Vilevolodon: the atavistic reappearance of post-dentary bones

Preface
I’ve been wondering about the traditional nesting of Multituberculata and kin outside of the Mammalia for years. All have a dentary jaw joint, but some have post-dentary bones. given the opportunity multituberculates nest with rodents and plesiadapiformes in the large reptile tree (LRT, 1047 taxa).  No other pre-mammals resemble them. Traditionally Haramiyava (Fig. 1) has been considered a pre-mammal link to Haramiyida + Multituberculata. In the LRT Haramiyava nests with the mammaliaforms Brasilodon, Sinoconodon and Therioherpeton – far from any other taxa considered Haramiyida + Multituberculata currently and provisionally nesting deep within the Mammalia.

Figure 1. Haramiyavia reconstructed and restored. Missing parts are ghosted. The fourth maxillary tooth appears to be a small canine. The post-dentary bones are imagined from Vilevolodon (figure 4).

Vilevolodon diplomylos
(Luo et al. 2017; Jurassic, 160 mya; BMNH2942A, B; Figs. 2-4) was originally considered a stem mammal (= mammaliaform), a eleutherodontid in the clade Haramiyida AND it had clearly defined gliding membranes (Fig. 2). By contrast the LRT nests Vilevolodon with the Late Jurassic para-rodent Shenshou and the extant rodents, Rattus and Mus, not far from members of the Multituberculata.

Figure 1. Vilevolodon in situ, plate, counterplate, original drawing, DGS color, and restored manus and pes. Note the gliding membrane (patagium) and fur.

Figure 2. Vilevolodon in situ, plate, counterplate, original drawing, DGS color, and restored manus and pes. Note the gliding membrane (patagium) and fur.

But there’s a big problem
Vilevolodon doesn’t have tiny ear bones, like mammals do. It has post-dentary bones, like pre-mammals do (Figs. 3, 4).

Figure 2. Vilevolodont skull in situ, without color, DGS color tracing, that tracing reconstructed and a CT scan form Luo et al. 2017.

Figure 3. Vilevolodont skull in situ, without color, DGS color tracing, that tracing reconstructed and a CT scan form Luo et al. 2017.

The ear problem in Jurassic rodents
Luo et al. report, “a mandibular middle ear with a unique character combination previously unknown in mammaliaforms.” Pre-mammals have post-dentary bones (articular, angular, surangular). Therian mammals shrink and migrate those bones to the base of the skull where they become middle ear bones with new names (malleus, incus, ectotympanic). The stapes remains the stapes in all tetrapods. So what is happening with Vilevolodon and its sisters? Why don’t the pre-mammal post-dentary bones define it as a pre-mammal? After all, that’s the current paradigm.

Figure 3. There is no doubt that Vilevolodon has a pre-mammal type of posterior jaw bones. Otherwise they nest with rodents and plesiadapiformes. This appears to be a mammal with an atavism, a reversal. These elements simply stopped developing as in other mammals.

Figure 3. There is no doubt that Vilevolodon has pre-mammal type post-dentary bones. There is also no doubt that the dentary formed the main jaw joint with the squamosal. How does one reconcile both sets of traits? In the LRT Vilevolodon nests with rodents. This appears to be a mammal with an atavism, a reversal. These elements simply stopped developing as in other mammals.

Mammals are defined by
the evolution and migration of their posterior jaw bones into middle ear bones with a jaw joint switch from quadrate/articular to dentary/squamosal. Multituberculates and haramiyids appear to bend or break that rule because they have cynodont-like posterior jaw bones, not tiny middle ear bones, and yet otherwise they nest with rodents and plesiadapiformes. This is one reason why you don’t want to pull a Larry Martin with post-dentary bones. You want to nest a taxon based on a long list of traits, not just one, two or a dozen.

The massive jaw joint
Mammals, such as Vilevolodon, with atavistic post-dentary bones also have a massive jaw joint with a long articulating surface on the dentary contacting the squamosal. All mammals have such a jaw joint. Pre-mammals don’t. While Vilevolodon has a large dentary/squamosal jaw joint, the post-dentary articular, still contacts the quadrate. It’s clearly not the main jaw joint.

Filan 1991
traced the development of post-dentary bones in embryonic Monodelphis specimens. She reported, “Neonates of Monodelphis possess neither mammalian (dentarysquamosal) nor reptilian (quadrate-articular) jaw articulations, nor does the contact between the incus and crista parotica offer a joint surface. Elasticity in Meckel’s cartilage allows minimal deflection of the lower jaw.” After all, those neonates are just sucking milk, not biting, and the embryos don’t even do that. Does that make neonates like this not mammals? No. The evidence indicates that in multituberculates and haramiyds the embryological transformation of posterior jaw bones stopped before development transformed them into middle ear bones. This is an atavism, a phylogenetic reversal. The timing of development changed. In the case of Vilevolodon, the middle ear bones stop evolving during embryological development and the post-dentary bones they would have evolved from continue to appear in adults. What was a rare mutation probably spread throughout an isolated population. Perhaps this had something to do with the increase in size of the dentary jaw joint.

Haramiyavia and the Haramiyida clade
Seems at this point that only Haramiyavia is a haramiyid, unless Brasilodon is one as well. Members traditionally assigned to the clade Eleutherodontidae also nest in various locations in the LRT, not all in one clade.

Meng et al. 2017 report,
“Stem mammaliaforms are morphologically disparate and ecologically diverse in their own right, and they developed versatile locomotor modes that include arboreal, semiaquatic, and subterranean specializations, which are all distinct from generalized mammaliaforms.” Unfortunately, the LRT nests a long list of mammaliaforms at various nodes within the Mammalia. They are not from a single diverse clade.

Contra Meng et al. 2017
the LRT reduces the niches and body shapes of stem mammals down to a few small, generalized taxa like Sinoconodon and Megazostrodon. Derived taxa nest at derived nodes.

The LRT nests rodents close to Plesidapiformes,
including the extant aye-aye, Daubentonia as first reported here. So it comes as no surprise when Luo et al. report, “Eleutherodontids show a marked similarity to the primate Daubentonia in the ventrally bent rostrum and deep mandible, and both features are interpreted to be reinforcement for incisor gnawing.” That’s the case only with Vilevolodon this time. Others may be by convergence.

Molars
The jaw joint of the rodent allows for rostral-caudal and dorsal-ventral motion of the jaws. Luo et al. report, in Villevolodon it is not possible for the mandible to move posteriorly or horizontally, but their images show a continuous anteroposterior trough/furrow in the three molars, though not to the extent seen in sister taxon Shenshou. Molars with a long and continuous trough for rostral-caudal grinding appear by convergence in several reptile/mammal clades.

Incisor replacement
Luo et al. report, “Incisor replacement is prolonged until well after molars are fully erupted, a timing pattern unique to most other mammaliaforms. In rodents incisors never stop growing. The growth pattern in Vilevolodon may be the first step toward that. Not sure why Luo et al. are missing all these strong rodent clues.

Gliding?
Meng et al. 2017 note: “They [Vilevolodon and kin] are the most primitive known gliders in mammal evolution, evolving approximately 100 million years before the earliest known therian gliders.” Earlier, with the appearance of the stem pangolin, Zhangheotherium at the start of the Cretaceous, the ghost lineage for primates, flying lemurs and bats was also set to that time or earlier. Before the advent of flying birds, but after the advent of predatory theropods, many mammals had evidently taken to the trees. And one way to get from tree to tree without descending to the dangerous turf is to jump, glide and fly. I predict we’ll find the big-handed ancestors of bats in Jurassic and Cretaceous strata someday. They are already volant shortly after the K-T extinction event.

Hearing in Vilevolodon
With the reappearance of post-dentary bones in taxa like Vilevolodon, the auditory acuity that was more highly developed in its ancestors must have suffered a setback. By the evidence provided, the massive jaw joint must have been more important for its survival.

Figure 8. Multituberculate Kryobaatar mandible in lateral and medial views. Here post-dentary bones are absent. The malleus (quadrate) and ectotympanic are on the skull.

Figure 4. Multituberculate Kryobaatar mandible in lateral and medial views. Here post-dentary bones are absent here. The malleus (quadrate) and ectotympanic are on the skull.

Getting back to the purported patagium of Maiopatagium
which we looked at yesterday. It is not apparent and the authors do not describe it. Rather, Meng et al. 2017 sidestep this by reporting, “Furthermore, we report a second eleutherodont specimen (BMNH2942) preserved with a halo of carbonized fur and patagial membranes, similar to those of Maiopatagium.” The patagial taxon remains unnamed in the Maiopatagium paper (Meng et al. 2017), but is named in a second paper appearing on the same day. It is today’s subject, Vilevolodon (Fig. 1)

References
Filan SL 1991. Development of the middle ear region in Monodelphis domestica (Marsupialia, Didelphidae): marsupial solutions to an early birth. Journal of Zoology 225(4): 577–588 DOI: 10.1111/j.1469-7998.1991.tb04326.x
Luo Z-X, Meng Q-J, Grossnickle DM, Neander AI, Zhang Y-G and Ji Q 2017. New evidence for mammaliaform ear evolution and feeding adaptation in a Jurassic ecosystem. doi:101.1038/nature 23483\
Meng Q-J, Grossnickle DM, Liu D, Zhang Y-G, Neander AI, Ji Q and Luo Z-X 2017.
New gliding mammaliaforms from the Jurassic. Nature (advance online publication)
doi:10.1038/nature23476
Jenkins FA, Jr, Gatesy SM, Shubin NH and Amaral WW 1997. Haramiyids and Triassic mammalian evolution. Nature 385(6618):715–718.
Luo Z-X, Gatesy SM, Jenkins FA, Jr, Amaralc WW and Shubin NH 2015. Mandibular and dental characteristics of Late Triassic mammaliaform Haramiyavia and their ramifications for basal mammal evolution. PNAS 112 (51) E7101–E7109.

wiki/Haramiyavia
wiki/Vilevolodon
wiki/Maiopatagium

Maiopatagium: perhaps another case of taxon exclusion

Meng et al. 2017 bring us
a new gliding mammaliaform (pre-mammal) from the Jurassic (160 mya) of China, Maiopatagium furculiferum (BMNH 2940, Figs. 1,2).

Unfortunately
it does not look like any pre-mammals tested here.

Figure 1. Maiopatagium in situ in white and UV light. The X marks an area surrounded by fur lacking proptagial data. Is the propatagium wishful thinking?

Figure 1. Maiopatagium in situ in white and UV light. The X marks an area surrounded by fur lacking proptagial data. Is the propatagium wishful thinking?

Meng et al nest Maiopatagium
between Sinoconodon and Haldanodon, taxa more primitive than mammals. By contrast the large reptile tree (LRT, 1044 taxa) nests Maiopatagium between the interatheres, Interatherium + Paedotherium and the former enigma taxa Groeberia + Vintana, all  marsupials, not Haramyidae, contra Meng et al. 2017, who do not appear to have tested against all ;possible candidate taxa.

Figure 2. Maiopatagium imagery from Meng et al. 2017, plus reconstruction of the extended manus and pes and some bones colorized.

Figure 2. Maiopatagium imagery from Meng et al. 2017, plus reconstruction of the extended manus and pes and some bones colorized. The purported gliding membrane may instead simply be loose skin. Pink area between fingers perhaps falsely adds gliding membrane.

There is another newly described and similar taxon,
Vilevolodon that I need to look at before proceeding further. I’ll have more to say about both taxa later. 

References
Meng Q-J, Grossnickle DM, Liu D, Zhang Y-G, Neander AI, Ji Q and Luo Z-X 2017.
New gliding mammaliaforms from the Jurassic. Nature (advance online publication)
doi:10.1038/nature23476

wiki/Maiopatagium

 

Purgatorius: What is it?

Wikipedia reports: 
“For many years, there has been a large debate as to whether Purgatorius is a primitive member of the Primates or a basal member of the Plesiadapiforms.” Here (Fig. 1) taxa from the Plesiadapiformes have giant procumbent (rat-like) incisors followed by a long diastema, followed by flat molars…completely UNLIKE Purgatorius. So what were they thinking?

Halliday et al. 2015
nested Purgatorius outside crown group placentals with Protunugulatum (Fig 1). That seems reasonable, though it is twice the size. However, the large reptile tree (LRT, 1044 taxa) was not able to replicate most of the Halliday team’s cladogram, which nested hyraxes with elephant shrews…and horses… and that clade with pre-odontocetes and an early artiodactyl. It just gets worse after that. Protunugulatum was originally allied with condylarths, large plant-eating mammals. Halliday et al. nested it outside the placentals. Wible et al. 2007 nested it with whales + artiodactyls (a clade not validated by the LRT).

Purgatorius is another one of those fossils
known from an incompleted mandible with teeth and little else. Based on a lack of other bones, this is the sort of fossil the LRT cannot successfully resolve and it does not make it onto the list. So we go to plan #2: visual comparisons.

Figure 1. Purgatorius compared to other basal and often Paleocene mammals.

Figure 1. Purgatorius compared to other basal and often Paleocene mammals. Given these choices, Purgatorius looks more like Palaechthon, the basal dermopteran, than any other taxa in the LRT. Taxa in yellow nest together in the LRT with primates. Taxa in pink nest with rats and rabbits. Maelestes is a basal tenrec.

Rat-sized Purgatorius unio
(Valen and Sloan 1965; Latest Cretaceous/Earliest Paleocene) gained some early notoriety as the earliest known primate. Ankle bones found in association with Purgatorius, but not articulation, show signs of being flexible like those of primates (Kaplan 2012).

I can describe Purgatorius in the simplest of terms
based on comparisons to related basal mammal taxa (Fig. 1) and without describing any molar cusps (except one).

  1. small in overall size (skull < 2cm in length)
  2. robust mandible with convex dorsal and ventral rims and straight in occlusal view
  3. incisors likely procumbent, but not large
  4. canine tiny
  5. three robust premolars and three robust molars with one very tall cusp
  6. Premolar #3 taller than other teeth

Based on a visual comparison
of candidate taxa (Fig. 1), Purgatorius looks more like Protungulatum and even more like Palaechthon. The latter nests with flying lemurs like Cynocephalus. So we’re close to the base of primates, but closer to their cousins, and far from plesiadapiformes.

Best I can do for now…

References
Halliday TJD, Upchurch P and Goswami A 2015. Resolving the relationships of Paleocene placental mammals Biological Reviews. | doi = 10.1111/brv.12242
Kaplan M 2012. Primates were always tree-dwellers. Nature. doi:10.1038/nature.2012.11423
Van Valen L and Sloan R 1965. The earliest primates. Science. 150(3697): 743–745.
Wible JR, Rougier GW, Novacek MJ and Asher RJ 2007. Cretaceous eutherians and Laurasian origin for placental mammals near the K/T boundary.” Nature volume 447: 1003-1006

wiki/Purgatorius

Goodbye Scrotifera. Goodbye Euarchontaglires. Goodbye Scandentia. etc. etc.

Earlier the large reptile tree
found that several former clades, like Parareptilia, PterodactyloideaCetacea, Testudinata (Chelonia) Notoungulata, Pseudosuchia, Ornithodira and Pinnipedia were not monophyletic… and that list keeps growing.

The large reptile tree (LRT, 1044 taxa) does not replicate the following mammalian clades:

  1. Scandentia – tree shrews: yes, closely related, but at the bases of different clades.
  2. Euarchontaglires – rodents, rabbits, tree shrews, flying lemurs and primates,  (Fig. 1)
  3. Euarchonta – tree shrews, flying lemurs, primates and plesiadapiformes.
  4. Glires – rodents, rabbits
  5. Scrotifera – Eulipotyphla (see below), bats, pangolins, Carnivora, Euungulata (including whales)
  6. Eulipotyphla – hedgehogs, shrews, solenodons, moles (moles are Carnivora))
  7. Euungulata – perissodactyls, artiodactyls (including whales)
  8. Tenrecidae – tenrecs, some are closer to shrews, others closer to odontocetes
  9. Macroscelidea – elephant shrews, some are closer to tenrecs
  10. Primates – Plesiadapiformes and extant primates, including Daubentonia (the aye-aye. No giant anterior dentary teeth in valid primates.
  11. there are a few more I’m overlooking. I’ll add them as they come to me.
Figure 1. Glires and Euarchonta are two clades within the Mammalia in the LRT.

Figure 1. Glires and Euarchonta are two clades within the Mammalia in the LRT.

Let’s focus on Plesiadapiformes
Bloch et al. 2007 found plesiadapiforms (Plesiadapis, Carpolestes and kin) more closely related to primates than to any other group. They did not test against rodents and multituberculates. The LRT does not replicate these results, but finds plesiadapiforms more closely related to multituberculates and rodents when included.

According to Bloch & Boyer 2002
“Plesiadapiforms share some traits with living primates, including long fingers well designed for grasping, and other features of the skeleton that are related to arboreality.” That’s fine, but there are other taxa in the tree topology with long fingers, too.

Paromomyidae
Krause 1991 reports, “Paromomyids …have long been regarded by most workers as members of the Plesiadapiformes.” Again, the LRT does not support this, but nests Paromomyids, like Ignacius (Fig. 2), with rodents, like Mus and Paramys. Paromomyids have squared off and flat molars, but Paromomys does not.

Figure 2. The skull of Ignacius nests with other rodents, not plesiadapiformes.

Figure 2. The skull of Ignacius nests with other rodents, not plesiadapiformes. Ironically it is closer to the squirrel-like Paramys than to Paromomys.

Beard 1990 thought paromomyids,
as plesiadapiforms, where close to colugos or “flying lemurs”. The LRT (Fig. 1) does not support this relationship. Rather paromomyids, like Ignacius, were squirrel-like, able to scamper both in the trees and on the ground. Ignacius graybullianus (USNM 421608, Fig. 1) is a new taxon that nests as a basal rodent in the LRT.

Figure 3. Ignacius clarkforkensis known parts.

Figure 3. Ignacius clarkforkensis known parts.

Remmber, no primates 
have giant anterior dentary teeth. The aye-aye, Daubentonia, has such teeth, but the LRT finds it nests with Plesiadapis and multituberculates and rodents, not primates. Yes, plesiadapiformes and Ignacius had long limbs, big brains and binocular vision, but by convergence with primates.

References
Beard KC 1990. 
Gliding Behavior and palaeoecology of the alleged primate family Paromomyidae (Mammalia, Dermoptera). Nature 345, 340-341.
Bloch J, Silcox MT, et al. 2007.
New Paleocene skeletons and the relationship of plesiadapiforms to crown-clade primates.  Proceedings of the National Academy of Science 104, 1159-1164.
Kay RF, Thewissen JG and Yoder, AD 1992. Cranial anatomy of Ignacius graybullianus and the affinities of the Plesiadapiformes. American Journal of Physical Anthropology. 89 (4): 477–498. doi:10.1002/ajpa.1330890409.
Krause DW 1984. Mammal Evolution in the Paleocene: Beginning of an Era. In: Gingerich, P. D. & Badgley, C. E. (eds.): Mammals: notes for a short course. Univ. of Tennessee, Department of Geological Sciences.
Krause DW 1991. Were paromomyids gliders? Maybe, maybe not. Journal of human evolution 21:177-188.

The origin of flight in bats: what we knew in 1992.

Famous for his whale studies,
JGM (Hans) Thewissen turned his attention to bats as a postdoctoral fellow in 1984. His co-author, SK Babcock, was a graduate student at the time.

Their introduction
includes their intention of reviewing then current controversies despite “extremely sparse” fossil evidence. They mentioned the hundreds of Eocene bat skeletons known from the Messel quarry near Darmstadt, Germany, but note that even late Paleocene bats were “nearly as specialized as their modern relatives.”  Their report preceded by several years the publication of Onychonycteris (Simmons, Seymour, Habersetze and Gunnell 2008), the most primitive bat known at present.

Two kinds of bats were noted, Megachiroptera and Microchiroptera.
“Megabats have a simple shoulder joint and a clawlike nail on thumb and index finger, whereas mi-crobats have a complicated shoulder joint and a claw only on the thumb.” Microbats use echolocation to eat insects with their sharp crested teeth. Megabats generally do not, but a few do. They are herbivores with blunt molars.

Earlier we looked at
the dual origins of turtles,  whales, seals and the four origins of the “pterodactyloid”-grade pterosaurs. Workers have wondered if mega bats and micro bats also had dual origins.  This was the main theme of the Thewissen and Babcock paper, penned before the widespread advent and adoption of computer-based phylogenetic analysis. Instead, everyone looked at a few to many traits and pulled a Larry Martin. Sometimes they were right. Othertimes, they were wrong to slightly wrong. Smith and Madkour 1980 first proposed a dual origin for bats by looking at the penis.

Thewissen and Bacock renege on their headline promise when they report,
“If the problem of bat origins is ever solved, it will be after a careful anal-ysis of all characterso f interesti n the bats and their potential relatives.” Of course this was shortly  before PAUP and MacClade came on the scene the same year.

Thewissen and Babcock report:
“Both microbats and megabats have a propatagial muscle complex, but it is surprisingly different in the two groups.” In mega bats this complex has four proximal origins,

  1. the back of the skull
  2. the side of the face
  3. the ventral side of the neck and
  4. the midline of the chest

compared to only two origins in micro bats (1 and 4). There is also variation within micro bats and within mega bats. As readers know, there is no way to understand this unless outgroups have one or the other pattern and they don’t (at present). Thewissen and Babcock report, “gliding flight has evolved six times in mammals.” But gliders don’t make good flyers. To fly one needs thrust provided by flapping. How and why bats started flapping has really been the key underlying, unanswered question, which we looked at earlier here and here.

Back in 1910
WK Gregory concluded after careful study that bats, flying lemurs, tree shrews, elephant shrews and primates were closely related and called that group (clade) Archonta. According to the large reptile tree (LRT, 1043 taxa) many of these taxa are indeed related. Elephant shrews are not, which Thewissen and Babcock later note. Elephant shrews are also the only ones from that list that are not arboreal climbers. Thewissen and Babcock add the clade Plesiadapiformes, which were thought to be rodent-like primates, but turn out to be primate-like rodents nesting close to multituberculates in the LRT.

Figure 1. Bat cladogram. Here pangolins are the nearest living relatives of bats.

Figure 1. Bat cladogram. Here pangolins are the nearest living relatives of bats.

Flying lemurs,
like Cynocephalus, also have a propatagium that originates from the side of the face and midline of the neck, but the nerves within them terminate in different places in bats. The LRT recovers flying lemurs close relatives to bats, but pangolins, like Manis, are closer.

Thewissen and Babcock conclude: 
“We believe that the evidence from the propatagial muscle complex of bats supports the idea that all bats share a single ancestor with wings. This idea is consistent with bats going through a flying lemur-like stage before acquiring active flight.”

Unfortunately
the LRT recovers a topology in which the last common ancestor of flying lemurs and bats was likely arboreal, but not a leaping glider. That means membranes developed in parallel (close convergence). Remember, gliders don’t become flappers. And flappers usually develop flapping for reasons other than flight, then co-opt flapping traits for flight.

The ancestors of bats and pangolins
have had a long time to diverge. Likely that was in the Late Jurassic because we have the pangolin ancestor, Zhangheotherium, appearing in the Early Cretaceous. That puts the last common ancestor of flying lemurs, pangolins and bats, Ptilocercus, back in the Middle Jurassic, several tens of millions of years after the likely first appearances of therian mammals, like the living and very late surviving Didelphis and Monodelphis sometime in the Early Jurassic. Earlier we looked at the origin of bats here, here and here.

Figure 2. Select basal cynodonts and mammals set chronologically. The divergence times for placentals (Eutheria), marsupials (Metatheria) and monotremes (Mammalia) are estimated here.

Figure 2. Select basal cynodonts and mammals set chronologically. The divergence times for placentals (Eutheria), marsupials (Metatheria) and monotremes (Mammalia) are estimated here.

References
Simmon NB, Seymour KL, Habersetzer J, Gunnell GF 2008. Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation. Nature 451 (7180): 818–21. doi:10.1038/nature06549. PMID 18270539.
Smith, J. D., and G. Madkour. 1980. Penial morphology and the question of chiropteran phylogeny. Pages 347-365 in D. E. Wilson and A. L. Gardner, eds. Proceedings of the 5th International Bat ResearchC onference. Texas Tech Press, Lubbock.
Thewissen JGM and Babcock SK 1992. The origin of flight in bats. BioScience 42(5):340–345.

wiki/Onychonycteris

 

New Como Bluff (Latest Jurassic) pterosaurs

Bits and pieces
of new Latest Jurassic pterosaurs are coming out of aquatic deposits in western North America according to McLain and Bakker 2017. The material is 3D and not very mineralized, so it is extremely fragile.

Specimen(s) #1 – HMNS/BB 5027, 5028 and 5029
“One proximal and two distal femora match a complete femur (BYU 17214) referred to Mesadactylus. Unexpectedly, both of the BBF distal femora possess a large intercondylar pneumatopore. BYU 17214 also possesses an intercondylar pneumatopore, but it is smaller than in the BBF femora. Distal femoral pnuematicity is previously recognized only in Cretaceous azhdarchoids and pteranodontids.”

The Mesadactylus holotype and referred specimens reconstructed to match the flightless pterosaur, Sos2428.

Figure 1. The Mesadactylus holotype (Jensen and Padian 1989) nests with the North American anurognathids. Several referred specimens (Smith et al. 2004), when reconstructed nest at the base of the azhdarchidae, with Huanhepterus and the flightless pterosaur SOS 2428.  The new BYU 17214 femur is essentially identical to the femur shown here.

Earlier we looked at two specimens referred to Mesadactylus. One is an anurognathid (Fig. 1). The other is a basal azhadarchid close to Huanhepterus, not far removed from its Dorygnathus ancestors in the large pterosaur tree. Instead McLain and Bakker compare the femora with unrelated and Early Cretaceous Dsungaripterus, which convergently has a similar femur. The better match is to the basal azhdarchid, so distal femoral pneumaticity does not stray outside of this clade. By the way, it is possible that Mesadactylus was flightless.

Specimen(s) #2 – HMNS/BB 5032 (formerly JHU Paleon C Pt 5)
“A peculiar BBF jaw fragment shows strongly labiolingually compressed, incurved crowns with their upper half bent backwards; associated are anterior fangs. We suspect this specimen is a previously undiagnosed pterosaur.”

These toothy specimens were compared to two Early Cretaceous ornithocheirids, one Middle Jurassic dorygnathid, and one Latest Jurassic bird, Archaeopteryx. None are a good match. A better, but not perfect,match can be made to the Early Jurassic pre-ctenochasmatid, Angustinaripterus (Fig. 2) which has relatively larger posterior teeth than does any Dorygnathus specimen.

The HMNS BB 5032 specimen(s) probably belong to a new species of Angustinaripterus or its kin based on the relatively large posterior teeth not seen among most Dorygnathus specimens.

The HMNS BB 5032 specimen(s) probably belong to a new species of Angustinaripterus or its kin based on the relatively large posterior teeth not seen among most Dorygnathus specimens.

As before,
we paleontologists don’t always have to go to our ‘go to’ taxon list of familiar fossils. Expand your horizons and take a fresh look at some of the less famous taxa to make your comparisons. You’ll find a good place to start at ReptileEvolution.com

References
McLain MA and RT Bakker 2017. Pterosaur material from the uppermost Jurassic of the uppermost Morrison Formation, Breakfast Bench Facies, Como Bluff,
Wyoming, including a pterosaur with pneumatized femora.

Pisanosaurus: dinosaur or silesaurid?

A new paper by Agnolin and Rozadilla 2017
includes new photographs of the holotype that shed new light on Pisanosaurus (Casamiquela 1967, Bonaparte 1976; Late Triassic). This taxon was previously known in the literature chiefly (not exclusively) from drawings. The large reptile tree (LRT, 1043 taxa) nested Pisanosaurus with Haya as a basal ornithischian, confirming prior assessments. Now Agnolin and Rozadilla provide evidence for a Silesaurus affinity among the Poposauridae. Echoing others, they report, “the poor preservation of the specimen is the largest difficulty to overcome when interpreting its morphology. Its phylogenetic position within ornithischians is problematic.”

So, with the new evidence,
let’s test and nest Pisanosaurus 2017! (There are so few traits that can be scored for Pisanosaurus, that the rest of the discussion might seem like I’m pulling a Larry Martin. That happens sometimes, but I’m trying to report results from the LRT.

Before we start…
with present data, shifting Pisanosaurus to Silesaurus in the LRT adds 24 steps. Moreover, Agnolin and Rozadilla did not mention the proximal relatives of Pisanosaurus in the LRT:  Haya, Daemonosaurus, Chilesaurus, Scelidosaurus and Emausaurus. This may be the key to their novel results: taxon exclusion… once again. 

Some general notes to start with:

  1. Silesaurus and other poposaurs have a metatarsus no longer than the longest digit. The same hold true for many basal phytodinosaurs, but Pisanosaurus has a longer metatarsus, like its sister in the LRT, Haya.
  2. The photo of the pelvis does little to clarify any issues. It is a broken up mess (Fig. 2) with, what appear to be smaller pelvis bones (greens)  and several sacral bones (blues) stirred up in a conglomeration. Not much matches the published drawings. And my earlier imagination describing a rotated pubis based on simple published drawings did not pan out.
  3. The anterior dentary appears to be missing a predentary bone, a trait common to the clade Ornithischia, but something like it also appears in Silesaurus.
  4. Pisanoaurus comes from South America, home of most of the other basalmost Triassic phytodinosaurs. Popposaurids, all except Sacisaurus, come from somewhere else on the globe. Haya, the LRT sister to Pisanosaurus, comes from China, but it is Late Cretaceous in age.
  5. Agnolin and Rozadilla consider Silesaurus part of a clade “that is currently recognized as the sister group to Dinosauria.” The LRT recovers Crocodylomorpha closer to Dinosauria and Silesaurus nests within the next proximal outgroup, Poposauridae.
  6. Agnolin and Rozadilla report, “because Pisanosaurus is a unique and very valuable specimen, it is not currently possible to [CT] scan it.”
  7. Authors have not agreed whether the pelvis, represented by fragments of bones and bone impressions in rock. is preserved in medial or lateral view. Agnolin and Rozadilla report, “the sacrum is articulated and preserved in life position with respect to the pelvis.”
Figure 1. The Pisanosaurus pelvis here flipped right to left along with drawings and reconstructions by Agnolín and Rozadilla, plus DGS colors applied to what I can see here. Nothing is clear, but it seems like the pelvic elements are smaller that published and that several sacral vertebrate are sprinkled in this mass. Perhaps a CT scan would be helpful here. Blue = vertebrae. Green = pelvi elements.

Figure 1. The Pisanosaurus pelvis here flipped right to left along with drawings and reconstructions by Agnolín and Rozadilla, plus DGS colors applied to what I can see here. Other than the sacral vertebrate on top, not much is clear, but it seems like the pelvic elements are smaller that published and that several sacral vertebrate are sprinkled in this mass. Perhaps a CT scan would be helpful here. Blue = vertebrae. Green = pelvi elements.

Agnolin and Rozadilla provided an emended diagnosis.
Pisanosaurus is a basal dinosaurifordiagnosable by the following autapomorphies:

  1. “central teeth bilobate in occlusal view, showing well-developed mesial and distal grooves;
  2. distal end of the tibia anteroposteriorly longer than transversely wide;
  3. bilobate astragalus in distal view;
  4. ascending process of the astragalus being subquadrangular and robust in lateral view;
  5. intense transversal compression of the calcaneum.”
Figure 3. Skull of Haya and restored skull of Pisanosaurus compared. The resemblance of preserved elements is apparent here. In both cases the mandibular fenestra is filled in. The other holes in the Pisanosaurus mandible are artifacts of taphonomy. Pisanosaurus data from Irmis et al. 2007b.

Figure 2. Skull of Haya and restored skull of Pisanosaurus compared. The resemblance of preserved elements is apparent here. In both cases the mandibular fenestra is filled in. The other holes in the Pisanosaurus mandible are artifacts of taphonomy. Pisanosaurus data from Irmis et al. 2007b.

Other factors of interest:

  1. The number of tooth positions (15) in Pisanosaurus matches both silesaurids and pertinent ornithischians.
  2. “Central teeth are bilobate in occlusal view, and show well-developed mesial and distal grooves, a condition unknown in other herbivorous taxa and a trait that may be an autapomorphy of Pisanosaurus.” Not sure if the teeth in Haya are the same, but they look similar in lateral view (Fig. 2). Neither have denticles. Silesaurid teeth are leaf-shaped.
  3. “the teeth do not form a palisade or continuous masticatory surface as advocated by some authors.” As in Haya.
  4. “Pisanosaurus is similar to saurischians and basal dinosauriforms in having overlapping proximal metatarsals, differing from the non-overlapping condition in ornithischians.” Except Haya.
Figure 1. Haya in lateral view.

Figure 3. Haya in lateral view. Note the dorsal laminae, similar to those in Pisanosaurus.

Agnolin and Rozadilla describe the dorsal vertebrae
as having a strong and complex system of laminae. Haya (Fig. 3).has similar laminae. Poposauridae do not.

Silesaurus

Figure 4 Silesaurus as a biped and occasional quadruped. Note the squareish cervicals, unlike the parallelograms in figure 5.

Agnolin and Rozadilla considered the vertebrae
(Fig. 5) very different from the cervical vertebrae described for basal dinosauriforms and ornithischians. But they did not look at Haya, which has similar cervicals 1 and 2 (Fig. 5). They considered the cervicals ‘indistinguishable from Sacisaurus cervicals, but Langer and Ferigolo 2013, did not refer the cervical to Sacisaurus due to its relatively large size. Concluding Agnolin and Rozadilla considered these verts to be on uncertain position.

Figure 4. Pisanosaurus cervical vertebrae in left lateral view (not right as published) matches cervical vertebrae 1 and 2 in Haya.

Figure 5. Pisanosaurus cervical vertebrae in left lateral view (not right as published) matches cervical vertebrae 1 and 2 in Haya – and does not match the simpler vertebrae in Silesaurus (Fig. 4).

Sacrals are preserved as moulds in Pisanosaurus. 
Various authors have interpreted five, to two sacrals. Agnolin and Rozadilla concurred with Irmis et al. 2007, who found no trace of sacral elements, reporting, “some features previously considered to be impressions of sacral ribs are actually cracks in the matrix, and there is insufficient fidelity to determine whether any of the centra are fused to each other.” 

Figure 6. Pisanosaurus right pes with digit 2 ghosted in and digit 4 rotated into in vivo position. PILS added. Nnte the brevity of the toes compared to the metatarsus, a trait shared with Haya.

Figure 6. Pisanosaurus right pes with digit 2 ghosted in and digit 4 rotated into in vivo position. PILS added. Nnte the brevity of the toes compared to the metatarsus, a trait shared with Haya.

Is the acetabulum open or closed?
Agnolin and Rozadilla ‘suggest’ it is closed, as in poposaurs. If so the closed portion is buried. With available evidence and phylogenetic bracketing, it was probably open. Haya has an acetabulum with a keyhole shape (Fig. 3).

The tibia, tarsus and metatarsus
in Pisanosaurus the cnemial crest does not peak at the knee, but somewhat lower. Haya is similar. The fibula diameter is 70% that of the tibia, as in Scelidosaurus. The fibula for Haya is unknown. Anolín and Rozadilla identified a calcaneal tuber. That is odd because it is so small that it does not extend as far as the fibula does. in Haya the calcaneum extends slightly beyond the astragalus. The astragalus of Pisanosaurus is longer than wide (when the medial condyle is included), which is distinctly different from Haya and other sister taxa and different from Silesaurus.

Figure 8. Calcaneum of Pisanosaurus. You can see why some authors saw a tuber while others did not.

Figure 8. Calcaneum of Pisanosaurus. You can imagine why some authors saw a tuber while others did not.

A flawed phylogenetic analysis
Other than excluding several taxa that nest close to Pisanosaurus in the LRT, Agnolin and Rozadilla employed the invalid Nesbitt (2011) database, also suffering greatly from taxon exclusion. It does not nest sauropodomorphs with ornithischians as phytodinosaurs, but nests sauropodomorphs, like Pampadromaeus, with Tawa and other theropods. In their first analysis, 20 trees resulted with Pisanosaurus nested as an unresolved polytomy of several dinos and non-dinos. After excluding wild card taxa, 82 trees resulted with Pisanosaurus within the Silesauridae. Bremer support is low in their analysis, but Bootstrap support is high in the LRT.

Discussion
Agnolín and Rozadilla discuss several traits of Pisanosaurus (typically related to herbivory) and their appearances elsewhere within the Archosauria. They find no epipophyses in the cervicals, but Haya lacks these, as well on the pertinent first two verts. Agnolín and Rozadilla note “The vertebral centra are very elongate and transversely compressed, differing from the short and stout dorsal vertebrae of known ornithischians, including heterodontosaurids.” They do not realize the close relationship of Pisanosaurus to sauropodomorphs like Saturnalia and the basalmost ornithischian, Chilesaurus, both with elongate dorsals. Agnolín and Rozadilla made a “tentative reconstruction” of the pelvis (Fig. 1), but it bear little to no resemblance to the in situ fossil. In every comparison made, Agnolín and Rozadilla delete or ignore Haya and related taxa and thus recover semi-blind results.

Today and in the future
we can’t keep going back to the same short lists of taxa for our inclusion sets. We know of so many more now that need to be included in phylogenetic analyses. The LRT can be your guide.

References
Agnolín FL and Rozadilla S 2017. Phylogenetic reassessment of Pisanosaurus mertii Casamiquela, 1967, a basal dinosauriform from the Late Triassic of Argentina. Journal of Systematic Palaeontology. http://dx.doi.org/10.1080/14772019.2017.1352623
Ferigolo and Langer 2006. A Late Triassic dinosauriform from south Brazil and the origin of the ornithischian predentary bone. Historical Biology, 2006; 1–11, iFirst article
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History, 352, 1–292.

wiki/Sacisaurus
wiki/Pisanosaurus
wiki/Haya