Uintatheres: Long lost bones reappear as horns and ridges

Get ready for some more heresy.
We’ve talked about the reappearance of long lost bones in various taxa, from digit zero on the hand of Limusaurus and Chauna, to the postorbital in primates like Archicebus. Among the many cranial bones lost from the surface in most mammals are the septomaxilla (the portion of the lacrimal contacting the naris), the prefrontal, the postfrontal, the postorbital and the supratemporal. All these can be seen on the surface of the skull in basal synapsids like Vaughnictis.

Adding the small uintathere
Bathyopsis fissidens (Fig. 1) to the large reptile tree (LRT, 1379 taxa) forced a review of the skull bones of Uintatherium, one of the bizarrely horned uintatheres of the Paleocene and Eocene (Fig. 1).

Yes, I’m learning as I go.
And yes, sometimes I find things that have been traditionally overlooked. And yes, I could be wrong. This needs to be looked at ‘with new eyes’  by several other workers.

Figure 1. Bathyopsis, Elachoceras and Uintatherium to the same fang-occiput length showing the reappearance of several bones that don’t appear in most mammals. See text for details.

Some bones reappear in uintatheres that most mammals don’t have:

1. The lacrimal originally extended to the naris, but the maxilla rose to meet the nasal and cover up the anterior lacrimal. In uinitatheres the typically hidden middle portion of the lacrimal rises to the surface and beyond between the nasal and maxilla to form the anterior horn.
2. The prefrontal reappears as a ridge in uintatheres over the orbit.
3. The postfrontal reappears in uintatheres over the posterior orbit and rises to form the anterior of the posterior horn.
4. The postorbital reappears in uintatheres first flat and atop the skull, then atop the posterior horn.
5. The supratemporal reappears in uintatheres along the posterior base of the posterior horn forming a lateral cranial ridge that other mammals don’t have.

Figure 2. Uintatherium skull with bones colored and labeled. Several of these bones have not been seen on mammal skulls, but once appeared on basal synapsid skulls. The hornier skulls are larger (Fig. 3).

Unitatherium anceps (Leidy 1872, Eocene 37 mya, 4m long, 1.7 m at shoulder) was a bulky basal ungulate and a sister to Coryphodon. Uintatherium had six bony processes over the skull. Wikipedia identifies it only as an herbivorous mammal. The LRT nests it with Arsinoitherium, Phenacodus and Gobiatherium. The tooth arcade of Uintatherium is less complete. The canines enlarge to saber teeth and a diastema appears with the loss of the anterior premolars. The pelvis widens. Five fingers and toes are retained.

The ‘horns’ in Giraffa, the giraffe,
are not homologous, nor analogous. The ossicone in Giraffa is a new ossification that sits atop the cranial bones with no reappearances of long lost bones detected.

Figure 3. Uintathere evolution from Wheeler 1961. Colors and eyeballs added.

Discoveries like this
require confirmation or refutation in the form of precise data. I’m looking forward to other workers re-examining the bone sutures of uintatheres with these new insights and possibilities in mind. If this is confirmed, remember, you heard it here first.

References
Cope ED 1881. On the Vertebrata of the Wind River Eocene beds of Wyoming. Bulletin of the United States Geological and Geographical Survey 6(1):183-202
Leidy J 1873. Contribution to the extinct vertebrate fauna of the Western Territories. Geological Survey of the Territories 1.
Osborn HF 1913. The skull of Bathyopsis, Wind River uintathere. Bulletin of the American Museum of Natural History 22:417–420 + plates.
Owen R 1845. Odontography; a treatise on the comparative anatomy of the teeth. Hippolyte Bailliere, London, 655pp.
Uhen MD and Gingerich PD 1995. Evolution of Coryphodon (Mammalia, Pantodonta) in the Late Paleocene and Early Eocene of Northwestern Wyoming. Contributions from the Museum of Paleontology, University of Michigan. 29 (10): 259–89.
Wheeler WH 1961. Revision of the Uintatheres. Peabody Museum of Natural History, Yale University bulletin 14: 93 pp. + plates.

wiki/Coryphodon
wiki/Uintatherium
wiki/Bathyopsis

wiki/Uintatheriidae

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Hapalodectes: when primates split from dolphins

Back when placental mammals were first diversifying in the Jurassic
they all looked like small arboreal marsupial didelophids, like Caluromys, and small arboreal placental tree shrews, like the extant Ptilocercus and Tupaia. Two distinct specimens, both given the genus name Hapalodectes (Fig. 1), are among these basal placental taxa in the large reptile tree (LRT, 1378 taxa).

The slightly smaller
IVPP V5235 specimen attributed to Hapalodectes (Ting and Li 1987) nests at the base of the primate clade. It had already taken on the appearance of a little basal lemur or adapid (Fig. 1).

Figure 1. Two Hapalodectes specimens. The smaller one nests at the base of the Primates. The larger one nests as the base of the anagalid-tenrec-odontocete clade.

The slightly larger
IVPP V12385 specimen attributed to Hapalodectes (Ting et al. 2004; Fig. 1) nests at the base of the anagalid-tenrec-odontocete clade and it had already taken on the appearance of a little anagalid or elephant shrew.

Other than size, the differences are subtle:

1. The basal primate has a postorbital ring. The basal anagalid does not.
2. The basal primate has three upper molars. The basal anagalid has four.
3. The basal primate cranium has no crest. The basal anagalid has a nuchal and parasagittal crest.
4. The basal primate anchors the squamosal further back, with a smaller ectotympanic (middle ear container bones below the cranium). The basal anagalid anchors the squamosal further forward, with a larger ectotympanic (for better hearing).

Hapalodectes hetangensis (Ting and Li 1987; 4.5cm skull length; Paleocene, 55 mya; IVPP V 5235) This skull was originally wrongly applied to the Mesonychidae, but here nests at the base of the primates, including Notharctus.  Note the transverse premaxilla, the large canine, and the encircled orbits rotated anteriorly.

?Hapalodectes ?hetangensis (Ting et al. 2004; 7 cm skull length; Early Eocene 50 mya; IVPP V 12385) was originally considered a tiny mesonychid. This species nests at the base of the anagale-tenrec-odontocete clade along with Maelestes, between Ptilocercus and Onychodectes. The large nuchal crest is a key trait found in later taxa. The premaxilla is largely missing, but likely was transverse in orientation.

References
Ting S and Li C 1987. The skull of Hapalodectes (?Acreodi, Mammalia), with notes on some Chinese Paleocene mesonychids.
Ting SY, Wang Y, Schiebout JA, Koch PL, Clyde WC, Bowen GJ and Wang Y 2004. New Early Eocene mammalian fossils from the Hengyang Basin, Hunan China. Bulletin of Carnegie Museum of Natural History 36: 291-301.

wiki/Hapalodectes

Walking Orobates video on YouTube and in Nature

This is a wonderful experiment/demonstration/simulation
and a wonderful fossil, matching a digitized 300 million-year-old Orobates skeleton to Orobates tracks.

This time the problem comes from basal tetrapod experts
One writes in the Dinosaur Mailing List, “As so much else in amniote phylogeny, it remains unclear whether the diadectomorphs are just outside Amniota or just inside. The question has never been tested in an analysis with enough taxa and enough characters; some matrices may have had close to enough of one, but definitely not of both, and there haven’t been many in total in the first place.”

Another comes from SmithsonianMag.com
“At first glance, the 300 million-year-old Orobates pabsti might look like a chunky lizard. In actuality, this animal from the Permian period is what experts know as a stem amniote—a vertebrate that’s part of the evolutionary lineage between amphibians, which reproduce in the water, and the last common ancestor of mammals and reptiles, which lay eggs on land.”

A third comes from the title of the Nature paper (Nyakatura et al. 2019)
“Reverse-engineering the locomotion of a stem amniote.” Clearly the authors have never heard of an amphibian-like reptile.

This is an example of wrong thinking.
The large reptile tree (LRT, 1378 taxa) nests Orobates deep inside the Reptilia (the clade Amniota is a junior synonym, see below). There are those who say the LRT needs more characters to… what? The LRT already lumps and splits virtually all of its taxa in complete resolution documenting a gradual accumulation of traits at every node. That is the yardstick by which all cladograms should be judged. How will adding characters suddenly shift taxa on the tree topology? Taxa nest where they do because they most closely resemble their sisters. And that clade most closely resembles their more distant sisters in a series that ultimately includes all tested taxa. All other possible nesting sites for taxa are provided in a wide gamut analysis.

Apparently basal tetrapod experts are hoping the LRT is somehow wrong. If so, which taxa are wrongly nested and where should they nest instead? They simply need to add the pertinent taxa listed in the LRT to their own analyses with their own character lists to find out for themselves and report the results. This is how science works. Anyone can repeat the experiment, but the experiment in this case, requires pertinent taxa, not more characters.

Case in point:
Remember how Hone and Benton 2007, 2009 deleted pertinent taxa in their purported quest to test two competing hypotheses on pterosaur origins? When they found out the fenestrasaurs were attracting pterosaurs, they deleted the fenestrasaurs and never did find out where pterosaurs originated.

Comment to Nature
“This is a wonderful experiment/demonstration/simulation. The problem comes from the systematics of Orobates. Testing a wide gamut of tetrapod taxa nests Orobates between Limnoscelis and Tseajaia + Tetraceratops. This clade nests between Saurorictus + Captorhinidae and Milleretta, all traditional amniotes. Phylogenetic analysis nests the amphibian-like reptiles Gephyrostegus (Late Carboniferous) and Silvanerpeton (Early Carboniferous) as the last common ancestors of all included amniote taxa. Three nodes of amphibian-like reptiles nest between these two and the Saurorictus + Captorhinidae clade. So Orobates nests well within the Amniota, now a junior synonym for the clade Reptilia. The wide gamut cladogram is found online here: http://reptileevolution.com/reptile-tree.htm”

References
Nyakatura JA, et al. (11 co-authors) 2019. Reverse-engineering the locomotion of a stem amniote. Nature.com PDF online.

Articles from the popular press:

https://www.smithsonianmag.com/science-nature/scientists-used-robot-study-how-prehistoric-lizards-evolved-walk-land-180971283/

Siamotherium: neither helohyid, cetartiodactyl, hippo nor anthracothere

Taxon exclusion again.
I know you’re getting tired of this, but Siamotherium (Fig. 1) is an anagalid, a sister to Anagale (Fig. 1) in the large reptile tree (LRT, 1378 taxa), basal to the tenrec-odontocete clade. These are taxa ignored in prior studies.

There is no guesswork here.
The LRT considers a wider gamut of mammal candidates and lets the taxa nest wherever they want to without restriction. Sometimes taxa nest in places that paleontologists had not yet imagined.

For those wondering what a helohyid is…
… and count me among that curious group, Helohyus (sorry, no Wikipedia entry), is the namesake for this primitive pig-like artiodactyl clade. More on this taxon in later posts.

The resemblance of Siamotherium to Anagale is strong.
(Fig. 1) One wonders why this similarity went unnoticed before.

Figure 1. Siamotherium to scale with Anagale. Both nest basal to the tenrec-odontocete clade. The mandible of Anagale fits well on the maxilla of Siamotherium when enlarged.

Anagale gobiensis (Simpson 1931; early Oligocene; 30cm in length; AMNH 26079) was originally considered an insectivore, close to the tree shrew Tupaia and tending to link to lemurs like Notharctus. Thirty years later McKenna 1963 argued against tupaioid affinities, but could not provide a more suitable nesting.

Here rabbit-sized Anagale nests with Siamotherium and they nest with 3x smaller Maelestes and the IVPP V2385 specimen of Hapalodectes. The closest living relative to these taxa is Rhynchcyon, the golden rumped elephant shrew (Fig. 3).

The teeth of Anagale were typically worn and the claws were shovel-shaped, suggesting a diet of subterranean worms and beetles. The peculiar combination of large fissured claws of the manus and distally spatulate unguals of the pes is uncommon in mammals. The ectotympanic bulla protecting the middle ear bones is quite large, and so is the eardrum that it framed.

Siamotherium pondaungensis (Suteethorn et al. 1988; Soe et al. 2017; Eocene) was originally considered a small anthracothere close to Hippopotamus, but here nests with Anagale. Siamotherium is larger, has a straight jugal and only three molars.

Sisters of these taxa
had a Mesozoic genesis. Distinct from other clades is the posterior rise of the post-parietal creating a nuchal crest. This crest is still present in the giant elephant shrew, Andrewsarchus, and odontocete whales (Fig. 2). Also of interest, the digitigrade hands and feet with fewer digits converge on those of basal artiodactyls (Fig. 3). No wonder these get confused and ignored in traditional paleontology.

Figure 2. Odontoceti (toothed whale) origin and evolution. Here Anagale, Andrewsarchus, Sinonyx, Hemicentetes, Tenrec Indohyus and Leptictidium precede Pakicetus. Maiacetus and Orcinus are aquatic odontocetes.

Like basal artiodactyls,
elephant shrews, like Rhynchocyon (Fig. 3), also have digitrade hands and feet. This has led to all sorts of confusion with regard to whales and their putative, but invalidated ancestors among the artiodactyls.

Figure 3. Skeleton of the elephant shrew, Rhynchocyon. Note the digitigrade manus and pes, like those of basal artiodactyls.

References
Simpson GG 1931. A new insectivore from the Oligocene, Ulan Gochu horizon, of Mongolia. American Museum Novitates 505:1-22.
Soe AN t al. (6 co-authors) 2017. New remains of Siamotherium pondaungensis (Cetartiodactyla, Hippopotamoidea) from the Eocene of Pondaung, Myanmar: Paleoecologic and phylogenetic implications. Journal of Vertebrate Paleontology 37(1):e1270290https://doi.org/10.1080/02724634.2017.1270290
Suteethorn V, Buffetaut E Helmcke-Ingava Rt JaegerJ-J and Jongkanjanasoontorn Y 1988. Oldest known Tertiary mammals from South-East Asia: Middle Eocene primate and anthracotheres from Thailand. Neues Jahrbuch f€ur Geologie und Pal€aontologie, Monatshefte 9:563–570.

wiki/Siamotherium (no Wikipedia entry yet)

Coeruleodraco: Traditional choristodere mistakes resurface

Occasionally within the Archosauriformes
the antorbital fenestra disappears. That is the case with the clade Choristodera, which Wikipedia describes as “an extinct order of semiaquatic diapsid reptiles. Cladists have placed them between basal diapsids and basal archosauromorphs, but the phylogenetic position of Choristodera is still uncertain.” 

That is so unnecessarily vague.
Just run the analysis. In the large reptile tree chorisotderes are derived from phylogenetically miniaturized proterosuchians like the BPI 2871 specimen and its sister Elachistosuchus.

Figure 1. Coeruleodraco skull as originally interpreted (below) and interpreted here (colors). This is a traditional error. Also note the remnants of an antorbital fenestra in this phylogenetically miniaturized taxon. The maxilla continues posterior to the orbit as in other choristoderes. Firsthand access does not guarantee better interpretations.

 

Matumoto, Dong, Wang and Evans 2018
bring us a new genus of short-snouted, small choristodere, Coeruleodraco jurassicus (Fig. 1; Late Jurassic). The authors use a ‘by default’ very distant outgroup for their choristodere cladogram: the basal diapsids, Petrolacosaurus and Araeoscelis, because “Outgroup choice is problematic for Choristodera, because the position of the group within Diapsida remains uncertain.” The LRT solved that problem years ago and posted it online. Unfortunatley, the authors did not test the listed outgroup taxa. That’s all they had to do.

Figure 2. Dorsal, lateral and palatal views of BPI 2871 with bones colorized above. Below, reconstructed images of BPI 2871 tracings. It is more complete than illustrated by Gow 1975.Note the tiny remnant of the antorbital fenestra in this phylogenetically miniaturized proterosuchid, basal to Choristodera.

A traditional mistake associated with choristoderes
is the mislabeling of the nasals as the prefrontals (Fig. 1). Both Coeruleodraco and outgroup taxa, like the BPI 2870 specimen demonstrate the ascending process of the premaxilla extends beyond the naris. That it becomes detached from the toothy lateral processes in Champsosaurus (Fig. 3) does not turn the premaxilla into a nasal. We looked at that earlier here and once again, it is due to the exclusion of taxa that clarify the issue. Choristodere workers are not looking at these outgroup taxa for guidance or analysis.

Figure 3. Champsosaurus skull with premaxilla in yellow.

The authors also messed up the finger identification.
The original interpretation of the Coeruleodraco manus (Fig. 4) misidentified the lateral and medial digits along with the olecranon and ulna (violet), which extends behind the humerus as in all other tetrapods. DGS revealed the middle phalanges of manual digit 4 behind the others. The apparently short digit 4 becomes the longest digit when reconstructed (Fig. 4). This matches the manus of other choristoderes.

Figure 4. Manus of Coeruleodraco as originally identified and repaired and reconstructed in color. Note frame that includes middle phalanges of digit 4. Digit 5 also has a semi-buried element.

Yes, I see things in fossils that others don’t see.
These are just a few of the many examples. In science it’s okay to point out where others have missed things, and the only way to convey that data over the Internet is by tracing and publishing photos (Fig. 4). Others are free to confirm or refute.

Firsthand access does not guarantee better interpretations.
It is important to understand what sister taxa are present and what traits they present. Without a good cladogram answers will not arrive. If there is any question, as in Champsosaurus and Coeruleodraco it’s okay to look at sister taxa for guidance.

Choristoderes are archosauriformes
in which the antorbital fenestra is reduced to absent. Others, like the Wikipedia authors, Matsumoto, Dong, Wang and Evans, who look only at a list of traits present or absent in a taxon are “Pulling a Larry Martin.” That’s a common problem that leads to taxon exclusion. The LRT is a science experiment that you can confirm or refute yourself. It’s time to put the choristodere enigma to rest.

References
Matsumoto R, Dong L, Wang Y and Evans SE 2019. The first record of a nearly complete choristodere (Reptilia: Diapsida) from the Upper Jurassic of Hebei Province, People’s Republic of China, Journal of Systematic Palaeontology
DOI:10.1080/14772019.2018.1494220

Thanks to co-author, Dr. S. Evans,
for sending a PDF link to the paper. I sent her a pdf of the LRT noting that it provided outgroups for choristoderes back to Devonian tetrapods, but no reply accompanied the pdf link.

wiki/Coeruleodraco

Gatesy’s blueprint for whale origins omits foundation taxa

Gatesy et al. 2012
attempted to provide “A phylogenetic blueprint for a modern whale.”

Unfortunately
Gatesy et al. did not realize that whales are diphyletic (or triphyletic). Gatesy et al. failed to include anagalid, elephant shrew and tenrec taxa basal to odontocetes and failed to include desmostylian taxa basal to mysticetes.

Not much else needs to be said.
Taxon exclusion, once again, is the fatal flaw.

References
Gatesy J et al. (7 co-authors) 2012. A phylogenetic blueprint for a modern whale. Molecular Phylogenetics and Evolution. PDF online.

The Miacis-Mustela split within Carnivora

Nesting as the proximal outgroup to all placentals in the LRT
is the slinky, omnivorous, often inverted marsupial didelphid, Caluromys. So that’s the morphology we start with. In the large reptile tree (LRT, 1376 taxa; subset in Fig. 2) Carnivora is the first placental clade to split off. Earlier we looked at the similarity in skulls between Caluromys and didelphid-like basalmost Carnivora, Volitantia, Primates, Glires and Maelestes (at the base of the tenrec-odontocete clade).

Always seeking ‘a gradual accumulation of derived traits’,
basal Carnivora, like civets (e.g. Nandinia) in the LRT are likewise slinky, omnivorous and often inverted. That starts to fade away with the raccoons, Procyon and Ailurus and later evolves to hypercarnivory in the extant mongoose (Herpestes). Based on the appearance of the mongoose sister, Cryptoprocta in Madagascar (135 mya) along with the Paleocene appearance of derived Carnivora, like Miacis and Palaeosinopa, basal Carnivora had their genesis early in the Mesozoic.

Gray 1821 defined Vivveridae
as consisting of the genera Viverra, Genetta, Herpestes, and Suricata. All tested taxa are basal members of the Carnivora in the LRT (subset in Fig. 2), so this clade is paraphyletic. Bowdich 1821 defined the clade Carnivora as it is used today.

Most derived Carnivora forsake their veggies
as they become highly specialized for predation. Two clades diverge from a common mongoose-like ancestor: one from a sister to Late Paleocene Miacis (Fig. 1), the other from a sister to Mustela, the European mink. Both are small, long-torsoed and short-legged still resembling the placental outgroup taxon, Caluromys.

Figure 1. Mustela and Miacis (the mink/weasel) compared to scale.

In the LRT
Miacis is basal to the clade of sea lions, dogs, cats, hyaenas and kin (Fig. 2).

Miacis parvivorus (Cope 1872; Heinrich et al. 2008; 30cm in length; Late Paleocene-Late Eocene) was originally considered a pre-carnivore, but here nests as a derived member of the Carnivora, arising from a Mesozoic sister to Herpestes, the mongoose. It was a sister to Mustela and Hyopsodus in the LRT. Miacis had a full arcade of 11 teeth (x4), but the canines and carnassial were smaller. Miacis had retractable claws, like a cat, and was likely arboreal.

In the LRT
extant Mustela is basal to the clade of wolverines, bears, seals and kin (Fig. 2).

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. It swims and dives skilfully. It is able to run along stream beds and stay underwater for one to two minutes. Mustela is basal to Puijila, Ursus and other bears, Phoca and other seals.

Importantly 
note the relatively close affinity of dogs (Canis) and cats (Panthera), in the LRT. That becomes a factor in a genomic study below.

Figure 2. Subset of the LRT focusing on Carnivora, the basalmost eutherian clade. The two derived clades arising from Mustela and Miacis are shown here.

 

 

How does the clade Carnivora look to traditional paleontologists?
Flynn et al.2005 (Fig. 3) attempted to “assess the impact of increased sampling on resolving enigmatic relationships within the placental clade, Carnivora, by using genomic testing” (so no fossils there). In Flynn et al. the extant Carnivora have their first dichotomy splitting cats from dogs (which are also closely related in the LRT, Fig. 2). No outgroup appears in the Flynn et al. cladogram, which mixes primitive and derived taxa, relative to the LRT. Note, seals + sea lions are monophyletic when fossils are not included. Minks are highly derived here, the opposite of the topology in the LRT. So some relationships are simply inverted, which sometimes happens when the outgroup is not correctly defined.

Figure 3. Carnivora according to Flynn et al. 2005 based on genomic testing. Cryptoprocota is a ‘Malagasy carnivore.”

Once again,
genomic testing does not replicate phenomic testing in deep time. That’s why the LRT is here. So you can test traits vs. genes, always seeking ‘a gradual accumulation of traits’ that echoes or models evolutionary events, without relying on the hope and faith that must come from any analysis that omits fossil taxa. The LRT also provides a list of outgroup taxa back to Devonian tetrapods.

Based on a trait list,
or a photo (Fig. 1), it is easy to see that Miacis and Mustela are closely related. However, in phylogenetic analysis each of these sisters nest at the base of a different derived clade of Carnivora. Cats and dogs remain closely related in the LRT, but both are highly derived relative to the outgroup and basal taxa. The LRT reveals cats are convergent with basal Carnivora, like the cat-like civets.

References
Bowdich TE 1821. An analysis of the natural classifications of Mammalia, for the use of students and travelers. 115 pp.
Cope ED 1872. Third account of new vertebrata from the Bridger Eocene of Wyoming Territory. Proceedings of the American Philosophical Society 12(86): 469-472.
Flynn JJ, Finarelli JA, Zehr S, Hsu J, Nedbal MA 2005. Molecular phylogeny of the Carnivora (Mammalia): Assessing the impact of increased sampling on resolving enigmatic relationships. Systematic Biology. 54 (2): 317–37.
Heinrich RE, Strait SG and Houde P 2008. Earliest Eocene Miacidae (Mammalia: Carnivora) from northwestern Wyoming. Journal of Paleontology. 82 (1): 154–162.
Linneaus C von 1761. Fauna Suecica sistens Animalia Sueciae Regni: Mammalia, Aves, Amphibia, Pisces, Insecta, Vermes. Distributa per Classes, Ordines, Genera, Species, cum Differentiis Specierum, Synonymis Auctorum, Nominibus Incolarum, Locis Natalium, Descriptionibus insectorum. Editio altera, auctior. Stockholmiae: L. Salvii, 48 + 578 pp.,

wiki/Mustela
wiki/Miacis
wiki/Hyopsodus
wiki/Carnivora