PterosaurHeresies 2016 – a quick review

On this last day in 2016
I’m pleased to report the large reptile tree (LRT) went from about 600 taxa in January to 907 today, the largest jump in the 6 years it has been up. Most of these were birds and mammals. This new total does not include the 200+ pterosaurs and 60+ therapsids in satellite trees, some duplicated in the LRT. Revised constantly, the LRT is stronger now than at any prior time with less average phylogenetic distance between sisters than ever before.

Some of the reptiles we met in 2016:

1. January was chiefly a dinosaur/theropod month, but ended with Bunostegos, a pareiasaur key to understanding turtle origins.
2. February – changes come to the tyrannosauroidea.
3. March – lots of lizards, but also a reader favorite: bat wing origins. And this poignant post featuring John Ostrom. A second flightless pterosaur.
4. April – Flapping before flight hypothesis re-re-re-confirmed.
5. May – The true shape of the Atopodentatus skull was published. A new ichthyosaur mimic discovered.
6. June – Tridentinosaurus traced and nested. A new stem snake: Tetrapodophis! And then there’s Vaughnictis, the last common ancestor of birds and bats in the LRT.
7. July – Started hitting mammals hard, starting with the elephant. Tenrecs are odontocete whale ancestors!
8. August – A Jurassic ancestor to rodents and multituberculates.
9. September – Vintana nested with wombats. Goodbye Notoungulata.
10. October – Carpolestes leaves the Primates. Two kinds of elephant shrews. Goodbye Cetacea!
11. November – Behemotops and the Mysticeti. Ozimek not a sharovipterygid and not a glider.
12. December – The aye-aye is not a primate. Indricotheres may be giant and hornless, but they are not rhinos.

Thank you
for your readership and your comments. Suggestions are always welcome.

As I’ve said before,
every taxon I approach and discuss I do so without prior knowledge. I learn as I go. Fortunately I have an increasingly powerful tool in the large reptile tree that keeps on working despite being ‘overstuffed’ with taxa.

Not sure what 2017 will bring,
but I imagine posts will be less frequent as most of the key amniote/reptile taxa have been covered by now. Hopefully several more PhDs will re-discover relationships that were first discovered and published here years ago, as several did this year. That’s a sign that the LRT is doing something right. I’m happy to see us all coming together in consensus, even if it takes awhile.

Maybe Paraceratherium is really a giant horse.

Figure 1. Subset of the large reptile tree focusing on ungulates and their kin.

Today’s heresy began when several ungulate taxa
were added to the large reptile tree (LRT, Fig. 1, now 907 taxa, completely resolved with 228 traits). Equus, the horse; Paraceratherium, the giant hornless ‘rhino’; Ceratotherium the white rhinoceros and Embolotherium, a  Mongolian brontothere.

It is widely accepted
and supported by the LRT that horses and rhinos share a common ancestor (Fig. 1). In this case, the LRT recovered either 1) an overlooked relationship, or 2) a case of convergence between Paraceratherium and Equus (Fig. 2). Wikipedia  notes that rhinos are more closely related to tapirs. In the LRT tapirs are basal to a sister clade to the rhino/horse clade. Hyracotherium and Heptodon are basal to the rhino/horse clade.

Figure 2. Equus and Paraceratherium currently nest together on the LRT. Additional taxa will, no doubt, change that, but at present, Paraceratherium shares more traits with Equus than Ceratotherium, the white rhino (Fig. 2). The long neck and premaxillay teeth, along with other traits, separate these two from extant rhinos.

Equus ferus (Linneaus 1758; Figs. 2,3) includes several extant horses, mules and zebras. Compared to Hyracotherium the Equus preorbital region is longer, the frontal produces a postorbital bar that contacts the squamosal. The premolars are molarized. All four limbs end in a single toe, digit 3.

Figure 3. Equus the extant horse has a postorbital bar, an elongate rostrum and a single toe on each limb.

Hyracotherium leporinum (Owen 1841; 78 cm long; Eocene, 55-45 mya; BMNH C21361) nests basal to the horse/rhino clade, Equus. Heptodon (Fig. 5) is an Eocene sister. Canines remained. A diastema separated the canine from the premolars. The manus has four hoofed toes. The pes has three hoofed toes. The premolars were becoming molarized. Compare the skull of dog-size Hyracotherium to the similar skull of Paraceratherium, one of the largest land mammals of all time and Equus, the horse.

Figure 4. Hyracotherium is an Eocene horse sister in the LRT. Skull bones are colorized here.

Heptodon (Pachynolophus) posticus (Cope 1882; Eocene, 50 mya; 1m in length) was derived from a sister to Tapirus and was itself a sister to Hyracotherium and the base of brototheres like Embolotherium (below). Heptadon had reduced canines and developed a diastema (lack of teeth) posterior to them. The posterior cranium was slightly elevated. The manus had four digits. The pes had three. 

Figure 5. Heptodon earlier nested with Tapirus, but with the addition of Equus, Hyracotherium, Paraceratherium and Embolotherium it nested closer to them.

The extant white rhinoceros
Ceratotherium simus (extant, Figs. 6, 7)) shares little in common with Paraceratherium, but shares a long list of traits with Embolotherium, including an oddly elevated pair of nasals and the near complete loss of the lumbar region. Both had smaller ancestors, so direct comparisons yield several possible convergences that currently nest as homologs. That’s what happens with taxon exclusion.

Figure 6. Ceratotherium, simum, the white rhinoceros with keratinous horns in dark brown. Note the elevated nasals and convex dentary ventral margin.

Figure 7. Ceratotherium (white rhino) skeleton, distinct from the long-legged Paraceratherium.

The last taxon to be added is
Embolotherium andrewsi (Osborn 1929; Late Eocene; 2.5m tall at the shoulder; Mongolia; Figs. 4, 5). It nests as a sister to the rhino, Ceratotherium, but this is likely to be overturned on convergence when additional taxa are added. This highly derived brontothere (= titanothere) has forked ‘horns’ (= rams). The rams are elevated nasal bones, hollow and fragile. These are in contrast to the solid rams of North American brontotheres. Click here to see the original AMNH illustration of the Embolotherium skull that portrays the area beneath the elevated nasal as a thick fleshy area. Alternatively Wikipedia reports, “the bony nasal cavity extends to the peak of the ram, thus implying that the nasal chamber was greatly elevated, possibly creating a resonating chamber.”

Figure 8. Brontotherium, a sister to Embolotherium, which is known from skulls, but no complete post-crania.

The skull of Embolotherium was 2x wider than tall at the orbits. The molars were much larger than the premolars, which were themselves molarized. The canines were vestiges. The posterior skull was greatly elevated. The dorsal spines were greatly elevated (Fig. 4). The lumbar region was reduced. The ilia were transverse. Four fingers are retained by the manus, indicating an early divergence from three-fingered horses and rhinos.

Figure 9. Embolotherium andrewsi animation modified from the AMNH website (see link above) to show a possible inflatable narial area, contra the original restoration with a fleshy, immobile sub-nasal area.

Figure 10. Paraceratherium pes. Note the reduced lateral and medial toes (2 and 4). As in Equus, and distinct from Ceratotherium, the central toe is much larger.

These are all perissodactyls
(odd-toed ungulates)
despite the fact that the manus has four digits. The pes (with toes) has an odd-number of digits (three or one). Wikipedia nests Desmostylia and Anthracobunidae among the perissodactyls, but they nest with hippos and mesonychids in the LRT.

Hyracodon
is not included here, but nests in the LRT between Hyracotherium and Heptodon, far from Paraceratherium. Apparently Equus and Paraceratherium have not been tested together in phylogenetic analysis under the assumption that one was a horse and the other a rhino.

Finally
note the large third digit of the pes of the giant three-toed horse, Paraceratherium (Fig. 10), as in Equus and distinct from Ceratotherium, which has three toes, but sub equal in size.

The above was dashed off
a little more quickly than usual. Please bring to my attention any typos or dangling hypotheses.

 

References
Cope ED 1882. Paleontological Bulletin 34:187.
Froehlich DJ 2002. Quo vadis eohippus? The systematics and taxonomy of the early Eocene equids (Perissodactyla). Zoological Journal of the Linnean Society. 134 (2): 141–256.
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Osborn HF 1929. Embolotherium, gen. nov., of the Ulan Gochu, Mongolia. American Museum novitates; no. 353.
Owen R 1841. Description of the Fossil Remains of a Mammal (Hyracotherium leporinum) and of a Bird (Lithornis vulturinus) from the London Clay. Transactions of the Geological Society of London, Series 2, VI: 203-208.

wiki/Equus
wiki/Hyracotherium
wiki/Embolotherium
wiki/Paraceratherium
wiki/Heptodon

Large vs. tiny vascular channels in tetrapods

Huttenlocker and Farmer 2016
have tied red blood cell (RBC) size to vascular diameter in the bones of fossilized tetrapods in part to determine when greater aerobic capacity evolved… something we actually already know based on stance, extant homologs, etc. Their conclusions support tradition and are broadly applicable (Fig. 1). This appears to be a lot of work with a large resulting dataset.

The Huttenlocker and Farmer abstract reports
“We find that several fossilizable aspects of bone microstructure, including the sizes of vascular and lacunar (cellular) spaces, provide useful indicators of RBC size in tetrapods.”

Figure 1. from Huttenlocker and Farmer 2016, white while labels added. The family tree shown here is not recovered in the LRT.

The Huttenlocker and Farmer graphic
show that turtles are about like amphibians in vascular and RBC size. (Fig. 1). It also indicates that, compared to extant mammals, cynodonts in the earliest Triassic sometimes had smaller vascular channels and RBCs, sometimes had similar RBCs and sometimes had larger RBCs. However, the chart also indicates that the pigeon has larger RBCs than a duck. Alligators and crocodiles are different from one another and two congeneric lizards are different from one another in RBC size, but not by much.

Results:
The shrew and only one of the rabbits appear to have the smallest RBCs, based on the figure 1 graphic. Based on the figure 2 graphic, the pigeon has more of the smallest vascular diameters.

Figure 2. Above: Vascular channels in an amphibian (left) and mammal (right). Below: Chart from Huttenlocker and Farmer detailing the vascular sizes recovered from their observations. Red lines and type were added by me. Gray area was also added by me. Red = mammals. Violet = birds. Blue = reptiles. Green = amphibians. 

A few questions arise:

1. Bone cross-sections in some warm-blooded mammals are similar to some cold-blooded reptiles if the largest channels are not considered. Does this mean anything?
2. White blood cells are often much larger than red blood cells. How does that work in the smaller channels?
3. How does ontogeny, especially degree of development at birth, affect RBC size and metabolism? Perhaps that’s the next step in this study.
4. How does body size alone correlate with RBC size?
5. How does relative level of activity alone correlate with RBC size? Perhaps adding sloths and hummingbirds would be appropriate. Perhaps sedentary vs, athletic humans, too.
6. Do active (warm-blooded) fish and sea turtles have smaller RBC sizes than passive fish and desert turtles?

Interesting study.

References
Huttenlocker AK and Farmer CG 2016. Bone microvaculature tracks red blood cells zip diminution in Triassic mammal and dinosaur forerunners. Current Biology online here.

Sciurumimus: a feathered sister to Ornitholestes and Microraptor

This specimen is old news for many.
It came to my attention in a YouTube video lecture you can see here.

Figure 1. Sciurumimus in situ. Only some off the tail filaments are colored here. Most of the skeleton as buried below the bedding plane. It would be interesting to dig out the remaining matrix behind the hands and legs with the understanding that sister taxon Microraptor has long feathers there. Total length ~ 60cm.

Sciurumimus albersdoerferi (Rauhut et al. 2012; Late Jurassic, 150 mya; Bürgermeister Müller Museum Solnhofen (BMMS) BK 11) is traditionally considered a basal coelurosaurian theropod, but was originally considered a basal megalosaur. Here it nests with Ornitholestes, close to Microraptor, also a Late Jurassic taxon. Microraptor is an Early Cretaceous taxon.

This specimen
(Fig. 1) has filament-like tail feathers growing in a pattern like squirrel tail hair over the proximal tail as in several ornithischians. There is a small egg-like shape between the ischia. Not sure what it is, but if you’re smiling right now, you’re guessing that this specimen is not a post-hatchling juvenile.

Figure 2. Skull of Sciurumimus with bones colorized.

It would be interesting
to dig out the remaining matrix behind the hands and legs with the understanding that sister taxon Microraptor has long feathers there.

Figure 3. Sciurumimus manus and pes using DGS to find the best elements from both extremities and reassemble them. Note the shift of pedal digit 2 to metatarsal 3 in situ, repaired in vivo.

Surprisingly
pedal digit 2 has taphonomically drifted to metatarsal 3. Pedal digits 1 and 5, if present, are string-like and spindly vestiges.

Size vs. Juvenile status
Sciurumimus is correctly sized as a basal coelurosaurian, but tiny compared to megalosaurids. Rauhut et al. considered their specimen a megalosaur “probably early-post-hatchling” with teeth that are “markedly similar to that of basal coelurosaurian theropods.”. They nested Sciurumimus between spinosaurs and Megalosaurus and kin.

So why did Rauhut et al. consider their find a megalosaur? And a juvenile?

From the Rauhut et al. diagnosis: 
Megalosauroid theropod with the following apomorphic characters:

1. axial neural spine symmetrically “hatchet-shaped” in lateral view;
2. posterior dorsal neural spines with rectangular edge anteriorly and lobe-shaped dorsal expansion posteriorly;
3. anterior margin of ilium with semioval anterior process in its dorsal half.

Unfortunately these traits also describe
Compsognathus and Ornitholestes, among other coelurosaurs. So, in theitr discussion Rauhut et al. list other synapomorphies of megalosaurids present in Sciurumimus.

1. An elongate anterior process of the maxillary body
2. a medially closed maxillary fenestra
3. a very slender anterior process of the lacrimal
4. a lateral blade of the lacrimal that does not overhang antorbital fenestra’
5. the presence of a deep fossa ventral to the basioccipital condyle
6. a splenial foramen that opens anteroventrally
7. a slightly dorsally expanded anterior end of the dentary
8. a pronounced ventral keel in the anterior dorsal vertebrae
9. the absence of a posteroventral process of the coracoid,
10.  and an enlarged manual ungual I.

Note:
The LRT recovers a different theropod tree topology and nests Sciurumimus apart from megalosaurs by using different character traits and by interpreting Sciurumimus differently. This was done without referring to more recent papers, like Godefroit et al. 2013, or having the specimen to study firsthand. According to Wikpedia, Godefroit et al. nested Sciurumimus with the much larger Sinraptor, among taxa tested here, and far from Ornitholestes. So now we have three competing theropod tree topologies. At least now Sciurumimus actually looks like a transition between Ornitholestes and/or Compsoognathus and micorraptors.

Juvenile traits present in Sciurumimus, according to Rauhut et al. include:

1. the body proportions, with a very large skull and rather short hindlimbs
2. lack of fusion in the skeleton (unfused neurocentral sutures in all of the vertebral column
3. unfused sacral vertebrae
4. lack of fusion between elements of the braincase
5. a coarsely striated bone-surface texture in all skeletal elements
6. and a very regular pattern of tooth development in the maxilla, possibly indicating that no teeth had been replaced.

FIgure 4. Ornitholestes nests as a sister to Sciurumimus, between Compsognathus and Microraptor. Sciurumimus is about the size of Microraptor at 60 cm in length.

Figure 5 Subset of the LRT that includes Sciurumimus and kin.

Note:
The Solnhofen formation, from which Sciurumimus was recovered, has no large megalosaurid theropods. But it does have small coelurosaurian theropods, like Compsognathus, which nests as a more primitive relative one node away in the LRT (Fig. 5).

As readers may recall
the LRT finds several clades of birds, near-birds and bird mimics, including a basal radiation of several clades of post-Archaeopteryx birds that became extinct by the end of the Cretaceous. Furthermore, as readers may recall, small theropods appear at the base of many theropod clades, including those that create giants. So, there may not have been a gradual size decrease leading to birds, throughout the Theropoda, just including the Troodontidae (which includes extant birds).

References
Rauhut OWM, Foth C, Tischlinger H and Norell MA 2012. Exceptionally preserved juvenile megalosauroid theropod dinosaur with filamentous integument from the Late Jurassic of Germany. Proceedings of the National Academy of Sciences. 109 (29): 11746–11751.

Godefroit P, Cau A, Hu D-Y, Escuillié F, Wu, W and Dyke G 2013. A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds. Nature. 498 (7454): 359–362.

Baby Limusaurus had teeth!

This is pretty remarkable.
Wang et al. 2016 reported on a growth series for Limusaurus (Xu et al. 2009; Jurassic, Oxfordian; 1.7m in est. length; IVPP V 15923; Figs. 1-5,) “the only known reptile to lose its teeth and form a beak after birth.”  

You might remember
Limusaurus became famous earlier for its tiny forelimbs complete with a digit 0 medial to digit 1, that made theropod workers go bonkers because they assumed the digits present were 1-4, not 0-3.

Figure 1. Limusaurus also has four fingers and a scapula with a robust ventral area, like Majungasaurus, but those four fingers are not the same four fingers found in Majungasaurus.

Wang et al. report,
“The available data are important for understanding the evolution of the avian beak.” Except… Limusaurus is not close to the avian line of ancestry anyway you look at it. The LRT nests Limusaurus, with or without teeth, with Khaan, a toothless, beaked oviraptorid. Wang et al. nest Limusaurus with Elaphrosaurus (Fig. 3) even though Khaan is part of their taxon list. So something is not scored right. Not sure about the discrepancy, but some of that could be due to the misidentification of manual digits 0-3.

Figure 2. Khaan, an oviraptorid that nests with Limusaurus in the large reptile tree AND the repaired Cau, Brougham and Naish tree.

Wang et al. report,
“The ontogenetically variable features (e.g. teeth/no teeth, etc.) have little effect on its phylogenetic position.” The LRT agrees. Wang et al. report that no matter which ontogenetic stage is tested for Limusaurus, it always nests with or near the ceratosaur, Elaphrosaurus (Fig. 3).The LRT disagrees.  In other words, with or without teeth, the topology does not change. In the LRT  toothed juvenile Limusaurus also nested with Khaan. Toothed Juravenator and Sinosauropteryx nest as sisters to that clade. The large Compsognathus specimen CNJ79 (Fig. 6) was a basal taxon. All of these sisters are closer to Limusaurus in size and morphology than is Elaphrosauru (Fig. 3).

Figure 3. Elaphrosaurus is known from a partial skeleton lacking a skull. Adult Limusaurus added to scale. Wang et al. consider these two to be sister taxa among basal theropods, which is not confirmed by the LRT.

The ontogenetic series of Limusaurus
is shown in figure 4. Not all the specimens are complete. None are shown to scale. All are portrayed as tiny rough tracings. I think this lack of detail is one shortcoming of the paper.

Figure 4. Specimens attributed to Limusaurus, not to scale, from Wang et al. 2016.

Wang et al. also provided
reconstructions of a juvenile and adult Limusaurus (Fig. 5). Unfortunately, Wang et al. filled in all the missing bones and gave both reconstructions something of a generic theropod character, lacking some of the traits unique to this genus.

Figure 5. Limusaurus reconstructions from Wang et al. 2016, to scale and not to scale. The angle of the pubis is difficult to determine.

That Limusaurus juveniles had teeth
and adults did not, tells us less about the avian line and more about the oviraptorid line of theropod dinosaurs.

Figure 6. The large (from Peyer 2006) and small Compsognathus specimens to scale. Several different traits nest these next to one another, but at the bases of two sister clades. Note the differences in the forelimb and skull reconstructions here. There may be an external mandibular fenestra. Hard to tell with the medial view and shifting bones.

References
Wang S, Stiegler J, Amiot R, Xu W, Du G-H, Clark JM, Xu X 2016. Extreme ontogenetic changes in a ceratosaurian theropod. Currently Biology 27:1-5 plus SupData.

Scale models from the vault

You can also title this post: Toys for Christmas.

Yesterday I presented
several full scale models of prehistoric reptiles. Today, some scale models are presented.

Figure 1. Camarasaurus adult scale model.

Camarasaurus (Fig. 1) is a Late Jurassic sauropod.

Figure 2. Mosasaurus? scale model.

Mosasaurus, or is this Tylosaurus (Fig. 2)? I can’t remember. The belly is sitting on a ‘rock’.

Figure 3. Kronosaurus scale model.

Kronosaurus (Fig. 3) is here based on the Yale skeleton, which was revised here with a bigger belly among other traits.

Figure 4. Styracosaurus and Albertasaurus to scale.

Styracosaurus (Fig. 4) is a ceratopsian, derived from Yinlong. Albertasaurus is a theropod, close to Tyrannosaurus.

Figure 5. Tapinocephalus scale model.

Tapinocephalus (Fig. 5) is an herbivorous tapinocephalid, close to Moschops.

Figure 6. Anteosaurus scale model.

Anteosaurus (Fig. 6) is an anteosaur known from the skull only, close to Titanophoneus, which here provides the body proportions.

These were produced 
back in my heyday, as models for paintings in books, and just to see how they would turn out. Most are made of Sculpey over a wire frame. After baking the soft clay turns into a hard plastic. So far these all remain on my shelves.

 

 

 

Full scale models from the vault

Back in the day
when I was writing and illustrating dinosaur books (1988~1992) I also built a few full scale models that I intended to use as subjects for paintings and museum displays. Here are most of them. Other models include the pterosaur skeletons you can see here.

Figure 1. Brachiosaurus skull, carved out of wood. Full scale.

At this point in my life
(1990s) the work (paintings / illustrations) was considered ‘acceptable.’ Even my papers were ‘acceptable.’ Unfortunately, when I started applying phylogenetic analysis to taxa and discovering new and overlooked relationships (published at ReptileEvolution.com, ) my work and manuscripts were no longer considered ‘acceptable,’ despite the fact that early discoveries made here are being re-discovered and validated years later by PhDs.

FIgure 2. Camarasaurus baby model. Full scale.

This Dimorphodon
(Fig. 3) was among the first of the models, based on Kevin Padian’s 1983 running illustrations.

Figure 3. Dimorphodon skull with dog hair for pycnofibers.

Not sure why I produced this plesiosaur
because it took up a bunch of garage space and only entertained the mailman. Ultimately it was purchased by the AMNH, but never put on display. Where it is now is anyone’s guess.

Figure 4. Plesiosaur model. Full scale. See figure 5 for the face.

Much of this plesiosaur
was fashioned at the late Bob Cassilly studios, who was a famous St. Louis sculptor and founder of The City Museum. Bob contacted me after seeing my book, Giants, because he had been commissioned to produce some of the giant marine animals pictured therein. Through that friendship in the 1990s, I was able to study specimens, including Sharovipteryx and Longisquama, from the traveling Russian Dinosaur Exposition that came to the City Museum for their first stop.

Figure 5. Plesiosaur model head detail. Full scale. Teeth are tree thorns.

Among the smaller full scale models
is this sparrow-sized Pterodactylus in a bipedal pose (Fig. 6), ready to take flight.

FIgure 6. Pterodactylus scolopaciceps (n21) model. Full scale. Later I learned that this genus was plantigrade (flat-footed), when quadrupedal. This one is about to take flight from a bipedal configuration. Digitigrady at this instance would have given Pterodactylus a bit more power in its initial leap during take-off.

And based on the evolution book

From the Beginning, these three (Fig. 7) are fleshed out steps in the evolution of tetrapods, cynodonts, mammals and man. Ichthyostega is a bit out of date now.

Figure 7. Ichthyostega, Osteolepis and Thrinaxodon, all more or less ancestral to humans. Full scale.

References
Padian K 1983. Osteology and functional morphology of Dimorphodon macronyx (Buckland) (Pterosauria: Rhamphorhynchoidea) based on new material in the Yale Peabody Museum, Postilla, 189: 1-44.

Titanoides: a rarely studied, but key mammal

Titanoides is rarely studied.
And it (Fig. 1) nests at the base of all large herbivorous mammals in the LRT (Fig. 2). That makes it more interesting than just another pantodont with a much smaller tail and larger canines than its phylogenetic sister, Barylambda nesting at the base of the Xenarathra (Fig. 2).

Figure 1. Titanoides nests between Barylambda (basal Xenarthra) and higher mammalian herbivores.

Titanoides primaevus (Gidley 1917; Late Paleocene, 58 mya; 3m in length) was originally considered a type of brontothere, but is now traditionally considered a pantodont mammal. Sabertooth canines mark this otherwise bear-like and bear-sized herbivore. Distinct from sister taxa, it had clawed digits. The skull was more than twice as wide as tall. Three premolars looked very much like molars. The jugal/zygomatic arch was slender and weak. The tail was a short vestige. Take a look at that odd lower canine (Fig. 1 orange tooth) with a concavity to accommodate the upper canine.

Figure 3. Subset of the LRT focusing on mammals. Titanoides nests at the base of all large herbivores.

Sharp-eyed observers
will see a few very minor taxon shifts in the LRT (Fig. 2). This is what happens when more taxa are added. I also reexamined several poor scores and found a few errors that further cemented and slightly shifted a few relationships.

Happy holidays, everyone!
It’s gratifying to see a growing list of subscribers and readers. I wish you all the best!

References
Gidley JW 1917. Notice of new Paleocene mammal, a possible relative of the Titanotheres. Proceedings of the United States National Museum 52(2187):431-435.

wiki/Titanoides

Two Ectocion specimens: neither is a phenacodontid

After reexamination
of the E. cedrus drawing, I determined that both taxa nest together with Procavia, the hyrax, at the base of the elephant/manatee clade.

Traditional paleontology considers
Ectocion osbornianus [osbornianum] (Cope 1882a, Granger 1915, Thewissen 1990; Fig. 1; Paleocene 55 mya)  a member of the Condylarthra or Phenacodontidae, alongside Phenacodus. Cope 1882a originally named the type, Oligotomus osbornianus from maxillary and dentary fragments with lophodont teeth. The specimen was renamed by Cope 1882e when he realized he had already given a fossil horse than generic name. The genus Ectocion is known from more than 500 jaws and hundreds of loose teeth. Skulls, evidently, are rare.

Figure 1. Ectocion nests with the rock hyrax, Procavia, giving rise to elephants + manatees.

While searching online I found
two distinct skulls referred to Ectocion (Fig. 1). Neither is the holotype which was described from teeth and fragments. The Ectocion on the left is from Thewissen 1990. The one on the right is from Wikipedia. See the difference?

Neither nests with Phenacodus
or any other tested phenacodontid in the LRT. Instead the LRT nests Ectocion with Procavia, the rock hyrax, giving rise to Elephas and Dusisiren all with incisors transforming into proto-tusks and completely lacking a large canine or a dipping transverse premaxilla.

When shifted to phenacodontids
these taxa add 11 steps.

References
Cope ED 1882a. Contributions to the history of the Vertebrata of the lower Eocene of Wyoming and New Mexico, made during 1881. Proceedings of the American Philosophical Society: 139-197.
Cope ED 1882e. Note on Eocene Mammalia. American Naturalist 16:522.
Granger W 1915. A revision of the lower Wasatch and Wind River faunas, Part III: Order Condylarthra, families Phenacodontidae and Meniscotheriidae. Bulletin of the American Museum of Natural History 34:329-361.
Mac Intyre GT 1962. Simpsonictis, a new genus of viverravine miacid (Mammalia, Carnivora). American Museum Novitates 2118: 1-4.
Mac Intyre GT 1966. The Miacidae (Mammalia, Carnivora) Part 1. The systematics of Ictidopappus and Protictis. Bulletin of the American Museum of Natural History 131(2):115-210.
Matthew WD 1937. Paleocene faunas of the San Juan basin, New Mexico. Transactions of the American Philosophical Society, new series 30: 1-510.
Simpson GG 1935. New Paleocene mammals from the Fort Union of Montana. Proceedings of the U. S. National Musem 83: 221-244.
Thewissen JGM 1990. Evolution of Paleocene and Eocene phenacodontidae (Mammalia, Condylarthra). University of Michigan Papers on Paleontology 29:1-107.

wiki/Ectocion

 

Multituberculates and rodents: cousins? or not?

The big question is: what are they?
The LRT nests multituberculates with rodents, but currently that’s a minority view of one.

Kielan-Jaworowska Z and Hurum 2001 wrote:
“Traditionally palaeontologists believed that multituberculates might have originated from cynodonts independently from all other mammals, or diverged from other mammals at a very early stage of mammalian evolution.” Unfortunately these authors do not say which taxa attract multis to the the pre-eutherian grades and clades.

Simpson (1945, p. 168) stated:
“The multituberculate structure was so radically distinctive throughout their history that it seems hardly possible that they are related to other mammals except by a common origin at, or even before, the class as such”

Hahn et al. (1989) and Miao (1993)
reported that multituberculates might be a sister taxon of all other mammals. On the other hand, Kielan-Jaworowska et al. 1986; Miao 1988; Wible 1991; Rougier et al. 1992; Wible and Hopson 1993, 1995; Hurum 1994, 1998a, b) demonstrated the homogeneity of the internal structure of the skull and vascular system of all mammals, including multituberculates.

Hurum et al. 1996; Rougier et al. 1996a report
Multituberculate ear ossicles display the same pattern as those of all other mammals.

The notion
that multituberculates might form a sister taxon of all other mammals is related to the idea that they are close relatives to the Haramiyidae, a family represented until recently only by isolated teeth, with numerous cusps arranged in longitudinal rows, known from the Late Triassic and Early Jurassic mostly in Europe. Key to these thoughts are the idea that most fossil material comes from teeth.

Jenkins et al. (1997)
described from the Upper Triassic of Greenland Haramiyavia clemmenseni, assigned to the Haramiyidae, represented by dentaries and partial maxillae with teeth and fragments of the postcranial skeleton. Haramiyavia has been interpreted as having orthal jaw movement (standard up-down rotation on a glenoid axis). On this basis Jenkins et al. excluded the Haramiyida from the Allotheria, which have propalinal (fore-and-aft) movement of the dentary and backward (palinal) power stroke. In turn Butler (2000) revised all known allotherians and argued that dental resemblance supports the hypothesis that the Multituberculata originated from the Haramiyida.

Kielan-Jaworowska Z and Hurum 2001 wrote:
“Finally, the most recent analyses of mammalian relationships, including analysis of the skeleton of a symmetrodont Zhangheotherium (Hu et al. 1997; here recovered as a pangolin ancestor), and the skeleton of the eutriconodont Jeholodens (Ji et al. 1999; here recovered as a tritylodontid), did not support multituberculate-therian sister-group relationship. In both of these papers the Multituberculata were placed between Monotremata (Ornithorhynchus) and Symmetrodonta (Zhangheotherium), being a sister taxon of all the Holotheria” (last common ancestor of Kuehneotherium and Theria). In other words, close to monotremes.

Kielan-Jaworowska Z and Hurum 2001 wrote about the multi brain:
“The multituberculate brain, designated cryptomesencephalic (characterised by an expanded vermis, no cerebellar hemispheres, and lack of the dorsal midbrain exposure) is very different from that in Theria, which originally had eumesencephalic brains (characterised by a wide cerebellum with extensive cerebellar hemispheres and large dorsal midbrain exposure).”

This appears to assume only one direction for brain development, with no evolutionary backsliding. Unfortunately Kielan-Jaworowska and Hurum employed a hypothetical ancestor for their multituberculate cladogram.

We’ve already seen teeth in whales reverse from the typical W and Y molar cusp patterns, to linear molar cusps to simple pegs.

Figure 1. Rodent and multituberculate right pedes dorsal view. Note the derived pes of Kryptobaatar based on the primitive pedes of Shenshou and Paramys. Multis have a reduced astragalus (orange) for a looser ankle joint for an arboreal niche.

Kielan-Jaworowska Z and Hurum 2001 wrote about the multituberculate foot:
“Another character neglected until recently in phylogenetic analyses of early mammals involves the foot structure. In the multituberculate foot the middle metatarsal (M3) is abducted from the longitudinal axis of the tuber calcanei, while the calcaneus contacts distally the 5th metatarsal (Kielan-Jaworowska and Gambaryan 1994). This type of foot appeared at that time to be unique among mammals, but Ji et al. (1999) described a similar type of foot in the eutriconodont Jeholodens. It follows that there are two groups of characters related to brain and foot structure, which ally multituberculates with eutriconodonts.”

Figure 2. Squirrel pes, not similar to a multi ankle yet still able to clamber and roared on tree trunks.

The trouble is
a large gamut analysis of mammalian relationships does not find a better nesting for those highly-derived, but primitive-brained, rodent-like mutituberculates than with rodents. They have similar teeth, similar extremities, similar skulls. And that twisted heel-bone (calcaneum) is a derived trait. So why are multis supposed to nest with mammals earlier than placentals?

If anyone can produce a pre-therian that attracts multis, please bring it to my attention. So far, I have failed to find out, and so multis continue to nest with rodents and plesiadapids.

References
Kielan-Jaworowska Z and Hurum JH 2001. Phylogeny and Systematics of multituberculate mammals. Paleontology 44, 389–429.