Speaking of taeniodont origins, there’s another candidate: Cimolestes

Yesterday we looked at the origin of taeniodonts, like Stylinodon. and found it nested with Mustela the mink and Phoca the seal. Other workers (Lillegraven 1969, Rook and Hunter 2013) indicated that Cimolestes (Fig.1, Late Cretaceous) was a suitable ancestor to the taeniodonts. So, let’s look at Cimolestes and compare it to related taxa.

Figure 1. Cimolestes mandible from Lillegraven 1969 compared to a phylogenetically basal eutherian the marsupial without a pouch, Monodelphis, the basal tenrec, Maelestes and Cimolestes. All have a slender mandible.

Figure 1. Cimolestes mandible from Lillegraven 1969 compared to a phylogenetically basal eutherian the marsupial without a pouch, Monodelphis, the basal tenrec, Maelestes and Cimolestes. All have a slender mandible without the anterior depth found in Stylinodon, Mustela and Martes in figure 2.

In comparison
Cimolestes is more like the basal eutherians Monodelphis and Maeilestes (Fig. 1) in having a rather slender mandible with incisors anterior to the canines. By contrast, the carnivores Martes, the martin, and Mustela (Fig. 2), and the taeniodonts, Wortmania (Fig. 3) and Stylinodon have a robust mandible, deep anteriorly with canines to the anterior and incisors between them.

Figure 2. Martes, the extant martin, and Mustela, the extant mink or polecat mandibles. Both are deeper in front, more like the taeniodont, Stylinodon.

Figure 2. Martes, the extant martin, and Mustela, the extant mink or polecat mandibles. Both are deeper in front, more like the taeniodont, Stylinodon. Note the number of teeth varies among these closely related taxa.

Lillegraven 1969 wrote: “A smaller carnivorous species described as new of Cimolestes probably represents a primitive stage in the development of miacids, and subsequently fissiped and pinniped carnivores.” Well, we’re all in the same ballpark and thinking along similar lines. Not sure where Cimolestes nests in the LRT yet. Not much is known of it, other than jaw fragments.

Figure 6. Wortmania as drawn freehand by Schoch compared to bones Photoshopped together.

Figure 3. Wortmania as drawn freehand by Schoch compared to bones Photoshopped together. Note the deep mandible, closer in shape to the minks in figure 2 than to Cimolestes in figure 1.

References
Lillegraven JA 1969. Latest Cretaceous mammals of upper part of Edmonton formation of Alberta, Canada, and review of marsupial-placental dichotomy in mammalian evolution. Article 50 (Vertebrata 12) The U. of Kansas Paleontological Contributions. 122pp.
Rook DL and Hunter JP 2013. rooting around the eutherian family tree: the origin and relations of the Taeniodonta. Journal of Mammal Evolution. DOI 10.1007/s10914-013-9230-9

wiki/Cimolestes

Stylinodon may be a giant herbivorous mink

In 1873 
O. C. Marsh 1874) found an extinct Eocene (50.3 to 40.4 Ma) mammal “of great interest. The lower molar teeth, all essentially alike, and inserted in deep sockets” were the most striking feature. He named it Stylodon mirus (Figs. 1,2). All the teeth grew with “persistent pulps” and had a thin layer of enamel. The specimen was considered close to Toxodon with some edentate affinities (Marsh 1897). Stylinodon was placed under the family Stylinodontidae and the order Tillodontia. According to Schoch 1986 (first issue of JVP!) its ancestors were like Onychodectes.

Stylinodon mirus (Marsh 1874; middle Eocene, 45 mya; Figs. 1-2) was originally considered a taeniodont, perhaps derived from Onychodectes. Here it nests with Mustela, the living European mink, among the Carnivora. There were twice as many molars (4), each with a single root, as in the two double rooted molars of the mink. Large claws and certain forelimb traits indicate that Stylinodon was a digger, not a cursor.

The present nesting
of Stylinodon mirus (YPM VP 011095, Marsh 1874; Figs. 1, 2) in the Carnivora occurred when I realized it was a poor fit at the base of the Condylarthra/Paenungulata, despite its herbivorous dentition and tusk-like teeth (canines, not incisors).

Figure 1. Stylinodon skull. Note the transverse premaxilla, a trait of the Carnivora.

Figure 1. Stylinodon skull. Note the transverse premaxilla, a trait of the Carnivora.

Distinct from condylarths
Stylinodon has a transverse premaxilla, essentially invisible in lateral view. The lower canine is the anteriormost tooth on the dentary. These traits are shared with other members of the Carnivora. In the present taxon list Stylinodon shares more traits with Mustela, the European mink (Fig. 1) despite the loss of molar cusps and increase in size. They both were diggers. Together they nest with Phoca, the seal, and Palaeosinopa, the amphibious piscivore, all derived from a sister to Procyon, the omnivorous raccoon (Fig. 2).

Figure 1. Stylinodon compared to Mustela, the European mink to scale.

Figure 2 Stylinodon compared to Mustela, the European mink to scale.

As in the earlier issue
with indricotheres, related taxa can have distinctively different types of teeth, one more reason to not weight dental traits too heavily, unless that’s all you have.

Figure 2. Mustela the European mink is an extant relative to Stylinodon.

Figure 3. Mustela the European mink is an extant relative to Stylinodon.

Mustela lutreola (Linneaus 1761; extant European mink; up to 43cm in length) is a fast and agile animal related to weasels and polecats. Mustela lives in a burrow, but it also swims and dives skilfully. It is able to run along stream beds, and stay underwater for one to two minutes. Mustela is derived from a sister to Phoca and other seals, all derived from a sister to Procyon. With this close relationship, Stylinodon (Fig. 2 a giant weasel with simple teeth.

Schoch and Lucas 1981
and Schoch 1983 considered Stylinodon and kin derived from a sister to the long-legged basal condylarth, Onychodectes. The large reptile tree (LRT, Fig. 2) does not support that nesting. Onychodectes has a long premaxilla lacking in taeniodonts.

Figure 2. Subset of the LRT showing the Carnivora nesting at the base of the Eutheria (placental mammals).

Figure 4. Subset of the LRT showing the Carnivora nesting at the base of the Eutheria (placental mammals).

Schoch and Lucas 1981
determined that Stylinodon had two upper incisors (one lower), a giant canine, four premolars and three molars, as in Onychodectes. That may be so, but the premolars and molars look alike.

 

Figure 6. Wortmania as drawn freehand by Schoch compared to bones Photoshopped together.

Figure 5 Wortmania as drawn freehand by Schoch compared to bones Photoshopped together.

Wortmania (Hay 1899, Williamson and Brusatte 2013; above) and Psittacotherium (Cope 1862; below) are related to Stylinodon. All are among the largest taxa in the early post-Cretaceous, derived from smaller weael-like basal mammals in the Cretaceous.

Figure 7. Psittacotherium in various views.

Figure 6.  Psittacotherium in various views. Overall it is elongated to more closely match related taxa.

It is rare but not unheard of
for members of the Carnivora to become omnivores and herbivores. Think of the giant panda and certain viverrids. Now the stylinodontid taeniodonts join their ranks.

References
Linneaus C von 1761. xxx
Marsh OC 1874. Notice of new Tertiary mammals 3. American Journal of Science. (3) 7i: 531-534.|
Marsh OC 1897. The Stylinodontia, a suborder of Eocene Edentates. The American Journal of Science Series 4 Vol. 3:137-146.
Rook DL and Hunter JP 2013. Rooting Around the Eutherian Family Tree: the Origin and Relations of the Taeniodonta. Journal of Mammalian Evolution: 1–17.
Schoch RM and Lucas SG 1981. The systematics of Stylinodon, an Eocene Taeniodont (Mammalia) from western North America. Journal of Vertebrate Paleontology 1(2):175-183.
Schoch RM 1983. Systematics, functional morphology and macroevolution of the extinct mammalian order Taeniodonta. Peabody Museum of Natural History Bulletin 42: 307pp. 60 figs. 65 pls.

 

wiki/Stylinodon
wiki/Mustela

There’s a Pteranodon wing at the University of Missouri

No doubt
it was reassembled into its present position, despite the in situ appearance.

Figure 1. There is just no way to avoid reflections on this stairwell specimen of Pteranodon, if you want to capture the whole specimen in one shot from a distance.

Figure 1. There is just no way to avoid reflections on this stairwell specimen of Pteranodon, if you want to capture the whole specimen in one shot from a distance.

Mizzou has very few other vertebrate fossils.
The University of Missouri (Mizzou) Geology Department has a wonderful and complete small ichthyosaur from the Holzmaden and they have a partial parasuchian skull from the Petrified Forest. I don’t think the Mizzou Pteranodon wing has a number. Small portions, like the wrist and free fingers are restored.

Figure 1. The Mizzou Pteranodon wing is average in size and not very robust or gracile compared to others shown here. Click to enlarge.

Figure 2. The Mizzou Pteranodon wing is average in size and not very robust or gracile compared to others shown here. Click to enlarge.

If we take the wing at face value
and place it in context with other Pteranodon wings (Fig. 2), we find that it is not the largest, nor the smallest, not the most robust, nor the most gracile. The scapulocoracoid is relatively small. This could be a chimaera.

And while we’re on the subject of variation,
it is worthwhile to consider the post-cranial variation in Pteranodon, a subject we touched on earlier here and in figure 2, but has not been adequately addressed elsewhere.  The lack of more than a few skulls matched to post-crania (Fig. 2) has hampered efforts, but a decent cladogram of Pteranodon interrelationships can still be managed.

Figure 2. The Tanking-Davis specimen compared to other forms. Specimen w and specimen z appear to be the closest to the Tanking-David specimen. Specimen 'w' = Pteranodon sternbergi? USNM 12167 (undescribed). Specimen 'z' = Pteranodon longiceps? Dawndraco? UALVP 24238. Click to enlarge.

Figure 2. The Tanking-Davis specimen compared to other forms. Specimen w and specimen z appear to be the closest to the Tanking-David specimen. Specimen ‘w’ = Pteranodon sternbergi? USNM 12167 (undescribed). Specimen ‘z’ = Pteranodon longiceps? Dawndraco? UALVP 24238. Click to enlarge.

Indricotheres: horse-like rhinos? Or rhino-like horses?

Earlier the large reptile tree (LRT, 993 taxa) nested the traditional giant rhinos, Paraceratherium (Fig. 1) and Juxia, with the horses Equus (one toe, Fig. 1) and Mesohippus (three toes) based on several traits lacking in Ceratotherium, the extant white rhinoceros. This heretical hypothesis of relationships is not in the academic literature. Evidently dental details separate horses from rhinos. The LRT employs very few dental traits.

So today’s quandary involves convergence.
Do we trust the teeth that say indricotheres are rhinos?
Or are the teeth convergent?
Do we trust the rest of thel traits that say indricotheres are three-toed horses?
Or are all the non-dental traits convergent?

Adding taxa
has solved issues like this in the past. Today we add the basal rhino, Hyrachyus. We add a taxon considerd basal to the indricotheres, Pappaceras. And we add a basal horse, Miohippus (Fig. 3) hoping for resolution and consensus.

Figure 1. Equus the horse shares many traits with Paraceratherium, the giant rhino/horse.

Figure 1. Equus the horse shares many traits with Paraceratherium. So is this a giant rhino-like horse? Or horse-like rhino?

First let’s go back to the literature…
I wrote to Dr. Don Prothero, a renown expert in rhinos, asking if he knew of any phylogenetic analysis that included both horses and rhinos and their last common ancestor. Since his answer did not include the title of any such paper, I went to his biography and found a few likely resources. Unfortunately the best of them (see below) predate the advent of software in phylogenetic analysis and often rhinos are tested separate from horses.

Prothero, Manning and Hanson 1986
describe a situation in which rhinos had been little studied. They report, “We have tried to straighten out some of the problems in rhinoceros relationships.” They open with a history of the study. “Osborn 1898 was the first to recognize our modern division of rhinocerotoids into three distinct families: Hyracodontidae (including giant indricotheres), Amynodontidae and Rhinocerotidae.” They presented a new hypothesis of relationships with a de-emphasis on dental traits. They employed Hyrachyus as their outgroup and did not include any horses. Their tree recovered Forstercooperia and Pappaceras (Fig. 2) as sisters to the indricothere clade and that clade a sister to the clade that included Hyracodon.

As a side note
Embolotherium, the titanothere currently nesting with the extant white rhino, did not make the rhino list of taxa.

Figure 2. Pappaceras is one of the closest known sisters to the indricotheres according to rhino cladograms. It nests between Mesohippus and Miohippus in the LRT.

Figure 2. Pappaceras is one of the closest known sisters to the indricotheres according to rhino cladograms. It nests between Mesohippus and Miohippus in the LRT (Fig. 3).

Basal to the indricotheres,
The Prothero, Manning and Hanson 1986 cladogram recovered:

  1. Rhinocerotoidea  diagnosed on the basis of dental traits plus a cylindrical odontoid process on the atlas and a fused intervertebral canal on the atlas.
  2. Hyracodontidae had a tridactyl manus, long limbs and metapodials, laterally compressed carpus and tarsus.
  3. Paraceratheriinae (= Indricotheriinae) had a large size, enlarged lower P1; upper M3 metacone reduced, conical incisors.

When I add
Hyrachyus to the LRT it nests basal to the rhinos confirming the hypotheses of prior workers. Surprisingly Mesohippus did not nest with Miohippus and Equus in the LRT. Furthermore, Pappaceras did not nest with Juxia and Paraceratherium in the LRT. Close… but the clades did not separate into rhinos and horses… and indricotheres did not nest with Hyracodon and the rhinos.

Figure 3. Subset of the LRT focusing on the hyracotheres, including horses and rhinos. Traditional rhinos are in light green. Traditional horses are in tan. Is this the result of convergence or taxon inclusion? 

Figure 3. Subset of the LRT focusing on the hyracotheres, including horses and rhinos. Traditional rhinos are in light green. Traditional horses are in tan. Is this the result of convergence or taxon inclusion?

Prothero et al. 1988 reported
“Hyraxes are closer to perissodactyls than to elephants and sirenians. Perissodactyls are closer to whales and elephants than they are to artiodactyls.” The LRT does not support those findings.

 

re: Miohippus
Wikipedia reports, “Miohippus also had a variable extra crest on its upper molars, which gave it a larger surface area for chewing tougher forage. This would become a typical characteristic of the teeth of later equine species.” 

Miohippus skull and skeleton. Is this a sister to the ancestor of horses and indricotheres?

Miohippus skull and skeleton. Is this a sister to the ancestor of horses and indricotheres? Compare the foot the that of Paraceratherium (Fig. 1).

And…
“Miohippus had two forms, one of which adjusted to the life in forests, while the other remained suited to life on prairies. The forest form led to the birth of Kalobatippus (or Miohippus intermedius), whose second and fourth finger again elongated for travel on the softer primeval forest grounds. The Kalobatippus managed to relocate to Asia via the Bering Strait land bridge,”

That’s all it takes
|to start a new clade. Wikipedia reports, Kalobatippus ate leaves and was characterized by unusually long legs.”

Summary
Let’s consider the possibility that indricotheres could be horses with rhino-like teeth, perhaps due to a similar herbivorous diet. Perhaps this result will stimulated further interest in the subject.

References
Marsh OC 1874. Notice of new equine mammals from the Tertiary formation. American Journal of Science 7(39):247-258.
Prothero DR, Manning E and Hanson CB 1986. The phylogeny of the Rhinocerotoidea (Mammalia, Perissodactyla). Zoological Journal of the Linnean Society 87:341-366.
Prothero DR, Manning EM and Fischer M 1988. The phylogeny of the ungulates Pp. 201-234 in The phylogeny and classification of the tetrapods, volume 2: Mammals (ed. Benton MJ) Systematics Association special volume 35B:
Wang H, Bai B, Meng J and Want Y-Q 2016. Earliest known unequivocal rhinocerotoid sheds new light on the origin of Giant Rhinos and phylogeny of early rhinocerotoids. Nature Scientific Reports 2016.
Wood H E 1963. A primitive rhinoceros from the Late Eocene of Mongolia. American Museum Noviates 2146:1–11.

wiki/Miohippus

What made those Early Triassic tracks?

Mujal et al. 2017
reported on an Early Triassic tracksite dominated by what they considered to be ‘archosauromorph’ trackmakers (Fig. 1), akin to coeval Euparkeria (Fig. 2).

Figure 1. Early Triassic tracks from Mujal et al. 2017 compared to Didelphis, the extant Virginia opossum to scale. I don’t see any lateral expansion due to a hooked metatarsal (as in Fig. 2) here.

Unfortunately, the track in question
identified as Prorotodactylus mesaxonichnus IPS-93867 had three long slender digits (2–4), about the same length, #2 a stitch shorter. #1 and #5 much shorter. The width is about 2 cm. The pes is much larger than the manus. All in all, it is close to the shape and size of Didelphis, the extant, but very ancient Virginia opossum (Fig. 1). Originally the track was assigned to a taxon near Euparkeria, and it’s a pretty good match, but there is no indication of a hooked metatarsal 5 and digit 3 is often the longest (BUT see below).

Figure 2. Euparkeria pes.

Figure 2. Euparkeria pes is similar in size and configuration to the Early Triassic trackmaker. Note the hooked lateral metatarsal (#5) and digit #3 the longest.

Among archosauriformes
in proterosuchids and Garjainia pedal digit 4 is the longest. Some chorisoderes retain this pattern. In some 3 and 4 are the longest. In Champsosaurus 3 is the longest. Similar patterns are found in phytosaurs. In basal proterochampsids digit 3 is the longest. In derived proterochampsids like Tropidosuchus and Lagerpeton digit 4 is not slender and it is the longest in the series. None are matches for the

Among euarchosauriformes
In Euparkeria, as in most euarchosauriformes, digit 3 is longer than 2 and 4 and much longer than 1 and 5. In erythrosuchids pedal digits 2 and 3 are slightly longer than 4, but all are short and large. Ornithosuchus has long toes and short fingers, but it is a much larger taxon. Pedal digit 3 is still the longest. Same with Qianosuchus and Ticinosuchus.

Among basal diapsids and enaliosaurs
the pes is typically asymmetric with digit 4 or digits 3 and 4 the longest. The same with lepidosaurs. Basal lepidosauromorphs have short digits.

Basal synapsids are no match, either.
because they, too, have asymmetric feet. That changes with therapsids, but most have short toes, similar sized manus and pes and are Permian in age. That changes with the pre-mammals, the tritylodontids, like Spinolestes, which extend into the Cretaceous. The only problem with many of the trackmakers with symmetrical pedes, they all had narrow-gauge trackways – distinct from the Early Triassic trackways, which are quite wide-gauge. We can’t discuss mammals, because they only developed in the Late Triassic, at the earliest.

There’s one more factor
To me it looks like the tracksite toes are webbed. If the trackmaker was mostly aquatic, it was more likely to have sprawling hind limbs.

So, in summary
the best match in terms of size, relative size, age, morphology and such… appear to be aquatic Early Triassic tritylodontids… or tiny unknown archosauromorphs somewhere between Proterosuchus and Euparkeria. That hypothetical taxon would have had a pes transitional between the long digit 4 of Proterosuchus and the long digit 3 of Euparkeria. I really could not find a better match for this tracksite maker. I could not nail it down with available candidates.

References
Mujal E, Fortuny J, Bolet A, Oms O, López JA 2017. An archosauromorph dominated ichnoassemblage in fluvial settings from the late Early Triassic of the Catalan Pyrenees (NE Iberian Peninsula). PLoS ONE 12(4): e0174693. https://doi.org/10.1371/journal.pone.0174693

New phylogeny of Stegosauria

A few problems here.
Raven and Maidment 2017 have produced a phylogeny of the clade Stegosauria (Fig. 1). Unfortunately it splits stegosaur proximal outgroups (in the large reptile tree (LRT, subset in Fig. 2) from stegosaurs. It splits stem or basal ankylosaurs from derived ankylosaurs. And it supports a clade, the Thyreophora, that was found to be paraphyletic in the LRT. Finally, it nests Laquintasaurus with Scutellosaurus, contra the LRT.

Figure 1. Phylogeny of Stegosauria according to Ravena and Maidment 2017. Yellow/green taxa are stegosaurs and their ancestors in the LRT. Gray taxa are nodosaurs and ankylosaurs. Blue taxon is a basal ceratopsian. Magenta taxon is lost. The LRT nests stegosaurs apart from ankylosaurs, thus the Thyreophora is paraphyletic and invalid.

Figure 1. Phylogeny of Stegosauria according to Ravena and Maidment 2017. Yellow/green taxa are stegosaurs and their ancestors in the LRT. Gray taxa are nodosaurs and ankylosaurs. Blue taxon is a basal ceratopsian. Magenta taxon is lost. The LRT nests stegosaurs apart from ankylosaurs, thus the Thyreophora is paraphyletic and invalid.

Raven and Maidment appear to have chosen outgroups
for Stegosauria instead of letting a larger gamut analysis choose them. So, once again, taxon exclusion lessens the effectiveness of and confidence in a hypothesis.

Figure 2. Phytodinosauria with a focus on Stegosauria (yellow green).

Figure 2. Subset of the LRT: Phytodinosauria with a focus on Stegosauria (yellow green).

References
Raven TJ and Maidment SCR 2017. A new phylogeny of Stegosauria (Dinosauria, Ornithischia). Palaeontology 2017:1–8.
Barrett PM, Butler RJ, Mundil R, Scheyer TM, Irmis RB, Sánchez-Villagra MR (2014) A palaeoequatorial Ornithischian and new constraints on early dinosaur diversification. Proceedings of the Royal Society B 281(1791): 20141147. http://dx.doi.org/10.1098/rspb.2014.1147

Laquintasaura: verrrry basal ceratopsian from the Early Jurassic

Figure 2. Phytodinosauria with a focus on Stegosauria (yellow green).

Figure 1. Subset of the LRT focusing on the Phytodinosauria. Here Laqunitasaura nests at the base of the Ceratopsia.

I still hold to the hypothesis|
that a phylogenetic analysis that is able to lump and separate taxa is better than one that cannot do this. In the large reptile tree (LRT, 989 taxa), Laquintasaura venezuelae (Barrett et al. 2014; Early Jurassic, 200mya ~1m in overall length; Fig. 2) nests at the base of the ceratopsia (outside of Hexinlusaurus and Yinlong) and not far from the base of the Ornithopoda (outside of Changchunsaurus). It is very plesiomorphic and very early even for an ornithischian, let alone a ceratopsian.

Figure 1. Laquintasaura and tooth from Barrett et al. 2014. The early and plesiomorphic ornithischian has a naris shifted dorsally and other traits that nest it between the base of the onithopoda (Changchunsaurus) and the base of the ceratopidae (Hexinlusaurus).

Figure 2. Laquintasaura and tooth from Barrett et al. 2014. The early and plesiomorphic ornithischian has a naris shifted dorsally and other traits that nest it between the base of the onithopoda (Changchunsaurus) and the base of the ceratopidae (Hexinlusaurus). Compare to premaxillary teeth in figure 3.

Barrett et al. were not so sure where Laquintasaura nested
as they reported, “A strict consensus of these 2160 MPTs places Laquintasaura in an unresolved polytomy with the major ornithischian clades Heterodontosauridae, Neornithischia and Thyreophora along with other early ornithischian taxa, such as Lesothosaurus.”

The Barrett et al. diagnosis reports:
“Laquintasaura can be differentiated from other early ornithischians by the following autapomorphic combination  of dental characters: cheek tooth crowns have isosceles-shaped outlines, which are apicobasally elongate, taper apically, are mesiodistally widest immediately apical to the root/crown junction, possess coarse marginal denticles extending for the full lengths of the crown margins, and possess prominent apicobasally extending striations on their labial and lingual surfaces. Postcranial autapomorphies include: sharply inflected dorsal margin of ischium dorsal to the obturator process; femoral fibula epicondyle medially inset in posterior or ventral views; and astragalus with a deep, broad, ‘U’-shaped notch in anterior surface.”

I had no access to the fossil(s).
And I had to trust the drawing produced by Barrett et al. (Fig. 1) for my data. Contra the Barrett et all. analysis, there was no loss of resolution with Laquintasaura in the LRT.

Figure 2. The skull of Yinlong a basal certatopsian.

Figure 3 The skull of Yinlong a basal certatopsian. Those premaxillary teeth are quite similar to those figure in Barrett et al. for Laquintasaura. Note the dorsal naris, horizontal ventral premaxilla.

References
Barrett PM, Butler RJ, Mundil R, Scheyer TM, Irmis RB, Sánchez-Villagra MR. 2014. A palaeoequatorial ornithischian and new constraints on early dinosaur diversification. Proceedings of the Royal Society B 281:20141147. http://dx.doi.org/10.1098/rspb.2014.1147