Cute Ancient Mammal Lived in Tough Cretaceous Times

A superbly preserved fossil of an early type of mammal found in sediments that date from 125 million years ago (Early Cretaceous), demonstrates that mammals had effectively evolved the same type of fur seen in extant mammals today.  Many of these mammals may have been very small.  Their fur provided them with a defence against attack from dinosaurs and other predators.  However, not everything was rosy in the Cretaceous garden for this little furry critter, in between dodging hungry dinosaurs and crocodiles it seems that it suffered from a fungal disease that attacked the hairs that made up its coat.

Mesozoic Mammals

The fossil was excavated from the limestone lake bed sediments at Las Hoyas in the Iberian mountains of Cuenca Province (central Spain).  It was discovered back in 2012, when a field team under the direction of Angela Buscalioni (a palaeontologist at the University of Madrid), was exploring the finely grained sediments in a bid to find more specimens of early birds, fossils of which, have made the Las Hoyas site one of the most important Lagerstätten sites in the world for vertebrate fossils dating from the Barremian faunal stage of the Cretaceous.  The almost intact fossil was brought to the University of Bonn.  A paper detailing the discovery has just been published in the journal “Nature”.

Fossils from Las Hoyas

The animal which was around 22 cm long, has been identified as a member of the Eutriconodonta, a diverse Order of primitive mammals which probably evolved in the Jurassic.  The phylogenetic relationship between eutriconodonts and modern mammals remains unclear, but many academics argue that these animals are closely to today’s mammals (monotremes, placentals and marsupials) than the Multituberculata.  Everything Dinosaur, earlier this month reported on the discovery of a multituberculate mammal from New Mexico, an animal that lived just a few hundred thousand years after the extinction of the non-avian dinosaurs.

To read about this Cenozoic multituberculate: Mammals Quick off the Mark after Dinosaur Extinction.

Spinolestes xenarthrosus

This new species has been named Spinolestes xenarthrosus.  The name roughly translates as “spiny, strange jointed one”.  It is derived from the spiny, defensive hairs found on the back, whilst the species name refers to the strengthened joints of the vertebrae.  A similar anatomical feature is seen in extant members of the Xenarthra such as anteaters, armadillos and sloths.  It is also observed in a small shrew from the Congo Basin.

The Prepared Fossil Specimen (Spinolestes xenarthrosus)

The prepared holotype specimen – S. xenarthrosus.

Picture credit: Georg Oleschinski with additional annotation by Everything Dinosaur

The picture above shows the prepared holotype specimen that has been set in resin.  The skull, seen towards the right of the photograph is viewed from below.  An arrow (top right) points to a patch of preserved skin that shows dermal hairs which acted as defensive spines.

An Illustration of Spinolestes xenarthrosus

Described as “cute” by scientists.

Picture credit: Oscar Sanisidro

Defensive Spines

As well as the defensive spines which probably broke off if a predator bit the back of this fast running mammal, letting Spinolestes escape but leaving the attacker with a mouthful of spines for their trouble, the rump of Spinolestes was partially covered in horny scutes.  Commenting on these points, lead author Professor Thomas Martin (Steinmann Institute of Geology, Mineralogy and Palaeontology of the University of Bonn), stated:

“We are familiar with these characteristics in modern spiny mice from Africa and Asia Minor.  If a predator grabs them by the back, the spines detach from the skin.  The mouse can escape and the attacker is left with nothing more than a mouthful of spines. It is possible that these structures served a similar purpose in the case of Spinolestes.”

Best Preserved Mesozoic Mammal (Spinolestes xenarthrosus)

The fossil may well represent the best preserved mammal known from the Mesozoic and although described as mouse-like in some media reports, Spinolestes was only distantly related to modern mice (rodents).

Professor Martin explained:

“We are not able to classify the finding in any of the groups of mammals alive today.  It displays characteristics which we also find in today’s mammals.  However, these are not signs of relatedness but rather they developed independently – throughout the course of evolution, they have been ‘invented’ many times.”

This is an example of convergent evolution.

A Magnified Area of the Fossil Showing Guard Hairs (Proto Spines)

SC = area showing dermal scutes on the skin.

Picture credit: University of Bonn

It is likely that Spinolestes had a similar lifestyle to that of a mouse or a rat, scurrying through the undergrowth and using its keen senses to keep out of trouble.  It may also have been nocturnal.  The Las Hoyas deposits may lack dinosaurs (only a handful of different dinosaurs are known from the site), but there were plenty of other predators around capable of making a meal out of this particular eutriconodont.

A Strong Back

Convergent evolution also accounts for the anatomical features seen in the vertebrae.  Individual bones in the back have supporting appendages that interlock the vertebrae together.  The back is incredibly strong, much stronger than the backs of other similar sized animals.  This feature is also found in the Hero Shrew (Scutisorex somereni) which comes from Central Africa.  The Hero Shrew uses its strong back to help force itself under logs as it looks for insects to eat.  It could be speculated that Spinolestes evolved a strong back for a similar purpose.

Signs of a Fungal Disease on the Fur

Such is the exquisite preservation of the fossil, that individual hairs of the fur can be studied.  The state of some of the tiny fossilised hairs suggests that this animal was suffering from a fungal disease of the fur.  This suggests that early mammals may have suffered from similar diseases as their modern counterparts.  This fossil may help scientists to assess the taxonomic position of the Eutriconodonta in relation to extant mammals.

For models and replicas of prehistoric animals and other Mesozoic creatures: Mojo Fun Prehistoric and Extinct Models.

Summarising the team’s research, Professor Martin stated:

“One hundred twenty-five million years ago, Spinolestes was very well adapted to its ecological niche – through horny scutes and spines on its back as well as through its reinforced spine.  We have to revise our thinking, mammals were indeed very small during the time of the dinosaurs.  But they were certainly not primitive.”

To read an article on a carnivorous dinosaur, whose fossils have been found at Las Hoyas: One Lump or Two for a Dinosaur.

Meat-Eating Dinosaurs Once Roamed Minnesota

The American State of Minnesota might border North and South Dakota but despite the treasure trove of dinosaur fossils from the Peace Garden State (North Dakota) and the Mount Rushmore State (South Dakota), the Land of a Thousand Lakes (Minnesota) has yielded only a couple of dinosaur fossil finds to date.

Theropod Dinosaur Claw Bone

However, that may be about to change as researchers from the Science Museum of Minnesota, based in Saint Paul, have announced the discovery of a theropod dinosaur’s claw bone.  This is only the third documented dinosaur fossil discovery from Minnesota.

Minnesota Dinosaur Claw

Cretaceous theropod Claw from Minnesota.

Picture credit: Mark Ryan, Science Museum of Minnesota

Fossil Claw

The lack of dinosaur fossils, or indeed Mesozoic fossils in general can be explained by the fact that the rocks that may have held such fossils have been eroded away.  Extensive glaciation in the north, central parts of the United States removed much of this material and indeed it is the action of glaciers that led to the unique geology and landscape of much of this part of America.  In addition, for much of the Mesozoic, this part of America was underwater.

The fossil claw that measures approximately four and half centimetres in length when measured with the curvature of the claw taken into account, was found at the Hill Annex Mine, part of the extensive iron ore rich Mesabi Iron Range in north-eastern Minnesota.

Minnesota’s Cretaceous Past

Although it is difficult to assign a dinosaur family to this fossil, palaeontologists from the Science Museum of Minnesota have suggested that it is the claw from a theropod dinosaur and that it dates from the Late Cretaceous, around 90 million years ago (Cenomanian/Turonian faunal stages).  Informed sources have stated that this is only the third documented dinosaur fossil found from this State.  Although many famous dinosaurs are known from the United States, the fossils of these long, extinct creatures are not spread uniformly across America.  In fact, more than a dozen States in the Union have no record of dinosaur fossils whatsoever.

With the discovery of a partial femur (thigh bone) from a theropod dinosaur last year, Washington State become the 37th U. S. State to have fossils of the Dinosauria recorded within its boundaries.  This prompted Everything Dinosaur team members to produce a map identifying which States in America had dinosaur fossils and which did not.

To read more about which States have dinosaurs: Washington State the 37th U.S. State with a Dinosaur.

Unable to Identify the Genus

Researcher at the Science Museum of Minnesota, John Westgaard explained that it was not possible to identify a dinosaur genus, but when questioned further he suggested that the fossil claw could have belonged to a Velociraptor-like dinosaur.

A spokesperson from Everything Dinosaur stated that it was not possible to be more specific about the fossil specimen but as the claw has been dated to around 90 million years ago, this was a significant discovery as little is known about the fauna of North America from this part of the Cretaceous.

To read about the discovery of the dinosaur thigh bone from Washington State: Washington State’s First Dinosaur.

Highlighting Minnesota’s Cretaceous Past

The other Minnesota dinosaur fossil finds are equally fragmentary and also date from the Late Cretaceous.  An unknown genus of duck-billed dinosaur is known from a few bones and teeth.

Everything Dinosaur stocks a range of replica dinosaur claws and dinosaur teeth: Dinosaur Claws and Dinosaur Teeth.

Kimbetopsalis simmonsae – Shedding Light on Ancient Mammals after the Dinosaur Extinction

A newly described species of ancient mammal, one that existed around half a million years or so after the Cretaceous mass extinction event that saw the demise of the dinosaurs – the dinosaur extinction, is helping scientists to understand more about how the Mammalia Order radiated and diversified.  The discovery from New Mexico (Nacimiento Formation), has been named Kimbetopsalis simmonsae, it seems that mammals were quick to take advantage of the vacuum left in terrestrial habitats by the dinosaurs.

Kimbetopsalis simmonsae

An Illustration of What Kimbetopsalis simmonsae Might Have Looked Like

An illustration of Kimbetopsalis simmonsae.

Picture credit: Sarah Shelley

A Lucky Find for a Student

The fossils, which consist of the back of the jaws, part of the brain case and incisors from the front of the mouth were found during an exhibition to the San Juan Basin of New Mexico last year.  Remarkably, the first evidence, the back of the jaws was found by University of Nebraska-Lincoln student Carissa Raymond, this was her first fossil hunting field trip.

The field team consisted of two other students, recruited by University of Nebraska-Lincoln palaeontologist Ross Secord and Steve Brusatte (University of Edinburgh).  Thomas Williamson, curator of palaeontology at the New Mexico Museum of Natural History and Science, based in Albuquerque and a specialist in Late Cretaceous/Early Palaeocene fauna was also part of the group.

The paper describing this new species of prehistoric animal has just been published in the journal of the Linnean Society.  K. simmonsae was a member of the multituberculates, a group of mammals that first evolved in the Jurassic.  They thrived during the age of dinosaurs, but were mostly small and many described species are thought to have been nocturnal.  Although, building up a more complete picture is difficult as most genera are known from only a few isolated teeth.

Beaver-sized Mammal

This beaver-sized mammal represents a relatively large example of this sub-order of mammals, the animal was named after the Kimbeto Wash area of the New Mexico Badlands, where the fossils were found.

Dr Stephen Brusatte, lead researcher on the study, explained:

“We realised pretty quickly that this was a totally new type of mammal that no-one has seen before, the other part of the name – psalis, means “cutting shears” and is in reference to the blade-like teeth [incisors].”

The Fossils of Kimbetopsalis simmonsae Note the Peculiar Cusps on the Molars and Premolars

Remarkable fossil find from New Mexico – Kimbetopsalis simmonsae.

Picture credit: Dr. Steve Brusatte University of Edinburgh

The Multituberculata Mammals

The multituberculate mammals are generally regarded as the earliest plant-eating mammals to have existed.  The teeth of K. simmonsae are typical of this group, the long chisel-like front teeth and the back teeth, the chewing teeth, with their parallel rows of cusps.  It is these back teeth with their distinctive cusps arranged in either two or three rows that gives the Multituberculata group their name.  This discovery is the first new multituberculate to be found in the San Juan Basin in more than a century.

Members of the Field Team Pose for a Photograph

left to right Sarah Shelley, Eric Davidson, Carissa Raymond, Steve Brusatte and Ross Secord

Picture credit: Thomas Williamson/Reuters

Fossils of another multituberculate from the genus Taeniolabis are known from this area, however, the newly described Kimbetopsalis simmonsae come from a geologically much older stratigraphic layer. Taeniolabis species represent some of the largest Multituberculata so far described, with some specimens estimated to about as big as an Alsatian dog and one species Taeniolabis taoensis possibly exceeding 100 kilogrammes in weight, although they were probably entirely herbivorous.

It has been proposed that Kimbetopsalis simmonsae may have been an ancestor of the Taeniolabis genus, part of a trend towards larger and larger mammals as the Mammalia radiated out and new species evolved to take advantage of the extinction of the dinosaurs.  It seems that the mammals may have been quick off the mark to exploit the niches left after the dinosaur extinction.

Extinction of the Multituberculates

This type of mammal was soon destined to go the same way as the dinosaurs.  By the Late Eocene, these creatures were becoming increasingly rare and by the Early Oligocene Epoch (around 32-30 million years ago), the Multituberculata were extinct.  Why these mammals died out, remains an area of debate amongst palaeontologists.  This group left no living descendants and a number of reasons why they became extinct have been proposed, one of the more plausible and popular explanations is increased competition from placental mammals, particularly rodents.

Rodents are the most diverse and most specious of all the types of mammal living today.  Perhaps it was the evolution and rapid spread of the rodents that finally led to the demise of the Multituberculata, a group that had outlived the Dinosauria.

To read an earlier article that traces the origins of the Multituberculata: Tracing the Origins of the Multituberculates.

Dinosaur Extinction

Commenting on the significance of this fossil discovery, Dr Thomas Williamson said:

“Finding this new mammal was a pleasant surprise.  It helps fill an important gap in the record of this group of mammals.  It’s interesting that this odd, now extinct group, was among the few to survive the mass extinction and thrive in the aftermath.  It may be because they were among the few mammals that were already well-suited to eating plants when the extinction came.  This new species helps to show just how fast they were evolving to take advantage of conditions in the post-extinction world.”

Visit Everything Dinosaur’s website: Everything Dinosaur.

Small-eyed Dinosaurs Let’s Keep Things in Proportion

Telephone calls and emails into the “dino den” otherwise known as the office at Everything Dinosaur last night, when the popular Radio 2 early evening show, Simon Mayo Drivetime, provided a prehistoric themed poser as part of a regular slot helping out with listener’s homework.  One of the two questions sent in involved the Dinosauria, why did dinosaurs have such small eyes?

Does Everything Dinosaur Have A View on Question B?

Any views on question two?

Picture credit: Simon May Drivetime Facebook

Small-eyed Dinosaurs?

In short, dinosaurs did not have small eyes, in fact, the eyes of some dinosaurs were quite large in proportion to the rest of their body and the word “proportion” is the key here, but more about that later.  You see, (no pun intended), it all depends on the type of dinosaur you look at.  Not all dinosaurs were the bus-sized, meat-eaters so popular with little boys and girls, as shown in the picture above.  That fearsome dinosaur looks like Carcharodontosaurus saharicus (Car-car-oh-dont-toe-sore-us, sa-har-ri-kus) as depicted in the BBC television series “Planet Dinosaur” which was first aired in the autumn of 2011.

The grey, long-necked dinosaurs in the background would have dwarfed even the largest carnivore.  They look like Paralititan stromeri, colossal animals that could have reached lengths in excess of thirty metres or more and perhaps weighed seventy tonnes.

Studying the Skull

Take a look at a skull of a much smaller dinosaur, a member of the Velociraptor family for example, and you will see that the orbit (the eye socket) is relatively large when the dimensions of the rest of the skull are taken into consideration.

Dromaeosauridae (Family) and Typical Dromaeosaurids such as the Velociraptorinae did not have Small Eyes

No small eyes here on a Velociraptor.

Dinosaurs such as Velociraptor are very closely related to modern birds.  Birds have very large eyes in proportion to their body size.  After all, if you are going to fly, having large eyes coupled with excellent eyesight makes a lot of sense.  Members of the bird Order (Aves), have the biggest eyes relative to their body mass amongst the vertebrates, some species have eyes so large that eye movement is limited within the orbit of the skull, when some birds want to have a good look around they have to turn their heads, the eyes cannot move independently in their sockets.

Turning Your Head to Have a Look Round

Turning your head to look around.  Picture credit: Everything Dinosaur.

What About Those Really Big Dinosaurs?

This is all very well, some dinosaurs had proportionately big eyes, but what about those really big dinosaurs, animals like  Carcharodontosaurus and the monstrous  Paralititan mentioned earlier?  It’s that word again “proportion”.  In proportion to their bodies, large dinosaurs did have relatively small eyes, this phenomenon is observed in large mammals today, elephants, rhinos and the largest animals of all the cetaceans (whales and dolphins).

Really big animals tend to have eyes that look small. The actual diameter of the eye might be much bigger than our own, but since the skull is so big compared to ours, then the eye seems much smaller in comparison.

Newly hatched dinosaurs had big eyes in proportion to their body size.  As the animal grew so its body proportions changed and gradually the eye became much smaller when compared to the rest of the body.

Baby Dinosaurs Had Bigger Eyes when Compared to the Adults

The baby Triceratops figure next to the adult Papo Triceratops.  Baby dinosaurs had proportionately bigger eyes than adult dinosaurs.

Picture credit: Everything Dinosaur

Perfectly Adapted to Their Environment

It’s worth remembering that despite a common public misunderstanding, dinosaurs were perfectly adapted to their environments and way of life.  As a clade, the Dinosauria has been around for some 800 times longer than our own species.  From what we know of the closest living relatives of the dinosaurs, the birds, these reptiles probably had excellent colour vision and in many cases their visual acuity, ability to see movement and their colour vision spectrum were much better than ours.

Think of it this way, studies of the internal structure of the skull of Tyrannosaurus rex indicate that this ferocious predator had a optic nerve about as thick as an adult man’s thumb.  That’s a lot of data going into that part of the brain dedicated to processing information from the eyes (occipital centre).

Tyrannosaurus rex

The orbits (eye sockets), in the skull of “Sue”, the largest mounted T. rex skeleton, measure nearly 10.5 cm across, this suggests that this dinosaur had eyeballs around 8 cm in size, that’s bigger than a tennis ball.  These eyes were held aloft some four metres in the air, an excellent viewing platform.  In addition, the position of the eyes in the skull gave this theropod a degree of binocular (stereoscopic vision), probably greater depth perception than ours.  Ideal if you are an ambush predator.

Forward Facing Eyes of an Apex Predator

A three-dimensional reconstruction of a T. rex skull.

“King of the Tyrant Lizards”

Research into the eyesight of Tyrannosaurus rex, published in 2006 by the University of Oregon concluded that big, Late Cretaceous meat-eaters like the “King of the Tyrant Lizards” may have had eyesight that was at least ten times* better than our own.  Vision may not have been the primary sense of T. rex, but those proportionately small eyes could have very probably spotted you before you had seen it and that’s quite a sobering thought.

Comparing the Orbits of Two Types of Tyrannosauroids

The orbit of a Tyrannosaurus rex is compared to the eye socket of a Raptorex kriegsteini.

Picture credit: Paul Sereno

Stevens, K.A. 2006 Binocular vision in theropod dinosaurs. Journal of Vertebrate Paleontology 26(2):321-330. *visual acuity up to thirteen times was stated in the paper.

For dinosaur themed toys, models and games: Visit Everything Dinosaur.