Tiny Abdalodon: a basal cynodont, drags in Lycosuchus

Today’s blogpost returns to basal Therapsida,
after several years of ignoring this clade.

Kammerer 2016 reidentifies an old Procynosuchus skull 
as an even more basal cynodont, now named Abdalodon (Fig. 1). The problem is: cynodonts arise from basal theriodonts (Therocephalia) and Abdalodon nests with another flat-head taxon, Lycosuchus (Fig. 1), a traditional therocephalian in every other cladogram, but not the Therapsid Skull Tree (TST, 67 skull-only taxa, Fig. 2), a sister cladogram to the LRT.

So, where is the cynodont dividing line?
(= which tested taxon is the progenitor of all later cynodonts and mammals?)

It would help if we knew the phylogenetic definition
of Cynodontia because we should never go by traits (which may converge), but only by taxon + taxon + their last common ancestor and all descendants to determine monophyletic clades.

From the Kammerer 2016 abstract:
“Phylogenetic analysis recovers Abdalodon as the sister‐taxon of Charassognathus, forming a clade (Charassognathidae fam. nov.) at the base of Cynodontia. These taxa represent a previously unrecognized radiation of small‐bodied Permian cynodonts. Despite their small size, the holotypes of Abdalodon and Charassognathus probably represent adults and indicate that early evolution of cynodonts may have occurred at small body size, explaining the poor Permian fossil record of the group.”

Figure 1. Abdalodon nests with the many times larger therocephalian Lycosuchus in the LRT.

Figure 1. Abdalodon nests with the many times larger therocephalian Lycosuchus in the LRT.

Hopson and Kitching 2001 defined  Cynodontia
(Fig. 2) as the most inclusive group containing Mammalia, but excluding Bauria. In the TT Abdalodon nests with Lycosuchus on the cynodont side of Bauria.

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

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

So that makes Lycosuchus a cynodont,
by definition.

Figure 2. Procynosuchus, a basal cynodont therapsid synapsid sister to humans in the large reptile tree (prior to the addition of advanced cynodonts including mammals).

Figure 3. Procynosuchus, a basal cynodont therapsid synapsid sister to humans in the large reptile tree (prior to the addition of advanced cynodonts including mammals). This skull has been overinflated dorsoventrally based on the preserved skull, which everyone must have thought was crushed in that dimension.

Earlier we looked at
some Wikipedia writers when they stated, “Exactly where the border between reptile-like amphibians (non-amniote reptiliomorphs) and amniotes lies will probably never be known, as the reproductive structures involved fossilize poorly…” 

Contra that baseless assertion,
with phylogenetic analysis and clades defined by taxa it is easy to determine which taxa are the last common ancestors, sisters to the progenitors of every derived clade in the TT, LRT or LPT. We can tell exactly which taxon was the first to lay amniotic eggs, without having direct evidence of eggs, simply because all of its ancestors in the LRT laid amniotic eggs. In the same way, we can figure out which taxon, among those tested, is the basalmost cynodont. Adding Bauria to the LRT made that happen today.

Let’s talk about size
The extreme size difference between Abdalodon and Lycosuchus (Fig. 1) brings up the possibility of cynodonts going through a phylogenetic size squeeze… retaining juvenile traits into adulthood… neotony… essentially becoming sexually mature at a tiny size for more rapid reproduction, reduced food needs, ease in finding shelters, etc. We’ve seen that before in several clades here, here and here, to name a few.

Figure 4. Charassognathus does not share more traits with Abdalodon than other taxa, like Bauria and Promoschorhynchops in the TT.

Figure 4. Charassognathus does not share more traits with Abdalodon than other taxa, like Bauria and Promoschorhynchops in the TT.

Kammerer 2016 mentioned another small taxon,
Charassognathus (Fig. 4). In the TST (Fig. 2) Charassognathus nests with Bauria and Promoschorhynchops, within the Therocephalia, distinct from, and not far from Abdalodon and the Cynodontia. So no confirmation here for Kammerer’s proposed clade, ‘Charassognathidae’ (see above).


References
Hopson JA and Kitching JW 2001. A Probainognathian Cynodont from South Africa and the Phylogeny of Nonmammalian Cynodonts” pp 5-35 in: Parish A, et al.  editors, Studies in Organismic and Evolutionary biology in honor of A. W. Crompton. Bullettin of the Museum of Comparative Zoology. Harvard University 156(1).
Kammerer CF 2016. A new taxon of cynodont from the Tropidostoma Assemblage Zone (upper Permian) of South Africa, and the early evolution of Cynodontia. Papers in Palaeontology 2(3): 387–397. https://doi.org/10.1002/spp2.1046

wiki/Bauria
wiki/Abdalodon
wiki/Lycosuchus

Antarctanax: a late-surviving basal synapsid, not a dino ancestor

Please see the notes in the following comments section. Most importantly after publication the authors report an errant scale bar, nearly doubling the apparent size of one of the pedes. 

Peecook, Smith and Sidor 2019
bring us news of a Early Triassic amniote from the Transantarctic Mountains, Antarctanax shackletoni (Figs. 1, 2), “known from a partial postcranial skeleton including cervical and dorsal vertebrae, a humerus, and both pedes.” 

Figure 1. Antarctanax manus and pes in situ with original tracing and color added here.

Figure 1. Antarctanax manus and pes in situ with original tracing and color added here.

Unfortunately,
if the scale bars are correct, and they seem to be, the smaller ‘pes’, the one surrounded by cervicals, is really a manus (Figs. 1, 2). Furthermore, the small manus matches the small humerus and radius. Added later: The scale were not correct, as noted at top.

Figure 2. Antarctanax manus and pes compared to those of Cabarzia and Aerosaurus, two basal synapsids.

Figure 2. Antarctanax manus and pes compared to those of Cabarzia and Aerosaurus, two basal synapsids. As you can see, basal synapsids rather quickly evolved similarly sized hands and feet.

The authors mislabeled
the robust, displaced metatarsal 5 as metatarsal 1, which lies beneath it (colored orange, Figs. 1, 2). Perhaps a reconstruction would have helped expose this error before submission.

The authors report,
“Our inclusion of A. shackletoni in phylogenetic analyses of early amniotes finds it as an archosauriform archosauromorph.” Their cladogram based on Ezcurra et al. 2014 nested Antarctanax in an unresolved polytomy with the basal archosauriforms, Proterosuchus, Erythrosuchus and Euparkeria. Their cladogram based on Ezcurra 2016 nested Antarctanax in an unresolved polytomy with other basal archosauriforms, FugusuchusSarmatosuchus. I am not aware of a manus or pes preserved for these two taxa. Of the above listed taxa, Proterosuchus (Fig. 3) comes closest, but has a hooked metatarsal 5 and metacarpal 3 is the longest, distinct from Antarctanax.

Synaptichnium

Figure 3. Synaptichnium compared to a slightly altered pes of Proterosuchus. Note a reduction of one phalanx in pedal digit 4 to match one less pad in the ichnite. The last two (or three phalanges) of pedal 4 are unknown in Proterosuchus.

This time it is not taxon exclusion, but bad timing.
When the manus and pes of Antarctanax are added to the large reptile tree (LRT, 1395 taxa), Antarctanax nests with basalmost synapsids, like Cabarzia (Figs. 2, 4) and Aerosaurus (Fig. 2). Aerosaurus was included in Ezcurra et al. 2014 and tested by Peecook, Smith and Sidor 2019. You’ll have to ask the authors why Antarctanax did not nest closer to Aerosaurus. Cabarzia trostheidei (Spindler, Werneberg and Schneider 2019, Fig. 3) could have influenced their thinking and scoring, but it was published only a few weeks ago, too late to include in their submission.

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 4. 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.

Peecock, Smith and Sidor did not provide a reconstruction
of Antarctanax, but online Discover magazine provided an in vivo painting and crowned it, “Dinosaur Relative Antarctanax.” According to the LRT, Antarctanax was a late-surviving (Early Triassic) basal member of our own lineage, the Synapsida, with a late Carboniferous genesis.

Therapsid synapsids were plentiful in Antarctica in the Early Triassic.
The headline should have focused on the unexpected presence of this sprawling, pre-pelycosaur, basal synapsid in the Mesozoic, surviving the Permian extinction event in this Antarctic refuge, alongside a closer relative of mammals, Thrinaxodon.


References
Ezcurra MD, Scheyer TM and Butler RJ 2014. The origin and early evolution of Sauria: reassessing the Permian saurian fossil record and the timing of the crocodile-lizard divergence. PLoS ONE 9:e89165.
Ezcurra MD 2016. The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms. PeerJ 4:e1778.
Peecook BR, Smith RMH and Sidor C 2019. A novel archosauromorph from Antarctica and an updated review of a high-latitude vertebrate assemblage in the wake of the end-Permian mass extinction. Journal of Vertebrate Paleontology e1536664 (16 pages) DOI: 10.1080/02724634.2018.1536664
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 Gesellschaf

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

 

Resurrecting extinct taxa: Pareiasauria, Compsognathidae and Ophiacodontidae

Earlier we looked at
four clades thought to be extinct, but are not extinct based on their nesting in the large reptile tree (LRT, 1366 taxa). Today, three more:

Figure 2. Another gap is filled by nesting E. wuyongae between Bunostegos and Elginia at the base of hard shell turtles in the LRT.

Figure 1. Another gap is filled by nesting E. wuyongae between Bunostegos and Elginia at the base of hard shell turtles in the LRT.

Pareiasauria
According to Wikipedia, “Pareiasaurs (meaning “cheek lizards”) are an extinct group of anapsid reptiles classified in the family Pareiasauridae. They were large herbivores that flourished during the Permian period.”

In the LRT two clades of turtles (Fig. 1) are derived in parallel from two small horned pareiasaurs.

Figure 1. Lately the two clades based on two specimens of Compsognathus (one much larger than the other) have merged recently.

Figure 2.  Lately the two clades based on two specimens of Compsognathus (one much larger than the other) have merged recently.

Compsognathidae
According to Holtz 2004, “The most inclusive clade containing Compsognathus longipes but not Passer domesticsus.” Traditionally Compsognathus nests outside the Tyrannoraptora, a clade that traditionally leads to birds.

In the LRT Compsognathus specimens nest at the base of several theropod clades (Fig. 2) including the tyrannosaurs and Mirischia, Ornitholestes and the feathered theropods leading to birds.

Figure 1. Varanosaurus, Ophiacodon, Cutleria and Ictidorhinus. 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. This new reconstruction of Ophiacodon is based on the Field Museum (Chicago) specimen. Click to enlarge.

Figure  3. Varanosaurus, Ophiacodon, Cutleria and Ictidorhinus. 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. This new reconstruction of Ophiacodon is based on the Field Museum (Chicago) specimen. Click to enlarge.

Ophiacodontidae
According to Wikipedia, “Ophiacodontidae is an extinct family of early eupelycosaurs from the Carboniferous and Permian. Ophiacodontids are among the most basal synapsids, an offshoot of the lineage which includes therapsids and their descendants, the mammals. The group became extinct by the Middle Permian.”

In the LRT Ophiacodon (Fig. 3) and Archaeothyris, neither members of the Pelycosauria, are more directly related to basal therapsids, including derived the therapsids: mammals.

References
Holtz TR 2004. Basal tetanurae. PP. 71–110 in The Dinosauria, U of California Press.

/wiki/Pareiasaur
wiki/Ophiacodontidae

 

Lisowicia: Already superlative, so no need to further exaggerate

A new 4.5 meter long Late Triassic dicynodont has been reported.
Lisowicia bojani
(Sulej and Niedzwiedzki 2018, Late Triassic; Fig. 1) is by far the largest dicynodont now known, greatly superseding the previous record holder, Stahleckeria (von Huene 1935; Fig. 1). That’s fantastic all by itself. So why would a world-famous paleontologist and the Smithsonian website further exaggerate this discovery?

Figure 1. Lisowicia compared to extant elephants and the previous largest dicynodont, Stahleckeria.

Figure 1. Lisowicia compared to extant elephants and the previous largest dicynodont, Stahleckeria, not itself a ‘small and unseen’ taxon, but forgotten or omitted in the present storyline. The young lady in the pink tie-dye shirt is five feet tall.

Online Smithsonian Magazine headlines the story:
“Early Mammals Were Thought to Be Small and Unseen in the Age of Dinosaurs. An Elephant-Sized Fossil Complicates That Story — At a time when proto-mammals and other creatures were getting smaller, this dicynodont bulked up with the thunder lizards”

Lisowicia is indeed elephant-sized,
in length, but not height. Lisowicia had shorter legs, like another dicynodont, bear-sized Stahleckeria (Fig. 1). So… while the early and proto-mammals were indeed small, other  ‘creatures’ were also ‘bulking up‘ in the Late Triassic, including dicynodonts, rauisuchians, erythrosuchians, poposaurs, protorosaurs, phytosaurs and proterochampsids, to name only the terrestrial tetrapods. Even in this company, Lisowicia is still extraordinary in size. On the other hand, and let’s be honest about this… in the Late Triassic Age of Dinosaurs, sauropodomorphs were really the only dinosaurs to also bulk up. The rest remained about human-sized or smaller.

Be careful not to create mythology
when discussing dinosaurs. Keep it real.

Author and paleontologist Dr. Stephen Brusatte
(U. of Edinborough) chimed in with this paragraph of inappropriate surprise and hyperbole: “Before these giant bones were discovered, you would have been called crazy if you ever suggested there were giant, elephant-sized mammal cousins living alongside some of the very first dinosaurs,” he says. “We used to think that after the end-Permian extinction [252 million years ago], when some 90-95 percent of all species went extinct, mammals and their relatives retreated to the shadows while dinosaurs rose up and grew to enormous sizes. That’s the story I tell my students in my lectures. But this new discovery throws a wrench into that simple tale.” 

We “used to think” nothing of the sort! 
If you are a student of Dr. Brusatte, find another professor! Dr. Brusatte has been on the wrong end of many paleo hypotheses. Use keyword “Brusatte” in the little white search box above for details on several past subjects ranging from dinosaur origins to footprint identification to multituberculates.

Brusatte also said in ScienceMag.org, “‘Who would have ever thought that there were giant, elephant-sized mammal cousins living alongside some of the very first dinosaurs?’marvels Stephen Brusatte, a vertebrate paleontologist at The University of Edinburgh.” 

Seems Dr. Brusatte is forgetting about Stahleckeria,
the previous record-holder for largest dicynodont at 3.3 meters in length. A taxon that size is definitely not “relatively in the shadows.” If you’re going to speak to the press, don’t omit pertinent details.

Lisowicia is already unique and spectacular
at twice the height of Stahleckeria. So there is no need to exaggerate the truth or reduce the size of comparables in order to make Lisowicia appear even more unique and spectacular. A comparative graphic like the one above would have made the point without the verbal hyperbole, omission and overkill.

Are dicynodonts really mammal cousins?
In the large reptile tree (LRT, 1337 taxa) dicynodonts and other herbivorous basal synapsids (Anomodontia) split from the carnivorous synapsids that led to mammals immediately following the pelycosaurs. So that’s one node. Basal anomodonts are separated from basal mammals by 12 nodes and then add 5 more nodes to get to Lisowicia nesting as a very derived anomodont.  So an inappropriate comparison to basal mammals is likewise stretching science journalism to an uncalled-for degree. If you want to educate the public, educate the public.

Lisowicia deserves some grand-standing.
Let’s just try to keep it real.

References
Sulej T; Niedźwiedzki G 2018. An elephant-sized Late Triassic synapsid with erect limbs. Science: eaal4853. doi:10.1126/science.aal4853
v. Huene F 1935. Lieferung 1. Anomodontia [Part 1. Anomodontia]. Die Fossilen Reptilien des Südamerikanischen Gondwanalandes. Ergebnisse der Sauriergrabungen in Südbrasilien 1928/29 [The Fossil Reptiles of South American Gondwanaland. Results of the Dinosaur Expeditions in southern Brazil 1928/29]. C. H. Beck’sche Verlagsbuchhandlung, München 1-82

https://en.wikipedia.org/wiki/Lisowicia
smithsonianmag.com/smart-news/elephant-size-mammal-cousin-mingled-dinosaurs
https://en.wikipedia.org/wiki/Stahleckeria

A reexamination of Milosaurus: Brocklehurst and Fröbisch 2018

I just found out that not one but two Aerosaurus specimens were tested and are to be found in the SuppData for this paper. So, what happened here? I’ll dig deeper to look for a solution. 

Solution: The cladistic analysis in the Brocklehurst and Fröbisch 2018 Milosaurus study recovered nearly 2000 most parsimonious trees for 60 taxa. So the phylogeny is not well resolved. By contrast the LRT is well resolved. Relatively few of the characters could be scored for Milosaurus in the Brocklehurst and Fröbisch study. None overlapped with Ianthodon, the purported closest relative. By contrast the LRT found a suite of traits that were shared by Milosaurus and Aerosaurus to the exclusion of all other tested taxa. 

Brocklehurst and Fröbisch 2018 reexamine
“a large, pelycosaurian-grade synapsid” not from the Early Permian, but from the Latest Carboniferous of Illinois Milosaurus (Fig. 1) was first described by DeMar 1970 as a member of the Varanopsidae (= Varanopidae). Brocklehurst and Fröbisch note, “Milosaurus itself has received little attention since its original description. The only attempt to update its taxonomic status was by Spindler et al. (2018). These authors included Milosaurus in a phylogenetic analysis that, although principally focused on varanopids, contained a small sample of pelycosaurs from other families. Milosaurus was found nested within Ophiacodontidae, as the sister to Varanosaurus.”

Ultimately
Brocklehurst and Fröbisch nested Milosaurus with Haptodus within the Eupelycosauria.

Figure 1. The pes of Milosaurus in situ, reconstructed and compared to Aerosaurus, its sister in the LRT.

Figure 1. The pes of Milosaurus (FMNH PR 701) in situ, reconstructed and compared to Aerosaurus, its smaller sister in the LRT. PILs added to restore distal phalanges.

By contrast
the large reptile tree nested Milosaurus with Aerosaurus (Fig. 1; Romer 1937, A. wellesi Langston and Reisz 1981), a taxon not listed by Brocklehurst and Fröbisch. Based on the pes alone, Milosaurus was twice the size of Aerosaurus. Aerosaurus is a basal synapsid more primitive than Haptodus and the Pelycosauria. Aerosaurus and Milosaurus nest between Elliotsmithia + Apsisaurus and Varanops.

Unfortunately
Brocklehurst and Fröbisch included the unrelated clade Caseasauria in their study of Synapsida, and did not include Aerosaurus. They also include Pyozia, not realizing it is a proto-diapsid derived from and distinct from varanopid synapsids. So, once again, taxon exclusion and inappropriate taxon inclusion are the reasons for this phylogenetic misfit.

Distinct from Haptodus, and similar to Aerosaurus
in Milosaurus metatarsals 2 and 3 align with p1.1, not mt1. The base of mt 5 is quite broad. Other traits also attract Milosaurus to Aerosaurus, including an unfused pubis + ilium. I was surprised that so few traits nested Milosaurus in the LRT as it continues to lump and split taxa with the current flawed list of multi-stage characters.

References
Brocklehurst N and Fröbisch J 2018. A reexamination of Milosaurus mccordi, and the evolution of large body size in Carboniferous synapsids. Journal of Vertebrate
Paleontology, DOI: 10.1080/02724634.2018.1508026
DeMar R. 1970. A primitive pelycosaur from the Pennsylvanian of Illinois. Journal of Paleontology 44:154–163.
Langston W Jr and Reisz RR 1981. Aerosaurus wellesi, new species, a varanopseid mammal-like reptile (Synapsida: Pelycosauria) from the Lower Permian of New Mexico. Journal of Vertebrate Paleontology 1:73–96.
Romer AS 1937. New genera and species of pelycosaurian reptiles. Proceedings of the New England Zoological Club 16:90-96.

wiki/Aerosaurus

SVP 2018: The evolution of varanopids

Reisz 2018 reports,
“Varanopidae is a clade of small to medium sized carnivorous synapsids whose fossil
record spans the Late Pennsylvanian to late Permian, one of the longest known temporal
ranges of any Paleozoic eupelycosaur clade. It has also been recently suggested that this clade may not be part of Synapsida, but may instead nest within Diapsida.”

In the large reptile tree (LRT, 1306 taxa, subset Fig. 1) Vaughnictis is the last common ancestor of Diapsida and Synapsida. Varanodon nests within the Synapsida. A series of former varanopids nest as pre-diapsids.

Figure 6. Subset of the large reptile tree showing the nesting of Vaughnictis at the base of the Synapsida and Prodiapsida.

Figure 1. Subset of the large reptile tree showing the nesting of Vaughnictis at the base of the Synapsida and Prodiapsida. Higher synapsids arise from Ophiacodon. Diapsids arise from the Broomia clade. If Reisz isn’t getting this topology, he may have to add taxa. 

Reisz 2018 concludes,
“A revised and expanded data matrix and phylogenetic analysis that integrates Permo-Carboniferous synapsids and reptiles does recover a monophyletic Varanopidae within Synapsida, with Varanodon and its varanodontine sister taxa, Watongia, Varanops, Tambacarnifex, as apex, gracile predators of the early Permian, contemporaries of the larger, more massively built sphenacodontid synapsids.”

Unfortunately taxon exclusion
prevents Dr. Reisz from seeing the big picture (subset Fig. 1), published online in 2015 here and expanded since then.

References
Reisz RR 2018. Varanodon and the evolution of varanopid synapsids. SVP abstracts.

Kayentatherium with 38 tiny hatchlings

Hoffman and Rowe 2018
bring us a large field jacket dotted with 38 tiny hatchlings of Kayentatherium, a tritylodontid synapsid the size of a cat (Figs. 1,2). In this wonderful and unique discovery the authors report, Here we present what is, to our knowledge, the first fossil record of pre- or near-hatching young of any non-mammalian synapsid. The single clutch comprises at least 38 individuals, well outside the range of litter sizes documented in extant mammals. This discoverconfirms that production of high numbers of offspring represents the ancestral condition for amniotes, and also constrains the timing of a reduction in clutch size along the mammalian stem.”

Figure 1. Kayentatherium adult.

Figure 1. Kayentatherium adult. Note the extremely narrow braincase on this herbivore. Note the pelvic opening here moved from the original drawing to provide an opening.

That last statement needs to be taken as conjecture
because we don’t have data for a long list of predecessor taxa going back to Devonian tetrapods. The authors’ statement could be true. On the other hand, the tritylodontids, being derived herbivores, might have created lots of babies, while their omnivore and carnivore ancestors, more in the line of mammal ancestry, laid smaller numbers of larger eggs. We just don’t know. The authors provided one puzzle piece. That’s not enough to make a conclusive statement.

Figure 2. Kayentatherium to scale with hatchling and in matching skull lengths for direct comparison. The orbit is larger, the rostrum and temple are smaller.

Figure 2. Kayentatherium to scale with hatchling and in matching skull lengths for direct comparison. The orbit is larger, the rostrum and temple are smaller.

Then Hoffman and Rowe double down:
The discovery of a large clutch in a stem mammal provides material evidence that producing high numbers of offspring is the ancestral condition for amniotes, and that small litters represent a derived mammalian trait.” Wait a minute… lobe-fin coelacanths embryos hatch within the female and only a few are produced at a time. What happened between coelacanths and tritylodontids? We just don’t have the data for a long list of taxa between these two. Best not to guess and make it sound like scientific canon.

Note the narrow braincase in Kayentatherium,
slightly narrower than in ancestors, like Sinoconodon (Fig. 3) and basal mammals, like Sinodelphys. A U of Texas article (ref. below) reports, “The 3D visualizations Hoffman produced allowed her to conduct an in-depth analysis of the fossil that verified that the tiny bones belonged to babies and were the same species as the adult. Her analysis also revealed that the skulls of the babies were like scaled-down replicas of the adult, with skulls a tenth the size but otherwise proportional. This finding is in contrast to mammals, which have babies that are born with shortened faces and bulbous heads to account for big brains.”

Figure 2. Sinoconodon skull(s) showing some variation in the way they were drawn originally.

Figure 3 Sinoconodon skull(s) showing some variation in the way they were drawn originally. Note the relatively large brains on this more primitive taxon.

“The discovery that Kayentatherium had a tiny brain and many babies, despite otherwise having much in common with mammals, suggests that a critical step in the evolution of mammals was trading big litters for big brains, and that this step happened later in mammalian evolution. ‘Just a few million years later, in mammals, they unquestionably had big brains, and they unquestionably had a small litter size,’ Rowe said.”

Actually brains stayed relatively small
until we get to more recent prototheres, more recent metatheres (by convergence) and more recent placentals (again, by convergence). Check out the following basal mammal taxa for cranium ‘narrowness’

  1. Sinodelphys
  2. Brasilitherium
  3. even Didelphis

Extant echidnas and platypuses, have bulbous skulls filled with brains, but not so their Cretaceous ancestors, Cifelliodon and Akidolestes.

To show that cranium width can narrow
or become relatively smaller in highly derived placental mammals check out the following taxa:

  1. Andrewsarchus
  2. Equus
  3. Lophiodon

So the skull can balloon, or narrow, depending on the situation over millions of years.

According to the authors, the skull length of a hatchling
was 1/20 that of an adult with an isometric rostrum and a smaller, allometric, temporal fenestra. Is that correct? See for yourself (Fig. 2). It looks like the orbit was larger, while the rostrum and temple were both smaller. Hate to nit-pick, but there you are…

Again, this was a wonderful find and a great presentation.
We just don’t want to get ahead of ourselves after one discovery, when other hypotheses are currently possible and now on the table.

References
Hoffman EA and Rowe TB 2018. Jurassic stem-mammal perinates and the origin of mammalian reproduction and growth.

utexas.edu/mammal-forerunner-sheds-light-on-brain-evolution

More evidence that euharamyidans are mislabeled Jurassic rodents

Figure 1. The Jurassic mammal Shenshou, which nests within Allotheria (Haramiyida + Mutituberculata) within the Mammalia, as I proposed based on the LRT without knowledge of this paper.

Figure 1. The Jurassic mammal Shenshou, which nests within Allotheria (Haramiyida + Mutituberculata) within the Mammalia, as I proposed based on the LRT without knowledge of this paper.

Euharamyidans include the squirrel-like Jurassic gliders
Shenshou (Figs. 1,2 ), Vilevolodon and Maiopatagium in the large reptile tree (LRT, 1265 taxa). These are sisters to the squirrel, Ratufa, the squirrel-like Paramys and two living rodents, Rattus and Mus (rat and mouse).

Mao et al. 2018 report, “The new evidence suggests presence of diphyodonty in euharamiyidans. While it will take time to amass data to resolve the discrepancy between competing phylogenetic hypotheses about ‘haramiyidans’, multituberculates, and/or allotherians, it is helpful to continue deepening our knowledge about the morphology of euharamiyidans. Our finding of potential diphyodonty in euharamiyidans provides an additional piece of evidence for mammalness of the peculiar group.”

Figure 2. Shenshou skull traced in colors.

Figure 2. Shenshou skull traced in colors.

Above:
The skull of Shenshou (Fig. 2), close to living squirrels. Evidently the molar cusps are convergent with those of Haramiyavia, but there are few other similarities.

Below:
Haramiyavia (Fig. 3), a pre-mammal cynodont with a small canine and large incisors not related to Shenshou. Note the dual articular/dentary jaw joint in Haramiyavia, missing (actually evolved into ear bones) in Shenshou. Such a jaw joint marks this taxon as a pre-mammal synapsid.

Figure 1. Haramiyavia reconstructed and restored. Missing parts are ghosted. Three slightly different originals are used for the base here. The last appears to be the least manipulated and it appears to fit the premaxilla better.  The fourth maxillary tooth appears to be a small canine. The groove on the dorsal premaxillary appears to be for the nasal, not the septomaxilla. Parts are taken from both mandibles

Figure 3. Haramiyavia reconstructed and restored. Missing parts are ghosted. Three slightly different originals are used for the base here. The last appears to be the least manipulated and it appears to fit the premaxilla better.  The fourth maxillary tooth appears to be a small canine. The groove on the dorsal premaxillary appears to be for the nasal, not the septomaxilla. Parts are taken from both mandibles

In the LRT, Haramyavia, a basal member of the Haramiyida
nests with other pre-mammals like Brasiliodon and Sinoconodon, hence: not related to euharamiyidans. Determining the clade based on traits (no matter what these traits may be) is the cause of the phylogenetic confusion based on tooth shape and replacement patterns, which can converge. Only a taxon’s placement on a cladogram can tell you what an animal really is. Sadly, that’s a current heresy, not widely appreciated.

According to Wikipedia
(ref below): Haramiyidans are a long lived lineage of mammaliaform cynodonts. Their teeth, which are by far the most common remains, resemble those of the multituberculates. However, based on Haramiyavia, the jaw is less derived; and at the level of evolution of earlier basal mammals like Morganucodon and Kuehneotherium, with a groove for ear ossicles on the dentary.[1] They are the longest lived mammalian clade of all time.”

As the LRT showed several years ago
the rodent-like Euharamiyidans (Fig. 1) nest with placental rodents in the clade Glires, not with the much more primitive pre-mammals like Haramiyavia (Fig. 3).

Mao et al. 2018 report, “presence of the diphyodont dentition alone is not diagnostic for mammals. This is because a diphyodont dentition exists not only in mammals but also in stem mammaliaforms, such as Morganucodon and docodonts, although there may be more than one replacement for the upper canine of Haldanodon (Martin et al., 2010b).”

By contrast, in the LRT
Morganucodon is a basal metatherian, not a stem mammaliaform. Which is one more reason why it has diphyodont dentition (milk teeth + permanent teeth). The late-surviving docodonts, Haldanodon and Castorocauda nest between the synapsids, Probainognathus and Pachygenelus in the LRT. Those four should be replacing all their teeth all the time. All four had a dual jaw joint that was not quite mammalian, but getting there!

Diphyodont dentition alone is diagnostic for mammals
because it implies toothless, milk-lapping/sucking hatchlings, (but be careful not to pull a Larry Martin here, because the LRT uses 231 traits and diphyodont dentition is not among them).

Among mammals
Mao et al. 2018 report, “tooth replacement is also complex among mammals. For instance, the molariform teeth of eutriconodonts show replacement and some species have the entire dentition replaced and show at least three tooth generations. Cheek tooth replacement is uncertain in “symmetrodontans”. In North American spalacotheriids deciduous canine and premolars were retained late in life and may never have been replaced; thus, their dentitions perhaps were monophyodont. This has been supported by the spalacolestine Lactodon from the Early Cretaceous Jehol Biota, in which there is no sign of cheek tooth replacement even though this taxon possesses deciduous-like antemolars. New CT scan data (unpublished) further confirmed that there is no tooth germ at any tooth locus, including incisors and canines, of Lactodon [= Lactodens”?]. Thus, presence of the diphyodonty in euharamiyidans, does not constitute a sufficient evidence for the group’s mammalian affinity.”

Let’s examine those arguments
in new light shed by the LRT.

  1. Eutriconodonts (Spinolestes, Gobiconodon and kin): These taxa do not nest within Mammalia in the LRT (contra Martin et al. 2015).
  2. Symmetrodontans (Zhangheotherium and kin): Zhangheotherium is a basal pangolin, hence the atavistic teeth, as in another placental clade, the archaeocete ‘whales’.
  3. Spalacotherids (Lactodon = Lactodens): Taxa like Lactodens nest within the prototheria in the LRT.

It always comes back down to phylogenetic analysis.
And the LRT answesr all such problems within its ken. The radiation of placental mammals was in the Early Jurassic based on the appearance of derived placental mammals in the Late Jurassic. Non-mammalian synapsids survived into the Middle Jurassic, so there was plenty of overlap.

Figure 4. Lactodens in situ. This Early Cretaceous protothere has tooth-lined jaws. At 72 dpi this is about 3x larger than life size.

Figure 4. Lactodens in situ. This Early Cretaceous protothere has tooth-lined jaws. At 72 dpi this is about 3x larger than life size.

PS. If you’re wondering about
Lactodens (= Lactodon; Fig. 4; Han and Meng 2018; Early Cretaceous) here it nests at the base of the echidna + platypus clade, two toothless (as adults) taxa. Perhaps that’s why the diphyodont dental rules start breaking down with this taxon, as described by Mao et al.

References
Mao F-Y et al. (5 co-authors) 2018. Evidence of diphyodonty and heterochrony for dental development in euharamiyidan mammals from Jurassic Yanliao Biota. Vertebrata PalAsiatica DOI: 10.19615/j.cnki.1000-3118.180803

https://en.wikipedia.org/wiki/Haramiyida

Oscar Reig: a paleoprophet separates archosaurs from lepidosaurs in 1967

But… for the wrong reasons.

Reig 1967 prophetically wrote:
“Archosaurs and lepidosaurs apparently have different origins; the former come from the pelycosaurs, and the latter come from the captorhinomorph cotylosaurs through the Millerettiformes.”

Considered heretical at the time,
Reig’s pronouncement echoes in the large reptile tree (LRT, 1151 taxa).

Here’s the full abstract:
“The characteristics of the first archosaurs, the proterosuchian thecodonts, show that neither of the supposed common ancestors of archosaurs and lepidosaurs could actually be an ancestor of archosaurs. Instead, the evidence seems to indicate that the archosaurian ancestors are probably in the ophiacodont-varanopsid group of the pelycosaurian synapsids. In particular, the Varanopsidae are strongly indicative of proterosuchian relationships, as they have evolved some characters which are elsewhere found only in archosaurs. Archosaurs and lepidosaurs apparently have different origins; the former come from the pelycosaurs, and the latter come from the captorhinomorph cotylosaurs through the Millerettiformes.”

The only thing he got wrong
(as everyone else got wrong until seven years ago) was not splitting the Varanopsidae into the Synapsida and the Prodiapsida, as demonstrated in the LRT. He also thought proterosuchids arose directly from varanopsids like Varanodon (Fig. 1), which converge with proterosuchids in size and skull shapes. There’s even an antorbital fenestra, or elongated naris and a drooping premaxilla in Varanodon. No wonder Reig got excited.

Figure 1. Varanodon the synapsid compared to its analog, Proterosuchus, the archosauriform.

Figure 1. Varanodon the synapsid compared to its analog, Proterosuchus, the archosauriform.

Archosauriforms do arise from
former
varanopsids, like Heleosaurus and Mycterosaurus, but not directly. They have to pass through the diapsid grade, then the basal terrestrial younginiform grade before evolving into proterosuchids.

Lepidosaurs do arise from
captorhinomorphs and millerettids in the LRT, but again, not directly. First they have to pass through the nycteroleterid, owenettid, and basal lepidosauriform grades before evolving into lepidosaurs.

The LRT recovered
two clades of diapsids one closer to lepidosaurs and another closer to archosaurs.

References
Reig OA 1967. Archosaurian reptiles: a new hypothesis on their origins.
Science 157(3788):565-8.