Sometimes the larger sister has the more juvenile traits.

A few posts ago we noted the interesting fact that the larger Garjainia  (Otchev 1958, Early Triassic ~240 mya, 2 m. long) had the relatively larger skull compared to its sister, Euparkeria  (Broom 1913 Early Triassic, ~240 mya, 60 cm). Generally a larger head is considered a juvenile trait. Garjainia also had a shorter tail and a shorter torso.

In the background is Garjainia, a basal erythrosuchid. Euparkeria is at its ankles, both to scale. Euparkeria is the more derived taxon. Below the tail of Euparkeria is a greatly reduced Garjainia. No fossils exist that show Garjainia to this size.

Figure 1. In the background is Garjainia, a basal erythrosuchid. Euparkeria is at its ankles, both to scale. Euparkeria is the more derived taxon. Below the tail of Euparkeria is a greatly reduced Garjainia as if a juvenile of Euparkeria. No fossils exist of Garjainia at this size.

On the other hand
Euparkeria did have the slightly larger orbit, a trait generally considered juvenile. The skull of Euparkeria also had smoother contours (no pmx/mx notch, less of a jugal descent).

Evolution Uses Premature Maturation
The greatly reduced size of Euparkeria is yet another example of a new clade arising from shrimps arising from old clades. Others have complained that size is not pertinent to phylogenetic matrices, but this example shows otherwise. Deciding where to draw “the line” will continue to be argued, no doubt.

Figure 3. Here Euparkeria nests between Garjainia, a basal erythrosuchid, and Ornithosuchus following the nestings recovered by the large reptile tree. All three share a suite of traits that do not include a long narrow rostrum and a dorsal naris, among other traits.

Figure 2. Here Euparkeria nests between Garjainia, a basal erythrosuchid, and Ornithosuchus, an ornithosuchid, following the nestings recovered by the large reptile tree. Note the relative size of the skull in Garjainia, much larger than the much smaller Euparkeria.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Broom R 1913. On the South-African Pseudosuchian Euparkeria and Allied Genera. Proceedings of the Zoological Society of London 83: 619–633.
Ewer RF 1965. The Anatomy of the Thecodont Reptile Euparkeria capensis Broom Philosophical Transactions of the Royal Society London B 248 379-435.
Otchev VG 1958. Novye dannye po pseudozukhiyam SSSR: Doklady Akademii Nauk SSR, 123(4):749-751.
Parrish JM 1992. Phylogeny of the Erythrosuchidae. Journal of Vertebrate Paleontology 12:93–102.

wiki/Euparkeria
wiki/Garjainia

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