Before the pterosaur – archosaur/lepidosaur wars…
There were the turtle – placodont/pareiasaur wars.
And they’re still ongoing.
Well-meaning and thoughtful scientists have supported the notion that turtles are placodont-sauropterygians kin. Some thought flippered sea turtles were close to flippered plesiosaurs. More recently, placodonts, some of which have a plastron and carapace, have been favored. Those in this group include: Baur, Buckland, Jaeckel, Broom, Rieppel, Reisz and deBraga,
Gregory wrote about this old argument
in his 1946 paper (available online). Gregory favored nesting diadectids and pareiasaurs with turtles, then compared turtles unfavorably to captorhinomorphs, seymouriamorphs and placodonts. He correctly noted the earlier more basal placodonts were far less turtle-like and show more affinities with plesiosaurs and nothosaurs.
Gregory (1946) wrote, “When I turned my attention to the pareiasaurs, I was surprised to find that apart from their gigantic size they seemed on the whole to afford an excellent starting point for the chelonian line, both in their general construction and in many features of the skull, vertebrae, ribs, girdles, limb bones, hands, and feet.” Gregory found it odd that neither Seeley nor Haughton and Boonstra compared turtles to the pareiasaurs they knew about.
Oddly and on the same note,
Gregory never compared turtles to Stephanospondylus, a taxon studied by his student Romer (1925) and earlier by Stappenbeck (1905). Neither paper made it to his bibliography.
Rieppel and Reisz (1991)
These two did not consider diadectids to be amniotes, which is falsified by the large reptile tree results. Reisz and Laurin 1991 discussed turtles originating out of procolophonids in their paper on Owenetta, which does not nest anywhere near Procolophon in the large reptile tree.
Lee 1993 supported a pareiasaur affinity with turtles.
DeBraga and Rieppel (1997) expanded the taxon list and found turtles nested with diapsids as a sister group to the Sauropterygia.
Rieppel and Reisz (1999)
renewed their interest in this problem. Lee examined the data matrix of deBraga & Rieppel (1991) and argued that many of the characters were incorrectly coded. Rieppel and Reisz (1999) agreed with the majority and made the changes. The new results duplicated their original results, nesting turtles at the base of the sauropterygia (placodonts + pachypleurosaurs). Lepidosauriformes nested as the proximal outgroup. Choristoderes and Prolacertiformes was that clade’s outgroup. Millerettids, lanthanoschids, Macroleter, Procolophon and pareiasaurs nested in a separate clade in a broad radiation at the base of the Amniota (standard for that day). Rieppel and Reisz (1999) pruned turtles and shifted them to pareiasaurs, adding 5 steps to a tree length of 793 steps.This study could have benefitted by fewer suprageneric taxa and more genus-based taxa.
Rieppel and Reisz (1999) reported, “we disagree with several of the proposed corrections, and for these retain the original coding. They include:  distinct basal tubera are absent in pareiasaurs, which show a secondarily derived condition, i.e., basal tubera on the parasphenoid;  the position of the mandibular joint relative to occiput is polymorphic in turtles; [I031 cervical centra of pareiasaurs are ridged but not keeled; [120, 1211 one coracoid ossification is present, and the coracoid foramen is enclosed by the coracoid and scapula, in pareiasaurs; [I 271 the presence of the ectepicondylar foramen in the humerus is polymorphic for turtles; [I401 a weak 4th trochanter is present in pareiasaurs and shifted to the edge of the femur; [I521 the first distal tarsal is retained as polymorphic in turtles.”
See, even the pros see the “facts” in different lights. And that’s okay. We’ll work it out. I don’t see anyone railing against these workers because they see things differently.
DNA has entered the fray, but to no avail. At the very least it has added to the confusion. Unfortunately DNA still can’t deal with Permian and Triassic taxa and we’ll always need to find closest kin in fossil forms from those eras.
The origin of turtles is one of the Holy Grails of paleontology.
Outmoded reliance on terms like “Diapsid” and “Anapsid” have only added to the confusion. In the large reptile tree, no suprageneric taxa are used. Among 341 possible nesting sites turtles nest with Millerosaurs / Pareiasaurs / Stephanospondylus with the near turtle, Odontochelys arising more directly and by convergence from Milleretta.
The whole point of this post is: Attitude and Bias
Once a paleontologist sinks his teeth into a particular hypothesis, no amount of verifiable data is going to shake him loose, whether you’re talking about pterosaurs or turtles. Many rely on suprageneric taxa to cherry pick traits favorable to their position. In that way it doesn’t matter whether basal taxa have a carapace and plastron or not.
It is so important to not use suprageneric taxa. It is also important to establish a large gamut study of generic taxa first so one has confidence that the correct taxa have been chosen for smaller, more focused studies. In the large reptile tree the traits carapace and plastron are not used, but could have appeared up to 8 times by convergence.
By the way,
in an earlier experiment, pterosaurs actually did nest more closely with turtles than with any archosaur. And absent all pareisaurs and millerettids, etc. etc. turtles and pterosaurs nested exactly at the base of the sauropterygia, as the earlier Rieppel studies indicated.
Now THAT’S the power of phylogenetic analysis!!!
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