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

The origin of fingers and toes in basal tetrapods

If you ever wondered
how five fingers and toes came to be the ‘standard’ for reptiles (including mammals), we can turn to the large reptile tree (LRT, 1426 taxa; subset Fig. 1) to sort out this question.

With so many taxa
among basal tetrapods known only from skulls, the following is an exercise in phylogenetic bracketing.

Figure 1. Graphing the presence of fingers and toes in basal tetrapods, updated today with the addition of 4 digits in Panderichthys.

Figure 1. Graphing the presence of fingers and toes in basal tetrapods, updated today with the addition of 4 digits in Panderichthys.

We start with lobefins
These are fish that have no fingers or toes. The most primitive bony fish, like Cheirolpis, had lobe fins and rays. Sarcopterygians emphasized the lobe part. Bony fish reduced the lobe part and emphasized the ray part. Within the lobe the humerus, radius, ulna and smaller parts appeared (one bone, two bones, many bones). Originally the radius was much longer than the ulna.

Dvinosauria
are the most primitive taxa in the LRT to have a sub equal radius and ulna (preserved in Laidleria) and a sub equal tibia and fibula (preserved in Gerrothorax). Gerrothorax is the most primitive taxa to preserve metacarpals. They were poorly ossified, but there were five in number.

Colosteus 
(Fig. 2) preserves four fingers (1-4) on a tiny forelimb. Only the front half of this taxon is known.

Pholidogaster
(Fig. 2) more or less preserves five toes. The manus was not preserved, but the radius and ulna were slender beneath a robust humerus.

Figure 6. Colosteus relatives according to the LRT scaled to a common skull length. Their sizes actually vary quite a bit, as noted by the different scale bars. Only Pholidogaster and Colosteus are taxa in common with traditional colosteid lists.

Figure 6. Colosteus relatives according to the LRT scaled to a common skull length. Their sizes actually vary quite a bit, as noted by the different scale bars. Only Pholidogaster and Colosteus are taxa in common with traditional colosteid lists.

The vast majority of basal tetrapods
retained this digit pattern: four on the forelimbs, five on the hind limbs.

Exceptions include
Acanthostega (Fig. 3) with 8 fingers and 8 toes. Ichthyostega has 7 toes (manus unknown).

Acanthostega demonstrates a reversal:
The radius is twice as long as the ulna, as in lobefin fish. Apparently neotony produces this reversal as Acanthostega became sexually mature as a more fully aquatic ‘tadpole’, much smaller than its ancestor, Ossinodus (Fig. 2), for which only a few toe parts are known.

We looked at the convergently more aquatic Ichthyostega
earlier here. Both are Late Devonian taxa, appearing tens of millions of years later than the Middle Devonian trackmaker.

Figure 1. Ossinodus is the more primitive taxon in the LRT compared to the smaller Acanthostega, the tadpole of the two.

Figure 3. Ossinodus is the more primitive taxon in the LRT compared to the smaller Acanthostega, the tadpole of the two.

Proterogyrinus had five fingers and five toes,
but it appears to have developed the extra digits all alone and convergent with amniotes (= reptiles) and their kin (see below).

Cacops and kin (Dissorophidae, Lepospondyli)
also developed five fingers and five toes by convergence with reptiles. Other lepospondyls, like the frog, Rana, did not have more than four fingers.

The first taxon in our lineage with five fingers and five toes
is Utegenia, which gave rise to the clade Seymouriamorpha and the clade Reptilomorpha (by definition, taxa closer to reptiles than to salamanders: Eusauropleura, Gephyrostegus, their last common ancestor and all their descendants).

As early as the Late Devonian
the basal reptilomorph, Tulerpeton (Fig. 4), developed an exceptional and tiny sixth finger. Since no more taxa in this lineage had a sixth finger, this is not a reversal, but a novel digit. Originally this taxon was thought to have six toes (digit 5 had to be fully restored), but new reconstructions do not confirm this hypothesis.

Figure 1. Tulerpeton pes reconstruction options using published images of the in situ fossil.

Figure 4. Tulerpeton peps in situ and several reconstruction options using published images of the in situ fossil. The one at upper left most closely resembles sister taxa and has more complete PILs (parallel interphalangeal lines).

The above LRT fish-to-tetrapod transition
only partially replicates and confirms the traditional one provided by Clack 2009 (Fig. 5) with far fewer taxa.

Figure 5. The classic paradigm illustrating the fish-to-tetrapod transition from Clack 2009.

Figure 5. The classic paradigm illustrating the fish-to-tetrapod transition from Clack 2009.

If anyone knows of taxa pertinent to this subject
please let me know and I will add them. At present very few taxa represent many more taxa (phylogenetic bracketing) since so many taxa in the above subset do not preserve extremities or they were overlooked and not collected or published.

References
Clack JA 2009. The fish-tetrapod transition: new fossils and interpretations. Evo Edu Outreach (2009) 2:213–223. DOI 10.1007/s12052-009-0119-2

Looking for a vestigial toe 5 on Jeholosaurus

Jeholosaurus is a small Early Cretaceous sister
to the Late Jurassic Chilesaurus and Late Triassic Daemonosaurus. All three nest as basalmost Ornithischia in the large reptile tree (LRT, 1399 taxa).

Phylogenetic bracketing indicates
a likely pedal digit 5 with a few phalanges should be found on all three taxa. Prior studies failed to reveal it. Current data does not include the pes for Daemonosaurus, nor show the ventral aspect of Chilesaurus, but Jeholosaurus does present the view we’re looking for (Fig. 1). I failed to notice pedal 5 before. I think others have overlooked it as well. Here it is:

Figure 1. Jeholosaurus pes in ventral aspect. DGS colors identify parts of pedal digit 5 disarticulated and broken on the sole of the foot and reconstructed at right.

Figure 1. Jeholosaurus pes in ventral aspect. DGS colors identify parts of pedal digit 5 disarticulated and broken on the sole of the foot and reconstructed at right. This observation is awaiting confirmation or refutation. Phylogenetic bracketing indicates this foot had a pedal digit 5 in vivo.

Finding pedal digit 5 on Jeholosaurus
was made a bit more difficult due to the vestige nature of the digit and its crushed and broken pieces, disarticulated from its traditional alignment lateral to pedal digit 4. This observation based on this photo awaits confirmation or refutation.


References
Han F-L, Barrett PM, Butler RJ and Xu X 2012. Postcranial anatomy of Jeholosaurus shangyuanensis (Dinosauria, Ornithischia) from the Lower Cretaceous Yixian Formation of China. Journal of Vertebrate Paleontology 32 (6): 1370–1395.
Xu X, Wang and You 2000. A primitive ornithopod from the Early Cretaceous Yixian Formation of Liaoning. Vertebrata PalAsiatica 38(4:)318-325.

wiki/Jeholosaurus
wiki/Daemonosaurus

 

 

Sphodrosaurus: here identified as a stem soft shell turtle

Known for decades as an enigma,
Sphodrosaurus pennsylvanicus nests here more primitive than Odontochelys and sheds light on the pareiasaur-to-soft shell turtle transition.

FIgure 1. Partial reconstruction of Sphodrosaurus based on tracings in figure 2.

FIgure 1. Partial reconstruction of Sphodrosaurus based on tracings in figure 2. This turtle is more basal than Odontochelys. Lots of loose parts here and no attempt was made to reassemble the manus or pes.

Colbert 1960
described Sphodrosaurus pennsylvanicus (Fig. 1) as, “A new Triassic procolophonid from Pennsylvania” based on North Museum No. 2321, a natural mold in ventral view of a partial skeleton (Fig. 2) resembling Hypsognathus and located less than a mile from the skull of this genus. In the large reptile tree (LRT, 1308 taxa; subset Fig. 3) Sphodrosaurus nests between the tiny pareiasaur Sclerosaurus (Fig. 4) and the basal soft-shell turtle (known only from skull material) Arganaceras.

Based on the appearance of a shape in the mudstone
beneath the ribs (in ventral view, thus dorsal in life), Sphodrosaurus appears to be (by observation and phylogenetic bracketing) the first taxon to have some sort of soft carapace without developing any sort of expanded ribs or any sort of plastron. Thus it informs on the likely appearance of the currently missing post-crania of Arganaceras. Some loose gastralia-like ossifications (in cyan) are apparent. These are plastron precursors (again, based on phylogenetic bracketing). These inform on a previously unknown genesis for the plastron in soft shell turtles. Sclerosaurus lacks them. Odontochelys has massive plastron elements.

Figure 2. Sphodrosaurus in situ with colors added to bones and possible soft carapace impression.

Figure 2. Sphodrosaurus in situ, ventral view, with colors added to bones and possible soft carapace impression overlooked originally. Colbert  1960 tracing also shown here.

Traditionally
Sclerosaurus nests with procolophonids, but that nesting is based on taxon exclusion. Sphodrosaurus is very similar to Sclerosaurus, but a little more derived toward the soft shell turtles.

Figure 3. Sphodrosaurus nests with other soft-shell turtles arising from pareiasaurs.

Figure 3. Sphodrosaurus nests with other soft-shell turtles arising from pareiasaurs without invoking the carapace.

Sphodrosaurus pennsylvanicus (Colbert 1960; North Museum No. 2321; Newark Supergroup, latest Carnian, Late Triassic). Distinct from Sclerosaurus, the femur is longer, the coracoid is smaller. The antebrachium is longer. As in Trionyx, pedal digit 5 is gracile. The specimen was found in mudstones. Note the wide, flat torso, the tall, slender scapula, sigmoidal femur and long-clawed toes… all turtle traits.

Colbert reported,
“The skull seems to have been unusually large in comparison to the size of the postcranial skeleton. The posterior portion of the skull is produced back into a “frill,” as is common in the advanced procolophonids, this frill covering about five cervical vertebrae. There are 25 presacral vertebrae, to which are articulated widely spreading holocephalous ribs. The scapula is rather slender, the ilium seemingly deep. The pubis and ischium are platelike bones, the former being proximally constricted and distally expanded. The hind limbs are large, the extended limb being approximately equal in length to the total length of the presacral series of vertebrae. In total length and in each of its component sections the linear dimensions in the hind limb are about double those in the fore limb. The metatarsals are rather slender, and long. The ungual phalanges of the pes are large, pointed claws.”

Figure 4. Sclerosaurus reconstructed.

Figure 4. Sclerosaurus reconstructed.

Colbert continues,
“Perhaps the most striking differences between this form and the established genera of procolophonids are in the great length and robust size of the hind limb in the Pennsylvania specimen, and the long, sharp claws of the pes. Such characters might lead one to doubt the true procolophonid relationships of Sphodrosaurus, but other characters, such as size, the obviously large skull, the extension of the back of the skull in a sort of frill over the cervical region, the evidently broad vertebral neural arches (as indicated by the separation of the heads of the ribs), and the holocephalous, flaring ribs, are all characters that point to procolophonid affinities for Sphodrosaurus.”

The following paper
was discovered after the reconstruction and phylogenetic analysis were made:

Sues, Baird and Olsen 1993 reexamined Sphodrosaurus
and determined that the specimen was not a procolophonid, but some sort of diapsid or neodiapsid. They note, Baird (1986) suggested rhynchosaurine affinities. They also note “This combination of characters has not been found in any other known diapsid.” 

The authors note
the preservation of the posterior mandibles, rather than a set of dorsal skull bones as Colbert reported. They failed to see the detached retroarticular process. The cervicals and anterior dorsals have a ventral ridge. So do soft-shell turtles, but the authors did not make that connection. What they identify as extremely long cervicals parallel to the spine and apparently coosified are interpreted here as clavicles. They remarked on the “great width of the trunk region,” as in pareiasaurs and turtles, but the authors did not make that connection. They note the scapula has a “slender  blade”, as do turtles, but the authors did not make that connection. They note the femur is sigmoidal, as in turtles, but the authors did not make that connection.

The authors conclude,
“The mode of preservation of the holotype and only known specimen of Sphodorsaurus pennsylvanicus leaves very few anatomical features for assessing its phylogenetic position.” This is true, but phylogenetic analysis over a wide gamut of potential candidates leaves no doubt in the LRT about where this specimen nests, based on the characters that are visible. There is no mention of pareiasaurs or turtles in the Sues, Baird, Olsen 1993 paper.

As in many enigma taxa studied here,
the solution to their nesting problem appears whenever the enigma taxon is permitted to be tested against a wide gamut of taxa. This minimizes initial bias and lets the software do what it was intended to do… keep human preconceptions from interfering in a cold-blooded scientific process.

Added later the same afternoon
Rice et al. 2016 report: “We show that plastron development begins at developmental stage 15 when osteochondrogenic mesenchyme forms condensates for each plastron bone at the lateral edges of the ventral mesenchyme.” In this way ontogenesis recapitulates the phylogenesis demonstrated by Sphodrosaurus.

References
Colbert EH 1960. A new Triassic procolophonid from Pennsylvania. American Museum Novitates 2022:1–19.
Rice R, Kallonen A, Cebra-Thomas J and Gilbert SF 2016. Development of the turtle plastron, the order-defining skeletal structure. PNAS 113 (19):5317–5322.
Sues H-D, Baird D and Olsen PE 1993. Redescription of Sphodrosaurus pennsylvanicus Colbert, 1960 (Reptilia) and a Reassessment of its Affinities. Annals of Carnegie Museum 62(3):245-253

wiki/Arganaceras
wiki/Sclerosaurus
http://reptileevolution.com/arganaceras.htm

North Museum of Nature and Science
Franklin and Marshall College
400 College Avenue
Lancaster, PA 17603
717.358.3941

The origin and evolution of bats part 4: distance vs. accuracy

Earlier
we looked at bat origins here, here and here from several perspectives. Some of these are now invalid given the following scenario.

Today we’ll take a fresh look at
the behavior and traits of the closest bat relatives in the large reptile tree (LRT, 1233 taxa, subset Fig. 1) and see what they can tell us about bat origins. This is called ‘phylogenetic bracketing‘. In such a thought experiment we can put forth an educated guess regarding an unknown behavior or trait for a unknown taxa (e.g. pre-bats) if all related specimens share similar behaviors and traits inherited from a known or unknown last common ancestor.

We start off with a cladogram
focusing on bat relationships (Fig. 1) and take things one logical step at a time.

Figure 1. Subset of the LRT focusing on basal placentals, including bats.

Figure 1. Subset of the LRT focusing on basal placentals, including bats.

One. Living sister taxa.
The closest tested sister taxa to bats here (Fig. 1) are pangolins and colugos (flying lemurs) in order of increasing distance. The origin of bats and pangolins has remained a traditional enigma. Like the origin of pterosaurs and Longisquama, the surprise is, they are most closely related to each other, despite their current differences.

Two. Ancestral taxa
Th bat/colugo/pangolin clade had its genesis near the original dichotomy of placental mammals, when Carnivora split off from all others. At the next dichotomy the bat/colugo/pangolin clade split off from all others. So this clade is not far from an ancestral clades with living genera. Monodelphis, the short-tailed opossum today restricted to South America, nests just outside of all mammals with a placenta. Nandinia, the African palm civet, is a basal member of the Carnivora, somewhat larger than its Mesozoic forebearers.

Three. Timing for clade origins
The bat/colugo/pangolin clade had its origin in the Early Jurassic based on the more primitive egg-layers, Megazostrodon, Brasilitherium and Kuehneotherium in the Late Triassic and the much more derived arboreal multituberculate/rodent, Megaconus, in the Middle Jurassic. As you can see, Jurassic mammals remain extremely rare, currently represented only by the likes of Megaconus. Others will, no doubt, be discovered in time.

Four. Arboreality (tree niche)
Some bats, colugos and pangolins live in trees, and so do their last common ancestors, short-tailed opossums and African palm civets.

Five. Climbing trees
Bats no longer have to climb trees because they can fly. Colugos and pangolins both climb trees in a series of symmetrical short hops/extended reaches (colugo video, pangolin video), distinct from palm civets and short-tailed opossums, which put forth one hand at a time, like primates do.

Six. Descending trees.
Bats fly between trees. Colugos glide between trees. Pangolins use their prehensile tail to ease themselves down. The African palm civet drops out of trees in play. It also descends tree trunks like a squirrel, head first.

Seven. Nocturnal
Most bats, colugos, pangolins, palm civets and short-tailed opossums prefer to be active at night.

Eight. Omnivorous diet
Some bats eat insects, others prefer nectar or hanging fruit. Colugos prefer leaves, shoots, flowers, sap, and fruit. Pangolins eat ants. Palm civets and short-tailed opossums are omnivorous. African palm civets feed by holding their prey in their hand-like front paws, biting it repeatedly and then once dead, swallowing it whole.

Nine. Extradermal membranes
Colugos and bats both have extradermal membranes to their unguals that extend their glides in the former and enable flapping flying in the latter. Such membranes are lost in living pangolins, but the Early Cretaceous pangolin, Zhangheotherium appears to have scale-lined membranes between the elbows and knees. These were overlooked in the original description. The gliding membrane in colugos is fur-covered and camouflaged dorsally, naked underneath. In bats the flying membrane is naked, translucent and never camouflaged.

Ten. Mobile clavicle, interclavicle and scapula
The basal pangolin, Zhangheotherium, has a mobile clavicle-interclavicle and the large scapula rises above the  dorsal vertebrae, as in bats, but not colugos.

11. Sprawling femora
Zhangeotherium and bats share sprawling hind limbs, distinct from the more erect hind limbs of most limbed mammals.

12. Silent vs. noisy
African palm civets are noisy. Colugos and pangolins are largely silent. Bats are constantly chirping to one another and (micro-bats only) as part of their sonar attack system.

13. Enemies
All current enemies of bats (e.g. birds, snakes) evolved during or after the Late Cretaceous. Jurassic trees might have been a refuge for small early climbing mammals, like colugo, bat and pangolin ancestors. However…the minimally feathered, small theropod dinosaur, Sinosauropteryx, contained the jaws of Zhangheotherium, perhaps caught after descending from the trees or plucked out of lower branches. Certain pterosaurs (e.g. giant anurognathids) might have preyed on arboreal  mammals in the Jurassic, but no evidence of this is yet known.

FIgure x. Calcaneal spur in Zhangheotherium. Not venomous, but perhaps to anchor a uropatagium.

FIgure 2. Calcaneal spur in Zhangheotherium. Not venomous, but perhaps to anchor a uropatagium as in bats.

14. Calcaneal spurs
Hurum et al. 2006 originally considered the small spurs found on the calcaneum of Zhangheotherium (Fig. 2) similar to venom spurs found on the platypus, Ornithorhynchus. Phylogenetic bracketing indicates the closer homolog is with the basal bat, Onychonycteris, which has longer calcaneal spurs framing a trailing uropatagium.

Figure x. Monodelphis babies in an open pouch. This is how placentals began, slowly evolving from the less open pouch.

Figure 3 Monodelphis babies in an open pouch. This is how placentals began, slowly evolving from the less open pouch.

15. Newborns and mothers
All basal placental mammals give birth to helpless newborns that ride with the mother until mature enough to go out on its own. Monodelphis demonstrates a primitive version of this, protecting its ten young with lateral flaps of skin (Fig. 3). Carnivore mothers make nests for newborns (2-4 for African palm civets), but colugo, bat and pangolin mothers take their one or two babies everywhere they go, like marsupial mothers do. Zhangheotherium might have been fossilized with several newborns. (Fig. 4) and extradermal membranes between elbows and knees, as in bats and colugos. As we know from colugos, these extradermal membranes in basal pangolins (and Chriacus?) likely formed a playpen or nursery for developing young riding beneath their mother during the earliest stages of development.

Figure x. Zhangheotherium showing possible extradermal membranes (green) with keratinous scales (red) and several newborns scattered in the abdominal area, similar to Monodelphis in figure x.

Figure 4. Zhangheotherium showing possible extradermal membranes (light blue and green) with keratinous scales (red) and several newborns scattered in the abdominal area, similar to Monodelphis in figure x. These amorphous blobs with tiny tail bones need further inspection. Some may just be stains and shapes.

16. Curling (flexing the spine)
Mother opossums, palm civets, colugos, bats and pangolins are able to curl their spines so much that the mother’s mouth is able to assist wiggling newborns climb to the abdominal nipples. This curling ability is co-opted by pangolins as they defend themselves by rolling into a tight ball and by bats that catch prey in their tail before curling up to bite the victim as it is brought close to the jaws. Higher mammals lose the ability to curl ventrally in this manner. Humans and other primates have a limited ability to do this. Instead they use their hands. More derived mammals with stiffer backs have more developed newborns.

17. Upside-down vs. right-side up nursery for the young
Colugos may rest right-side up (preferring to hang from below a slightly leaning tree trunk) or upside down hanging by all fours beneath a horizontal branch. When doing so the mother’s extradermal membranes form walls making a protective nursery for the young ones.

By contrast, bats rest up-side down, sometimes hanging by only one locked foot. To fly bats simply release this foot lock, then plummet and start flapping. Bat membranes also provide a protective nursery for their young as they cling to their mothers’ chest and her wings fold over them.

Nowadays pangolins roll into a ball while nursing their young. Later in life, babies ride on the mother’s back and tail when able to do so. Zhangheotherium (Fig. 4) appears to have provided a colugo-like, but scale-lined membrane nursery for several growing babies. The late-surviving pre-bat, Chriacus (Fig. 5), likely did the same, based on phylogenetic bracketing.

18. Claws
Short-tailed opossums and African palm civets use their claws to climb trees and grab prey and fruit, bringing it to the mouth. So do basal primates. Colugos, bats and pangolins use their larger, curved claws principally to hang from trees, though living pangolins have co-opted their large claws to dig out ant and termite nests from trees and underground.

19. Distance vs. accuracy
Colugos leap and turn away from their tree trunk base in order to launch themselves into a glide. Can they do this while hanging beneath a branch? I don’t know. With their long limbs, colugos can just leap (without gliding) across gaps of 5m or more. With limbs extended, they can glide for 136m at 10m/second. Gliding is good for a quick escape from predators, and access to patches of food that are otherwise inaccessible. It does not save them energy to glide, let along climb back to a gliding height.

Bats drop from trees, then fly wherever they please, typically landing upside down on another high branch or cavern roof. The origin of bat flight enabled by flapping hyper-elongated webbed fingers is the key question here, and it is answered by combining all of the above numbered traits.

Before bats could fly Jurassic pre-bats had to climb trees, probably like colugos and pangolins do (see #5 above), before standing bipedally, but upside-down, on a horizontal branch. Why would they do that? To prepare to dive bomb insects on and in the leaf litter below. Here is where sonar became valuable, detecting insects in the leaf litter at night. Here is where the leaf litter became valuable, cushioning the early awkward landings of small dive-bombing pre-bats. Here is where flapping, even with small hands around colugo-like dermal membranes became valuable, at first in panic, then in gradually learning how to better direct the fall to cover the prey below.  (By analogy birds flap their wings vigorously while dropping to slow their descent.)

Upon landing the extended pre-bat nursery membranes ‘put a lid’ on the prey. Then, curling the tooth-line jaws toward the tail and the tail toward the jaws (see #16 above) spelled doom for the captured food item. Over time, larger fingers made better flapping parachutes. Ultimately flapping bats  learned how to hover before diving bombing their prey, like owls do. Later, after further development, bats gained the power and morphology to enable flight, slowly at first, then better and better to escape ground-dwelling predators and avoid having to climb a tree for the next attack. Only later did bats learn to use their sonar and flying skills on flying insects.

So what began as a small pouch, then a larger nursery membrane for bat and colugo infants became a killing zone for bat prey on the ground, another example of co-opting an old trait for a new behavior in derived taxa. Distinct from birds and pterosaurs, which used their nascent flapping behavior to ascend tree trunks to escape predators, create threat displays and slow their descents from branches, bats used their nascent flapping ability only to slow and direct their descent from branches. Distinct from colugos, which glided for distance, bats dropped for accuracy. Distance came later, after flight developed.

Remember the fall need not be far at first. Conifers can have very low branches and leaf litter can be a soft cushion for a mouse-sized mammal. Graduating slowly to higher branches provides bats a wider ‘field-of-view’ for their slowly developing sonar, and more time to develop flapping. Bat hind limbs are not long or heavily muscled. They are not good at leaping, like colugos.

Fruit eating bats could not have developed until flowering and fruit-bearing trees developed, later in the Cretaceous. The LRT and the fossil record indicates that fruit-eating bats are derived relative to smaller insect-eating bats. So sonar-emitting apparently was lost in fruit-eating bats, rather than never a part of their lineage. The great variation now seen in sonar-emitting bat morphology was likely developed during and after the Cretaceous, based on the current fossil record. I think we’ll find fully volant fossil bats in the Cretaceous someday.

I happened upon this idea while watching a pigeon descend from a roofline to a balcony beneath it and wondered if accuracy was more important for bats, while distance was more important for colugos. That distinction seems to be the key driver in both clades. In any case, it is important that any proposed scenario be viable at every point during the gradual evolution of new traits and behaviors. In this case, developing flapping forelimbs had to originate with a bipedal configuration, even it inverted. Developing sonar had to originate from simply listening to nocturnal insects and other small prey rustling in the leaf litter, not far below, gradually getting better in those families that randomly had slightly better skills once dive-bombing and trapping became the method for predation.

20. Bat ontogeny
Recapitulates this phylogenetic scenario. The fingers elongate last. 

21. Solitary vs. communal
Colugos and pangolins are solitary. So are African palm civets except when food is plentiful. Bats are communal, whether nesting in trees or caves. According to Kerth 2008, “Variable dispersal patterns, complex olfactory and acoustic communication, flexible context-related interactions, striking cooperative behaviors, and cryptic colony structures in the form of fission-fusion systems have been documented. tropical bats often form groups year-round, whereas sociality in temperate-zone species is sometimes restricted to certain times of the year. In most species, females form so-called maternity colonies to rear their young communally, whereas males are solitary, form groups of their own, or join female groups. In only a few species are both sexes solitary, meeting only to mate.”

Kerth concludes, “None of the three factors that I identify as important for the evolution of sociality in bats (ecological constraints, physiological demands, and demographic traits) can fully explain the frequency and diversity of group living in bats.”

Figure 1. Basal placentals at two scales, all arising from a Middle Jurassic sister to Monodelphis, based on the Earliest Cretaceous appearance of Zhangheotherium, in the lineage of pangolins.

Figure 5. Basal placentals at two scales, all arising from a Middle Jurassic sister to Monodelphis, based on the Earliest Cretaceous appearance of Zhangheotherium, in the lineage of pangolins..

22. Soles of the feet oriented opposite to those of most mammals
Distinct from most mammals, the knees of bats are splayed laterally, which should extend the toes laterally. However, the ankle is rotated another 90º producing a foot in which the soles are ventral during flight and while hanging. In the case of long-legged fish-eating bats, the feet help bring captured fish back to the mouth.

FIgure 1. Wondering if Chriacus had an inverted stance and dermopteran membranes? Comparisons to Onychonycteris and Pteropus.

FIgure 6. Wondering if Chriacus had an inverted stance and dermopteran membranes? Comparisons to Onychonycteris and Pteropus are shown. Yes, the knees are straight in derived fruit bats, bent in Onychonycteris and micro bats. The uropatagia are spread while inverted and while flying. Chriacus appears to be a much larger and much later-surviving version of much smaller Jurassic pre-bats. The membranes are conjectural and may have been lost in this large specimen, but it illustrates the possibility of a dive bombing taxon that covered prey like a casserole lid.

Why do bats hang upside down?
Without a phylogenetic or deep-time perspective, the following video is the best answer current bat workers can provide:

Bats are not using their wings to cool off.
A recent heat wave killed many fruit bats. They fell dead out of the trees (see below). None were creating a cooling breeze with their wings or extending their wings in a cooling fashion, like elephants sometimes do. Microbats that live in caves never have this problem.

Bat wings notes:

  1. Finger flexibility during flight varies greatly in bats.
  2. The flight stroke is otherwise bird-like with elbows raised above the back, nearly meeting at the midline, for maximum power at low airspeed, or less so for cruising at higher airspeeds.
  3. The large fingers do nothing else but push air for thrust and lift. They are not extended to cool the bat, nor do they extend or flash during courtship.
  4. Bat fingers hyper flex at the wrist to tuck away the flight membrane and reduce its surface area when not in use, as in pterosaurs and birds. When flexed they do little but envelope the bat and its clinging young.

Miscellaneous notes:

  1. Zhangheotherium was originally considered a symmetrodont mammal, but its teeth seems to converge with archaeocete whales in this regard. The reappearance of a more primitive symmetrodont molar shape is here considered an atavism in the evolution of toothlessness in both certain odontocetes and pangolins by convergence.
  2. The uncoiled cochlea of highly derived Zhangheotherium and multituberculates, has been traditionally considered a trait that nests these taxa in more basal branches of the mammal family tree. Here, in the LRT, these traits appear to be neotonous or atavistic developments that, taken alone, tend to confuse systematics. No traits should ever be taken alone to determine systematics. That would be ‘pulling a Larry Martin.’
  3. The initial splitting up of Pangaea in the Early Jurassic gave the previously dry climate a more lush, subtropical parade of cycads, conifers, ginkgoes and tree ferns. So there were plenty of standing and fallen trees for early mammals to gambol upon, learning how to climb and leap. The forest floor was likely cushioned with a carpet of leaves and fronds to absorb accidental falls and hunger-driven dive bombs mediated by fluttering pre-wings and large membranes co-opted for eventual flight.

Addendum
Video showing a bat descending on a mouse in leaf litter appears here.

References
Byrnes, Libby, Lim & Spence. 2011. Gliding saves time but not energy in Malayan colugos. Journal of Experimental Biology http://dx.doi.org/10.1242/jeb.052993
Hurum JH, Luo Z-X and Kielan-Jaworowska Z 2006. Were mammals originally venomous? Acta Palaeontologica Polonica 51(1): 1–11.
Kerth G 2008. Causes and Consequences of Sociality in Bats. BioScience, Volume 58, Issue 8, 1 September 2008, Pages 737–746, https://doi.org/10.1641/B580810
Online here.

Tulerpeton restoration

A reconstruction
puts the in situ bones back into their in vivo places.

A restoration
imagines the bones and soft tissues that are missing from the data. Adding scaled elements from a sister taxon is usually the best way to handle a restoration as we await further data from the field.

Figure 1. Tulerpeton restored based on the bauplan of Silvanerpeton and to the same scale.

Figure 1. Tulerpeton restored based on the bauplan of Silvanerpeton and to the same scale.

We looked at
Tulerpeton, the Upper Devonian taxon known chiefly from its limbs, earlier. I reconstructed the limbs several ways, but did not attempt a restoration. Here (Fig. 1) that oversight is remedied based on the bauplan of Viséan sister, Silvanerpeton. 

Among the overlapping elements,
in Tulerpeton the pectoral girdle and forelimbs are larger. An extra digit is present laterally.

References
Clack JA 1994. Silvanerpeton miripedes, a new anthracosauroid from the Visean of East Kirkton, West Lothian, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 84 (for 1993), 369–76.
Coates MI and Ruta M 2001
 2002. Fins to limbs: What the fossils say. Evolution & Development 4(5): 390–401.
Lebedev OA 1984. The first find of a Devonian tetrapod in USSR. Doklady Akad. Navk. SSSR. 278: 1407–1413.
Lebedev OA and Clack JA 1993. Upper Devonian tetrapods from Andreyeva, Tula Region, Russia. Paleontology36: 721-734.
Lebedev OA and Coates MI 1995. postcranial skeleton of the Devonian tetrapod Tulerpeton curtum Lebedev. Zoological Journal of the Linnean Society. 114 (3): 307–348.
Mondéjar-Fernandez J, Clément G and Sanchez S 2014. New insights into the scales of the Devonian tetrapods Tulerpeton curtum Lebedeve, 1984. Journal of Vertebrate Paleontology 34:1454-1459.

wiki/Silvanerpeton
wiki/Tulerpeton

Juvenile articulated Eusaurosphargis discovered

Scheyer et al. 2017
bring us a new largely articulated juvenile Eusaurosphargis specimen (PIMUZ A/III 4380; Figs. 1–3) very similar to the adult disarticulated specimen described by Nosotti and Rieppel 2003 (BES SC 390; Middle Triassic, ~240 mya, ~20 cm snout to vent length). Scheyer et al. had trouble nesting Eusaurosphargis correctly as a derived thalattosaur largely due to taxon exclusion (see below).

Figure 1. Adult and juvenile Eusaurosphargis specimens to scale.

Figure 1. Adult and juvenile Eusaurosphargis specimens to scale. The adult was disarticulated.

The old ‘adult’ specimen
was considered more closely related to Helveticosaurus (Fig. 4) than to placodonts. Here both Eusaurosphargis and Helveticosaurus nest within the Thalattosauriformes close to armored Vancleavea. Here Eusaurosphargis does not nest close to turtle-like Sinosaurophargis. The adult skeleton is completely disarticulated. That makes reconstruction particularly difficult. Thus the order of the traced vertebrae in dorsal view (Fig. 1) is largely guesswork. Likewise, the skull included some guesswork helped by phylogenetic bracketing.

Figure 2. The in situ juvenile specimen of Eusaurosphargis, the original tracing and DGS tracing of dorsal ribs (blue) and sternal ribs (green).

Figure 2. The in situ juvenile specimen of Eusaurosphargis, the original tracing and DGS tracing of dorsal vertebrae and elongated transverse processes (blue) and dorsal ribs (green). The specimen was exposed from below, but preserved right side up, hence the slight disarticulation of dorsal elements and the skull in marine sediments. CT scans indicate the buried sacral ribs were longer than traced here. 

The new ‘juvenile’ specimen
has a disarticulated skull, but most of the elements appear to be present, though some were originally unidentified and the squamosal, now a jugal, was misidentified.

Figure 3. Eusaurosphargis juvenile skull, pectoral and pelvic girdles reconstructed.

Figure 3. Eusaurosphargis juvenile skull, pectoral and pelvic girdles reconstructed. GIF animation second frame shows two views of the in situ skull. The juvenile includes articulated extremities. Boxed elements are the purported squamosals, here identified as jugals. Scheyert et al. did not attempt a skull reconstruction.

Scheyer et al. report
the armor and other elements “support an essentially terrestrial lifestyle for Eusaurosphargis and and that within the marine reptile ‘superclade’ E. dalsassoi potentially is the sister taxon of Sauropterygia.” Neither are supported by the large reptile tree (LRT 1027 taxa), which resurrected the clade, Enaliosauria for Scheyer’s ‘superclade.’

The elongated dorsal transverse processes
and osteoderms are convergent with those in placodonts and sinosaurosphargids.

The jugals are much larger than the squamosals
as in Helveticosaurus and Vancleavea. For reasons unknown, Scheyer et al. erroneously compared these elements with those of the more distantly related Askeptosaurus, which ALSO has tiny squamosals, like most, if not all, thalattosaurs.

Phylogenetic analysis
The Scheyer et al. inclusion set excludes so many pertinent taxa that it nests turtles with archosaurs and lepidosaurs. It also nests Eusaurosphargis close to placodonts. Correctly it nests Eusaurosphargis close to Helveticosaurus and Thalattosauriformes. Vancleavea was not included. It is clear that Scheyer et al. have no idea how the major taxa are actually arranged as documented in the LRT for the last seven years. They also employed suprageneric taxa. There’s no reason for such unprofessional  guessing to continue in professional studies.

Figure 4. Helveticosaurus had cheek teeth that look like baleen strainers and long fangs anteriorly. It was also much larger than Eusaurosphargis but was coeval. Vancleavea is shown to scale and to the same length.

Figure 4. Helveticosaurus had cheek teeth that look like baleen strainers and long fangs anteriorly. It was also much larger than Eusaurosphargis but was coeval. Vancleavea is shown to scale and to the same length.

‘Homologies’ reported by Scheyer et al.:
“PIMUZ A/III 4380 shares with Palatodonta bleekeri (and placodonts such as Paraplacodus broilii and Placodus gigas) the deep skull shape and wide snout with large external nares, as well as the double tooth row in the upper jaw (on the maxillae and palatines) and a single row in the lower jaw.” These traits are likewise found by homology in Helveticosaurus and Vancleavea where known. Scheyer et al. feel the freedom to make these comparisons to placodonts because their incorrect (based on massive taxon exclusion) cladogram nests Eusaurosphargis close to placodonts. This is the authority of the LRT and its large gamut, specimen-based taxon list at work. When Scheyer et al. have a comparable taxon list, then we can discuss differences in scoring, if they arise.

Terrestrial?
Scheyer et al. report, “Given the large number of pachypleurosaurs of similar size range, among a plethora of thousands of other fossils, we corroborate the previous idea that E. dalsassoi had a terrestrial habitat preference.” This makes no sense. In the LRT pachypleurosaurs arise from marine taxa and give rise to marine taxa. Thus, based on phylogenetic bracketing. pachypleurosaurs are marine (or at least aquatic), too,

Scheyer et al. report, “the short and proximally dorso-ventrally wide tail would be similarly inefficient in providing propulsion.” You don’t have to get around fast in order to be aquatic. The flattened turtle-like appearance of several saurosphargids and placodonts have similar short-comings. And look at Helveticosaurus, the acknowledged sister (Fig. 4).

Scheyer et al. report,The stylopodial elements (humerus and femur) are tubular, moderately thin-walled bones with large marrow cavities” typical of terrestrial, not marine diapsids. They do not report similar tests on the universally accepted sister taxon, Helveticosaurus (and Vancleavea), but the proximal limb elements look similar from the outside (Fig. 4).

The All-Aquatic Superclade of Chen et al. 2014
does not include mosasaurs, but does include a few representatives of most other marine clades (but not nearly the number of taxa as in the LRT). While this is confirmation of the results first reported here in 2011, the topology of the Chen et al. cladogram has serious problems all based on taxon exclusion. Such problems are minimized in the LRT based on its large gamut where there is no need to ‘delete problematic characters’ in order to achieve a result that makes sense. 

A larger gamut phylogenetic analysis
nests Helveticosaurus, Vancleavea and Eusaurosphargis within the Thalattosauriformes, despite over 1020 opportunities to nest elsewhere. Their disparate morphologies hint at further transitional and unusual morphologies to come.

Congeneric? Yes. Conspecific? No.
The smaller Eusaurosphargis nests with the larger one in the LRT. So they could be congeneric. However, comparing the reconstructions of the two shows several differences in the skull bones that preclude the two from being conspecific. Such juvenile/adult conspecific relationships in fossils found years apart and miles apart are, by their very nature, very rare, but they do occur.

References
Chen X-H, Motani R, Cheng L, Jiang D-Y and Rieppel 2014. The Enigmatic Marine Reptile Nanchangosaurus from the Lower Triassic of Hubei, China and the Phylogenetic Affinities of Hupehsuchia. PlosOne online.
Nosotti S and Rieppel O 2003. Eusaurosphargis dalsassoi n.gen. n.sp., a new, unusual diapsid reptile from the Middle Triassic of Besano (Lombardy, N Italy). Memories of the Italian Society of Natural Science and the Museum of Natural History in Milan, XXXI (II).
Scheyer T et al. (5 other authors) 2017. A new, exceptionally preserved juvenile specimen of Eusaurosphargis dalsassoi (Diapsida) and implications for Mesozoic marine diapsid phylogeny. Nature.com/scientific reports online.

wiki/Eusaurosphargis

Variation among indricotheres (giant horse-rhinos)

Earlier we looked at the now heretical nesting of giant indricothere perissodactyls closer to horses than to living rhinos, their traditional relatives. We also touched on that subject here and here.

Also
there has been a movement (Lucas and Sobus 1989) to make many of the largest indricotheres congeneric. A look at the skulls (Figs. 1) suggests otherwise.

Figure 1. Indricothere skulls to scale along with horse and rhino skulls.

Figure 1. Indricothere skulls to scale along with horse and rhino skulls. Clearly the giant skulls, all indricotheres, are not congeneric. Aceratherium is more closely related to the extant horned rhino Ceratotherium.

Wikipedia reports
Indricotheriinae is a subfamily oHyracodontidae, a group of long-limbed, hornless rhinoceroses convergently similar to the sauropod dinosaurs that evolved in the Eocene epoch and continued through to the early Miocene.” By contrast, in the large reptile tree (LRT, 1012 taxa) Hyracodon nests at the base of extant rhinos, apart from the horse/indricothere branch.

Figure 2. GIF movie (3 frames) showing what is known of the skeletons of Baluchitherium and Indricotherium. Note the more horse-like morphology.

Figure 2. GIF movie (3 frames) showing what is known of the skeletons of Baluchitherium and Indricotherium. Note the more horse-like morphology. All reconstructions are chimaeras of known specimens. That doesn’t mean they are congeneric.

A new Pappaceras illustration
(Wood 1963; fig. 3) is more horse-like than others in having an orbit in the (probable) posterior half of the skull.

Figure 3. Pappaceras confluens A.M.N.H. No. 26660 and A.M.N.H. No. 26666 (mandible)

Figure 3. Pappaceras confluens A.M.N.H. No. 26660 and A.M.N.H. No. 26666 (mandible). With such posetriorly-placed eyes, this skull is more horse-like than other rhinos. 

The post-crania of Indricotherium
appears to include the only vertebral column known for this clade. IF so the vertebrae cannot be imagined as similar to that of a rhino (Fig. 2). And maybe, just maybe those indricothere limbs were covered with more gracile muscles and thinner skin, like those of a horse, not a rhino, tradition not withstanding. based on phylogenetic bracketing.

References
Chow M and Chiu C-S 1964. An Eocene giant rhinoceros. Vertebrata Palasiatica, 1964 (8): 264–268.
Forster-Cooper C 1911. LXXVIII.—Paraceratherium bugtiense, a new genus of Rhinocerotidae from the Bugti Hills of Baluchistan.—Preliminary notice. Annals and Magazine of Natural History Series 8. 8 (48): 711–716.
Forster-Cooper C 1924. On the skull and dentition of Paraceratherium bugtiense: A genus of aberrant rhinoceroses from the Lower Miocene Deposits of Dera Bugti. Philosophical Transactions of the Royal Society B: Biological Sciences. 212 (391–401): 369–394.
Granger W and Gregory WK 1935. A revised restoration of the skeleton of Baluchitherium, gigantic fossil rhinoceros of Central Asia. American Museum Novitates. 787: 1–3.
Lucas SG and Sobus JC 1989. The Systematics of Indricotheres”. In Prothero DR and Schoch RM eds. The Evolution of Perissodactyls. New York, New York & Oxford, England: Oxford University Press: 358–378. ISBN 978-0-19-506039-3.
Osborn HF 1923. Baluchitherium grangeri, a giant hornless rhinoceros from Mongolia. American Museum Novitates. 78: 1–15. PDF
Pilgrim GE 1910. Notices of new mammalian genera and species from the Tertiaries of India. Records of the Geological Survey of India. 40 (1): 63–71.
Wood HE 1963. A primitive rhinoceros from the Late Eocene of Mongolia. American Museum Novitates 2146:1-11.

wiki/Juxia
wiki/Paraceratherium

Where is the rest of Lanthanolania?

It was back in 2011
when the post-crania of Lanthanolania (Fig. 1) was reported in an abstract by Modesto and Reisz. Prior to that, in 2003, only the skull was described by the same authors. Over the last six years the post-crania of Lanthanolania has not been published.

From the 2011 SVPCA abstract:
“The evolutionary history of Diapsida during the Palaeozoic Era is remarkably poor. Following the reclassification of the Early Permian Apsisaurus witteri as a synapsid last year, only a handful of taxa span the large temporal gap between the oldest known diapsid Petrolacosaurus kansensis and the Late Permian neodiapsid Youngina capensis. These include two Middle Permian neodiapsids, the recently described Orovenator mayorum from Oklahoma, USA, and Lanthanolania ivakhnenkoi from the Mezen region, northern Russia. A recently collected, nearly complete skeleton of Lanthanolania permits a thorough reexamination of the phylogenetic relationships of these two taxa.

“Phylogenetic analysis of 188 characters and 30 diapsid taxa positions these two small forms as stem saurians and the oldest known neodiapsids (recently redefined by the authors as the sister taxon of Araeoscelidia). Interestingly, our results suggest that the lower temporal bar was lost by the ancestral neodiapsid relatively soon after the evolution of the diapsid temporal morphology, and conversely, that the temporal configuration of the Late Permian Youngina capensis is a secondary condition. In addition, the skeletal anatomy of Lanthanolania provides evidence of limb proportions that suggest that this small reptile is the oldest known bipedal diapsid.”

Figure 1. Kuehneosaurid skulls from Palaegama to Coelurosauravus and Mecistotrachelos, and to Lanthanolania, Pamelina, Kuehneosaurus, Icarosaurus and Xianglong. Some of these taxa were not previously recognized as kuehneosaurids or their ancestors.

Figure 1. Kuehneosaurid skulls from Palaegama to Coelurosauravus and Mecistotrachelos, and to Lanthanolania, Pamelina, Kuehneosaurus, Icarosaurus and Xianglong. Some of these taxa were not previously recognized as kuehneosaurids or their ancestors.

Earlier (2011) the large reptile tree (LRT) nested Lanthanolania with the so-called rib gliders between Coelurosauravus and Icarosaurus. Back then we looked at those issues here.

Modesto and Reisz (2003) had a hard time
nesting Lanthanolania and considered it ‘enigmatic’. The closest they came was to nest Lanthanolania at the base of the lepidosauriformes (Rhynchocephalia + Squamata) and in other tests, with Coelurosauravus, which they split apart from the lepidosauriformes by adding intervening unrelated ‘by default’ taxa.

Unfortunately
with their small taxon list, Modesto and Reisz (2003) did not recover the basal split among reptiles that had occurred between the new Lepidosauromorpha and Archosauromorpha at Gephyrostegus + kin at the earliest Carboniferous. Thus the formerly monophyletic clade Diapsida is diphyletic in the LRT. Modesto and Reisz  mixed taxa from the two major clades and that muddied their results. Parts of their results were essentially correct, just unintelligible due to the addition of unrelated intervening archosauromorph basal diapsids.

Traditional paleontology
has likewise never nested coelurosauravids with kuehneosaurids, like Icarosaurus, perhaps based in part on the rib/dermal rod issue.

Problems and guesses:

  1. “Phylogenetic analysis of 188 characters and 30 diapsid taxa positions these two small forms as stem saurians and the oldest known neodiapsids (recently redefined by the authors as the sister taxon of Araeoscelidia).” — Sauria (= last common ancestor of archosaurs and lepidosaurs), is a junior synonym for Reptilia in the LRT. Neodiapsida (= includes all diapsids apart from araeoscelidians (= Petrolacosaurus and Araeoscelida)) or all taxa more closely related to Youngina than to Petrolacosaurus. Thus, in their thinking, Sauria is a clade within Neodiapsida. Modesto and Reisz do not yet recognize that Diapsida is no longer a monophyletic clade. In the LRT Orovenator and Lanthanolania are not related. The former is a basal diapsid archosauromorph. The latter is a basal lepidosauriform lepidosauromorph.
  2. “Interestingly, our results suggest that the lower temporal bar was lost by the ancestral neodiapsid relatively soon after the evolution of the diapsid temporal morphology,” — According to the LRT, the lower temporal bar was not lost nor was it present in the lepidosauromorph ‘rib’ gliders, including Lanthanolania. By contrast, Orovenator is one of the most basal archosauromorphs with an upper temporal fenestra.  Petrolacosaurus is older.
  3. “and conversely, that the temporal configuration of the Late Permian Youngina capensis is a secondary condition.” — In the LRT, it is not a secondary configuration, but is derived from basal diapsid taxa like Orovenator.
  4. “In addition, the skeletal anatomy of Lanthanolania provides evidence of limb proportions that suggest that this small reptile is the oldest known bipedal diapsid.” — I can only guess why they promoted this hypothesis: short torso and long hind limbs? Icarosaurus has such proportions. So does Kuehneosaurus. So does their last common ancestor, Palaegama (Fig. 2) which lacks wire-like dermal ossifications.
Figure 3. Palaegama, close to the origin of all Lepidosauriformes.

Figure 2. Palaegama, close to the origin of all Lepidosauriformes.

The question today is
where is the paper that describes the above-mentioned post-crania of Lanthanolania? Is the post-crania definitely referable?

If the referred specimen came from similar sediments
the matrix was described in 2003 as ‘extremely hard to work with’. Perhaps it is still being worked on. Or it has been shelved.

Phylogenetic bracketing
indicates that the new specimen might or should have wing-like wire/rod dermal elements, like those found in both Coelurosauravus and Icarosaurus, but traditionally considered ribs in Icarosaurus. They are not ribs, as we learned earlier here. The real ribs are short and fused to the vertebrae, appearing to be long transverse processes, but no related taxa have long transverse processes and not all of the ribs are fused to the vertebrae, betraying their identity. Since a mass of dermal rods was not mentioned in the abstract, one  wonders if the new specimen was actually closer to Palaegama than to Lanthanolania?

Late news from Sean Modesto about Lanthanolania:
“The project is currently in the hands of Dr. Reisz. No “ETA” as yet!”

Problems like this one
are a good reason to include the taxa the LRT suggests one include in smaller, more focused studies.

References:
Modesto SP and Reisz RR 2003. An enigmatic new diapsid reptile from the Upper Permian of Eastern Europe. Journal of Vertebrate Paleontology 22 (4): 851-855.
Reisz RR and Modesto SP 2011. The neodiapsid Lanthanolania ivakhnenkoi from the Middle Permian of Russia, and the initial diversification of diapsid reptiles.SVPCA abstract published online.

 

Phylogenetic bracketing and pterosaurs – part 2

Two posts ago we looked at part 1 of this topic.

Since pterosaurs (and other tritosaurs) nest between rhynchocephalians and squamates, there are a few traits they likely shared based on phylogenetic bracketing (unless specifically excepted based on fossil evidence). Putting the rhynchocephalians aside for the moment, according to Evans (2003) squamate traits include:

(1)  a specialized quadrate articulation with a dorsal joint typically supplied by the deeply placed supratemporal, reduced squamosal, and distally expanded paroccipital process of the braincase; reduction/loss of pterygoid/quadrate overlap; loss of quadratojugal — all present in basal tritosaurs, but quadrate becomes immobile in Macrocnemus and later taxa.

(2) loss of attachment between the quadrate and epipterygoid, with the development of a specialized ventral synovial joint between the epipterygoid and pterygoid — also present up to Huehuecuetzpalli, but absent in Macrocnemus and later taxa.

(3) subdivision of the primitive metotic fissure of the braincase to give separate openings for the vagus nerve (dorsally) and the perilymphatic duct and glossopharyngeal nerve (via the lateral opening of the recesses scalae tympani ventrally). This leads to the development of a secondary tympanic window for compensatory movements and is associated with expansion of the perilymphatic system and closure of the medial wall of the otic capsule — in fossil tritosaurs these details may not be known and certainly not by me… yet.

(4) loss of ventral belly ribs (gastralia) — Basal tritosaurs, up to Homoeosaurus have gastralia. Then they don’t until Macrocnemus and all later taxa.

(5) emargination of the anterior border of the scapulocoracoid — Basal tritosaurs share this trait. Macrocnemus and tanystropheids refill the emargination. Fenestrasaurs, including pterosaurs expand the emargination resulting in a strap-like scapula and stem-like coracoid, both representing the posterior rims of these bones.

(6) hooked fifth metatarsal with double angulation — shared with tritosaurs and more complex mesotarsal joint — in tritosaurs the mesotarsal joint is simple.

(7a) a suite of soft tissue characters including greater elaboration of the vomeronasal apparatus;

(7b) a single rather than paired meniscus at the knee;

(7c) the presence of femoral and preanal organs;

(7d) fully evertible hemipenes;

(7e) and pallets on the ventral surface of the tongue tip — none of these have been noted in soft tissue fossils.

References
Evans SE 2003. At the feet of the dinosaurs: the origin, evolution and early diversification of squamate reptiles (Lepidosauria: Diapsida). Biological Reviews, Cambridge 78: 513–551.