A tiny 10-cm dinosaur that ate bugs

July 29, 2020 • 9:00 am

Note: The classification of “dinosaur” above isn’t totally accurate, for the creature discussed below is an archosaur, a member of the group that gave rise to dinosaurs, pterosaurs, and crocodilians. But we might as well call it a dinosaur, as few people know what an “archosaur” is.

The ancestors of the dinosaurs could not have been big, for they evolved from amphibians, and amphibians, for a number of reasons, are limited in size.  But this new paper in PNAS shows that some of the earliest ancestors of dinos were very small—not just small, but tiny. The new species described below, which falls into a group that later diverged into pterosaurs (flying reptiles) and the dinosaurs, was only 10 cm tall, the distance between my index fingers in the photo below:

Click on screenshot to read the paper; the pdf is here, and reference at bottom of post.

The partial skeleton of this tiny creature, whose dentition suggests it ate insects, was discovered in 1998 in Southwestern Madagascar. Although the age of the specimen is a bit uncertain, a good estimate is about 237 million years.

Here are some drawings of the parts of the skeleton they recovered, including leg bones, a forearm bone, and the jaws (interpreted as coming from single individual), and a figure showing where they fit into the body (figure F). The size, estimated from the bones, which clearly put the species in the ancestral group Ornithodira (also known as Avemetatarsalia), show that the creature was only about 10 cm tall. It must have been really cute: a pet-sized reptile. Note that the length of the scale bar on the left, showing the femurs, is one centimeter (about 4/10 of an inch), while on the right the scale bar for the jaws is only about 40 mm (1.6 inches):

(from paper): Anatomy of the femur and maxilla of Kongonaphon kely gen. et sp. nov. (UA 10618). (A) Right femur in anterolateral, (B) posteromedial, and (C) proximal views. (D) Right maxilla in right lateral and (E) palatal views. (F) Preserved elements in the holotype, UA 10618, presented in a silhouette of Kongonaphon. aof, antorbital fenestra; at, anterior trochanter; fht, tip of femoral head; fp mx, facial process of maxilla; ft, fourth trochanter; mx f, maxillary foramen; pf, palatine fossa; pmt, posterior medial tubercle; t, maxillary tooth. Illustrations credit: American Museum of Natural History/Frank Ippolito.

The authors named the fossil Kongonaphon kely, meaning “tiny bug slayer”. They explain the etymology:

. . . derived from kongona (Malagasy, “bug”) and φον (variant of ancient Greek φονεύς, “slayer”), referring to the probable diet of this animal; kely (Malagasy, “small”), referring to the diminutive size of this specimen.

The teeth, as you can see in the drawing above, were simple ones: conical and without serrations. That suggests that the creature lived on insects (I used “bug” in the title as a generic word for insects, though technically, bugs are in the order Hemiptera). The estimated size of 10 cm comes from the size of the preserved femur, which is only about 1.6 inches long. The specimen wasn’t a juvenile, as the authors saw signs of arrested growth in the fossil bones. The bones also indicate strongly that K. kely was bipedal, like T. rex and the theropods.

To place this individual in the phylogeny of dinosaurs and their ancestors, the authors did a computer analysis of 422 characters derived from these bones, and K. kely fell out in group B of the phylogeny below, which includes the dinosaurs and the pterosaurs (the relative size of this tiny species is shown to the right). I’ve put a box around K. kely.

B is the base of the Ornithodira, the group that gave rise to all dinosaurs and pterosaurs, and you see that K. kely is an early (“basal”) member of this group

(from paper): Body size of early avemetatarsalian (bird line) archosaurs mapped onto a consensus supertree, based on the current phylogenetic analysis (SI Appendix) and recent analyses (22). Silhouettes are scaled to estimated femoral lengths for the labeled nodes (SI Appendix, Table S1): A, base of Avemetatarsalia (represented by Teleocrater); B, base of Ornithodira (represented by Ixalerpeton); C, base of Dracohors (Silesauridae + Dinosauria) (represented by Silesaurus); and D, base of Saurischia (represented by Herrerasaurus). Silhouettes credit: Phylopic/Scott Hartman/Mathew Wedel, which is licensed under CC BY 3.0. Silhouette of Kongonaphon to the right of the taxon label is to scale.

Here’s a reconstruction of K. kely, eyeing a beetle, from Science Alert;  (artist’s impression by Alex Boersma):

Now the diminutive size of this creature doesn’t mean that the common ancestor of all dinos and peterosaurs was this small. But it does imply that the ancestor of those groups, which falls out in a “reconstruct-the-size” analysis, was smaller than we thought. K. kely itself could have been the result of a “miniaturization event” in which a somewhat larger ancestor produced some tiny descendants. The estimated size of ancestral Ornithodiran  is estimated fo be about 13.3 cm, or about 5.3 inches tall, and the ancestral species of the Dinosauromorphs, which includes dinos and birds but not pterosaurs, is even smaller, about 6.5 cm (2.5 inches)!

What are the implications of this beyond showing that the ancestral dino and ancestral dino/pterosaur were likely a lot smaller than we thought? Well, first of all, we have no idea why these early creatures were so small. My own guess is that since insects had already evolved, there was an “open niche” to specialize in eating them, and if you want to make a living as a terrestrial reptile eating insects, you can’t be the size of a T. rex.

The authors note that the small size of this species (and probably its close relatives) accounts for the absence of ornithodirans in Early and Middle Triassic faunas, for small creatures have tiny, fragile bones that aren’t easily preserved. In fact, our best knowledge of early Ornithodirans previously came from sediments in Argentina whose nature allowed for the preservation of small animals.

Finally, the authors speculate that these small species would have a problem with heat retention, since they were ectothermic (“cold blooded”). Small creatures have a higher surface area/volume ratio than larger ones, which means more heat lost by radiation. Thus, suggest the authors, the filaments covering the bodies of some dinos and pterosaurs—which might have been homologous to feathers that eventually covered the theropods—would have been useful as insulation. This sounds good, but of course there are plenty of extant small insect-eating reptiles, like geckos and anoles, that make a fine living without feathers. But it would still be useful to look at these early, small species to see if there is any evidence for filamentous body cover.

___________________

Kammerer, C. F., S. J. Nesbitt, J. J. Flynn, L. Ranivoharimanana, and A. R. Wyss. 2020. A tiny ornithodiran archosaur from the Triassic of Madagascar and the role of miniaturization in dinosaur and pterosaur ancestry. Proceedings of the National Academy of Sciences 117:17932-17936.

 

36 thoughts on “A tiny 10-cm dinosaur that ate bugs

  1. Very good. Since interpretations of this fossil have been considerably revised, it stands now as a fine example of the “self corrective” nature of science. It can start out wrong, but it gets there eventually.

  2. Most interesting. A lucky preservation.

    237 mya is early. Pangaea had not yet broken up. Hot and cold climate, so thermal regulation could have been important.

    I assume from the diagram that K. kely was quadrupedal, and the bipedal theropods evolved much later.

    To a bug, K. kely on its hind legs would have looked like a T.rex.

  3. I realize the hair’s gotten a bit unmanageable, boss, but you realize we still recognize you even if you block out the eyes the way they used to in those grainy old photographs in 1950s’ scandal mags?

  4. Good to see that the hair is still somewhat like student days; but without the pic, could have described to the poor benighted that 10 cm is 4 inches to within a whisker–whiskers (as hair) galore maybe were there in student days but are not prominent on that chin now!

    Anyway, this discovery is very interesting,
    ‘tyrannos bug-rex’.

  5. Just to drop in a random question, what the heck is going on over at The Panda’s Thumb? They went offline a couple months ago, apparently due to a server problem. But they are still completely gone.
    Hoping for a miracle resurrection!

    1. My experience is that there is fairly little evangelical creationist activity nowadays. Maybe PT is losing interested authors and readers?

      1. They’re probably too busy enjoying their new leader in Trump & getting all the things they ever wished for to usher in the Second Coming.

      2. They’re probably too busy enjoying their new leader in Trump & getting all the things they ever wished for to usher in the Second Coming.

  6. There is a similar animal to this new taxon called Scleromochlus taylori, an archosauriform that has been suggested to be ancestral to pterosaurs, but that has been contestably disputed.

    Recently, Chris Bennett proposed that this animal wasn’t related to ornithodirans, but a doswellid, another basal archosauriform.

    https://peerj.com/articles/8418/

  7. An interesting parallel with mammalian evolution which began with the diminutive tree shrew, or some such, which were also believed to be insectivores.

  8. > The ancestors of the dinosaurs could not have been big, for they evolved from amphibians, and amphibians, for a number of reasons, are limited in size.

    Aren’t archosaurs reptilians? And could you elaborate on why amphibians are limited in their size? I thought that animals living in water can grow larger than animals living on land.

    1. Amphibians have primitive lungs. Some do not have lungs at all! In their adult terrestrial stage, amphibians actually breathe through their skin, in part or whole. Geometry implies that, as the size of the animal increases, the ratio of its surface skin area to its body volume falls. A large amphibian would therefore have too little surface area to respire efficiently.

      However, there is a large salamander that can measure up to five feet long. I imagine it is rather slow.

      1. I really enjoyed that, never seen it before myself–area goes up as square of length but volume goes up as cube, much faster. The connection to breathing, though obvious once someone tells me about it, is still an example that needs a creative thinker to come up with.

        I guess it’s similar to why the elephant has such thick legs.

    2. Actually, some amphibians reached meters in length. The Triassic “super-salamander” Metoposaurus with its body length of 2 m preyed on early dinosaurs.

  9. That’s a mighty thin layer of feathers on that poor beastie. Good for slowing radiation loss, but the slightest breeze and those insectivorous teeth would be chattering (said the ectotherm, using his natural go-to metaphor). Heck, even for radiation loss, more layers are better.

  10. The authors note that the small size of this species (and probably its close relatives) accounts for the absence of ornithodirans in Early and Middle Triassic faunas, for small creatures have tiny, fragile bones that aren’t easily preserved. In fact, our best knowledge of early Ornithodirans previously came from sediments in Argentina whose nature allowed for the preservation of small animals.

    The discussion on preservation and the thread discussion on revised interpretations resonates with the other dinosaur article that popped up in my feed today, on the split between Ornithischians and Saurischians [ http://news.mit.edu/2020/study-timing-dinosaurs-evolution-0729 ].

    The team reanalyzed fossils of Pisanosaurus, a small bipedal dinosaur that is thought to be the earliest preserved Ornithiscian in the fossil record. The researchers determined that the bird-hipped herbivore dates back to 229 million years ago, which is also around the time that the earliest lizard-hipped Saurischians are thought to have appeared.

    The new timing suggests that Ornithiscians and Saurischians first appeared and diverged from a common ancestor at roughly the same time, giving support to the classical view of dinosaur evolution.

    The researchers also dated rocks from the Ischigualasto Formation, a layered sedimentary rock unit in Argentina that is known for having preserved an abundance of fossils of the very earliest dinosaurs. Based on these fossils and others across South America, scientists believe that dinosaurs first appeared in the southern continent, which at the time was fused together with the supercontinent of Pangaea. The early dinosaurs are then thought to have diverged and fanned out across the world.

    However, in the new study, the researchers determined that the period over which the Ischigualasto Formation was deposited overlaps with the timing of another important geological deposit in North America, known as the Chinle Formation.

    The middle layers of the Chinle Formation in the southwestern U.S. contain fossils of various fauna, including dinosaurs that appear to be more evolved than the earliest dinosaurs. The bottom layers of this formation, however, lack animal fossil evidence of any kind, let alone early dinosaurs. This suggests that conditions within this geological window prevented the preservation of any form of life, including early dinosaurs, if they walked this particular region of the world.

    “If the Chinle and Ischigualasto formations overlap in time, then early dinosaurs may not have first evolved in South America, but may have also been roaming North America around the same time,” says Jahandar Ramezani, a research scientist in MIT’s Department of Earth, Atmospheric, and Planetary Sciences, who co-authored the study. “Those northern cousins just may not have been preserved.”

    Decades before Ramezani and his colleagues set out for Las Lajas, other paleontologists had explored the region and unearthed numerous fossils, including remains of Pisanosaurus mertii, a small, light-framed, ground-dwelling herbivore. The fossils are now preserved in an Argentinian museum, and scientists have gone back and forth on whether it is a true dinosaur belonging to the Ornithiscian group, or a “ basal dinosauromorph” — a kind of pre-dinosaur, with features that are almost, but not quite fully, dinosaurian.

    “The dinosaurs we see in the Jurassic and Cretaceous are highly evolved, and ones we can nicely identify, but in the late Triassic, they all looked very much alike, so it’s very hard to distinguish them from each other, and from basal dinosauromorphs,” Ramezani explains.

    His collaborator Max Langer from the University of São Paulo in Brazil painstakingly reanalyzed the museum-preserved fossil of Pisanosaurus, and concluded, based on certain key anatomical features, that it is indeed a dinosaur — and what’s more, that it is the earliest preserved Ornithiscian specimen.

    This make it sound like the whole Triassic is a bit of a preservation mess.

    1. This comment is way too long for a normal comment. I’ve let it through, but there was no need to give such an extensive quote from another source. In the future please keep them short rather than essays like this. Thanks.

      1. Thanks, and noted!

        The essay format was forced on me – I want to quote small – since I wanted to capture a lot. IIRC the dinosaur finding, the classification issue and the bias gap in the fossil record for the different discussions in the thread.

        And they went on and on and on…

  11. Enjoyed this post. I wish I had filamentous body cover. Might help with lumbar problems. Then something worse would occur…I know.

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