Tuesday, September 1, 2015

How To Build A Primate Tooth V: The Toothcomb



A toothcomb is a dental specialization in which the lower incisors and canines combine to form a structure that sort of resembles a comb. In the diagram to the right you can see how the mandibular incisors project forward, alongside the canines (which actually sort of resemble incisors rather than canies) to create this structure.

The toothcomb is unique to strepsirrhine primates (lemurs, lorises, and galagos). The fossil record, in conjunction with molecular clock estimates, suggest that lemurs and lorises diverged in the Paleocene, over 60 million years ago. This tells us that the toothcomb has very deep evolutionary origins in the strepsirrhine primate lineage.

The only extant strepsirrhine that lacks a toothcomb is the ugliest of the lemurs, the Aye-Aye (Daubentonia madagascariensis). In the past this lead some researchers to suggest that the toothcomb may have evolved twice, once in the lemur clade, and then again among the lorises and galagos. A good old classic debate over homoplasy, parallel, and convergent evolution was brewing.

Then a primate anatomist by the name of Freiderun Ankel-Simons came along and demonstrated that if you look at the deciduous dentition (the baby teeth) of the Aye-Aye there's a very strong indication that they had a toothcomb earlier on in their ancestry and have since lost this specialization much more recently.

Today, the evolutionary debate surrounding the toothcomb surrounds questions of it's origin and function. Most strepsirrhines use the toothcomb for purposes of grooming, but some strepsirrhines, such as mouse lemurs (Microcebus), Fork-marked lemurs (Phaner), and the Needle-clawed bushbabies (Euoticus), use their toothcombs to scrape gums and resins from trees. The question now becomes: did the toothcomb evolve for grooming purposes and then it was co-opted for feeding OR did the toothcomb evolve for feeding purposes and then get co-opted for grooming? It's difficult to say either way. Among extant strepsirrhines the toothcomb is most commonly used for grooming, but just because a morphological feature might be used for a particular function in the present, it could have easily been evolved for an entirely different function in the past.

Aye-aye, there's the rub.

Monday, August 31, 2015

Miocene Mammal Monday: Komba

Komba winamensis (McCrossin, 1992)
Komba is an extinct genus of strepsirrhine primate from the early and middle Miocene of East Africa. As I spend most of my time reading and writing about Anthropoid primates, I had to review the basics of Strepsirhine phylogeny in order to understand the evolutionary significance of Komba. Extant strepsirrhine primates can be placed into two superfamilies; Lemuroidea and Lorisoidea. Lorisoidea can be further subdivided into two distinct families: lorises and galagos. Geographically, Lemurs are restricted to the island of Madagascar. Lorises and galagos have a much wider distribution being found throughout Africa and Asia. All of these taxa form a sister taxa relationship with the extinct group of primates known as Adapiformes.


So, where does Komba fit into this nest hierarchy? According to paleoanthropologist Monte McCrossin, Komba is most likely ancestral to the Galagidae (aka galagos, aka bush babies). Komba shares four four craniodental features with modern galagos: "1) strong inflation of the auditory bulla; 2) a distolingual distension of the  upper M2 hypocone, leaving a deep notch in the distal margin of the crown between the metacone and hypocone; 3) a mandibular corpus of even depth and with a smooth basal margin; and 4) the presence of a distinct metaconid on lower P4."

The placement of Komba in this phylogenetic position by McCrossin had implications for other fossil strepsirrhines, particularly Progalago. As it's name suggests, Progalago was originally thought to be a stem galago, but the discovered of Komba demonstrated that Progalago was more likely to be ancestral to the Lorisidae. This is another lesson on why it's unwise to name fossil taxa after an assumed phylogenetic position. New fossil discoveries can shift old fossil discoveries around. It's probably better to give fossil species names which tell us about their geographic location. Sure, as more fossils might be found, that geographic region might be expanded, but that won't change the location of where the first members of a particular genus or species were discovered.

Sunday, August 30, 2015

Neil Young - Are You Passionate? (2002)


Release date: April 9, 2002
Producers: Neil Young, Booker T. Jones, Duck Dunn, and Poncho Sampedro
Track listing: You're My Girl, Mr. Disappointment, Differently, Quit (Don't Say You Love Me), Let's Roll, Are You Passionate?, Goin' Home, When I Hold You in My Arms, Be With You, Two Old Friends, She's a Healer
Musicians: Neil Young (vocals, guitar, piano), Booker T. Jones (organ, vibes, vocals), Duck Dunn (bass, vocals), Steve Potts (drums, bongs, tambourine), Poncho Sampedro (guitar, vocals), Tom Bray (trumpet), Peggi and Astrid Young (backup vocals), and Billy Talbot and Ralph Molina (bass and drums on "Goin' Home").

After making a few albums with Duck Dunn on bass, Neil decided to recruit the rest of Booker T and the MGs to make a full length soul album, Are You Passionate? To the uninitiated, Booker T and the MGs, were the house band for Stax Records. Throughout the 1960's and 1970's they supplied the music for Otis Redding, Wilson Pickett, Isaac Hayes, Albert King, and Al Green to name a few. They even had a mild hit with their own instrument material song "Green Onions". Although the original drummer, Al Jackson Jr., was murdered in 1975, Al's cousin Steve has playing drums for the MGs ever since. Noticeably absent is MGs guitarist, Steve Cropper, but with both Neil and Poncho present on guitar, there probably wasn't a lot for Steve do to on this album anyway. Peggi and Astrid Young supply backup vocals. Tom Bray, from the Bluenotes, supplies some trumpet.

This album starts out strong with a perfect trifecta;"You're My Girl", "Mr. Disappointment", and "Differently". Three strong, powerful, and dynamically different tunes. Although Neil might be exploring a musical style that typically deals with the subject of love and love gone wrong (actually you could say that about a lot of musical genres), the lyrical content of these songs runs a little deeper than the usual boy meets girl falls in love story line. The love Neil sings about in these songs is the love he has for his family, children, wife, and the way sometimes he has trouble doing or saying the right thing when it's needed most.

Are You Passionate? is an album that has been said to one that steps outside the typical Neil Young sound. I'm not sure what that means exactly. After listening to a different Neil Young albums for going on 35 straight weeks now, the only thing I know for sure is that there is no such thing as a typical Neil album. I guess that means this isn't a country, folk, or rock album. But neither were Trans, Landing on Water, or This Note's For You. Of those three albums, Are You Passionate? probably allies closest with the This Note's For You. Just replace the big band sound  with one of the world's most important soul bands.

When I first heard this album, nearly ten years ago, I didn't think much of it. Although I loved the sound of Neil's fuzzy guitar leads colliding with the smooth sounds of the MGs rythm section, I found the songs lacking. This time around, however, I really grew to like the material. At first, it was just the first three songs, then it was the first five songs. Originally I was going to argue that Neil should have cut the album there and just made an EP. As the week went on and I continued to listen, I began to like the whole album.

Getting back to that fifth song, "Let's Roll" is about the events of 9/11, United Airlines Flight 93, and standing up to terrorists. It might be thought of as a bit of knee jerk reaction, but after the past two week's events in Syria, the death of Khaled al-Asaad, and the destruction of the ancient temples at Palmyra, it sounds as necessary as ever. I'm really ready to be done with faith based terrorism in the twenty first century.

This album does have a few weaker moments. "Going Home" is the lone Crazy Horse song of the album. This song might sound better on a Crazy Horse record, here it's jarring and out of place. Contrasting the smooth flowing style of Steve Potts drums with the pounding thump of Ralph Molina is like listening to drum off between Buddy Rich and an orangutan. She's a Healer" on the other hand, is a plain jam song that goes nowhere special.

Other great moments include "When I Hold You in My Arms" which I find oddly brings the Hank (both Williams and Snow) out in Neil's voice. Also "Be With You" is great song, that actually sounds a bit more Motown, and a little less Stax, but that's not a bad thing at all.

All and all, a pretty good, fun album.

NEXT WEEK:
 Neil Young & Crazy Horse: Greendale (2003)

Tuesday, August 25, 2015

How To Build A Primate Tooth IV: What's in a Tooth?

With all this talk about dental evolution and teeth morphology I think it's time to take a step back and look at the basics. I mean, what's a tooth made out of anyway? The answer is kinda neat and it gives us some insight as to why teeth tend to preserve better than bones when it comes the fossil record.

As you can see in the diagram to the left the main ingredients in a tooth are enamel, dentine, cementum, and dental pulp.

Simply put, enamel is the hardest biological material in any animal's body. It's primarily composed on an inorganic calcium phosphate mineral known as hyrdoxyapatite [Ca5(PO4)3(OH)]. In contrast bone is dense connective tissue that consists of both hydroxyapatite and collagen. As enamel is 96% mineral it tends to withstand the fossilization process better. That's why some fossil primates, particularly many Middle Miocene apes, are known exclusively by their teeth.

Dentine is a calicified tissue that makes up the bulk of the tooth. It's not as mineralized as enamel, so it's typically softer than enamel, but still harder than bone. Like bone, dentine is composed of both hydroxyapatie and collagen. This means it's more compressible and elastic than enamel. When teeth are extremely worn down, parts the enamel surface of
the tooth crown can disappear and reveal the underlying dentine.

Cementum is another mineral structure which is softer than dentine and covers the exterior surface of the tooth root. In comparison to enamel, which is 96% hydroxyapatite, cementum is only about 45% mineral. The remaining organic component consists of collagen and proteins known as proteoglycans. Cementum is responsible for attaching teeth to the alveolar bone of the mandible and maxilla by anchoring it with connective tissues known as periodontal fibres..

Finally, dental pulp is the living center of the tooth. It's made up of living cells called odontoblasts which are responsible for the the creation of dentine. Along with cells called ameloblasts, odontoblasts also create enamel in initial steps of tooth formation. Nerves and blood vessels innervate the pulp chamber, thus supplying nutrients to the tooth and providing a means of sensory perception. 

Monday, August 24, 2015

Miocene Mammal Monday: Amphicyon

Amphicyon igens (Clemens v. Vodelsang)
Amphicyon was a large carnivorous bone crushing mammal that lived from 20 to 9 million years ago. A member of the Amphicyonidae family, common known as bear-dogs, Amphicyon had a large geographic distribution. Currently there are five recognized species: Amphicyon giganteus, (20.4–15.9 MA) which lived in Europe and Namibia. Amphicyon major (16.9–9.0 MA), which is found at several fossil sites across Europe. Amphicyon galushai (18.8–17.5 Ma), the earliest known North American species. Amphicyon frendens (17.5–15.9 Ma), also from North America. And finally, Amphicyon ingens (15.3-14.0 Ma), the youngest the North American species. Although no Amphicyon have been found in Asia, their presence in Europe and North America suggests they likely also inhabited that region of the world as well.

Amphicyon igens (Roman Uchytel)
Morphologically, Amphicyon had physical features which resembled both bears and dogs. They were extremely large bodied mammals. The largest species, A, igens, had a maximum length of 2.5 m (8 ft) and body mass of 600 kg (1,3200 lb). Amphicyonidae are members of the Caniformia suborder, meaning they are related to bears (Ursidae), red pandas (Ailuridae), weasels (Mustelidae), raccoons (Procyonidae), and seals (Pinnipeds). Their closest living relative, however, are dogs (Canidae) with whom they form a sister taxa relationship. As such as their teeth somewhat resemble those of a wolf, although the carnassial teeth are typically not as specialized as those of modern canids.

Sunday, August 23, 2015

How to Build a Primate Tooth III: Dental Formulas


So far in this series I've discussed of the evolution of teeth differentiation and molar cusp morphology. This time around I want to take a look at dental formulas. A dental formula is a way of simply and clearly expressing the number and type of teeth possessed by an animal. Different mammals and primate clades have unique numbers of teeth. Comparing these similarities and differences can tell us about the relative changes which have taken place as mammals diversified and evolved throughout the Mesozoic and Cenozoic eras.

A dental formula is typically written as a fraction, with the numerator representing the upper teeth and the denominator representing the bottom teeth. It should be noted, that these numbers only represent one side of the dentition (a dental quadrant), starting from the incisor midline and moving posteriorly to the molars.

The original permanent mammalian dental formula is 3-1-4-3 / 3-1-4-3. That means 3 incisors, 1 canine, 4 premolars, and 4 molars per quadrant. Although the numbers are the same on top and bottom, they aren't always as such. Tarsiers, for example, have fewer lower incisors. There are four primate dental formulas:

Lemurs, lorises, and galagos: 2-1-3-3 / 2-1-3-4
Tarsiers: 2-1-3-3 / 1-1-3-3
New World Monkeys (except callitrichidae): 2-1-3-3 / 2-1-3-3
Callitrichidae (marmosets and tamarins): 2-1-3-2 / 2-1-3-2
Old World Monkeys and Apes: 2-1-2-3 / 2-1-2-3

As you can see primates have a reduced number of teeth compared the original permanent mammalian dental formula. This is true of most mammals living today. It's of particular importance to remember this when we look at the nomenclature used to refer to specific teeth. This is the reason why humans only have two premolars, but these are referred to as the third and fourth premolars. The first and second premolars were lost by our pre-primate and early Oligocene primate ancestors during the course of their evolution, millions and millions of years ago.

Saturday, August 22, 2015

Neil Young - Road Rock Vol. 1: Friends and Relatives (2000)

Release date: Dec 5, 2000
Producers: Neil Young and Ben Keith
Track listing: Cowgirl in the Sand, Walk On, Fool for You Love, Peace of Mind, Words, Motorcyle Mama, Tonight's the Night, All Along the Watchtower
Musicians: Neil Young (vocals, guitar), Ben Keith (pedal steel, lap steel, guitar, vocals), Spooner Oldham (piano, organ, electric piano), Duck Dunn (bass) Jim Keltner (drums), Peggi and Astrid Young (backup vocals), and Chrissie Hynde (guitar & vocals on "All Along the Watchtower")

We've been through some things together, with trunks of all memories still come. This isn't my favourite live album we've been through, and I know we still have trunks of live albums to come. This is Neil's seventh official live album and features a familiar group of players: Ben Keith, Spooner Oldham, Duck Dunn, and Jim Keltner. with backup vocals from Peggi and Astrid Young.

Rock Rock Vol. 1: Friends and Relatives starts with an 18 minute long version of "Cowgirl in the Sand" and it's simply just okay. It's a great song, but this version isn't anything particularly special or unique. Starting the album with Crazy Horse song is a rather bizarre way to start a non-Crazy Horse live album. I think the Crazy Horse songs should stick with Crazy Horse, unless Neil and friends find a way to breathe new life into it.

Following the initial track the album picks up some steam with a brilliant version of On The Beach's "Walk On". A great song with a guitar lead that is somewhat uncharacteristic of Neil's style. This song as always stood out to me as being particularly amazing to me. It's a catchy tune with a distinct, upbeat, and fast moving pace. Peggi and Astrid's backup vocals really bring this song alive, giving it a greater depth.

The other great moments on this album come from two of Neil's songs from the 1970's. The version of "Words" found on this record is best take I've ever heard of this song. Better than Harvest or Journey Through the Past. Ben's pedal steel, accented by Spooner's piano and Keltner's tight, seemingly effortless drumming are spot on. Neil is free to get creative with the guitar leads, but doesn't drag the song out too long. It's quite perfect. I also really enjoyed "Peace of Mind", which I originally appeared on Comes A Time (an album I'm somewhat lukewarm about). Again, I prefer this version to the original.

There's also a new song, "Fool for Your Love" which I found to be somewhat mediocre and a tad generic. Similarly, "Motorcyle Mama" falls into the same uninspired trap. I didn't particularly care from this song on Reactor,  and I'm still not a big fan of it here.

Road Rock ends with a rendition of Bob Dylan's "All Along the Watchtower" which is backed up by a special appearance from the Pretender's Chrissie Hynde. It's okay, but Bob and Jimi have already mastered this song in their own individual ways. Sadly, Neil and Chrissie's version doesn't really offer anything new.

So, this album is just kind okay. A few great moments, but otherwise it's pretty forgettable. Although I do appreciate Neil taking a stab a non-Crazy Horse live album, it's just kinda middle of the road. Want a good live album? Get Time Fades Away, Live Rust, or Weld.

NEXT WEEK: Neil Young - Are You Passionate? (2002)