Tuesday, 17 September 2019

CANGREJO FÓSIL: COSTACOPLUMA

Cuticular structure in a Late Maastrichtian crab, Costacopluma mexicana, from deposits near the town of from near Paredón, Ramos Arizpe in what is now southern Coahuila (formerly Coahuila de Zaragoza), north-eastern Mexico. We see this same species in the Upper Cretaceous Moyenne of Northeast Morocco and from the Pacific slope, Paleocene of California, USA. This beauty is in the collection of José F. Ventura‎.

While the crustacean cuticle has been the subject of study for over 250 years (Reaumur, 1712, in Drach, 1939), the focus of that early work has been the process of moulting.

Because crabs and other crustaceans have a hard outer shell (the exoskeleton) that does not grow, they must shed their shells through a process called moulting. Just as we outgrow our shoes, crabs outgrow their shells.

In 1984, Roer and Dillaman took a whole new approach, instead looking at the exoskeleton as a mineralized tissue. The integument of decapod crustaceans consists of an outer epicuticle, an exocuticle, an endocuticle and an inner membranous layer underlain by the hypodermis. The outer three layers of the cuticle are calcified.

The mineral is in the form of calcite crystals and amorphous calcium carbonate. In the epicuticle, the mineral is in the form of spherulitic calcite islands surrounded by the lipid-protein matrix. In the exo- and endo-cuticles the calcite crystal aggregates are interspersed with chitin-protein fibres which are organized in lamellae. In some species, the organization of the mineral mirrors that of the organic fibres, but such is not the case in certain cuticular regions in the xanthid crabs.

Control of crystal organization is a complex phenomenon unrelated to the gross morphology of the matrix. Since the cuticle is periodically moulted to allow for growth, this necessitates a bidirectional movement of calcium into the cuticle during post-moult and out during premolt resorption of the cuticle.

These movements are accomplished by active transport affected by a Ca-ATPase and Na/Ca exchange mechanism. The epi- and exo-cuticular layers of the new cuticle are elaborated during pre-moult but do not calcify until the old cuticle is shed. This phenomenon also occurs in vitro in the cuticle devoid of living tissue and implies an alteration of the nucleating sites of the cuticle in the course of the moult.

We're still learning about the relationship between the mineral and the organic components of the cuticle, both regarding the determination of crystal morphology and about nucleation. While the Portunidae offers some knowledge of the mechanisms and pathways for calcium movement, we know nothing concerning the transport of carbonate. These latter areas of investigation will prove fertile ground for future work; work which will provide information not only on the physiology of Crustacea but also on the basic principles of mineralization. The bidirectional nature of mineral transport and the sharp temporal transitions in the nucleating ability of the cuticular matrix provide ideal systems in which to study these aspects of calcification.

Torrey Nyborg, Francisco J. Vega and Harry F. Filkorn, Boletín de la Sociedad Geológica Mexicana, Vol. 61, No. 2, Número especial XI Congreso Nacional de Paleontología, Juriquilla 2009 (2009), pp. 203-209. Coahuila paleo coordinates:25°32′26″N 100°57′2″W

Monday, 16 September 2019

FOSSIL RELIC: AMIIFORMES

This well-preserved fossil fish skull is from Calamopleurus (Agassiz, 1841), an extinct genus of bony fishes related to the heavily armoured ray-finned gars.

They are fossil relics, the sole surviving species of the order Amiiformes. Although bowfins are highly evolved, they are often referred to as primitive fishes and living fossils as they retain many of the morphologic characteristics of their ancestors.

This specimen was found in Lower Cretaceous outcrops of the Santana Formation in the Araripe Basin UNESCO Global Geopark of northeastern Brazil. Collection of David Murphy

Sunday, 15 September 2019

NOTOCHORDS: CHORDATES OR CALAMARI

You and I are vertebrates, we have backbones. While we sometimes use the term to denote character, having a backbone or spinal column is what sets apart almost 70,000 species on this big blue planet.

So which lucky ducks evolved one? Warm-blooded birds and mammals can claim those bragging rights. They're joined by our cold-blooded, ectothermic friends, the fish, amphibians and reptiles. All these lovelies share this characteristic.

And whether they now live at sea or on land, all of these lineages evolved from a marine organism somewhere down the line, then went on to develop a notochord and spinal column. Notochords are flexible rods that run down the length of chordates and vertebrates. They are handy adaptations for muscle attachment, helping with signalling and coordinating the development of the embryonic stage. The cells from the notochord play a key role in the development of the central nervous system and the formation of motor neurons and sensory cells. Alas, we often take our evolution for granted.

Let's take a moment to appreciate just how marvellous this evolutionary gift is and what it allows us to do. Your backbone gives your body structure, holds up that heavy skull of yours and connects your tasty brain to your body and organs. Eating, walking, fishing, hunting, your morning yoga class, are all made possible because of this adaptation. Pick pretty near anything you love to do and it is only possible because of your blessed spine.

And it sets us apart from our invertebrate friends.

While seventy thousand may seem like a large number, it represents less than three to five percent of all described animal species. The rest is made up of the whopping 97%'ers, our dear invertebrates who include the arthropods (insects, arachnids, crustaceans, and myriapods), mollusks (our dear chitons, snails, bivalves, squid, and octopus), annelids (the often misunderstood earthworms and leeches), and cnidarians (our beautiful hydras, jellyfish, sea anemones, and corals). You'll notice that many of our invertebrate friends occur as tasty snacks. Having a backbone provides a supreme advantage to your placement in the food chain. Not always, as you may include fish and game on your menu. But generally, having a backbone means you're more likely to be holding the menu versus being listed as an appetizer. So, enjoy your Sunday 'downward dog' and thank your backbone for the magical gift it is.

Saturday, 14 September 2019

HEXAGONAL COLUMNS: COOLING BASALT

The Giant's Causeway is a spectacular expanse of interlocking hexagonal basalt columns formed from volcanic eruptions during the Paleocene some 50-60 million years ago.

These columns tell a story of the cooling and freezing of the lava flows that formed them. As lava at the surface cools and freezes, it also shrinks as its molecules rearrange themselves into a solid structure. This happens much more quickly at the surface where the lava comes in contact with moist, cool air. As the basalt cools and shrinks, pressure increases in intensity and cracks begin to form. A way to dissipate this huge stress is to crack at an angle of 120 degrees, the angle that gives us a hexagon.

We see this beautifully illustrated at the Giant's Causeway in Ireland. Here, highly fluid molten basalt intruded through chalk beds which later cooled, contracted and cracked into hexagonal columns, creating a surreal visual against a dark and stormy Irish Sea.

Friday, 13 September 2019

DORIPPE SINICA OF JAPAN

A beautiful example of the decapod, Dorippe sinica, from Holocene deposits near Shizuoka, Japan. This regal fellow has a strongly sculptured carapace. He looks like he would have been quite the bruiser moving about on the seafloor looking for tasty snacks. He likely enjoyed just about any form of meat, potentially dining on fish, worms, eggs, squid, starfish or even a few of his slow-moving cousins.

The carapace is deeply grooved with conspicuous wart-like tubercles; anterolateral margin, between the base of the exorbital tooth and cervical groove, smooth, without tubercles or denticles.

The teeth on the lower orbital margin in the cluster. Carpus of cheliped distinctly granulated on the upper surface and with a conspicuous row of granules along the anterior margin. Though missing here, the merus of second and third pereiopods are almost cylindrical. (Türkay 1995). This specimen was collected and is the collection of the deeply awesome Takashi Ito of Japan

ARANDASPIDA: AGENTS OF SHIELD

The oldest and most primitive pteraspidomorphs were the Astraspida and the Arandaspida. You'll notice that all three of these taxon names contain 'aspid', which means shield.

These early fishes and many of the Pteraspidomorphi possessed large plates of dermal bone at the anterior end of their bodies. This dermal armour was very common in early vertebrates, but it was lost in their descendants. Arandaspida is represented by two well-known genera: Sacabampaspis, from South America and Arandaspis from Australia. Arandaspis have large, simple, dorsal and ventral head shields. Their bodies were fusiform, which means they were shaped sort of like a spindle, fat in the middle and tapering at both ends. Picture a sausage that is a bit wider near the centre with a crisp outer shell. Image: Tamura (http://spinops.blogspot.com) - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=19460450

Thursday, 12 September 2019

TIKTAALIK OF ELLESMERE ISLAND

Tiktaalik was a fish with some advantageous tetrapod-like features that proved to be useful to an adaptation to land. Their head was detached from their shoulder girdle meaning they could lift their heads to take a look around. This was a new adaptation for our marine friends. The bones in the front limb were strong enough and adapted to support their bodies.

Tuesday, 10 September 2019

PAKICETUS: UNLIKELY WHALES

The unlikely creature bearing the title of "the first whale," is a fellow named Pakicetus. He is definitely not how we picture whales living today. Pakicetus is an extinct genus of cetaceans that lived about 50 million years ago.

They were mammals and looked like large rodents. They were also quite small by whale standards, reaching about four-feet in length. They ate meat, sometimes fish and are the ancestors of whales, porpoises and dolphins.

The only real clue of their connection to our aquatic friends is the shape of their skulls. Pakicetus had a long skull and an ear bone that is unique to whales. Oddly, they also had ankle bones that share characteristics with some of our even-toed mammals. They lived along the shores of a large shallow sea known as the Tethys. Although rare, there are several examples of mammals heading back to a life at sea. Photo: Kevin Guertin from Ottawa, Ontario, Canada - DSCF1201, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=36657302

Monday, 9 September 2019

DENMAN ISLAND CONCRETION

Northumberland Fm, Upper Cretaceous Nanaimo Group
A concretion found eroding out of the grey shales at Denman Island.

Thee Upper Cretaceous Nanaimo Group of southwest British Columbia is a >4 km-thick succession consisting mostly of deep marine siliciclastics deposited directly on the Insular Superterrane. As such, this succession has been the focus of several paleomagnetic, isotope geochemistry, paleontology, and sedimentology studies in attempts to elucidate the tectonic history and paleolatitude of the Insular Superterrane and associated entities during the critical time of Nanaimo Group deposition, 90 to 65 million years ago. The upper two-thirds of the succession is continuously and well exposed on Denman and Hornby islands and represents the best example of this part of the succession in the northern half of what we consider the single Nanaimo Basin. A concretion found on the beach at Denman, eroding out of the grey shales of the Upper Cretaceous Nanaimo Group

Sunday, 8 September 2019

NOOTKA ISLAND

Nootka Sound, Photo: Dan Bowen
Rugged West Coast VIPS Fossil Field Trip to Late Eocene - Early Oligocene, Hesquiat formation of Nootka Island, west coast of Vancouver Island, British Columbia, Canada.

The area is known for its exceptional natural beauty and bounty of beautifully preserved decapod fossil specimens. The formation is named for the Hesquiaht people of the Nuu-chah-nulth, of Nootka Sound.

Saturday, 7 September 2019

UPPER CRETACEOUS NANAIMO GROUP AT HORNBY ISLAND

Hornby Island is formed from sediments of the upper Nanaimo Group which are also widely exposed on adjacent Denman Island and the southern Gulf Islands. On this island, a total stratigraphic thickness of 1350 m of upper Nanaimo Group marine sandstone, conglomerate and shale are partially exposed. Four formations underlie the island from oldest to youngest, and from west to east: the Northumberland, Geoffrey, Spray and Gabriola.

During the upper Cretaceous, between ~90 to 65 Ma, sediments derived from the Coast Belt to the east and the Cascades to the southeast poured seaward to the west and northwest into what was the large ancestral Georgia Basin. This major forearc basin was situated between Vancouver Island and the mainland of British Columbia.

The Nanaimo Group as a whole represents largely coarse-grained units deposited in deep-sea fan systems. In this environment, deeper channels continuously cut through successive shale and sandstone bodies. The channels funnelled density currents into the basin, while also building levee deposits. Turbidity currents travelled down the channels, and also overtopped the levees spilling across backslope areas. The sequential sediment formations, from significantly coarse-grained sandstones and conglomerates to fine silts and shale units of the Nanaimo Group, are considered to be partly due to eustacy, but more significantly related to relative sea-level changes induced by regional tectonics in an active forearc setting.

The Northumberland Fm consists of a massive, dark-grey mudstone which is locally interlaminated and interbedded with siltstone and fine-grained sandstone. There are abundant calcium carbonate concretions, parallel and current ripple laminations, clastic dikes and folded layers due to slumping. In the Gulf Islands to the south, this formation has been found to contain abundant and diverse foraminifera indicating marine paleodepths of 150-1200 m.

The more resistive Geoffrey Fm consists of thick-bedded sandstone and conglomerate. It is highly channelized, and some sandstone has exposed parallel and ripple laminations. The Spray Fm exposed on the east end of the island is a massive olive-grey mudstone with interlaminations of sandstone.

Furthest to the east, the youngest exposures on Hornby Island are from the Gabriola Fm, which outcrops on the eastern peninsula. This is again a thick-bedded and channelized sequence of conglomerates and massive sandstone with minor mudstone interbeds. South, in the Gulf Islands, this formation has contained ammonites, gastropods and pelecypods. Paleowater-depth from foraminiferal assemblages has been set at 200 m.

Katnick, D.C. and P.S. Mustard (2001): Geology of Denman and Hornby Islands, British Columbia (NTS 92F/7E, 10); British Columbia Geological Survey Branch, Geoscience Map 2001-3.

England, T.D.J. and R. N. Hiscott (1991): Upper Nanaimo Group and younger strata, outer Gulf Islands, southwestern British Columbia: in Current Research, Part E; Geological Survey of Canada, Paper 91-1E, p. 117-125.

Friday, 6 September 2019

BIODIVERSITY AT SEA AND ON LAND

Most of the Earth's surface is an ocean. When I think of the Earth, it is our oceans that I picture. Life began there. We began there. Most of the major animal groups can trace their lineage back to the seas and the Cambrian explosion, an orgy of breathtaking species diversification.

Since that time, a shocking half a billion years ago, our seas have played host to an astonishing array of species. If I'd visited our Earth back in the Cambrian, I would have bet good money that our watery planet's future was in the seas not on the land. But that 's not the case. Quite surprisingly, it is our humble rock and soil who now boast more species. Five times that of those living in the oceans. I know, shocking but true. Our oceans certainly had the running start on both numbers and diversity of species. But it is our fungi, our flowering plants, mindblowing variety of insects, trees, bees and fleas that make up the bulk of Earth's species these days.

It is something I'm interested in learning more about as it does not make good sense to me. 80 percent of Earth's species live on land today. About 15 percent call our oceans home and another 5% or so live in freshwater. Why more species live on land than in the ocean has puzzled others as well. Robert May, a zoologist at the University of Oxford, mulls this very question in an article from 1994 titled, “Biological Diversity: Differences between Land and Sea.” He continued with his research and published "The future of biological diversity in a crowded world," in Current Science, Vol. 82, No. 11 (10 June 2002), pp. 1325-1331.

Here he questions how well we know the plants, animals and micro-organisms with which we share this beautiful planet. His focus in the paper was to question how many species are there and how fast are some going extinct? You'll be interested to know that his best guess in 2002 was somewhere between 1.7 to 1.8 million. That's a considerable increase from Carl Linneaus' work back in 1758, the Swedish botanist, zoologist, and physician took a stab at the same question and came up with an estimate of about 9,000 species. While his numbers were off by a long margin, he did give us the binomial nomenclature system we use for naming organisms, so he still gets a hall pass.

May is a boy about town. His work is referenced everywhere. You may enjoy an article by the Atlantic from 2017 that delves into the topic for the lay audience with an eye to popularized reading. May, R. (2002). The future of biological diversity in a crowded world. Current Science, 82(11), 1325-1331. Retrieved from http://www.jstor.org/stable/24105996 / The Atlantic article: https://www.theatlantic.com/science/archive/2017/07/why-are-there-so-many-more-species-on-land-than-in-the-sea/533247/

Thursday, 5 September 2019

ICHTHYOSAURS: WARM-BLOODED DOLPHINS OF THE MESOZOIC

Ichthyosaurs are an extinct order of marine reptiles from the Mesozoic era. They were visibly dolphin-like in appearance but seem to share some other qualities as well. They were warm-blooded, used their coloration as camouflage and had insulating blubber to keep them warm.

"Ichthyosaurs are interesting because they have many traits in common with dolphins, but are not at all closely related to those sea-dwelling mammals," says research co-author Mary Schweitzer, professor of biological sciences at NC State with a joint appointment at the North Carolina Museum of Natural Sciences and visiting professor at Lund University. "We aren't exactly sure of their biology either. They have many features in common with living marine reptiles like sea turtles, but we know from the fossil record that they gave live birth, which is associated with warm-bloodedness. This study reveals some of those biological mysteries."

We find their fossil remains in outcrops spanning from the mid-Cretaceous to the earliest Triassic. As we look through the fossils, we see a slow evolution in body design moving towards that enjoyed by dolphins and tuna by the Upper Triassic, albeit with a more narrower, more pointed snout.

Johan Lindgren, Associate Professor at Sweden's Lund University and lead author of a paper,  describing the work, worked with twenty-one other ichthyosaur researchers to analyze the 180 million-year-old specimen, Stenopterygius, from outcrops in the Holzmaden quarry in Germany.

"Both the body outline and remnants of internal organs are clearly visible," says Lindgren. "Remarkably, the fossil is so well-preserved that it is possible to observe individual cellular layers within its skin."  Researchers identified cell-like microstructures containing pigment organelles on the surface of the fossil. This ancient skin revealed a feature we recognized from marine dwelling animals, the ability to change colour, providing camouflage from potential predators. They also found traces of what might have been the animal's liver. When they put some of the tissue through chemical analysis, it was consistent with what we'd look for in adipose tissue or blubber. Not surprising as dolphins today use blubber for buoyancy and to help thermally insulate for thermal regulation in cold seas.  might find in a vertebrate that uses blubber as a means of maintaining body temperatures independent of ambient conditions.

Today, blubber is an important part of the anatomy of seals, whales and walruses. It covers the core of their bodies, storing energy, insulating them from cold seas and provide extra buoyancy. While they do not have blubber on their fins, flippers and flukes. Not all marine animals need blubber. Our cold-blooded marine friends: sharks, crabs, fish, are able to let their body temperatures dropdown to very chilly levels, some as low as 36 degrees Fahrenheit. They have a few tricks up their sleeves to make this happen. Sharks have evolved specialized physiology to keep their metabolic rate high and their hearts are able to contract in the icy depths because of a special protein. These adaptations allow sharks to enjoy a wide range of habitats and follow their food from warm tropical seas to the icy waters of the North Pacific. 

Johan Lindgren, Peter Sjövall, Volker Thiel, Wenxia Zheng, Shosuke Ito, Kazumasa Wakamatsu, Rolf Hauff, Benjamin P. Kear, Anders Engdahl, Carl Alwmark, Mats E. Eriksson, Martin Jarenmark, Sven Sachs, Per E. Ahlberg, Federica Marone, Takeo Kuriyama, Ola Gustafsson, Per Malmberg, Aurélien Thomen, Irene Rodríguez-Meizoso, Per Uvdal, Makoto Ojika, Mary H. Schweitzer. Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur. Nature, 2018; DOI: 10.1038/s41586-018-0775-x

North Carolina State University. (2018, December 5). Soft tissue shows Jurassic ichthyosaur was warm-blooded, had blubber and camouflage. ScienceDaily. Retrieved September 7, 2019, from www.sciencedaily.com/releases/2018/12/181205134118.htm

Wednesday, 4 September 2019

OSTRACODERMS TO ANGLERFISH

The festive lassie you see here is an Anglerfish. They always look to be celebrating a birthday of some kind, albeit solo. This party is happening deep in our oceans right now and for those that join in, I hope they like it rough.

The wee candle you see on her forehead is a photophore, a tiny bit of luminous dorsal spine. In anglerfish' world, it's dead sexy. It's an adaptation used to attract prey and mates alike.

Deep in the murky depths of the Atlantic and Antarctic oceans, hopeful female anglerfish light up their sexy lures. When a male latches onto this tasty bit of flesh, he fuses himself totally. He might be one of several potential mates. She's not picky, just hungry. Lure. Feed. Mate. Repeat.

A friend asked if anglerfish mate for life. Well, yes.... yes, indeed they do.

Mating is a tough business down in the depths. Her body absorbs his over time until all that's left are his testes. While unusual, it is only one of many weird and whacky ways our fishy friends communicate, entice, hunt and creatively survive and thrive.

The evolution of fish began about 530 million years ago with the first fish lineages belonged to the Agnatha, a superclass of jawless fish. We still see them in our waters as cyclostomes but have lost the conodonts and ostracoderms to the annals of time. Like all vertebrates, fish have bilateral symmetry; when divided down the middle or central axis, each half is the same. Organisms with bilateral symmetry are generally more agile, making finding a mate, hunting or avoiding being hunted a whole lot easier.

When we envision fish, we generally picture large eyes, gills, a well-developed mouth. The earliest animals that we classify as fish appeared as soft-bodied chordates who lacked a true spine. While they were spineless, they did have notochords, a cartilaginous skeletal rod that gave them more dexterity than the cold-blooded invertebrates who shared those ancient seas and evolved without a backbone. Fish would continue to evolve throughout the Paleozoic, diversifying into a wide range of forms. Several forms of Paleozoic fish developed external armour that protected them from predators. The first fish with jaws appeared in the Silurian period, after which many species, including sharks, became formidable marine predators rather than just the prey of arthropods.

Fishes in general respire using gills, are most often covered with bony scales and propel themselves using fins. There are two main types of fins, median fins and paired fins. The median fins include the caudal fin or tail fin, the dorsal fin, and the anal fin. Now there may be more than one dorsal, and one anal fin in some fishes.

The paired fins include the pectoral fins and the pelvic fins. And these paired fins are connected to, and supported by, pectoral and pelvic girdles, at the shoulder and hip; in the same way, our arms and legs are connected to and supported by, pectoral and pelvic girdles. This arrangement is something we inherited from the ancestors we share with fishes. They are homologous structures.

When we speak of early vertebrates, we're often talking about fishes. Fish is a term we use a lot in our everyday lives but taxonomically it is not all that useful. When we say, 'fish' we generally mean an ectothermic, aquatic vertebrate with gills and fins.

Fortunately, many of our fishy friends have ended up in the fossil record. We may see some of the soft bits from time to time, as in the lovely fossil fish found in concretion in Brazil, but we often see fish skeletons. Vertebrates with hard skeletons had a much better chance of being preserved. In British Columbia, we have lovely two-dimensional Eocene fossil fish well-represented from the Allenby of Princeton and the McAbee Fossil Beds. We have the Tiktaalik roseae, a large freshwater fish, from 375 million-year-old Devonian deposits on Ellesmere Island in Canada's Arctic. Tiktaalik is a wonderfully bizarre creature with a flat, almost reptilian head but also fins, scales and gills. We have other wonders from this time. There are also spectacular antiarch placoderms, Bothriolepsis, found in the Upper Devonian shales of Miguasha in Quebec.

There are fragments of bone-like tissues from as early as the Late Cambrian with the oldest fossils that are truly recognizable as fishes come from the Middle Ordovician from North America, South America and Australia. At the time, South America and Australia were part of a supercontinent called Gondwana. North America was part of another supercontinent called Laurentia and the two were separated by deep oceans.

These two supercontinents and others that were also present were partially covered by shallow equatorial seas and the continents themselves were barren and rocky. Land plants didn't evolve until later in the Silurian Period. In these shallow equatorial seas, a large diverse and widespread group of armoured, jawless fishes evolved: the Pteraspidomorphi. The first of our three groups of ostracoderms. The Pteraspidomorphi are divided into three major groups: the Astraspida, Arandaspida and the Heterostraci.

The oldest and most primitive pteraspidomorphs were the Astraspida and the Arandaspida. You'll notice that all three of these taxon names contain 'aspid', which means shield. This is because these early fishes and many of the Pteraspidomorphi possessed large plates of dermal bone at the anterior end of their bodies. This dermal armour was very common in early vertebrates, but it was lost in their descendants. Arandaspida is represented by two well-known genera: Sacabampaspis, from South America and Arandaspis from Australia. Arandaspis have large, simple, dorsal and ventral head shields. Their bodies were fusiform, which means they were shaped sort of like a spindle, fat in the middle and tapering at both ends. Picture a sausage that is a bit wider near the centre with a crisp outer shell.

Tuesday, 3 September 2019

PRIMITIVE FISH OF THE CHENGJIANG LAGERSTÄTTE

Three genera of Lower Cambrian fish are known from the 530 million-year-old Chengjiang Lagerstätte in Yuxi, Yunnan Province, southern China. The locality is just north of Fuxian Lake and about a half-hour drive south from the city of Kunming.
  • Haikouichthys ercaicunensis
  • Myllokunmingia fengjiaoa
  • Zhongjianichthys rostratus
The first two of these are fusiform in shape, whereas the third is eel-like. Myllokunnmingial and Haikouichthys have fusiform bodies and pairs of large eyes within the dorso-anterior lobe. Zhongjianichthys has eyes behind the dorso-anterior lobe.

A friend of mine, Eldon Grupp from the USA, found an 18 mm specimen on a mortality slab of Haikouella from Chengjiang. Apparently, no one had noticed it before shipping. Not surprising as Zhongjianichthys are easy to overlook. I've asked him if I can get a photo of that mortality plate to share with you. It's quite stunning. Haikouella, of course, are not vertebrates, but advanced craniate chordates. The specimen in question, however, was a vertebrate. Eldon has assigned this specimen to genus Zhongjianichthys based on its eel-like characteristics and its large eyes located behind the anterior or rostral lobe instead of within it. Even so, family affiliation is uncertain.

Monday, 2 September 2019

SIRENIA: MANATEES AND DUGONGS

I'd always grouped the dugongs and manatees together. There are slight differences between these two groups. Both groups belong to the order Sirenia. They shared a cousin in the Steller's sea cow, Hydrodamalis gigas, but that piece of their lineage was hunted to extinction by our species in the 18th century. Dugongs have tail flukes with pointed tips and manatees have paddle-shaped tails, similar to a Canadian Beaver.

Both of these lovelies from the order Sirenia went from terrestrial to marine, taking to the water in search of more prosperous pastures, as it were.

They are the extant and extinct forms of the oddball manatees and dugongs. They inhabit rivers and shallow coastal waters, making the best use of their fusiform bodies that lack dorsal fins and hind limbs. I've been thinking about them in the context of some of the primitive armoured fish we find in the Chengjiang biota of China, specifically those primitive species that were also fusiform.

We find dugongs today in waters near northern Australia and parts of the Indian and Pacific Oceans. They favour locations where seagrass, their food of choice, grows plentiful and they eat it roots and all. While seagrass low in fibre, high in nitrogen and easily digestible is preferred, dugongs will also dine on lower grade seagrass, algae and invertebrates should the opportunity arise. They've been known to eat jellyfish, sea squirts and shellfish over the course of their long lives. Some of the oldest dugongs have been known to live 70+ years, which is another statistic I find surprising. They are large, passive, have poor eyesight and look pretty tasty floating in the water; a defenceless floating buffet. Their population is in decline but yet they live on.


Sunday, 1 September 2019

THE LURE OF THE SEA

Many land animals have returned to the sea throughout evolutionary history. We have beautifully documented cases from amphibians, reptiles, birds and mammals from over 30 different lineages over the past 250 million years.

Our dear penguins, seals, sea lions, walruses, whales, crocodiles and sea turtles were once entirely terrestrial. Some dipped a toe or two into freshwater ponds, but make no mistake, they were terrestrial. Each of these animals had ancestors that tried out the sea and decided to stay. They evolved and employed a variety of adaptations to meet their new saltwater challenges. Some adapted legs as fins, others became more streamlined, and still, others developed specialized organs to extract dissolved oxygen from the water through their skin or gills. The permutations are endless.

Returning to the sea comes with a whole host of benefits but some serious challenges as well. Life at sea is very different from life on land. Water is denser than air, impacting how an animal moves, sees and hears. More importantly, it impacts an air-breathing animal's movement on a pretty frequent basis. If you need air and haven't evolved gills, you need to surface frequently. Keeping your body temperature at a homeostatic level is also a challenge as water conducts heat much better than air. Even with all of these challenges, the lure of additional food sources and freedom of movement kept those who tried the sea in the sea and they evolved accordingly.

This is an interesting article from Alicia Ault writing for the Smithsonian who interviewed Nick Pysenson and Neil Kelley about some of their research that touches on this area. They published a paper on it in the journal Science back in 2015.

Here's the link: https://science.sciencemag.org/content/348/6232/aaa3716

And Ault's work is definitely worth a read: https://www.smithsonianmag.com/smithsonian-institution/take-deep-dive-reasons-land-animals-moved-seas-180955007/