Coletta – first lepidosaur precursor with a lateral temporal fenestra

Tiny Coletta (Fig. 1, Modesto et al. 2002) is an important little reptile. According to the large reptile tree, Coletta is the first in the phylogenetic lineage of lepidosaur “diapsids” to have a lateral temporal fenestra (= ltf) — at least one that is homologous to the modern lizard ltf.

Figure 1. Emeroleter, Coletta and Owenetta, a phylogenetic lineage ancestral to lizards, all to scale. Getting smaller is associated with losing cheek bone material. The naris remains the same size, no matter the skull size. The parietal shelf of Coletta has been restored. Perhaps its fragile nature was the key to its destruction during taphonomy.

Figure 1. Emeroleter, Coletta and Owenetta, a phylogenetic lineage ancestral to lizards, all to scale. Getting smaller is associated with losing cheek bone material. The naris remains the same size, no matter the skull size. The parietal shelf of Coletta has been restored. Perhaps its fragile nature was the key to its destruction during taphonomy.

According to Modesto et al. (2002)
Coletta is a procolophonid from the Early Triassic nesting between Owenetta and Contritosaurus (Fig. 2) with Procolophon and Hypsognathus as more derived taxa. This assumption has proven to be invalid when applied to the larger gamut of taxa in the large reptile tree.

The large reptile tree
nested Procolophon and Hyposognathus with Diadectes and thus Coletta and Owenetta were only very distantly related to Procolophon (at least 10 nodes of intervening taxa). Instead the large reptile tree nested Coletta between Owenetta and Emeroleter (Contritosaurus has not been tested). Thus the Modesto et al. 2002 tree appears to be upside down with basal taxa at derived nodes. Modesto et al. 2002 did not include Diadectes or any lepidosaurs or any of the intervening taxa recovered in the large reptile tree. Thus taxon exclusion in an apparently too small phylogenetic analysis resulted in a tree that cannot be duplicated in a larger study.

Contritosaurus is close to Owenetta and Coletta according to Modesto et al. 2002.

Figure 2. Contritosaurus (=Phaanthosaurus, Chudinov and Vjushkov 1956) is close to Owenetta and Coletta according to Modesto et al. 2002 and that appears to be so. That little downturned jugal looks like it might be flipped vertically to fit into that little dotted line area.

Other ltfs have come and gone.
The ltf in Lanthanosuchus, for instance, is not homologous with those of lizards. The ltfs in synapsids, archosaurs and millerettids (including caseasaurs) are also not homologous, according to the large reptile tree.

Incomplete from the start
The ltf in lepidosaurs is primitively incomplete in that there is no jugal-quadratojugal bar and the fenestra does not form in a typical fashion, between three surrounding bones. Later taxa with a complete lower temporal fenestra bar, like Sphenodon, arrive at that secondarily.

Not derived from Youngina
The traditional paradigm holds that both archosaurs and lepidosaurs find a common ancestor close to Youngina. The large reptile tree found Youngina to be ancestral only to archosaurs and their kin, not to lepidosaurs, which nest in the other major branch of the Reptilia (= Amniota). The actual last common ancestor of lepidosaurs and archosaurs is Cephalerpeton, at the very base of the Reptilia.

Clearing up these common misconceptions in palaeontology is the major role for the large reptile tree found here. Owenettids, like Coletta, need to be removed from all procolophonid studies. And vice-versa. These distinct reptile clades are not closely related.

References
Chudinov PK and Vjushkov BP 1956. New Data on Small Cotylosaurs from the Permian and Triassic of the USSR. Doklady Akademii Nauk SSSR 108 (3): 547–550 [In Russian].
Modesto SP, Damiana RJ and Sues H-D 2002.
 A reappraisal of Coletta seca, a basal procolophonid reptile from the lower Triassic of South Africa. Palaentology 45(5):883-895.

4 thoughts on “Coletta – first lepidosaur precursor with a lateral temporal fenestra

  1. Given that the lower temporal fenester in Lepidosaurs in boardered by different bones (The postorbital contributes to the upper margin in lepidosaurs instead of the Jugal), I think it is extremely unlikely that they are homologous. The fact that they appear to be so is probably due to the lack of definition of the fenestra in the characters; if you’re going to do a phylogeny including groups with lots of different fenestrae, you need to define the fenestrae by bones boardering them, not just whether they are low on the skull or high.

    • Neil, I encourage you to go through the pre-lepidosaur lineage in reptileevolution.com to see exactly how the bones rearranged during this period in their evolution. I think it will all make more sense to you if you do so. I will post on this change in the near future to make it clear.

      • But if you don’t test the effect of define the fenestrae by bones boardering them, then you run the risk of circularity: at the momment, simply calling both a lower temporal fenestra encourages the phylogenetic program to treat homology as the most parsimonious solution, and then you use the phylogeny based on this assumption to show that they are homologous.

        what you should do is treat the fenestrae with different morphologies seperately (or maybe as a multistate character would be better than separate characters), and then if the phylogeny still puts your two clades together, THEN start working out the morphological transition from one fenestra to the other.

  2. I have written and illustrated your answer and will post it in the next few days and later show the same evolution in the archosauromorph line. I think you’ll see the progression is rather basic and involves the same bones throughout.

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