Whales: Are they artiodactyls or tenrecs?

According to Wikipedia
Artiocetus (Gingerich et al. 2001; meaning essentially = artiodactyl + whale) was the first fossil to show that early whales possessed artiodactyl-like ankles (Fig. 1). The sizes, shapes and configurations are indeed similar. And this was a valid conclusion, but it was based on taxon exclusion. Other taxa have such ankles.

Figure 1. A selection of two whale ankles and one artiodactyl (Antilocapra, the pronghorn antelope). Such comparisons are the basis for aligning whales with artiodactyls.

Figure 1. A selection of two whale ankles and one artiodactyl (Antilocapra, the pronghorn antelope). Such comparisons are the basis for aligning whales with artiodactyls, but tenrecs were not considered.

Contra the artiodactyl hypothesis
the large reptile tree nests the basal whale, Maiacetus, with a clade of small and large, extinct and extant tenrecs like Hemicentetes, Andrewsarchus and Leptictidium.

So, to shed light on this disparity
here are two whale feet and ankles alongside the foot and ankle of Hemicentetes (Fig. 2), the tenrec without a tail (some other tenrecs have long tails (Figs. 5, 6), but extant examples don’t have online skeletons).

Figure 2. The evolution of the tenrec (Hemicentetes) pes, through the land whale Rhodhocetus and Basilosaurus.

Figure 2. The evolution of the tenrec (Hemicentetes) pes, through the land whale Rhodhocetus and Basilosaurus. Rhodocetus loses pedal digit 1. Basilosaurus loses pedal digit 2.  Note the lack of sharp claws and the lack of artiodactyl hooves in all taxa. Note the plantigrade pes here, not the digitigrade pes of artiodactylus. Note the reduction of distal tarsals (cuneiforms) down to dt3 (lateral cuneiform) in all taxa.

To the credit of the tenrec-whale clade:

  1. Hemicentetes has a short pedal digit 1. Rhodhocetus loses pedal digit 1. Basilosaurus loses pedal digit 2 (Fig. 2) where the vestigial pes is no longer in use.
  2. Tiny hooves on relatively slender digits
  3. Lack of tightly appressed artiodactyl metatarsals in all taxa.
  4. Plantigrade pes in all taxa
Figure 3. A basal artiodactyl, Ancodus, pes. As in Rhodhocetus pedal digit 1 is absent and the distal tarsals are reduced to one. This led to the artiodactyl hypothesis, and that is a great first guess! But it is not supported by the LRT.

Figure 3. A basal artiodactyl, Ancodus, pes. As in Rhodhocetus pedal digit 1 is absent and the distal tarsals are reduced to one. This led to the artiodactyl hypothesis, and that is a great first guess! But it is not supported by the LRT.

To the credit of the artiodactyl-whale clade hypothesis:

  1. Four pedal digits only, digit 1 is already absent
  2. The calcaneal heel is elongate.
  3. Metatarsals 2 and 5 axially rotate behind 3 and 4.
Figure 4. Maiacetus is a basal whale with legs and it is also a giant tenrec. Compare Leptictidium (Figs. 5, 6).

Figure 4. Maiacetus is a basal whale with legs and it is also a giant tenrec. Compare Leptictidium (Figs. 5, 6).

Further notes

  1. In both artiodactyls and tenrecs: reduction of distal tarsals (cuneiforms, yellow here) down to dt3 (the lateral cuneiform) in all taxa and a long list of other similar traits, both shared with proto-whales.
  2. Leptictidium (Fig. nests closer to whales and has a longer calcaneal heel with appressed metatarsals and reduced digits 1 and 5, but all toes are slender as in Rhodhocetus and it has a long muscular tail.

Artiodactyls came to the mind of Gingerich first
because artiodactyls had similar ankles to his land whale discoveries and were of similar size. Few workers both to study tenrecs — but tenrecs should have been included as they have similar pedes and taxon exclusion often arises with enigma taxa, as whales were.

  1. Artiodactyls are herbivores. Whales and tenrecs are not.
  2. Artiodactyls are digitigrade. Whales and tenrecs are not.
  3. Artiodactyls do not echolocate. Some tenrecs and some whales do.
  4. Artiodactyls do not have a large muscular tail for aquatic locomotion. Some tenrecs and all whales do.
  5. In the large reptile tree Maiacetus nests with a long list of tenrecs, not with artiodactyls, when given the opportunity, not with Ancodus.
  6. Several former mesonychids now nest with tenrecs and away from Mesonyx. clearing up that lingering issue.
  7. And a long list of traits in the skull and elsewhere…
Figure 2. Elements of Leptictidium from Storch and Lister 1985.

Figure 5. Elements of Leptictidium from Storch and Lister 1985. Note the long calcaneal heel here.

Added a few days later: here (Fig. 5a) is the double-pulley shape of the Leptictidium astragalus (n yellow).

Figure added later. The ankle of Leptictidium includes a spool-shaped double-pulley astragalus.

Figure 5a. The ankle of Leptictidium includes a spool-shaped double-pulley astragalus.

Figure 5. Leptictidium - Often considered a kangaroo like hopper (saltator), the loose sacral connection and phylogenetic bracketing suggest this was a dorsoventral undulatory swimmer instead. 

Figure 6. Leptictidium – Often considered a kangaroo like hopper (saltator), the loose sacral connection and phylogenetic bracketing suggest this was a dorsoventral undulatory swimmer instead.

Figure 6. Science magazine cover for Gingerich et al. 2001. Artist: John Klausmeyer.

Figure 7. Science magazine cover for Gingerich et al. 2001. Artist: John Klausmeyer. The hands and feet are far from being ungulate hooves, but close to tenrec paws.

Earlier notes
here, herehere and here. Unfortunately, as in several other taxonomic enigmas and mismatches, taxon exclusion prevented Gingerich et al. from making the tenrec connection.

References
Gingerich PD, Haq M, Zalmout I, Khan I and Malkani M 2001. Origin of whales from early artiodactyls: hands and feet of Eocene Protocetidae from Pakistan”. Science293 (5538): 2239–42.

Gingerich’s website
has more information. His Elomeryx is very close to Ancodus.

wiki/Artiocetus

Imagining the unknown: the skulls of Amphitherium and Docodon

Often enough
tiiny Jurassic synapsids, like Amphitherium prevosti  (von Meyer 1832; Middle Jurassic, 170 mya) and Docodon victor (Marsh 1881; Late Jurassic, 2 cm skull length), are known only from mandibles with teeth (Fig. 1).

We can guess what the skull looks like
because the molars occlude and the rest of the teeth interlock, slide past one another or meet at or near their tips. Plus we have clues from sister taxa that set parameters for possibilities in a method known as phylogenetic bracketing. In such cases some scores are less risky to guess, like the number of molars. Others are more risky, like the presence of caniniform canines.

Figure 1. Amphitherium and Docodon with skulls imagined.

Figure 1. Amphitherium and Docodon with skulls imagined. The large number of molars nests both these taxa with Monotremata.

References|
Marsh OC 1881. Notice of new Jurassic mammals: American Journal of Science, ser. 3, 21: p. 511-513.
Meyer H von 1832. Palaeologica, zur Geschichte der Erde und ihrer Geschöpfe. Schmerber, Frankfurt a/M, xi, 560 pp.

Mammalian nomenclature problems

Several putative stem mammal clades
have not been recovered in the LRT, like the ‘Notoungulata’ and the ‘Allotheria.‘ Similarly several putative reptile clades were also not recovered.

Now
the base and stem of the mammal clade are showing some nomenclature problems relative to traditional results.

First, I added a few mammals
(Mus, Taeiniolabis, Paulchaffatia) just be sure I was comparing listed taxa (see below) with listed taxa. If you know of any pertinent taxa that will change the current tree topology back to traditional topologies, please let me know. So far, I’m coming up short. These are the changes recovered so far:

Carrano et al. (editors) 2006
reports the following pertinent definitions. Comments follow (not in boldface).

Mammalia Linneaus 1758
The least inclusive clade containing Ornithorhynchus and Mus. In the LRT, Sinoconodon is the last common ancestor and Pachygenelus nests at the base of the outgroup clade, the Trithelodontidae (including the Tritylodontidae). So, no problems with this definition.

Trithelodontidae Broom 1912
The most inclusive clade containing Pachygenelus, but not Tritylodon and Mus. In the LRT Pachygenelus is basal to both Tritylodon and Mus, so the most inclusive clade containing Pachygenelus includes Mammalia and Tritylodontidae, contra prior studies.

Tritylodontidae Kühne 1956|
The most inclusive clade containing Tritylodon, but not Pachygenelus or Mus. In the LRT, this clade is monophyletic, and now includes Repenomamus.

Mammaliamorpha Rowe 1988
The least inclusive clade containing Tritylodon, Pachygenelus and Mus. In the LRT this clade is a junior synonym of the Trithelodontidae (see above).

Mammaliformes Rowe 1988
The most inclusive clade containing Mus, but not Tritylodon or Pachygenelus. In the LRT, this clade is a junior synonym for the clade Mammalia because Pachygenelus is the proximal outgroup taxon to Mammalia.

Theria  Parker and Howell 1897
The least inclusive clade containing Mus and Didelphis. In the LRT this clade is monophyletic and unchanged.

Theriimorpha Rowe 1988
The most inclusive clade containing Mus but not Ornithorhynchus. In the LRT this clade is a junior synonym for Theria.

Metatheria Huxley 1880
The most inclusive clade containing Didelphis, but not Mus. This definition was meant to include all marsupials, but in the LRT the clade that includes most marsupials does not include Didelphiswhich nests basal to and outside both monophyletic Marsupialia and Placentalia. So, strictly speaking, Metatheria in the LRT currently includes only Didelphis and perhaps its sister, Ukhaatherium.

Allotheria Marsh 1880
The most inclusive clade containing Taeniolabis, but not Mus or Ornithorhynchus. This was meant to indicate that Taeniolabis nested outside the Mammalia, but in the LRT Taeniolabis nests with Plesiadapis and Carpolestes and this clade is a sister to the clade containing Mus and the Multituberculata — within the Glires and Placentalia.

Multituberculata Cope 1884
The least inclusive clade containing Taeniolabis and Paulchofattia. This was meant to  include all the multituberculates and have them nest outside of the Mammalia, but in the LRT Taeniolabis nests with Plesiadapis and Paulchofattia nests with Carpolestes. So that is a clade of four taxa at present and it does not include Ptilodus and other multituberculates, the clade with a large and grooved lower last premolar. These traditional multis now need a new clade name. They are derived from a sister to the rodent clade in the LRT and they leave no descendants. Carpolestes is a sister to the ancestor of rodents and multis and Carpolestes (Fig. 1) has a large and barely-grooved lower last premolar, a precursor to that identifying trait in that second clade of multis.

Figure 1. Carpolestes simpsoni skull shows that large lower precursor premolar.

Figure 1. Carpolestes simpsoni skull shows that large lower premolar with just a few grooves. Here in the LRT Carpolestes nests close to the base of the traditional multituberculates that emphasize this trait. But see text for strict definitions of this clade.

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.

New paper on Ardeosaurus and Eichstaettisaurus as geckos

Ardeosaurus and Eichstaettisaurus (Fig. 1) have been traditional enigmas in paleo studies. Here is some progress from Simões et al. 2016, who nest these two with geckos, as they were initially placed. The large reptile tree nests these two at the base of snakes, as sisters to the gecko clade. So very close!
Eichstattisaurus and Ardeosaurus.

Figure 1. Eichstattisaurus and Ardeosaurus. Two Jurassic lizards in the lineage of snakes – but very close to geckos.

From the Simões abstract:
“Late Jurassic lizards from Solnhofen, Germany, include some of the oldest known articulated lizard specimens, sometimes including soft tissue preservation. These specimens are thus very important to our understanding of early squamate morphology and taxonomy, and also provide valuable information on squamate phylogeny. Eichstaettisaurus schroederi and Ardeosaurus digitatellus are two of the best-preserved species from that locality, the former being represented by one of the most complete lizard specimen known anywhere in the world from the Jurassic. 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 corroborate their initial placement as geckoes (stem gekkotans, more specifically), and illustrate a number of climbing adaptations that indicate the early evolution of scansoriality in gekkonomorph lizards.”

A PDF has been requested.
We’ll see if they included any basal snakes in their analysis.
This just in. The PDF arrived
The Simoes et al. cladogram nests snakes within skinks, derived from amphisbaenids. I don’t see Tetrapodophis or other pre-snakes in their cladogram.
References
Broili F 1938. Ein neuer fund von ?Ardeosaurus H. von Meyer. S.-B. bayer. Akad. Wiss. München, math.-naturw. Abt. 97-114.
Conrad JL and Daza JD 2015. Naming and rediagnosing the Cretaceous gekkonomorph (Reptilia, Squamata) from Öösh (Övörkhangai, Mongolia). Journal of Vertebrate Paleontology 35:5, e980891
Conrad JL and Norell MA 2006. High-resolution x-ray computed tomography of an Early Cretaceous gekkonomorph (Squamata) from Öosh ( €Ov€orkhangai; Mongolia). Historical Biology 18:405–431.
Daza JD, Bauer AM and Snively E 2013. Gobekko cretacicus (Reptilia: Squamata) and its bearing on the interpretation of gekkotan affinities. Zoological Journal of the Linnean Society 167:430–448.ischen Akademie der Wissenschaften, München 1938: 97–114.
Evans SE, Raia P and Barbera C 2004. New lizards and rhynchocephalians from the Lower Cretaceous of southern Italy. Acta Palaeontologica Polonica 49:393-408.
Hoffstetter R 1953. Les Sauriens anté−crétacés. Bulletin de la Museum Nationale d’Histoire Naturelle 25: 345–352.
Kuhn O 1958. Ein neuer lacertilier aus dem fränkischen Lithographie−schiefer. Neues Jahrbuch für Geologie und Paläontologie, Monatshefte 1958: 437–440.
Mateer NJ 1982. Osteology of the Jurassic Lizard Ardeosaurus brevipes (Meyer). Palaeontology 25(3):461-469. online pdf
Meyer H von 1860. Zur Fauna der Vorwelt. Reptilien aus dem lithographischen Schiefer des Jura in Deutschland mit Franchreich. Frankfurt-am-Main.
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

The Stem-Mammals–a Brief Primer (with remarks)

Preface added the day after posting: M. Mortimer gratefully informed me that some authors consider all taxa closer to mammals than to other living taxa as ‘stem’ mammals. Perhaps that is how ‘stem’ taxa are defined. That came as news to me because I understood the term ‘stem’ to refer to immediate outgroups only based on the terms usage in other works. So you learn as you go. The broad definition quickly loses relevance and adds to confusion. In M. Mortimer’s example, Diplodocus is a ‘stem’ bird. Please read the following with these caveats in mind. 

Preface added 10/26/2016: Just found out there is are two definitions for ‘stem’ taxa, one in the wider sense and one in the narrower sense, the one is was familiar with. Learn more at Wikipedia here

Usually I cover published academic papers
here at PterosaurHeresies.WordPress.com. Today we’ll cover a Tetrapod Zoology blog post published online by Dr. Darren Naish a month ago. Unfortunately the post was sprinkled with traditional misconceptions.

Below
the Naish text is copied in italic and his captions are copied in their original ALL CAPS. Remarks are in red. You can see the original blogpost here. This is how all good referees mark up submitted manuscripts, with precise comments intended to help the writer improve the next draft. To that end, Naish notes he is currently writing a book that includes this subject.

The Stem-Mammals–a Brief Primer
Mammals are but the only surviving members of a far grander, older lineage
By Darren Naish on September 20, 2016

Figure 1. Strangely Naish labeled this illustration "Non-synapsid-mammal-montage" Most of these taxa, caseids and Tetraceratops exempted, are indeed synapsids. The problem is, all of the red taxa are not stem mammals, nor are they in the mammal lineage at any node. Rather they represent extinct offshoots.

PROVISIONAL AND IN-PREP MONTAGE (FOR MY TEXTBOOK ON VERTEBRATE HISTORY) DEPICTING A SELECTION OF STEM-MAMMALS. I’VE DRAWN FAR MORE THAN THE SELECTION SHOWN HERE. CREDIT: DARREN NAISH Strangely Naish labeled this illustration “Non-synapsid-mammal-montage” Most of these taxa, caseids and Tetraceratops exempted, are indeed synapsids. The problem is, all of the red taxa are not stem mammals, nor are they in the mammal lineage at any node. Rather they represent extinct and distant offshoots. Virtually all science journalists accept what they read in publication without criticizing it. But Naish is also a PhD, so it is his duty to keep a laser focus on his headline topic, not to stray off subject, and most importantly, to clarify for his readers the inconsistencies present. Otherwise, as above, there is confusion and lack of clarity for the reader.

“For some considerable time now I’ve been promising that one day — one day — I’ll devote time and energy to coverage of that enormous, diverse, long-lived tetrapod group that we variously term the non-mammalian synapsids or stem-mammals. The most traditional term for them is ‘mammal-like reptiles’: while still in use, this term should be avoided given that the animals concerned are simply not part of the reptile lineage. Not true. According to the large reptile tree (LRT) all descendants of the first reptile/amniote, Gephyrostegus, are also reptiles, and that includes mammals and their long list of descendants. Unfortunately Naish is repeating an old and invalid tradition. The vernacular terms protomammal and paramammal have both been used for the group as well, though both have problems. Stem-mammals will be used here. If so, it is important that Naish restrict his discussion to just the immediate precursors of mammals, not the long list going back to basal synapsids, but that is not what he does.

Anyway, we’re talking about that group of tetrapods that are not mammals but are ancestral to them, and which occupy all those points on the mammal lineage outside of Mammalia. The presence of a laterotemporal fenestra (a single skull opening behind the eye socket) is a key feature distinguishing them from other amniotes. Not true. Several clades by convergence developed such a skull opening including 1. the millerettid clade and their descendants from Oedaleps to Australothyris, including the caseids. Emeroleter and Lanthanosuchus had that fenestra. So did bolosaurids. And then there are the prodiapsids from Heleosaurus to Archaeovenator and the last common ancestor of synapsids and diapsids, VaughnictisThe early members of this segment of the mammal lineage have often been called pelycosaurs while the members of the more mammal-like segment of the lineage are termed therapsids. Actually finback pelycosaurs are an offshoot clade, not in the lineage of mammals, which proceeds from a sister to Ophiacodon to Cutleria without including finbacks. The importance of these animals concerns the fact that their comparatively excellent fossil record charts transition from an ancestral ‘reptile-like’ form to mammals via a near-perfect series of intermediates. Alas, their relative obscurity and the lack of good popular syntheses means that they are not the poster-children of evolution that they really should be… at least, not outside the palaeontological community.  Those animals were featured on both versions of Cosmos.

TETRACERATOPS FROM THE EARLY PERMIAN OF THE USA, AN EARLY SYNAPSID SOMETIMES IDENTIFIED AS ONE OF THE OLDEST THERAPSIDS BUT LATER RE-INTERPRETED AS OCCUPYING A MORE ROOT-WARD POSITION IN THE TREE. CREDIT: DMITRI BOGDANOV WIKIPEDIA CC BY 3.0. The LRT nests Tetraceratops with Tsejaia and Limnoscelis, whether it had a lateral temporal fenestra or not. Massive crushing adds doubt to that. It doesn't look like any other synapsid and it nests better with other reptiles, so why include it?

TETRACERATOPS FROM THE EARLY PERMIAN OF THE USA, AN EARLY SYNAPSID SOMETIMES IDENTIFIED AS ONE OF THE OLDEST THERAPSIDS BUT LATER RE-INTERPRETED AS OCCUPYING A MORE ROOT-WARD POSITION IN THE TREE. CREDIT: DMITRI BOGDANOV WIKIPEDIA CC BY 3.0. The LRT nests Tetraceratops with Tsejaia and Limnoscelis, whether it had a lateral temporal fenestra or not, far from the synapsids. Massive crushing adds doubt to that. It doesn’t look like any other synapsid and it nests with other reptiles, so why include it?

This article is not the time and place to start a group-by-group review of the many lineages concerned… I know from experience how those projects quickly expand into gargantuan multi-part monsters that can never be finished. Rather, this is just a brief primer, a placeholder. If you want to see the lineage of mammals going back to stem tetrapods, click here then peruse at your leisure the taxa that interest you.

COVER OF KEPT (1982). THE BEST BOOK ON THE GROUP OF ANIMALS SO FAR. NOW OUT OF PRINT (BUT AVAILABLE AT REASONABLE PRICES ONLINE. CREDIT: ACADEMIC PRESS LONDON. This is indeed the go-to book for synapsid data.

COVER OF KEPT (1982). THE BEST BOOK ON THE GROUP OF ANIMALS SO FAR. NOW OUT OF PRINT (BUT AVAILABLE AT REASONABLE PRICES ONLINE. CREDIT: ACADEMIC PRESS LONDON. This is indeed the go-to book for synapsid data and has been for more than 30 years. See ReptileEvolution.com for updates since then. 

Before anyone asks, the one crippling, punishing problem with these animals is that – even today – there is no single, good, up-to-date, go-to volume on their diversity, history, evolution and biology. But you can go online here for the latest data. Yes, there are books on these animals, but they’re technical and mostly out of print. The best is Tom Kemp’s Mammal-Like Reptiles and the Origin of Mammals (Kemp 1982). There’s also Nick Hotton et al.’s The Ecology and Biology of Mammal-like Reptiles (Hotton et al. 1986) (a collection of papers by different authors). I have a substantial, well illustrated chapter on these animals in my giant textbook (on which go here, if you wish), but a good, dedicated, modern volume just does not exist. There are several decent review articles on the group as a whole, among the most recent being Angielczyk (2009).

MUCH-SIMPLIFIED CARTOON CLADOGRAM OF STEM-MAMMALS BASED ON TOPOLOGIES RECOVERED IN SEVERAL RECENT STUDIES. EXPANDED VERSIONS BEING PREPARED FOR MY IN-PREP TEXTBOOK (MORE HERE). CREDIT: DARREN NAISH As above, caseids are not related. Pelycosaurs are offshoots. The basal dichotomy of therapsids separated the Anomodonts from the Kynodonts.

MUCH-SIMPLIFIED CARTOON CLADOGRAM OF STEM-MAMMALS BASED ON TOPOLOGIES RECOVERED IN SEVERAL RECENT STUDIES. EXPANDED VERSIONS BEING PREPARED FOR MY IN-PREP TEXTBOOK (MORE HERE). CREDIT: DARREN NAISH As above, caseids are not related. Pelycosaurs are offshoots. The basal dichotomy of therapsids separated the Anomodonts from the Kynodonts.

The oldest stem-mammals date to the Moscovian part of the Carboniferous (here again, an inappropriate use of the term ‘stem’) and have conventionally been depicted as very reptilian in appearance. That’s because they are or were reptiles, as recovered by the LRT.  This is probably true in broad terms but is open to some question, there being indications that their integument and so on was not ‘reptilian’ as we conventionally imagine it. Likely without scales, based on the scant evidence at hand, but living dinosaurs are also without scales, except for those transformed from feathers. These early forms belong to those lineages conventionally lumped together as ‘pelycosaurs’ – a term that clearly refers to a paraphyletic assemblage given that therapsids evolved from somewhere among them. Not true. The LRT recovers a clade of pelycosaurs, a resurrected clade Pelycosauria. 

SOMEWHAT DATED SCHEMATIC REPRESENTATION OF SYNAPSID EVOLUTION WHICH I INCLUDE BECAUSE IT DOES A NICE JOB OF ILLUSTRATING BOTH CRANIAL VARIATION WITHIN THE GROUP, AND SOME OF THE MAIN DIFFERENCES OBVIOUS BETWEEN 'PELYCOSAURS', THEROCEPHALIAN-GRADE ANIMALS, AND CYNODONTS. CREDIT: PALAEOS, ORIGINALLY BY THOMAS KEMP. If Naish is trying to show us what we used to think, he's doing a good job, but wasting time when his whole point was to update his readers on the latest, which can be found at ReptileEvolution.com

SOMEWHAT DATED SCHEMATIC REPRESENTATION OF SYNAPSID EVOLUTION WHICH I INCLUDE BECAUSE IT DOES A NICE JOB OF ILLUSTRATING BOTH CRANIAL VARIATION WITHIN THE GROUP, AND SOME OF THE MAIN DIFFERENCES OBVIOUS BETWEEN ‘PELYCOSAURS’, THEROCEPHALIAN-GRADE ANIMALS, AND CYNODONTS. CREDIT: PALAEOS, ORIGINALLY BY THOMAS KEMP. If Naish is trying to show us what we used to think, he’s doing a good job, but wasting time when his whole point was to update his readers on the latest, which can be found at ReptileEvolution.com.

Animals from this ‘pelycosaur’ part of the tree include the long-snouted, mostly predatory varanopids and ophiacodontids, the omnivorous and herbivorous caseasaurs, and the edaphosaurids and sphenacodontids, the latter including the famous Dimetrodon. Why waste time on these non stem-mammals? While many of these animals (especially the early members of these groups) were small (less than 50 cm long), large size (3 m or more) evolved several times independently. There are lots of other significant events here as well, including the evolution of high-fibre herbivory and the independent evolution of dorsal sails.  Why waste time on these non stem-mammals? Even in these animals there are indications of social behaviour and parental care (Botha-Brink & Modesto 2007, 2009).

RECONSTRUCTION OF AN ASSEMBLAGE (A FAMILY GROUP?) OF THE VARANOPID HELEOSAURUS, PICTURED IN THE POSE IN WHICH THEIR SKELETONS WERE DISCOVERED. CREDIT: BOTHA-BRINK & MODESTO (2009). This is Heleosaurus, which is a pro-diapsid, an outgroup to the Synapsida, but the concept is probably true of young ones nesting with an adult.

RECONSTRUCTION OF AN ASSEMBLAGE (A FAMILY GROUP?) OF THE VARANOPID HELEOSAURUS, PICTURED IN THE POSE IN WHICH THEIR SKELETONS WERE DISCOVERED. CREDIT: BOTHA-BRINK & MODESTO (2009). This is Heleosaurus, which is a pro-diapsid, an outgroup to the Synapsida, but the concept is probably true of young ones nesting with an adult.

Dimetrodon – one of the most familiar and famous of all stem-mammals (Not true, merely an offshoot)– is a fascinating creature that has recently undergone something of an image change: ideas regarding the evolution, function and anatomy of its sail have all been challenged, its ecology and lifestyle have been the source of some debate, and its life appearance and gait have undergone revision in recent years. I plan to devote an article to these issues.

YOU MIGHT HAVE SEEN THIS ANIMAL BEFORE. IT'S DIMETRODON. CREDIT: D'ARCY NORMAN WIKIMEDIA CC BY 2.0 Not sure why Naish is bothering with these popular but irrelevant taxa.

YOU MIGHT HAVE SEEN THIS ANIMAL BEFORE. IT’S DIMETRODON. CREDIT: D’ARCY NORMAN WIKIMEDIA CC BY 2.0 Not sure why Naish is bothering with these popular but irrelevant taxa when so many taxa much closer to mammals, the REAL stem mammals also make for good stories. Seems like he doesn’t know or doesn’t care. 

Animals close to sphenacodontids gave rise to therapsids. A more erect gait and faster metabolism occurred at the time of this transition, numerous additional changes associated with dentition, palatal structure, limb posture and so on occurring as well. It’s within this vast group (Therapsida) that we find the often herbivorous, beak-jawed dicynodonts and kin, the often predatory biarmosuchians, gorgonopsians and therocephalians, and the often striking, often large dinocephalians. That last group includes both predators and herbivores, hippo-sized animals, and species with thickened skull roofs probably used in head-butting. They dominated many continental animal communities in the Permian, being best known from the fossil records of South Africa and Russia. Still not talking about stem mammals here. When are we going to get to them? The text does not follow the headline. 

TAPINOCEPHALID DINOCEPHALIANS - LIKE TAPINOCEPHALUS DEPICTED HERE - HAD THICKENED SKULL ROOFS THAT LIKELY HAD A DISPLAY OR COMBAT FUNCTION. THE BIGGEST OF THESE ANIMALS WERE OVER 3 M LONG. CREDIT: DIBDG WIKIMEDIA CC BY SA 3.0 While fascinating, this is not a stem-mammal.

TAPINOCEPHALID DINOCEPHALIANS – LIKE TAPINOCEPHALUS DEPICTED HERE – HAD THICKENED SKULL ROOFS THAT LIKELY HAD A DISPLAY OR COMBAT FUNCTION. THE BIGGEST OF THESE ANIMALS WERE OVER 3 M LONG. CREDIT: DIBDG WIKIMEDIA CC BY SA 3.0 While fascinating, this is not a stem-mammal, but another offshoot.

Gorgonopsians and therocephalians are exciting groups that include various macropredatory, often ‘sabre-toothed’ species; both have been the subject of various recent revisions. Species within these groups have been likened to weasels, wolves and bears in approximate body form, though any resemblance would have been highly superficial. Sometime during the Late Permian, cynodonts arose from an ancestor closely related to therocephalians (both groups form the therapsid clade Eutheriodontia): Cynodontia is the group that includes mammals as well as a number of additional lineages that have their own histories and evolved their own specializations. Now we’re getting closer to the stem-mammals, members of the clade Tritylodontia within the Cynodontia!

And because this was meant to be a very, very brief primer, that is all I’ll say for now. There is so much more to do… WAIT! Naish never once wrote about or illustrated a stem-mammal here! I read this whole blog post without learning anything new about the stem-mammals, the Tritylodontidae and their immediate predecessors.. As we’ve seen before, Naish sometimes cruises on the invalid past rather than exploring today’s cutting edge data and latest discoveries. Pity, all that talent going for the low-hanging fruit. Darren, as you write your book on synapsid relationships, feel free to reference ReptileEvolution.com and the large reptile tree. It will help you understand the issues and enigmas generated in Kemp’s 1982 book.

Stem-mammals have been covered on scant occasions at Tet Zoo. But see…

Sometimes Dr. Naish referees manuscripts offered for academic publication. With his stuck-in-the-past bias, good luck if he referees your submission. I would not want wish that on my worst enemy, especially if you’re promoting new hypotheses.

Many scientists like to play it safe, resisting and waiting for the tide to shift on advancing new hypotheses before jumping on the bandwagon. Don’t be like that. Follow the data. Test as much as you can yourself. Be a skeptical Scientist, not a nodding Journalist. 

What do I expect from these remarks?
Based on his vocal antipathy toward the results recovered by the LRT, Dr. Naish will probably cling to his invalid traditions. After all, based on his writings, he has ‘painted himself into a corner’ from which he cannot escape without an about face apology and acknowledgment. That’s something primates, like us, do very very rarely. PhDs are not wired for it. But if Naish did run the tests he would find what I found. If not, I’d like to hear why not.

Refs – –
Angielczyk, K. D. 2009. Dimetrodon is not a dinosaur: using tree thinking to understand the ancient relatives of mammals and their evolution. Evolution: Education and Outreach 2, 257-271.
Botha-Brink, J. & Modesto, S. 2007. A mixed-age classed ‘pelycosaur’ aggregation from South Africa: earliest evidence of parental care in amniotes? Proceedings of the Royal Society B 274, 2829-2834.
Botha-Brink, J. & Modesto, S. 2009. Anatomy and relationships of the Middle Permian varanopid Heleosaurus scholtzi based on a social aggregation from the Karoo Basin of South Africa. Journal of Vertebrate Paleontology 29, 389-400.
Hotton, N., MacLean, P. D., Roth, J. J. & Roth, E. C. 1986. The Ecology and Biology of Mammal-like Reptiles. Smithsonian Institution Press, Washington and London.
Kemp, T. S. 1982. Mammal-Like Reptiles and the Origin of Mammals. Academic Press, London.

A Jurassic digger, Docofossor, has a living sister: Notoryctes

Updated July 18, 2018 with a new nesting for Docofossor with two other digging marsupials, Notoryctes and Anebodon.

Docofossor brachydactylus (Luo et al. 2015; Jurassic, 160 mya; BMNH 131735; 9 cm in precaudal length) was originally considered a member of the Docodontidae (Docodonta) along with Docodon and Haldanodon (and other taxa listed in figure 4), nesting outside of the Mammalia, chiefly based on their relatively ‘sophisticated(?)’ molar shape. Here Docofossor nests as a sister to the fossorial Early Cretaceous Anebodon and the extant fossorial (digging) Notoryctes (marsupial mole). There is ample opportunity for Docofossor to nest outside of the Mammalia, but it does not do so in the large reptile tree (LRT, 1251 taxa, Subset Fig. 4).

Figure 1. Docofossor in situ with DGS tracings.

Figure 1. Docofossor in situ with DGS tracings.

Broad, short-fingered hands,
larger than the feet, along with other traits mark Docofossor as a digging animal, similar to moles like the carnivore Talpa and and rodent-like Chrysochloris. So the Jurassic is the first time that mole-like mammals evolved. The two others followed later.

Figure 2. Docofossor partly reconstructed from DGS tracing in figure 1. 

Figure 2. Docofossor partly reconstructed from DGS tracing in figure 1.

Perhaps the main reason
for not including docodonts within the Mammalia is their possession of a medial groove on the posterior dentary (mandible) that should contain tiny, splint-like posterior jaw elements, like the angular, surangular and articular. These splints are rarely if ever found, but are assumed to produce the jaw joint in lieu of or alongside the squamosal/dentary joint common to all mammals. Sometimes the grooves remain after the splints are gone.

Figure 4. Subset of the LRT focusing on the Metatheria (=Marsupials). Here the diprotodont dentition evolved twice.

Figure 4. Subset of the LRT focusing on the Metatheria (=Marsupials). Here the diprotodont dentition evolved twice.

And here’s the subset of the LRT
(Fig. 4) showing where Docofossor nests within the Metatatheria. Several included members of the Docodonta are split up into distinct clades, indicating that this putative clade is paraphyletic.

References
Luo Z-X, Meng QJ, Ji Q, Liu D, Zhang Y-G, Neande AI 2015.Evolutionary development in basal mammaliaforms as revealed by a docodontan. Science. 347 (6223): 760–764.

wiki/Docofossor

A skeletal reconstruction of Volaticotherium

Revised July 27, 2018
with a new nesting for Volaticotherium closer to Eomaia.

Figure 1. Scientific American recently featured Volaticotherium on its cover. James Gurney is the illustrator here.

Figure 1. Scientific American recently featured Volaticotherium on its cover. Did Volaticotherium have a patagium and bushy tail? Good question. James Gurney is the illustrator here. Note the fangs!

Volaticotherium antiquus (Meng et al. 2006; ?Middle Jurassic to ?Earliest Cretaceous, 164 mya; 3 cm skull length; IVPP V14739; Figs. 1-3) was described a few years back as a gliding mammal of uncertain affinity, based on a preserved patagium, or gliding membrane, complete with short hair and skin. Oddly, the patagium was preserved, but not the basic skin and fur, usually preserved as a halo around the skeleton.

Figure 2. Volaticotherium in situ, in X-ray, as originally traced (line drawing) and DGS traced (colors).

Figure 2. Volaticotherium in situ, in X-ray, as originally traced (line drawing) and DGS traced (colors). Patagium is the large tan ovoid. The X-ray has different outlines and so may represent the counter plate. You can see some of the distortion necessary to align elements.

Unfortunately
the skin has slipped off the scattered roadkill skeletal elements like a bath towel (Fig. 2) leaving some doubt as to where it connected to the body and limbs. If a patagium, its symmetrical counterpart, if present, is not preserved and the skin itself seems to be fully stretched out, at odds with patagia of other flying and gliding animals, that tend to shrink went not in use. Interesting, perhaps, that the patagial outline roughly corresponds to what the basic skin of Volaticotherium would have to be. No such skin was mentioned in the text or is visible in the fossil as a halo or scattering of fur. Sister taxa, such as Eomaia and Didelphis (Fig. 5), do not have a bushy tail, as illustrated above (Fig.1).

Did female Volaticotherium glide
with exposed underdeveloped young attached only by jaws on nipples?  Bats leave their young at the roost while feeding, until they are hold enough to cling well and they have one pup at a time.  Colugos likewise have a single pup at a time and carry them in their nursery/gliding membranes. See image here. Wikipedia reports, “Colugos raise their young in a similar fashion to marsupials. Newborn colugos are underdeveloped and weigh only 35 g (1.2 oz).[9] They spend the first six months of life clinging to their mother’s belly. The mother colugo curls her tail and folds her patagium into a warm, secure, quasi-pouch in order to protect and transport her young.”

Figure 3. Volaticotherium reconstructed. Here the patagium appears to be able to just drape over the head and torso, unlike the much larger membrane in Cynocephalus, the flying lemur. Shown as a biped here, that was likely only a temporary pose, like a squirrel on its haunches. Occipital bones are not shown.

Figure 3. Volaticotherium reconstructed. Here the patagium appears to be able to just drape over the head and torso, unlike the much larger membrane in Cynocephalus, the flying lemur. Shown as a biped here, that was likely only a temporary pose, like a squirrel on its haunches. Occipital bones are not shown.

There’s much more to this extraordinary mammal that is not controversial.
The molars resemble rotary saw blades, the external naris is divided by an ascending process of the premaxilla (rare among higher cynodonts and mammals), proximally the femur has no ‘neck’ and not much of a ‘head’, and the tail is extraordinarily long. Not listed by Meng et al., The mandible is not gently convex, but is sharply convex ventral to the canines, then gently concave, a shape not otherwise seen until higher primates. We also see a deeper mandible medial to sabertooth fangs in Thylacosmilus, and this may be the reason for the oddly deeper chin here.

Volaticotherium was deemed so different
from all other known mammals that it was given its own order, the Volaticotheria, nesting between basalmost mammals (Proteutherians) and Therians.

Here
in the large reptile tree, despite its many autapomorphies and convergent traits, Volaticotherium nests between the Eomaia clade and all higher marsupials. This is appropriate, given its Late Jurassic age. The two were roughly comparable in size.

The femoral head
of Volaticotherium was about as shallow as it could be and evidently not due to crushing. Generally a spherical femoral head provides strength and maneuverability. Cartilaginous or connective tissue may have substituted for bone in Volaticotherium. 

Other arboreal features
The hallux (big toe) diverged from the other metatarsals at 35º angle, flexor sesamoids and curved phalanges with small sharp claws indicate an arboreal niche for Volaticotherium. The limbs were all described as elongated, but only the forelimb appears elongated relative to the femur (Fig. 3). The distal phalanges would appear to be fully flexed, tucked beneath the proximal phalanges, but the X-ray does not reveal them. The long tail was likely used in balancing and leaping, like a lemur. The cervicals were very short, as in the basal primate, Notharctus, and in Longisquama, a lemur-like lepidosaur. The scapula was relatively small, as in Notharctus and Longisquama. The calcaneum was relatively short and flexible, enabling rotation of the foot for better grasping of tree trunks while heading in any direction.

There is another Jurassic sister taxon out there:
Argentoconodon (Gaetano and Rogier 2011; Fig. 6), known from teeth and scattered jaw fragments. Like Volaticotherium, the molar cusps are aligned as in pre-mammalian triconodonts. Unlike Volaticotherium, the medial incisor is the size of a canine, which appears suspect.

The holotype genus
for the triconodonts, Triconodonprovides evidence for the replacement of its lower fourth premolar, erupting and coming into use when at least three out of its four molars were already fully erupted, which is a mammal trait. Note the very low jaw articulation and sub canine ‘chin’, traits shared with Volaticotherium.

Perhaps this triconodont clade
evolved a simplified, more primitive-type tooth with aligned cusps. If so, it’s not alone. Toothed cetaceans, for instance, have only simple conical teeth.

Figure 7. This reconstruction of Argentoconodon is built from many small fragments and appears to have a few problems. Nevertheless, these fragments are similar enough to Volaticotherium to warrant interest.

Figure 6. Line art (w/o color) from Gaetano and Rougier 2011. This reconstruction of Argentoconodon is built from many small fragments and appears to have a few problems. Nevertheless, these fragments and those molars are similar enough to Volaticotherium to warrant interest.

I thank Dr. Meng
for sending me a pdf of his paper describing an important early arboreal mammal. I have an inquiry for him, still awaiting a reply, wondering if the simplified (primitive) molar structure of Volaticotherium, might be a derived reversal… an atavism.

References
Gaetano GW and Rougier GW 2011. New materials of Argentoconodon fariasorum (Mammaliaformes, Triconodontidae) from the Jurassic of Argentina and its bearing on triconodont phylogeny. Journal of Vertebrate Paleontology 31(4):829-843.
Meng J, Hu YM, Wang YQ, Wang XL and Li CK 2006. A Mesozoic gliding mammal from northeastern China. Nature 444:889-893.

wiki/Volaticotherium

Here’s a pterosaur proposal doomed to a crashlanding

I can’t believe
the quad launch hypothesis (Fig. 1)  is still alive… but it is. Perhaps just barely.

Rayfield, Palmer and Martin have an offer
for a budding paleontologist/engineer student designed to frustrate that young talent because they know their conclusion before they initiate experiments and they will not investigate more promising hypotheses.

According to Rayfield, Palmer and Martin (links below):
“The main objective of this proposal is to investigate the effectiveness of the quadrupedal launch [of pterosaurs] and by comparing it with the bipedal launch of birds, test if it was one of the factors that enabled pterosaurs to become much larger than any bird, extant or extinct.” (Fig. 1 – and note: they are not testing the hypothetical quad launch of pteros against the hypothetical bipedal launch of pteros)

Figure 1. Quad launch of giant pterosaur as envisioned by Dr. Emily Rayfield. See text for list of problems.

Figure 1. Quad launch of giant pterosaur as envisioned by Rayfield, Palmer and Martin. See text for list of problems. Note how the pterosaur literally floats off the Earth here, achieving great height, higher than any kangaroo leap from a standing start, prior to the first down stroke of the wings. Note the placement of the fingers in the final frame, unlike the ichnite evidence that shows lateral to posterior orientation of the fingers. Fossils show wing membrane fold to near invisibility prior to flight and the wing membrane is stretched between the elbow and wingtip. Artwork by Colin Palmer.

Choose to accept this assignment and you will be asked to:
“Create anatomical reconstructions of possible azhdarchid morphologies and using kinematic simulation software to create a simple baseline bipedal launch model, validated against published data for birds and humans and tested for sensitivity to assumptions and modeling detail. 

Your reward for doing so:
“The student will join the large and vibrant Bristol palaeobiology community and receive training in anatomical and computational techniques.”

Main supervisor:
Prof Emily Rayfield
Co-supervisor(s):
Dr Colin Palmer (University of Bristol),
Ms Elizabeth Martin (University of Southampton)

Quetzalcoatlus running like a lizard prior to takeoff.

Figure 2. Quetzalcoatlus running like a lizard prior to takeoff. Click to animate. This configuration gets both the legs and the wings working together to build up airspeed prior to takeoff — if possible. This mode also powers rapid running — if flight is not possible.  Note the large mass of thigh muscles here, anchored on the long ilium and prepubes, much larger than the forelimb bones anchored on that small pectoral girdle.

According to Rayfield, Palmer and Martin [objections in bold]
“Pterosaurs adopted a quadrupedal stance 1, which meant that their forelimbs were used for both flight and locomotion, including launch 2, so carried less baggage once airborne 3 Hypothesised quadrupedal launch behaviour provided a long launch stroke and recruitment of large muscle mass to power take-off (Habib 2008) 4; proportionately larger than that available to birds. While the underlying concept of the quadrupedal launch is now widely accepted 5, the kinematic and anatomical details are poorly understood meaning that estimates of available launch power are very imprecise.6, Increasing our understanding of the take-off process will shed new light on the role it played in pterosaur gigantism and to help refine our estimates of pterosaur maximum size.”

“The project will establish the differences between the ground launch dynamics of birds and pterosaurs, how these relate to differences in morphology, scale with and enforce upper limits to size, before ultimately establishing the most effective morphology to maximise launch capability. This will be achieved by creating anatomical reconstructions of possible azhdarchid morphologies and using kinematic simulation software to create a simple baseline bipedal launch model, validated against published data for birds and humans and tested for sensitivity to assumptions and modelling detail. This baseline model will then be modified to incorporate quadrupedal launch morphology. The effect of varying muscle morphologies on power output and the effects of varying size and subsequent allometric relationships will be determined. Finally, anatomically correct simulation models will be constructed to model quadrupedal launch capability and potential upper limits to size.”

Okay let’s take a closer look at those boldface objections

  1. Not all pterosaurs were quadrupedal. We know this from bipedal pterosaur tracks other workers tend to avoid and from reconstructions showing awkward configurations when quadrupedal. The sacrum is reinforced with fusion and additional vertebrae (Fig. 6) to support the lever arm produced by the presacral area in a bipedal configuration. Sister taxa to pterosaurs, including Langobardisaurus, Cosesaurus, Sharovipteryx and Longisquama were all either facultative or obligate bipeds.
  2. Take a look at several of the animations pictured in this blog and see for yourself which model makes more sense when gravity is part of the equation. All pterosaurs were built so they could lift their forelimbs from the substrate while keeping balanced over their toes in order to simply walk, to flap their wings prior to flight, to flap their wings for added thrust during terrestrial locomotion, to frighten predators and intimidate rivals, to mate, etc. etc.
  3. The ‘baggage’ referred to here means the hind limbs in birds, which are not used in flight. Pterosaurs used their hind limbs as horizontal stabilizers in flight, as evidence by their uropatagia, and so legs were not ‘baggage,’ but key aerodynamic control and lift surfaces. This hypothesis is ignored by the Rayfield team.
  4. The muscle mass for pterosaur hind limbs has traditionally been underestimated. The Habib model also accepts that the force of quadrupedal launch is transformed down the large wing metacarpal (Fig. 3). Unfortunately ALL known pterosaur tracks show only the tiny three free fingers contact the substrate — and they were not built to transfer the great forces involved in quadrupedal launches. More unfortunately, the Habib figure (Fig. 3) cheats the length of the tiny free fingers, making them smaller still in order to enable the Habib hypothesis.
  5. The quadrupedal launch hypothesis is widely accepted among a very small group of paleontologists based in the South of England. There is no fossil ichnite evidence for quadrupedal launch. No animal larger than a vampire bat is capable of this feat, and they have traits that pterosaurs (and other bats) do not.
  6. This final confession by the Rayfield team is welcome and a long time coming. Pity they are shoving their problem over to a naive student, not well-versed in the history of this problem, unless he/she is a reader of this blog!
The so-called catapult mechanism in pterosaurs

Figure 3. Left: The so-called catapult mechanism in pterosaurs. Note the falsely reduced fingers enabling wing contact with the substrate. Right. The actual pterosaur morphology that keeps the wing off the substrate.

The proposal objective (above) is flawed.
Rayfield, Palmer and Martin want to test bipedal birds vs. quadrupedal pterosaurs, leaving out any study of bipedal pterosaurs. This assumes the validity of the quadrupedal launch a priori to finding hard evidence for it in the fossil record. Ignoring and deleting competing hypotheses and data is something we’ve seen from other pterosaur workers, also from southern England. Their must be some sort of factor of influence there.

Unsuccessul Pteranodon wing launch based on Habib (2008).

Figure 4. Unsuccessful Pteranodon wing launch based on Habib (2008) in which the initial propulsion was not enough to permit wing unfolding and the first downstroke.

Pteranodon attempting a quadrupedal take-off
(Fig. 4) cannot open its wing fingers, which are like long bamboo poles held against the back of the wrist when quadrupedal, fast enough to open the wings before the first downstroke and gravity causes a crash — even if given one heck of a leap in a quadrupedal mode – a leap no kangaroo could match.

On the other hand
when Pteranodon starts with wings ready for the first downstroke at the moment of hind limb leap, then all the forces Pteranodon can muster are at play at the moment of take-off. A little more take-off speed could be added with a short, speedy, lizardy sprint while flapping for thrust and airspeed (Fig. 2).

Successful heretical bird-style Pteranodon wing launch

Figure 5 Successful heretical bird-style Pteranodon wing launch in which the hind limbs produce far less initial thrust because the first downstroke of the already upraised wings provides the necessary thrust for takeoff in the manner of birds. This assumes a standing start and not a running start in the manner of lizards. Note three wing beats take place in the same space that only wing wing beat takes place in the widely accepted wing launch model of Habib (2008).

There is nothing wrong with a bipedal Pteranodon
I modeled one myself (Fig. 6). There is something wrong with a pole-vaulting Pteranodon, trying to lift its wings off the ground while at the same time forcing them against the substrate, rotate them parasagittally to the open position, extend the wings horizontally, lift the wing tips above its head, then apply the downstroke, all before crashing on its face. Evidently several English workers have invested far too much time and pages in the academic literature to turn back now. Professional pride is at stake and no one will notice if some of the evidence is overlooked and avoided.

Standing Pteranodon

Figure 6. Standing Pteranodon. Note the high number of sacral vertebrae here to support the long lever arm of the presacral area.

References
Project description
Earls KD 2000. Kinematics and mechanics of ground take-off in the starling Sturnis vulgaris and the quail Coturnix coturnix. Journal of Experimental Biology 203, 725 – 739.
Habib  MB 2008. Comparative evidence for quadrupedal launch in pterosaurs. Zitteliana B28, 159-166.
Heers AM and Dia KP 2014. Wings versus legs in the avian bauplan: Development and evolution of alternative locomotor strategies. Evolution 69, 305-320.
Witton MP 2013. Pterosaurs: Natural History, Evolution, Anatomy (Princeton University Press, Princeton.

Project enquiries
Email: e.rayfield@bristol.ac.uk
Contact number: 0117 394 1210
Host institution: University of Bristol
CASE Partner: Ginko Investments Ltd

Elephant shrews are diphyletic

I never thought it would get this far
and so deep when I started ReptileEvolution.com. I keep thinking I”m coming to the end. But there’s more to be found in the metaphorical and literal leaf litter here than I ever imagined five or so years ago when this all began…

Earlier we nested the extant short-eared elephant shrew, Macroscelides (Fig. 1), with the tree shrew, Tupaia and the golden mole, Chrysochloris. Today we nest the gold-rumped elephant shrew, Rhynchocyon (Fig. 2) with the mesonychid-like tenrec, Sinonyx.

How can that be?
They’re both elephant shrews!!

Once you see them together,
(Figs. 1, 2) you’ll see the many differences that separate them. And that’s the way they also test in the large reptile tree. These two putative elephant shrews are not closely related because several non-elephant shrews phylogenetically separate them. And that’s why these two are diphyletic. Macroscelides arises from within Glires, the rodent and rabbit clade. Rhynchocyon arises from within Tenreccetacea, or tenrecs + whales.

Not sure how the others will line up. We’ll save those for later…

Figure 3. Macroscelides proboscideus skull. Note the several basic differences between the this skull and that of Ryhncocyon and you'll be as surprised as I was that these were not noticed in prior studies. If so, please bring them to my attention.

Figure 1. Macroscelides proboscideus skull. Note the several basic differences between the this skull and that of Ryhncocyon and you’ll be as surprised as I was that these were not noticed in prior studies. If so, please bring them to my attention. Imarge from Digimorph.org and used with permission.

The canines on Rhynchocyon
(Fig. 2) were the first clue that not all elephant shrews were sisters. Few skull traits unite Rhynchocyon and Macroscelides, but both do have an elongate flexible nose and long slender legs poking out from fur ball bodies.

Perhaps you’ll be as surprised as I was
that these differences were not noticed in prior studies. If so, please bring them to my attention. A Google search reveals relatively little literature on this/these clade(s) and none (so far) pertinent to the present discussion.

Figure 2. Rhynchocyon skull with select bones colored. Note the large canines, angled rostrum and just the genesis of the high cranial crest seen in the much larger Sinonyx.

Figure 2. Rhynchocyon skull with select bones colored. Note the large canines, angled rostrum and just the genesis of the high cranial crest seen in the much larger Sinonyx.

Unfortunately
there are no skeletons of Rhynchocyon on the net or in published literature that comes up in a Google search.

Figure 4. Skeleton of Macroscelides proboscides from Digimorph.org and used with permission. Note the high sacral spines and elongate metatarsals here.

Figure 3. Skeleton of Macroscelides proboscides from Digimorph.org and used with permission. Note the high sacral spines and elongate metatarsals here.

In life
(Fig. 4) you can see how earlier workers could have allied these two taxa. And you can see how traits they have in common could be plesiomorphic and/or could be homoplastic (a result of convergence).

Figure 6. Rhynchocyon (above) and Macroscelides (below) compared. Though both are considered elephant shrews, they nest in separate major mammal clades in the LRT.

Figure 4. Rhynchocyon (above) and Macroscelides (below) compared. Though both are considered elephant shrews, they nest in separate major mammal clades in the LRT. Note how the lips cover the fangs in Rhynchocyon.

On a lighter note…
This little movie character has not gone unnoticed in this discussion. This is Scrat, the sabertooth ?squirrel from the Ice Age movie franchise. Perhaps a close cousin to Rhynchocyon ~ after the nose job and lip tuck.

Figure 7. Scrat, the sabertooth squirrel, from the Ice Age movie franchise, has fangs, a long rostrum and short cranium like Rhynchocyon -- by convergence, no doubt.

Figure 5. Scrat, the sabertooth squirrel, from the Ice Age movie franchise, has fangs, a long rostrum and short cranium are like Rhynchocyon — by convergence, no doubt. Different nose.

Digimorph.org