Mesosaurus revisited

Piñeiro et al. 2021
recognize only the genus Mesosaurus (Figs. 1–4) in the Paraná (Brazil) and Karoo (South Africa) basins. The authors suggest that coeval genera, Sterosternum and Brazilosaurus (Figs. 1–4), are “nomina dubia taking into account that the autapomorphies that supported these taxa cannot be confirmed to be absent in Mesosaurus.”

No phylogenetic analysis was presented.
Rather the authors made a trait-by-trait report and several ratio comparisons across many specimens. So they went deep into charts and statistics.

I’ve seen statistical support studies fail. Bennett’s studies on Pteranodon come to mind in which he found gender differences where none appear in a cladogram.

Only 23 of 305 specimens preserved a skull
in association with a complete cervical series. Note the holotype of Stereosternum (Fig. 4) is one of the headless specimens.

Figure 1. From Piñeiro et al. 2021, the holotypes of Mesosaurus, Stereosternum and Brazilosaurus. Only two of these preserve a skull.

Prior to this paper
in the large reptile tree (LRT, 1941+ taxa) Brazilosaurus sanpaukebsus (Shikama and Ozaki 1966; Piñeiro et al. 2021; Permian, Brazil) nested between Sterosternum and Mesosaurus with complete resolution. The holotypes were not tested then. They are being added now, starting with Mesosaurus.

Mesosaurus tenuidens (Gervais 1864-66; MNHN 1865-77; Early Permian ~290 mya, up to 100 cm in length), was long considered a basal reptile related to those that never had temporal openings. Not so. Here the temporal opening are secondarily closed off.

Stereosternum tumidum (Cope 1885; Early Permian ~290 mya, 30 cm in length) Here both temporal openings are present.

Figure 2. Manus tracings and reconstructions from the holotypes of Brazilosaurus, Stereosternum and Mesosaurus. These appear to be generically different.

Mesosaurus teeth appear to be much longer than those of related mesosaurs.
Piñeiro et al. report, “Modesto (1996, 1999) suggested that the marginal teeth in specimens assigned to Mesosaurus are longer than those in specimens assigned to Stereosternum
because he found that the largest teeth in Mesosaurus are equivalent to the length of five tooth positions, whereas in Stereosternum, the longest teeth would occupy the length of only three sockets. However, these comparative measures are to be taken carefully, considering that there is a great variability in the distance among tooth sockets in mesosaurs, including an important degree of deformation that occurs during fossilization processes.”

Figure 3. Fossils and tracings of the three mesosaur holotypes (Fig. 1), Brazilosaurus, Stereosternum and Mesosaurus, all to the same scale. Which traits do all three preserve? The forelimb (see figure 2).

The authors wrote:
“identification of new specimens using the available diagnostic characters are arbitrary and influenced by high subjectivity.”

A phylogenetic analysis is essential. Reconstructions (Fig. 2) are helpful. As in many genera (e.g. Triceratops, Pteranodon, Rhamphorhynchus), it is possible that no two individual specimens are alike.

Figure 1. Mesosaurus origins recovered by the LRT. The fossil record appears to be topsy turvy here with the basal taxa appearing 30 million years later. Fossils are rare and discovery is rarer. Things like this sometimes happen.
Figure 4. Mesosaurus origins recovered by the LRT. The fossil record appears to be topsy turvy here with the basal taxa appearing 30 million years later. Fossils are rare and discovery is rarer. Things like this sometimes happen.

The authors still believe (without testing) the invalid myth that mesosaurs were basal amniotes. They are not. In the large reptile tree (LRT, 1941+ taxa) mesosaurs nest with thalattosaurs and ichthyosaurs, derived from pachypleurosaurs (Fig. 4) and basal aquatic diapsids.

The authors wrote:
“After the detailed revision of the type specimens of the three currently accepted mesosaur taxa, for which we include here good-quality photographs, and considering the lack of statistical support for the most applied putative diagnostic features such as the different ratio found when comparing skull and cervical region lengths and the low or higher intensity of pachyosteosclerosis observed in dorsal ribs, which can be controlled by taphonomic and ecological conditions, we recognize Mesosaurus as the only mesosaurid taxon in the Paraná and Karoo basins, probably including dwarf individuals.”

IMHO the authors should have analyzed just these three holotype mesosaur specimens (with proper outgroups) to determine similarities and differences, rather than inundate themselves with 305 specimens juveniles, adults, partials, etc. Thereafter, once morphological patterns had emerged (or not) then expand the study to other specimens to see which genus each new one was closest to, dropping them in one at a time, as done here in the LRT. A phylogenetic analysis is usually essential, but usually only at the generic level and above. DGS reconstructions also help to organize fossils.

Figure 5. Modesto attributed this BHM 999 specimen to Stererosternum even though it looks like a Mesosaurus in the cranium (Fig. 6) and was tested under the taxon ‘Mesosaurus’ in the LRT. Very confusing unless we go back to the holotypes and use specimen numbers.
Figure 6. Mesosaurus taxon tested in the LRT. Ten years agp, this was the only data used in the LRT for Mesosaurus, despite the many, many specimens available.

Here’s a possible, perhaps probable, problem:
If you study 305 specimens of three closely related genera, the chance that you are going to see a transitional spectrum of taxa is much greater. The differences will be harder to tell, as Piñeiro et al. 2021 demonstrate. The differences blur and blend… as they should! As an example, Modesto 1999 attributed the BHM 999 specimen (Fig. 5) to Stererosternum even though it has a Mesosaurus-like cranium. Start with the holotypes. Then work from there.

Gervais P 1865. Du Mesosaurus tenuidens, reptile fossile de l’Afrique australe. Comptes Rendus de l’Académie de Sciences 60:950–955.
Modesto SP 1999. Observations on the structure of the Early Permian reptile Stereosternum tumidum Cope. Palaeontol. Afr. 35, 7–19.
Piñeiro G, Ferigolo J, Mones A and Demarco PN 2021. Mesosaur taxonomy reappraisal: Are Stereosternum and Brazilosaurus valid taxa? Revista Brasileira de Paleontologia 24(3):205–235. A Journal of the Brazilian Society of Paleontology.
Shikama T and Ozaki H 1966. On a Reptilian Skeleton from the Palaeozoic Formation of San Paulo, Brazil. Transactions and Proceedings of the Palaeontological Society of Japan. New Series. 64: 351–358.


Omosudis, another fanged swordfish relative, enters the LRT

Omosudis lowii (Günther 1887; 23cm; Figs. 1, 2) is the extant deep sea hammerjaw. Traditionally it is related to lizardfish (Trachinocephalus).

in the large reptile tree (LRT, 1941+ taxa) the hammerjaw is related to the fanged lancetfish, Alepisaurus (Fig. 3) and the fangless swordfish, Xiphias (Fig. 4), taxa they more closely resemble.

Figure 1. Skull of Omosuis from Gregory 1933, colorized here.

This fast swimmer
is a hermaphrodite feeding on squid and fish large enough to stretch out the thin skin of its stomach. In turn, the hammerjaw is prey to lancetfish (Fig. 3) and tuna. Note the large dentary and palatine fangs, something swordfish lack as adults (Fig. 4).

Figure 2. Omosudis overall in lateral view, head in dorsal view. Note the tiny pelvic fins.
Figure 1. Alepisaurus, the lancet fish nests with swordfish and eels in the LRT.
Figure 3. Alepisaurus, the lancet fish nests with swordfish and eels in the LRT.
Figure 4. Swordfish ontogeny (growth series). Hatchings have teeth, a short bill and an eel-like body still lacing pelvic fins.
Figure 4. Swordfish ontogeny (growth series). Hatchings have teeth, a short bill and an eel-like body still lacking pelvic fins, gone after the first stage shown here.

Günther ACLG 1887. Report on the deep-sea fishes collected by H.M.S. “Challenger” during the years 1873–76. Report on the Scientific Results of the Voyage of H. M. S. “Challenger” during the Years 1873-76 under the Command of Captain George S. Nares, R.N., F.R.S. and the Late Captain Frank Tourle Thomson, R.N. 22: i-lxv, 1-268, pls. 1-73.


Where is the anterior spike-tooth in the Uppsala Pteranodon UUPI R197?

This challenge came in from a reader, Anton Larsson,
who sent a digital photo of the Uppsala specimen of Pteranodon (Wiman 1920; Figs. 1–3; originally discovered in Kansas) with a challenge: Where is the anterior spike-tooth in this specimen? It is missing here.

Figure 1. Closeup of the Uppsala Sweden specimen of Pteranodon. The spike-like anterior tooth is definitely missing. Where is it? All the clues you would need are present here. See other figures for answer.

as we learned earlier (in 2011) a spike-like tooth is found in the anterior premaxilla (and dentary) of all other descendants of Altmuehlopterus rhamphastinus (formerly Germanodactylus rhamphastinus). In the large pterosaur tree (LPT, 260 taxa) that includes this specimen of Pteranodon. So, in this case, where is the spike-tooth? Where did it go? Was it ever there? It is definitely missing here, but it left a clue to its disappearance.

Figure 2. The facial part of the UUPI 1197 Uppsala specimen of Pteranodon. Here’s the clue to the spike-tooth disappearance. Look carefully. This is the inside of the face.

The Uppsala Pteranodon skull
preserves only the left side of the face and rostrum (Fig. 2) along with a projecting occiput and partial palate, exposing the inside of the skull. Now let’s take another look at the rostral tip.

Figure 3. Progressively closer pictures of the UUPI 197 Uppsala specimen of Pteranodon. The tooth is missing. It left a depression where its root was. The red graphic above shows the probable extent of the missing tooth spike not found elsewhere on this fossil.

The rostral tip also exposes the rostrum interior in medial view.
What we see here (Fig. 3) is the alveolus wherein the spike tooth, now missing, once grew. You can see here how deep that spike-tooth root grew. How far it protruded is a guess based on related specimens (Figs. 6, 7).

Figure 4. Reconstruction of the Uppsala specimen UUPI 1197 of Pteranodon, from Kanasas.
Figure 4. Reconstruction of the Uppsala specimen UUPI 1197 of Pteranodon, from Kanasas.

The Uppsala specimen in phylogenetic analysis
is one of the more primitive Pteranodon specimens. Only two others (based on relatively complete skull traits, Fig. 5) are more primitive.

Figure 2. The DMNH specimen is in color, nesting between the short crest KS specimen and the long crest AMNH specimen.
Figure 5. The Uppsala specimen is labeled ‘M’ here. Specimen ‘R’ is AMNH FR7515 (Fig. 7) one of the few to preserve the spike tooth in the premaxilla. Black zones are restored. Click here to enlarge.

Here in the year 2021
no other pterosaur paleontologist identifies a spike tooth in the rostrum of any Pteranodon, nytcosaurid, tapejarid, dsungaripterid or any other germanodactylid descendant. As you can see (Fig. 5), almost always the anterior rostrum is missing in Pteranodon. Unfortunately, even when the spike tooth is preserved (Fig. 6), other workers keep their blinders on. They don’t see it. This is nothing new. We’ve seen a reticence to accept valid observations over and over again in paleontology, and not only in pterosaurs.

Figure 3. Dsungaripterus single teeth at the tips of the jaws. Phylogenetically these began with Germanodactylus (Fig. 4).
Figure 6. Dsungaripterus single spike teeth at the tips of the jaws. Phylogenetically these began with Germanodactylus.

In a second comment (via email), a day before this publication,
Anton Larsson wrote, “And second, I don’t mean any bad to you, but I have taken close looks on the Pteranodon sp. specimen, in person even, as I have already said, and I just don’t find the single tooth, nowhere, impossible for me to see. I think actually you see things that aren’t there, sorry Peters.”

Figure 7. Pteranoodn with rarely preserved spike tooth, AMNH FR7515.
Figure 7. Pteranoodn with rarely preserved spike tooth, AMNH FR7515. Compared to Dsungaripterus, the spike tooth here appears to be jammed into the bone. Note the deformation near the root confirming taphonomic trauma.

Anton Larsson is correct. The tooth is not present.
But the alveolus is present. That in itself is rare. Rarely are Pteranodon jaw tips present (Figs. 5, 7). This is when it pays to have seen and tested many related specimens. This is when it pays to run an analysis. This is when phylogenetic bracketing comes in handy. When you expect to find a spike tooth and don’t find one in members of this clade, then look for a clue to the disappearance of the spike-tooth. In this case the tooth root, the alveolus, left an impression. With the Uppsala specimen we are given a rare peek inside the skull of a Pteranodon. Originally Anton Larsson provided no clue that he realized he was looking at the inside of the skull. He was also following the paradigm of the toothless Pteranodon portrayed in every prior academic paper and children’s book. That’s why this blogpost is called “Pterosaur Heresies” because here prior observations are tested for veracity.

In this case,
I was able to restore the presence of something that wasn’t there (a spike-tooth in the Uppsala specimen, Figs. 4, 5) because it left a clue to its presence (an alveolus). Phylogenetic bracketing indicates the same.

Look carefully. Look at dozens of specimens. Even photos of specimens.
Workers are missing important traits and clues to those traits. AND they are dismissing amateur workers who put in the effort to study and analyze specimens they are not only glossing over but omitting from analysis. Textbooks will only take you so far, and too often far afield. Continue your studies beyond the textbooks, as we are doing here.

I have made 150,000 mistakes over the last ten years.
This was not one of them. I am learning from my naive freshman errors. I hope you do, too. Making mistakes is part of the process. Don’t cling to errors like some professors do.

Thank you for your readership
as we move into an 11th year of blogging with over 3600 posts to date.

Wiman C 1920. Some reptiles from the Niobrara Group in Kansas. Bulletin of the Geological Institution of the University of Uppsala, 18:9-18.


The strangest mouth in vertebrates: Phractolaemus

This extant freshwater African fish looks rather ordinary
until it starts feeding. Meet the hingemouth, Phractolaemus, one of the most basal ray fin fish in the LRT (subset Fig. 5). “Basal” means it had a long time to develop it’s very strange mouth parts as the rest of it’s anatomy remained rather primitive.

Figure 1. Phractolaemus skeleton and in vivo diagrams. Arrow points to vertebral transition from dorsal to caudal, far posterior to the pelvic fins.

Phractolaemus ansorgii
(Boulenger 1901; 20cm) is the extant hingemouth, an African freshwater fish not previously associated with Cromeria, itself something of an enigma taxon. Unlike any other gnathostome, the maxilla rotates on the front axis of the dentary, acting like a sweeper to fling small bottom detritus into the dorsal mouth.

Figure 2. Phractolaemus skull figures from figure 1 here colorized with tetrapod homologs based on sister taxa, like Cromeria, figure 4, in the LRT.

How that evolved and how that actually and economically works
remains a mystery. The traditional axis of the mandible remains at the contact with the long, prone quadrate is located anterior to the nares, at the back of the mandible. Note: when the mandible closes, the maxilla + premaxilla also closes. Perhaps resulting suction or lift draws food particles into the dorsal mouth.

Figure 3. Phractolaemus skull animation. Some bones absent to show red axes and mandible (dark blue) anchor elements, like the quadrate (red), pterygoid (gray red), hyomandibular (green) and preopercular (light yellow). Maxilla is bright green. Premaxilla is yellow. Note: when the mandible closes, the maxilla + premaxilla also closes. Perhaps suction draws food particles into the dorsal mouth.

Here the preopercular is completely ventral to the quadrate.
Only two teeth remain on the dentary. Two sensory barbels probe and sense the substrate. The swim bladder can act as a lung.

Figure 4. Cromeria is a sister to Phractolaemus in the LRT. They share a common ancestor at present unknown other than Anableps (Fig. 5), itself highly derived. Compare to more primitive Lepidogalaxias (Fig. 5).

These fish are part of the first radiation of basal bony fish
beginning with Prohalecites, known from the Middle Triassic with a radiation that goes back to the Silurian, according to phylogenetic chronological bracketing.

Figure 5. Subset of the LRT focusing on basal ray fin taxa prior to the addition of Phractolaemus.

Watch the hingemouth feeding here.

Figure 6. Hingemouth closeup showing barbel and strange dorsal mouth parts.

Boulenger GA 1901. Diagnoses of new fishes discovered by Mr. W. L. S. Loat in the Nile. Annals and Magazine of Natural History, Including Zoology, Botany and Geology, Being a Continuation of the ‘Magazine of Botany and Zoology’, and of Louden and Charlesworth’s ‘Magazine of Natural History’, Series 7 8: 444-446.

The Moorish idol, Zanclus, enters the LRT

Figure 1. The Moorish idol, Zanclus cornutus, in vivo.

Zanclus cornutus (Linneaus 1758; 23cm; Figs. 1, 2) is the extant Moorish idol, a disc-shaped coral reef nibbler. Traditionally a member of the Perciformes, here it nests with Scorpis (Fig. 3), the silver sweep, far from Perca. Note the horns anterior to the eyes. The teeth are long, creating a beak.

Figure 1. From Gregory 1933, the skull of Zanclus cornutus, the Moorish idol. Figure 1. From Gregory 1933, the skull of Zanclus cornutus, the Moorish idol.
Figure 2. From Gregory 1933, the skull of Zanclus cornutus, the Moorish idol. Colors added here on this highly derived skull.
Figure 2. Scorpis skull from Gregory 1938. Colors added here. No asymmetry is present on this outgroup to the flatfish and Moorish idol.
Figure 3. Scorpis skull from Gregory 1938. Colors added here. No asymmetry is present on this outgroup to the flatfish and Moorish idol. Note the more plesiomorphic traits.

Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.


Fossil Friday a week ago: Sept 17, 2021

Frame from YouTube video podcast: Fossil Friday for September 17, 2021

This YouTube podcast featured preparator Jared Heuck, MSc,
who tells us about whales, snails and rodents. Odd mix. No worries. It all works out at the end (see below). This video presentation runs about an hour.

Heuck follows his out-of-date textbook in recognizing an invalid clade ‘Cetacea‘ that he posits split into Odontoceti and Mysticeti 40 million years ago.

By contrast, when more taxa are added to analysis,
as in the large reptile tree (LRT, 1941+ taxa), the tree shrews that will someday evolve to become odontocetes split off from those that will someday become mysticetes in the Early Jurassic, some 190 million years ago. That split was documented online in 2016.

Figure 1. Three species attributed to Aetiocetus. Academic workers consider these basal to baleen whales, but those workers don’t include tenrecs and desmostylians in their analyses.

In Heuck’s whale cladogram
he properly nests Mammalodon (Fig. 2) in the ancestry of mysticetes, but mistakenly interjects Aetiocetidus (an odontocete ancestor, Fig. 1) and omits proximal mysticete ancestors, desmostylians (Fig. 3). Once again, he’s only following several papers written in the last decade.

Figure 2. Mammalodon nests within the clade Anthracobune basal to desmostylians and mysticetes. Those teeth are not ‘raptorial’. They are hippo-like to desmostylian-like at best.

Heuck describes mammalodontids and aetiocetids as raptorial.
This is inappropriate in that no relatives of Mammalodon are raptorial in the LRT. By contrast, Aetiocetus was definitely a killer, but not related to Mammalodon and mysticetes. Heuck is confused due to taxon exclusion on the part of the whale workers who wrote papers on these taxa still believing that Cetacea was a monophyletic clade. This is why it is SO important to ALWAYS start off with a valid phylogeny that minimizes taxon exclusion.

Heuck misdescribes Mammalodon and Aetiocetus
as “toothed baleen whales” following a term used in several recent papers describing aetiocetids. That is wrong on both counts. Phylogenetic bracketing (Fig. 3) gives Mammalodon legs, not flippers. So it is not yet a whale of either kind. And Aetiocetus is not related to baleen whales. ‘Whales’ with teeth are all odontocetes.

Figure x. Origin of the Mysticeti according to the LRT. Figure x. Origin of the Mysticeti according to the LRT.
Figure 3. Origin of the Mysticeti according to the LRT. All are to the same scale except the bottom two skeletons.

Where do the snails and rodents come in?
Heuck uses these to determine the age of an aetiocetid fossil jaw fragment (with multicusped teeth) found during a California highway excavation.

After analysis by Hueck
he labeled the toothed aetiocetid from California cf. Wahaora (Fig. 5) in his cladogram. Evidently the software Heuck used recovered his toothed specimen close to a more completely known toothless highly derived, but extinct mysticete from New Zealand, Wahaora. Not sure how that could have happened. Toothed and toothless ‘whales’ do not nest together, except in ‘by default’ cladograms that omit pertinent taxa, like the paper that described the original Wahaora (Boessenecker and Fordyce 2015b). It ends up nesting toothed aetiocetids with toothless mysticetids.

Figure 8. Odontoceti (toothed whale) origin and evolution. Here Anagale, Andrewsarchus, Sinonyx, Hemicentetes, Tenrec Indohyus and Leptictidium precede Pakicetus. Maiacetus and Orcinus are aquatic odontocetes.
Figure 4. Odontoceti (toothed whale) origin and evolution. Here Anagale, Andrewsarchus, Sinonyx, Hemicentetes, Tenrec Indohyus and Leptictidium precede Pakicetus. Maiacetus and Orcinus are aquatic odontocetes.

Earlier we looked at the mistake whale workers make
when they attempt to maintain a monophyletic Cetacea. By default flat-headed mysticetes, like Tokarahia and Wahaora (Fig. 5), nest with flat-headed odontocetes, like Aetiocetus (Fig. 1). Simply adding taxa (Figs. 3, 4) splits them far apart.

Figure 1. Tokarahia compared to Wahaora, below, with a more slender and flatter skull.
Figure 5. Tokarahia compared to Wahaora, below, with a more slender and flatter skull. Note the complete lack of teeth. These are derived mysticetes, not primitive taxa. The cladogram by Boessenecker and Fordyce 2015b is essentially upside-down because it introduced unrelated taxa.

Jared Heuck strikes me as extremely sharp, serious and well read.
He could be a major force in paleo as the years go by. At his young age, like all of us, he’s following the textbooks and papers that have been coming out about the origin of baleen whales, all of them flawed due to taxon exclusion. These mistakes can be corrected. Add these taxa (Figs. 3, 4) to clarify all whale issues.

There is another Fossil Friday at noon CDT
on desmostylians (Fig. 3) hosted by another young paleontologist, Gabriel Santos.

Here’s the promo copy for the live video presentation:
“Have you ever heard of a desmostylian? Fossils of these odd and amazing extinct marine mammals have been known for over a century, but we really still don’t know that much about them. On this episode, we dive in with Alf Museum paleontologist, Gabriel Santos, as we talk about my mysteries and wonderful weirdness of these elephant-sized, hippo-like sea creatures!”

Suggestion: If you don’t know much about a taxon, add taxa. Phylogenetic bracketing will teach you what you aren’t seeing in the fossil itself. In the video frame below, you’re looking at an ancestor to right whales, Desmostylus (Fig. 3).

Boessenecker RW and Fordyce RE 2015b. Anatomy, feeding ecology, and ontogeny of a transitional baleen whale: a new genus and species of Eomysticetidae (Mammalia: Cetacea) from the Oligocene of New Zealand. PeerJ 3:e1129
Peters D 2013. Unpublished, The Triple Origin of Whales on

The footballfish, Himantolophus, enters the LRT with a humerus, ulna and radius

As in other deep sea anglers,
females are large, up to 60cm. Toothless males are only 4cm, but not parasitic, unlike the other deep sea anglerfish. These poor swimmers are pudgy, sedentary, sit-and-wait predators.

Figure 1. Himantolophus, a rotund deep-sea angler, enters the LRT close to frogfish. Note the lack of pelvic fins.

the pectoral fin of Himantolophus (Fig. 1) consists of a humerus, radius and ulna not found in related fish. Unexpected convergence here. No other fish workers have labeled these bones with tetrapod analogs, but others have labeled this zone the ‘lobe’ of the fin.

There are several rayfins in the lobefin half of the bony fish dichotomy
in the large reptile tree (LRT, 1940+ taxa). Deep-sea anglers and frogfish are the closest thing rayfins have to a lobefin.

Figure 2. Several deep sea anglers from Tate Regan. Colored here.

Strongly resembling the related frogfish
(Antennarius, Fig. 3), Himantolophus groenlandicus lacks any trace of a pelvis or pelvic fin.

Figure 3. Antennarius the frogfish. Note the presence of pelvic fins anterior to the pectoral fins.

In the LRT,
a lack of pelvic fins moves the footballfish away from frogfish (Antennarius) and toward nearby puffers Lagocephalus, queen trigger fish (Balistes) and molas (Mola), all of which also lack pelvic fins. This is likely by convergence because more derived bottom-dwelling stargazers (Uranoscopus) goosefish (Lophius) and tripod fish (Bathypterois) have pelvic fins. Slow swimming yet related flabby whalefish (Cetostoma) also lack pelvic fins by convergence.

Reinhardt JCH 1837. Ichthyologiske bidrag til den Grönlandske fauna. Kgl. Danske Vidensk. Selsk. Natur. Math. Afhandl., 7: 83-196, pls. 1-8.


Eoletes enters the LRT

Never heard of it?
Neither did I. Currently Wikipedia does not even have a page for Eoletes (Figs. 1,2).

When added
to the large reptile tree (LRT, 1938+ taxa) Eoletes nests at the base of the tapirs, which nest at the base of the crowngroup Perissodactylia. Outgroups include Diadophorus at the base of the chalicothere clade and Ectocion at the base of the hyrax-elephant-manatee clade.

Figure 1. From Lucas et al. 1997. Compare to fiigure 2.
Figure 2. Skull of Eoletes from Lucas et al. 1997, colors added here.

Eoletes gracilis
(Biryukov 1974; Lucas SG, Emry RJ and Bayshashov BU 1997; KAN 5088/69; Middle Eocene, 45mya) nests as a basal tapir in the LRT, close to the origin of Perissodactyla. The skull is quite narrow. The premolars are molarized. Lower premaxillary teeth were present, not preserved. The frontals formed a postorbital bar.

Lucas et al. 1997 considered Eoletes a “lophialetid ceratomorph”.
According to the American Museum of Natural History: Ceratomorpha = tapirs and rhinos. In the LRT this traditional clade is paraphyletic because it excludes horses. If it included horses it would be a junior synonym for Perissodactyla. Lophialetes expeditus is the first known lophialetids, a type of tapir known from a jaw with teeth only.

Why did I look up this taxon?
Still trying to figure out why all others say paraceratheres are rhinos, while the LRT nests them with horses. I still can’t find a software-era cladogram that includes rhinos, horses and paraceratheres. If you know of one, let me know.

Biryakov MD 1974a. Novye rod semysva Lopioletidae iz eosena Kazakhstana [New genus of the family Lopialetidae from the the eocen of Kazakhstan.] Akademiya Nauk Kazakhskoy, SSR Institut Zoologii Materiali po istoriii flori Kazakhstana [Academy of Sciences of the Kazakh SSR Institute of Zoology Material for the History of the Fauna and Flora of Kazakhstan] 6:57–73.
Lucas SG, Emry RJ and Bayshashov BU 1997. Eocene Perissodactyla from the Shinzhaly River, Eastern Kazakhstan. Journal of Vertebrate Paleontology 17(1):235–246.

The search for a paracerathere ancestor: rhino? or horse?

Everyone agrees
extant tapirs, horses and rhinos are closely related. These are all perissodactyls. Tapirs are the most primitive perissodactyls in the the large reptile tree (LRT, 1938+ taxa), but not at the AMNH website.

According to the American Museum of Natural History:
Ceratomorpha = tapirs and rhinos. According to the AMNH, horses split off earlier. In the LRT ‘Ceratomorpha’ is paraphyletic because it excludes horses. If Ceratomorpha included horses it would be a junior synonym for crown Perissodactyla. Rhinos and horses share a last common ancestor close to Hyracotherium (Fig. 1) in the LRT.

Figure 2. Hyracotherium is an Eocene horse sister in the LRT. Skull bones are colorized here.
Figure 1. Hyracotherium is an Eocene horse and rhino ancestor in the LRT. Skull bones are colorized here.

In the pre-software era (prior to 1985~1995)
all family trees were built on the insight and experience of the paleontologist (Fig. 2). Despite this shortcoming at least these topologies were built on visible measurable traits, not molecules.

Figure 2. Cladogram from Lucas et al 1981 showing their conception of the ancestry of paraceratheres.
Figure 2. Rhino cladogram from Wang et al. 2016 focusing on paraceratheres.
Figure 3. Rhino cladogram from Wang et al. 2016 focusing on paraceratheres.

Contra tradition
(Figs. 2, 3) the LRT nests long-necked, long-legged paraceratheres (Fig. 4) with horses rather than hyracodontid rhinos. According to rhino and horse experts (see below) no cladogram from the software era, other than the LRT, include rhinos, horses and paraceratheres.

Figure 1. Equus the horse shares many traits with Paraceratherium, the giant rhino/horse.
Figure 4. Equus the horse shares many traits with Paraceratherium, the giant rhino?/horse?

According to Wikipedia,
Rhinoceros fossils are identified as such mainly by characteristics of their teeth, which is the part of the animals most likely to be preserved. The upper molars of most rhinoceroses have a pi (π) shaped pattern on the crown, and each lower molar has paired L-shapes.”

By contrast,
the LRT does not test cusp shapes, but does test 238 other multi-state traits from snout to tail tip, including several dental traits.

Figure 5. Life restoration of Indricotherium and its skeleton. Note the horse-like proportions.

Holbrook and Lapergola 2011 report,
“Perhaps a more important reason for caution is the nature of of the (primarily) dental characters used in the analyses and the prevalence of parallelism in perissodactyl dental characters.”

Figure 6. Various ungulates and kin subset of the LRT. Here Aceratherium, a hornless rhino, does not nest with Paraceratherium, a giant three-toed horse. Ghosted image is Juxia. Note the horse-like proportions.

I asked rhino and horse experts
“Has there ever been a phylogenetic analysis that included lots of rhinos and horses along with their last common ancestor? I’m still wondering if Juxia and the giant long-necked, slender hornless rhinos aren’t closer to Mesohippus.”

“There have been many. Juxia had LOTS of rhino synapomorphies not found in ANY horse, and Mesohippus is loaded with equid synapomorphies not found in any rhino. Look at my cladograms, MacFadden’s, and all the rest. EXTREMELY UNPARSIMONIOUS (and contradicted by the plethora of other closely related fossils)”

“Please send titles of papers that have modern cladograms that include horses, rhinos and paraceratheres. I’ve run an analysis and find paraceratheres nest with three-toed horses. In some fossils it is clear that the weight is carried on the central toe.”

“My “recent” phylogeny of horses (not strictly a cladogram) and 20 years old—published in Science. I don’t have anything with rhinos or paraceratheres.
Let me know if you cannot find the former”.

Was wondering if there are any cladograms in the software era that include horses, rhinos and paraceratheres (indricotheres)?I am more interested in those that include non-dental traits.”

“None come to mind. Anything that includes indricotheres would at most include some hippomorphs as outgroups. You might try asking Bai Bin at IVPP; he has been working on a larger phylogenies of perissodactyls, there has been recent work on indricotheres from IVPP by Haibin Wang that he might be incorporating.”

“Was wondering if Miohippus and Equus were included in your analysis of indricotheres? Please send a PDF if available.”

“Yes, indricotheres are allied with rhinos primarily by their teeth, but also skull structure. Foot structure is hyracodontid (see attached). The similarity to equid feet is convergent.”

Figure 4. A variety of horse and paracerathere skulls.
Figure 7. A variety of horse, rhino and paracerathere skulls.

From Prothero 2009a:
“By the late Eocene, they had diversified into three branches: the hippolike amynodonts, the long-legged running hyracodonts, and the true rhinoceroses, family Rhinocerotidae. Each family shows considerable diversification and evolution, with the hyracodonts evolving into the gigantic indricothere Paraceratherium (formerly called Baluchitherium or Indricotherium), the largest land mammal that ever lived. It was a hornless rhino from the Oligocene of Asia that reached 7 meters tall at the shoulder and weighed at least 20 tons, larger than any elephant. Yet despite its huge size, it retained the relatively long slender limbs and toes of its hyracodont ancestry and did not develop the stubby graviportal toes seen in elephants and larger dinosaurs.”

From the LRT:
Traits in horses and paraceratheres, not rhinos:

1. skull not shorter than cervicals
2. premaxillary-maxillary notch < 45º
3. dentary tip descends
4. naris axis < 30º
5. naris posteriorly elongated (not Miohippus)
6. diastema without mx notch
7. cervicals do not decrease cranially
8. mid-cervical >1.5x mid dorsal length
9. sacral vertebrae > 2
10. sacral spines > acetabulum height over ilium
11. metacarpal 5 absent
12. tarsus < 0.6x pedal 4 (digit + metatarsus) includes Hyracotherium

not tested in the LRT: weight born on central toe, much larger than lateral toes

Figure x. Uintaceras, a basal rhino, compared to Forstercooperia, a basal indricothere close to Equus and Mesohippus, two horse taxa.
Figure 8. Uintaceras, a basal rhino, compared to Forstercooperia, a basal indricothere closer to Equus and Mesohippus, two horse taxa, in the LRT. Note resemblance of Forstercooperia to Equus in figure 9.

Moving taxa:
moving Mesohippus + horses + paraceratheres to Uintaceras adds 4 steps
moving horses + paraceratheres to Uintaceras adds 10 steps
moving paraceratheres to Uintaceras adds 14 steps

Figure 1. Equus the extant horse.
Figure 9. Equus the extant horse.

Convergence and parallelism
The Holbrook Lab @ Rowan reports, “The independent evolution of similar traits is a common observation in evolutionary biology, and the evolutionary history of perissodactyls exhibits this in several complex traits, such as body size and tooth surface complexity. We explore the evolution of these traits using three-dimensional geometric morphometrics and comparative phylogenetic methods.”

Bottom line:
Maximum parsimony is the rule in phylogenetic analysis. At present academics are following traditions, dental traits and taxon exclusion. The LRT is currently the only cladogram that includes horses, paraceratheres and rhinos.

If perissodactyl workers add a few horses to their rhino cladograms
and still nest paraceratheres with rhinos, then the long neck, long, slender legs, central toe and other traits (listed above) of paraceratheres are convergent with horses. We need an independent test to figure this out. Taxon exclusion is the number one problem in paleo today. Let’s fix that.

Chow M and Chiu C 1963. New genus of Giant Rhinoceros from Oligocene of Inner Mongolia. Vertebrata PalAsiatica 7(3):230-239.
Lucas SG and Sobus JC 1989. The Systematics of Indricotheres. In Prothero, D. R.; Schoch, R. M. (eds.). The Evolution of Perissodactyls. New York, New York & Oxford, England: Oxford University Press. pp. 358–378. ISBN978-0-19-506039-3. OCLC19268080.
Prothero DR 2013. Rhinoceros giants: The paleobiology of Indricotheres Rhinoceros Giants: the Paleobiology of Indricotheres. 1-141. 
Prothero DR 2009a. Evolutionary Transitions in the Fossil Record of Terrestrial Hoofed Mammals Evolution: Education and Outreach. 2: 289-302. DOI: 10.1007/S12052-009-0136-1 
Prothero DR 2009b. Missing links found: Transitional forms in the fossil mammal record For the Rock Record: Geologists On Intelligent Design. 39-58. 
Prothero DR. MacFadden, B. J. 1993(4). Fossil horses: systematics, paleobiology, and evolution of the family Equidae. Cambridge University Press. ISBN: 0-521-34041-1. Journal of Evolutionary Biology. 7: 119-121. DOI: 10.1046/J.1420-9101.1994.7010119.X 
Prothero DR, Manning E, Hanson CB 1986. The phylogeny of the Rhinocerotoidea (Mammalia, Perissodactyla) Zoological Journal of the Linnean Society. 87: 341-366. DOI: 10.1111/J.1096-3642.1986.Tb01340.X
Wang H, Bai B, Meng J and Wang 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.