Friday mystery object #430 answer

Last week we had a second guest mystery object from Rohan Long, who is based at the Harry Brookes Allen Museum of Anatomy and Pathology at the University of Melbourne.

It was a genuine mystery object and it certainly proved quite tricky. There were quite a few suggestions of gibbon, but the proportions of the long bones aren’t right, with gibbon radius and ulna bones proportionally far longer in relation to the humerus or any of the the bones of the legs than what we see above. The skull does look quite ~~gibbony~~ ~~gibbonesque~~ gibbon-like, but generally gibbons have an auditory bulla (the region on the underside of the skull that houses the hearing apparatus) that strongly curves, almost like a boomerang, whereas here the feature is much straigher.

The teeth tell us that the mystery object is from one of the Cercopithecidae (Old World Monkeys) since there are only two premolars instead of the three that you find in the Platyrrhini (New World Monkeys). That helps a bit, but there are still over 150 species in the Cercopithecidae to consider.

Some can be ruled out fairly easily, such as members of the Papionini, like baboons and macaques, which have adults that are more prognathic (their jaws jut forward) that this specimen. This is less true for juveniles (jaws jut more as the animal grows and matures), but we can ignore that here, since the mystery specimen has well-fused sutures and visible wear on the teeth, so we know it’s an adult.

One thing that can be useful to consider when trying to identify primate skulls is the shape and position of the nasal opening. This can vary within species and it can be a feature sensitive to the angle at which a photograph is taken (making it more difficult to assess from images), but overall it can help narrow down possibilities without having to get into too much fine detail early in the identification process.

The Mammalian Crania Picture Archive has well standardised images, including a reasonable variety of primates with males, females and animals of different ages represented. They also provide some measurements for each specimen, that may be useful when making comparisons. The primate page is here in case you’re not familiar with this very valuable resource.

Over the last week I’ve taken a look through a wide variety of skulls from different primate taxa and I’m confident that the mystery specimen is from the Colobinae. I think the position of the nasal opening (especially the top part of the opening in relation to the eyesockets) is helpful in distinguishing possible species within the subfamily. This makes sense when you consider that a third of the genera in the Colobinae are in a group known as the “odd-nosed monkeys”.

In this specimen the nasal opening forms a shield shaped hole with a flat top that starts quite high in relation to the eye sockets. In most species it starts lower, sometimes well below the line of the bottom margin of the eye socket. The Red Colobus is superficially quite similar, but when you look at other features it doesn’t look right – for example, if you look at the underside of the skull it has several different features, include a differently shaped incisor arcade and the pterygoids (the wing-shaped bits of bone that spread to either side, just behind the palate) are a different shape.

However, I did find a species which matches much better, so I am tentatively suggesting that the mystery object may be a Black-crested Sumatran Langur (AKA Mitred Leaf Monkey or Sumatran Surili) Presbytis melalophos (Raffles, 1821). If not that species I think the mystery specimen will be in the same Genus. There will undoubtedly be additional species with similar skulls that I’ve not seen, but within the limits of the resources at my disposal I don’t think I can do any better than that.

Oddly enough, I have had a skull of this species as a mystery object before, but it appears to be from a much younger individual, so at first glance it looks quite different, but the general features of the nose still remain:

My thanks to everyone for your suggestions and many thanks to Rohan for sharing this mystery object. It’s been an interesting one and has reinforced my conclusion that primate skull identification can be REALLY difficult!

Friday mystery object #430

This week we have another guest mystery object from Rohan Long:

Today’s mystery object is another item from the Harry Brookes Allen Museum of Anatomy and Pathology at the University of Melbourne. In contrast to our last offering – a partial skull with most of the diagnostic features frustratingly absent – this is a full skeleton of a small primate. We have many classroom sets in our collection comprising complete, disarticulated skeletons of mammals, mostly marsupials and primates. The primate sets overwhelmingly consist of macaques (Macaca sp.) which I presume were lab animals from the University. Additionally, there are sets of a few baboons, a few chimpanzees, and one Sacred Langur (Semnopithecus entellus). Then there’s this one.

I had originally described it as, “large macaque”, but after cataloguing dozens of macaque skeletons, it stood out as something different. It kept bugging me, and I had committed myself to giving every specimen in our comparative anatomy collection a proper identification. I had found some previous blog posts by Paolo while researching how to identify primate specimens, and that’s what prompted me to initially get in touch. In regards to provenance, our comparative anatomy collection was mostly amassed in the early 20^th century, and many specimens are associated with Frederic Wood Jones, Anatomy Department Head from 1930-1937. Wood Jones and his colleagues had strong international networks, and there are species in this collection from all over the world.

As ever you can leave your observations, thoughts and suggestions about which species this might be in the comments section below. Have fun with this one!

Friday mystery object #378 answer

Last week I gave you this specimen from the Dead Zoo to have a go at identifying:

It was a bit of a tricky one, since the specimen has been sectioned down the midline and the bone of the maxilla has been removed to show the roots of the teeth.

However, many of you were stuck at home and had a chance to get into detail in the comments. There were some fantastic answers where the features were discussed, so I think it’s well worth sharing some of them:

March 20, 2020 at 5:21 pm

Rémi said:

We are confined at home, so we searched together with my 5 years old daughter. Here are our thoughts :
– foramen magnum in a downward position, low-crown teeth, bony part behind orbite, orbites facing toward the front, so we are dealing with a primate
– but a special primate because the orbites are open to the temporal fossa. And also it has a long snout with the orbites below the nasal bone. The orbites are not big enough for a nocturnal monkey. And also the very special lower incisors in horizontal position, also know as teeth-comb. We think it is a lemur-like animal.
The brain case is not round enough for a Lorisidae. We could not find pictures of all the lemur and sportive lemur species. But we saw the picture of a skull of the cat-ish one and it fits very well.

Then

March 22, 2020 at 10:55 pm

steveryder said:

Second thoughts: we cannot quite see this but in my own notes on lemur;
Canine often incisiform and procumbent, arranged laterally with incisors in toothcomb, creating array of 3.
Ist mandibular premolar often caniniform

This would then be 3 premolar, 3 molar and therefore not Varecia but more probably Eulemur….

and…

March 25, 2020 at 12:16 am

katedmonson said:

While some lemurs don’t have upper incisors, this one has small peg-like ones. A Ruffed lemur (Varecia variegate), while having the same dentition, has more of an orbital thickness.
Since the skull has been dremeled out, I am not sure how much of a diastema was between the canine and upper premolars. If there was one there, I will vote for a Ring tailed lemur (Lemur catta), female, because of the smoother occipital and more slender lower mandible. The size fits as well.

These comments all highlight features of the skull that belong to lemurs, but there is a little confusion caused by the bone removed from around the teeth.

Ring-tailed Lemur was the most popular answer, but the diastema (or gap) between the upper canine tooth and the first upper premolar that katedmonson mentioned would not be present on this specimen, even if the bone was still there. Also, that lower first premolar has a fairly simple conical/triangular shape with just one cusp – which makes it caniniform, as mentioned by steveryder.

Rather than the Ring-tailed Lemur, this is the skull of a Ruffed Lemur Varecia variegata Kerr, 1792. I think it’s probably from a female or young animal (or both) as it’s more gracile than some other specimens I’ve seen. This accounts for the reduced orbital thickness, slender mandible and smoother occipital mentioned by katedmonson.

Black and white ruffed lemur by Charles J Sharpe, 2018

I should say, on Twitter Michael English and Gabriella Κογντογριδη also recognised this as a Ruffed Lemur. Worth mentioning that if you use Twitter and you like identifying skulls (well OBVIOUSLY you like skulls if you’re reading this) then it’s well worth checking out the #GuessTheSkull hashtag started by Yara Haridy.

A new mystery object next week – stay safe and healthy!

Friday mystery object #266 answer

Last week I gave you this distinctively weird looking skull to identify:

mystery266

As I suspected, many of you worked out what it was straight away, but I wonder if it would have been as easy if the side view hadn’t included the mandible?

The upper dentition, especially the pair of incisors, is somewhat similar to that of a rodent, but that mandible is ludicrously massive and could only really belong to the weirdest primate in the world: the Aye-aye Daubentonia madagascariensis É. Geoffroy, 1795

So very well done to Tone Hitchcock, henstridgesj, Chris, Cindy Nelson-Viljoen, Daniel Jones, steve torna, Agata Stachowiak, palfreyman1414, boneman2014Lee Post, joe vans, Allen Hazen, Dave Taylor, Michelle, witcharachne, and Daniel Calleri.

The Aye-aye’s incisors are an adaptation for gnawing holes in wood to get at grubs inside. It finds these tasty morsels using a tapping finger and crazy bat-like ears to detect the tunnels the larvae create when feeding, with a system a bit like seismic ground response analysis.

Aye-aye by Frank Vassen 2008

Once the squishy prey has been detected and an entry point has been gnawed, the Aye-aye fishes it out using a specially adapted long, thin finger with a hooked claw.

Aye-aye fingers by Dr. Mirko Junge 2009

Basically, the Aye-aye feeds rather like a woodpecker, but with the benefit of fingers and teeth. Perhaps it’s weird, but it’s most definitely wonderful! Aye_aye

Friday mystery object #265 answer

Last week I gave you this lovely primate skull from the Grant Museum of Zoology to identify:

mystery265

When I first saw it I assumed it was a Macaque of some kind. It’s obviously in the Cercopithecidae (or an Old World Monkey) based on the number of premolars – 4 in the upper jaw instead of the 6 you’d get in a Platyrrhini (or New World Monkey). Macaques are common in collections and they have a similar overall appearance to this specimen.

However, I then noticed the particularly deep hollows under the eyesockets and the flaring of the maxilla where it meets the nasals, which is not a characteristic of Macaques.

Monkey_skull

It actually reminded me a bit of a toned down version of a Mandrill skull, so I started by looking at the phylogeny of primates to get an idea of which species were more closely related to the genus Mandrillus.

Primate phylogeny from Goodman et al. 2005. Trends in Genetics. 21(9):511–517

As you can see the Mandrills share a sister relationship with the genus Cercocebus, which are the White-eyelid Mangabeys, so that’s where I started looking. It turns out that these infraorbital depressions are a Mangabey feature, so I then looked at the various types of Mangabey (not just those in the genus Cercocebus).

It wasn’t easy finding specimens for comparison, but I did find a very useful (if a bit old) paper on Mangabeys by Groves (1978), which gave good descriptions of the various species, allowing me to rule out the Sooty Mangabey and narrow the likely species down to the Golden-bellied Mangabey or, my personal preference, the Agile Mangabey Cercocebus agilis (Milne-Edwards, 1886).

These monkeys have a shorter, relatively broader face than the more familiar Sooty Mangabey, with deeper and broader hollows under the orbits.

So well done to everyone who recognised that this skull belonged to an Old World Monkey, with particular congratulations to Cindy Nelson-Viljoen and palfreyman1414, who all came close in terms of taxonomy and a big round of applause for inkydigit who narrowed it down to the right genus!

More mysteries to come next week…

Aquatic Ape – the body fat observation

Recently I wrote about the Aquatic Ape Hypotheses, inspired by a conference being held on the subject.

Unsurprisingly, other people have also been busy discussing the topic and there has been a fun pseudoscientific parody called the “Space Ape Theory” which took off rather nicely on Twitter and is doing a good job of highlighting problems with the AAH.

Space Ape

This post will only be short, because other people have been dealing with this issue perfectly well without the need for my input, but I thought it might be useful to make visible the outcome of an extended conversation I had with AAH proponent Marcel F. Williams, in the comments section of my earlier post.

I decided to check some independent evidence about an inference made by Alister Hardy that led to the development of the AAH in the first place – the idea that having layers of subcutaneous fat was a trait unique to humans and aquatic mammals. This idea is still regularly cited by AAH proponents (especially Elaine Morgan) as a line of evidence for evolutionary convergence between humans and marine mammals due to the sharing of an aquatic habitat.

However, on checking the literature on primate husbandry it turns out that other primates have levels of subcutaneous fat that are directly comparable to humans if the animals have a ready supply of food, suggesting that humans are no different to other primates except in having a more stable food supply and leading a more sedentary life. This is supported by data from modern hunter-gatherer groups, who exhibit far lower fat levels than either farming or Western populations. Here’s a summary of the data with a link to the research:

Body fat – man vs monkey
Rhesus macaques in labs that are identified as being in the ‘optimal’ weight range have an average body fat content of 25% with individuals in the obese range averaging 42.7% [link opens pdf]

Autopsies of male orangutans show body fat levels range from 15% to 45% [link opens pdf]

Average body fat in Hadza hunter-gatherers averages 13.5% for men and 20% for women. In Western populations men average 22.5% and women average 37.9% [link opens pdf]

In short, humans are by no means unique in the primates with regard to their proportion of subcutaneous fat, so if any AAH proponent pulls out that old chestnut in conversation, be sure to put them right.

Oshine the morbidly obese orangutan

Friday mystery object #191 answer

On Friday we had this skull submitted by Dr Ben Swift for identification:

mystery191c

Now this is quite obviously a primate, as it has a bony ring around the orbit, a bony back wall to the orbit and just eight incisors as opposed to the twelve that forms the basal condition for mammals. The teeth also tell us that this is an Old World Monkey (Cercopithecidae), since these primates only have eight premolars instead of the twelve you find in the New World Monkeys (Platyrrhini). The small canines suggest that this is the skull of a female.

From there it starts getting a bit more difficult. The fairly small size of the specimen ruled out a few genera, but the main features that helped narrow down the possibilities were the very flat face, the heavy bony rings around the orbits, the flaring of the zygomatic arches (cheekbones) and the short and rounded braincase. Effectively the only way to consider these features is to look at a lot of comparative specimens (the excellent Mammalian Crania Photographic Archive proved very useful for this).

After a lot of consideration I found myself in agreement with the suggestion of something from the genus Continue reading →

Friday mystery object #98 answer

On Friday I gave you this skull to identify:

Everyone spotted that it was from a monkey, perhaps unsurprisingly since monkeys have a very characteristic appearance, with a globular braincase and forward-facing eyes. The orbit is enclosed by a solid bony ring and there is a post-orbital wall made up of the sphenoid and ethmoid bones, that produces a cup-shaped eye socket.

But there are a lot of different monkey species – around 286 if you include the Apes (as you should). We can see that this specimen belongs to the Catarrhini clade (the Old World Monkeys and Apes) since it only has 2 premolars instead of the 3 premolars you’d expect in a New World Monkey (N.B. some extinct Catarrhines known from fossils have 3 premolars, so this useful distinction doesn’t actually help define the clade).

The size of the skull and the the shape of the nose region and the mandible isn’t quite right for an Ape, or a typical Cheek-pouch Monkey (like Macaques or Baboons), leaving us with the Colobinae (which includes Colobus Monkeys, Doucs, Langurs, Leaf Monkeys, Proboscis Monkeys, Snub-nosed Monkeys and Surelis).

Once we get this far it becomes rather more tricky to identify what species we’re dealing with (and it doesn’t help that the names are applied somewhat inconsistently), so I must offer congratulations to Jake, jonpaulkaiser, curatorialtrainee, henstridgesj, carlos grau and Steven D. Garber, PhD – all of whom suggested perfectly possible candidates amongst the Langurs and Snub-nosed Monkeys.

This skull is actually from a Continue reading →