Killing-off Scottish Mammaliamorphs

With all that’s been going on in the last couple of months (including attending #2017SVP, Friends of  Hugh Miller’s conference, and #SVPCA2017), I’ve dropped the ball on this blog a little. But this week past, I had a new paper out with my colleagues, and I’d like to tell you a little more of the story behind it.

When I started my PhD on the fossil material of the Isle of Skye, one thing really surprised me. There is this whole group of cynodonts (the group that includes mammals and their nearest relatives) that no one ever talks about. They are called tritylodontids (Tritylodontidae), and despite being one of the most successful clades of cynodont – lasting from the Late Triassic to the Early Cretaceous - they are often overlooked by palaeontologists. We find one of them, called Stereognathus, on the Isle of Skye.

Perhaps the best piece of tritylodontid palaeoart, Stereognathus by Mark Witton - find out about him and support his amazing work.

Why should we care about these extinct animals? Well, they’re considered by most to be the sister-group to stem-mammals, and share many similarities in their skeleton. They would have had fur and whiskers, and you might mistake one for a mammal if you didn’t look too closely. But there are some interesting differences. Tritylodontids kept the so-called “reptilian” jaw joint, between the articular and quadrate bones (not the dentary squamosal contact as in mammals). They also didn’t go through the same extreme reduction in body size we see in the first mammals. In fact some tritylodontids were pretty big, like Kayentatherium from the Early Jurassic, which was about a metre long. Unlike the earliest mammals, tritylodontids appear to have been almost exclusively herbivorous. 

All in all, they were occupying quite a unique ecological space in the Mesozoic. 

The first tritylodontid to be described was the Middle Jurassic genus, Stereognathus, named by Charlesworth in 1855 and figured by Richard Owen shortly after. Unfortunately though, this genus is represented by only a few molar teeth in a fragment of jaw, a bunch of isolated teeth, and some individual bits of limb that might belong to Stereognathus, but it’s uncertain. Most of this material came from sites in Oxfordshire, England.

Owen's original figures from 1857, scanned courtesy of BHL

Charlesworth called this first Stereognathus species, S. ooliticus, after the rocks they were found in, the Great Oolite Group. More than 100 years later, Robert Savage and Michael Waldman found teeth they identified as belonging to Stereognathus on the Isle of Skye. They named it S.hebridicus, after the Inner Hebrides islands, to which Skye belongs. Unfortunately, their only diagnostic feature was that S. hebridicus was bigger than S. ooliticus. More recently, field work has recovered more S. hebridicus teeth. I decided to set out with my co-authors to test this size difference, and see if we could find other details of the shape of the teeth that would support S. hebridicus as a separate, Scottish species.

A photo of the most intact Stereognathus specimen, found and photographed by Andrzej Wolniewicz during fieldwork on the Isle of Skye.

We microCT scanned all the new material, and the two holotypes of S. ooliticus and S. hebridicus. We measured every tooth of Stereognathus we could, many being too broken up or worn to give reliable measurements. Even the original S. ooliticus specimen figured by Owen was in a poor state: comparing it to his original drawings, it seems over 150 years of handling hasn’t been kind. 

We didn’t find any good evidence that S. hebridicus is a separate species from S. ooliticus. Although the holotypes are radically different in size, when you take all of the rest of the teeth we have and plot them (below), they fall along a line of size change you’d see from baby to adult. In other words, size differences are explained by ontogeny: development from earliest stage of life to maturity.

All of the measureable upper postcanines of Stereognathus. Empty diamonds and squares indicate less certain measurements (due to breakage or wear). I expect field work over the coming years will fill this out to show a full growth series of size.

To my horror, I’ve sunk the only Scottish tritylodontid! Unless new fossils tell us differently, it looks like S. hebridicus is no more. This makes it a junior synonym to S. ooliticus. It’s a shame to see our Scottish species go, but I’m glad that it was the new, more physically intact fossil material from Skye that allowed us to make a proper reassessment of the genus. 

Who knows, perhaps there is still another species of tritylodontid to be found on the rocky shores of the misty Isle? I'll keep looking and get back to you...

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Panciroli E, Walsh S, Fraser NC, Brusatte SL, and Corfe I. 2017. A reassessment of the postcanine dentition and systematics of the tritylodontid Stereognathus (Cynodontia, Triltylodontidae, Mammaliamorpha) from the Middle Jurassic of the United Kingdom. Journal of Vertebrate Paleontology.

Waldman M, and Savage RJG. 1972. The first Jurassic mammal from Scotland. Journal of the Geological Society of London.

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Reconstructing Wareolestes

I recently blogged about the paper I published with colleagues on a little lower jaw from the Isle of Skye, belonging to a Middle Jurassic mammaliaform called Wareolestes rex. Like many people, I believe palaeoart is a vitally important part of palaeontology, particularly as it forms a quick visual bridge between palaeontologists and the public (and other scientists!) So I'd like to share the palaeoart reconstruction I did for Wareolestes, and talk about the science behind it, and the informed speculations.

My reconstrction of Wareolestes rex. The only bit we have is the jaw, so much of the rest is informed speculation - informed by scientific evidence and living relatives. It was done in pencil and watercolour.

Mesozoic mammal art is often not especially inspiring. This is partly because, until recently, most Mesozoic mammal fossil material comprised mostly teeth, which doesn't make for exciting reconstruction. As a result, artists often choose to have their early mammals snarling to show off their teeth - the only certain part of the art! Also, there is a strange notion that small mammals are boring; but a quick google search will soon show you that they come in a huge range of sizes, shapes, colours and behaviours: inspiration for great art. However, palaeoartists have shied away from speculating about fur, whiskers, ears and eyes, erring on the side of caution and producing identikit snarling, splayed mice.

I wanted to try and do a reconstruction in an informed, but moderately speculative way. So I started work on reconstructing Wareolestes while I was still writing the paper, hoping to make informed scientific decisions based on the fossil record, and then spice it up by examining the appearance of small modern mammals.

There is a bit of a tradition among Mesozoic mammal workers of comparing our fossil beasties to the modern American opossum (Didelphis). I therefore decided to use them as the inspiration for the reconstruction. Google 'opossum', and you'll find this animal has a penchant for bearing its teeth. While I shy away from those snarling Mesozoic mammals on the whole, our Wareolestes fossil is a lower jaw with teeth, so this open-mouthed expression was fitting in this instance. Forgive me for breaking my own rules; in future reconstructions of fossils (especially those with known postcranial skeletons) I'll avoid teeth-bearing if I can help it.

The opposum Didelphis is a wonderfully charismatic creature, and often photographed bearing its teeth - handy if your fossil is a jaw with teeth and nothing else.

Our digital reconstructions (from microCT scans) were the base for drawing the mouth and teeth. As not all of the teeth were present in the Scottish fossil, I modelled the other premolars, canines, and incisors on two closely related genera: Dinnetherium and Megazostrodon. On reflection, I think the front of the snout should have been a little longer... but at this point we don't know for sure. I based the rest of the skull on Morganucodon, as Wareolestes is a morganucodontid. However, I made it more robust, because Wareolestes was larger and chunkier than it's geologically older relative.

Amazing skull and muscle reconstruction of Morganucodon by Lautenschlager et al 2016

So far, so good. But from here on, things get more speculative. We don't have much in the way of preserved fur or skin, except for a few exceptional specimens from China (but not of this genus). Undoubtedly Wareolestes and other Mesozoic mammals had fur, inherited from their non-mammal ancestors. They almost certainly had whiskers: we know this thanks to evidence in the fossil record for innervation in the snout. Whiskers probably developed in earlier non-mammalian cynodonts, which would have used them to sense their way through burrows. Therefore, whiskers are very likely to have existed in the earliest insectivorous, nocturnal mammals, being used to sense their environment and hunt for food.

I chose the shrew and the Solenodon (see below) as inspiration for the whiskers. Their whiskers extend quite far up the face, and point in multiple directions.

Beautiful shrew, showing off those sensitive whiskers. (By David Chapman, from the Cornwall Mammal Group)

The nose and ears of Mesozoic mammals, being entirely composed of soft tissue, are also impossible to reconstruct without speculation. Mesozoic mammals had well-developed olfactory bulbs, so they had a good sense of smell. I went for an opossum-like nose, simply because I liked the look of it.

This sleeping opposum's nose might be the cutest thing EVER. Will the squeeing ever stop? (I got this off pintrest, contact me if you can ID the source)

At this point in their evolution, mammals still had their post-dentary bones attached to the inside of the jaw. These bones would later reduce and detach, becoming incorporated into the middle ear. This allowed mammals to develop exquisite hearing, especially at higher frequencies. So what did they hear when the bones were still attached to the jaw? The answer is: we don't know. The postdentary bones were certainly used in hearing though. I decided a small proto-ear was fitting, based on a slightly crumpled version of a Solenodon ear. I kept them simple, small, and placed low on the head.

Close up of a Hispaniolan Solenodon (Source)

The Solenodon is a small, nocturnal insectivorous mammal found on some Caribbean Islands. It is weird on so many levels, not just because it has venomous saliva, but also as it is the only genus surviving in its family, the Solenodontidae. Phylogeneticists trace their origins back to the Cretaceous, making this an altogether unique animal and a good analogue to find inspiration for the life appearance of Mesozoic mammals. Because of this, I chose the dark back and upper face of the Solenodon as inspiration for the colour pattern on Wareolestes. However, I then decided to add a little cheek and eye patterning.

Finally, the eyes. It's hard to say how large the eye would have been relative to the head. I decided to go for something I know and love: the eye of a rat. This is a total bias on my part, because as a many-time rat-owner, I was always delighted by those dark chocolate beady eyes greeting me each morning, staring with demented twitchiness and tiny black pupils pointing in opposite directions. Mental. However it does leave me open to all the "aren't Mesozoic mammals just a bunch of rats anyway?" comments people just can't restrain themselves from making... sigh*.

So there you have it. This was my process in creating a Wareolestes rex reconstruction. I played it kind of safe - I could have speculated about the rest of the body, but decided it was a step too far. This is my first proper go at palaeoart, so theres still a lot to learn. Hopefully in the coming field seasons we'll find more of the skeleton and I'll be able to revise the image based on more evidence. In the meantime, I'd love to hear you opinions, ideas, and comments - get in touch on twitter: @gsciencelady

*Wareolestes is of course not a rodent, as rodents didn't evolve for another 100 million years. The resemblence is superficial, anatomically they are totally different.


References
 
Benoit J., Manger P. and Rubidge BS. 2016 Palaeoneurological clues to the evolution of defining mammalian soft tissue traits. Scientific Reports.

Lautenschlager S., Gill P, Luo Z-X., Fagan MJ., and Rayfield EJ. 2016 Morphological evolution of the mammalian jaw adductor complex. Biological Reviews.

Panciroli E., Benson RBJ., and Walsh S. 2017 The dentary of Wareolestes rex (Megazostrodontidae): a new specimen from Scotland and implications for morganucodontan tooth replacement. doi: 10.1002/spp2.1079

Elizabeth Anderson Grey - Scottish Lady Palaeontologist

Have you heard of Elizabeth Anderson Gray? She was one of the most important and prolific female Scottish fossil collectors of her time, responsible for amassing collections that are still vital to our knowledge of the stratigraphy and species composition of the Ordovician and Silurian rocks of Scotland.

Born in Alloway, Ayreshire, to an Innkeeper, Elizabeth’s family then relocated to become farmers in Girvan, a small coastal town 60 miles south of Glasgow. Although she moved occasionally in her life (to Glasgow and to Edinburgh), it was from the rocks around Girvan that Elizabeth would collect most of her specimens during her long lifetime.

Elizabeth Anderson Gray spent her entire life fossil hunting. Her collections were vital to our understanding of early life on earth. (Picture from Carrick Scotland: Beyond the Tourist Guides)

Elizabeth’s father, Thomas Anderson (who had a trilobite and a coral named after him), introduced her to geology and fossil collecting when she was a child. From this point onwards she collected assiduously, continuing until the autumn before her death, at the age of 93. Like many women collectors, Elizabeth Anderson Gray was overshadowed publically by her husband Robert Gray, co-founder of The Natural History Society of Glasgow (NHSG), under whose name much of their joint wor was presented. This was necessary in the 1800s as most Societies where their finds might be presented did not admit women until the turn of the century.

 

Elizabeth Gray was dedicated to record keeping and extending our understanding of the diversity of early Palaeozoic life. Despite her modest early education, her lifelong learning was augmented in 1869 when she was invited to attend geology lectures for women at the University of Glasgow.

Elizabeth was clearly an astute woman. She ensured the importance of her finds was recognised by having them formally described by established scientists (who were of course, all men). Her legacy also survived in the Gray Collections, which were sold to museums across the United Kingdom, the main ones being the Natural History Museum in London and the Hunterian in Glasgow. Many of her finds are type specimens, the material that defines a species taxonomically, such as Hudsonaster grayae (an early starfish), Archophiactis grayae (also an echinoderm), and Lophospira trispiralis (a type of mollusc).

One of the fossils from the Gray Collection. ©The Trustees of the Natural History Museum, London

Many specimens collected by Elizabeth are referred to in the proceedings of the Natural History Society of Glasgow between 1868 and 1878, and unlike many other women geologists of her time (notably Mary Anning) she even had the honour of having some named after her – although it was the surname she shared with her husband, rather than forename, that was mostly used for this purpose. Other material was named for Girvan, the area she found it in.

Using her detailed observational skill, Elizabeth presented a list of the fossils she collected in Ayrshire which was extensively used by other geologists in both Scotland and England. It formed an important contribution to the British Geological Survey’s volume on Silurian Scottish rocks.

The Grays were friends with the well-known geologist Charles Lapworth and fossil collector Jane Donald Longstaff.  Although considered by both herself and the professionals of the day as an amateur, Elizabeth was undeniably a skilled one; responsible for uncovering a great deal of the diversity of Palaeozoic rocks in Scotland. Years of collecting led Elizabeth to be well versed in geology and sedimentology, keeping careful records of her work. It is because she recorded the locations, geology and associations of each of her specimens that Gray’s collections remain invaluable to those studying the Ordivician and Silurian today. 

After her husband’s death in 1887, Elizabeth continued to collect fossils, often with the help of her two daughters, Alice and Edith, who undoubtedly knew a great deal thanks to the many “geologising” family holidays taken over the years. In 1900 Elizabeth’s contributions to geology were recognised by the Geological Society of Glasgow, who made her an honorary member. The Natural History Society of Glasgow followed suit a year later.

In 1903, at the stately age of 72, Elizabeth was awarded the Murchison Geological Fund from the Geological Society of London, for her lifelong contribution to early Palaeozoic geological research. She continued to collect and disseminate her material until the year before her death from bronchitis on 11th February, 1924. 

Elizabeth's daughters continued her work, they were known as "the Misses Grey". ©The Trustees of the Natural History Museum, London

She had spent almost a century working in the field, and yet so few people know her name. Her daughters – referred to as “the Misses Gray” - continued to collect; diligently uncovering new specimens as their mother had before them. They eventually sold her remaining collection to the Natural History Museum, ensuring their mother’s work would survive and remain available for future scientific study. 

Without her, our understanding of the early Palaeozoic in Scotland and the UK would be much the poorer.

(this article first appeared on Trowelblazers.com 27/5/15)

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To find out more about the Gray collection at the Natural History Museum in London, search for her fossils here: http://data.nhm.ac.uk/

For more on the geology of Girvan, and the rest of Scotland, try http://www.scottishgeology.com/geo/regional-geology/southern-uplands/girvan-to-ballantrae-coast/

References

Burek, C. V., & Higgs, B. (2007) The Role of Women in the History of Geology. The Geological Society; Bath.

MacBride E. W., & Spencer W. K (1938) Two New Echinoidea, Aulechinus and Ectinechinus, and an Adult Plated Holothurian, Eothuria, from the Upper Ordovician of Girvan, Scotland. Philosophical Transactions of the Royal Society of London, Vol. 229

McCance M. (2002) Hugh Miller, 1802-1856, Geologist and Writer: His Links with 19th Century Girvan. Ayrshire Notes No.23

Peach, B. N, Horne, J., & Teall, J. J. H. (1899) The Silurian rocks of Britain: Vol. I.Scotland. Glasgow: J. Hedderwick & Sons. Available from: https://archive.org/details/silurianrocksbr00tealgoog

 

Weddel, R.  ‘Some Significant Women in the Early Years of the Natural History Society of Glasgow’ [online]. Available from: http://www.glasgownaturalhistory.org.uk/gn25_3/weddle_women.pdf