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.

 

Maybe horses are just tall, skinny, hornless rhinos…

Short one today,
With yesterday’s addition of two more basal rhinos to the large reptile tree (LRT 1010 taxa) maybe it’s time to change our thinking from ‘either horse or rhino’ to ‘horses are a type of rhino’. We know they are related. Maybe they are more intimately related than we first thought. That would make indricotheres like Paraceratherium giant hornless rhinos again, if you prefer it that way.

Figure 3. Subset of the LRT with the addition of Metamynodon and Amynodon, two former rhinos.

Figure 1. Subset of the LRT with the addition of Metamynodon and Amynodon, two former rhinos.

Even though,
in the LRT (subset Fig. 1) fewer taxa intervene at present between indricotheres and horses than indricotheres and extant rhinos, like Ceratotherium. Sort of like, you know, birds are a type of dinosaur. It just takes some getting used to – creating a new mental paradigm following the present data without excluding pertinent taxa.

 

Two more odd ‘hornless rhinos’ nest slightly elsewhere in the LRT

First a little backstory
Earlier, Paracerathierium and Juxiatwo traditional hornless rhinos, nested with three-toed horses in the large reptile tree (LRT, 1009 taxa, Fig. 3).

Figure 1. Metamynodon nests with Eotitanops. It had large fangs and a bulky body like a hippo.

Figure 1. Metamynodon nests with Eotitanops. It had large fangs and a bulky body like a hippo.

Today
the giant hippo-like traditional rhino, Metamynodon planifroms (Scott and Osborn 1867; Early Eocene; 4m long), nests with Eotitanops, the basal brontothere, though not far from Ceratotherium, the white rhino.

Figure 2. Amynodon was formerly linked to Metamynodon as a basal rhino, but here nests with Mesohippus.

Figure 2. Amynodon was formerly linked to Metamynodon as a basal rhino, but here nests with Mesohippus.

And
the smaller long-necked traditional rhino, Amynodon, nests with Mesohippus, the basal horse. Both were derived from a sister to Hyracotherium, basal to both rhinos and horses.

Amynodon advenus (Marsh 1877; 1m in length; Oligocene-Eocene, 40-23 mya) was originally considered an aquatic rhino. Here it nests with Mesohippus. The long neck and other traits are more horse-like than rhino-like. Manual digit 5 was retained. The skull was deeper as in basal forms like Hyracotherium.

Figure 3. Subset of the LRT with the addition of Metamynodon and Amynodon, two former rhinos.

Figure 3. Subset of the LRT with the addition of Metamynodon and Amynodon, two former rhinos.

Traditional cladograms
nest horses separate from tapirs + rhinos. The LRT nests horses with rhinos both derived from a sister to Hyracotherium and a sister to tapirs + chalicotheres. Traditional cladograms also avoid mixing brontotheres, horses and rhinos, like we do here.

References
Marsh OC 1877. Notice of some new vertebrate fossils. American Journal of Arts and Sciences 14:249-256
Scott WB and Osborn HF 1887. Preliminary account of the fossil mammals from the White River formation contained in the Museum of Comparative Zoology. Bulletin of the Museum of Comparative Zoölogy at Harvard College 13(5):151-171.

wiki/Mesohippus
wiki/Amynodontidae
wiki/Metamynodon

Advice for would be paleontologists: stay professional!

What do I mean by ‘stay professional’?
First of all, follow accepted scientific methods. Explore a wide gamut of possible solutions. And, more to the point of this blog: If you are going to make a comment about what a paleontologist has put forth as a hypothesis, keep your comments to the subject at hand. Use data, logic, your higher brain centers. Don’t abuse the author with personal insults that reflect how your inner monkey is feeling. In the professional world those forays into negativity can be labeled ‘ad hominem attacks” and they are not tolerated in academic publications (see below). More importantly, such comments can backfire on your professional reputation.

Several readers of this blog
have sunk below their professional dignity in their comments, perhaps because they became frustrated with what was being reported. It’s okay to feel frustrated. Just don’t let that enter your comments to anyone, anywhere. Stay professional in your demeanor.

The fact that Wikipedia
has a topic devoted to ad hominem attacks and various academic publications, like PlosOne forbid it (see below), tells you that it is commonplace.

Here are a few pulled quotes
from a recent blog on the subject.

  1. Aristotle argued that the ethos of a speaker is relevant to the persuasiveness of what they have to say. (ethos = the characteristic spirit)
  2. Everyone with critiques should continue coloring inside the lines, because that works. 
  3. There is no place for naming and shaming.
  4. “Trash talk” didn’t emerge only with social media: it has always been there. Case in point: the first Astronomer Royal called Edmond Halley, “a lazy and malicious thief” who manages to be just as “lazy and slothful as he is corrupt”. (Edmond Halley is widely revered today for his discoveries as an astronomer.)
  5. Avoid the ad hominem response: Just because you take offense, is not proof that offense was intended. Trying to separate that out makes it easier to see past the words and into the actual content, and gain analytic perspective.
  6. We have a lot to learn about each other and how to communicate in ways that get ideas across without diminishing people.
  7. Resist giving in to defensive emotion as much as you can: it clouds your vision.
  8. Pushing the envelope and collaborating in the open will push science forward.

From the PlosOne comments section:
Please follow our guidelines for comments and review our competing interests policy. Comments that do not conform to our guidelines will be promptly removed and the user account disabled. The following must be avoided:

  1. Remarks that could be interpreted as allegations of misconduct
  2. Unsupported assertions or statements
  3. Inflammatory or insulting language

Finally
When you go to conferences (= symposia), as I hope you will, and you meet your peers face to face, you will want to happily greet friends and colleagues, share dinner, discussions and hypotheses. This goes so much better when you haven’t tried to shame and disparage them.

The origin of the Mosasauria in the LRT

Figure 1. Tylosaurus represented by three species. T. kansasensis, T. proriger and T. dyspelor. Note the differences in flipper size.

Figure 1. Tylosaurus represented by three species. T. kansasensis, T. proriger and T. dyspelor. Note the differences in flipper size.

Wikipedia reports,
Mosasauria: “The exact phylogenetic position of the clade containing mosasaurids and their closest relatives (aigialosaurids and dolichosaurs) within Squamata remains uncertain. Some cladistic analyses recovered them as the closest relatives of snakes, taking into account similarities in jaw and skull anatomies; however, this has been disputed[ and the morphological analysis conducted by Conrad (2008) recovered them as varanoids closely related to terrestrial monitor lizards instead. Longrich, Bhullar and Gauthier (2012) conducted a morphological analysis of squamate relationships using a modified version of the matrix from the analysis of Gauthier et al. (2012); they found the phylogenetic position of the clade containing mosasaurs and their closest relatives within Squamata to be highly unstable, with the clade “variously being recovered outside Scleroglossa (as in Gauthier et al., 2012) or alongside the limbless forms”.

By contrast
the large reptile tree (LRT. 1006 taxa) nests the mosasaurs Tethysaurus and Tylosaurus with Aigialosaurus and this clade is a sister to the clade Saniwa + (Estesia + Varanus). All have a common ancestor that is a sister to Bahndwivici and Yabeinosaurus + Sakurasaurus. In other words, not close to snakes, earless monitors, Gila monsters or amphisbaenids.

Figure 2. Tylosaurus and other mosasaurs. Boxed: The shoulder girdle, left paddle and cartilaginous sternal cartilages of Tylosaurus in dorsal view. These broad ribs and sternum anchored powerful pectoral muscles to the front paddles.

Figure 2. Tylosaurus and other mosasaurs. Boxed: The shoulder girdle, left paddle and cartilaginous sternal cartilages of Tylosaurus in dorsal view. These broad ribs and sternum anchored powerful pectoral muscles to the front paddles.

Tylosaurus proriger (Marsh 1872, Late Cretaceous) was a giant mosasaur, a clade that traditionally and currently nests with small Aigialosaurus. Mosasaurs were sea-going giant varanoid lizards that gave live birth and had extra phalanges on the medial digits as the hands and feet were transformed into paddles. Large teeth appear on the pterygoids, but these are convergent with those found on basal marine snakes like Pachyrhachis. The nasals were fused together and fused to the premaxilla ascending process.

Figure 3. Aigialosaurus, a small mosasauroid, compared to Coniasaurus, an even smaller mosasauroid, not related to Dolichosaurus and snakes.

Figure 3. Aigialosaurus, a small mosasauroid, compared to Coniasaurus, unrelated to mosasaurs, but related to  Dolichosaurus and snakes.

Other much more distantly related aquatic squamates include
dolichosaurs like Dolichosaurus, Adriosaurus and Pontosaurus. Those are in the lineage of pre-snakes, like Tetrapodophis in the LRT.

On a side note:
Caldwell 2012 asked, “What, if anything is a mosasaur?”

From the Caldwell abstract:
“This treatise critically assesses Camp’s [1923] diagnostic characters for Anguimorpha, Platynota, Varanoidea, and Mosasauroidea, concluding that Camp’s data permit mosasaurs to be viewed only as anguimorphans, not platynotans nor varanoids. A similar critical assessment is given for the characters used to diagnose anguimorphans and varanoids in Estes et al. [1988], concluding here that not a single character out of twenty-two is shared between varanoids and mosasaurs… It is concluded here that there is no character-based evidence to support phylogenetic hypotheses that mosasaurs are derived aquatic varanoid lizards. It is recognized that the concept and term “mosasaur” has ceased to exist in any biologically meaningful way, and that the future requires the construction of a new suite of terms and concepts to convey what we now think we know about these animals.”

The LRT agrees
with the above hypothesis (Fig. 4) to an extent. Mosasaurs and varanids shared a common ancestor, probably as early as the Permian. TA1045 (Rößler et al. 2012; yet unnamed) is one of the earliest known lepidosaurs. It lived during the Permian. Saniwa lived during the Eocene much later than the Cretaceous mosasaurs. I could not locate any Mesozoic varanids, though they were undoubtedly present.

Estesia is not considered a varanid, but it nests with them in the LRT. Rather, Wikipedia reports that Estesia is close to the living Gila monster, Heloderma, a desert lizard.

Figure 4. Mosasaur cladogram showing related taxa.

Figure 4. Mosasaur cladogram showing related taxa.

On an another note
I just learned about this website: http://homepages.vodafone.co.nz/~jollyroger_wave/DinoNew/links2.htm
listing blogs and other web pages related to prehistoric topics. Both PterosaurHeresies and ReptileEvolution are listed. Thank you Vodphone/JollyRoger/DinoNews!

References
Caldwell M 2012. A challenge to categories: “What, if anything, is a mosasaur?” Bulletin de la Société Géologique de France 183(1): DOI: 10.2113/gssgfbull.183.1.7
Marsh OC 1872. Note on Rhinosaurus. American Journal of Science 4 (20):147.
Rößler R, Zierold T, Feng Z, Kretzschmar R, Merbitz M, Annacker V and Schneider JW 2012. A snapshot of an early Permian ecosystem preserved by explosive volcanism: New results from the Chemnitz Petrified Forest, Germany. PALAIOS, 2012, v. 27, p. 814–834

wiki/Mosasaur
wiki/Tylosaurus
wiki/Tethysaurus
wiki/Saniwa

Long carpals on crocodylomorphs = quadrupedal stance?

Figure 1. Terrestrisuchus is a bipedal basal crocodylomorph with elongate proximal carpals.

Figure 1. Terrestrisuchus is a bipedal basal crocodylomorph with elongate proximal carpals.

Long proximal carpals,
like the radiale and ulnare in Terrestrisuchus (Figs. 1, 2; Crush 1984), distinguish most crocodylomorphs from all basal dinosaurs (Fig. 2).

The question is:
why did long carpals develop? A recent comment from a reader suggested they enabled quadrupedal locomotion. But looking at the proportions of Terrestrisuchus does not inspire great confidence in that hypothesis. Terrestrisuchus has elongate carpals AND it seems to be comfortably bipedal with hands that only descend to the knees. And the pectoral girdle is relatively gracile.

Figure 2. Manus of several crocodylomorphs compared to the basal dinosaur, Herrerasaurus. Not sure what those two bones are on Junggarsuchus as they were cut off as shown when published.

Figure 2. Manus of several crocodylomorphs compared to the basal dinosaur, Herrerasaurus. Not sure how long those two proximal carpals are on Junggarsuchus. They were cut off as shown when published. Since the distal carpals are labeled (dc) I assume  proximal carpals are cut off below them. Oddly the radiale is much smaller than the ulnare if so, or rotated beneath it, unlike the other crocs.

Looking back toward more primitive taxa
provides only one clue as to when the proximal carpals first started elongating: with Terrestrisuchus. The following basal and often bipedal croc taxa unfortunately do not preserve carpals.

  1. Lewisuchus
  2. Gracilisuchus
  3. Saltopus
  4. Scleromochlus
  5. SMNS 12591
  6. Litargosuchus
  7. Erpetosuchus

Phylogenetic bracketing suggests that all
were bipedal or facultatively bipedal. Post-crania is missing or partly missing in several of these specimens.

Gracilisuchus

Figure 3. Gracilisuchus does not preserve the hands or carpals, but was possibly experimenting with bipedal locomotion based on its proximity to taxa that were obligate bipeds. Note the tiny pectoral girdle.

The distal carpals,
wherever preserved (Figs. 2, 3), appear to be small, scarce and flat, the opposite of a supple flexible wrist. So the proximal carpals of crocs comprise the great majority of the wrist, distinct from dinosaurs (Fig. 2).

Figure 3. Alligator carpals.

Figure 3 Alligator carpals. Of course, this is a quadruped that has inherited long carpals from bipedal ancestors in the Triassic.

So… what do other bipedal taxa do with their hands?
Cosesaurus, a bipedal ancestor to pterosaurs, probably flapped, based on the shape of its  stem-like coracoid and other traits. Herrerasaurus, a bipedal ancestor to dinosaurs had elongate raptorial unguals (claws) lacking in any basal crocodylomorph (Fig. 2). Such claws were probably used in grasping prey in dinos… not so much in crocs.

The elongate proximal carpals in crocodylomorphs
appear to extend the length of the slender antebrachium (forearm) of Terrestrisuchus for only one reason at present. The offset lengths of the shorter radius and longer ulna become subequal again with the addition of the longer radiale and shorter ulnare. So there is no simple hinge joint at the antebrachium/proximal carpal interface. So that joint was relatively immobile. The lack of deep distal carpals also suggests a lack of mobility at the metacarpal/distal carpal interface in basal taxa. However in extant crocs, that hinge appears to be more flexible.

Figure 5. Trialestes parts. Note the much larger ulna relative to the radius and the much longer forelimb relative to the bipedal basal crocs.

Figure 5. Trialestes parts. Note the much larger ulna relative to the radius and the much longer forelimb relative to the bipedal basal crocs.

In Trialestes
(Fig. 5) the elongate fore limbs more closely match the hind limbs. So the elongate carpals in Trialestes do appear to enhance a secondarily evolved quadrupedal stance.

Also take a look at
Hesperosuchus, Dromicosuchus, Protosuchus. Saltoposuchus, Dibrothrosuchus, Baurusuchus, Simosuchus, and Pseudhesperosuchus. After long carpals first appeared in Terreistrisuchus, they do not change much despite the many other changes in the morphology of derived taxa. Bipeds have them. Quadrupeds have them. Long-bodied taxa have them, Short-bodied taxa have them.

Some thoughts arise
when considering the first crcoc with elongate carpals, Terrestrisuchus.

  1. At some point in the day Terrestrisuchus probably rested on its elongate pubis bone (the first in this lineage), flexing its long hind limbs beneath itself to do so. In that pose elongate carpals may have been useful in steadying the animal as it balanced on the pubis tip and whenever it rose to a bipedal stance.
  2. A male Terrestrisuchus may have used its hands to steady itself while riding on the back of a female while mating. The carpals were elongated as part of the balancing act performed during this possibly awkward bipedal conjugation.
  3. Coincidentally, the coracoids in crocodylomorphs begin to elongate in this taxon. So freed from quadrupedal locomotion duties, basal crocs may have done some early form of flapping as part of a secondary sexual behavior, long since lost in extant taxa.

So, in summary
I think the elongate carpals developed in crocs with a really long pubis to steady it while resting. Very passive. Not sure what other explanation explains more.

Did I miss anything?
Has anyone else promoted similar or competing hypotheses?

References
Crush PJ 1984. A late upper Triassic sphenosuchid crocodilian from Wales. Palaeontology 27: 131-157.

wiki/Terrestrisuchus

When fish scales evolved into reptile scales

Figure 1. Tulerpeton parts from Lebedev and Coates 1995 here colorized and newly reconstructed. Note the well-preserved scales, studied in detail by Mondéjar-Fernandez et al. 2014.

Figure 1. Tulerpeton parts from Lebedev and Coates 1995 here colorized and newly reconstructed. Note the well-preserved scales, studied in detail by Mondéjar-Fernandez et al. 2014.

The scales of Tulerpeton
were made of compact bone lacking enamel, dentine and isopedine layers found in more basal sarcopterygians (Mondéjar-Fernandez et al. 2014). This was the first step in a process that ultimately also removed bone from scales leaving only keratin scales arising from the epidermis.

Several times later
bone reappeared in the dermis producing osteoderms.

Earlier the Devonian tetrapod Tulerpeton heretically nested as the oldest known of the basalmost amniotes, the last common ancestors of all living reptiles, birds and mammals.

References
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/Tulerpeton