Tiny Cretaceous stickleback ancestor for the extant giant oarfish

Figure 1. Tiny Plectocretacicus now nests at the closest sister to the giant oarfish, Regalecus (Figs. 2, 3). Plectocretacicus retains all the stickleback spines found in the freshwater stickleback, Gasterosteous. Skull bones are revised here from their earlier interpretation. The quadrate is taphonomically too far forward in this figure. It should articulate at the posterior of the mandible.

Figure 1. Tiny Plectocretacicus now nests at the closest sister to the giant oarfish, Regalecus (Figs. 2, 3). Plectocretacicus retains all the stickleback spines found in the freshwater stickleback, Gasterosteous. Skull bones are revised here from their earlier interpretation. The quadrate is taphonomically too far forward in this figure. It should articulate at the posterior of the mandible.

According to Wikipedia
Plectocretacicus is an extinct genus of prehistoric ray-finned fish that lived during the lower CenomanianIt contains a single species, P. claraePlectocretacicus is the earliest known member of the order Tetraodontiformes.”

By contrast,
the large reptile tree nests tiny Plectocretacicus ancestral to the extant giant oarfish, Regalecus glesne (Figs. 2, 3). Both are derived from the stickleback, Gasterosteus.

FIgure 2. Skull of the giant oarfish (Regalecus glesne). Note similarities to Plectocretacicus in figure 1.

FIgure 2. Skull of the giant oarfish (Regalecus glesne). Note similarities to Plectocretacicus in figure 1.

Figure 1. The giant oarfish, Regalecus glesne, to scale with a couple of swimmers. Sometimes it swims vertically, often at great depths.

Figure 1. The giant oarfish, Regalecus glesne, to scale with a couple of swimmers. Sometimes it swims vertically, often at great depths. Note the anterior placement of the pelvic spines. The rest is all tail.

Plectocretacicus clarae (Sorbini 1996, Fig. 1; early Late Cretaceous; about 3cm) is traditionally known as the earliest known tetraodontiform, the clade that includes queen trigger fish, ocean sunfish and pufferfish. The small size of this taxon follows a pattern seen in other vertebrates of phylogenetic miniaturization at the genesis of new clades. Distinguishing traits, such as the spine-like pectoral fins, show that this taxon had a more ancient sister with more plesiomorphic traits.

Regalecus glesne (Ascanius 1772; typically 3m in length, rarely to 11m) is the extant giant oarfish. Like the seahorse it nests with, the mouth is vertical, the dorsal fin provides the propulsion. The oarfish often swims vertically, sometimes at great depth. It feeds on plankton and small fish. The pelvic fins remind one of oars, but they do not contribute to propulsion. The oarfish is nearly all tail (caudal vertebrae). Distinct from seahorses, the snout is quite short.


References
Ascanius P 1772. Philine quadripartita, et förut obekant sjö-kräk, aftecknadt och beskrifvet. Kongliga Vetenskaps Academiens Handlingar 33 (10-12): 329-331, pl. 10.
Sorbini L 1979. Segnalazione di un plettognato Cretacico Plectocretacicus nov. gen. Bollettino del Museo Civico di Storia Naturale di Verona, 6:1–4.

Tyler JC and Sorbini L 1996. New Superfamily and Three New Families of Tetraodontiform Fishes from the Upper Cretaceous: The Earliest and Most Morphologically Primitive Plectognaths. (PDF)Smithsonian Contributions to Paleobiology82: 1–59.

wiki/Plectocretcicus
wiki/Giant_oarfish

Gregorius rexi: not a ratfish in the LRT

Revised November 07, 10 and 17 2019
with a revision to the LRT that moves Gregorius closer to Hybodus, basal to Placodermi.

Talk about a transitional taxon…
Gregorius rexi (Lund and Grogan 2004; 11cm long; Early Carboniferous; CM 35490) is a small fish from the famous Bear Gulch Formation in Montana. Traditionally it is considered a type of ratfish.

By contrast,
in the large reptile tree (LRT, 1593 taxa; Fig. 3), Gregorius is a late surviving member of an Early Devonian genesis representing the most primitive ray-fin fish splitting from Hybodus. Gregorius is the last common ancestor of all bony fish and placoderms. Ratfish are a bit more primitive.

Figure 1. Gregorius rexi enlarged and to to scale with its cousin in the LRT, Robustichthys. Gregorius still has a dorsal spine and an odd soft of diphycercal tail.

Figure 1. Gregorius rexi enlarged and to to scale with its cousin in the LRT, Coccosteus.  Gregorius still has a dorsal spine and an odd soft of diphycercal tail.

Gregorius is not far from catfish,
still tucked inside the placoderms. Thunnus, the tuna, is the most primitive extant ray-fin fish among taxa derived from a sister to Gregorius.

Figure 5. Subset of the LRT focusing on fish. Pachycormus nests at the base of the revised Telostei (green) clade.

Figure 2. Subset of the LRT focusing on fish. Pachycormus nests at the base of the revised Telostei (green) clade.

In the meantime,
I’ve been learning more about ray fin fish. Some taxa have moved around as mistakes are discovered and corrections are made. The four-eyed fish now nests with the mudskipper, as an example. The general topology of the tree has otherwise stayed much the same as the Bootstrap scores get better. When that portion is complete, we’ll review the changes.


References
Lund R and Grogan E 2004. Five new euchondrocephalan Chondrichthyes from the Bear Gulch Limestone (Serpukhovian, Namurian E2b) of Montana, USA. Recent Advances in the Origin and Early Radiation of Vertebrates 505-531.

https://people.sju.edu/~egrogan/BearGulch/pages_fish_species/Gregorius_rexi.html

SVP abstracts – Ichthyornis and the origin of extant birds

Benito et al. 2019 dive into bird phylogeny
with a study of the Late Cretaceous toothed bird, Ichthyornis (Fig. 1).

Figure 1. Skull of Ichthyornis in 3 views from Field et al. 2018 and overall skeleton.

Figure 1. Skull of Ichthyornis in 3 views from Field et al. 2018 and overall skeleton.

From their abstract
“The origin of crown birds is poorly understood

By contrast, in the large reptile tree (LRT, 1592 taxa) the origin of crown birds is well understood back to Silurian jawless fish. Ichthyornis is a member of the clade of crown birds in the LRT, not an ancestor to it.

“…and the study of their early evolution must incorporate data from their closest relatives among Mesozoic stem birds. The postcranial morphology of the Late Cretaceous toothed bird Ichthyornis dispar may be more representative of the ancestral condition of crown birds than that of any other known Mesozoic avialan, and its study has crucial implications for understanding morphological evolution prior to the great radiation of the avian crown group.”

By contrast, in the LRT Vegavis (Latest Cretaceous) is basal to all extant birds including Mesozoic toothed birds like Icthyornis. It was a late survivor from an earlier genesis.

“Here we present high resolution scans of new, exquisitely preserved three dimensional specimens of Ichthyornis from the Late Cretaceous of Kansas. These correspond to a partial skeleton from a single individual, more complete and in better condition than the classic material known since the 19th Century. The new material includes a complete sternum and shoulder girdle with evidence of extensive pneumatization. This new skeleton shows certain morphological differences from the classic material, including the absence of some previously proposed autapomorphies of I. dispar. Thus, the new material may represent a previously unknown species, or it could indicate that morphological variation within I. dispar was greater than previously appreciated.”

Good to have these new data.

Figure 3. Subset of the LRT focusing on early birds, including Ichthyornis.

Figure 2. Subset of the LRT focusing on early birds, including Ichthyornis.

Benito et al. continue:
“Phylogenetic analyses incorporating our new morphological data corroborate recent results and recover a grade of predominantly marine taxa close to the origin of crown birds. I. dispar is recovered stemward of Hesperornithes and Iaceornis marshi, which is recovered as the sister taxon to all crown birds. Additional information on the crownward-most portion of the avian stem group will help confirm these results and provide critical information on the ancestral ecology of the crown bird radiation.”
I don’t know if Benito et al. employed all the taxa shown here (Fig. 2) in this subset of the LRT, but you can see Ichthyornis nests in the LRT within the clade of extant/crown birds. Here Ichthyornis is a highly derived member of its own small clade of toothed birds, within extant birds between megapodes and seriemas. Other taxa closer to the main line of Cretaceous bird evolution would probably make a better model for studies like this.

References
Benito J et al. 2019. New Ichthyornis specimens: shedding new light on modern bird origins. Journal of Vertebrate Paleontology abstracts.

Tooth whorls: Helicoprion, Ischnagnathus and Onycodontus

After decades of wondering and guessing,
Tapanila et al. 2013 provided µCT scans of the enigmatic basal vertebrate (fish) Helicoprion vessonowi (Figs. 1-3; Karpinsky 1899; Permian, 290-270 mya; possibly 12m in length). Helicoprion is represented by several fossils whorls of teeth of decreasing size over several spiraling revolutions representing growth of this whorl without tooth loss. Often enough such tooth whorls are found in phosphate mines.

https://www.wired.com/2011/03/unraveling-the-nature-of-the-whorl-toothed-shark/

FIgure 1. Helicoprion fossil. Evidently this was an adult based on the number of smaller teeth present here.

According to Wikipedia,Helicoprion is a genus of extinct, shark-like eugeneodontid holocephalid fish.” Ratfish are considered the closest extant relatives. Chimaera is the closest tested taxon in the large reptile tree (LRT, 1592 taxa). No other eugeneotontids have been tested yet.

According to Brian Switek writing for NatGeo.com,
“A very special fossil – IMNH 37899 – preserved both the upper and lower jaws in a closed position, finally solving the mystery of what the ratfish’s head actually looked like. But determining the exact placement of that vexing spiral was just an initial step.”

As you can see
(Figs. 2, 3), traditional reconstructions over the past 6 years have featured a long-snouted shark-like form, based on the data in Tapanila et al. The evidence indicates that the only portion of the skull (sans mandible) recovered in the µCT scans is a narrow set of palate cartilage (pterygoids + palatines), a narrow set of mandibles and a cartilage plate covering the center of the whorl. Despite everyone from Tapanila et al. to Switek calling this a ratfish, paleoartists keep providing a shark-like image (Fig. 2) lacking pelvic fins. Sharks typically have a wider skull. Ratfish skulls (Figs. 2, 3) are typically taller and narrower, providing a closer match to the recovered palate and mandible shapes. Tapanila et al. regarded Helicoprion as a member of the Holocephalia, the clade of ratfish (see below). Finally note the jaws cannot completely close because the tooth whorl gets in the way.

Figure 1. Helicoprion µCT scans, model made from scans, in vivo image with shark-like proportions, and matched against chimaera (Hydrolagus) jaws.

Figure 2. Helicoprion µCT scans, model made from scans, in vivo image with shark-like proportions, and matched against chimaera (Hydrolagus) jaws. See figure 2 for closeup.

From the Tapanila et al. abstract, 
“New CT scans of the spiral-tooth fossil, Helicoprion, resolve a longstanding mystery concerning the form and phylogeny of this ancient cartilaginous fish. We present the first three-dimensional images that show the tooth whorl occupying the entire mandibular arch, and which is supported along the midline of the lower jaw. Several characters of the upper jaw show that it articulated with the neurocranium in two places and that the hyomandibula was not part of the jaw suspension. These features identify Helicoprion as a member of the stem holocephalan group Euchondrocephali. Our reconstruction illustrates novel adaptations, such as lateral cartilage to buttress the tooth whorl, which accommodated the unusual trait of continuous addition and retention of teeth in a predatory chondrichthyan. Helicoprion exemplifies the climax of stem holocephalan diversification and body size in Late Palaeozoic seas, a role dominated today by sharks and rays.”

FIgure 3. Closeup of figure 2.

FIgure 3. Closeup of figure 2.

The YouTube videos below
further emphasize the shark-like hypothesis and high-energy, fast-swimming method of cutting soft squid-like prey in half with the pieces falling to the sea floor. The videos don’t show the shark actually swallowing any prey. That is left to the imagination.

If instead, a chimaera body form is employed,
complimenting the authors’ statement that the specimen is a type of ratfish, then a low-energy, slow-swimming lifestyle should be inferred (using phylogenetic bracketing). Fossils are found in phosphate mines. In the present day deep cold waters carry three times as much phosphate as do warmer surface waters. Beyond those limits phosphate can precipitate out to form sea sediment in all phases and temperatures of phosphate solutions. That includes the weathering of terrestrial phosphatic rocks into nearby shallows.

Helicoprion teeth rarely show wear,
which is otherwise a good reason for getting rid of old, dull teeth in most vertebrates. Helicoprion throats may be tall, but they are also extremely narrow, AND blocked by the large median tooth whorl. That makes eating large prey difficult. Finally, Helicoprion grew to be giants that swam over phosphatic sea floors. Given these parameters and limitations,  what did Helicoprion swallow and how did it subdue prey?

According to Wikipedia
“The spotted ratfish swims slowly above the seafloor in search of food. Location of food is done by smell. Their usual hunting period is at night, when they move to shallow water to feed.” Ratfish feed on crabs and clams, along with shrimp, worms, small fish, small crustaceans, and sea stars, all bottom-dwelling prey.

What was available to eat back then
in sufficient quantities to sustain Helicoprion and never break off any teeth? Well, as it happens the largest prey items on the Permian seafloor (Fig. 5) were also the softest, slowest, most plentiful and easiest to find and graze on at night for a growing Helicoprion: the tall sponges. How Helicoprion fed (= what technique it used) on those sponges remains something to be imagined at present. Did Helicoprion nibble from the top of each sponge stalk? That’s my guess. If so, a central tooth whorl might have worked to break up each sponge stalk like a pizza cutter. Thereafter the mouth and gills worked together to suck in the broken sponge pieces.

Figure 5. Permian sea floor at night. The largest prey items here are also the softest and most plentiful and easiest to graze on at night for a growing Helicoprion: the tall sponges. Just guessing giving the present data.

Figure 5. Permian sea floor at night. The largest prey items here are also the softest, slowest, most plentiful and easiest to find and graze on at night for a growing Helicoprion: the tall sponges. Just guessing giving the present data.

Final note on sponges and precipitating phosphates
Colman 2015 reports, “The authors present strong evidence for polyphosphate (poly-P) production and storage by sponge endosymbionts. Zhang et al. also may have detected apatite, a calcium phosphate mineral, in sponge tissue. This work has major implications for our understanding of nutrient cycling in reef environments, the roles played by microbial endosymbiont communities in general, and aspects of P cycling on geologic timescales.”

Figure 2. Onychodus and Ischnacanthus share enough traits to make them sisters, apart from Brachyacanthus + Pteronisculus.

Figure 4. Onychodus and Ischnacanthus share enough traits to make them sisters, apart from Brachyacanthus + Pteronisculus.

For comparison
and by convergence two other fish have a median tooth whorl, though much smaller and much more conservative in both cases: Onychodus and Ischnacanthus (Fig. 4). So tooth whorls are in the gene pool, though rarely expressed.

PS Added November 30, 2019
Just ran across a new paper on the functional morphology of Helicoprion.  Ramsay et al. 2014 report, “Here, we use the morphology of the jaws and tooth-whorl to reconstruct the jaw musculature and develop a biomechanical model of the feeding mechanism in these early Permian predators… Helicoprion was better equipped for feeding on soft-bodied prey. Posterior teeth cut and push prey deeper into the oral cavity, while middle teeth pierce and cut, and anterior teeth hook and drag more of the prey into the mouth.”

Ramsay et al. (6 co-authors) 2014. Eating with a saw for a jaw: Functional morphology of the jaws and tooth-whorl in Helicoprion davisii. Journal of Morphology 276(1):47–64.


References
Bendix-Almgreen SE 1966. New investigations on Helicoprion from the Phosphoria Formation of south-east Idaho, U.S.A. Biologiske Skrifter udgivet af det Kongelige Danske Videnskabernes Selskab, 14:1–54.
|Coleman AS 2015. Sponge symbionts and the marine P cycle. PNAS 112(14):4191-–4192.
Karpinsky AP 1899. On the edestid remains and its new genus Helicoprion. Zapiski Imperatorskoy Akademii Nauk, 7:1–67. (In Russian)
Lebedev O 2009. A new specimen of Helicoprion Karpinsky, 1899 from Kazakhstanian Cisurals and a new reconstruction of its tooth whorl position and function. Acta Zoologica, 90:171–182.
Mutter RJ and Neuman AG 2008a. New eugeneodontid sharks from the Lower Triassic Sulphur Mountain Formation of Western Canada. Geological Society, London, Special Publications 295:9–41.
Mutter RJ and Neuman AG 2008b. Jaws and dentition in an Early Triassic, 3-dimensionally preserved eugeneodontid skull (Chondrichthyes) Acta Geologica Polonica, 58 (2), 223-227.
Purdy RW 2008. The Orthodonty of *Helicoprion. *http://paleobiology.si.edu/helicoprion/
Zhang et al. 2015. Phosphorus sequestration in the form of phosphate by microbial symbionts in marine sponges. PNAS 112(14):4381–4386.

https://www.nationalgeographic.com/science/phenomena/2014/09/03/bizarre-prehistoric-ratfish-chomped-prey-with-buzzsaw-jaws/

Brian Switek writing in Wired.com 2011.

wiki/Helicoprion

SVP abstracts – Ornithocheirid hip range of motion (ROM)

Griffin et al. 2019 report on their study
of the Coloborhynchus (Figs. 3) pelvis during a hypothetical launch. We looked at this issue earlier here following publication of Witton and Habib 2010.

From the abstract:
“Pterosauria includes the largest animals to achieve powered flight. How medium to large-sized pterosaurs were able to launch into the air is a matter of debate.”

Oh, no. Not this invalid hypothesis again. Griffin et al. believe that giant azhdarchids could fly. They could not. Look how short their wings are compared to volant giant seabirds, pteranodontids and ornithocheirids (Fig. 1).

Figure 1. Click to enlarge. The largest flying and non-flying birds and pterosaurs to scale.

Figure 1. Click to enlarge. The largest flying and non-flying birds and pterosaurs to scale.

Griffin et al. continue:
“Birds employ their legs to accelerate their bodies into the air, but the difficulties large birds face in becoming airborne suggests take-off may limit the maximum size of birds. It has been suggested that pterosaurs employed their fore and hindlimbs in take-off, the so-called quadrupedal launch mechanism, overcoming the size constraint.”

That suggestion is not documented in the fossil record. Quad launch is not only dangerous, it is untenable and clearly inferior to using both the wings and legs to produce massive amounts of thrust as large volant birds do. Flightlessness in man-sized and smaller birds made possible flightless giant birds. The same was true for pterosaurs. All the giant pterosaurs had clipped wings (vestigial distal phalanges).

Unsuccessul Pteranodon wing launch based on Habib (2008).

Figure 2. Unsuccessul Pteranodon wing launch based on Habib (2008) in which the initial propulsion was not enough to permit wing unfolding and the first downstroke.

Griffin et al. continue
“Range of motion (ROM) studies are a common way of determining the viability of hypothetical poses in extinct animals. Here we use ROM mapping of the hip joint of a mid-sized pterosaur, Coloborhynchus (SMNK PAL 1133. Fig. 2) to test whether the joint surfaces of the acetabulum and femur were capable of achieving a bipedal and/or a quadrupedal stance during the range of motion required for take-off.” 

Figure 2. GIF animation showing stages in the bipedal take off of Coloborhynchus. Please imagine the wings talking their first mighty flap at the moment of takeoff, relieving the hind limbs from most of the stress.

Figure 3. GIF animation showing stages in the bipedal take off of Coloborhynchus. Please imagine the wings talking their first mighty flap at the moment of takeoff, relieving the hind limbs from most of the stress. In the invalid quadrupdal pose, note the proximal wing finger makes an impression, which never happens in pterosaur tracks.

Griffin et al. continue:
“Using the software programs Maya and MATLAB, possible intersections and orientations between different bones of the hip joint were identified and coded as viable or unviable. Osteological ROM mapping reveals a quadrupedal stance is more likely in launch, with maximum crouch during quadrupedal launch and flight positions being possible.”

See, they had a preconceived bias and did not comparatively test the bipedal configuration. Remember, in the bipedal pose the wings are ready to provide thrust BEFORE the legs launch the pterosaur into the air (Fig. 3). So the legs are not working alone. By contrast in the quad launch scenario, the wings are not unfolded, and not raised above the shoulders when the pterosaur is at the apogee of whatever feeble take-off abducting the antebrachium can provide (Fig. 2).

Figure 1. The as yet undescribed SMNS PAL 1136 specimen is much larger than comparable bones in the new specimen, MPSC R 1221.

Figure 4. The as yet undescribed SMNS PAL 1136 specimen is much larger than comparable bones in the new specimen, MPSC R 1221. This is a resting pose. When walking or preparing to flap the wings would have to rise off the substrate. This sort of giant-winged, small footed, volant creature rarely landed, IMHO.

Griffin et al. continue:
“However, it is important to consider not just osteological ROM but also the effects of soft tissues. ROM simulations can approximate the effect of different soft tissue such as ligamentous constraints and joint cartilage. We find that the required orientation for bipedal launch was not possible without the presence of cartilage. In order to achieve a bipedal stance in this specimen, a minimum of 3 mm of cartilage is required to sufficiently increase the ROM.”

3mm. That’s not very much, and well within the range of possibilities for a large pterosaur. I look forward to seeing their bipedal launch configuration. Having dealt with pterosaur workers cheating morphology to support their bias (e.g. Elgin, Hone and Frey 2011), I’m always suspicious  based on reputation and history.

“A ROM study that included ligaments in addition to cartilage reduced the available viable orientations. This ROM generated in this study does not rule out the possibility of a quadrupedal launch in pterosaurs, and provide greater support for the quadrupedal rather than the bipedal launch hypothesis.”

These authors mistakenly believe that pterosaurs were archosaurs. Testing reveals they are lepidosaurs (Peters 2007). Ligament issues need to based on lepidosaur pelves and hind limbs, not archosaur. Did the authors sprawl the femora, matching femoral head axis to pelvic socket axis? Having built several pterosaur skeletons, I can tell you, the bipedal stance works best. The ROM at the hips is the LEAST of their worries if they are trying to launch a pterosaur with ventrally folded wings.


References
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica 56 (1), 2011: 99-111. doi: 10.4202/app.2009.0145
Griffin BW et al. 2019.
Simulated range of motion mapping of different hip postures during launch of a medium-sized ornithocheirid pterosaur. Journal of Vertebrate Paleontology 2019.
Peters D 2007.The origin and radiation of the Pterosauria.Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27
Witton MP and Habib MB 2010. On the Size and Flight Diversity of Giant Pterosaurs, the Use of Birds as Pterosaur Analogues and Comments on Pterosaur Flightlessness. PLoS ONE 5(11): e13982. https://doi.org/10.1371/journal.pone.0013982

SVP abstracts – Silurian gnathostome

Zhu et a. 2019 bring us
a new Silurian fish they claim is close to the origin of jawed vertebrates (= Gnathostomata).

From the abstract:
“Modern jawed vertebrates or crown-group gnathostome include the last common ancestor of living bony and cartilaginous fishes and all its descendants. The gross morphology of the earliest modern jawed vertebrates, and how they arose from stem gnathostomes, were previously unknown due to a lack of articulated fossils.”

These taxa are not unknown in the large reptile tree (LRT, 1592 taxa). Put enough taxa in an analysis and one will end up close to the origin of gnathostomes. There will be a last common ancestor. In the LRT Thelodus, a ?jawless (phylogenetic bracketing indicates some sort of transverse jaws are present) Silurian fish is the current proximal outgroup to all tested taxa with jaws. In LRT the extant whale shark (Rhincodon), angel shark (Squatina) and horn shark (Heterodontus) are basal members of the Gnathostomata and the first taxa with primitive tooth carpets.

“The recent discovery of the Xiaoxiang Fauna from the Silurian of South China revolutionarily adds to the diversity of Silurian jawed vertebrates. However, considerable morphological gap is still present between stem- and crown-group gnathostomes.”

Not so, when appropriate taxa are included.

“Here, we report a new bony fish very close to the crown-group gnathostome node, also from the Xiaoxiang Fauna. The attributed specimens include a head, jaws and an articulated postcranial skeleton.”

“The new fish displays a unique suite of characters: the dermal pectoral girdle condition transitional between Entelognathus and osteichthyans, the braincase profile recalling the condition in Janusiscus and early chondrichthyans, and the premaxillae and lower jaw largely showing osteichthyan features. This mosaic character combination suggests the tentative phylogenetic position of this new taxa in the most basal segment of the osteichthyan stem, possibly forming a quintessential component of the evolutionary transition between placoderms and osteichthyans.”

In the LRT taxa between placoderms and osteichthyans are either acanthodians (spiny sharks) on one branch, or catfish (also with spiny fins) on the other branch. Catfish are whales-shark mimics with regard to their jaws and teeth, likely representing some sort of reversal to that basal condition.

“For the first time, we are able to look into a near-complete bony fish close to the last common ancestor of all the living jawed vertebrates, and reconstruct the acquisition sequence of osteichthyan characters based on a series of fossils in morphological proximity. The fact that most of these fossils are from the Silurian Xiaoxiang Fauna, suggests that this fauna is unprecedentedly close to the initial radiation of jawed vertebrates.” 

Figure 2. Updated subset of the LRT focusing on basal vertebrates (fish). Arrow points to Hybodus. This tree does not agree with previous fish tree topologies.

Figure 1. Updated subset of the LRT focusing on basal vertebrates (fish). Arrow points to Hybodus. This tree does not agree with previous fish tree topologies. Check out the LRT for a slightly updated version of this cladogram.

This is all very interesting, and welcome, but let them look at the structure of Rhincodon as it relates to Thelodus at least once before settling down with the Zhu et al. hypothesis.

Figure 4. Manta compared to Thelodus and Rhincodon. All three have a terminal mouth essentially straight across, between the lateral eyes.

Figure 4. Manta compared to Thelodus and Rhincodon. All three have a terminal mouth essentially straight across, between the lateral eyes.


References
Zhu et al. 2019. A new Silurian bony fish close to the common ancestor of crown gnathostomes.

SVP abstracts – Are meiolaniform turtles stem turtles?

Kear et al. 2019 talk about
‘stem’ turtles with skull horns and club tails: the meiolaniforms.

From the abstract:
“Meiolaniforms (Meiolaniformes) are an enigmatic radiation of stem turtles with an exceptionally protracted 100 million-year evolutionary record that spans the mid-Cretaceous (Aptian–Albian) to Holocene. Their fossils have been documented for over 130 years, with the most famous examples being the derived Australasian and southern South American meiolaniids – bizarre horned turtles with massive domed shells and tail clubs that are thought to have been terrestrial and probably herbivorous.”

In the large reptile tree (LRT, 1592 taxa, subset Fig. 2) meiolaniforms (Fig. 1) are not enigmatic. They are basalmost hard-shell turtles derived from similarly-horned Elginia-type small pareiasaurs in parallel with Sclerosaurus-type small pareiasaurs basal to soft-shell turtles.

Figure 2. Another gap is filled by nesting E. wuyongae between Bunostegos and Elginia at the base of hard shell turtles in the LRT.

Figure 2. Another gap is filled by nesting E. wuyongae between Bunostegos and Elginia at the base of hard shell turtles in the LRT.

“Despite a long history of research, the phylogenetic affinities of meiolaniids have proven contentious because of ambiguous character state interpretations and incomplete fossils
representing the most ancient Cretaceous meiolaniform taxa.”

This problem is contentious only because of taxon exclusion. Prior workers have not included analyses of meiolaniforms and Elginia.

“Here, we therefore report the significant discovery of the stratigraphically oldest demonstrable meiolaniform remains, which were excavated from Hauterivian–Barremian high-paleolatitude (around 80°S) deposits of the Eumeralla Formation in Victoria, southeastern Australia. Synchrotron microtomographic imaging of multiple virtually complete skulls and shells provides a wealth of new data, which we combine with the most comprehensive meiolaniform dataset and Bayesian tip-dating to elucidate relationships, divergence timing and paleoecological diversity.”

Did the authors include Elginia, Sclerosaurus, Arganceras and Bunostegos? The abstract does not mention them.

“Our results reveal that meiolaniforms emerged as a discrete Austral Gondwanan lineage,
and basally branching sister group of crown turtles (Testudines) during the Jurassic.”

The LRT invalidated a monophyletic Testudines. Rather soft-shell and hard-shell turtles had separate parallel origins from within the small horned pareisaurs.

Figure 5. Subset of the LRT focusing on turtle origins and unrelated eunotosaurs.

Figure 5. Subset of the LRT focusing on turtle origins and unrelated eunotosaurs.

“We additionally recover a novel dichotomy within Meiolaniformes, which split into a unique Early Cretaceous trans-polar radiation incorporating apparently aquatic forms with flattened shells and vascularized bone microstructure, versus the larger-bodied terrestrial meiolaniids that persisted as Paleogene–Neogene relic species isolated in Patagonia and Australasia.”

That’s interesting. The LRT sort of separates the meiolaniform Niolama from the meiolaniform Meiolania + Proterochersis + Proganochelys. The latter taxon also has a club tail. Perhaps more meiolanforms would continue to nest with one or the other.

“Finally, our analyses resolve the paraphyletic stem of crown Testudines, which otherwise includes endemic clades of Jurassic–Cretaceous turtles distributed across the northern Laurasian landmasses. These had diverged from the Southern Hemisphere meiolaniforms by at least the Middle Jurassic, and thus parallel the vicariant biogeography of crown turtles, which likewise diversified globally in response to continental fragmentation and possibly climate.”

Outgroups are key to understanding turtle evolution in the LRT. So is taxon inclusion. Based on the dual origin of turtles from horned small pareiasaurs in the LRT, the list of stem turtles now includes pareiasaurs, if the concept of a monophyletic turtle still stands with a last common ancestor lacking a carapace and plastron within the pareiasaurs.


References
Kear BP et al. 2019. Cretaceous polar meiolaniform resolves stem turtle relationships. Journal of Vertebrate Paleontology abstracts.

SVP abstracts – Earliest avemetatarsalian?

Patellos et al. 2019 brings us
news of the earliest archosaur in the lineage of birds (rather than crocs).

Okay. That’s already wrong. In the large reptile tree (LRT, 1592 taxa) only crocs and dinos make up the Archosauria. Nesbitt et al. does not understand that hypothesis of interrelationships due to taxon exclusion and poor scoring going back to Nesbitt 2011. The purported clade, ‘Avemetatarsalia’ (= Ornithodira) was invalidated by the LRT.

From their abstract:
“Understanding of the evolution of the earliest avemetatarsalian (bird-line) archosaurs and the morphology of the hypothetical common ancestor of Archosauria is hampered by a poor fossil record.”
Incorrect. The common ancestor of Archosauria has been identified in the LRT as the PVL 4597 specimen wrongly attributed to Gracilisuchus. After that: Turfanosuchus (Fig. 1).
Figure 2. Skull of Turfanosuchus compared to Herrerasaurus, the basalmost dinosaur.

Figure 1. Skull of Turfanosuchus compared to Herrerasaurus, the basalmost dinosaur.

Patellos et al. 2019 continue:
“The earliest-diverging avemetatarsalians known, such as Teleocrater, are separated from the earliest diverging pseudosuchian (crocodylian-line) archosaurs, and the closest outgroups of Archosauria by a clear morphological gap.”
The LRT invalidates the traditional clade, ‘Pseudosuchia.’ Crocodylian-line archosaurs are Crocodylomorphs, distinct from bird-line archosaurs, dinosaurs. Remember, these authors consider the lepidosaurian pterosaurs to be closely related to dinosaurs, a theory with as much evidence as tail-dragging dinosaurs.
“Here we describe a potential early-diverging avemetatarsalian from the Middle Triassic (~ 230 Ma) “Basal Isalo II” beds of Madagascar, which appears to bridge these gaps. This new taxon is represented by a well-preserved partial skeleton including articulated cervical
vertebrae with articulated osteoderms; a scapulocoracoid; a partial femur; isolated trunk, sacral, and caudal vertebrae; and an ilium.”
“Noteworthy features of the neck region include: anteroposteriorly elongated vertebrae with laterally expanded dorsal ends of the neural spines, and an articulated set of osteoderms dorsal to the vertebrae. The cervical osteoderms, three pairs per vertebra, arranged in paramedian row, and bear tapering anterior processes.” 
“Potential synapomorphies of this specimen with avemetatarsalians include: femur with an incipient anterior trochanter, 1st sacral vertebra with a dorsoventrally expanded sacral rib, and ilium possessing a notch on the articulation surface with the ischium. This combination of features places the new taxon represented by this specimen at the base of Avemetatarsalia, outside aphanosaurs + dinosaurs, but this position is poorly supported.”
The best known members of the invalid Aphanosauria include Yarasuchus and Teleocrater (Fig. 2), taxa nested with a long line of non-Aphanosauria by the LRT between Rauisuchia and Archosauria.
Figure 3. Yarasuchus, Qianosuchus and Turfanosuchus nest together in Nesbitt et al. 2017 after rescoring.

Figure 2. Yarasuchus, Qianosuchus and Turfanosuchus nest together in Nesbitt et al. 2017 after rescoring.

Patellos et al. 2019 continue:
“More broadly, this new specimen indicates that cervical osteoderms were present in the earliest avemetatarsalians and were soon lost in the lineage.”
There’s no need for such phylogenetic gymnastics in the LRT.
“The generally plesiomorphic morphology of the new taxon also underscores the difficulty of identifying early avemetatarsalians from incomplete skeletons. Presence of an early diverging avemetatarsalian together with a lagerpetid and silesaurid in the “Basal Isalo II” beds of Madagascar documents the co-occurrence of multiple avemetatarsalian subgroups in Gondwana during the Triassic.”
They wish. The LRT resolves all such problems with high resolution. Blame S. Nesbitt for relying on his own poorly scored cladogram, inventing the ‘Aphanosauria’ and supporting the ‘Avemetatarsalia.’ Blame M. Benton for inventing the clade ‘Avemetatarsalia’.
Don’t trust those clades. Don’t trust the LRT. Run your own tests so you’ll know. In science this is the first, last and best option to resolve all such disagreements.

References
Patellos E et al. 2019. A new reptile from the ?Middle Triassic of Madagascar may represent the earliest-diverging avemetatarsalian (Archosauria). Journal of Vertebrate Paleontology abstracts.

SVP abstracts – Ambolestes and the origin of placentals

Bi S-D et al. 2019 discuss Early Cretaceous Ambolestes
(Figs. 1, 2) and the Early Mesozoic marsupial/placental split.

Figure 1. Ambolestes tracing from Bi et al. 2018.

Figure 1. Ambolestes tracing from Bi et al. 2018.

From the abstract:
“Extant placental and marsupial mammals are the dominant vertebrates in many ecosystems, which makes the placental-marsupial dichotomy a significant event in Earth’s history.”

The large reptile tree (LRT, 1592 taxa) splits placentals from marsupials as shown below (Figs. 3, 4). The Early Cretaceous marsupial Bishops splits from the placental outgroup taxon, the extant marsupial Caluromys (Fig. 6). More timely, derived placental multituberculates, like Megaconus (Fig. 5), have been found in Middle Jurassic strata. That means a long line of undiscovered small, arboreal, placentals extends back to the Late Triassic/Earliest Jurassic.

Figure 3. Ambolestes skull reconstructed. Jaw tips restored.

Figure 2. Ambolestes skull reconstructed. Jaw tips restored.

Bi et al. continue:
“Molecular estimates of the divergence of placentals and marsupials (and their broader clades Eutheria and Metatheria) fall primarily in the Jurassic.”

Since Early Jurassic Megazostrodon is the proximal outgroup for all mammals, and Early Triassic Morganucodon is a marsupial, and Middle Jurassic Megaconus the LRT supports a Late Triassic split for placentals and marsupials.

Figure 1. Select basal cynodonts and mammals set chronologically. The divergence times for placentals (Eutheria), marsupials (Metatheria) and monotremes (Mammalia) are estimated here.

Figure 3. Select basal cynodonts and mammals set chronologically. The divergence times for placentals (Eutheria), marsupials (Metatheria) and monotremes (Mammalia) are estimated here. Note the large gaps of time in which fossils are not known.

Bi et al. continue:
“In support, the oldest purported eutherian, Juramaia, is reported to be from the early Late Jurassic (160 million-years ago) of Liaoning Province, northeastern China.”

In the LRT (subset Fig. 1) Juramaia nests as a basal prototherian, an egg laying basal mammal.

“The oldest purported metatherian, Sinodelphys, is 35 million-years younger from the
Early Cretaceous Jehol Biota also in Liaoning Province, northeastern China.”

In the LRT Sinodelphys is another monotreme.

“In 2018, we reported a new eutherian, Ambolestes zhoui, also from the Jehol Biota. The fossil, a nearly complete skeleton, preserves anatomical detail unknown from contemporaneous eutherians including the hyoid apparatus and ectotympanic. The complete hyoid is the first known for any Mesozoic mammaliaform, and the ectotympanic resembles that in some extant didelphid marsupials.”

In the LRT (Fig. 1) Ambolestes (Figs. 3, 4) is a metathere/marsupial close to the extant Virginia opossum, Didelphis.

Figure 1. Subset of the LRT focusing on the Kynodontia and Mammalia. Non-eutherian taxa in red were tested in the LRT but not included because they reduce resolution. Eutherian taxa in red include a basal pangolin and derived xenarthran, clades that extend beyond the bottom of this graphic. The pink clade proximal to mammals was considered mammalian by Lautenschlager et al. due to a convergent mammalian-type jaw joint.

Figure 4. Subset of the LRT focusing on the Kynodontia and Mammalia. Non-eutherian taxa in red were tested in the LRT but not included because they reduce resolution. Eutherian taxa in red include a basal pangolin and derived xenarthran, clades that extend beyond the bottom of this graphic. The pink clade proximal to mammals was considered mammalian by Lautenschlager et al. due to a convergent mammalian-type jaw joint.

Bi et al. continue:
“In our phylogenetic analysis concentrating on the eutherian-metatherian 
dichotomy, the closest relative of Ambolestes was Sinodelphys, and both fell within Eutheria.”

As shown above, the LRT does not confirm that hypothesis of interrelationships.

Figure 1. Subset of the LRT focusing on Glires and subclades within.

Figure 5. Subset of the LRT focusing on Glires and subclades within.

Bi et al. continue:
“With Sinodelphys as a eutherian, postcranial differences formerly thought to indicate different invasions of a scansorial niche by meta and eutherians in Jehol are only variations among the early members of the placental lineage. Additionally, the earliest known metatherians are approximately 15 million years younger than previously thought and their

fossils, isolated teeth and fragmentary jaws, are from North America. Our tree results in a 50 million-year ghost lineage for Metatheria, accepting the 160 million-years age for Juramaia. 

The LRT confirms a 210 mya origin for Metatheria, starting with Morganucodon, so no ghost is necessary.

Figure 8. Caluromys, the largest of the mouse opossums, to scale with its LRT sister, Vulpavus, a basal member of Carnivora.

Figure 6. Caluromys, the largest of the mouse opossums, to scale with its LRT sister, Vulpavus, a basal member of Carnivora and Placentalia.

Bi et al. continue:
“A possibility raised elsewhere is that the age of Juramaia is incorrect; rather than Late Jurassic, perhaps it is from the Early Cretaceous Jehol Biota. In our study, Juramaia is in a clade with Albian/Aptian Prokennalestes and Late Cretaceous eutherians by having a more molariform ultimate upper premolar. In contrast, Ambolestes, as in the outgroups, has a non-molariform ultimate upper premolar. Although resolution of this intriguing debate is not currently possible, our understanding of the issues has been furthered by the discovery of Ambolestes.”

As shown above, the LRT does not confirm the Bi et al. hypothesis of interrelationships.


References
Bi S-D et al. 2019. The Early Cretaceous eutherian Ambolestes and its implications for the Eutherian/Metatherian dichotomy. Journal of Vertebrate Paleontology abstracts.

SVP abstracts – Perleidus joins the LRT

Argyriou and Romano 2019
study an Early Triassic fish, Perleidus woodwardi (Fig. 1).

Figure 1. Perleidus woodwardi in situ and with skull reconstructed.

Figure 1. Perleidus woodwardi in situ and with skull reconstructed. The new reconstruction differs from the traditional one in Gregory 1938.

From the abstract:
“Despite decades of research, the deep-time origins and ancestral morphologies of crown actinopterygian evolutionary lineages remain obscure, with the membership of late Paleozoic-Triassic taxa being particularly fluid with respect to the actinopterygian crown group. Lack of data on the endoskeleton of important fossil groups, and a disjunction among phylogenetic matrices aimed at resolving different branches of the actinopterygian tree of life, are the major causes of this gap of knowledge.”

The large reptile tree (LRT, 1592 taxa) solved this problem over the last few months by including more taxa than in prior studies without much data from the endoskeleton of fish.

The abstract continues:
“The Triassic ‘perleidids’ have been historically viewed as early members of Neopterygii, the most successful group of modern actinopterygians.”

That is confirmed in the LRT.

“Yet, recent research has cast  doubts not only on their evolutionary affinities, but also their monophyly, though no stable phylogenetic alternatives have been provided. Based on previously undescribed material in museum collections in Paris and Zurich, we reappraise ‘Perleidus’ woodwardi, from the early Olenekian (Early Triassic) of Spitsbergen. Exquisitely preserved exoskeletons provide novel data on the osseus constituents of the ethmoid region, and the anatomy of the tail fin, which is now shown to lack obvious epaxial rays. In addition, using μCT, we studied a recently collected, three-dimensionally preserved cranium and pectoral girdle, which revealed a wealth of phylogenetically important information.”

“The braincase and endocast of ‘P’. woodwardi broadly resemble those of Australosomus, with the presence of a posteriorly elongate parasphenoid in the former being a notable difference between the two.” 

Australosomus is another Early Triassic ray-fin fish. The rest of the abstract provides various skeletal traits of interest without making additional comparisons.

Figure 3. Pholidophorus in situ and two skulls attributed to this genus. Perleidus (Fig. 1) nests between this Triassic fish and the bronze featherback, Notopterus (Fig. 3).

Figure 3. Pholidophorus in situ and two skulls attributed to this genus. Perleidus (Fig. 1) nests between this Triassic fish and the bronze featherback, Notopterus (Fig. 3).

In the LRT
Perleidus nests between the tuna-like Triassic ray-fin, Pholidophorus (Fig. 2) and the derived extant bronze featherback, Notopterus, taxa not mentioned in the Arygriou and Romano abstract.

Figure 3. Perleidus shares many traits with the extant knife fish, Notopterus, a taxon not mentioned in the abstract.

Figure 3. Perleidus shares many traits with the extant bronze featherback, Notopterus, a taxon not mentioned in the abstract.

Earlier
the LRT was able to nest Pholidophorus with the distinctively different NotopterusPerleidus provides the perfect transitional taxon. In fact, it is so midway between the two sister taxa that there is complete loss of resolution between the three.


References
Arygriou T and Romano C 2019. New fins or old fins? Skull and pectoral girdle of Early Triassic ‘Perleidus’ woodwardi revisited using µCT. Journal of Vertebrate Paleontology abstract.