Arktocara yakataga – May Hold Key to Freshwater Dolphin Evolution

Back in the early fifties, when geologist Donald J. Miller (United States Geological Survey), was mapping the area of Alaska that would eventually become Yakutat City, he came across an ancient skull of a whale. The snout had been broken off and lost but the preserved cranium led to the conclusion that the cranial material and associated teeth belonged to an ancient dolphin.  The fossils were despatched to the Smithsonian’s National Museum of Natural History, where they remained until a newly published study revealed their significance.

For models of sea monsters including prehistoric cetaceans: Models of Sea Monsters.

A New Species of Prehistoric Dolphin

The fossils represent a new species of prehistoric dolphin, an animal that lived around twenty-five million years ago and it represents the most northerly specimen of this type of toothed whale ever found.  The genus name translates from the Latin as “Face of the North” a reference to the high latitude location of the fossil discovery and the fact that the skull has been designated the holotype.

A Line Drawing (A) and a View of the Fossil Skull (B)

A dorsal view of the skull of Arktocara (right) and associated line drawing (left)

Picture credit: James Di Loreto, Smithsonian Institute

Ancient Dolphin Fossil

Published in the academic journal “PeerJ”, palaeontologists Nicholas Pyenson and Alexandra Boersma describe the fossils and place it within the toothed-whale group, specifically the Platanistoidea.  Ironically, the only extant members of this group are confined to freshwater river systems, but the fossil record indicates that these types of dolphins evolved in marine environments.  The scientists hope that this new fossil discovery, a specimen that had languished in the Smithsonian fossil collection for more than half a century, will help to shed light on the phylogeny of the Platanistoidea as well as assisting in the research to determine how these particular toothed whales evolved.

Alex Boersma, currently based at the California State University, commented:

“It’s a lovely skull, which is probably the first thing I noticed about it”.

The Skull and Other Fossil Elements

The fossil Arktocara yakataga (resting on an 1875 ethnographic map of Alaska) belonged to a dolphin that swam in subarctic marine waters around 25 million years ago.

Picture credit: James Di Loreto, Smithsonian Institute

The researchers are confident that more strange cetacean skulls may be awaiting discovery in northern latitudes and Alex is sure that this specimen “could answer questions about how this once cosmopolitan group dating back over twenty million years dwindled down to just a few freshwater species.”

The Poul Creek Formation

The fossil comes from the Poul Creek Formation, but the exact location remains unknown, however, the scientists estimate that the fossil dates from between 29 and 24 million years ago, an important period in the history of whale evolution as the two main groups the toothed-whales “Odontoceti” and the baleen whales “Mysticeti” were diversifying and radiating into a number of new genera.

Measuring a little under two and a half metres in length, Arktocara yakataga was about the size of a modern Common Bottlenose Dolphin (Tursiops truncatus).  Although the scientists cannot be absolutely certain where the animal died, after all, bones can be transported considerable distances prior to burial and fossilisation, it seems reasonable to assume that this mammal did live in a marine environment.  The research team stress that many other types of important fossil may be lingering within the collections of museums, their significance having not yet been realised due to incorrect labelling or inaccurate classification.

An Illustration of Arktocara yakataga

An illustration of Arktocara.

Picture credit: Linocut print art by Alexandra Boersma

To read a recently published article about the origin of high frequency hearing in whales: How High Frequency Hearing in Whales May Have Evolved.

Unique Elbows of Thylacoleo Hints at Hunting Strategy

The fearsome Thylacoleo (Thylacoleo carnifex), commonly referred to as the “Marsupial Lion” may have had a unique hunting strategy.  The anatomy of the limbs indicate that this native of Australia up until around 46,000 years or so ago, had very robust front legs, but it was not a fast runner.  It was probably an ambush specialist, but how did this 100-kilogramme-mammal despatch its prey?  After all, it did not have the teeth typical of a carnivore.  For example, Thylacoleo lacked canines in the lower jaw and although they were present in the upper jaw, they were extremely small (a feature no doubt noted by Richard Owen, later Sir Richard Owen, who named and described this genus back in 1859).

The Fearsome Thylacoleo – but How Did it Hunt and Kill?

Capable of climbing trees and with strong forelimbs for despatching prey.

Picture credit: Peter Trusler/Australian Post

In a new paper, published in the academic journal “Paleobiology”, scientists from the University of Málaga (Spain), in collaboration with colleagues from Bristol University conclude that Thylacoleo used its big but blunt incisors to grab prey before carrying out the “coup de grâce” with a swipes from its powerful paws which possessed a formidable set of claws including a super-sized claw on its first digit, (the equivalent digit in our species being the thumb).

For models and replicas of prehistoric animals: Prehistoric Animal Models.

Comparing Elbows

How was this conclusion made?  It’s relatively simple really, the scientists studied the fossilised elbows of Thylacoleo and compared them to a number of living mammals (placental as well as marsupial).  It turns out that this pouched predator had a unique elbow joint amongst carnivorous mammals.

One of the authors of the newly published paper, Christine Janis (Marie Curie Research Fellow at the University of Bristol, currently on a leave of absence from a professorship at Brown University, United States), explained that this study indicates that there is a strong association between the anatomy of the humerus where it articulates with the ulna and radius (the elbow) and the way in which animals move about.

Examining Elbow Joints

Specialised runners like canids (dogs) have an elbow joint indicating movement restricted to a back and forwards motion, helping to stabilise their bodies on the ground, great for running, whilst mammals that are confident climbers, monkeys for example, have an elbow joint that allows for rotation of the hand.

Felidae (cats), have an elbow joint of intermediate shape, as they use their forelimbs to wrestle prey and many types of cat are adroit when it comes to climbing.

In contrast, the unique elbow joint of Thylacoleo permitted extensive rotation of the hand but it also possessed features not seen in extant mammals that permitted the elbow to stabilise the limb when the animal was on the ground.  The “Marsupial Lion” has long been thought to have been at home in the trees, an animal capable of an arboreal existence, although ironically a number of the most complete and best preserved Thylacoleo fossils have been found in limestone caves in the Nullabor Plain region of Australia (Nullabor loosely translates as “no trees”).

Christine Janis stated:

“If Thylacoleo had hunted like a lion using its forelimbs to manipulate its prey, then its elbow joint should have been lion-like.  But, surprisingly, it had a unique elbow-joint among living predatory mammals , one that suggested a great deal of rotational capacity of the hand, like an arboreal mammal, but also features not seen in living climbers, that would have stabilised the limb on the ground (suggesting that it was not simply a climber).”

The Marsupial Lion Had an Extreme Amount of Forelimb Manoeuvrability

Christine and her colleagues group Thylacoleo with living animals that have an extreme amount of forelimb manoeuvrability, animals such as primates, sloths and anteaters.  The analysis showed that it had a greater degree of manoeuvrability than any living, meat-eating placental mammal and the team concludes that Thylacoleo was mainly terrestrial but with some climbing abilities and the forelimbs were used to overpower prey.

The African lion (Panthera leo) does not possess such flexible forelimbs and when the unique elbow joint is considered in conjunction with that over sized first digit claw, the researchers hypothesise that the “Marsupial Lion” used its claws to kill.  The big, but blunt incisors in the jaws were probably used to clamp down on prey and then with the large and retractable claw on the semi-opposable thumb (the dew claw), Thylacoleo could have slashed at its victims.

Visit Everything Dinosaur’s website: Everything Dinosaur.

The First Human Inhabitants of Australia Knew All About the Marsupial Lion

However, it hunted, Thylacoleo was one creature that you would not want to have encountered in the outback.   The first Australians, the ancestors of the today’s aboriginal people, would have known Thylacoleo and probably they were wise enough to give it a wide berth.

The scientific paper: “Ecomorphological determinations in the absence of living analogues: the predatory behaviour of the marsupial lion (Thylacoleo carnifex) as revealed by elbow joint morphology”

To read an earlier article which examined the link between scratches made on cave walls and the climbing abilities of the Marsupial Lion: Don’t Climb a Tree to Avoid a Thylacoleo!