I'd copy-and-pasted some of the lengths and weighs into the wrong Odonatids and had to edit the previous post.

Speaking of which.

That's extremely large for a meganeurid and way heavier than they actually were. An engineering model puts their mass at around 100 to 150 grams, or between a third and a quarter of a pound.
Glanced through that paper and it includes some figures for bodyweight of regular dragonflies.

That's very handy, since I can use them to fact check whether my weights are OK.

If I calculate what these Odonates would weigh if I scaled them up to a metre long I can compare the weights of the resulting "Metre Bulk Index" (MBI). A term I just make up inspired by the BMI (Body Mass Index) used to guess whether humans are too fat or thin.

Species​

Dragonfly​

Length (mm)​

Mass (g)​

MBI​

Epitheca cynosuraCommon Baskettail200.17521.875 kg
Micrathyria atraBlack Tropical Dasher20.50.21424.840 kg
Anax juniusGreen Darner400.80412.562 kg
Anax juniusGreen Darner401.03816.219 kg
Macromia taeniolataRoyal River Cruiser551.187.0924 kg
Petalura ingentissimaGiant Petaltail702.05.8309 kg
NamurotypusNamurotypus (Extinct)165184.0070 kg
Meganeura monyiMeganeura (Extinct)3501383.2187 kg
Odonate (4 ft., 50 lb.)Small Giant Dragonfly1,22022,70012.50 kg
Odonate (4½ ft., 50 lb.)Small Giant Dragonfly1,372.2522,7008.78 kg
Odonate (6 ft., 50 lb.)Giant Damselfly1,83022,7003.79 kg
Odonate (30 ft., 4k lb.)Tropical Giant Damselfly9,1501,816,0002.37 kg

So the Small Dragonfly is roughly similar in build to an Green Darner (Anax junius) or Royal River Cruiser (Macromia taeniolata) dragonfly but is built about half as heavy as the bulkiest species, the Black Dasher (Micrathyria atra) and Common Baskettail (Epitheca cynosura).

Meanwhile, the Giant Damselfly and Tropical Giant Damselfly are both lighter than the lightest dragonfly in the table, the Giant Petaltail (Petalura ingentissima, The former is 65% as heavy, while the latter is 40.6% as heavy. Considering how skinny helicopter damselflies are compared to dragonflies, that seems reasonable. If scaled evenly, that'd make the tropical damselfly is 63.75% narrower in build than the Petaltail, which feels about right.

Interestingly, the Giant Damselfly is very close to the paper's estimates for Meganeura monyi.

I could maybe modify the weights to be a bit higher or have a range of weights in order to match the table better, but the current values seem in the right ballpark and it'd have to be quite a wide range since the heaviest dragonfly is 4.2 times sturdier built than the lightest, implying that it's a bit over twice as thick.

If the Small Dragonfly weighed, say 50 to 80 pounds then a metre-long specimen of the same build would weigh between 20 kg and 8.78 kg while a Giant Damselfly with the same range would be 3.79 to 5.9 kg.

Doing the same to the regular Giant Dragonfly would make it 250-400 pounds, the Imperial becomes 1,000 to 1,600 pounds and the Tropical 4,000 to 6,400.

Don't really like those figures though. For a start, 80 pounds seems too heavy for a Small creature unless it's a particularly hefty one.

I think I'll leave the weights as they are, since the dragonflies are within the range of the table.

EDIT: Came across another data point from Wikipedia's List of largest insects which I'll add here for later reference. It's hardly peer-reviewed though.

Might add other entries later if I come across any that are interesting.


That seems a bit low.

Most sources I see say Tetracanthagyna plagiata goes up to 100mm not the 120mm Wikipedia said. If I use that body length with the same weight the MBI is very close to the Royal River Cruiser (Macromia_taeniolata), which judging by the similar-looking build seems about right.

It's also within acceptable distance to my Small Giant Dragonfly's MBI, for what that's worth.

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