Perhaps the biggest bony fish in the Mesozoic Leedsichthys problematicus (Woodward 1889, Martill et al. 1999; Middle Jurassic; holotype BMNH P.6921; Fig. 1) is known from several impressively large specimens including a caudal fin, pectoral fins, a hyomandibular pllus gill basket (Fig. 1). Large gill rakers appear to have been capable of filtering plankton.
Figure 1. Bonnerichthys used as a blueprint for parts of Leedsichthys.
According to Wikipedia, Leedsichthys is a giant member of the Pachycormidae. That seems reasonable, given what is known. These are too few parts published in articulation to add to the LRT.
Skeletons were largely cartilaginous, rather than bone. Length estimates have varied considerably from nine meters to thirty meters (100 feet). Recent research considers 16m a plausible estimate. Here, using Bonnerichthys as a template, that matches precisely those ‘plausible’ estimates. The big caudal fins is from specimen NHM P.10000 (from Liston et al.. 2013).
References Liston J, Newbrey M, Challands T and Adams C 2013, Growth, age and size of the Jurassic pachycormid Leedsichthys problematicus (Osteichthyes: Actinopterygii) in: Arratia, G., Schultze, H. and Wilson, M. (eds.) Mesozoic Fishes 5 – Global Diversity and Evolution. Verlag Dr. Friedrich Pfeil, München, Germany, pp. 145–175. Woodward AS 1889. Notes on some new and little-known British Jurassic Fishes. Annals of the Magazine of natural History, series 6, 4: 405-407.
Today’s post had its genesis in a blogpost at Synapsida, “Before owls ate mice.”Synapsida is a Blogger.com site about paleontology who reported on the two Eocene bird specimens discussed below. One is more owl-like than the other, but both were reported to be and accepted as owls.
DS Peters (no relation) 1992 described a new species of owl from the Eocene Messel oil shale. Palaeoglaux artophoron (Fig. 1) was small, headless, has a “pnuematic coracoideum“, a “narrow proximal end of the ulna”, has “peculiar feathers”, “the osseous arch of the radius seems to be a unique character for owls” and “displays a mixture of tytonid and strigid characters.”
Here in the large reptile tree (LRT 1821+ taxa) Palaeoglaux does not nest with owls, but with Fulica, the coot (Fig. 2) and a skull-only coot sister, Asterornis from the Cretaceous. Based on just the headless but otherise relatively complete and articulated post-crania, only five extra steps are needed to move Palaeoglaux to the owls. Note the distinctly different toe 4 length (Fig. 1) in Palaeoglaux compared to owls. The rest of the differences are more subtle.
Figure 1. Palaeoglaux artophoron (Eocene) in situ above, feet reconstructed below. Colors and scale bars added here along with feet from two owls, Primoptynx (Eocene) and Bubo (extant). Note the tail feathers at lower right.
The feathers on the trunk are only 1mm wide and 2cm long, without barbs. Such feathers are typically found in birds that display bright colors during daylight, but owls are nocturnal, so DS Peters 1992 wondered if this was an exceptional diurnal owl.
Synapsida at Blogger.com write: “To understand the origin of owls, then, it’s helpful to look at these even older species, some of which date back to not long after the extinction of the non-avian dinosaurs.”
Figure 2. The coot, Fulica, nests with Palaeoglaux in the LRT. The coot has longer cervicals, smaller wings, and more gracile feet than Palaeoglaux.
That’s one way to do it. The other way is to drop taxa into a phylogenetic analysis to see which taxa are last common ancestors with this new taxon. In other words, broaden the range of possibilities to let the software decide. Bird expert DS Peters, now 89, knew he had an owl from the start based on my reading of the text of his paper. He saw owl characters and odd characters in his specimen.
Figure 3. Bubo the extant owl compared to Primoptynx, the Early Eocene owl. See figure 1 for pedal closeups. Note the brevity of pedal 4.
Synapsida and DS Peters 1992 note that Palaeoglaux is the exception to the rule that other earliest owls are represented by just a bone or two. Synapsida also reports on Primoptynx poliotaurus (Mayr, Gingerich and Smith 2020; Figs. 1, 3) an owl from the Greybull formation (Early Eocene), 55 mya, with beak, vertebrae, sternum, wing and both legs. “The ungual phalanges of the hallux and the second toe of the new species are distinctly larger than those of the other toes. Current data do not allow an unambiguous phylogenetic placement. Concerning the size of the ungual phalanges, the feet of P. poliotauros correspond to those of extant hawks and allies (Accipitridae). We therefore hypothesize that it used its feet to dispatch prey items in a hawk-like manner, whereas extant owls kill prey with their beak.”
The Synapsida author presented a cladogram based on a genomic test by Jarvis et al. 2014 that nested owls with kingfishers + woodpeckers, further on with hawks and condors, then with falcons + parrots + songbirds. The LRT does not confirm a relationship of owls with kingfishers or either with woodpeckers, nor a relationship between falcons and parrots, as proposed earlier by Mayr 2011. We know better not to trust genomic tests. Too many false positives recovered with DNA and other gene studies in deep time subjects. Epigenetics must be changing the genomes because so many clades become geographic.
In the LRT about half the scored traits are cranial, so lacking a cranium and jaws is a real handicap. Even so, the LRT, by virtue of testing a wider gamut of taxa, was able to lump and separate taxa that were not previously considered.
Too many science bloggers, from Synapsida, to Nat Geo, Scientific American, the Guardian, and others do not use their scientific know-how to test the claims of workers. Instead they simply disseminate, repeating without questioning. Let’s start testing and questioning published claims.
References Jarvis ED et al. (several dozen co-authors) 2014. Whole-genome analyses resolve early branches in the tree of life of modern birds. Science 346(6215):1320–1331. Mayr G, Gingerich PD and Smith T 2020. Skeleton of a new owl from the early Eocene of North America (Aves, Strigiformes) with an accipitrid-like foot morphology. Journal of Vertebrate Paleontology 40(2): e1769116 Mayr G 2000a. A new raptor-like bird from the Lower Eocene of North America and Europe. Senckenbergiana lethaea 80:59–65. Mayr G 2005. The postcranial osteology and phylogenetic position of the Middle Eocene Messelastur gratulator Peters, 1994—a morphological link between owls (Strigiformes) and falconiform birds? Journal of Vertebrate Paleontology 25(3):635–645. Mayr G 2011. Well-preserved new skeleton of the Middle Eocene Messelastur substantiates sister group relationship between Messelasturidae and Halcyornithidae (Aves, ? Pan-Psittaciformes). Journal of Systematic Palaeontology 9(1):159-171. Peters DS 1992. A new species of owl (Aves: Strigiformes) from the Middle Eocene Messel oil shales. In Papers in Avian Paleontology Honoring Pierce Brodkorb. edited by Kenneth Campbell, Jr. NO. 36 Science Series. Natural History Museum of Los Angeles County, Science series No 36: 161-169. Peters DS 1994.Messelastur gratulator n. gen. n. spec., ein Greifvogel aus der Grube Messel (Aves: Accipitridae). Courier Forschungsinstitut Senckenberg 170:3–9.
Pikaia gracilens (Fig. 1) is an extinct, primitive chordate animal known from the Middle CambrianBurgess Shale of British Columbia. Mallatt and Holland 2013 mistakenly located the anus at the very end of the hagfish-like body, opposite the end with the sensory tentacles.
The Royal Ontario Museum website reports, “Pikaia is considered to represent a primitive chordate (Conway Morris, 1979; Conway Morris et al., 1982) possibly close to craniates (Janvier, 1998); a stem-chordate (Smith et al., 2001); or a cephalochordate (Shu et al., 1999). Its exact position within the chordates is still uncertain and this animal awaits a full redescription.”
Figure 1. Pikaia diagram and in situ specimens from Mallatt and Holland 2013. Here a post-anal tail is identified (red arrow), distinct from the diagram (red x).
Here in the large reptile tree (LRT, 1820+ taxa; subset Fig. 2) Pikaia nests with the lancelet, Branchiostoma, basal to the hagfish, Myxine. Lancelets are chordate ancestors to hemichordates and echinoderms, as briefly described here and here. Pikaia is closer to hagfish, Myxine, and the rest of the craniates, vertebrates and gnathostomes.
Mallatt and Holland 2013 wrote: “We deduce that Pikaia, not amphioxus, is specialized. We performed a cladistic analysis that showed the character interpretations of CMC are consistent with their wide‐ranging evolutionary scenario, but that these interpretations leave unresolved the position of Pikaia within chordates.”
The LRT sees things differently. Pikaia is a suitable transitional taxon between the nematode Enoplus (a taxon omitted or ignored by Mallatt and Holland and all other prior workers) and higher chordates. The term ‘specialized’ can only be applied to amphioxus (= lancelets, = Branchiostoma) which has the specialized atrium not found in other chordates, but retained by all hemichordates and echinoderms. In addition, lancelets have a specialized semi-sessile adulthood with their tail buried in the substrate while filter feeding. No other chordates are semi-sessile, but tunicates and crinoids are sessile and filter feed.
The ROM web page on Pikaia reports, “Walcott placed Pikaia in a now defunct group called the Gephyrea with other vermiform fossils such as Banffia, Ottoia and Oesia. Pikaia was later considered to be a primitive chordate (Conway Morris, 1979; Conway Morris et al., 1982), an interpretation which has since been followed to some degree in most discussions about early chordate evolution (e.g., Janvier, 1998). Pikaia played a major part in Gould’s interpretations of the Burgess Shale fossils in Wonderful Life (Gould, 1989; see also Briggs and Fortey, 2005). A full redescription of this animal is currently under way (Conway Morris and Caron, in prep.).”
“Pikaia is relatively rare, known from more than 60 specimens, all from the Walcott Quarry where it represents 0.03% of the specimens counted in the community (Caron and Jackson, 2008). Maximum size: 55 mm. The eel-like morphology and musculature of the animal suggest that it was likely free-swimming, although it probably spent time on the sea floor. The tentacles may have had a sensory function, and the presence of mud in its gut suggests that Pikaia was potentially a deposit feeder.”
Future reversals Several times in vertebrate history eel-like forms re-appeared. Think of the moray eel, Gymnothorax, for instance. This morphology is always in the gene pool, going back to Pikaia.
References Conway Morris S 1979. The Burgess Shale (Middle Cambrian) fauna. Annual Review of Ecology and Systematics, 10(1): 327-349. Conway Morris SHB, et al. (4 co-authors) 1982. Atlas of the Burgess Shale. Palaeontological Association, 31 p. + 23 pl. Mallatt J and Holland N 2013.Pikaia gracilens Walcott: Stem Chordate, or Already Specialized in the Cambrian? Journal of Experimental Zoology Molecular and Developmental Evolution 320(4):247–271. Walcott CD 1911. Cambrian geology and paleontology. Middle Cambrian annelids. Smithsonian Miscellaneous Collections 57(5):109–144.
Stubbs et al. 2021 looked at 241 croc taxa (some firsthand, some photos, some diagrams), all skulls and jaws, no post-crania in order to “show that crocodylomorph ecomorphological variation peaked in the Cretaceous, before declining in the Cenozoic, and the rise and fall of disparity was associated with great heterogeneity in evolutionary rates.”
241 taxa should be enough to touch all aspects of a clade, but co-author and professor Mike Benton skipped several basal bipedal crocodylomorphs (list below and see Fig. 2) recovered by the large reptile tree (LRT, 1820+ taxa; subset Fig. 3), including a favorite Benton subject, Scleromochlus (Fig. 1). Benton 1999 and others keep hoping that Scleromochlus is a pterosaur sister. That’s been a mistake since… forever. Keeping it out of the data matrix is one trick you can use if you are Mike Benton trying to keep Scleromochlus out of the Crocodylomorpha. He likewise purposely omitted taxa in Hone and Benton (2007, 2009),
Figure 1. Scleromochlus, a basal bipedal crocodylomorph in the LRT and well known to co-author Mike Benton, was omitted from this study on Crocodylomorpha.
The authors note, “Missing species either lacked skull or jaw material, or the specimens were too damaged or distorted.”True in some cases, not others. But that brings up another issue… this study was based on skull landmarks, nothing from the informative post-crania, and that’s where at least half the attention ought to be, especially in crocs (Fig. 2). Maybe there was a burst of disparity in the Late Triassic, too, but they’ll never know just looking at skulls and omitting taxa.
Figure 2. Sample taxa from the clade Crocodylomorpha.
Stubbs et al. report, “A composite crocodylomorph supertree was assembled following other recent macroevolutionary studies. The supertree topology is largely based on Godoy et al. and modified from the formal supertree of Bronzati et al. We manually added more taxa, guided by published taxonomic and phylogenetic evidence, to maximize coverage and match the landmark data (see detailed description in the electronic supplementary material). The full supertree includes 373 crocodylomorphs and three pseudosuchian outgroup taxa.”
The LRT found that the traditional clade, Pseudosuchia is paraphyletic. Even so, the three outgroup taxa cherry-picked by the Stubbs team are hard to determine since their .xls file is alphabetical and Stubbs et al. do not list them outright. Worse yet, their published cladograms (their Fig. 3) list no taxa. No taxa at all. The first time I’ve seen this. They show the topology of the tree and a few silhouettes, but their trees lack any taxa. Benton keeps on rolling his own way!
A thorough examination of the Stubbs et al. .xls file of 241 taxa revealed no obvious or traditional non-crocodylomorph taxa listed there. If someone wants to point them out, please send that list of three.
The following are crocodylomorph taxa in the LRT omitted or ignored by Stubbs et al.:
Most of these are basal bipedal crocodylomorphs. Dyoplax is a basal marine croc in the LRT.
The authors were seeking disparity and semblance and to turn that data into evolutionary rate (rapid or slow) results. They conclude, “Our work highlights the importance of ecological opportunity in driving innovation, even in a once diverse clade with now diminished biodiversity.”
Figure 3. Subset of the LRT focusing on Crocodylomorpha.
The croc post-crania documents more diversit in the Triassic. One wonders if this study had any need to be done other than to keep Benton’s students occupied during their expensive education. Some other of Benton’s students have a good story to tell about how they got their PhD under his tutelage and guidance.
References Benton MJ 1999.Scleromochlus taylori and the origin of the pterosaurs. Philosophical Transactions of the Royal Society London, Series B 354 1423-1446. Online pdf Stubbs TL et al. (5 co-authors) 2021. Ecologicial opportunity and the rise and fall of crocodylomorpha evolutionary innovation. Proc. R. Soc. B 288: 20210069. https://doi.org/10.1098/rspb.2021.0069
Note in passing: WordPress has changed from Classic Editor, which was simple, intuitive and great for 3400 posts. Now the OS, called Block Editor, is frustrating and time consuming by comparison. They got rid of the good stuff and added crap.
We’ll start today’s post with a question with an obvious, but overlooked answer. Did you ever wonder why the most primitive extant birds, those that survived the K-T extinction event and gave rise to all other birds, from hummingbirds to petrels, are all poor flyers (megapodes) and non-flyers (ratites)?
Hospitaleche and Worthy 2021 bring us new data on the holotype of Vegavis (Fig. 1) by freeing the bones we’ve seen before (Clark et al. 2005) of this latest Maastrichtian bird from Antarctica.
We looked at Vegavis earlier, before the elements were freed from the stone matrix that entombed them for the last 66 million years. Based on that data, the large reptile tree (LRT, 1819+ taxa) nested Vegavis as the proximal outgroup to crown birds (all extant birds and their fossil relatives) basal to the extant Kiwi, Apteryx, and the more similar Early Eocene Pseudocryptus (Fig. 1).
Figure 1. Vegavis reconstruction from Hospitaleche & Worthy 2021 compared to Vegavis bones applied to Pseudcrypturus blueprint.
Hospitaleche and Worthy report “A basal position, excluded from the Neornithes, was also proposed by McLachlan et al. (December 2017), three months later than the LRT and twelve years after Clarke et al. 2005 did the same.
From the Hospitaleche and Worthy abstract: “Vegavis iaai has key importance as the most complete of the few neornithine birds known from the Cretaceous, yet its phylogenetic relationships remain controversial. The skeleton reveals a mix of features supporting enhanced diving ability for the bird. We make three-dimensional scans and high-quality images of all bones in the holotype available for further comparisons.”
The drawing of Vegavis provided by Hospitaleche and Worthy 2021 (Fig. 1) does indeed look like a diving bird, but it does not look like the bones of Vegavis (Fig. 1). Vegavis bones resemble those found in Pseudocrypturus (Fig. 1). That’s why everyone nests Vegavis just outside the clade of crown birds where Apteryx and Pseudocrypturus are the birds just inside the clade of crown birds.
If anyone knows why the Hospitaleche and Worthy 2021 drawing of Vegavis does not match the Vegavis bones, please drop a line and let us know. I suspect it’s because Hospitaleche and Worthy 2021 were looking at tiny details and ignoring the overall proportions. There is no mention of Archaeornithura or Pseudocrypturus in Clarke et al. 2005 or Hospitaleche and Worthy 2021 who both considered Vegavis a type of goose. In the LRT, it is much more primitive.
Getting back to that opening question about primitive barely volant birds… Apparently all the good-flying birds of the Mesozoic became extinct along with the classic dinosaurs at the K-T boundary. Good flyers evolved again and re-radiated early in the Paleocene. The refugium for these poor-flying birds had to be somewhere on the planet left less scarred by the calamity that devastated the rest of the planet. Could that place be the most remote continent on the planet, Antarctica? The phylogenetic nesting and geological placement of Vegavis makes a case for this hypothesis.
But, wait, there’s more to consider. Mesozoic toothed birds are phylogenetic descendants of Vegavis in the LRT. That means Vegavis had its genesis in the Early Cretaceous and its last stand at the K-T boundary. As we learned earlier, Paleocene birds are known from every continent except Antarctica and they were a diverse lot, including pre-penguins. That means there might have bird refuges everywhere around the globe, unless the K-T bird radiation out of Antarctica was extremely swift and varied. A lot came happen in one million or one hundred thousand years. More Mesozoic crown bird fossils, if they are out there, will resolve this issue.
References
Clarke JA, Tambussi CP, Noriega JI, Erickson GM and Ketcham RA 2005. Definitive fossil evidence for the extant avian radiation in the Cretaceous. Nature 433, 305–308. Hospitaleche CA and Worthy TH 2021. New data on the Vegavis iaai holotype from the Maastrichian of Antarctica. Cretaceous Research https://www.sciencedirect.com/science/article/abs/pii/S0195667121000653
This is the first blogpost produced after WordPress changed its format for the worse. Now it is no longer possible to access previous illustrations by indexing text content. Only the last few dozen figures, the one most recently uploaded, are shown on a page. Hopefully WordPress will revert this problem to the earlier format, the one that worked so well for the last ten years.
Earlier we looked at the many homologies that unite primitive round worms (= aquatic enoplid nematodes, Fig. 1), with primitive chordates (= hagfish. Fig. 1).
Now let’s look at overlooked evidence
that unites nematodes and hagfish with… primitive molluscs (= slugs, Figs. 1, 2).
Largely (but not completely) overlooked until now,
nematodes (= amphistomes) could have given rise to both hagfish (chordates, deuterostomes) and slugs (molluscs, protostomes). These three taxa are all long, worm-like, bilaterals with sensory tentacles, rasping retreating mouth parts, and for one reason or another depend on producing slime from their skin.
I say ‘not completely overlooked’
because Clark and Uyeno 2019 portrayed cutaway diagrams of a slug and hagfish to show their ‘convergent’ mouth parts.
Figure 1. Nematodes, hagfish and slugs have so many traits in common, one wonders why they are not related to one another.
With that short list, I could be accused
of “Pulling a Larry Martin” by listing only a few traits. The fact is, these simple, soft-bodied taxa only have a few traits, and they still share these few traits 600 million years after their last common ancestor in the Ediacaran.
Figure 2. A selection of slugs (basal molluscs) to scale. Compare to hagfish in figure 1.
Tiny nematodes wriggle through and eat whatever falls on the sea floor.
Slugs slide over and eat whatever falls on the sea floor. Hagfish swim above and eat whatever falls on the sea floor. In the Ediacaran the only food source was the planktonic seafloor and its tiny burrowing and crawling inhabitants.
Side note: Chaetognaths (arrow worms)
(Fig. 3) document yet another clade of swimming nematode descendants with hard mouth parts and fins that evolved by convergence with those of chordates. Notably, on vertically undulating chaetognaths swimming fins appear on the lateral surfaces, distinct from horizontally undulating chordates with vertical fins. Yes, it’s that simple.
Figure 3. Chaetognath (arrow worm) diagram. Note the lateral fins and lateral caudal fin together with the grasping mouth parts.
One reference
(Barnes 1980) considered arrow worms deuterostomes. Wikipedia labeled them protostomes, but reported, “Chaetognaths are traditionally classed as deuterostomes by embryologists. Molecular phylogenists, however, consider them to be protostomes. Thomas Cavalier-Smith places them in the protostomes in his Six Kingdom classification. The similarities between chaetognaths and nematodes mentioned above may support the protostome thesis.”
We’ve already seen that nematodes are amphistomes and that gene studies too often recover false positives. So let’s consider those gene studies unreliable. As noted above, visual examination shows chaetognaths to be deuterostomes, whether by convergence or homology.
Try Googling ‘hagfish + slugs’
and you won’t find any prior discussions of this interrelationship in the online academic literature. Any mention of worm-like ancestors for hagfish or any mention of nematode ancestors for molluscs are also rare to absent in the online literature.
Distinct from annelids, arthropods and any other segmented animals,
chordates and molluscs have no body segments.
Traditionally the most primitive mollusc
is the chiton (with eight separate plates of armor) or the heliconelid (with a slightly spiral-shaped shell).
However,
if you start with a flatworm (Platyhelminthes), as you must… then a ribbon worm (Nemertea), as you must… then a round worm (Nematoida), as you must… you’re looking for only minor adjustments to the basic worm shape in both descendants: hagfish and slugs. In this scenario hard mollusc shells are derived traits that evolve after the slug morphology was established. Thus, contra academic tradition naked slugs represent the basal condition in molluscs. They didn’t lose their shells. Slugs never had shells. Those evolved later.
Figure 4. From Peters 1991 a diagram splitting deuterostomates from protostomates. Now this has to be updated by putting molluscs closer to chordates and nematodes.
Traditional invertebrate clades:
Bilateria (Flatworms, single digestive opening)
Amphistomia (aquatic nematodes, anus and mouth at the same time)
Chaetognatha (arrow worms) or direct from Amphistomia
Lophotrochozoa (molluscs, with protostome embryos convergent with segmented invertebrates)
Chitin vs. keratin
Chordates have keratin teeth. Molluscs have chitin teeth. Wikipedia reports, “The structure of chitin is comparable to another polysaccharide, cellulose, forming crystalline nanofibrils or whiskers. It is functionally comparable to the protein keratin. The only other biological matter known to approximate the toughness of keratinized tissue is chitin.”
Chordates and molluscs had a last common ancestor 600 million years ago. Numerous references discuss nematode ‘teeth’, but do not describe them as either chitinous or keratinous. So I don’t know which is the more primitive substance.
This is not the first time that professional systematists have left ‘low hanging fruit‘ for amateurs to pluck from a long list of traditionally overlooked, ignored and enigma interrelationships. Putting taxa together that have never been put together before is what we should all do to understand our world better. Every so-called enigma taxon is the result of Darwinian evolution and thus did not and can not stand alone. Relatives are out there for all the oddballs. It’s our job to find them.
The hagfish-nematode-slug relationship seems to be a novel hypothesis
of interrelationships. If not, please send a valid citation so I can promote it.
PostScript:
I found this YouTube video of velvet worms, arthropods, Hallucigenia (shown on the screen shot) and other segmented worm-like members of Protostomia. Seems velvet worms also have sensory tentacles and eversible teeth made of chitin (close to keratiin) and spray mucous slime from glands on the side of their head. There’s a deep connection with nematodes here as well.
References Barnes RD 1980. Invertebrate Zoology 4th ed. Saunders College, Philadelphia 1–1089. Clark AJ and Uyeno TA 2019. Feeding in jawless fishes. In: Bels V., Whishaw I. (eds) Feeding in Vertebrates. Fascinating Life Sciences. Springer, Cham. https://doi.org/10.1007/978-3-030-13739-7_7 Peters D 1991. From the Beginning – The story of human evolution. Wm Morrow.
Losing its maxilla
(Fig. 1) did not stop this taxon from sporting a lot of other teeth in the palatine, ectopterygoid and maybe the vomer, even though only the premaxillary teeth line up with dentary teeth.
Figure 1. Skull of Proteus the white olm. Colors added. Note the lack of a lacrimal and maxilla.
Proteusthe white olm
(Figs. 1, 2), is a blind cave salamander with a long torso, tiny limbs and external gills (Fig. 2).
Figure 2. Skeleton of Proteus, the white olm.
Proteus anguinus (Laurenti 1768) nests with Necturus, the mudpuppy. The lacrimal and maxilla are absent. The postorbital and postfrontal are stretched out. External gills enable Proteus to remain underwater. Apparently the dorsal portion of the vertebral column is very short (about 5 vertebrae), with the majority comprised of lumbar vertebrae (without dorsal ribs).
References Laurenti JN 1768. Synopsin Reptilium. J.T. de Trattnern, Viennae, pp. 35–36.
While reviewing the terrestrial descendants of tree shrews yesterday, the Late Jurassic Fruitafossor (Figs. 1, 2) stuck out as a chronological misfit as it nested in the otherwise Tertiary edentates (= Xenarthrans).
Here is the problem,
and the solution.
A Jurassic edentate? No. Fruitafossor windscheffeli (Luo and Wible 2005) used to nest in the LRT with digging edentates, like the armadillo-mimic, Peltephilus (Miocene), and for good reason…
Wikipedia reports, “The teeth of Fruitafossor bear a striking resemblance to modern armadillos and aardvarks. Its vertebral column is also very similar to armadillos, sloths, and anteaters (order Xenarthra). It had extra points of contact among similar to the xenarthrous process that are only known in these modern forms.”
By contrast, Wikipedia concludes, “Its shoulder-girdle is similar to a platypus or reptile, but many other features are more similar to most other modern mammals.”
What would Larry Martinsay?
Run a complete analysis. Don’t rely on one, two or a dozen traits. And the Late Jurassic is so early in mammal evolution that it becomes important, too. There were fewer mammal clades back then. Edentates had not yet arrived.
Figure 1. Several drawings from Zhou and Wible that one must trust for accuracy. The verification data is too fuzzy to validate.
So is Fruitafossor a Late Jurassic edentate? Or an edentate-mimic in the Late Jurassic?
With current scoring in the LRT, shifting Fruitafossor from the edentates to the base of the Monotremata adds 23 steps. Shifting to Early Cretaceous Lactodens within the Monotremata adds just 17 steps, the lowest number I could find. Lactodens has typical differentiated teeth and five fingers with small, sharp claws, traits not shared with Fruitafossor + edentates. Lactodens nests with the echidnas, Tachyglossus (extant, Figs. 3–5) and Cifelliodon (Early Cretaceous; Fig. 3). The latter has simple blunt teeth and the former is a known digger.
Figure 2. Fruitafossor in situ from Digimorph.org and used with permission and here colorized to an uncertain extent.
So let’s reexamine scored traits… and solve this conundrum. Has the LRT met its match? Very few skull traits are known from Fruitafossor. Even so, earlier I overlooked or mis-scored the following that gain importance in hindsight:
Fruitafossor:
orbit contacts the maxilla
4 rather than 5 sacrals,
coracoid present
I could not score hind limb length without a pes and estimates won’t do
proximal sesamoid of fibula present
fibula diameter greater than half of tibia
dorsal osteoderms absent (I misinterpreted scattered elements at Digimorph.org)
Tachyglossus:
retroarticular process present as in Fruitafossor
metacarpal 1 and 2 are the longest as in Fruitafossor
longest manual digit 3 as in Fruitafossor
manual digit 4 narrower than 3 as in Fruitafossor
Cifelliodon:
three molars, as in Fruitafossor
Figure 3. Early Cretaceous Cifelliodon is ancestral to the living echidna, Tachyglossus according to the LRT. The lack of teeth here led to toothlessness in living echidnas. The skull of Tachyglossus is largely fused together, lacks teeth and retains only a tiny lateral temporal fenestra (because the jaws don’t move much in this anteater. Compared to Cifelliodon the braincase is greatly expanded, the lateral arches are expanded and the two elements fuse, unlike most mammals.
Figure 4. Tachyglossus skeleton, manus and x-rays. Note the perforated pelvis.
Figure 5. The echidna (genus: Tachyglossus) in life. This slow-moving spine-covered anteater has digging claws.
Results (as you might imagine, given these changes): Fruitafossor is an edentate-mimic nesting basal to Cifellidon and Tachyglossus as a Late Jurassic echidna and monotreme in the LRT. Glad to get rid of that problem!
In their original description of Fruitafossor,
Luo and Wible 2005 nested their discovery between a monotreme clade and a clade with the mammal-mimic, Gobiconodon at its base, then a clade with another egg-laying mammal, Tinodon at its base, then a pangolin ancestor, Zhangheotherium, then a rabbit ancestor Henkelotherium, then two other monotremes, Dryolestes, Amphitherium and the carnivorous marsupial, Vincelestes. Luo and Wible tested Tachyglossus, but not Cifelliodon, which was published in 2018. Note the simple, blunt teeth in Cifelliodon, nearly matching those in Fruitafossor. Given that the only fossil of Fruitafossor is a bit jumbled, it is possible that it, too, had five fingers in vivo, like other monotremes. With only four fingers (Fig. 1) Fruitafossor had a good excuse for pretending to be an edentate.
So, yes, the LRT was up to the challenge.
But it took insight, lacking until now, to provide the correct matrix scoring. I’m happy to announce that the twenty or so corrections made yesterday were added to the 120,000 or so corrections made over the past ten years. With these corrections the LRT gets better and stronger every week. Minimizing taxon exclusion maximizes the opportunity to correctly nest new and enigma taxa with old and established taxa, even if the new and old specimens are incomplete or scattered about.
The earlier August 2017 blogpost for Fruitafossor
was updated yesterday to erase old errors and enter the corrections.
References Huttenlocker AD, Grossnickle DM, Kirkland JI, Schultz JA and Luo Z-X 2018. Late-surviving stem mammal links the lowermost Cretaceous of North America and Gondwana. Nature Letters Link to Nature Luo Z-X and Wible JR 2005. A late Jurassic digging mammal and early mammal diversification. Science 308:103–107. Shaw G 1792. Musei Leveriani explicatio, anglica et latina.
During the reign of the dinosaurs tree shrews, like Ptilocercus (Fig. 1) and Tupaia (Fig. 1), stayed in the trees, evolving into tree-dwelling members of the Carnivora (Genetta, Fig. 1), Volitantia (bats, pangolins and dermopterans), Glires (including multituberculates led by Tupaia) and Primates (Microcebus, Fig. 1) in the large reptile tree (LRT, 1818+ taxa) distinct from all gene studies and all other prior trait studies (due to taxon exclusion). The LRT is the first study that found tree-dwelling Caluromys (Fig. 1), an extant tree shrew-like marsupial, as the proximal outgroup to the Placentalia. Based on chronological bracketing, Caluromys relatives lived in the Early Jurassic.
Figure 1. Mammals at the base of the Placentalia include the outgroup taxon: Caluromys, a basal placental: Genetta, a basal Carnivora: Eupleres, a basal Volitantia: Ptilocercus, a basal Primates: Microcebus, and basal Glires: Tupaia.
After the Cretaceous some tree shrews became terrestrial. Leptictids, elephant shrews (Rhynchocyon, Fig. 2 and tenrecs (Tenrec) were phylogenetically among the first of the former tree shrews to become fully terrestrial. They were all small. After the Cretaceous some terrestrial tree shrew descendants began to increase in size. Some became elephants, others horses, still others baleen whales, all following Cope’s Rule.
Figure 2. Rhynchocyon, a living elephant shrew, is a living leptictid and a former tree shrew.
Once established on the ground
and spreading beyond the jungles, the following Early Paleocene terrestrial placentals became cat to tiger size: Onychodectes(Fig. 3), Alcidedorbignya (Fig. 3) and Pantolambda(Fig. 3).
Figure 3. Onychodectes, Alcidedorbignya and Pantolambda are former tree shrews now terrestrial of increasing size in the Early Paleocene. Note the lost of sharp claws replaced by pre-hooves.
By the late Paleocene
taxa like massive Barylambda showed further increases in size. This taxon was basal to giant glyptodonts and ground sloths, some of which ultimately became smaller and returned to the trees as tree sloths.
Figure 4. Late Paleocene Barylambda looks like a large ground sloth for good reason. It is a sister to the direct ancestor and nests at the base of the Xenarthra along with Orycteropus, the aardvark.
PS… saving the best for last.
Writing this blogpost inevitably brought my gaze back to Fruitafossor(Luo and Wible 2005), a small, Late Jurassic digging mammal with four robust fingers, xenarthran lumbars and single cusp, tubular teeth. When first encountered and based on these traits the LRT mistakenly nested Fruitafossor with edentates for the last four years. That Late Jurassic temporal discontinuity in an otherwise Tertiary clade of edentates required a review and revision of taxon scores for Fuitafossor. That review ultimately re-nested Fruitafossor more plausibly and parimoniously basal to echidnas in the LRT. Fruitafossor is a basal echidna from Colorado. That story comes to you tomorrow.
References Luo Z-X and Wible JR 2005. A late Jurassic digging mammal and early mammal diversification. Science 308:103–107.
Dr. Thewissen is a professor
at Northeast Ohio Medical University.
According to the Discover article by Joshua Rapp Learn: “Cetaceans include everything from dolphins to whales.”
By contrast,
in the large reptile tree (LRT, 1818+ taxa; subsets Figs. 5, 6) Cetacea is no longer a clade. That’s because traditional ‘whales’ are diphyletic with separate ancestries still not recognized by whale experts like Dr. Thewissen. Odontocetes (toothed whales, Figs. 2, 6) arise from tenrecs (which also echolocate). Mysticetes (baleen whales, Figs. 3–5) arise from mesonychids, hippos, anthracobunids and desmostylians.
Figure 2. Odontoceti (toothed whale) origin and evolution. Here Anagale, Andrewsarchus, Sinonyx, Hemicentetes, Tenrec Indohyus and Leptictidium precede Pakicetus. Maiacetus and Orcinus are aquatic odontocetes.
According to the Discover article: “Indohyus belonged to the even-toed group of ungulates, which today includes giraffes, horses, pigs and cetaceans. Indohyus basically looked like a tiny little deer, a deer the size of a cat,” says Hans Thewissen, a professor at Northeast Ohio Medical University who has studied whale evolution for years and wrote thebookThe Walking Whales: From Land to Water in Eight Million Years. Today, a distant deer-like relative called the water chevrotain (or African mouse-deer) can be found from central to southern Africa. These deer eat flowers and fruits and live near rivers, which they use as escape routes to flee land-based predators or even eagles.
Ungulates have no relationship to whales in the LRT.
Think of it. Four, two or one-toed hooves to flippers? That’s untenable, but evidently that’s what taxon exclusion gives you. Simply adding taxa in the LRT (Figs. 2–4) shows that Thewissen’s study suffered from taxon exclusion prior to Pakicetus (Fig. 2), the most basal taxon common to both studies.
Figure 3 Rorqual evolution from desmostylians, Neoparadoxia, the RBCM specimen of Behemotops, Miocaperea, Eschrichtius and Cetotherium, not to scale.
Figure 4. Taxa in the lineage of right whales include Desmostylus, Caperea and Eubalaena. The tiny bit of jugal posterior to the orbit (in cyan) is found in all baleen whales tested so far. The frontals over the eyes are just roofing the eyeballs in Desmostylus, much wider in Caperea and much, much longer in Eubalaena.
According to the Discover article: “Thewissen’sresearch examining stable isotopes in Indohyus fossils shows they ate land plants, but their dense bones suggest they spent a lot of time in the water. The hippopotamus — the closest living relative of whales that live outside the ocean — also has dense bones, which help weigh it down while walking along the bottom of lakes or rivers. The evolutionary descendant of Indohyus, called Pakicetus, began to adopt a more aquatic lifestyle as they abandoned a vegetarian diet, based on the way their teeth look, Thewissen says.”
So this explains why Thewissen did not answer my emails. Two years earlier he had authored a book (Fig. 1) that promoted the myth of a single origin of all whales originating from hoofed ungulates. The news I sent him, that whales were not a single clade, was probably upsetting, considering the time, treasure and reputation Thewissen put into his career and his publications. You can’t fix print once it is printed.
Figure 5. The oreodont-mesonychid-hippo-desmoystlian-mysticete clade subset of the LRT
It should be up to professionals and PhDs
to build matrices and run analyses of fossil taxa. That’s what they are getting paid to do. They are the ones who know how to run the analyses. They are the ones who have access to fossils. They have professional colleagues, post-docs, PhD candidates, undergrads, volunteers and grants. Since the pros and PhDs have chosen to exclude so many pertinent taxa, amateurs are taking up the slack, hoping to contribute to this ancient science we call paleontology.
Figure 6. Subset of the LRT focusing on the odontocetes and their ancestors.
Taxon exclusion remains the number one problem
vexing paleontology and paleontologists. Adding taxa to minimize taxon exclusion is what the LRT is all about. It resolves problems like the origin of whales with taxa that document in detail the gradual accumulation of traits (Figs. 3, 4) we expect from microevolution over deep time, now back to Ediacaran nematodes.
Since this is science, anyone can repeat this experiment simply by following the materials and methods. You don’t have to be a scientist. You don’t have to be an expert. That will come with time and study, the same way it comes with time and study for those who pay dearly for their education. Don’t trust me. Don’t trust others, even paid professionals with PhDs. Build your own matrix and run the analyses yourself to find out for yourself that deer, or any other ungulate, did not give rise to whales.
References Thewissen JGM et al. (4 co-authors) 2007. Whales originated from aquatic artiodactyls in the Eocene epoch of India. Nature 450:1190–1194.
The Pterosaur Heresies 