Early Permian Cabarzia enters the LRT on two legs

Spindler, Werneberg and Schneider 2019
bring us news of a new headless, but otherwise complete skeleton from the Early Permian of Germany. The authors considered Cabarzia trostheidei (Figs. 1, 2, 5; NML-G2017/001) a close match to the Middle Permian protodiapsid Mesenosaurus (Fig. 2) from the Middle Permian of Russia and the oldest evidence for bipedal locomotion, 15 million years earlier than Eudibamus.

Figure 1. Cabarzia in situ and tracing distorted to fit the photo from Spindler, et al. 2019. Inserts show manus and pes with DGS colors and reconstructions. Scale bar = 5 cm.

Figure 1. Cabarzia in situ and tracing distorted to match the photo from Spindler, et al. 2019. Inserts show manus and pes with DGS colors and reconstructions. Scale bar = 5 cm. Pelvis enlarged in figure 4.

In slight contrast
the large reptile tree (LRT, 1385 taxa; subset Fig. 4) nests Cabarzia on the synapsid side of the Synapsida-Protodiapsida split within the new Archosauromorpha. Skull-less Cabarzia nests with the synapsids, Apsisaurus and Aerosaurus, also from the Early Permian. This is only a node or two away from Mesenosaurus.

In an earlier Spindler et al. 2016 phylogenetic analysis,
the last outgroup to the Synapsida-Protodiapsida split, Vaughnictis nested with the new Lepidosauromorpha caseid, Oedaleops (Fig. 3) far from the synapsids, but close to Feeserpeton and other taxa with a lateral temporal opening not related to synapsids. That error and the mistaken monophyly of the clade Varanopidae, are common to in all current paleontological books. Both are due to taxon exclusion at the base of the Reptilia (see below) and the lack of diapsid taxa in synapsid studies and vice versa.

Figure 2. Two specimens attributed to Mesenosaurus compared to scale with Cabarzia. Scale bar = 5cm.

Figure 2. Two specimens attributed to Mesenosaurus compared to scale with Cabarzia. Scale bar = 5cm.

Spindler et al. 2016 (the Ascendonanus paper)
presented a phylogenetic analysis that included Vaughnictis, which nested with the Lepidosauromorph caseid, Oedaleops, (Fig. 3) without providing enough taxa to recover a basal Lepidosauromorpha-Archosauromorpha split recovered by the LRT that separates caseids from synapsids and nests them with other bulky herbivores with a lateral temporal fenestra, like Eunotosaurus. Cabarzia was then known as the Cabarz specimen, then considered a member of the Varanopidae (Fg. 3).

FIgure 3. Spindler et al. 2016 cladogram suffering from massive taxon exclusion.

FIgure 3. Spindler et al. 2016 cladogram suffering from massive taxon exclusion. The red panel highlights taxa that nest within the new Lepidosauromorpha in the LRT. The dark gray panel highlands various actual and putative varanopids nesting paraphyletically. In the LRT they nest together. Note the proximity of the Cabarz specimen (Cabarzia) to Elliotsmithia, but some distance from Apsisaurus, Aerosaurus, Varanops and and Varanodon.

The LRT
(subset Fig. 4) does not suffer from taxon exclusion. At least, so far… Rather this wide gamut study illuminates previously unrecognized splits, like those within the traditional Varanopidae that produced the Protodiapsida.

Figure 4. Subset of the LRT focusing on basal Archosauromorpha including Vaughnictis and Cabarzia nesting at the base of the Protodiapsid-Synapsid split. Note all the large varanopids nest together here in the Synapsida, separate from small varanopids in the Protodiapsida.

Figure 4. Subset of the LRT focusing on basal Archosauromorpha including Cabarzia nesting at the base of the -Synapsida. Note all the large varanopids nest together here in the Synapsida, separate from small varanopids in the Protodiapsida.

Bipedal locomotion
Spindler et al. report, “Although the proportions of the entire postcranium of Cabarzia roughly resemble those of Eudibamus, these genera can easily be distinguished based on their vertebrae.” 

Citing Berman et al. 2000b and Sumida et al. 2013,
Spindler et al. list the adaptations of functional bipedalism. (my notes added)

  1. short neck (but Chlamydosaurus has a long neck)
  2. long hindlimbs
  3. short forelimbs
  4. short and slender trunk
  5. and a long robust tail (but Chlamydosaurus has a long attenuated tai)
  6. a rearward shift of the center of body mass

Spindler et al. 2018 note: “Decreased asymmetry of the hindlimb is seen in basal varanopids and mesenosaurines. Eudibamus has remarkably narrow caudal vertebrae; this may indicate that it evolved active bipedalism, facilitating slow bipedal locomotion.” We talked earlier here about the basal diapsid with a long neck and super slender tail, Eudibamus and its putative bipedal abilities. Spindler et al. do not cite the most active scientist currently working with bipedal lizards, Bruce Jayne and his video of lizards on treadmills.

FIgure 4. Pelvis of Cabarzia colored with DGS. Note the offset femoral head perforating the pelvis, the anterior process of the illiim and the four sacral vertebrae, all pointing to bipedal locomotion. Some of this was overlooked by Spindler et al.

FIgure 4. Pelvis of Cabarzia colored with DGS. Note the offset right femoral head perforating the pelvis, the anterior processes of the illi a and the four sacral vertebrae, all pointing to bipedal locomotion. Some of this was overlooked by Spindler et al. The left femur is too long due to the split. The pink linear bones are probably displaced gastralia.

The traditional touchstones of bipedal locomotion in lizards
(e.g. Chlamydosaurus kingii) are also present in Cabarzia. These include (according to Shine and Lambeck 1978, Snyder 1954; my notes added in bold):

  1. Bipedal reptiles are generally small, having experienced phylogenetic miniaturization –  outgroup taxa, Protorothyris and Vaughnictis, are not larger than Cabarzia.
  2. Bipeds are terrestrial and/or arboreal – present in most tetrapods
  3. Longer hind limbs than forelimbs – present in many tetrapods
  4. Anterior process of the illiim, no matter how small – present in Cabarzia 
  5. Typically stronger or more sacral connections to the ilium – present in Cabarzia 
  6. Typically a long neck and short torso  unknown in Cabarzia 

In Cabarzia we also find

  1. perforated acetabulum
  2. elongate and offset cylindrical femoral head

Overlooked by Spindler et al.:
Cabarzia provides a more complete look at the post-crania of basalmost synapsids, which include humans. No one has ever considered the possibility that bipedal locomotion in the Early Permian was part of that story. It is also common knowledge that more derived taxa in the lineage of synapsids, therapsids and mammals retained  quadrupedal locomotion, an imperforated acetabulum and only two sacrals. So bipedalism was a dead-end for Cabarzia, producing no known ancestors.

Figure 5. Cabarzia compared to Vaughnictis and Apsisaurus to scale. Finger 1 and other phalanges were identified in published photos of this specimen (Fig. 1) using DGS tracing and reconstruction methods.

Figure 5. Cabarzia compared to Vaughnictis and Apsisaurus to scale. Finger 1 and other phalanges were identified in published photos of this specimen (Fig. 1) using DGS tracing and reconstruction methods.

Despite the similar and coeval red bed matrices
of Aerosaurus, ApsisaurusVaughnictis and Cabarzia, the former three come from the western USA (Colorado) while Cabarzia comes from central Germany. Back then they were closer to one another, not separated by an Atlantic Ocean (Fig. 6).

Figure 6. Early Permian Earth, prior to the separation of Europe from North America.

Figure 6. Early Permian Earth, prior to the separation of Europe from North America.

References
Shine R and Lambeck R 1989.Ecology of Frillneck Lizards, Chlamydosaurus kingii (Agamidae), in Tropical Australia. Aust. Wildl. res. Vol. 16: 491-500.
Snyder RC 1954.
 The anatomy and function of the pelvic girdle and hind limb in lizard locomotion. American Journal of Anatomy 95:1-46.
Spindler F, Werneberg R and Schneider JW 2019. A new mesenosaurine from the lower Permian of Germany and the postcrania of Mesenosaurus: implications for early amniote comparative osteology. PalZ Paläontologische Gesellschaft

 

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