DIMORPHODON: TWO TOOTH PTERODACTYLUS

This remarkable fellow is Dimorphodon — a genus of medium-sized pterosaur from the Early Jurassic. He is another favourite of mine for his charming awkwardness.

You can see this fellow's interesting teeth within his big, bulky skull. Dimorphodon had two distinct types of teeth in their jaws — an oddity amongst reptiles — and also proportionally short wings for their overall size. 

Just look at him. What an amazing beast. We understand their anatomy quite well today, but can you imagine being the first to study their fossils and try to make sense of them. 

The first fossil remains now attributed to Dimorphodon were found in England by fossil collector Mary Anning, at Lyme Regis in Dorset, United Kingdom in December 1828. While she faced many challenges in her life, she was blessed to live in one of the richest areas in Britain for finding fossils. 

She walked the beaches way back in the early 1800s of what would become the Jurassic Coast UNESCO World Heritage Site. The Jurassic Coast holds some of the most interesting fossils ever found — particularly within the strata of the Blue Lias which date back to the Hettangian-Sinemurian. It is one of the world’s most famous fossil sites. Millions come to explore the eroding coastline looking for treasures that provide delight and inspiration to young and old.

 

These fossil treasures provide us with tremendous insights into our world 185 million years ago when amazing animals like Dimorphodon ruled the skies. 

Mary's specimen was acquired by William Buckland and reported in a meeting of the Geological Society on 5 February 1829. Six years later, in 1835, William Clift and William John Broderip built upon the work by Buckland to publish in the Transactions of the Geological Society, describing and naming the fossil as a new species. 

As was the case with most early pterosaur finds, Buckland classified the remains in the genus Pterodactylus, coining the new species Pterodactylus macronyx. The specific name is derived from Greek makros, "large" and onyx, "claw", in reference to the large claws of the hand. The specimen, presently NHMUK PV R 1034, consisted of a partial and disarticulated skeleton on a slab — notably lacking the skull. Buckland in 1835 also assigned a piece of the jaw from the collection of Elizabeth Philpot to P. macronyx. 

Later, the many putative species assigned to Pterodactylus had become so anatomically diverse that they began to be broken into separate genera.

In 1858, Richard Owen reported finding two new specimens, NHMUK PV OR 41212 and NHMUK PV R 1035, again partial skeletons but this time including the skulls. Having found the skull to be very different from that of Pterodactylus, Owen assigned Pterodactylus macronyx its own genus, which he named Dimorphodon. 

His first report contained no description and the name remained a nomen nudum. In 1859, however, a subsequent publication by Owen provided a description. After several studies highlighting aspects of Dimorphodon's anatomy, Owen finally made NHMUK PV R 1034 the holotype in 1874  — 185 million years after cruising our skies the Dimorphodon had finally fully arrived.

MAMMUTUS PRIMIGENIUS: WOOLLY MAMMOTH

This fellow is Mammutus primigenius a Woolly Mammoth from the Pleistocene of Siberia, Russia. 

Mammoths have a wonderful display of mammoth teeth, the diagnostic flat enamel plates and the equally distinct pointy cusped molars of the mastodons. He was a true elephant, unlike his less robust cousins, the mastodons. Mammoths were bigger — both in girth and height — weighing in at a max of 13 tonnes. 

They are closely related to Asian elephants and were about the size of the African elephants you see roaming the grasslands of Africa today.

If you stood beside him and reached way up, you might be able to touch his tusks but likely not reach up to his mouth or even his eyes. He would have had a shaggy coat of light or dark coloured hair with long outer hair strands covering a dense thick undercoat. His oil glands would have worked overtime to secrete oils, giving him natural waterproofing.

Some of the hair strands we have recovered are more than a meter in length. These behemoth proboscideans boasted long, curved tusks, little ears, short tails and grazed on leaves, shrubs and grasses that would have been work to get at as much of the northern hemisphere was covered in ice and snow during his reign. It is often the teeth of mammoths like those you see in the photo here that we see displayed. 

Their molar teeth were large and have always struck me as looking like ink plates from a printing press. If they are allowed to dry out in collection, they fall apart into discreet plates that can be mistaken for mineralized or calcified rock and not the bits and pieces of mammoth molars that they indeed are. Their large surface area was perfect for grinding down the low nutrient, but for the most part, plentiful grasses that sustained them.

Mammoth Tusk, Wrangel Island, Chukotka Okrug, Russia

How did they use their tusks? Likely for displays of strength, protecting their delicate trunks, digging up ground vegetation and in dry riverbeds, digging holes to get at the precious life-giving water. 

It's a genius design, really. A bit like having a plough on the front of your skull. In the photo here you can see a tusk washed clean in a creek bed on Wrangel Island.

Their size offered protection against other predators once the mammoth was full grown. Sadly for the juveniles, they offered tasty prey to big cats like Homotherium who roamed those ancient grasslands alongside them.

They roamed widely in the Pliocene to Holocene, roaming much of Africa, Europe, Asia and North America. We see them first some 150,000 years ago from remains in Russia then expanding out from Spain to Alaska. They enjoyed a very long lifespan of 60-80 — up to 20 years longer than a mastodon and longer than modern elephants. 

They enjoyed the prime position as the Apex predator of the megafauna, then declined — partially because of the environment and food resources and partially because of their co-existence with humans. In places where the fossil record shows a preference for hunting smaller prey, humans and megafauna do better together. We see this in places like the Indian Subcontinent where primates and rodents made the menu more often than the large megafauna who roamed there. We also see this in present-day Africa, where the last of the large and lovely megafauna show remarkable resilience in the face of human co-existence.  

The woolly mammoths from the Ukrainian-Russian plains died out 15,000 years ago. This population was followed by woolly mammoths from St. Paul Island in Alaska who died out 5,600 years ago — and quite surprisingly, at least to me, the last mammoth died just 4,000 years ago in the frosty ice on the small island of Wrangel in the Arctic Ocean — their final days spent scratching out a dwindling existence of genetic mutations, howling winds, rain-darkened hills and subsistence on tough grasses grown in thin soil. 

Further reading: Laura Arppe, Juha A. Karhu, Sergey Vartanyan, Dorothée G. Drucker, Heli Etu-Sihvola, Hervé Bocherens. Thriving or surviving? The isotopic record of the Wrangel Island woolly mammoth population. Quaternary Science Reviews, 2019; 222: 105884 DOI: 10.1016/j.quascirev.2019.105884

COELACANTHS: LIVING FOSSILS

Coelacanths are members of a now-rare order of fish, the Coelacanthiformes, that includes two extant species in the genus Latimeria: the West Indian Ocean coelacanth — Latimeria chalumnae — primarily found near the Comoro Islands off the east coast of Africa and the Indonesian coelacanth — Latimeria menadoensis. 

The name originates from the Permian genus Coelacanthus, which means hollow spine and was published by Swiss-born American biologist and geologist Jean Louis Rodolphe Agassiz in 1839. 

The type species Coelacanthus granulatus was described from the Late Permian, Wuchiapingian of Kupferschiefer of Germany and England. Coelacanthus is primarily known from Late Permian and Early Triassic deposits in Europe and Canada, although the referred species C. welleri, known from Iowa, is of Late Devonian, Famennian age. They survived the Permian–Triassic extinction event, and one species, C. banffensis, is known from the Early Triassic.

Coelacanths belong to the subclass Actinistia, a group of lobed-finned fish related to lungfish and certain extinct Devonian fish such as osteolepiforms, porolepiforms, rhizodonts, and Panderichthys. The oldest known coelacanth fossils are over 410 million years old. Coelacanths were thought to have become extinct in the Late Cretaceous, around 66 million years ago, but were rediscovered in 1938 off the coast of South Africa.

Coelacanths follow the oldest-known living lineage of Sarcopterygii, lobe-finned fish and tetrapods, which makes them are more closely related to lungfish and tetrapods — which includes amphibians, reptiles, birds and mammals — than to ray-finned fish. They are found along the coastline of Indonesia and in the Indian Ocean. The West Indian Ocean coelacanth is a critically endangered species.

The coelacanth was long considered a living fossil because scientists thought it was the sole remaining member of a taxon otherwise known only from fossils, with no close relations alive, and that it evolved into roughly its current form approximately 400 million years ago. Several more recent studies have shown that coelacanth body shapes are much more diverse than previously thought.

CHELICERATA: EURYPTERIDS, SPIDERS AND HORSESHOE CRABS

Sanctacaris uncata

This lovely is Sanctacaris uncata — a wonderful example of Chelicerata.

We first see them emerge in our ancient oceans in the Middle Cambrian, some 508 million years ago, as the arthropod Sanctacaris uncata (Briggs & Collins, 1988) known from the Glossopleura Zone, Stephen Formation of Mount Stephen in the Burgess Shale, British Columbia, Canada. 

Sanctacaris is proof positive that chelicerates, although rare, were present in the Middle Cambrian sea. Even at this early stage of evolution, Sanctacaris had the number and type of head appendages found in modified form in the eurypterids and xiphosurids, the major Palaeozoic groups that succeeded it. Even more interesting is that Sanctacaris had all the characteristics of later chelicerates except chelicerae — placing this early arthropod in a primitive sister group of all other chelicerates.

An extinct marine creature half a billion years old may sound otherworldly, but you know some of their more well-known marine brethren — sea spiders, the sexy eurypterids, chasmataspidids and horseshoe crabs — and some of their terrestrial cousins — spiders, scorpions, harvestmen, mites and ticks. 

They are grouped together because, like all arthropods, they have a segmented body and segmented limbs and a thick chitinous cuticle called an exoskeleton. Add those characteristics to a body system with two body segments — a cephalothorax and an abdomen. 

Like all arthropods, chelicerates' bodies and appendages are covered with a tough cuticle made mainly of chitin and chemically hardened proteins. 

Since this cannot stretch, the animals must moult to grow. In other words, they grow new but still soft cuticles, then cast off the old one and wait for the new one to harden. 

Until the new cuticle hardens the animals are defenceless and almost immobilized.  This also helps to explain why you find so many cephalons or moulted head shields — or whatever else our good arthropod friends shed and regrow — in the field and far fewer body fossils of the whole animal.

Some chelicerate are predatory animals that patrol the warm waters near thermal vents. They can be found feeding upon other predators and fish. Although the group were originally solely predatory, they have diversified to use all sorts of feeding strategies: predation, parasitism, herbivory, scavenging and dining on bits of decaying organic matter. 

Although harvestmen can digest solid food it is more akin to a mashed pulp by the time they do. The guts of most modern chelicerates are too narrow to digest solid food, instead, they generally liquidize their chosen meal by grinding it with their chelicerae and pedipalps then flooding it with digestive enzymes. 

To conserve water, air-breathing chelicerates excrete waste as solids that are removed from their blood by Malpighian tubules, structures that also evolved independently in insects — another case of convergent evolution.

The evolutionary origins of chelicerates from the early arthropods have been debated for decades. And although there is considerable agreement about the relationships between most chelicerate sub-groups, the inclusion of the Pycnogonida in this taxon has recently been questioned and the exact position of scorpions is still controversial, though they were long considered the most primitive or basal of the arachnids. 

We still have much to explore to sort out their evolutionary origins and placement within the various lineages but we will get there with time.

Image One: Reconstruction of Sanctacaris uncata, a Cambrian Habeliidan arthropod (stem-Chelicerata: Habeliida). by Junnn11 @ni075; Image Two: Chelicerata by Fossil Huntress

Aria C, Caron JB (December 2017). "Mandibulate convergence in an armoured Cambrian stem chelicerate". BMC Evolutionary Biology. 17 (1): 261. doi:10.1186/s12862-017-1088-7. PMC 5738823. PMID 29262772.

Legg DA (December 2014). "Sanctacaris uncata: the oldest chelicerate (Arthropoda)". Die Naturwissenschaften. 101 (12): 1065–73. doi:10.1007/s00114-014-1245-4. PMID 25296691.

Briggs DE, Collins D (August 1988). "A Middle Cambrian chelicerate from Mount Stephen, British Columbia" (PDF). Palaeontology. 31 (3): 779–798. Archived from the original (PDF) on July 16, 2011. Retrieved April 4, 2010.

Briggs DE, Erwin DH, Collier FJ (1995). Fossils of the Burgess Shale. Washington: Smithsonian Institution Press. ISBN 1-56098-659-X. OCLC 231793738.