Since you asked… Mammals!

Sugar gliders vs. Flying squirrels

Sugar glider = marsupial, endemic to Australia & New Guinea
Flying squirrels = placental mammal, several genera distributed around the world

We briefly discussed these two organisms in class as an example of analogous traits: both have extended flaps of skin between their fore and hind limbs & use this skin to glide between trees. However, this is not a trait shared by all species in the most recent taxon they share in common (Class Mammalia), indicating that the characteristic is analogous instead of homologous. This is also an example of convergent evolution: The same type of trait developed independently multiple times, because of similar selective pressures on different species.

To see why these two types of organisms are only distantly related, let’s take a look at their taxonomic classification.

  1. Both are in class Mammalia: have hair & mammary glands, among other characteristics distinguishing them from reptiles.
  2. There are two large subclassifications of mammals: Those that have live birth (Metatheria & Eutheria) and those that have shelled eggs (Monotremes)
  3. Within those that have live birth: Eutheria (young protected and supplied with nutrition internally by a placenta, may also be nursed externally), Metatheria (no placenta forms to maintain the young, typically nursed in externally a pouch for an extended period)
    1. Sugar gliders are in the clade Metatheria, and are marsupials (infraclass Marsupialia) currently native to Australia (superorder Australidelphia): Their young are born very vulnerable and without fur. They have an external pouch, in which they nurse these young for ~110 days. Video
      • Not all marsupials have pouches either, though all nurse non-placental young outside their bodies.
      • Incidentally, females also have two uteri (uterus x 2) and males have a bifurcated penis, both of which are common in marsupials.
    2. Flying squirrels are in the clade Eutheria, and are rodents (order Rodentia): there are two main taxa of flying squirrels, one found in the Americas, the second found in northern Eurasia. All are placental, though their young are still born hairless and need a great deal of protection. They are still nursed (typically for at least a month), though not in a pouch. Video

For all practical purposes they both function similarly, but their physiological differences & the comparative immaturity of their young at birth are key differences between these two taxa.

The Story: Some time long after the evolutionary divergence between eutherian and metatherian mammals, natural selection in different locations favored the physical and behavioural characteristics that permit both sugar gliders and flying squirrels to glide.


Mini “Huzzah!” Moment

It’s always a great moment…
…to see evidence that my students are paying attention in class.

  • The general Beer’s Law equation in the lab manual: Molecule Concentration = Absorbance(at a specific wavelength) * Constant
  • The general Beer’s Law equation I wrote on the board: [molecule]=A??? x constant
  • What several of my students put on the postlab: [molecule]=A??? x constant

There’s nothing really wrong with writing the “book” version, but it was nice to see that my simple version stuck with them.

Nightingale Woman

“Nightingale Woman” was a poem by Tarbolde, written in 1996 on the Canopus Planet. It was said to be one of the most passionate love sonnets of its time. An excerpt of the sonnet from page 387 is all that is known from Star Trek lore (the first two lines).

MacHuginn, Cleric of Deneir, completed the sonnet, writing it for his love, the kenku Karrakaniin.

My love has wings – slender, feathered things,
With grace in upswept curves and tapered tips.
In every beat she strikes a chord that rings
As true as cherished words from readied lips.

My love’s dark eyes are quick, and undismayed
To pierce the shadowed veil of deepening night.
Oh, smould’ring gaze of moonlit thoughts betrayed
By sable feathers limned in silver light.

My lover’s mind takes flight, she claims my eyes,
As wingtips brush with whispered, promised, notes.
Each silken touch, a slow caress, gives rise
To fierce, enchanted cries from joyous throats.

Her slender curves my upswept wings now trace –
Stars gasp to watch our shimmering embrace.

featured image: one of MacHuginn’s feather darts