Kammerer 2019 nests a new dicynodont

Figure 1. Cladogram of the anomodontia and dicynodontia from Kammerer 2019. Blue taxa are proximal outgroups.

Figure 1. Partial cladogram of the Anomodontia (including Dromasauria) and Dicynodontia from Kammerer 2019. Blue taxa are proximal outgroups in this cladogram.

In a description of a new dicynodont, Thliptosaurus,
Kammerer 2019 presented a comprehensive cladogram of the dicynodonts, the dromasaurs and several outgroup taxa (Fig. 1), including the dinocephalians, Biseridens (Fig. 2), Archaeosyodon and Titanophoneus.

Figure 1. Biseridens and Phthinosuchus, two related therapsids that have been giving paleontologists fits.

Figure 2. Biseridens and Phthinosuchus, two related therapsids. According to Kammerer 2019, Biseridens is the proximal outgroup to the Anomodontia, who’s

Unfortunately 
Kammerer 2019 excluded several outgroup and ingroup taxa pertinent to the origin of dicynondonts and anomodonts. In the Therapsid Skull Tree (TST,  67 taxa, Fig. 4), the Anomodontia (dicynodonts, dromasaurus and kin) arise from basalmost therapsids, like Cutleria, Stenocybus (Fig. 3) and Hipposaurus. These appear prior to Biarmosuchus. Elsewhere on the cladogram, Biseridens and Titanophoneus arise from more derived tapinocephalids unrelated to basal Anomodontia, more distant descendants of Biarmosuchus.

Figure 3. The ancestry of dicynodonts includes Patranomodon and Galeops.

Figure 3. The ancestry of dicynodonts includes Patranomodon and Galeops.

Kammerer 2019 was attempting to produce a cladogram
of the clade Anomodontia. I cannot comment on the tree topology of dicynodonts, because the TST includes so few of them. However, Kammerer followed tradition by including Biseridens and Titanophoneus as outgroup taxa, omitting those recovered by the LRT and TST.

So… taxon exclusion
put a small damper on an otherwise comprehensive report. This happens way too often in paleontology.

Figure 4. TST revised with new data on Patranomodon and sister taxa.

Figure 4. TST revised with new data on Patranomodon and sister taxa.


Biseridens (Fig. 2) was too distinct

to be the ancestor to the tiny dromasaurs, Suminia and Galepus (Fig. 3) and the rest of the Anomodontia. The taxa shown above (Fig. 3) demonstrate a more gradual accumulation of traits, better modeling deep time events.

Yesterday we looked at the uncontroversial key role
two small dromasaurs, Patranomodon and Galeops (Fig. 3), played in the origin of the Dicynodontia. Kammerer’s tree and the TST are in agreement on that point. Likewise the two trees agree that Eodicynodon is the basalmost dicynodont and that Suminia is closely related to Otsheria + Ulemica, close relatives of Venjukovia.


References
Kammerer CF 2019. A new dicynodont (Anomodontia: Emydopoidea) from the terminal Permian of KwaZulu-Natal, South Africa. Palaeontologia africana 53: 179–191. ISSN 2410-4418.

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

 

Ophiacodon and the origin of mammals: bone studies are supportive

A recent paper
by Shelton and Sander 2015 provides confirmation to the heretical hypothesis that Ophiacodon is a Therapsid/Mammal precursor, discussed here several years ago.

Figure 1. Varanosaurus, Ophiacodon, Cutleria, Biarmosuchus and Nikkasaurus. These are taxa at the base of the Therapsida. Ophiacodon did not cross into the Therapsida, but developed a larger size with a primitive morphology.

Figure 1. Varanosaurus, Ophiacodon, Cutleria, Biarmosuchus and Nikkasaurus. These are taxa at the base of the Therapsida. Ophiacodon did not cross into the Therapsida, but developed a larger size with a primitive morphology.

From the abstract: “The origin of mammalian endothermy has long been held to reside within the early therapsid groups. However, shared histological characteristics have been observed in the bone matrix and vascularity between Ophiacodontidae and the later therapsids (Synapsida). Historically, this coincidence has been explained as simply a reflection of the presumed aquatic lifestyle of Ophiacodon or even a sign of immaturity. Here we show, by histologically sampling an ontogenetic series of Ophiacodon humeri, as well as additional material, the existence of true fibrolamellar bone in the postcranial bones of a member of ‘Pelycosauria’. Our findings have reaffirmed what previous studies first described as fast growing tissue, and by proxy, have disproven that the highly vascularized cortex is simply a reflection of young age. This tissue demonstrates the classic histological characteristics of true fibrolamellar bone (FLB). The cortex consists of primary osteons in a woven bone matrix and remains highly vascularized throughout ontogeny providing evidence to fast skeletal growth. Overall, the FLB tissue we have described in Ophiacodon is more derived or “mammal-like” in terms of the osteonal development, bone matrix, and skeletal growth then what has been described thus far for any other pelycosaur taxa. Ophiacodon bone histology does not show well-developed Haversian tissue. With regards to the histological record, our results remain inconclusive as to the preferred ecology of Ophiacodon, but support the growing evidence for an aquatic lifestyle. Our findings have set the evolutionary origins of modern mammalian endothermy and high skeletal growth rates back approximately 20 M.Y. to the Early Permian, and by phylogenetic extension perhaps the Late Carboniferous.”

References
Shelton C and Sander PM 2015. Ophiacodon long bone histology: the earliest occurrence of FLB in the mammalian stem lineage. PeerJ PrePrints 3:e1262
doi: https://dx.doi.org/10.7287/peerj.preprints.1027v1 preprints

The comings and goings of archosauromorph ears

You may recall that all living and extinct reptiles can be divided into two clades, the new Archosauromorpha and the new Lepidosauromorpha. Yesterday we looked at lepidosauromorph ears. Today we’ll examine archosauromorph ears.

The ear in three living archosauromorphs, crocs, mammals and birds.

Figure 1. The ear in three living archosauromorphs, crocs, mammals and birds. The ear flap seen in crocs and the platypus is by convergence, perhaps to keep the water out.

Living members of the new Archosauromorpha (Fig. 1, crocs, birds and mammals) all have well-developed ears, but only higher mammals have the erect external ears we typically think of.

At the base of the Archosauromorpha we don’t see evidence for ears. The stapes, the first and typically (except in mammals) the only ear bone, tends to be robust, helping to support the jaws. That evidence for an eardrum frame first appears in basal therapsids as a creation of an angular flange that thereafter thins to become a gracile encircling eardrum frame (Fig. 2). In higher mammals the

Reptile Ears, basal Archosauromorpha. If external ears were present, they did not leave any obvious frame, as in lepidosauromorpha.  Basal therapsids developed an eardrum frame derived from the angular bone.

Figure 2. Reptile Ears, basal Archosauromorpha. If external ears were present, they did not leave any obvious frame at the back of the skull, as in lepidosauromorphs. Basal therapsids developed an eardrum frame derived from the angular bone. Some workers think the large stapes in basal reptiles did not permit sound reception. Others think the large stapes supported a very large eardrum not otherwise supported (not sure how that could be kept taut).

There is likewise not much of a clue in basal diapsids with regard to their hearing. We skip the enaliosaurs, which were underwater creatures and don’t see a lepidosauromorph-like eardrum frame on any taxa before protorosaurs like Czatkowiella (Fig. 3) and perhaps some younginids, but data is sparse on them at present. Prehistoric crocs and dinosaurs probably developed like living crocs and birds.

Reptile eardrums - diapsids, crocs and birds.

Figure 3. Reptile eardrums – diapsids, crocs and birds. No marine reptiles of the clade Enaliosauria are included because no clear evidence for ears appears in that underwater clade. Crocs have ears higher on the skull than birds. All other eardrum placements are guesses. Like lepidosauromorphs the squamosal appears to have framed the eardrum at the back of the skull as shown.

Bird middle ear cross section. The stapes is the only bone in the link.

Figure 5. Bird middle ear cross section. The stapes is the only bone in the auditory link.

The more birdy or croc-like a taxon gets, the easier it seems to be able to imagine an eardrum framed at the back of the skull and deeper than at the surface.

Here, if anyone has additional data, I will gladly add it later.

The Evolution and Origin of Man

Updated November 10, 2020
This post is now 9 years old. About 1500 additional taxa have been added to the large reptile tree, many of which are human ancestors not known to me (and often others) in 2011. Some taxa listed below are now on side branches. Dozens of fish and basal tetrapods were added that precede the listed basal tetrapods.

The Latest List of Human Ancestors
The evolution of humans from australopithecines and beyond has been well chronicled. We know the beginning and we know the end. That list of what happened in between keeps growing as more transitional taxa are added to fill in the present gaps, which keep getting smaller and smaller.

The best represented lineage hasn’t changed much since the publication of From The Beginning, a book I wrote that was published by Little Brown in 1991. At the time it was a first of its kind. FTB illustrated 36 steps in the evolution of humans: from raw chemicals, through bacteria, worms, fish, and the rest of our clade. Every turn of the page introduced the reader to a new taxon that added, modified and/or subtracted various body parts, abilities and behaviors. That list of 36 has held up pretty well in the last twenty years, with only a few exceptions. Now Ophiacodon and Nikkasaurus would replace Haptodus. Tree shrews would be dropped in favor of a primitive carnivore, Vulpavus.

Human evolution.

Figure 1. Human evolution back to the cynodonts — and beyond. Click to enlarge. From “From the Beginning” (Peters 1991).

Bush or Ladder?
As in From the Beginning, this blog and reptileevolution.com seek to provide the latest insight into the origin and evolution of various animals (including humans). Everyone knows the process of evolution produces a branching bush, but if you want to focus on just one lineage, to see how your own body parts were modified by evolution over time and generations, it’s an unbroken ladder. By that I mean, every one of our ancestors, in an unbroken chain, successfully grew to maturity, mated and reproduced. They weren’t eaten, killed while hatching or destroyed by an asteroid impact. Our ancestors always found safe haven. Some of their offspring were a little taller, a little shorter, a little more aggressive, a little less able to breathe with gills, etc. They evolved a little bit at a time. Over time all those little bits added up.

Of the millions of ancestors we all share in common, here’s an abbreviated and clickable list that will provide more information about each step in the process of human evolution going back to the first of our ancestors to walk on land. It’s like the book From the Beginning, only its on the web.

Tetrapoda
1. Ichthyostega, Acanthostega and Pederpes. 2. Proterogyrinus.  3. Seymouria.
4. Silvanerpeton. 5. Gephyrostegus.

Reptilia
6. Cephalerpeton. 7. Casineria. 8. Paleothyris. 9. Coelostegus. 10. Hylonomus.

Synapsida
11. Elliotsmithia 11a. Apsisaurus 12. Archaeothyris. 13. Ophiacodon 14. Nikkasaurus. 15. Biarmosuchus. 16. Stenocybus. 17. Eotitanosuchus and Scymnognathus. 18. Aelurognathus. 19. Procynosuchus. 20. Thrinaxodon. 21. Chiniquodon. 22. Pachygenelus.

Mammalia
23.  Megazostrodon. 24. Amphitherium. 25. Asioryctes and Eomaia. 26. Vulpavus. 27. Notharctus. 28. Aegyptopithecus. 29. Proconsul. 30. Ardipithecus. 31. Australopithecus. 32. Homo.

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

No references this time.

>> Returning visitors will note a small edit based on updated data at positions 10 and 11.