SVP abstract 19: Hanging on to the invalid ‘Notoungulata’

Perini, Casali and Flynn 2020
try to resurrect an invalid clade in the LRT (subset Fig. 1), ‘Notoungulata‘. Either that or they never thought to test it for validity.

From their abstract:
“During most of the Cenozoic, South America (SA) was an isolated continent, leading to evolution of an unique and endemic fauna. Among these were the Notoungulata, an extinct group of ungulate-like mammals that included a wide array of species assigned to 14 families and more than 150 genera, occupying many distinct herbivorous niches and showing convergent morphologies with distantly related mammalian herbivore groups.”

That ‘wide array of species’ is a clue that this traditional clade is not monophyletic. The large reptile tree (LRT, 1751+ taxa, see Fig. 1) nests various traditional notogunulates in various disparate clades, some placental, others marsupial. This makes the Notoungulata invalid (in 2016, Fig. 1) due to polyphyly.

“Despite this diversity, few studies have addressed the evolution of morphological disparity among notoungulates.”

In counterpoint, the LRT addressed the evolution of morphological disparity in this traditional clade, and found its diversity spelled its doom.

“In this study, we applied modern comparative methods to investigate macroevolutionary patterns within the clade.”

...and that’s there main mistake. They assumed they had a monophyletic clade. Don’t assume! Test by adding taxa. Don’t cherry pick taxa, especially if those taxa are on traditional lists. Add taxa and add more taxa until all the taxa in your study nests in monophyletic clades, as shown online in the LRT. When this is done the traditional members of the Notoungulata fail to remain monophyletic (Fig. 1).

“We used a comprehensive morphological matrix to perform a Bayesian phylogenetic analysis, obtaining a fully resolved phylogeny and divergence time estimates for the major groups of notoungulates.”

Cherry-picking taxa makes this possible. Cherry-picking = cheating or laziness or reliance on others, none of which makes good science.

Figure 1. A selection of purported notoungulates (in amber) were added to the LRT and they did not nest together. That means they're not a clade.

Figure 1. From 2016: A selection of purported notoungulates (in amber) were added to the LRT and they did not nest together. That means they’re not a clade.

Perini, Casali and Flynn 2020 continue:
“This phylogeny supports the division of Notoungulata into Toxodontia and Typotheria, including many traditionally recognized families, as well as indicates paraphyly of some groups such as “Notohippidae”, “Notopithecidae”, and “Isotemnidae”. The diversity of Notoungulata rose steadily from the beginning of the Paleocene, reaching its apex by the end of the Oligocene, with marked decreases in the beginning, middle, and end of the Miocene, until final extinction in the Pleistocene. Toxodontia and Typotheria show no overlap, but occupy increasingly more distinct areas of the morphospace over time. Etc.”

Some traditional notoungulates are marsupials. Others are placentals in the LRT. You can weed out convergence by adding taxa. I’ll keep saying that until it becomes rote and the standard operating principle.

Figure 3. Toxodon and the much smaller Eurygenium to scale.

Figure 2. Toxodon and the much smaller Eurygenium to scale.

Nothing should proceed in detail
until a valid phylogenetic context is present. Otherwise you are wasting your time. Once you have your wide gamut cladogram, the kind that minimizes taxon exclusion, like the LRT, you will have a tool that you can use over and over again with little additional effort. It’s like a Periodic Table of Elements you can refer to. If you never have such a tool you will always risk taxon exclusion and the specter of convergence.


References
Perini FA, Casali DD and Flynn J 2020. Notoungulata, an endemic radiation of extinct South American herbivorous mammals. SVP abstracts 2020.

wiki/Notoungulata

 

Hegetotherium and Pachyrukhos: not ungulates and not notoungulates

Hegetotherium and Pachyrukhos
were recently redescribed by Seoane and Cerdeño 2019 who considered them to be members of the Notoungulata, an invalidated polyphyletic clade with former members now nesting in various hooved marsupial and hooved placental clades.

Traditionally notoungulates are considered placentals and ungulates.
Seoane and Cerdeño report, “Hegetotheriidae is one of the most derived clades in the Order Notoungulata, the most abundant and diverse group of South American native ungulates.” The key word in there is ‘diverse’. Notungulates are SO diverse some of them are not related to the others.

Figure 1. Image from Cassini 2013. Pink taxa are marsupials. Others are placentals.

Figure 1. Image from Cassini 2013. Pink taxa are marsupials. Others are placentals.

We looked at Hegetotherium,
earlier. In the large reptile tree (LRT, 1517 taxa) Hegetotherium nests with Mesotherium and Interatherium at the base of the marsupial Toxodon clade, derived from the wombat (Vombatus) clade. All those are derived from the Paedotherium clade (e.g. Paedotherium, Phalanger, Petaurus and Thylacoleo). In Seoane and Cerdeño, Paedotherium is a taxon nesting close to Pachyrukhos, a taxon not included in the LRT.

The Seoane and Cerdeño taxon list also includes
PaedotheriumMesotherium and Hegetotherium, but not InteratheriumToxodon, Phalanger, Petaurus and Thylacoleo. So taxon exclusion and lacking a wide gamut viewappear to be twin problems here. Seoane and Cerdeño did not realize the taxa in their study were marsupials close to phalangers and wombats. They assumed, by tradition, they were dealing with placental ungulates, close to cows and deer.


References
Cassini G 2013. Skull Geometric Morphometrics and Paleoecology of Santacrucian (Late Early Miocene; Patagonia) Native Ungulates (Astrapotheria, Litopterna, and Notoungulata). Ameghiniana 50 (2):193–216. DOI: 10.5710/AMGH.7.04.2013.606
Seoane FD and Cerdeño E 2019. Systematic revision of Hegetotherium and Pachyrukhos (Hegetotheriidae, Notoungulata) and a new phylogenetic analysis of Hegetotheriidae. Journal of Systematic Palaeontology http://dx.doi.org/10.1080/14772019.2018.1545146

Hey! Some of those Miocene ‘ungulates’ are marsupials!

More heresy today
courtesy of taxon inclusion.

Cassini 2013
looked at several traditional Miocene South American ‘ungulates’ (Fig. 1) unaware that these taxa do not nest in monophyletic clade any more specific than Theria in the large reptile tree (LRT, 1401 taxa). Cassini was reporting the results of “an ecomorphological study based on geometric morphometrics of the masticatory apparatus.” So he was working from prior cladograms and focusing on the mechanics of eating.

Figure 1. Image from Cassini 2013. Pink taxa are marsupials. Others are placentals.

Figure 1. Image from Cassini 2013. Pink taxa are marsupials. Others are placentals.

Earlier
here and here the traditional clade Notoungulata was splintered by the LRT into several clades, some among the marsupials, other among the placentals.

Traditional ‘Litopterna’
Diadiaphorus (Fig. 1) nests at the base of this clade. Theosodon (Fig. 1) nests as a derived taxon. Also included, but not listed: Chalicotherium and other chalicotheres.

Considering its member taxa,
the clade Litopterna (Ameghino 1889) is a junior synonym for Chalicotheridae (Gill 1872) in the LRT.

Considering its member taxa,
the clade Astrapotheria (Lydekker 1894) is a junior synonym for Meniscotheriinae (Cope 1882) and both nest within Phenacodontidae (Cope 1881).

Interatheriidae (Ameghino 1887) traditionally includes Interatherium, Protypotherium, Miocochilius and other taxa listed here. In the LRT Interatherium nests close to the ancestry of the Toxodon clade + the kangaroo clade within Metatheria. By contrast, Protypotherium and Miocochillus nest with Homalodotherium deep within the Eutheria. Homalodotherium traditionally nests with the the metatherian Toxodon. According to the LRT, all the above taxa developed similar enough traits by convergence that all were mistakenly lumped together in the invalid placental clade ‘Notoungulata’.

This is not the first time
metatherians were split from convergent eutherians. Most creodonts are marsupial predators, phylogenetically distinct from their traditional sisters in the clade Carnivora, within the clade Eutheria (Placentalia).

New taxa added to the LRT:

  1. Hegetotherium (Fig. 1) nests with Mesotherium between Interatherium and the Toxodon clade in the Metatheria. 
  2. Diadiaphorus (Fig. 1), the horse-mimic, nests at the base of the Litopterna/Chalicotheriidae, just basal to Litolophus.

I did not know these two, so I added these two to better understand them.

References
Cassini G 2013. Skull Geometric Morphometrics and Paleoecology of Santacrucian (Late Early Miocene; Patagonia) Native Ungulates (Astrapotheria, Litopterna, and Notoungulata). Ameghiniana 50 (2):193–216. DOI: 10.5710/AMGH.7.04.2013.606

SVP abstracts 2017 – Notoungulata reexamined

Remember when
members of the clade Notoungulata were dismantled and shipped to various other clades within Theria in the large reptile tree (LRT, 1051 taxa)? Keep that in mind as you read this abstract by West 2017.

From the West 2017 abstract:
“Notoungulata is an extremely diverse and disparate, entirely extinct order of placental
mammals, largely endemic to South America, which persisted through Cenozoic. There
are disagreements on intraordinal relationships among notoungulates, but the roots of the
order within Placentalia are even more enigmatic. A critical challenge is the lack of DNA
(though one taxon now has yielded collagen protein sequences), thus the greater impact
of the interpretation of morphological homology across superorders, particularly for
herbivorous ungulate placentals. This is because most characters used in higher-level
analyses of Placentalia do not adequately capture the nuances of unguligrady,
cursoriality, lophodonty, and hypsodonty, hindering accurate phylogenetic
reconstructions.

“A long-held, recently reinforced, morphology-based hypothesis for Notoungulata is that
they are most closely related to Tethytheria, an afrothere group including elephants and
manatees. An alternative hypothesis, recently corroborated by ancient collagen sequence
data, is that notoungulates and litopterns (another extinct South American ungulate order)
are sister to Perissodactyla. To test these starkly different alternatives, as well as the
hypothesis implicit in both that Notoungulata is monophyletic, I built on a published
large total-evidence matrix that was built to test placental interordinal relationships. I
added seven notoungulate and one litoptern species, a 10% taxon sampling increase. I
expanded character sampling, adding two morphological characters often used in
notoungulate intraordinal systematics, one dental and one cranial, and I added the
recently published collagen loci that had linked notoungulates and litopterns to
Perissodactyla. In multiple analyses of the total-evidence dataset and its partitions, my
results show that notoungulates form a clade sister to Tethytheria, supporting the
morphological hypothesis and overturning the hypothesis based only on the collagen
data. Intriguingly, nested consistently within the notoungulate clade in my results is an
extant taxon that also has oscillated from Perissodactyl to Afrothere: hyraxes. Molecular
data put hyraxes in Paenungulata (Afrotheria); I found new morphological character
support for this, and for the placement of Notoungulata.

“In testing affinities of fossil taxa, morphology retains critical importance even in light of
ancient molecular data. My results also reinforce the value of well-constructed homology
statements and thorough taxon sampling.”

Note that West 2017

  1. Bemoans the lack of DNA for this purported clade, not realizing that DNA analyses do not bring insight to morphological studies, but constantly confuse topologies.
  2. Discusses characters like cursoriality, but those have no business in analysis.
  3. Tests the concept of a monophyletic Notoungulata. Thats’ good! Recovers a monophyletic notoungulata. That’s probably due to taxon exclusion. Many former notoungulates now nest with marsupial wombats.
  4. Recovered hyraxes with purported notoungulates, not with elephants and manatees. This is a red flag showing some sort of error in the data set.
  5. Does not list the genera sampled.
  6. Recovers Afrotheria. That’s probably due to the DNA in the dataset.

West should
remove DNA characters, add many more fossil taxa (including wombats) and report findings afterwards. That we’d all like to see.

West AR 2017. Resolving the affinities of Notoungulata; Character selection, taxon sampling,and the influence of ancient molecular data. SVP abstracts 2017.

Notostylops: another former notoungulate

This used to be big news,
when a taxon no longer nested in a traditional clade and moved to another. But with the breakup of the Notoungulata, this has become commonplace for former members of this clade and I expect the trend to continue.

Figure 1. Notostylops skull colorized in three views.

Figure 1. Notostylops skull colorized in three views.

Now
in the large reptile tree (LRT) Notostylops murinis  (Ameghino 1897, Riggs and Patterson 1935; 75cm in esitmated length; Eocene; FMNH-P13319) nests with the Ectocion specimen that nests with elephants, not the one that nests with carnivores (Fig. 2).

FIgure 3. Subset of the LRT focusing on the hyrax, elephant and manatee clade.

FIgure 3. Subset of the LRT focusing on the hyrax, elephant and manatee clade.

In Notostylops, the anterior incisors were enlarged as in other elephant and sea cow ancestors, but the anterior jaws narrowed, so the incisors became close together, like those of rodents. The mandible itself was more robust. No canines were present. The premolars were molarized.

Of course all this is
based in the literature, not firsthand observation of the pertinent specimens. I encourage others to test these taxa to confirm these hypothetical interrelationships.

I became aware of this taxon
after reading Billet (2010), who wrote: “Intriguing similarities are also detected in the anterior dentition of Pyrotherium and the Casamayoran notoungulate Notostylops. These resemblances suggest a unique relationship between Pyrotheria and Notoungulata, specifically between Pyrotheria and Notostylops.” The large reptile tree does not confirm that relationship. Rather the former (Fig. 3) is a derived marsupial while the latter is a derived placental.

Figure 3. Pyrotherium is a marsupial, not a relative to Notostylops, contra Billet 2010.

Figure 3. Pyrotherium is a marsupial, not a relative to Notostylops, contra Billet 2010.

References
Ameghino F 1897. Mamiferos Cretaceos de la Argentina – Boletin Instituto Geografico Argentino 18:406-521.
Billet G. 2010. New Observations on the Skull of Pyrotherium (Pyrotheria, Mammalia) and New Phylogenetic Hypotheses on South American Ungulates. Journal of Mammal Evolution. 17:21-59.
Riggs ES and Patterson B 1935.
 Description of some notoungulates from the Casamayor (“Notostylops) beds of Patagonia. Proceedings of the American Philosophical Socity 75(2):163-215.

wiki/Notostylops

More notoungulates leave this extinct clade.

Some of the taxa I met this weekend, and you’ll meet shortly,
I’ve never heard of before. Even so, here’s another paleo story waiting to be told.

When I added
Protypotherium (Fig. 1) and Miocochilius (Fig. 2) to the large reptile tree (now 828 taxa, but not yet updated), I learned that they were both considered members of the Interatheridae, which Wikipedia considers,  “an extinct family of notoungulate mammals from South America.”

Figure 1. Protypotherium nests with Miocochilius and Homalodotherium in the LRT between mesonychids and paenungulates.

Figure 1. Protypotherium nests with Miocochilius and Homalodotherium in the LRT between mesonychids and paenungulates.

Earlier we learned
that all tested members of the Notoungulata do nest not with each other, but with a variety of established clades within the Theria. Some members of the invalid Notoungulata nested with wombats, others with various placentals. And today this issue keeps dragging on…

Figure 2. Miocochilius has reduced it imprint to just two functional toes.

Figure 2. Miocochilius has reduced it imprint to just two functional fingers and toes. Look at those long horse-like teeth exposed by erosion of the bone.

So where there’s an Interatheridae…
there should be an Interatherium. And there is one (Fig. 3). Trouble is, the Interatherium skull with that crooked diastema did not look like the straight jawed full set of teeth found in Protypotherium and Miocochilius. So I added Interatherium to the LRT to find out.

Turns out, like many notoungulates before, 
that Interatherium nests with wombats, between Vombatus and Toxodon even though Interatherium is much smaller, longer, and leaner than its sisters. It also lacks digit 1 on all four extremities. Apparently there is a wide range of wombat/marsupial morphologies that we’re just now beginning to appreciate and identify. For instance, that notch and descending maxillary palate in Interatherium (Fig. 3) resemble those of the bizarre marsupial beaver-mimic wombat, Vintana, which also nests nearby.

Figure 3. Interatherium does not nest with notoungulates or other purported interotheres. Rather cat-sized Interatherium nests with wombats, between Vombatus and the giant Toxodon.

Figure 3. Interatherium does not nest with notoungulates or other purported interotheres. Rather cat-sized Interatherium nests with wombats, between Vombatus and the giant Toxodon.

If Interatherium is a marsupial, 
the two placentals, Protypotherium and Miocochilius, cannot be interatheres. Or if they were defined as interatheres, that definition should be modified. Best to just call Protypotherium and Miocochilius typotheres — unless Typotherium turns out to be unrelated to these two, too.

Now,
as I look up “Typotherium,” I see it is better known by its senior synonym, Mesotherium, originally named, according to Wikipedia, in the belief that it was a transitional taxon between rodents and pachyderms. I have not tested Mesotherium (Fig. 4) yet, but with that diastema, it looks more like Interatherium, the wombat, than Protypotherium and Miocochilius, the condylarths. Only testing will tell, though…

Figure 4. Mesotherium. What is it, if not the long lost link between rodents and elephants? : )

Figure 4. Mesotherium. What is it, if not the long lost link between rodents and elephants?  Just kidding! I don’t see scale bars for this taxon, but Wiki reports it was the size of a small sheep at 55 kilograms (121 pounds. So it probably had a skull the size of a small sheep.

But wait, there’s more…
There was, indeed, a larger member of the Protypotherium and Miocochilius clade. Seems that the  clawed browser, Homalodotherium (Fig. 5), which I earlier nested with the clawed ungulate, Chalicotherium, now nests with Protypotherium and Miocochilius given the opportunity to do so (taxon exclusion rises again!). These three form a clade nesting between mesonychids (including hippos and Paleoparadoxia) and paenungulates (elephants, hyraxes and sea cows) where big front teeth rule, but tusks are not yet present in these three (yet-to-be-named clade) taxa. Maybe we should call this clade of three (so far) the new ‘Notoungulata’. Does that work for you? If someone can send me the reference for the origin of this term, we’ll see if that will fit or not.

Figure 6. Bear-sized Homalodotherium nests with cat-sized Protypotherium and Miocochilius. They all have a full arcade (11x4) of relatively flat teeth.

Figure 6. Bear-sized Homalodotherium nests with cat-sized Protypotherium and Miocochilius. They all have a full arcade (11×4) of relatively flat teeth. Note the resemblance to Chalicotherium here, by convergence.

I’m catching up
but still behind in updating the pertinent web page at ReptileEvolution.com. It’s not easy, but I’m getting there.

References
Ameghino F 1882. Ungulata, Typotheria, Interatheridae. Catalog de la Prov. de Buenos Aires en la Expedicion Cont. Sud-America. March 1882. Boletino Instituto Geologia Argentino, June 1882. Cont. Conocimenient Mamif. Fosil. Repub. Argentina, in Accd. Nac. Cien., Cordoba 6:474-480. 1889.
Croft DA 2007. The Middle Miocene (Laventan) Quebrada Honda wildlife, southern Bolivia and a description of ITS Notoungulates. Palaeontology 50(1):277-303.
Huxley TH 1870. Anniversary address of the President of the Geological Society. Quarterly Journal of the Geological Society of London 26:42-64.
Stirton RA 1953. A new genus of interatheres from the Miocene of Colombia. University of California Publications in Geological Sciences 29: 265-348

wiki/Homalodotherium
wiki/Protypotherium
wiki/Miocochilius

 

 

Say ‘No’ to Notoungulata. Turns out, it’s not a clade.

This is where testing takes us out on yet another limb
because the Notoungulata has been a clade for over 100 years (Roth 1903). If you are unfamiliar with this clade, as I was… you can get a basic education on the Notoungulata here,

According to
Darin Croft, PhD, Paleomammalogist, the Notoungulata is a clade of diverse South American Tertiary mammals all united, “by characters of their ear region and their teeth, including the presence of a loph on their upper molars known as the ‘crochet‘.” 

The clade Notoungulata produced taxa convergent with:

  1. buffalo/rhinos: Toxodon
  2. elephants/hippos: Pyrotherium. Astrapotherium
  3. chalicotheres: Homalodotherium
  4. peccarys: Thomashuxleya
  5. rabbits:  Protypotherium
  6. and others

Unifortunately
as I keep adding notoungulates to the large reptile tree (Fig. 1; 808 taxa at present), they keep nesting not with each other, but with a diverse selection of placental and marsupial mammals. That should not be happening, unless a false paradigm is present.

Figure 1. A selection of purported notoungulates (in amber) were added to the LRT and they did not nest together. That means they're not a clade.

Figure 1. A selection of purported notoungulates (in amber) were added to the LRT and they did not nest together. That means they’re not a clade.

Are dental characters
over-emphasized in traditional studies? including the Notoungulata? Do the cusps and valleys of molars trump the rest of the mammal’s morphology? Is it more reasonable to posit that teeth might be converging in these disparate taxa? For instance, Homalodotherium is an excellent sister to Chalicotherium, but I did not test the tooth cusps. And Toxodon is an excellent wombat. We’ll take closer looks at those taxa in future blogs.

Questioning basic assumptions is okay
because this is Science and everything is up for discussion. If a test does not deliver promised results, it’s okay to wonder why.

If we were to take the Notoungulata at face value
we would have to accept the wide range of morphologies within this one clade, as in the clade that includes tenrecs and whales. Unfortunately, testing shows that the range of body types in the Notoungulata is more readily matched by other clades, including the wombats within the marsupials and the chalicotheres within the placentals.

The loss of the clade ‘Notoungulata’
follows a list of other clades that have been lost based on the results of the LRT.

  1. Amniota is now a junior synonym for Reptilia
  2. Ornithodira is now a junior synonym for Reptilia
  3. Parareptilia is now a junior synonym for Reptilia
  4. Pterodactyloidea is paraphyletic
  5. Allotheria:  no mammals form a clade between Metatheria and Eutheria
  6. And others…

In counterpoint,
several new clades have been erected, resurrected or revised here:

  1. Archosauromorpha
  2. Lepidosauromorpha
  3. Enaliosauria = plesiosaurs + ichthyosaurs and their kin
  4. Tritosauria – a previously unrecognized squamate clade
  5. Prosquamata – another previously unrecognized squamate clade
  6. Fenestrasauria (goes back 16 years to Peters 2000, but still not used in academic publication
  7. Tenreccetacea = tenrecs + whales
  8. And several others…

Share your thoughts on this matter,
if you wish…

References
Billet G 2011. Phylogeny of the Notoungulata (Mammalia) based on cranial and dental characters. Journal of Systematic Palaeontology 9:481-497.
Cifelli RL 1993. The phylogeny of the native South American ungulates; pp. 195-216 in F. S. Szalay M J Novacek, and MC McKenna (eds.), Mammal Phylogeny: Placentals. Springer-Verlag, New York.
Roth S 1903. Los Ungulados Sudamericanos. Anales del Museo de La Plata (Sección Paleontológica). 5: 1–36. OCLC 14012855.
Scott WB 1932. Mammalia of the Santa Cruz Beds. Volume VII, Paleontology. Part III. Nature and origin of the Santa Cruz Fauna with additional notes on the Entelonychia and Astrapotheria. ; pp. 157-192 in W. B. Scott (ed.), Reports of the Princeton University Expeditions to Patagonia, 1896-1899. Princeton University, E. Schweizerbart’sche Verlagshandlung (E. Nägele), Stuttgart.

wiki/Notoungulata