group were noted in these collections; particularly lacking were ammonites and inoceramid bivalves. For this reason, the hypothesis began to emerge that the Appian Way Beds of Oyster Bay were of younger, post-Cretaceous, age than thought previously. 

Just how young, however, has been a source of some controversy, with different parties continuing to favour the traditional Campanian age — based on lithostratigraphy — others a Paleocene age, and still others an Eocene age — based on plant macrofossils.

Fossil Collecting at Shelter Point:

Fossil Collecting at Shelter Point

At the northern end of Shelter Bay, turn east onto Heard Road, which ends at a public access to Shelter Point. 

Low tide is necessary in order to collect from these shales. Some friends are looking to explore this site over the next week. If you see some keen beans on the beach, check to see if they are the New family, Chris and Bonnie. Welcome them — they are lovely folk!

Industrious collectors unwilling to wait for the tide have employed rubber boots to wade through knee-deep water — rubber boots are highly recommended in any case — and even headlamps to capitalize on low tides during the night. Bring eye protection and sunscreen to safely enjoy this lovely family trip.   

The fossils, mainly the crab, Longusorbis and the straight ammonite Baculites, occur only in the gritty concretions that weather out of the shale. You'll need a rock hammer to see the lovelies preserved inside. Best to hold the concretion in your hand and give it one good tap. Aside from the fossils, check out the local tide pools and sea life in the area. Those less interested in the fossils can look for seals and playful otters basking on the beaches.

References:

Haggart, J. et al. 58 million and 25 years in the making: stratigraphy, fauna, age, and correlation of the Paleocene/Eocene sedimentary strata at Oyster Bay and adjacent areas, southeast Vancouver Island, British Columbia; https://geoscan.nrcan.gc.ca/starweb/geoscan/servlet.starweb?path=geoscan/fulle.web&search1=R=308471

ANDROGYNOCERAS LATAECOSTA

This gorgeous Lower Pliensbachian macroconch of the ammonite Androgynoceras lataecosta was found as a nodule from the Green Ammonite beds, Lower Pliensbachian, Stonebarrow Marl Member, Charmouth Mudstone Formation (190 MYA) at Charmouth Beach, Dorset Coast. 

This specimen was found, prepped and photographed by the lovely and talented Lizzie Hingley of Stonebarrow Fossils. 

And what a delightful surprise! It is quite a small nodule to contain a macroconch of this species. Generally, these smaller concretions contain the diminutive male microconchs of Androgynoceras (Hyatt, 1867) if you are lucky — sometimes a Tragophylloceras loscombi (Sowerby, 1814) — or nothing at all if you are not. 

We see a great variation in this species and the ammonite species that make up this population. Murray Edmunds from Chipping Norton, UK shared some of his insights on why we see such variation and how a phylogenetic species concept may be masking a continuum that tells a very different story.  

We are starting to recognise that these could all be variants of one interbreeding population — with a highly variable duration of a juvenile Capricorn stage. Palaeontologists use a phylogenetic species concept as you cannot test reproductive isolation in any but the most recent of fossils.

By definition, individuals within an interbreeding population cannot belong to different species, let alone different genera. In palaeontology we can only interpret what we see with reference to what we understand of biology. 

In the Davoei Zone Liparoceratidae we have a single lineage that evolves into Oistoceras. The microconchs (putative males) are small Capricorns, and the macroconchs (putative females) are very variable: they have a Capricorn juvenile stage that can be expressed for only a few mm (or not at all), or for many cm. But eventually, the adult macroconch body chamber acquires liparoceratid ornament — inflated and bipinnate with numerous secondary ribs. 

Unfortunately, the green ammonite beds at Charmouth preserve only juvenile macroconchs so we don’t get to appreciate the similarity of the mature adult shell form. We see them at a size where individuals can look very different from each other. 

Historically, this difference in appearance led to all the individuals — both micro and macroconchs — with prolonged Capricorn morphology being assigned to Androgynoceras and those macroconchs lacking the juvenile Capricorn stage (as is typical in their Ibex zone ancestors) to be called Liparoceras. 

Different species were named for different variants. But this is a purely morphological approach to nomenclature and does not reflect the taxonomy used for extant organisms where we try to reflect phylogeny.

But as more and more examples are collected, we start to see that these specimens form a continuum. And as we follow them up through time, we see that all of them (microconchs and macroconchs, regardless of the extent of the Capricorn stage — although that tends to become more prolonged through time — simultaneously evolve progressively forwardly projected ribs across the venter, culminating in Oistoceras. 

This simultaneous evolutionary change across the entire Liparoceratid population more or less proves that we have a single interbreeding clade. And that it is separate from Becheiceras – through that’s another story! And they all go extinct simultaneously too, whereas Becheiceras carries on into the Margaritatus Zone. If you're a grad student looking to do your thesis, there is a very interesting story you could tell!

If you fancy a web stroll through some beautifully prepped specimens from Jurassic Coast, UK, or if you'd like to get some prepped, you can check out Lizzie's superb skill here: https://www.stonebarrowfossils.co.uk/  / Photos: Lizzie Hingley, Stonebarrow Fossils

ORYGMASPIS SPINULA OF THE MCKAY GROUP

This calcified beauty is Orygmaspis (Parabolinoides) spinula (Westrop, 1986) an Upper Cambrian trilobite from the McKay Group near Tanglefoot Mountain in the Kootenay Rockies. 

Orygmaspis is a genus of asaphid trilobite with an inverted egg-shaped outline, a wide headshield, small eyes, long genal spines, 12 spined thorax segments and a small, short tail shield, with four pairs of spines.

The outline of the exoskeleton Orygmaspis is inverted egg-shaped, with a parabolic headshield — or cephalon less than twice as wide as long. 

The glabella, the well-defined central raised area excluding the backward occipital ring, is ¾× as wide as long, moderately convex, truncate-tapering, with 3 pairs of shallow to obsolete lateral furrows. 

The occipital ring is well defined. The distance between the glabella and the border (or preglabellar field) is ±¼× as long as the glabella. This fellow had small to medium-sized eyes, 12-20% of the length of the cephalon. These were positioned between the front and the middle of the glabella and about ⅓ as far out as the glabella is wide. 

The remaining parts of the cephalon, the fixed and free cheeks — or fixigenae and librigenae — are relatively flat. The fracture lines or sutures — that separate the librigenae from the fixigenae in moulting — are divergent just in front of the eyes. These become parallel near the border furrow and strongly convergent at the margin. 

From the back of the eyes, the sutures bend out, then in, diverging outward and backward at approximately 45°, cutting the posterior margin well within the inner bend of the spine — or opisthoparian sutures. 

The thorax or articulating middle part of the body has 12 segments. The anteriormost segment gradually narrows into a sideward directed point, while further to the back the spines are directed outward and the spine is of increasing length up until the ninth spine, while the spine on the tenth segment is abruptly smaller, and 11 and 12 even more so. 

This fellow has a wee pygidium or tail shield that is only about ⅓× as wide as the cephalon. It is narrowly transverse about 2× wider than long. Its axis is slightly wider than the pleural fields to each side, and has up to 4 axial rings and a terminal and almost reaches the margin. Up to 4 pleural segments with obsolete interpleural grooves and shallow pleural furrows. The posterior margin has 3 or 4 pairs of spines, getting smaller further to the back. 

References:

Chatterton, Brian D. E.; Gibb, Stacey (2016). Furongian (Upper Cambrian) Trilobites from the McKay Group, Bull River Valley, Near Cranbrook, Southeastern British Columbia, Canada; Issue 35 of Palaeontographica Canadiana; ISBN: 978-1-897095-79-9

Moore, R.C. (1959). Arthropoda I - Arthropoda General Features, Proarthropoda, Euarthropoda General Features, Trilobitomorpha. Treatise on Invertebrate Paleontology. Part O. Boulder, Colorado/Lawrence, Kansas: Geological Society of America/University of Kansas Press. pp. O272–O273. ISBN 0-8137-3015-5.

TRIASSIC BEAUTY: ALBERTONIA

Triassic Fossil Fish, Albertonia sp. 

This beauty with the graceful sail-like fins is the Early Triassic ganoid fish, Albertonia sp., an extinct bony fish from British Columbia, Canada. 

Specimens of this lovely have been found in the Vega-Phroso Siltstone Member of the Sulphur Mountain Formation near Wapiti Lake in British Columbia and the Lower Triassic Montney Formation of Alberta. 

Early Triassic fish have been described from several outcrops in the Western Canada Sedimentary Basin of the Rocky Mountains. The best known and most prolific of these are from sites near Wapiti Lake in northeastern British Columbia. Here specimens of bony fish with their heavy ganoid and cosmoid scales are beautifully preserved. Four genera of Early Triassic fishes — the ray-finned actinopterygians Albertonia, Bobasatrania, Boreosomus, and the lobe-finned coelacanth (sarcopterygian), Whiteia — are found in abundance in the Wapiti Lake exposures.

This particular species is one of my favourites. Albertonia is a member of the ganoid fish family Parasemionotidae, which is amongst the most advanced and abundant of Triassic subholostean families of fish. The preservation here really shows the beauty of form of this species who likely died and was preserved in sediment at the bottom of an ocean with an anoxic environment. 

These fellows lived in deep marine waters, dining on plankton & other small organisms. Most specimens are 35-40cm in length. They have a large, sail-shaped dorsal fin and rather smallish ventral fins. Their pectoral fins were incredibly long compared to the rest of the body, and they too resembled sails. The preservation here is quite remarkable with each square-shaped scale preserved in minute detail.

ANCIENT ARTHROPOD FROM PAIWU

This large, showy bivalved arthropod is a Tuzoia sinesis (Pan, 1957) from Cambrian deposits of the Balang Formation. The Balang outcrops in beautiful Paiwu, northwestern Hunan Province in southern China. 

The site is intermediate in age between the Lower Cambrian Chengjiang fauna of Yunnan and the Lower to Middle Cambrian, Kaili Lagerstätten of Guizhou in southwestern China.

This specimen was collected in October 2019 and is one of the many new and exciting arthropods to come from the site. Balang has a low diversity of trilobites and many soft-bodied fossils similar in preservation to Canada's Burgess Shale. 

Some of the most interesting finds include the first discovery of anomalocaridid appendages — Appendage-F-Type. These were found along with the early arthropod Leanchoiliids — with his atypical frontal appendages and questionable phylogenetic placement — and the soft-shelled trilobite-like arthropod, Naraoiidae.

While the site is not as well-studied as the Chengjiang and Kaili Lagerstätten, it looks very promising. The exceptionally well-preserved fauna includes algae, sponges, chancelloriids, cnidarians, worms, molluscs, brachiopods, trilobites and a few non-mineralized arthropods. It is an exciting time for Cambrian palaeontology. The Balang provides an intriguing new window into our ancient seas and the profound diversification of life that flourished there.

THE DUDLEY BUG

Calymene blumenbachii, Theresa Paul Spink Dunn

A lovely example of the trilobite Calymene blumenbachii from outcrops in the UK. This wee rolled beauty is in the collections of Theresa Paul Spink Dunn. This Silurian trilobite is from the Homerian, Wenlock Series, Wrens Nest, Dudley, UK.

Calymene blumenbachii, sometimes erroneously spelled blumenbachi, are found in the limestone quarries of the Wren's Nest in Dudley, England. This locality name was charmingly highjacked by an 18th-century quarryman birth the nickname the Dudley Bug — both a symbol of the town and a key feature on the Dudley County Borough Council Coat-of-Arms. Calymene blumenbachii is commonly found in Silurian rocks — 422.5-427.5 million years ago — that formed near shallow water, low energy reefs.

This particular species of Calymene — a fairly common genus in the Ordovician-Silurian — is unique to the Wenlock series in England and comes from the Wenlock Limestone Formation in Much Wenlock and the Wren's Nest in Dudley. These sites seem to yield trilobites more readily than any other areas on the Wenlock Edge. The rock here is dark grey and quite fossiliferous. Just a few miles away in Church Stretton and along other parts of the Edge, it is yellowish or whitish — an indication that there were local changes in the environment in which the rock was deposited. The Wenlock Edge quarry is closed to further collecting but may reopen for future research projects.

THALASSINA ANOMALA: MUD LOBSTER

This fellow is the scorpion mud lobster, Thalassina anomala (Herbst, 1804), a species of decapod crustacean in the family Thalassinidae. He's a little sweetie with very interesting anatomy. 

Lobsters have their brains in their throats and they breathe and listen with their legs. To top all that wackiness off, they taste with their feet.

These fellows are not as desired as their larger cousins as food for us hoomins. True to their name, they taste a bit muddy. 

Thalassina anomala is an important member of the mangrove ecosystems in which they live. They are night borrowers who excavate om their search for tasty organic material to snack on. They push organic-rich soil from deep in the ground back up to the surface — creating huge mounds. Their burrowing also helps to aerate tidal waters. 

The mud mounds they build are pretty massive in scale in comparison to these fellows. The specimen you see here is 6.5 cm long but others can grow up to 30 cm and build mounds up to 3 metres in height. These mounds provide important habitat for other animals including Odontomachus malignus (an ant), termites, Episesarma singaporense (tree-climbing crab), Wolffogebia phuketensis (mangrove mud shrimp), Acrochordus granulatus (file snake), and plants such as the tree Excoecaria agallochoa and ferns.

Lobsters are members of the phylum Arthropoda, Euarthropoda. They are crustaceans, like crabs, crayfish, krill, shrimp and prawns. Crustaceans belong to the arthropods, a group of animals with an armoured external skeleton (an exoskeleton), a segmented body and jointed legs. The hard exoskeleton is the part that’s preserved as a fossil. This fellow has the typical tall, ovoid carapace and presumably, a short rostrum — though his rostrum is partially hidden in the matrix. 

The specimen you see here hails from Pleistocene deposits near Gunn Point, an outer rural locality sandwiched between the Howard and Adelaide Rivers east of Darwin in the Northern Territory of Australia. His cousins can be found burrowing in the muds of brackish mangrove swamps and estuaries of the Indian Ocean and the western Pacific Ocean today. 

HOMARUS KARELSNSIS: LOBSTER FROM LEBANON

An artfully enhanced example of Homarus hakelensis, an extinct genus of fossil lobster belonging to the family Nephrophidae. Homarus is a genus of lobsters, which include the common and commercially significant species Homarus americanus (the American lobster) and Homarus gammarus (the European lobster).

The Cape lobster, which was formerly in this genus as H. capensis, was moved in 1995 to the new genus Homarinus.

Lobsters have long bodies with muscular tails and live in crevices or burrows on the seafloor. Three of their five pairs of legs have claws, including the first pair, which are usually much larger than the others.

Highly prized as seafood, lobsters are economically important and are often one of the most profitable commodities in coastal areas they populate. Commercially important species include two species of Homarus — which looks more like the stereotypical lobster — from the northern Atlantic Ocean, and scampi — which looks more like a shrimp — the Northern Hemisphere genus Nephrops and the Southern Hemisphere genus Metanephrops. Although several other groups of crustaceans have the word "lobster" in their names, the unqualified term lobster generally refers to the clawed lobsters of the family Nephropidae.

Clawed lobsters are not closely related to spiny lobsters or slipper lobsters, which have no claws or chelae, or to squat lobsters. The closest living relatives of clawed lobsters are the reef lobsters and the three families of freshwater crayfish. This cutie was found in Cretaceous outcrops at Hâdjoula. The sub‐lithographical limestones of Hâqel and Hâdjoula, in north‐west Lebanon, produce beautifully preserved shrimp, fish, and octopus. The localities are about 15 km apart, 45 km away from Beirut and 15 km away from the coastal city of Jbail. 

PHYLLOCERAS VELLEDAE

Lovely defined sutures on this rather involute, high-whorled ammonite from the middle part of the Lower Albian in the Mahajanga Province, northwestern Madagascar. This specimen of Phylloceras velledae (Michelin) has a shell with a small umbilicus, arched, acute venter, and at some growth stage, falcoid ribs that spring in pairs from umbilical tubercles, disappearing on the outer whorls.

While the large island of Madagascar off the southeast coast of Africa is known more for exotic lemurs, rainforests & beaches, it also boasts some of the world's loveliest fossils.

This specimen is from a quarry near the top of an escarpment, 3 km to the west of the village of Ambatolafia (coordinates: Lat. 16.330 23.600 S, Long. 46.120 10.20 E). Judging from plate tectonic reconstruction (Stampfli & Borel, 2002), the area was located in middle latitudes within the tropical-subtropical climatic zone at palaeo-latitudes of 40E45.S in the late Early Cretaceous of the early Albian approximately 113.0 ± 1.0 Ma to 100.5 ± 0.9 Ma. 

Madagascar was carved off from the African-South American landmass early on. The prehistoric break-up of the supercontinent Gondwana separated the Madagascar–Antarctica–India landmass from the Africa–South America landmass around 135 million years ago. Madagascar later split from India about 88 million years ago, during the Late Cretaceous, so the native plants and animals on the island evolved in relative isolation. It is a green and lush island country with more than it's fair share of excellent fossil exposures. 

Along the length of the eastern coast runs a narrow and steep escarpment containing much of the island's remaining tropical lowland forest. If you could look beneath this lush canopy, you'd see rocks of Precambrian age stretching from the east coast all the way to the centre of the island. The western edge is made up of sedimentary rock from the Carboniferous to the Quaternary. The beauty you see here is from sedimentary exposures from northwestern Madagascar and is in my personal collection. There is an exceptionally well-preserved and unusually large specimen in the collections of João Da Costa that I'll photograph and include in a future post.

SULPHATES AND CLIMATE CHANGE

The main direct effect of sulfates on the climate involves the scattering of light, effectively increasing the Earth's albedo. The term albedo was introduced into optics by Johann Heinrich Lambert in his 1760 work Photometria.

Albedo is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that reflects all incident radiation. The average albedo of the Earth from the upper atmosphere, its planetary albedo, is 30–35% because of cloud cover, but widely varies locally across the surface because of different geological and environmental features.

This effect is moderately well understood and leads to cooling from the negative radiative forcing of about 0.4 W/m2 relative to pre-industrial values, partially offsetting the larger (about 2.4 W/m2) warming effect of greenhouse gases. The effect is strongly spatially non-uniform, being largest downstream of large industrial areas.

% of Diffusely Reflected Sunlight

The first indirect effect is also known as the Twomey effect. Sulfate aerosols can act as cloud condensation nuclei and this leads to greater numbers of smaller droplets of water. Many smaller droplets can diffuse light more efficiently than a few larger droplets. 

The second indirect effect is the further knock-on effects of having more cloud condensation nuclei. It is proposed that these include the suppression of drizzle, increased cloud height, to facilitate cloud formation at low humidities and longer cloud lifetime. Sulfate may also result in changes in the particle size distribution, which can affect the clouds radiative properties in ways that are not fully understood. 

Chemical effects such as the dissolution of soluble gases and slightly soluble substances, surface tension depression by organic substances and accommodation coefficient changes are also included in the second indirect effect.

The indirect effects probably have a cooling effect, perhaps up to 2 W/m2, although the uncertainty is very large. Sulfates are therefore implicated in global dimming. Sulfate is also the major contributor to a stratospheric aerosol formed by oxidation of sulfur dioxide injected into the stratosphere by impulsive volcanoes such as the 1991 eruption of Mount Pinatubo in the Philippines. This aerosol exerts a cooling effect on climate during its 1-2 year lifetime in the stratosphere

Diagram: The percentage of diffusely reflected sunlight relative to various surface conditions. By CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=1060378

References: 

• Lewis, Gilbert N. (1916). "The Atom and the Molecule". J. Am. Chem. Soc. 38: 762–785. doi:10.1021/ja02261a002. (See page 778.)
• Pauling, Linus (1948). "The modern theory of valency". J. Chem. Soc.: 1461–1467. doi:10.1039/JR9480001461.
• Coulson, C. A. (1969). "d Electrons and Molecular Bonding". Nature. 221: 1106. Bibcode:1969Natur.221.1106C. doi:10.1038/2211106a0.
• Mitchell, K. A. R. (1969). "Use of outer d orbitals in bonding". Chem. Rev. 69: 157. doi:10.1021/cr60258a001.

PYRITE PRESERVATION

Ammonite Preserved in Pyrite. Fossil Huntress

We sometimes find fossils preserved by pyrite. They are prized as much for their pleasing gold colouring as they are for their scientific value as windows into the past. Sometimes folk add a coating of brass to increase the aesthetic appeal. Though this practice is frowned upon in paleontological communities.

Pyrite is a brass-yellow mineral with a bright metallic lustre. It has a chemical composition of iron sulfide (FeS2) and is the most common sulfide mineral. It forms at high and low temperatures usually in small quantities, in igneous, metamorphic, and sedimentary rocks.

When we find a fossil preserved with pyrite, it tells us a lot about the conditions on the seabed where the organism died. Pyrite forms when there is a lot of organic carbon and not much oxygen in the vicinity. 

The reason for this is that bacteria in sediment usually respire aerobically (using oxygen), however, when there is no oxygen, they respire without oxygen (anaerobic) typically using sulphate. Sulphate is a polyatomic anion with the empirical formula SO2−4. It is generally highly soluble in water. Sulfate-reducing bacteria, some anaerobic microorganisms, such as those living in sediment or near deep-sea thermal vents, use the reduction of sulfates coupled with the oxidation of organic compounds or hydrogen as an energy source for chemosynthesis.

High quantities of organic carbon in the sediment form a barrier to oxygen in the water. This also works to encourage anaerobic respiration. Anaerobic respiration using sulphate releases hydrogen sulphide, which is one of the major components in pyrite. So, when we find a fossil preserved in pyrite, we know that it died and was buried in sediment with low quantities of oxygen and high quantities of organic carbon.

AMMOLITE

Ammolite is an opal-like organic gemstone found primarily along the eastern slopes of the Rocky Mountains of North America. It is made of the fossilized shells of ammonites, which in turn are composed primarily of aragonite, the same mineral contained in nacre, with a microstructure inherited from the shell. It is one of few biogenic gemstones; others include amber and pearl.

The chemical composition of ammolite is variable, and aside from aragonite may include a mix of calcite, silica, pyrite or other minerals. The shell itself may contain a number of trace elements based on the chemical composition of the original sediments. They can include aluminium, barium, chromium, copper, iron, magnesium, manganese, strontium, titanium, and vanadium. 

Its crystallography is orthorhombic. Its hardness is 3.5–4.5, and its specific gravity is 2.60–2.85. The refractive index of Canadian material (as measured via sodium light, 589.3 nm) is as follows: α 1.522; β 1.672–1.673; γ 1.676–1.679; biaxial negative. Under ultraviolet light, ammolite may fluoresce a mustard yellow.

Ammolite comes from the fossil shells of the Upper Cretaceous disk-shaped ammonites Placenticeras meeki and Placenticeras intercalare, and to a lesser degree, the cylindrical baculite, Baculites compressus. The ammonites that form our Alberta ammolite inhabited a prehistoric, inland subtropical sea that bordered the Rocky Mountains — this area is known today as the Cretaceous or Western Interior Seaway. As the ammonites died, they sank to the bottom and were buried by layers of bentonitic mud that eventually became shale. Many gem-quality ammonites are found within siderite concretions. These sediments preserved the aragonite of the shells, preventing it from converting to calcite.

Ammolite from the Bearpaw Formation

An iridescent opal-like play of colour is shown in fine specimens, mostly in shades of green and red; all the spectral colours are possible, however. The iridescence is due to the microstructure of the aragonite: unlike most other gems, whose colours come from light absorption, the iridescent colour of ammolite comes from interference with the light that rebounds from stacked layers of thin platelets that make up the aragonite. 

The thicker the layers, the more reds and greens are produced; the thinner the layers, the more blues and violets predominate. Reds and greens are the most commonly seen colours, owing to the greater fragility of the finer layers responsible for the blues. When freshly quarried, these colours are not especially dramatic; the material requires polishing and possibly other treatments in order to reveal the colours' full potential.

Ammolite itself is very thin. It is generally 0.5–0.8 millimetres (0.02–0.03 inches) thick. This thin coating covers a matrix typically made up of grey to brown shale, chalky clay, or limestone. 

Frost shattering of these specimens is common. If left exposed to the elements the thin ammolite tends to crack and flake. Prolonged exposure to sunlight can also lead to bleaching of the generally intense colouration. The cracking results in a tessellated appearance, sometimes described as a "dragon skin" or referred to as a stained glass window pattern. 

Ammolite mined from deeper deposits may be entirely smooth or with a rippled surface. Occasionally a complete ammonite shell is recovered with its structure well-preserved: fine, convoluted lines delineate the shell chambers, and the overall shape is suggestive of a nautilus. While these shells may be as large as 90 centimetres (35.5 inches) in diameter, the iridescent ammonites (as opposed to the pyritized variety) are typically much smaller. Most fossilized shells have had their aragonite pseudomorphously replaced by calcite or pyrite, making the presence of ammolite particularly uncommon.

In 1981, ammolite was given official gemstone status by the World Jewellery Confederation (CIBJO), the same year commercial mining of ammolite began. It was designated the official gemstone of the City of Lethbridge, Alberta in 2007.

Ammolite is also known as aapoak — Kainah for "small, crawling stone" — gem ammonite, calcentine, and Korite. The latter is a trade name given to the gemstone by the Alberta-based mining company Korite. Roughly half of all ammolite deposits are contained within the Kainah (Kainaiwa) reserve, and its inhabitants play a major role in ammolite mining. Marcel Charbonneau and his business partner Mike Berisoff were the first to create commercial doublets of the gem in 1967. They went on to form Ammolite Minerals Ltd.

FOSSIL PRESERVATION: REPLACEMENT

Ancient life can be preserved as fossils in a number of ways. Replacement is one of the ways both shellfish and wood can be preserved as fossils. Replacement occurs as the original atomic composition of the living organism is replaced cell by cell by a new chemical structure. 

It is the chemical composition of the groundwater that determines what the composition of the fossil will be. A common type of replacement is silification. Silification is the process by which silica minerals such as quartz, chalcedony, and opal fill pores or replace existing minerals, rock, or wood.

Silicification occurs in the earth’s interior through the action of hydrothermal and cold water saturated with silica. As aluminosilicate rock is weathered, a great deal of silica is freed and dissolves. Much of the dissolved silica is carried to the sea, but in places, it moves downward and replaces various rock. 

Hydrothermally silicified carbonate rock is frequently associated with ores of mercury, antimony, and other nonferrous metals. At ordinary temperatures, loose rock on the bottom of lakes and seas is subject to silicification, as is solid rock; this occurs most frequently with limestones and dolomites, more rarely with clays and phosphorites. 

Accumulations of fine-grained quartz form when carbonate rocks are replaced and aggregates of quartz and chalcedony develop when clayey rock is replaced. The presence of fine-grained quartz and quartz and chalcedony aggregates in ultrabasic rock indicates that deposits of silicate ores of nickel and cobalt may be found. Excellent examples of silification are fossil molluscs and petrified forests.

AMMONITES: CHAMBERED BEAUTY

Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids — octopus, squid, and cuttlefish — than they are to shelled nautiloids such as the living Nautilus species. The earliest ammonites appear during the Devonian, and the last species vanished in the Cretaceous–Paleogene extinction event. 

The chambered part of the ammonite shell is called a phragmocone. It contains a series of progressively larger chambers, called camerae — the singular is camera — that are divided by thin walls called septa —the singular is septum. You can see the interior of an ammonite with the discreet chambers in this lovely sliced Cleoniceras sp. from Madagascar.

Only the last and largest chamber, the body chamber, was occupied by the living animal at any given moment. As it grew, it added newer and larger chambers to the open end of the coil. Where the outer whorl of an ammonite shell largely covers the preceding whorls, the specimen is said to be involute. Anahoplites is a good example of this. Where it does not cover those preceding, the specimen is said to be evolute, something we see in the ammonite Dactylioceras.

A thin living tube called a siphuncle passed through the septa, extending from the ammonite's body into the empty shell chambers. Through a hyperosmotic active transport process, the ammonite emptied the water out of these shell chambers. This enabled it to control the buoyancy of the shell and thereby rise or descend in the water column.

A primary difference between ammonites and nautiloids is the siphuncle of ammonites — excepting Clymeniina — which runs along the ventral periphery of the septa and camerae — the inner surface of the outer axis of the shell — while the siphuncle of nautiloids runs more or less through the centre of the septa and camerae.

Clymenia has a closely coiled evolute shell that may be faintly ribbed. The dorsum, on the inside of the whorl, is slightly impressed, a result of the outermost whorl slightly enveloping the previous. The venter may be rounded or acute. The suture is simple, with a broad ventral saddle, broad lateral lobe, a dorsolateral saddle, and a moderately deep hidden dorsal lobe. Septal necks are usually short and do not form a continuous tube. The suture and siphuncle are characteristic of the family found in Europe and Western Australia.

If you fancy a read, check out the Treatise on Invertebrate Paleontology, Part L Ammonoidea; Geological Society of America and Univ of Kansas Press, 1964.