Teraterpeton news – SVP abstract 2016

Updated January 06, 2019
with new data in the form of photos of the skull of Teraterpeton and a new nesting with Trilophosaurus to match the original nesting by Sues in 2011.

To start with
in the large reptile tree the genus Teraterpeton (Fig. 1, Late Triassic) nests as a sister to Trilophosaurus as a rhynchocephalian lepidosaur.

Figure 1. Skulls of Teraterpeton and Trilophosaurus compared.

From the Pritchard and Sues 2016 abstract (abridged)
“Teraterpeton hrynewichorum, from the Upper Triassic (Carnian) Wolfville Formation of Nova Scotia, is one of the more unusual early archosauromorphs, with an elongate edentulous snout, transversely broadened and cusped teeth, and a closed lateral temporal fenestra. Initial phylogenetic analyses recovered this species as the sister taxon to Trilophosaurus spp.

1. New material of Teraterpeton includes the first-known complete pelvic girdle and hind limbs and the proximal portion of the tail. These bones differ radically from those in Trilophosaurus, and present a striking mosaic of anatomical features for an early saurian
2. The ilium has an elongate, dorsoventrally tall anterior process similar to that of hyperodapedontine rhynchosaurs.
3. The pelvis has a well-developed thyroid fenestra, a feature shared by Tanystropheidae, Kuehneosauridae, and Lepidosauria. 
4. The calcaneum is ventrally concave, as in Azendohsaurus.
5. The fifth metatarsal is proximodistally short, comparable to the condition in Tanystropheidae.
6. Much as in the manus, the pedal unguals of Teraterpeton are transversely flattened and dorsoventrally deep. 
7. Phylogenetic analysis of 57 taxa of Permo-Triassic diapsids and 315 characters supports the placement of Teraterpeton as the sister-taxon of Trilophosaurus in a clade that also includes Azendohsauridae and, rather unexpectedly, Kuehneosauridae.
8.  In the current phylogeny, the aforementioned amalgam of characters in Teraterpeton were all acquired independently from the other saurian lineages. We partitioned the dataset based on anatomical region to examine metrics of homoplasy across early Sauria. The CI of the partitions are not markedly different, but the RI of the pelvic girdle and hindlimb partitions are markedly higher than the others. Although the characters in the hindquarters partitions underwent a similar number of homoplastic changes, a higher proportion of them contribute to the overall structure of this phylogenetic reconstruction. The mosaic condition in Teraterpeton underscores the importance of thorough taxon sampling for understanding the dynamics of character change in Triassic reptiles and the use of apomorphies in identifying fragmentary fossils.”

Notes

1. Seems like Prtichard and Sues do not reject the Trilophosaurus relationship.
2. No trilophosaurids or rhynchosaurs have a thyroid fenestra. Other than Amotosaurus, no tanystropheids have a thyroid fenestra. Rather a separate pubis and ischium are not joined ventrally.
3. I don’t see any other examples of ventrally concave calcaneal tubers in candidate taxa, nor is this apparent in the Nesbitt et al. 2015 reconstruction of Azendohsaurus.
4. No candidate taxa have a metatarsal 5 as short as the one in Tanystropheus.
5. They may have just metaphorically ‘shot themselves in the foot’ as kuehneosaurids are unrelated to any previously mentioned candidate taxa. They are the arboreal gliding reptiles. This throws doubt on any and all of their scoring and results.
6. None of the candidate taxa listed by Pritchard and Sues have an antorbital fenestra or a long narrow snout with a very short cranial/temporal region like Teraterpeton has (Fig. 1). It’s an autapomorphy or taphonomic damage.

References
Pritchard AC, Sues H-D 2016. Mosaic evolution of the early saurian post cranium revealed by the postcranial skeleton of Teraterpeton hrynewichorum (Archosauromorpha, Late Triassic). Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.

Is Palacrodon a rhynchocephalian? – SVP abstract 2016

Originally (Broom 1906)
considered what little is known of Palacrodon browni (= Fremouwsaurus geludens; Early Triassic; Fig. 1) a member of the Rhynchocephalia. This year, Jenkins and Lewis 2016 tested Palacrodon against rhynchcephalians and procolophonids and found it nested with the former. This genus was so obscure that Wikipedia ignored it when this was first posted. The few specimens are poorly known, only a few fragments of skull + teeth from South Africa and Antarctica.

Here in a large gamut analysis Palacrodon nests
in the large reptile tree (LRT) at the base of the Placodontia (Fig. 1) between sharp-toothed and big-eyed Palatodonta + Pappochelys and the much larger, pavement-toothed, smaller-eyed Paraplacodus.

Figure 1. A comparison of basal placodonts to scale (and Paraplacodus reduced to one-third shows how Fremouwsaurus (Palacrodon) is transitional between the small spike-tooth ancestors like Palatodonta and Pappochelys and the pavement toothed Paraplacodus.

Unfortunately recent work by Jenkins and Lewis 2016
did not include basal placodonts in their limited taxon analysis. The anterior maxillary teeth are still needle-like as in ancestral taxa. One can readily wonder if this is how the transition from one tooth type to the other occurred. Note the anterior maxillary teeth of Paraplacodus are still a bit sharp. I flipped the drawing of the quadrate from its original concave posterior. We have no palatal material for Palacrodon, but ancestral taxa display short robust teeth.

From the Jenkins and Lewis 2016 abstract
“Palacrodon browni is an Early Triassic reptile found on both the South African and Antarctic continents. The taxon has been classified as a diapsid, rhynchocephalian, and procolophonid in descriptions dating from 1906 to 1999, and consensus has not been reached regarding its phylogentic relationship within Lepidosauria. A refined phylogenetic placement of this reptile would push back stem dates of Lepidosauria from the Middle to the Early Triassic. It is possible Palacrodon is part of the faunal assemblage that experienced a decrease in body size as a result of the Lilliput effect noted in several Early Triassic lineages. There is also a noted range shift which occurred within the first 20 million years of the Triassic. The change in size and range suggest Palacrodon was strongly affected by the Permian mass extinction. Using high-resolution computed tomography, two dentaries were scanned and digitally segmented using AMIRA 6.2 to examine tooth implantation type (i.e., acrodont or thecodont) and reveal characters for better resolving the phylogenetic position of Palacrodon. Thirteen additional tooth-bearing elements, made available by the Evolutionary Institute at the University of Witwatersrand in Johannesburg, were also assessed for externally visible characters. Characters were scored against known Rhynchocephalia and procolophonid specimens using MacClade 4.08 and using an apomorphy-based approach specific to characters relating to dentition and tooth-bearing bones. Preliminary data suggest rhynchocephalian association due to acrodont dentition implantation in combination with possible protothecodont dentition in posterior teeth, and additional posterior dentition typical of sphenodontians. Initial survey also exhibits extreme wear on the occlusal surface of the teeth, a pattern typical of acrodont vertebrates and certainly rhynchocephalians. Phylogenetic analysis reveals Palacrodon’s familial association to be within Lepidosauria and its close relationship to crown Rhynchocephalia. A better understanding of the taxa that survived the Permian extinction may be beneficial to understanding and predicting the survival patterns of the current extinction, which shares any similarities to the Permian event. Change in body size and range behavior may be examples of these patterns which can be assessed in Palacrodon.”

Neenan et al. 2014
looked at tooth replacement in placodonts and found, “The plesiomorphic Placodus species show many replacement teeth at various stages of growth, with little or no discernible pattern.  Importantly, all specimens show at least one replacement tooth growing at the most posterior palatine tooth plates, indicating increased wear at this point and thus the most efficient functional crushing area.”

When head-less taxa meet head-only taxa.
The nesting of head-only Palacrodon with head-less Majaiashanosaurus immediately leads to rampant speculation worthy of Dr. Frankenstein. So… what if we put the enlarged head of the former on the body of the latter. Well, it might work (Fig. 2).

Figure 2. The head of Palacrodon and the headless body of the Majiashanosaurus compared at the same scale (left) and enlarged (at right).

References
Broom R 1906. On a new South African Triassic rhynchocephalian. Transactions of the Philosophical Society of South Africa 16:379-380.
Gow CE 1992. An enigmatic new reptile from the Lower Triassic Fremouw Formation of Antarctica. Palaeontologia Africana 29:21-23.
Gow CE 1999. The Triassic reptile Palacrodon brown Broom, synonymy and a new specimen.
Jenkins KM and Lewis PJ. 2016. Triassic lepidosaur from southern Gondwana. Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.
Neenan JM, Li C, Rieppel O, Bernardini F, Tuniz C, Muscio G and Scheyer TG 2014. Unique method of tooth replacement in durophagous placodont marine reptiles, with new data on the dentition of Chinese taxa. Journal of Anatomy 224(5):603-613.

wiki/Palacrodon

Chometokadmon is a basal gekko

A few years ago,
Evans et al. 2006 re-introduced us to the Lower Cretaceous lizard, Chometokadmon fitzingeri (MPN 539) from Italy. That genus was originally described by Costa 1864. The Evans team nested Chometokadmon between Dorsetisaurus and Xenousauridae at the base of the Anguimorpha (varanids + helodermatids). Note that Xenosaurus and Heloderma have laterally facing nares, not dorsal nares.

Figure 1. Chometokadmon in situ. Known for over 100 years, this flat skulled gekko had longer toes than typical.

The large reptile tree (LRT) nests Chometokadmon at the base of the geckos, between Tchingisaurus and Gekko smithii. Like geckos, Chometokadmon lacks a postorbital and thus has a confluent orbit + both temporal fenestra. Helodermatids have a similar temporal architecture lacking temporal bars, but do not have a triangular rostrum in dorsal view.

Perhaps
the Evans team made a mistake in identifying a quadrate alone as a quadrate + squamosal (Fig. 2). In most geckos, the quadrate is a tall slender bone, but in the basalmost gecko in the LRT, Tchingisaurus (Fig. 2), the lateral quadrate has an anterior rim that dorsally bends posteriorly, like the purported squamosal in Chometokadmon. No close relatives have a squamosal with the shape proposed by Evans et al. The triangular outline of the skull in dorsal view along with the short teeth are also gekko traits not found in candidates proposed by the Evans team.

FIgue 2. Skull and reconstruction of Chometokdamon by Evans et al. 2006. Note the loss of the postorbital and jugal bars.

A comparison to other geckos
(Fig. 3) makes the case rather clear to Chometokdamon may be one of them. A skull twice as wide as tall plus the confluence of the orbit with the both the upper and lower temporal fenestrae are gecko traits.

Figure 3. Tchingisaurus, a basal Gekkotan, according to the large reptile tree.

Figure 4. Gekko smithii is an extant member of a genus that extends to the Early Cretaceous. Note the lack of temporal bars and the forward extension of the supratemporal along the lateral parietal, as in Chometokadmon.

As a basal gekko
Chometokadmon joins two rather closely related and coeval basal pro-snake genera Ardeosaurus and Eichstattisaurus that we discussed earlier here and were mistakenly  considered basal geckos by Simoes et al. 2016. Their mistake, once again, was taxon exclusion, a problem often solved by the large gamut of taxa in the LRT.

References
Costa OG 1864. Paleontologia del Regno di Napoli, III. Atti dell’Accademia Pontaniana 8, 1e198.
Evans SE, Raia P, Barbera C 2006. The Lower Cretaceous lizard genus Chometokadmon from Italy. Cretaceous Research 27:675-683.
Simões TR, Caldwell MW, Nydam RL and Jiménez-Huidobro P 2016. Osteology, phylogeny, and functional morphology of two Jurassic lizard species and the early evolution of scansoriality in geckoes. Zoological Journal of the Linnean Society (advance online publication) DOI: 10.1111/zoj.12487 http://onlinelibrary.wiley.com/doi/10.1111/zoj.12487/fullwiki/Ardeosaurus

wiki/Chometokadmon

Stem geckos? Or stem snakes? – SVP abstract 2016

Earlier Simoes et al. 2016 published their paper and today their SVP abstract of Eichstaettisaurus and Ardeosaurus, two Jurassic squamates. Here’s how the LRT (subset Fig. 1, complete tree here) recovered geckos, snakes and stem snakes like Eichstaettisaurus and Ardeosaurus, the dual subjects of Simoes et al. 2016 paper and abstract.

Figure 1. Subset of the LRT focusing on geckos snakes and stem snakes that nest close to geckos.

From the Simoes et al. 2016 abstract:
“Late Jurassic lizards from Solnhofen, Germany, are some of the oldest known articulated lizard specimens in the world (1), and are also the most complete Jurassic squamates. These specimens are thus very important to our understanding of early squamate evolution, with valuable information regarding morphology, taxonomy, and phylogeny. Eichstaettisaurus schroederi and Ardeosaurus digitatellus are two of the best  preserved species from that locality, the former being represented by the most complete Jurassic lizard specimen known anywhere in the world. Despite their relevance to broad questions in squamate evolution, their morphology has never been described in detail, and their systematic placement has been under debate for decades. Here, we provide the first detailed morphological description, species level phylogeny and functional morphological evaluation of E. schroederi and A. digitatellus. We identified previously undescribed features of E. schroederi linking this taxon to gekkotans, such as the Meckelian canal being closed and fused medially, ectopterygoid lying dorsal to transverse process of pterygoid, and autopodial digit symmetry. Using a revised and updated dataset containing 610 characters and 193 taxa (2), we corroborate their initial placement as geckoes—stem gekkotans, more specifically. This is of fundamental importance to the early evolution of squamates, as it demonstrates the existence of yet another major extant squamate clade (Gekkonomorpha) in the Jurassic (3). Additionally, both taxa illustrate a number of climbing adaptations (e.g. shape of unguals, penultimate phalanges, and body proportions), which indicates a scansorial lifestyle arose earlier in the evolution of geckos than previously known. Autopodial modifications associated with digital hyperextension and adhesive toepads (e.g. depressed and reduced intermediate phalanges, and arcuate penultimate phalanges), which provide geckoes with a highly sophisticated climbing apparatus, are not present. Therefore, our findings further suggest that morphological adaptations for scansoriality evolved in geckoes prior to the first known occurrence of adhesive toepads in the Cretaceous. Our results provide support from the fossil record to most molecular and combined evidence estimates of the origin of most major clades of squamates, including geckoes, which usually place divergence times for their stem back in the Jurassic or the Triassic.”

Figure 1. From Simoes et al 2016, their cladogram of the squamates separate varanids from mosasaurs, link snakes to skinks and shows how close pre-snakes are to basal geckos.

Notes

1. In the LRT lepidosaurs extend back to the Early Permian (TA 1045 specimen, close to Saniwa) and Lacertulus (Late Permian).
2. The Ardeosaurus/Echstaettisaurus clade lies outside the geckos, inside the Pro-serpentes in the LRT as a single clade, but 3 ways by Simoes et al.
3. No wonder those two taxa form a separate clade outside the geckos in the Simoes et al. report. The do so as well in the LRT, at the base of all snake and pro snakes.
4. The LRT is a single, fully resolved tree, not the consensus of 3174 MPTs.

References
Simoes TR, Caldwell MW, Nydam RL and Jimenez Huidobro P 2016. Osteology, phylogeny and functional morphology of two Jurassic lizard species indicate the early evolution of scansoriality in geckoes. Abstract from the 2016 meeting of the Society of Vertebrate Paleontology.
Simões TR, Caldwell MW, Nydam RL and Jiménez-Huidobro P 2016. Osteology, phylogeny, and functional morphology of two Jurassic lizard species and the early evolution of scansoriality in geckoes. Zoological Journal of the Linnean Society (advance online publication) DOI: 10.1111/zoj.12487 http://onlinelibrary.wiley.com/doi/10.1111/zoj.12487/fullwiki/Ardeosaurus

You heard it here first… four years ago. Diandongosuchus is a stem phytosaur.

WordPress.com timestamps every post
This one comes from August 29, 2012. “Diandongosuchus. Not a basal poposauroid. A basal phytosaur.” Click here to see the original discovery and post. Click here to see the ReptileEvolution.com page on Diandongosuchus (Fig. 1). Click here to see the nesting of Diandongosuchus in the large reptile tree.

Figure 1. Diandongosuchus nests as a basal phytosaur when choristoderes and basal younginoids are included, far from Qianosuchus, which also does not nest with poposaurs, which are all bipedal (or formerly bipedal) herbivores, a far cry from Diandongosuchus.

 

 

Today, delivering a SVP abstract, Stocker et al. report
“… A recently described taxon from the Ladinian of China, Diandongosuchus, was proposed as a poposauroid largely because of similarities (e.g., premaxillary elongation) to the basal form Qianosuchus. We reassessed the systematics of Diandongosuchus within an extensive analysis of archosauriform phylogenetic relationships and show that Diandongosuchus is not a poposauroid, but is the sister taxon to all phytosaurs. First-hand evaluation of Diandongosuchus reveals an interdigitated premaxilla-maxilla suture, wide distal end of the quadrate, broad postorbital-squamosal bar, hooked coracoid, broad interclavicle, and backswept scapula, all apomorphies of Late Triassic phytosaurs. Our reinterpretation of Diandongosuchus as a phytosaur indicates that the postcranial modifications of phytosaurs occurred well prior to rostral elongation, supports that the clade was located across Pangea, and hypothesizes saltwater tolerance….”

Since some things cannot be discovered twice
I thought this might interest the readers of PterosaurHeresies that some things done here are later confirmed by other workers when they expand their taxon lists. Not sure how I feel about the Stocker team claiming credit for this…

You’ll note
the Stocker team could have read about their ‘reinterpretation” at any time over the past four years by googling “Diandongosuchus“. Not sure how long it will take Wikipedia to catch up. As I write this on the 26th, Wiki is respecting the SVP embargo.

BTW
the Stocker team thesis on the origin of the long snout on phytosaurs can be traced beyond Diandongosuchus to its ancestry within the wide variety of Proterosuchus, Elaphrosuchus and Chasmatosaurus specimens in the LRT. It’s a powerful tool, available free to everyone.

Not sure if there will be any credit given for this
from Dr. Naish after all the discredit heaped upon ReptileEvolution.com earlier. This is what some would call vindication, and others would call confirmation, of a tested hypothesis of interrelationships. Test your enigmas by expanding your taxon inclusion lists and let’s see how many other confirmations (and refutations if they arise) we can find together.

References
Stocker MR, Nesbitt SJ, Zhao L-J, Wu X-C and Li C 2016. Mosaic evolution in phytosauria: the origin of longsnouted morphologies based on a complete skeleton of a phytosaur from the Middle Triassic of China. Abstracts of the Society of Vertebtate Paleontology meeting 2016.

 

 

 

Stem taxa: wider vs. narrower definitions

The following is as much a learning experience for me
as it may be for you, as I come to an understanding of a definition with which I was previously unfamiliar — Stem Taxa in the ‘wider sense’. There is also a ‘narrower sense’, with which I was more familiar (see below).

Stem taxa in the wider sense
are extinct taxa closer to one clade of living taxa than to any other living taxa. In more precise terms, according to Wikipedia: “A stem group is a paraphyletic group composed of a pan-group or total-group, above, minus the crown group itself (and therefore minus all living members of the pan-group).”

Figure 1. CLICK TO ENLARGE and retrieve a PDF file. Stem taxa are the closest ancestors to living taxa, but not the living taxa. Here in the wider sense marine enaliosaurs, including ichthyosaurs, are stem archosaurs. Triceratops is a stem bird. Diadectids are stem turtles. Pterosaurs are stem squamates.

The stem reptiles
in the LRT (Fig. 1, click here for PDF enlargement) are not the same stem taxa found in traditional studies, like Benton 1999, who includes pterosaurs among the stem birds. In the LRT (Fig. 1) pterosaurs are stem squamates, not squamates, but closer to squamates than to Sphenodon, the extant tuatara. Stem amphibians are not listed here, because the only listed extant taxon in that clade is Rana, the bull frog. Here plesiosaurs, ichthyosaurs and mesosaurs are all stem archosaurs. All dinosaurs are stem birds. Diadectids are stem turtles.

Paleontological significance
According to Wikipedia, “Placing fossils in their right order in a stem group allows the order of these acquisitions to be established, and thus the ecological and functional setting of the evolution of the major features of the group in question. Stem groups thus offer a route to integrate unique palaeontological data into questions of the evolution of living organisms. Furthermore, they show that fossils that were considered to lie in their own separate group because they did not show all the diagnostic features of a living clade, can nevertheless be related to it by lying in its stem group.” Unfortunately, these benefits get fuzzier as the phylogenetic distance increases.

Stem group: the narrower sense
According to Wikipedia (referencing Czaplewski, Vaughan and Ryan 2000), “Alternatively, the term “stem group” is sometimes used in a narrower sense to cover just the members of the traditional taxon falling outside the crown group. Permian synapsids like Dimetrodon and Anteosaurus are stem mammals in the wider sense but not in the narrower one. From a cynodont ancestry, the stem mammals arose in the late Triassic, slightly after the first appearance of dinosaurs.”

That narrower definition
is the one I was following and is certainly more useful, more targeted, etc. Since both definitions are in play in the wider world, be sure you specify which one you are discussing. Dr. Naish embraced the wider one while ignoring the narrower one.

And that’s okay.

References
Benton MJ 1999. Scleromochlus taylori and the origin of the pterosaurs. Philosophical Transactions of the Royal Society London, Series B 354 1423-1446.
Czaplewski TA, Vaughan JM and Ryan NJ 2000. Mammalogy (4th ed.). Fort Worth: Brooks/Cole Thomson Learning. p. 61.

wiki/Crown_group#Stem_groups

 

Whales are diphyletic. Goodbye ‘Cetacea’!

Updated November 8. 2016 with a revision to the nesting of Janjucetus after the inclusion of the desmostylian and mysticete sister, Behemotops.

You might have suspected this all along
since the two orders of whales, Odontoceti and Mysticeti, are so different from one another. The present study indicates we will never find a last common ancestor with flippers and fins for all living whales because the two orders arose from two widely separated mammal orders with legs.

Baleen whales (Mysticeti) arise from Paleoparadoxia and Anthracobune in the large reptile tree. So there IS now evidence in the LRT for a hippo relationship, as these taxa are more or less related to hippos. But the hippo clade (Mesonychidae) is separated from the artiodactyls by several nodes, so even mysticete whales are not close to artiodactyls.

Toothed whales (Odontoceti) still arise from tenrecs as noted here earlier.

That makes living whales diphyletic
and the order name ‘Cetacea’ invalid and useless because it is not monophyletic. It will probably take a century to disappear because it is so ingrained.

DNA tests validated
at least for Mysticeti as they relate to hippos, the only living mesonychids. Not sure if Odontoceti has been tested against tenrecs in DNA testing.

Discovered during testing
When you include living odontocetes and mysticetes in the same cladogram these taxa will nest together with either tenrecs or mesonychids in two separate trees due to their massive convergence. However, when you enter them in separate tests (Fig. 1) the two orders of whales will nest separately based on the present taxon and character lists.

Figure 1. Subset of the LRT, higher placental mammals with a focus on whales (yellow) and their ancestral clades, the Tenrecidae and Mesonychidae. Both are a fair distance from artiodactyls. This cladogram updates an earlier one that nested Janjucetus with Balaenoptera.

This we learn
after adding Janjucetus hunderi (Fig. 2; Fitzgerald 2006; Late Oligocene; NMV P216929 (Museum Victoria Palaeontology Collection, Melbourne, Australia), Orcinus (killer whale; Fig. 5) and Balaenoptera musculus (blue whale; Fig. 4) to the large reptile tree (Fig. 1).

Figure 2. Janjucetus is known from a well-preserved skull, a scapula rib and not much else. Here it is as a whale compared to Paleoparadoxia to scale. Janjucetus had legs, not flippers and flukes based on phylogenetic bracketing.

That low wide skull
and procumbent premaxillary teeth of Janucetus (Fig. 3) are obvious early clues that we’re not dealing with giant carnivorous tenrecs here, but with herbivores at home underwater, like hippos and desmostylians (including Paleoparadoxus (Fig. 2). Baleen whales also lack echolocation skills, something toothed whales got from tiny tenrecs.

Wikipedia reports
“Desmostylians are the only known extinct order of marine mammals.”
Not any more.

From the Fitzgerald abstract
“Unlike all other mysticetes, this new whale was small, had enormous eyes and lacked derived adaptations for bulk filter-feeding. Several morphological features suggest that this mysticete was a macrophagous predator, being convergent on some Mesozoic marine reptiles and the extant leopard seal (Hydrurga leptonyx).”

That’s because Janjucetus is not a whale, but a whale ancestor more closely related to Anthracobune (Fig. 1).

Figure 3. The skull of Janjucetus in 3 views. Images from Fitzgerald 2006. Colors added. This is an incredible find that I just yesterday became aware of.

From the Fitzgerald text
“The origins and early evolution of the two extant suborders of Cetacea (Odontoceti and Mysticeti) remain poorly understood. Among the latter two groups, the origins of the Mysticeti (baleen whales), and their unique feeding mechanism,have proved particularly baffling.In this study, I report a new Late Oligocene toothed mysticete from Australia that is more basal than any previously described.”

Hate to report this, but it’s anthracobune, not a whale. The desmostylian, Behemotops makes a better  (more parsimonious) ancestor to baleen whales.

Figure 4. Blue whale (Balaenoptera musculus) skull and skeleton. Note the lack of a thumb goes back to Mesonyx and Paleoparadoxia

Unfortunately
Fitzgerald did not test Janjucetus and other whales against any of the taxa in the tenrec clade. Hippopotamus was the outgroup taxon. Has the monophyly of the Cetacea ever been questioned or tested before?

Figure 5. The killer whale (Orcinus orca) skeleton and skull with parts colorized. Note the retention of five fingers and a sternal series. This, too, is a giant aquatic tenrec.

A few days ago
we looked at the double-pulley shape of the artiodactyl and whale astragalus (ankle bone). Today I added an image of the Leptictidium (tenrec) ankle, also sharing a double-pulley ankle joint. You can see it here.

Figure 7. Sperm whale (Physeter macrocephalus) with bones colorized for clarity. Note the five fingers and fewer dorsal ribs.

Whales and molars
In the very little time that I’ve looked at whales and their ancestors it appears that the molars shrink and disappear, losing cusps and size, making room for more canines and more canine-like premolars. The incisors are missing from the premaxilla of the killer whale. Teeth are morphologically plastic and change their shape, size and number often, not only in mammals, but in many other reptile clades. I’m not a whale dentist, so if one is out there, please send any data you may have on whale tooth identification and eruption patterns and I will share it.

And finally,
as you probably know, dugongs are whale-like herbivores with fins and whale-like flukes. So the separation of odontocetes from mysticetes should come as less of a shock. If I’ve made any errors here, please let me know. I’m still a newbie at whale morphology.

References
Fitzgerald EMG 2006. A bizarre new toothed mysticete (Cetacea) from Australia and the early evolution of baleen whales. Proceedings of the Royal Society B 273:2955-2963.

Docodon and molar count

The genus Docodon (Marsh 1881; Late Jurassic, 170 mya; Fig. 1) is represented by a jaw with several more molars than typical (Fig. 1). Hard to tell the premolars from the molars in lateral view. See the dorsal view for the distinct difference. Even so, the count may be off, because molars are not molars based on shape, but on the fact that they appear once and are not replaced during growth. I cannot tell, note have I found references that say where the division is in Docodon.

Figure 1. The holotype of Docodon has 4 incisors, 4 premolars and a whopping 7 molars. diplocynodon has 8 according to Osborn, who confirms the 7 in Docodon.

More than four molars in a mammal jaw is relatively rare.
But not rare in ancestral monotremes. Among tested taxa  Amphitherium, Kuehneotherium and Akidolestes have 6.

Figure 1. The addition of teeth in Kuehneosaurus and Akidolestes led to the loss of teeth in Ornithorhynchus.

There is also “a rule” that says
only one canine appears, but the other teeth can vary greatly in number. I’m wondering if that is true. Sometimes there will be a small, simple tooth arising between the canine and the double-rooted premolars. Is that a tiny canine? or a tiny premolar? Maybe someone out there has not only the answer, but the reason why.

And yes,
I’m aware of the convention that numbers premolars 1-4. But the anterior one, is almost always the smallest, as if it just arrived.

References
Marsh OC 1881. Notice of new Jurassic mammals. American Journal of Science. (3) xxi: 511-513.

wiki/Docodon

 

The Eutriconodonta is also paraphyletic in the LRT

Triconodon, Docodon, and Kuehneotherium are known form dentary bones with most of their teeth in place. Generally I avoid adding such partial specimens to the large reptile tree (LRT-updated at 848 taxa) because so few scores are generated for them with the current character list that they lead to loss of resolution at their nodes…

But curiosity won out
when wondering about members of the putative clade Eutriconodonta (Kermack et al. 1973), a clade that ostensibly replaces the paraphyletic Triconodonta. Some of these mandible-only taxa I added to the tree only to delete them later, just to see where they nested (often at the base of the Monotremata, as one would guess given their Mid-to Late Jurassic ages).

According to Wikipedia
“The Eutriconodonta  is a [presumeably monophyletic] order of mammals” broadly, though not exclusively characterized by molar teeth with three main cusps on a crown that were arranged in a row.  “Eutriconodonts retained classical mammalian synapomorphies like epipubic bones, venomous spurs and sprawling limbs. Eutriconodonts had a modern ear anatomy, the main difference from therians being that the ear ossicles were still somewhat connected to the jaw via the Meckel’s cartilage.

“Phylogenetic studies conducted by Zheng et al. (2013), Zhou et al. (2013) and Yuan et al. (2013) recovered monophyletic Eutriconodonta containing triconodontids, gobiconodontids, Amphilestes, Jeholodens and Yanoconodon. The exact phylogenetic placement of eutriconodonts within Mammaliaformes is uncertain.”

“Traditionally seen as the classical Mesozoic small mammalian insectivores, discoveries over the years have ironically shown them to be among the best examples of the diversity of mammals in this time period, including a vast variety of bauplans, ecological niches and locomotion methods.”

Traditional Eutriconodont taxa (see Martin et al. 2015) presently included in the LRT nest in a variety of clades:

1. Gobiconodon – pre-mammal tritylodontid
2. Repenomamus – pre-mammal tritylodontid
3. Spinolestes – pre-mammal tritylodontid
4. Jeholodens – pre-mammal tritylodontid
5. Volaticotherium – basal placental 
6. Triconodon – basal monotreme
7. Trioracodon – basal monotreme
8. Yanoconodon – pre-mammal (Fig. 1).

We’ve seen this sort of splitting
of traditionally established clades based chiefly on tooth traits before with the Docodonta (Fig. 1). As in molecule trees, tooth trees are not replicated in the LRT, which recovers a distinctly new tree topology without the odd logic jumps that traditional clades, like Afrotheria, produce.

Figure1. Repeat of an early subset of the LRT, this time highlighting putative eutriconodonts and where they nest. No wonder they are described as a diverse clade!

For the most part
eutriconodonts nest more or less together very close to the base of the Mammalia, whether in or out. Those slender posterior jaw bones are not typically preserved, but the long groove in which they are attached is typically preserved. Caution must be exercised, as fully mammalian taxa like Monodelphis, can also preserve a remnant of this groove despite the complete evolution of the post-dentary bones into tiny ear bones.

Figure 2. Mondelphis domestics with its posteromedial jaw groove highlighted in red. The ear bones are tiny and enclosed within the auditory bulla beneath the cranium.

So.. about those venomous ankle spurs…
Ornithorhynchus, the platypus, has them and likely so do its sisters. The authors of the Volaticotherium paper make no mention of either venom nor spur and score it as a “?”. The Yanoconodon tarsi are a challenge to reconstruct based on their preservation. The authors and yours truly note no spur-like bones present.

A new evolution website has launched
Check out www.TimeTree.org for a tremendous amount of phylogenetic information. For instance, one can input two well-known taxa, like Gallus and Homo, and the tree will determine the estimated date of their last common ancestor, in this case Vaughnictis (which is a taxon not in their current database).

References
Editors: Carrano MT et al. 2006. Amniote Paleobiology: Perspectives on the Evolution of Mammals, Birds and Reptiles. University of Chicago Press.  online here.
Kermack KA, Mussett F, Rigney HW 1973. The lower jaw of Morganucodon. Zoological Journal of the Linnean Society.53 (2): 87–175.
Martin T et al. 2015. A Cretaceous eutriconodont and integument evolution of early mammals. Nature 526:380-384. online.

wiki/Eutriconodonta

Turtles as Hopeful Monsters – Future book and past essay by O. Rieppel

Figure 1. Turtles as Hopeful Monsters by O. Rieppel, a book due to be published in 2017. The cover pictures Odontochelys, the earliest known soft shell turtle. The 2001 summary with the same title by O. Rieppel is the subject of the present blogpost.

Summary of this blogpost:
Without a large gamut phylogenetic analysis, such as the large reptile tree, that recovers two turtle clades derived from two phylogenetically reduced pareiasaur clades, any discussion of the origin of turtles is handicapped and will suffer from a surfeit of guesswork and error due to taxon exclusion. Sclerosaurus, Meiolania and Elginia are rarely considered in such studies, but are key to understanding turtle origins. Thankfully we have excellent embryological studies that more or less recapitulate phylogeny.

Dr. Rieppel has long been an advocate of a diapsid/placodont ancestry for turtles, and has applied molecule evidence to link turtles with archosaurs. He was part of the Odontochelys (Fig.1 ) team.

The hopeful monsters hypothesis is a biological theory which suggests that major evolutionary transformations have occurred in large leaps between species due to macro mutations. The LRT does not support major evolutionary transformations. All transitional taxa greatly resemble their nested sisters and microevolution is the only factor at play here.

From the Rieppel summary:
“A recently published study on the development of the turtle shell highlights the important role that development plays in the origin of evolutionary novelties.”

“Early theories attempted to explain the evolution of the turtle shell in the context of a step-wise, hence gradual process of transformation. The distant ancestor of turtles was hypothesized to have had a body loosely covered by osteoderms. Within the evolutionary lineage leading to turtles, the number of osteoderms would have gradually increased, until the bony plates would eventually have provided a complete covering of the trunk, thus forming an epitheca. Thecal ossifications would have developed below the epi- theca at later stages in the evolution of the turtle body plan, while epithecal ossifications would subsequently be lost at even more advanced stages of turtle evolution. This theory met with various difficulties, however, such as the fact that the earliest fossil turtle (Proganochelys) from the Upper Triassic of Europe (215 Mio years) has a complete theca. Furthermore, epithecal ossifications appear later than ossifications of the theca in development and, in modern turtles, epithecal ossifications tend to form in evolutionarily relatively advanced forms only.

“Turtles are unique among tetrapods, however, in that the shoulder blade (scapula) lies inside the rib cage (Fig. 3). The reason for this inverse relationship of the scapula is the close association of the ribs with the costal plates of the theca. The scapula of turtles comes to lie inside the rib cage because of a deflection of rib growth to a more superficial position. Recent developmental work has identified inductive interaction generated by the carapacial ridge as probable cause of this deflection of rib growth.

“A recent theory proposed the evolution of turtles from Paleozoic Pareiasaurs by a process of “correlated progression”. Correlated key elements of this progressive transformation are an increase in the number of osteoderms until they form a closed dorsal shield (carapace), the broadening of the ribs below this dorsal hield, the shortening of the trunk, the immobilization of the dorsal vertebral column and a backwards shift of the pectoral girdle.”

In the phylogenetic analysis provided by the LRT
turtles have two parallel origins, both from pareiasaurs: One for the domed, hard-shell clade (Bunostegos > Elginia > Meiolania) and one for the flattened soft-shell clade (Sclerosaurus > Odontochelys > Trionyx). In both these cases it appears that the tall scapula extended to either side of the narrow, cervical-like dorsal ribs. Then the anterior dorsal ribs rotated anteriorly over the tall scapulae, paralleling the rotation of the elbow anteriorly. You’ll note that turtles have more cervicals and fewer dorsals than pareiasaurs. The posterior cervicals in turtles appear to be the former dorsals of pareiasaurs. So, the pectoral girdle did not shift, but the posterior cervicals and anterior dorsals transformed around them. And this occurred during phylogenetic miniaturization.

Figure 3. Soft shell turtle evolution featuring Arganaceras, Sclerosaurus, Odontochelys and Trionyx.

Distinct from other reptiles
turtles do not have lateral movement in the torso with precursors in the short-torsoed, heavily ribbed pareiasaurs. “This repositioning of the vertebrae relative to the primary body segments is achieved by resegmentation of the somites. Each somite splits in half, and the posterior part of one somite recombines with the anterior part of the succeeding somite to form a vertebra,” reports Rieppel.

Figure 1. Hard shell turtle evolution with Bunostegos, Elginia, Meiolania and Proganochelys. The narrow and tall scapulae of pareiasaurs are carried forward in their descendant turtles during phylogenetic miniaturization. 

More from Dr. Rieppel
“As a turtle embryo grows and develops, the contours of the future carapace are soon mapped out by an accelerated growth and a thickening of the skin on its back.”

“The ribs of turtles are unique among vertebrates in that they chondrify within the deep layers of the thickened dermis of the carapacial disk.”

It has been known for over 100 years that in turtles, the neural arches of the dorsal vertebrae shift forward by half a segment, carrying the ribs with them, again a unique condition in amniotes.”

Embryological studies
(Ruckes 1929) indicate, “the scapula of turtles comes to lie inside the rib cage because of a deflection of rib growth to a more superficial position. The ribs come to lie lateral to the no longer functional intervertebral joints. The functional reason for this anterior shift of the neural arches is not clear, other than that it may contribute to the mechanical strength of the carapace, as the neural plates come to alternate with the costal plates. Neural and costal plates are endoskeletal components of the turtle carapace, and cannot be derived from a hypothetical ancestral condition by fusion of exoskeletal osteoderms. All other parts of the turtle carapace are exoskeletal.” Rieppel reports, “The turtle body plan is evidently highly derived, indeed unique among tetrapods.”

I’m going to say ‘not true’ here…
Several turtle-like forms developed among placodonts and the two turtle clades developed independently in parallel. Glyptodon had a turtle-like carapace, but no plastron. Even Minimi, the phytodinosaur, developed a club tail, convergent with meiolaniids.

Moreover, only the shells of the two clades of turtles are unique unto themselves, as most other of their body parts are microevolutionary adjustments from their separate micro pareiasaur bauplans. And, based on current fossil chronology, they had 25 to 45 million years to develop their respective shells from their proximal outgroup sisters.

References
Gilbert SF, Loredo GA, Brukman A, Burke AC. 2001.  Morphogenesis of the turtle shell: the development of a novel structure in tetrapod evolution. Evol Dev 2001;3:47 ± 58.
Götte A 1899. Über die Entwicklung des knoÈ chernen RuÈ ckenschildes (Carapax) der SchildkroÈten. Z wiss Zool 1899;66:407±434.
Lee MSY 1996. Correlated progression and the origin of turtles. Nature 1996;379:811- 815.
Rieppel O 1996. Turtles as diapsid reptiles. Nature 384 (6608), 453-455
Rieppel O 2001. Turtles as hopeful monsters. BioEssays 23:987-991.|
Rieppel O 2012. The Evolution of the Turtle Shell. Morphology and Evolution of Turtles. Part 2, 51-61. DOI: 10.1007/978-94-007-4309-0_5
Rieppel O 2017. Turtles as Hopeful Monsters. Origins and Evolution. Indiana University Press. 212 pp.. Online here.
Ruckes H. 1929 (12) Studies in chelonian osteology. Part II. The morphological relationships between girdles, ribs and carapace. Ann NY Acad Sci 1929;31:81-120.

Rieppel book summary online