Kongonaphon
Kongonaphon Temporal range: Mid to Late Triassic,
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Life restoration | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Ornithodira |
Clade: | †Pterosauromorpha |
Family: | †Lagerpetidae |
Genus: | †Kongonaphon Kammerer et al., 2020 |
Type species | |
†Kongonaphon kely Kammerer et al., 2020
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Kongonaphon is an
Kongonaphon is notable for its minuscule size, even compared to other small early avemetatarsalians. The proportionally elongated femur was only about 4 cm (1.6 inches) long, and the total height of the animal was estimated at around 10 cm (3.9 inches). Alongside other miniaturized archosaurs such as Scleromochlus, it suggests that avemetatarsalians experienced an abrupt reduction in size early in their evolution. This may explain the poor preservation and scarcity of early and middle Triassic avemetatarsalian fossils. A small size also may have helped them exploit a variety of new ecological niches. The most successful avemetatarsalian subgroups, pterosaurs and dinosaurs, may have evolved as a result of this abrupt size reduction. Miniaturization has been correlated with the evolution of flight (a defining feature of pterosaurs) and the acquisition of bipedalism (which was utilized by many dinosaurs). It would also lead to poor heat retention, encouraging the evolution of feathers or other filamentous structures.
Although Kongonaphon is clearly an
Discovery
Kongonaphon is based on
The skeleton was recovered in 1998
Kongonaphon was first reported in a 2019 conference abstract, though at the time it was unnamed.
Description
The maxilla is tall and has a relatively wide front portion when seen from above. The front edge is also concave, similar to early pterosaurs. Six teeth are preserved in the maxilla, though the rear part of the bone is missing. The teeth were peg-like and conical, with a circular cross-section and no serrations. The teeth are ornamented by irregular pitting, a texture which in modern animals is correlated with a diet of insects. A limb bone fragment has been tentatively identified as the lower part of a humerus. This fragment has poorly differentiated condyles (unlike the humerus of Ixalerpeton) but is also markedly asymmetrical (like Ixalerpeton).[1]
The femur is very slender, sigmoid, and has a prominent fourth trochanter. The femoral head shares many similarities with other lagerpetids. It is strongly hooked and has a concave emargination on its lower edge. When seen from above, the femoral head has a large posteromedial tuber, a small anterolateral tuber, and no anteromedial tuber. The outer side of the femoral head also has an anterior trochanter, a muscle scar which is present in some lagerpetids but absent in others. At least in Dromomeron gregorii, it seems to develop only in fully grown individuals. The blade-like fourth trochanter has a folded inner edge and an outer edge which smoothly transitions to the shaft of the femur. Both of these features are more similar to Ixalerpeton than Lagerpeton (or Dromomeron, which has a fourth trochanter which is small and mound-like in some species and absent in others). The bent inner edge of the fourth trochanter overlooks a depression which is split in two by a thin ridge. The femur is extended and narrows significantly towards its broken and eroded lower extremity. This contrasts with other lagerpetids, which have a femur that expands towards the knee.[1]
Tibia fragments are slightly curved and expanded near the knee, similar to other lagerpetids. A pair of long and closely appressed bones have been identified as metatarsals, though this is uncertain due to the unusually bent appearance of one of the bones. Pedal phalanges (toe bones) are hourglass-shaped and have strongly developed joints. The long and narrow caudal (tail) vertebra has a concave lower edge and fused neurocentral sutures.[1]
Classification
To test its relationships to other reptiles, Kongonaphon was placed in a phylogenetic analysis modified from Müller et al. 2019.[6] This analysis did not originally include Scleromochlus, a tiny archosaur often considered distantly related to pterosaurs. The first iteration of the analysis found Kongonaphon and other lagerpetids to be the earliest-diverging dinosauromorphs, more closely related to dinosaurs than to pterosaurs. This result is common among archosaur-focused analyses. The following cladogram illustrates the first iteration:[1]
Avemetatarsalia |
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Scleromochlus was added in the second iteration of the analysis. Unusually, lagerpetids shifted from dinosauromorphs to pterosauromorphs (closer to pterosaurs) in this iteration. Pterosauromorpha is justified by several
Avemetatarsalia |
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Paleobiology
The teeth of Kongonaphon are similar to those of insect-eating modern animals in both shape and texture. This is among the most convincing evidence for an insectivorous diet in early avemetatarsalians, especially lagerpetids (for which teeth were previously unknown).[1] This diet has also been suggested for Silesaurus based on referred coprolites,[8] but Silesaurus's tooth wear suggests it was primarily herbivorous.[9]
Histology and development
A
Despite its tiny size, histology supports the idea that the Kongonaphon individual was not a hatchling or young juvenile. Parallel-fibered bone, lines of arrested growth, and flattened osteocyte lacunae are all correlated with the animal having been alive for quite some time prior to dying and becoming fossilized. The first characteristic in particular suggests that its growth was slower than early pterosaurs or dinosaurs. Other skeletal features also suggest that the individual was an adult. These including fused neurocentral sutures on the vertebra and smoothly textured limb bones. Additionally, several characteristics of Kongonaphon's femur are absent in young individuals of certain other lagerpetid species. Nevertheless, a lack of remodeling and widely distributed vascular canals indicate that the animal was still growing. This means that other individuals perhaps may have been able to grow slightly larger.[1]
References
- ^ PMID 32631980.
- S2CID 228077525.
- ISSN 0012-8252.
- ^ "Tiny Ancient Relative of Dinosaurs and Pterosaurs Discovered". American Museum of Natural History. July 6, 2020.
- ^ Kammerer, Christian F.; Nesbitt, Sterling J.; Flynn, John J.; Ranivoharimanana, Lovasoa; Wyss, Andre (October 2019). "A new lagerpetid archosaur from the Triassic of Madagascar and the importance of miniaturization in ornithodiran evolution" (PDF). Society of Vertebrate Paleontology Abstracts of Papers, 79th Annual Meeting: 127.
- S2CID 133873065.
- S2CID 37918101.
- PMID 31031991.
- S2CID 55024625.