In the north—in Laurasia's connected lands
Where Asia and Europe and North America
Were joined by land bridges and the bands
Of temperate forest, the chimera
Of Boreos' radiation was the greatest
Mammalian explosion the world had seen:
More orders, more families, the latest
And most overwhelming act of the Cenozoic scene.
For Boreos had what Afrotheros and Xenarthros lacked:
Connected continents—the land bridge at Beringia
Let the Asian and American mammals act
As one enormous gene pool—the criteria
For speciation met a continent-sized
Arena of competition and of space,
And the result was diversified
Beyond the isolated island's pace.
Two great houses branched from Boreos' blood:
Euarchos—the "true rulers"—whose children
Would include the strangest flood
Of associations: the primates and the buildin'
Of the rodent empire, the rabbits,
The tree shrews, the flying lemurs—all
Descended from a tree-dweller whose habits
Of grasping and of climbing the tall
Canopy of the Paleocene's forests
Became the primate's inheritance—
But that is a tale for later choruses;
For now, the other branch's dance.
Laurasios—the northern one—bore children
More diverse than any single line
Before: the carnivores, the herd-building
Ungulates, the bats whose design
Of powered flight was the only one
That any mammal ever achieved.
Chiropteros—the bat—was born and spun
Into the nighttime air and believed
In echolocation before the whale did:
The bat mapped the darkness with its voice,
Each shriek of ultrasound that the palate slid
Into the air was an active choice
Of perception—for the bat does not listen
For the sounds the world makes on its own
But sends its own sound out, the glistening
And rapid pulse that strikes the bone
And wing and body of the moth and bounces
Back—and from the echo's delay
And frequency and angle, the bat pronounces
The shape of the world, the moth's way
And speed and distance, all computed
In a brain the size of a walnut
In milliseconds—the undisputed
Master of the acoustic result.
And the bat took the insect-rich nighttime sky
That the birds had left unclaimed—
For the bird is diurnal, and the nocturn's cry
Of the moth and the beetle was unnamed
And unhunted until the bat arrived
And claimed the darkness as the bird
Had claimed the daylight—and the bat thrived
In every cave and forest, the unheard
And unseen hunter of the insect world.
The ungulates—the hoofed ones—rose
From Laurasios' line as the world unfurled
Its grasslands in the Miocene's prose
Of cooling and of drying—and the hoof
Was the grassland's answer to the claw:
The hard and narrow tip, the proof
Of a foot designed for running on the raw
And open ground where the forest's cover
Had retreated, and the predator
Could see you coming, and the only lover
Of your life was speed—the indicator
Of the grassland mammal's single art:
To run, to run, to run—and the hoof
Was the engineering of that start,
The hard and narrow contact's proof
Against the pounding distance of the plain.
From Laurasios' northern line would come
The horse, the rhinoceros, the mane
Of the lion, the antler, and the drum
Of the hoofbeat on the steppe—but these
Are stories for the chapters yet to come.
Honor Boreos—whose northern expertise
Of connected continents and the sum
Of space and competition and the bridge
Of Beringia's land-crossing made
The largest mammalian radiation's ridge—
The northern one, whose parade
Of orders and of families and of species
Is the majority of every mammal that you know.