FIBULACARIS NEREIDIS: A NEW BIVALVED CAMBRIAN ARTHROPOD

Fibulacaris nereidis / Artwork by Danielle Dufault @MesozoicMuse

Fibulacaris nereidis is a new species joining the ranks of the Cambrian bivalved arthropod. Alejandro Izquierdo-López and Jean-Bernard Caron published on this new species, closely related to Pakucaris back in 2019. 

The wonderful illustration above by the talented Danielle Dufault shows how bizarre or alien some of these animals can be. 

The origin of the arthropod carapace, an enlargement of cephalic tergites, can be traced back to the Cambrian period. Even so, its disparity and evolution are still not fully understood. It is the detailed study of species such as this new ‘bivalved’ arthropod, Fibulacaris nereidis gen. et sp. nov., that will help us get closer to the truth. 

Interpretive Cladogram

The team had plenty of material to work with for this analysis. This new species is based upon 102 specimens from the middle Cambrian, Wuliuan Stage,  Burgess Shale, Marble Canyon area in British Columbia's Kootenay National Park, Canada. 

The laterally compressed carapace covers most of the body. It is fused dorsally and merges anteriorly into a conspicuous postero-ventrally recurved rostrum as long as the carapace and positioned between a pair of backwards-facing pedunculate eyes. 

The body is homonomous, with approximately 40 weakly sclerotized segments bearing biramous legs with elongate endopods, and ends in a pair of small flap-like caudal rami. Fibulacaris nereidis is interpreted as a suspension feeder possibly swimming inverted, in a potential case of convergence with some branchiopods. 

A Bayesian phylogenetic analysis places it within a group closely related to the extinct Hymenocarina. Fibulacaris nereidis is unique in its carapace morphology and overall widens the ecological disparity of Cambrian arthropods and suggests that the evolution of a ‘bivalved' carapace and an upside-down lifestyle may have occurred early in stem-group crustaceans.

Fibulacaris nereidis contributes to the increasing morphological, functional, ecologic and taxonomic diversity of bivalved arthropods known from the Cambrian period. The shape of the carapace, with its single posteriorly directed ventral rostrum, appears to be morphologically unique not only among Cambrian and other fossil species but similarly rare across extant crustaceans or other arthropods. The carapace, including the rostrum, most probably had a protective role, but as in other extant arthropods, could have contributed to swimming performance and the creation of feeding currents. 

F. nereidis may have moved through our ancient seas swimming in an inverted position — rare across arthropods and analogous to that observed in anostracans and some cladocerans. This highlight the importance of the carapace morphology in palaeo-ecological reconstructions and show that the arthropod carapace was already both a morphologically and functionally diverse character in the Cambrian period. 

Bivalved Cambrian Arthropods / Alejandro  Izquierdo-López

Their phylogenetic analysis reveals a potential new group of mandibulate deposits and suspension feeders with homonomous legs and segments — some lacking certain mandibulate characters, such as antennae or mandibles — which may be related to an adaptation to this ecological niche and further illustrate a case of convergent evolution with some branchiopod taxa. 

These results suggest that the bivalved carapace could have been a basal trait for all Mandibulata or may even have had an earlier origin if this and the bivalved carapace of the Isoxyiidae were found to be homologous. 

Homologies between arthropod carapaces, bivalved or not, and structures such as radiodont shields, non-crustaceomorph univalved carapaces (e.g. Burgessia, Naraoia) and head shields (e.g. fuxianhuiids, habeliids, nauplius) are still quite poorly understood. We will need to find more examples to fully flesh out a comprehensive evolutionary analysis on this trait. 

Besides, new data and morphological revisions on key bivalved arthropods could reshape the present phylogenetic analyses. Nonetheless, Cambrian bivalved arthropods certainly show a high ecological and taxonomic disparity, that is increasingly contributing to the understanding of the evolution of early arthropods and the Cambrian period as a whole.

Top Image by the talented Danielle Dufault @MesozoicMuse. Composite Bivalved Cambrian Arthropods by Alejandro Izquierdo-López. 

Illustration: Interpretative cladogram based on a consensus tree from a Bayesian analysis using a Markov k model on a morphological dataset with 90 taxa and 213 characters. There is some interpretation here. Numbers next to nodes are posterior probabilities. The yellow box indicates the new monophyletic group to which Fibulacaris belongs. The green box highlights the group Hymenocarina.

Reference link: A Burgess Shale mandibulate arthropod with a pygidium: a case of convergent evolution. https://onlinelibrary.wiley.com/doi/abs/10.1002/spp2.1366

PAKUCARIS APATIS: A PAC-MAN-LIKE-CRAB OF THE GODDESS OF DECEIT

Pakucaris apatis. Illustration by Danielle Dufault, ROM

Meet Pakucaris apatis — the Pac-Man-like Crab of the Goddess of Deceit Apate — from the heart of the Canadian Rockies.

This fresh look at evolutionary trends during the Cambrian Explosion landed in my inbox — straight off the press from its June 15, 2021 publication in Papers in Palaeontology. 

In it, Alejandro Izquierdo-López and Jean-Bernard Caron untangle the evolutionary mysteries of Cambrian bivalved arthropods — a polyphyletic group of carapace-bearing arthropods that includes stem euarthropods, stem mandibulates and crustaceans. 

They describe Pakucaris apatis gen. et sp. nov., a new stem mandibulate bivalved arthropod from the middle Cambrian, Wuliuan Stage, Burgess Shale at Marble Canyon, Kootenay National Park, British Columbia, Canada. 

This new half a billion-year-old Burgess Shale mandibulate arthropod is the first we are seeing with a pygidium — an exciting case of convergent evolution. 

In Pakucaris, the pygidium — the plate-like region formed by the fusion of posterior body segments — has limbs similar to the preceding thorax/trunk. In this case, it convergently evolved between trilobites, mollisoniids and Pakucaris apatis — though Kylinxia also had a pygidium. 

Pakucaris apatis, a new Cambrian bivalved arthropod

Although similar structures appear in crustaceans, this is the first time we see a pygidium in a mandibulate (crustaceans + myriapods). What are we seeing in these Cambrian arthropods? 

The authors note that the number of segments in the thorax and pygidium of Pakucaris apatis increase at the same rate. 

If this occurs — as it does in trilobites — then the rate of segment generation in the pygidium must have exactly matched the rate of segment release. 

In our new friend, Pakucaris apatis only a few specimens have ever been found, so we have only two morphotypes of this wee arthropod from 11.6–26.6 mm long, which differ mainly in their size and number of segments — possibly reflecting sexual dimorphism (the differences between male and female of a species) or different anamorphic stages. 

Most specimens are around ~1 cm long but a single specimen is ~3 cm long. Given the limited number of specimens, we cannot yet speculate if we are seeing differences between males and females or post-embryonic growth and moulting stages within the species as seen in proturans and millipedes. Either possibility could be the case. We will hopefully find more of these lovelies within the Burgess Shale and elsewhere as a base of comparison.

Pakucaris apatis Alejandro Izquierdo @trichodes

The carapace is a dorsal crest that extends anteriorly into a small recurved rostrum and two anterolateral processes. 

Pakucaris also have some very interesting filiform structures at their head. These likely originate before the eyes and could be related to the labrum complex. The labrum is that flat extension of the head (below the clypeus), we see covering the mandibles of arthropods. Unlike other mouthparts, the labrum is a single, fused plate — though it originally was—and embryonically is—two structures.

The filiform structures we see in Pakucaris pop up in many arthropods, and their evolution provides an interesting puzzle.

Around 20% of the posterior-most body segments and limbs are covered by a large spine-bearing shield. The head bears a pair of eyes, a possible pair of unsegmented appendicular projections and two pairs of segmented appendages. 

The thorax is multisegmented, homonomous, with weakly sclerotized segments bearing biramous limbs, composed of a stenopodous endopod with c. 20 podomeres and a paddle-shaped exopod. 

Pakucaris is interpreted as a nektobenthic suspension feeder. Bayesian phylogenetic analysis implies a position within Hymenocarina as stem mandibulates. 

The posterior shield is regarded as a pygidium and represents a case of morphofunctional convergent evolution between mandibulates, artiopodans and mollisoniids. 

Trilobite Anatomy for Comparison

What is most interesting about Pakucaris apatis is it adds to a growing number of pygidium-bearing arthropods, potentially hinting at a common developmental pattern across early arthropod evolution. 

Many of our Cambrian arthropod friends faced similar living conditions and challenges — and adapted to them in similar means. Is this what we are seeing in Pakucaris? Maybe. 

Pakucaris does have a rather fetching posterior shield, which may be analogous to a trilobite pygidium — the plate-like fused segments used for protection and sometimes enrolment. Arthropods have evolved this feature multiple times convergently. And many crustaceans technically go through a pygidium phase — the oddity there being retaining it into adulthood.

This study not only increases our understanding of the early evolution of mandibulates but also illustrates a unique case of early evolutionary convergence during the Cambrian Explosion.

The name Pakucaris apatis means Pac-Man-like crab of the goddess of deceit Apate. Maryam A., the collection managers at the Royal Ontario Museum suggested it after noting the resemblance to the videogame character. She was a huge contribution to the team pulling this paper together.

Bivalved Cambrian Arthropods / Alejandro Izquierdo

Pakucaris belongs to a group of Cambrian arthropods termed bivalved arthropods. These have a carapace that covers their cephalothorax, in many cases, the only structure preserved. Exceptional preservation has allowed us to know more about these animals, albeit often only the hard parts of them.

Overall, Pakucaris shows us how different Cambrian bivalved arthropods can be — making our current phylogenies more difficult to clarify — and presents different features (frontal filaments, pygidium) which may be important as we look to understand early arthropod evolution.

Their paper was made possible by the University of Toronto and Royal Ontario Museum along with la Asociación de Becarios de la Caixa — funding research that expands our knowledge of nature. So far Pakucaris is classified in Hymenocarina — stem-crustaceans or mandibulates with bivalved carapaces — joining other Cambrian arthropods like Waptia fieldensis — but there is still much we do not know about this group and additional research — and research funding — will help us solve these mysteries.

Photos / Illustrations: Alejandro Izquierdo, University of Toronto. Art by Danielle Dufault, Palaeo-Scientific Ilustrator, Research Assistant at the Royal Ontario Museum, Host of Animalogic

References: A Burgess Shale mandibulate arthropod with a pygidium: a case of convergent evolution. https://onlinelibrary.wiley.com/doi/10.1002/spp2.1366

MEET ACICULOLENUS ASKEWI: A NEW UPPER CAMBRIAN TRILOBITE

A new species of trilobite from the upper Cambrian McKay Group was introduced in March of 2020: Aciculolenus askewi.  The species is named after Don Askew, an avid fossil hunter of Upper Cambrian trilobites from Cranbrook, British Columbia, Canada, who has discovered several new species in the East Kootenays. 

Don was the first to brave the treacherous cliffs up the waterfall on the west side of the ravine below Tanglefoot mountain. That climb led to his discovery of one of the most prolific outcrops in the McKay Group with some of the most exciting and best-preserved trilobites from the region. 

The faunal set are similar to those found at site one — the first of the trilobite outcrops discovered by Chris New and Chris Jenkins — an hours hike through grizzly bear country.

The specimens found at the top of the waterfall are not in calcite wafers, as they are elsewhere, instead, these exceptionally preserved specimens are found complete with a thin coating of matrix that must be prepped down to the shell beneath. 

Askew was also the skill preparator called upon to tease out the details from the 'gut trilobite' recently published from the region. In all, this area has produced more than 60 new species — many found by Askew — and not all of which have been published yet.

I caught up with Don last summer on a trip to the region. He was gracious in openly sharing his knowledge and a complete mountain goat in the field — a good man that Askew. 

Not surprising then that Brian Chatterton would do him the honour of naming this new species after him. 

Chatterton, Professor Emeritus at the University of Alberta, is an invertebrate palaeontologist with a great sense of humour and a particular love of trilobites. Even so, his published works span a myriad of groups including conodonts, machaeridians, sponges, brachiopods, corals, cephalopods, bivalves, trace fossils — to fishes, birds and dinosaurs.

Brian Chatterton has been visiting the East Kootenay region for many years. In 1998, he and Rolf Ludvigsen published the pivotal work on the "calcified trilobites" we had begun hearing about in the late 1990s. There were tales of blue trilobites in calcified layers guarded by a resident Grizzly. This was years before logging roads had reached this pocket of paleontological goodness and hiking in — bear or no bear — was a daunting task. 

In his Cambridge University Press paper, Chatterton describes the well-preserved fauna of largely articulated trilobites from three new localities in the Bull River Valley. 

The Dream Team at Fossil Site #15, East Kootenays, August 2, 2020

All the trilobites from these localities are from the lower or middle part of the Wujiajiania lyndasmithae Subzone of the Elvinia Zone, lower Jiangshanian, in the McKay Group. 

Access is via a bumpy ride on logging roads 20 km northeast of Fort Steele that includes fording a river (for those blessed with large tires and a high wheelbase) and culminating in a hot, dusty hike and death-defying traipse down 35-degree slopes to the localities.

Two new species were proposed with types from these localities: Aciculolenus askewi and Cliffia nicoleae. 

The trilobite (and agnostid) fauna from these localities includes at least 20 species that read like a who's who of East Kootenay palaeontology: 

Aciculolenus askewi n. sp., Agnostotes orientalis (Kobayashi, 1935), Cernuolimbus ludvigseni Chatterton and Gibb, 2016, Cliffia nicoleae n. sp., Elvinia roemeri (Shumard, 1861), Grandagnostus? species 1 of Chatterton and Gibb, 2016, Eugonocare? phillipi Chatterton and Gibb, 2016, Eugonocare? sp. A, Housia vacuna (Walcott, 1912), Irvingella convexa (Kobayashi, 1935), Irvingella flohri Resser, 1942, Irvingella species B Chatterton and Gibb, 2016, Olenaspella chrisnewi Chatterton and Gibb, 2016, Proceratopyge canadensis (Chatterton and Ludvigsen, 1998), Proceratopyge rectispinata (Troedsson, 1937), Pseudagnostus cf. P. josepha (Hall, 1863), Pseudagnostus securiger (Lake, 1906), Pseudeugonocare bispinatum (Kobayashi, 1962), Pterocephalia sp., and Wujiajiania lyndasmithae Chatterton and Gibb, 2016.

Chris New, pleased as punch atop Upper Cambrian Exposures

It has been the collaborative efforts of Guy Santucci, Chris New, Chris Jenkins, Don Askew and Stacey Gibb that has helped open up the region — including finding and identifying many new species or firsts including Pseudagnostus securiger, a widespread early Jiangshanian species not been previously recorded from southeastern British Columbia. 

Other interesting invertebrate fossils from these localities include brachiopods, rare trace fossils, a complete silica sponge (Hyalospongea), and a dendroid graptolite. 

The species we find here are more diverse than those from other localities of the same age in the region — and enjoy much better preservation. 

The birth of new species into our scientific nomenclature takes time and the gathering of enough material to justify a new species name.

Fortunately for Labiostria gibbae, specimens had been found of this rare species had been documented from the upper part of Wujiajiania lyndasmithae Subzone — slightly younger in age. 

Combined with an earlier discovery, they provided adequate type material to propose the new species — Labiostria gibbae — a species that honours Stacey Gibb and which will likely prove useful for biostratigraphy.

Reference: https://www.cambridge.org/core/journals/journal-of-paleontology/article/abs/midfurongian-trilobites-and-agnostids-from-the-wujiajiania-lyndasmithae-subzone-of-the-elvinia-zone-mckay-group-southeastern-british-columbia-canada/E8DBC8BD635863E840715122C05BB14A#

Photo One: Aciculolenus askewi by Chris Jenkins, Cranbrook, British Columbia

Photo Two: L to R: Dan Bowden, Guy Santucci, Chris Jenkins, Dan Askew and John Fam at Fossil Site #15, East Kootenay Region, British Columbia, Canada, August 2, 2020.

Photo Three: Chris New pleased as punch atop of Upper Cambrian Exposures in the East Kootenay Region, British Columbia, Canada

GUT TRILOBITE: TAGMOSIS IN AGLASPIDID ARTHROPODS

Orygmaspis (Parabolinoides) contracta with gut structure

This specimen lovely chocolate brown trilobite specimen is Orygmaspis (Parabolinoides) contracta — one of the most exciting trilobites to come out of the McKay Group in the East Kootenay Region of British Columbia, Canada.

And what is most exciting about this specimen is that there is clear preservation of some of the gut structures preserving this trilobite's last meal.

Documentation of non- or weakly biomineralizing animals that lived during the Furongian is essential for a comprehensive understanding of the diversification of metazoans during the early Palaeozoic. 

Biomineralization, biologically controlled mineralization, occurs when crystal morphology, growth, composition, and location is completely controlled by the cellular processes of a specific organism. Examples include the shells of invertebrates, such as molluscs and brachiopods. The soft bits of those same animals tend to rot or be scavenged long before mineralization or fossilization can occur — hence, we find less of them.

So, not surprisingly, the fossil record of soft-bodied metazoans is particularly scarce for this critical time interval. To date, the fossils we do have are relatively rare and scattered at a dozen or so localities worldwide. 

Location and stratigraphy of the Fossil Locality

This is one of the reasons that the soft gut structures from this Orygmaspis contracta trilobite are particularly exciting. 

This specimen was found in Upper Cambrian exposures in the Clay Creek section at the top of the left fork of the ravine below Tanglefoot Mountain, 20 km northeast of Fort Steele. 

It was the keen eyes of Chris Jenkins who noticed the interesting structures worthy of exploration.

Lerosey-Aubril along with colleagues, Patterson, Gibb and Chatterton, published a great study on this trilobite in Gondwana Research, February 2017. 

Their work looked at this new occurrence of exceptional preservation in Furongian (Jiangshanian) strata of the McKay Group near Cranbrook, British Columbia, Canada. Their study followed up on the work of Chatterton et al. studying trilobites with phosphatised guts in this same 10-m-thick interval. 

Lerosey-Aubril et al.'s paper looked at two stratigraphically higher horizons with soft-tissue preservation. One yielded a ctenophore and an aglaspidid arthropod, the other a trilobite with a phosphatised gut belonging to a different species than the previously described specimens. 

Undetermined ctenophore

The ctenophore represents the first Furongian record of the phylum and the first reported occurrence of Burgess Shale-type preservation in the upper Cambrian of Laurentia. 

The aglaspidid belongs to a new species of Glypharthrus, and is atypical in having twelve trunk tergites and an anteriorly narrow ‘tailspine’. These features suggest that the tailspine of aglaspidids evolved from the fusion of a twelfth trunk segment with the telson. 

They also confirm the vicissicaudatan affinities of these extinct arthropods. Compositional analyses suggest that aglaspidid cuticle was essentially organic with a thin biomineralised (apatite) outer layer. 

Macro imagery of the trilobite reveals previously unknown gut features — medial fusion of digestive glands — possibly related to enhanced capabilities for digestion, storage, or the assimilation of food. 

These new fossils show that conditions conducive to soft-tissue preservation repeatedly developed in the outer shelf environment represented by the Furongian strata near Cranbrook. Future exploration of the c. 600-m-thick, mudstone-dominated upper part of the section is ongoing by Chris New, Chris Jenkins and Don Askey. There work and collaboration will likely result in more continued discoveries of exceptional fossils.

Glypharthrus magnoculus sp.

The specimen you see here was expertly prepped by Don Askew of Cranbrook, British Columbia. It now resides in collections at the Royal BC Museum.

Photo One: Orygmaspis (Parabolinoides) contracta (Trilobita) from the Jiangshanian (Furongian) part of the McKay Group, Clay Creek section, near Cranbrook, British Columbia, Canada. A–D, specimen RBCM.EH2016.031.0001.001, complete dorsal exoskeleton preserved dorsum-down and showing ventral features, such as the in situ hypostome and phosphatised digestive structures. 

A, general view, specimen immersed under ethanol; B, detail of the digestive structures, specimen under ethanol; C, same as B, electron micrograph; D, same as B and C, interpretative drawing with digestive tract in blue-purple and digestive glands in pink. 

Abbreviations: Dc 1 and 2, cephalic digestive glands 1 and 2, Dt1 and 5, thoracic digestive glands 1 and 5, hyp, hypostome, L2, glabellar lobe 2, LO, occipital lobe, T1 and 5, thoracic segments 1 and 5. Scale bars represent 2 mm (A) and 1 mm (B–D). For interpretation of the references to the colours in this figure legend, you'll want to read the full article in the link below. 

Photo Two:  Undetermined ctenophore from the Jiangshanian (Furongian) part of the McKay Group, Clay Creek section, near Cranbrook, British Columbia, Canada. A, B, specimen UA 14333, flattened body fragment with oral-aboral axis oriented parallel to bedding; specimen photographed immersed under dilute ethanol with presumed oral region facing to the bottom. A, general view. B, detailed view showing comb rows and ctene. Scale bars represent 1 cm (A) and 5 mm (B). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)  

Photo Three: Glypharthrus magnoculus sp. nov. from the Jiangshanian (Furongian) part of the McKay Group, Clay Creek section, near Cranbrook, British Columbia, Canada. A–H, holotype, UA 14332, almost complete dorsal exoskeleton; photographs (A–C) and electron micrographs (D, backscattered; E–H, secondary) of the specimen in dorsal view with anterior facing to the top. A, B, general view in normal (A) and inverted (B) colours; C, D, detail of posterior trunk region, showing T12 and its contacts with T11 and the spiniform telson (arrows); the core of the fossil is made of a clay mineral and was initially entirely covered by an apatitic thin layer (white areas on D); E, left eye; F, right posterolateral glabellar lobe; G, rounded tubercles on right posterior border of cephalon; H, triangular tubercles pointing backwards (bottom right corner) on trunk axial region. Scale bars represent 5 mm (A, B), 1 mm (C, D), 500 μm (E, F), and 100 μm (G, H).

Link to the paper: https://www.researchgate.net/publication/309549546_Exceptionally-preserved_late_Cambrian_fossils_from_the_McKay_Group_British_Columbia_Canada_and_the_evolution_of_tagmosis_in_aglaspidid_arthropods

ORYGMASPIS: ASAPHID TRILOBITE

This calcified beauty is Orygmaspis (Parabolinoides) spinula (Westrop, 1986) an Upper Cambrian trilobite from Furongian strata of the McKay Group near Tanglefoot Mountain in the East Kootenay Region of British Columbia, Canada. 

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. 

Asaphida is comprised of six superfamilies found as marine fossils that date from the Middle Cambrian through to the Ordovician — Anomocaroidea, Asaphoidea, Cyclopygoidea, Dikelocephaloidea, Remopleuridoidea and Trinucleioidea. It was here, in the Ordovician, that five of the six lineages met their end along with 60% of all marine life at the time. They did leave us with some wonderful examples of their form and adaptations. 

The stubby eyed Asaphids evolved to give us Asaphus kowalewskii with delightfully long eyestalks. These specialized protrusions would have given that lovely species a much better field of view in which to hunt Ordovician seas — and avoid becoming the hunted.

Only the hardy Superfamily Trinucleiodea pushed through. They were to meet their end in the final days of the Silurian where yet another cataclysmic event wiped out much of the life on Earth, including the last remains of Asaphida (Fortey & Chatterton, 1988).

The outline of the exoskeleton Orygmaspis is inverted egg-shaped, with a parabolic headshield — or cephalon less than twice as wide as long. Picture a 2-D egg where the head is wider than the tail.

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.

GENTLE GENTOO PENGUINS

These black, white and grey cuties — looking very smart in their natural colouring akin to formal wear — are gentoo penguins.

They are foraging predators — dining on crustaceans, fish and squid in the cold nearshore waters of the Antarctic Peninsula, Falkland Islands, South Georgia and Sandwich Islands.

South Georgia, the South Sandwich Islands and the Falklands are inhospitable British Overseas Territories in the southern Atlantic Ocean.

The first scientific description of these romantic seabirds was done by Johann Reinhold Forster in 1781. He used the Falkland Islands population for both the type specimen and locality. These diminutive penguins are in the genus Pygoscelis, and are most closely related to their penguin cousins — the Adélie and Chinstraps. 

The gentoo penguin is one of three species in the genus Pygoscelis. Mitochondrial and nuclear DNA evidence suggests the genus split from other penguins around 38 million years ago, about 2 million years after the ancestors of the genus Aptenodytes. 

In turn, the Adelie penguins split off from the other members of the genus around 19 million years ago, and the chinstrap and Gentoo finally diverged around 14 million years ago.

Very fetching Gentoo penguins

Two subspecies of this penguin are recognised: Pygoscelis papua papua (the subantarctic Gentoo) and the smaller Pygoscelis papua ellsworthi (the Antarctic Gentoo). 

We will likely need to reclassify the gentle Gentoos into a species complex of four morphologically similar but separate species: the northern gentoo penguin (P. papua sensu stricto), the southern gentoo penguin (P. ellsworthi), the eastern gentoo penguin (P. taeniata), and the newly-described South Georgia gentoo penguin (P. poncetii).

We find breeding colonies of gentoo penguins on ice-free surfaces either directly on the shoreline or far inland. 

They prefer shallow coastal areas and often nest between tufts of grass. In South Georgia, breeding colonies are 2 km inland. 

In colonies farther inland, where the penguins nest in grassy areas, they shift location slightly every year because the grass will become trampled over time.

Gentoos breed on many sub-Antarctic islands. The main colonies are on the Falkland Islands, South Georgia and the South Sandwich Islands, and Kerguelen Islands; smaller colonies are found on Macquarie Island, Heard Islands, Crozet Islands, South Shetland Islands, and the Antarctic Peninsula. 

Their breeding populations number well over 600,000 birds. Once a breeding pair decide that their romance is a go, they stay together for life. 

These lovelies breed monogamously and infidelity is frowned upon. Punishment is banishment from the colony — strict but these birds know how to draw a firm line in the pebbles. 

Nests are usually made from a roughly circular pile of stones and can be quite large — up to 20 cm (7.9 in) high and 25 cm (9.8 in) in diameter. The chosen rocks are prized and jealously guarded. 

Just who owned which pebble is the subject of many noisy debates — some escalating to nasty physical altercations between disagreeing parties. "That rock is mine. Mine!" 

The pebbles are especially prized by the females, to the point that a male penguin can woo his lady love and secure a lifetimes' devotion by proffering a particularly choice stone — not unlike some human females.

TRIASSIC FOSSILS OF SVALBARD

Ice, Snow, Reindeer & Ichthyosaurs — Svalbard is just what I imagine my version of Valhalla to be like, without all the mead, murder and mayhem. 

Svalbard is a Norwegian archipelago between mainland Norway and the North Pole. 

One of the world’s northernmost inhabited areas, it is known for its rugged, remote terrain of glaciers and frozen tundra sheltering polar bears, reindeer and Arctic fox. 

The Northern Lights or Nordlys are visible during winter, and summer brings the Midnight sun — sunlight 24 hours a day.

The Botneheia Formation is made up of dark grey, laminated shales coarsening upwards to laminated siltstones and sandstones. South of the type area, the formation shows several (up to four) coarsening-upward units. 

The formation is named for Botneheia Mountain, a mountain in Nordenskiöld Land at Spitsbergen, Svalbard. It has a height of 522 m.a.s.l., and is located south of Sassenfjorden, east of the valley of De Geerdalen. 

I was asked recently if folk head out in the torrential rain or ice and snow to fossil collect. I would generally say yes for those where the potential prize always outweighs the weather. For Svalbard, it is a resounding yes. 

You have to remove the snow cover — or ice if you are impatient or unlucky — to get to the outcrops here. It is well worth the effort. Beneath the icy cover, you find lovely ammonoids and bivalves. 

Tastier still, ichthyosaur remains are found here. We had been expecting to, but it was not until the early 2000s that the first bones were found after a whole lot of looking.

Two specimens have of ichthyosaur have been recovered. They comprise part of the trunk and the caudal vertebral column respectively. 

Some features, such as the very high and narrow caudal and posterior thoracic neural spines, the relatively elongate posterior thoracic vertebrae and the long and slender haemapophyses indicate that they probably represent a member of the family Toretocnemidae. 

Numerous ichthyosaur finds are known from the underlying Lower Triassic Vikinghøgda Formation and the overlying Middle to Upper Triassic Tschermakfjellet Formation, the new specimens help to close a huge gap in the fossil record of the Triassic ichthyosaurs from Svalbard. There is a resident research group working on the Triassic ichthyosaur fauna, the Spitsbergen Mesozoic Research Group. 

Lucky for them, they often find the fossil remains fully articulated — the bones having retained their spatial relationship to one another. 

Most of their finds are of the tail sections of primitive Triassic ichthyosaurs. In later ichthyosaurs, the tail vertebrae bend steeply downwards and have more of a fish-like look. 

In these primitive ancestors, the tail looks more eel-like — bending slightly so that the spines on the vertebrae form more of the tail. 

Maisch, Michael W. and Blomeier, Dierk published on these finds back in 2009: Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen Band 254 Heft 3 (2009), p. 379 - 384. Nov 1, 2009.

Svalbard was so remote that there were no First Nation settlements. It is certainly possible an earlier people came through these islands, but they did not leave any trace of their travels. 

The first documented travellers to explore Spitsbergen arrived in 1795 as part of a hunting expedition. They included people from the arctic town of Hammerfest in Norway's far north. They were an excellent choice as they were used to barren, inhospitable lands and sailed to discover more. 

We know them as the Coast Sámi — a hearty, rugged people probably best known in history for their chieftain, Ottar. He left Hammerfest in the 9th century to visit then join King Alfred the Great's court in a newly forming England. 

Expeditions to the remote islands of Svalbard continued into the early 1800s and finally, a settlement was eked out of the cold landscape and slowly expanded to the rest of the century. While today the islands are called Svalbard, I would have named them for the Norwegian word for remote — fjernkontroll.

This marvellous block is filled with Aristoptychites (syn = Arctoptychites) euglyphus (Mojsisovics, 1886) and Daonella sp., oyster-like clams or bivalves from the Middle Triassic, Ladinian, rugged windswept outcrops at the top of the Daonella Shales, Botneheia Formation, Spitzbergen, Edgeøya and Barentsøya, eastern Svalbard, Norway. 

Daonella and Monotis are important species for our understanding of biostratigraphy in the Triassic and are useful as Index fossils. 

Index fossils are fossils used to define and identify geologic periods (or faunal stages). To be truly useful, they need to have a short vertical range, wide geographic distribution and rapid evolutionary development.

Daonellids preferred soft, soupy substrates and we tend to find them in massive shell beds. Generally, if you find one, you find a whole bunch cemented together in coquina. The lovely block you see here is in the collections of the deeply awesome John Fam. 

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LANDMANNALAUGAR: AURORA BOREALIS

The Northern Lights over a sea of wildflowers in the marsh near Landmannalaugar, part of the Fjallabak Nature Reserve in the Highlands of Iceland.

Landmannalaugar is at the northern tip of the Laugavegur hiking trail that leads through natural geothermal hot springs and an austere yet poetically beautiful landscape. 

Here, you can see the Northern Lights play through the darkness of a night sky without light pollution and bask in the raw geology of this rugged land.

The Fjallabak region takes its name from the numerous wild and rugged mountains with deeply incised valleys, which are found there. 

The topography of the Torfajokull, a central volcano found within the Fjallabak Nature Reserve, is a direct result of the region being the largest rhyolite area in Iceland and the largest geothermal area (after Grimsvotn in Vatnajokull).

The Torfajokull central volcano is an active volcanic system but is now in a declining fumarolic stage as exemplified by numerous fumaroles and hot springs. The hot pools at Landmannalaugar are but one of many manifestations of geothermal activity in the area, which also tends to alter the minerals in the rocks, causing the beautiful colour variations from red and yellow to blue and green, a good example being Brennisteinsalda. Geologists believe that the Torfajokull central volcano is a caldera, the rim being Haalda, Suðurnamur, Norður-Barmur, Torfajokull, Kaldaklofsfjoll and Ljosartungur.

The bedrock of the Fjallabak Nature Reserve dates back 8-10 million years. At that time the area was on the Reykjanes – Langjokull ridge rift zone. 

The volcano has been most productive during the last 2 million years, that is during the last Ice Age Interglacial rhyolite lava (Brandsgil) and sub-glacial rhyolite (erupted under ice/water, examples being Blahnukur and Brennisteinsalda are characteristic formations in the area. 

To the north of the Torfajokull region, sub-glacial volcanic activity produced the hyaloclastites (Moberg) mountains, such as Lodmundur and Mogilshofdar.

Earlier this year, on March 19, 2021, a volcanic eruption started in the Geldingadalir valley at the Fagradalsfjall mountain on the Reykjanes peninsula, South-West Iceland. The volcano is situated approximately 30 km from the country’s capital city, Reykjavík. The eruption is ongoing and the landscape in the valley and its surrounding area is constantly changing as a result.

Prior to the eruptive display earlier this year, volcanic activity over the past 10.000 years has been restricted to a few northeast-southwest fissures, the most recent one, the Veidivotn fissure from 1480, formed Laugahraun (by the hut at Landmannalaugar), Namshraun, Nordurnamshraun, Ljotipollur and other craters which extend 30 km, further to the north Eruptions in the area tend to be explosive and occur every 500 – 800 years, previous known eruptions being around AD 150 and 900.

HALENDID: ICELANDIC HIGHLANDS

Glaciers, mountains, active volcanoes — Iceland has it all. 

Sitting at the junction of the North Atlantic and Arctic Oceans is the ruggedly beautiful island of Iceland. It is Europe's second-largest island after Great Britain. 

Geologically, Iceland is part of the Mid-Atlantic Ridge — a wee bit of the oceanic crust sitting just above a mantle plume, hence all the showy volcanic eruptions and lava flows.

The interior of Iceland is usually referred to as the central highlands or as the locals call it — Halendid — which roughly translates to Highlands in Icelandic. It is considered one of the last great wilderness areas in all of Europe, covering nearly 40,000 square kilometres. Truly one of the last untamed regions on earth. Halendid contains high concentrations of waterfalls, volcanoes, glaciers, and rivers. Large expanses of black sand, lava fields, and fragile vegetation are found throughout the region.

Still, one of the features that make this region so unique are the rivers. These rivers carry glacial runoff and sediment from the interior of the island to the ocean. Along the way, this mix of minerals and water produces dramatic colours, complex systems, and vibrant patterns.

AMMONITE TIME PIECE: INDEX FOSSILS

Ammonites were prolific breeders that evolved rapidly. If you could cast a fishing line into our ancient seas, it is likely that you would hook an ammonite, not a fish.

They were prolific back in the day, living — and sometimes dying — in schools in oceans around the globe.  We find ammonite fossils, and plenty of them, in sedimentary rock from all over the world. In some cases, we find rock beds where we can see evidence of a new species that evolved, lived and died out in such a short time span that we can walk through time, following the course of evolution using ammonites as a window into the past.

For this reason, they make excellent index fossils. An index fossil is a species that allows us to link a particular rock formation, layered in time with a particular species or genus found there. Generally, deeper is older, so we use the sedimentary layers of rock to match up to specific geologic time periods, rather like the way we use tree rings to date trees.

GORGONS: APEX PREDATORS OF THE PERMIAN

The Mighty Gorgons — Apex Predators of the Permian. 

Back in the Paleozoic, some 540 million years ago, life in the seas was teaming with life but life on life amounted to a bit of moss and some low fungi. 

Cut to 240 million years later, the vertebrate animals evolved and a huge spectrum of variety was living on land. 

Gorgons or Gorgonopsia were sabre-toothed therapsids who roamed our ancient Earth from the Middle to Upper Permian — 265 to 252 million years ago — with their long claws, lizard eyes and massive canines.

I learned about the Karoo, and indeed the Gorgons, by a book of the same name by the deeply awesome Peter Ward. His introduction to what life and fieldwork are like in the arid, inhospitable ancestral home of the Gorgons in South Africa made me laugh out loud. It is a highly enjoyable read.

The Great Karoo formed in a vast inland basin 320 million years ago, at a time when the part of Gondwana which would eventually become Africa lay over the South Pole. The Karoo records a wonderful time in our evolutionary history when the world was inhabited by interesting amphibians and mammal-like reptiles — including the apex predators of the day, the Gorgons.

The link below will take you to the Fossil Huntress Podcast where you can travel back in time to visit the Great Karoo with me.

https://anchor.fm/.../The-Great-Karoo-of-South-Africa...

If you fancy a read, check out more geeky goodness over on the ARCHEA blog at https://fossilhuntress.blogspot.com/

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Photo: National Geographic

LIPAROCERAS IN SEPTARIAN NODULE

Robin Hoods Bay is a small fishing village and a bay located in the North York Moors National Park, 5 miles (8 km) south of Whitby and 15 miles (24 km) north of Scarborough on the coast of North Yorkshire, England. 

Bay Town, its local name, is in the ancient chapelry of Fylingdales in the wapentake of Whitby Strand.

Here, 552 kilometres (343 miles) to the north of the Kimmeridge Clay exposures, near the picturesque town of Robin Hoods Bay on the Yorkshire Coast we find beautiful septarian nodules — and when we are very lucky, ammonites and other fossilized material along with them.

These photos show a delightful example of a lovely Liparoceras sp. from Robin Hoods Bay with some interesting septarian veins radiating away from the ammonite. The awesome Harry Tabiner gets full credit — and my unending respect — for the find, preparation and photo of this lovely Lower Jurassic, Lower Lias specimen.

Around Robin Hood’s Bay, well-developed platforms cut across outcrops of Liassic shales. The cliffs are primarily till resting on the Lias. Cliff falls at this location are common. The cliffs are about 50 m in height in the northern part of the bay where they are cut by two steep-sided valleys, Mill Beck and Stoupe Beck. Here the Lower Lias forms most of the slope, with near-vertical lower cliffs comprised entirely of Lower Lias rocks.

The rocks in the lower cliffs are dark grey marine shales from the Redcar Mudstone Formation. The Lias Group at Robin Hood’s Bay is represented, in ascending order, by the Redcar Mudstone Formation, Staithes Sandstone Formation, Cleveland Ironstone Formation and Whitby Mudstone Formation and contains stratotypes for several zones and horizons.

Most fossils are found either from the foreshore exposures during scouring conditions or in rocks, boulders and nodules. They can also be found after cliff falls. To search for septarian nodules, head north for several miles along the coast from Robin Hoods Bay.

Be mindful of the tides as this location should only be attempted on a retreating tide. Minerals can be found in both the large Septarian nodules and partially replacing the many fossilized tree limbs and roots found in the sandstone blocks from higher up in the cliffs. This site can be dangerous and is not appropriate for children.

To look for fossils, search through the rocks and concretions along the foreshore. Ammonites can often be found this way, but you will need the right tools and good eye protection.

Fossils loose on the foreshore are rare. You generally need to work for finds at this location. A few good storms help with collecting here. Robin Hood’s Bay yields little during the summer months. The best time to collect is after the winter storms.

The north side of the bay is rich in ammonite remains and these can mostly be found after cliff falls. The ammonites (Platypleuroceras, Tropidoceras, Acanthopleuroceras and Androgynoceras) can be found, along with the large bivalve, Pinna. Within the calcareous shales, exposed in the low tide reefs at the centre of the bay, you can find the ammonites, Arnioceras and Caenisites.

Robin Hoods Bay Directions from the good folk at UK Fossils Network:

At Robin Hood’s Bay village, you can park in either the small car park at the top of the hill or the second larger one just a short walk away.

• From here, the best end to visit is the north side. You will find a footpath at the top of the hill, to the left of the main street leading to the beach. This winds around and passes a picnic area.
• You can also visit the south and middle part of the bay. To do this, go down into the main street at the bottom of the hill and follow round to the right. You will see some steps, which follow the sea defence and lead to the shore.
• Paleo-coordinates: 54.43442°N, 0.53079°W

Photos: The deeply awesome Harry Tabiner gets full credit (and my unending respect) for the find, preparation and photo of this lovely Liparoceras sp. in a septarian nodule, Lower Jurassic, Lower Lias specimen.

Reference: Humberside Geologist No. 14, Humberside Geologist Online, The geology of East Yorkshire coast.http://www.hullgeolsoc.co.uk/hg146t.htm

Reference: UK Fossils Network: https://ukfossils.co.uk/2007/03/18/robin-hoods-bay/ This website provides a wealth of information and is very well done. Highly recommend checking them out!
Reference: https://www.mindat.org/loc-267536.html

ROCKY MOUNTAIN TRENCH

Trapper Cabin on Isaac Lake / Bowron Provincial Park

The Bowron Canoe Circuit is a 149,207 hectare geologic wonderland, where a fortuitous combination of plate tectonics and glacial erosion have carved an unusual 116 kilometre near-continuous rectangular circuit of lakes, streams and rivers bound on all sides by snow capped mountains.

From all descriptions, something like heaven.

The east and south sides of the route are bound by the imposing white peaks of the Cariboo Mountains, the northern boundary of the Interior wet belt, rising up across the Rocky Mountain Trench, and the Isaac Formation, the oldest of seven formations that make up the Cariboo Group (Struik, 1988).

Some 270 million years ago, had one wanted to buy waterfront property in what is now British Columbia, you’d be looking somewhere between Prince George and the Alberta border. The rest of the province had yet to arrive but would be made up of over twenty major terranes from around the Pacific. The rock that would eventually become the Cariboo Mountains and form the lakes and valleys of Bowron was far out in the Pacific Ocean, down near the equator.

With tectonic shifting, these rocks drifted north-eastward, riding the continental plate until they collided with and joined the Cordillera in what is now British Columbia. Continued pressure and volcanic activity helped create the tremendous slopes of the Cariboo Range we see today with repeated bouts of glaciation during the Pleistocene carving their final shape.

PLIENSBACHIAN APODEROCERAS OF DORSET

The lovely large specimen (macroconch) of Apoderoceras pictured here is likely a female. Her larger body perfected for egg production.

Apoderoceras is a wonderful example of sexual dimorphism within ammonites as the macroconch (female) shells grew to diameters in excess of 40 cm – many times larger than the diameters of the smaller microconch (male) shells.

Apoderoceras has been found in the Lower Jurassic of Argentina, Hungary, Italy, Portugal, and most of North-West and central Europe, including as this one is, the United Kingdom. This specimen was found on the beaches of Charmouth in West Dorset and prepped by the wonderfully talented Lizzie Hingley.

Neither Apoderoceras nor Bifericeras donovani are strictly index fossils for the Taylori subzone, the index being Phricodoceras taylori. Note that Bifericeras is typical of the earlier Oxynotum Zone, and ‘Bifericeras’ donovani is doubtfully attributable to the genus. The International Commission on Stratigraphy (ICS) has assigned the First Appearance Datum of genus Apoderoceras and of Bifericeras donovani the defining biological marker for the start of the Pliensbachian Stage of the Jurassic, 190.8 ± 1.0 million years ago.

Apoderoceras, Family Coeloceratidae, appears out of nowhere in the basal Pliensbachian and dominates the ammonite faunas of NW Europe. It is superficially similar to the earlier Eteoderoceras, Family Eoderoceratidae, of the Raricostatum Zone, but on close inspection can be seen to be quite different. It is, therefore, an ‘invader’ and its ancestry is cryptic.

The Pacific ammonite Andicoeloceras, known from Chile, appears quite closely related and may be ancestral, but the time correlation of Pacific and NW European ammonite faunas is challenging. Even if Andicoeloceras is ancestral to Apoderoceras, no other preceding ammonites attributable to Coeloceratidae are known. We may yet find clues in the Lias of Canada. Apoderoceras remains present in NW Europe throughout the Taylori Subzone, showing endemic evolution. It becomes progressively more inflated during this interval of time, the adult ribs more distant, and there is evidence that the diameter of the macroconch evolved to become larger. At the end of the Taylori Subzone, Apoderoceras disappeared as suddenly as it appeared in the region, and ammonite faunas of the remaining Jamesoni Zone are dominated by the Platypleuroceras–Uptonia lineage, generally assigned (though erroneously) to the Family Polymorphitidae.

In the NW European Taylori Subzone, Apoderoceras is accompanied (as well as by the Eoderoceratid, B. donovani, which is only documented from the Yorkshire coast, although there are known examples from Northern Ireland) by the oxycones Radstockiceras (quite common) and Oxynoticeras (very rare), the late Schlotheimid, Phricoderoceras (uncommon) Note: P. taylori is a microconch, and P. lamellosum, the macroconch), and the Eoderoceratid, Tetraspidoceras (very rare).

DACTYLIOCERAS OF THE HOLDERNESS

Dactylioceras ammonite, Photo: Harry Tabiner

A lovely Dactylioceras ammonite from the Lower Jurassic Upper Lias Holderness of the Yorkshire Coast. This beauty measures over 8cm with especially attractive colouring.

Holderness is an area of the East Riding of Yorkshire, on the east coast of England. An area of rich agricultural land, Holderness was marshland until it was drained in the Middle Ages. Topographically, Holderness has more in common with the Netherlands than with other parts of Yorkshire. To the north and west are the Yorkshire Wolds.

Geologically, Holderness is underlain by Cretaceous chalk but in most places, it is so deeply buried beneath glacial deposits that it has no influence on the landscape.

The landscape is dominated by deposits of till, boulder clays and glacial lake clays. These were deposited during the Devensian glaciation. The glacial deposits form a more or less continuous lowland plain which has some peat filled depressions (known locally as meres) which mark the presence of former lake beds. There are other glacial landscape features such as drumlin mounds, ridges and kettle holes scattered throughout the area.

Dactylioceras ammonite, Photo: Harry Tabiner

The well-drained glacial deposits provide fertile soils that can support intensive arable cultivation. Fields are generally large and bounded by drainage ditches. There is very little woodland in the area and this leads to a landscape that is essentially rural but very flat and exposed. The coast is subject to rapid marine erosion.

The Geology of Yorkshire in northern England shows a very close relationship between the major topographical areas and the geological period in which their rocks were formed. The rocks of the Pennine chain of hills in the west are of Carboniferous origin whilst those of the central vale are Permo-Triassic.

The North York Moors in the north-east of the county are Jurassic in age while the Yorkshire Wolds to the southeast are Cretaceous chalk uplands. The plain of Holderness and the Humberhead levels both owe their present form to the Quaternary ice ages.

The strata become gradually younger from west to east. Much of Yorkshire presents heavily glaciated scenery as few places escaped the direct or indirect impact of the great ice sheets as they first advanced and then retreated during the last ice age. This beauty is in the collection of the deeply awesome Harry Tabiner.

CRETACEOUS AFRICA SUPER CROC

Sarcosuchus imperator

An impressive Super Croc tooth and scute from Sarcosuchus imperator, an extinct genus of giant crocodile-like reptiles that lived in the rivers of an ancient tropical plain in the Sahara of Africa during the Lower Cretaceous.

Sarcosuchus were ambush hunters, eating anything that entered their watery homes from wee fish to large dinosaurs. These big beasties were the precursors to our modern crocodiles -- and they were big. Really big. 

Almost twice as large as their modern saltwater cousins, weighing in at 8-10 tons. They lived 50-60 years. Modern Saltwater & Nile crocodiles live 70-100 years on average. This scute and tooth are from the Elrhaz Formation, Gadoufaoua, Ténéré Desert, Niger. Photo care of the deeply awesome Andy Chua.

SARCOSUCHUS IMPERATOR

This mighty beast is Sarcosuchus. He is an extinct genus of crocodyliform, so not quite a crocodile as we know them but the distant relative of crocodylians that lived ~129-112 million years ago. 

We have learned about them through fossil remains that date from the Lower Cretaceous of what is now Africa and South America.

Strictly speaking, Sarcosuchus was not a crocodile as we know them today, but a kind of pre-crocodile. These early croc-types were Crocodylomorphs.

This crocodylian lineage (clade Pseudosuchia, formerly Crurotarsi) was a very diverse and adaptive group of reptiles. We used to lump all known living and extinct crocodiles indiscriminately into the order Crocodilia. Sometime in the late 1980s, we finally moved all living species into the order Crocodilia, segregating closely related extinct relatives such as Mekosuchus. Our true "modern" crocodiles, now all safely ensconced in the order Crocodilia without their ancient ancestors, arrived millions of years after the first crocodylomorphs, with the first members of the modern species arriving on the scene in the Upper Cretaceous.

The Crocodylomorpha were a very ancient group of animals, at least as old as the dinosaurs, who evolved into a very diverse spectrum of weird and wonderful forms you might not recognize as croc-like. During the Jurassic and the Cretaceous, marine Crocodylomorphs in the family Metriorhynchidae, such as Metriorhynchus, evolved forelimbs that were paddle-like and had a tail similar to modern fish. Dakosaurus andiniensis, a species closely related to Metriorhynchus, had a skull that was adapted to feast upon large marine reptiles. We see several (unexpected) herbivorous terrestrial species during the Cretaceous, such as the tiny and adorable Simosuchus clarki and Chimaerasuchus paradoxus, both roughly the size of a dog. During the Cenozoic, a number of lineages left their ancient river homes and became wholly terrestrial predators.

Sarcosuchus was one of the largest early crocodile-like reptiles, reaching up to 9.5 m in body length and weighing up to 8 to 10 tons. He was almost twice as long as our modern saltwater crocodiles, so one big croc! These big beasts lived and hunted in ancient rivers, grabbing and crushing prey that came too close to the water.

The first remains were discovered during field expeditions in the Sahara led by French paleontologist, Albert-Félix de Lapparent, from 1946 to 1959. Remains were found of skull fragments, vertebrae, teeth, and scutes.

In 1964, an almost complete skull was found in Niger by the French CEA, but it was not until 1997 and 2000 that most of its anatomy became known to science when an expedition led by the American paleontologist Paul Sereno discovered six new specimens, including one with about half the skeleton intact and most of the spine.

A common method to estimate the size of crocodiles and crocodile-like reptiles is the use of the length of the skull measured in the midline from the tip of the snout to the back of the skull table since in living crocodilians there is a strong correlation between skull length and total body length in subadult and adult individuals irrespective of their sex, this method was used by Sereno et al. (2001) for Sarcosuchus due to the absence of a complete enough skeleton. Two regression equations were used to estimate the size of S. imperator, they were created based on measurements gathered from 17 captive gharial individuals from northern India and from 28 wild saltwater crocodile individuals from northern Australia, both datasets supplemented by available measurements of individuals over 1.5 m (4.92 ft) in length found in the literature.

The largest known skull of Sarcosuchus imperator (the type specimen) is 1.6 m (5.25 ft) long (1.5 m (4.92 ft) in the midline), and it was estimated that the individual it belonged to had a total body length of 11.65 m (38.2 ft), its snout-vent length of 5.7 m (18.7 ft) was estimated using linear equations for the saltwater crocodile and in turn, this measurement was used to estimate its body weight at 8 tonnes (8.8 short tons). These new measurements meant Sarcosuchus was able to reach a maximum body size not only greater than previously estimated but also greater than that of the Miocene "Beak crocodile" Rhamphosuchus, the Late Cretaceous Deinosuchus crocodilian related to our modern alligators, and the Miocene Purussaurus.

However, extrapolation from the femur of a subadult individual as well as measurements of the skull width further showed that the largest S. imperator was significantly smaller than was estimated by Sereno et al. (2001) based on modern crocodilians. O’Brien et al. (2019) estimated the length of the largest S. imperator specimen at 9.5 meters and body weight at 4.7 tons based on longirostrine crocodylians skull width to total length ratio. This estimate is very close to the femur based estimate is 9.1 m (29.9 ft).

Sereno, Paul C.; Larson, Hans C. E.; Sidor, Christian A.; Gado, Boubé (2001). "The Giant Crocodyliform Sarcosuchus from the Cretaceous of Africa". Science. 294 (5546): 1516–9. Bibcode:2001Sci...294.1516S. doi:10.1126/science.1066521. PMID 11679634.