Consider a small sauropod of length x, as shown on the left above. Its mass is proportional to x cubed, it stands on leg bones whose cross-sectional area is x squared, and it ingests food through a gullet whose cross-sectional area is x squared. Now consider a larger sauropod of length 2x, as shown on the right above. Its mass is proportional to 2x cubed = 8x, it stands on leg bones whose cross-sectional area is 2x squared = 4x, and it ingests food through a gullet whose cross-sectional area is 2x squared = 4x. The bigger sauropod has to carry proportionally twice as much mass on its leg bones, and ingest proportionally twice as much food through its gullet. (Similarly, a 104-foot tall gorilla, 20 times as tall as a real one, is only 400 times as strong but 8000 times as heavy — which is why we can’t have Skull Island.)
In practice, big animals tend to have adaptations such as thicker limb bones that mean the numbers aren’t quite as bad as this, but the principal holds: the bigger an animal gets, the worse the problems imposed by scaling. It’s not possible to “solve” this problem because so many biological properties scale this way. Something is always the limiting factor. Suppose it were leg-bones or gullet. If somehow a hypothetical ultra-sauropod evolved extra thick leg-bones and gullet, scaling of respiration would suffocate it, or scaling of digestion would starve it, or scaling of heat-loss through the skin would boil it. The fundamental reason that you can’t just scale an animal up is that some parts of its function scale with volume while most — respiration, digestion, etc. — scale with surface area.
How papers are published, in 343 words
February 7, 2022
Many aspects of scholarly publishing are presently in flux. But for most journals the process of getting a paper published remains essentially the same as decades ago, the main change being that documents are sent electronically rather than by post.
It begins with the corresponding author of the paper submitting a manuscript — sometimes, though not often, in response to an invitation from a journal editor. The journal assigns a handling editor to the manuscript, and that editor decides whether the submission meets basic criteria: is it a genuine attempt at scholarship rather than an advertisement? Is it written clearly enough to be reviewed? Is it new work not already published elsewhere?
Assuming these checks are passed, the editor sends the manuscript out to potential reviewers. Since review is generally unpaid and qualified reviewers have many other commitments, review invitations may be declined, and the editor may have to send many requests before obtaining the two or three reviews that are typically used.
Each reviewer returns a report assessing the manuscript in several aspects (soundness, clarity, novelty, perhaps perceived impact) and recommending a verdict. The handling editor reads these reports and sends them to the author along with a verdict: this may be rejection, in which case the paper is not published (and the author may try again at a different journal); acceptance, in which case the paper is typeset and published; or more often a request for revisions along the lines suggested by the reviewers.
The corresponding author (with the co-authors) then prepares a revised version of the manuscript and a response letter, the latter explaining what changes have been made and which have not: the authors can push back on reviewer requests that they do not agree with. These documents are returned to the handling editor, who may either make a decision directly, or send the revised manuscript out for another round of peer review (either with the original reviewers or less often with new reviewers). This cycle continues as many times as necessary to arrive at either acceptance or rejection.
How birds breathe, in 184 words
February 3, 2022
Windpipe and lungs in pink, air sacs in teal. Steps 1 and 3 happen at the same time — one breath of air is moving through the lungs and into the air sacs in back (1) at the same time as an earlier breath of air is moving out of the lungs and into the air sacs up front (3). Steps 2 and 4 happen at the same time as well — the air sacs in back are blowing air through the lungs (2) while the air sacs in front are blowing air out the windpipe (4). Each breath of air is inside the bird for two inhalations and exhalations.
Our lungs are made up of millions of tiny bags. Breath in, fill the bags with fresh air, breathe out, empty the bags of spent air. But bird lungs are very different. They’re made up of millions of tiny tubes, like bundles of drinking straws, and those tubes are connected to big, empty air sacs, like balloons that spread throughout the body. When birds breathe in, some of the air goes through the lungs, and some skips the lungs and goes into the air sacs. Then when the bird breathes out, the air in the air sacs gets pushed through the tubes in the lungs. So birds get oxygen-rich air blown through their lungs both when they inhale and when they exhale. The lungs and air sacs of birds also send mini air sacs into the skeleton, and these create air-filled spaces inside the bones, akin to our sinuses. These air spaces in the skeleton are the footprint of the respiratory system. A lot of extinct dinosaurs have the same pattern of air spaces in their skeletons, so we think they breathed like birds.
— Jessie Atterholt and Matt Wedel
Sauropod Vertebra Picture of the Week 
