Denizens of Madrid’s Miocene woods: the Bear-Dogs

For most of the early and midlle Miocene, cat-like carnivorans had to play a subordinate role in the predator guild of Madrid’s woodlands and prairies. The dominant hunters and scavengers in those ecosystems belonged to the Caniformia (which is the “dog half” of the order Carnivora), and they included two groups known with the confusing popular names of “Bear-Dogs” and “Dog-Bears”. The “Dog-Bears” or hemicyonines, were close relatives of today’s bears, and will be discussed in a different post.
The “Bear-Dogs” or Amphicyonids, were neither dogs nor bears, but a separate family distantly related to both. Most of them had a rather unspecialized dentition with a nearly complete set of premolars and molars, resembling in some ways the dentition of dogs, and suggesting a similarly varied diet. But their skeleton was not especially dog-like in most cases, and instead it resembled a mixture between a bear and a big cat in terms of body proportions and locomotor adaptations.
One of the most common and well-known members of this family was Amphicyon major, an animal similar in size to a modern brown bear and whose remains are found in several fossil sites in Madrid. Well adapted to a life as an active hunter, scavenger and omnivore, it would keep the modest cats of the time (the largest of which was leopard-sized) easily at bay.

Here is a reconstruction of Amphicyon major in the middle Miocene environments of Casa de Campo, an area that today is covered with mediterranean bush and woodland, but which during the Aragonian was part of a savannah-like floodplain with gallery woods near water. These two individuals are disputing a carcass of Triceromeryx.
amphicyon Casa de Campo

Posted on 14/07/2014, in Uncategorized. Bookmark the permalink. 6 Comments.

  1. Awesome reconstruction as usual sir! What are some of the basic apomorphies that unite the clade?

  2. The Amphicyonidae are defined by their basicranial structure, with the ectotympanic being the main element contributing to the auditory bulla (a “Type A” bulla in the sense of Hunt); and by the upper molar pattern with a basically triangular (not quadrate) M1 crown with three main cusps, and lack of a talon or heel in the posterior edge of the M2.

  3. Thank you again. Time to open up the Dogs and their fossil relatives book to compare the differences 🙂 Can’t wait for the hemicyonines

  4. Hello, I found this post on bear-dogs intriguing. I wish there was a way we could directly observe these and other extinct animals alive so that we could get a better understanding of their biology and ecology, especially ones with no close living parallel.
    One little detail though about the reconstruction could not escape my notice. A ripped up carcass is pictured with the bear-dogs fighting over it. It seems as if they have been consuming it but I do not not see any blood on either of the bear-dogs. I was just wondering what would be the reason for that.
    Also I was wondering if the lower canines of these animals would have rested behind the upper canines when the mouth was closed. If that is the case wouldn’t that be unique for Carnivora? It seems from the pictures of the skull that I have seen they would have. I also noticed that their sagittal crest was very large . What would be the implications of these details?
    Thank you very much.

    • You are right to observe that there are no blood stains on either bear-dog. The story behind this detail is that the bear-dogs would have stumbled upon this Triceromeryx when the animal was long dead and its blood had stopped flowing. The cause of death I leave as an open question but it serves me to stress the fact that amphicyionids were opportunistic scavengers.
      In amphicyionids, as in all other carnivorans, the lower canine would be positioned ahead of the upper canine when the jaws were closed, although it is possible that the postmortem deformation of some fossil skull may suggest otherwise. The saggital crest was usually large in amphicyionids but some specimens, such as the Amphicyon ingens skeleton mounted at the AMNH in New York, display exceptionally large crests. This feature indicates the presence of large and powerful temporalis muscles, in turn suggesting a powerful bite and even the ability to crush bone, as indicated also by the morphology of its cheek teeth.

      • That makes sense why there are no blood stains on either animals.
        I thought that it would be unusual for the lower canines to be behind the upper canines.
        It was my understanding that the temporalis muscles gave the strength in a more anterior bite, producing power behind the canines and incisors, and the masseters were for chewing. It sounds like the temporalises would have been helpful for chewing as well though.It looks to me is that they would have been very proficient at ripping up a carcass using both a strong anterior bite to hold the carcass, perhaps, and a strong neck to do the actual destruction, articulating dorso-ventrally. Just a thought.
        Once again, very interesting post.

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