I hope this isn’t spamming :-).
I’ve started self-publishing a small OSR supplement (8 pages, 3 dollars) called A Wretched Menagerie, and to kick the whole thing off, I started with the most boring monster available: Ungulates.
Goats, sheep, horses, rhinoceroses, elk, centaurs, triceratops, hippocamps . . . herd animals and ungulates of all stripes to fill out your OSR bestiary. Is Animal, Herd really sufficient for your trek across the savannah?
Contains 86 specific animals, a table for quickly estimating ungulate statistics based on animal weight, and a small selection of rules and conversion notes for using the book.
About A Wretched Menagerie: Written in a compact (some would say cramped) style with minimal fuss and no art, each manuscript in this series covers a narrow niche of creatures. Tools for estimating statistics based on size and ferocity, rationalized statistics for a wide variety of real world (and fantastical) creatures within the niche, and a small selection of extra rules will be standard for each.
The default rules I work from are unlabeled LL/ACKS, so the stat blocks are compatible; and if you just hang around on these forums but use a different flavor, there are some conversion notes at the end for the minimal work required.
The central conceit is based on some chart analysis I did of animals in the various bestiaries: except for a few outliers here and there, monsters within a given “type” tend to follow a power law of (apparent) mass and Hit Dice. That led to hunting through lists of animals and looking up their real-world masses and movement rates, plotting things out, and then developing a (hideous, utterly hideous) chart. Which led to noticing all of the gaps. Which led to trying to fill those gaps in . . . and because I love me some taxonomy, I ended up with pages and pages and pages of categorized stat block collections.
I took one of those collections, cleaned it up, and made Ungulates.
The next one, Furry Pests, will cover miacids, rodents, and a few miscellaneous-but-tiny families of animals. The one after that . . . I haven’t decided yet. I have a few dozen categories, and I’m not sure if I want to do all of the mundane sets first, or mix in the elementals, undead, oozes, and similar to break up the mundanity.