I asked Jay and this is his answer: My note is that these are creation dates not release dates. Plus no-one knew how to do rotations back then and all the scenery/foliage/rocks have needed to be updated since.
I cannot be 100% sure, since I might not have everything from then. The oldest ".ucs" or ".uca" file I have (which is in the ZT Spreadsheet) is:
November 2, 2001 - Buyable Snowman - 129722_TycResSnowman.ZTD
Tycoon Resource made a few more things the next day, on November 3, 2001:
10:40 AM - Tycoon Resource Brass Lamp - 129726_TycResBrasslamp.ZTD
10:40 AM - Tycoon Resource Dead Tree - 129727_TrcResDeadTree.ZTD
10:41 AM - Tyc Res Bouncy Face - 129723_TycResSmileyFace.ZTD (which uses the sample graphics that came with the first APE)
10:47 AM - Tycoon Resource Gnome Statue - 129729_TycResGnome.ZTD
2:04 PM - Tyc Res Bear Carving - 129745_TycResBearSculpture.ZTD
The earliest user made animal in the ZT Spreadsheet is:
November 20, 2001 - American Alligator - amerigator.Ztd
Several user made animals were in December, 2001:
December 13, 2001 - Albino Giraffe - 137770_AlbinoGiraffe.ztd
December 13, 2001 - Tyc Res Farting Beastie - 137646_TycResFartingBeastie.ZTD (which uses the sample graphics that came with the first APE)
December 14, 2001 - Tyc Res Pink Elephant - 137736_TycResPinkElephant.ZTD
December 14, 2001 - Emu - Emu.ZTD
December 16, 2001 - Western Grey Kangaroo - Westgrey-beta1.ztd
December 16, 2001 - Water Buffalo - 145260_ZooUnlimited_Waterbuffalo.ZTD
December 17, 2001 - Caribbean Flamingo - caribbeanflamingo.ZTD
December 29, 2001 - Red Wolf - 145894_ZooUnlimited_Redwolf.ZTD
The first user made structure was made on:
December 31, 2001 - "Coca Cola Vending Machine.ZTD" (but its ID later conflicted with the in-game Laboratory)
Edit: Continuing with the ZT user made firsts, it looks like the first user made fence was May 3, 2002 with Pink_Fence_v1-0.ztd, although it was changed after that. And it looks like the first user made path was August 10, 2002 with the Baskin Robbins Path in BR_Path.ztd.