Did the turtle nuchal evolve from cleithra?

Lyson et al.  2013
propose a homology of the turtle nuchal (central anterior roof-like bone of the carapace) with the primitive cleithra (singular: cleithrum, slender, stem-like bone anterior to the scapula). In order to do so, they produced a set of turtle ancestors (or engineering models) that is not validated by the large reptile tree (LRT, 1395 taxa).

Frogs, lepidosaurs, diadectids and para-caseasaurs,
according to Lyson et al., model the ancestry of turtle shoulders and shells (Fig. 1).

Figure 1. On the left, from Lyson et al. 2013 with graphics added. On the right taxa basal to turtles according to the LRT.

Figure 1. On the left, from Lyson et al. 2013 with graphics added. On the right taxa basal to turtles according to the LRT. The right sequence documents a more gradual accumulation of traits. Even so, the gap between Bunostegos and Meiolania includes the complete development of the carapace and plastron… but almost everything else was present. A skull-only taxon, Elginia, nests between the two.

By contrast,
in the LRT Milleretta, is basal to Stephanospondylus, which is basal to diadectids on one branch and pareiasaurs, like Bunostegos, and the basal turtle Meiolania, on the other, documenting a more gradual accumulation of traits without introducing frogs and lepidosaurs. In the LRT, the gap between Bunostegos and Meiolania includes the unchronicled development of the carapace and plastron. Given that issue, almost everything else was present in the skeleton. A skull-only taxon, Elginia (not shown in Fig. 1), nests between the two. There is an online paper on turtle ancestors here.

Taxon exclusion is once again the problem.
Since Lyson et al. used inappropriate and unrelated taxa to demonstrate their hypothesis, it was invalid from the get-go. To my knowledge (let me know if I am wrong):

  1. No one recently suggested that frogs, like Rana, are basal to turtles.
  2. No one recently suggested that Diadectes is basal to turtles.
  3. No one recently suggested that Sphenodon is basal to turtles.
  4. Several authors (many from the Lyson et al. list) have suggested that Eunotosaurus was basal to turtles, but they did not test the above-listed LRT competing candidates when they published.

From Wikipedia Diadectidae
“Paleontologist E.C. Case compared diadectids to turtles in 1907, noting their large pectoral girdles, short, strong limbs, and robust skulls. Case described them as “lowly, sluggish, inoffensive herbivorous reptiles, clad in an armor of plate to protect them from the fiercely carnivorous pelycosaurs.”

The better method
for figuring out anything about turtles is to employ the valid ancestors of turtles, validated by testing against all other published candidates. I know, from testing, that all other candidates, like Eunotosaurus, nest far from turtles.

Getting back to our headline
and the title of the Lyson et al. paper, the genesis of the turtle carapace in hard-shell turtles is not preserved in the fossil record at present. Even so, the rarely preserved cleithrum gives little to no indication that it evolved into an anterior carapace bone… at present. Some day it may.

Lyson et al. note:
“unlike the other midline carapacial elements, the nuchal develops from paired mesenchymal condensations each of which contains a separate ossification center… first observed by Vallén (1942) and led him to conclude the nuchal was homologous with the supracleithra.”

The supracleithrum
by definition, “is a bone of the pectoral girdle situated dorsal to the cleithrum in some fishes and amphibians.”  That definition does not include reptiles.

If we look for a pre-nuchal in pareiasaurs
it is easy to find parasagittal osteoderms (Fig 2). Lyson et al. do not mention the word ‘pareiasaur’ in their paper.

Figure 2. The pareiasaur, Deltavjatia, with osteoderms in orange. Note the anterior set is simple and paired.

Figure 2. The pareiasaur, Deltavjatia, with osteoderms in orange. Note the anterior set is simple and paired, as hoped for by Lyson et al. but not found, except in turtle embryos, by Lyson et al.

Taxon exclusion can ruin a paper.
You can talk about thousands of characters for Eunotosaurus, but if you don’t include one pareiasaur, you’ll in the wrong ballpark on game day. Deltavjatia (Fig. 2) does not preserve a cleithrum. Rather, given its close, but not direct relation to turtles, the turtle nuchal likely arises from the osteoderms that are in place in Deltavjatia. They are the right size, in the correct orientation, and used for the same reason. So the nuchal probably arose from the foremost osteoderms on the torso, while those on the neck became neck armor. Remember, early turtles could not withdraw their neck.

It’s probably worthwhile to remind you of other body parts
that evolve in the ancestry of turtles until they become turtle traits at this time.

Figure 6. Turtle pelvis evolution. Here are the changes in the pelvis of pre-turtles and basal hard-shelled turtles.

Figure 3. Turtle pelvis evolution. Here are the changes in the pelvis of pre-turtles and basal hard-shelled turtles.

Take the turtle pelvis, for instance.
Similar precursors can be seen in stem turtle pareiasaurs (Fig. 3). And the skull is interesting. Workers have discussed Elginia with pareiasaurs and Meiolania with turtles, but never Meiolania with pareiasaurs or Elginia with turtles. That you heard here first in a three-part series five years ago.

Figure 2. Hard shell turtle evolution featuring Bunostegos, Elgenia, Meiolania and Proganochelys - NOT to scale.

Figure 4. Hard shell turtle evolution featuring the skulls of  Bunostegos, Elgenia, Meiolania and Proganochelys – NOT to scale. Note the long list of shared traits, longer than in any competing candidate.

If you know one of the seven authors
of Lyson et al. 2013, please make sure they become aware of this critique. A few of them are among those who rejected the submitted manuscript on the origin of turtles. Evidently they prefer the invalid status quo rather than this novel hypothesis for turtle origins.

References
Case EC 1907. Restoration of Diadectes. The Journal of Geology. 15 (6): 556–559.
Lyson TR, Bhullar B-AS, Bever GS, Joyce WG, de Queiroz K, Abzhanov A and Gauthier JA 2013. Homology of the enigmatic nuchal bone reveals novel reorganization of the shoulder girdle in the evolution of the turtle shell. Evolution & Development 15(5):317–325. DOI: 10.1111/ede.12041
Vallén E 1942. Beiträge zur Kenntnis der Ontogenie und der vergleichenden. Anatomie des Schildkrötenpanzers. Acta Zool. Stockholm 23: 1–127.

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Excellent YouTube Video on Mosasaurs

This one features paleoartist, Brian Engh
working with the Mike Triebold’s fossil company (Triebold Paleontology, Inc).

Sadly
Triebold’s Pteranodons are leaping on their forelimbs and their Jeholopterus has giant scleral rings (eyes) in the antorbitral fenestra. Both were based on my originals, which did not have these invalid modifications. Those are market forces at work, veering away from evidence.

References
DontMessWithDinosaurs.com
TrieboldPaleontology.com

Taxon exclusion mars Mesozoic mammal study

King and Beck 2019
bring us a new phylogenetic analysis restricted to Mesozoic mammals. This represents a massive case of taxon exclusion of basal mammals as demonstrated earlier here, because so many basal mammals are still alive! Think of all the tree shrews, arboreal didelphids, and nearly every little creeping taxon in Glires that nest basal to known Mesozoic mammals. You cannot restrict the taxon list to just those extremely rare Mesozoic mammals.

On the plus side,
King and Beck confirm earlier tree topologies recovered by the large reptile tree (LRT, 1394 taxa) that nest haramiyidans apart from euharamiyidans when they reported, “Tip-dating applied to Mesozoic mammals firmly rejects a monophyletic Allotheria, and strongly supports diphyly of haramiyidans, with the late Triassic Haramiyavia and Thomasia forming a clade with tritylodontids, which is distant from the middle Jurassic euharamiyidans.”

Taxon exclusion
made the authors nest Vintana with euharamiyidans rather than the wombats recovered by the LRT. Other than Vintana, no wombats were included in the King and Beck study—because they are alive. Furthermore, no rodents and aye-ayes were included—because they are alive. So, sans living taxa, King and Beck’s cladogram had no idea where to nest euharamiyidans in the mammal family tree. The wide gamut taxon list of the LRT solves most problems that arise from restricted studies like the King and Beck study.

Figure 4. Mesozoic euthrerians (placentals, in black). Later taxa in light gray. All taxa more primitive than Mesozoic taxa were likely also present in the Jurassic and Cretaceous. None appear after Onychodectes. Madagascar separated from Africa 165-135 mya, deep into the Cretaceous with a population of tenrecs attached. No rafting was necessary. 

Figure 1. Mesozoic euthrerians (placentals, in black). Later taxa in light gray. All taxa more primitive than Mesozoic taxa were likely also present in the Jurassic and Cretaceous. None appear after Onychodectes. Look at all the taxa King and Beck could have added to their analysis!  …and we’re not even looking at the Metatheria and Prototheria here.

More on Mesozoic mammals
here.

References
King B and Beck R 2019. Bayesian Tip-dated Phylogenetics: Topological Effects,
2 Stratigraphic Fit and the Early Evolution of Mammals. PeerJ
doi: http://dx.doi.org/10.1101/533885.

What is Gracilisuchus? Add more taxa to find out.

We first and last looked at Gracilisuchus (Romer 1872)
a few years ago here and here. According to a recent paper by Lecuona et al. 2017, six specimens have been attributed to Gracilisuchus (Fig. 1). However, of three tested, only two are congeneric in the large reptile tree (LRT, 1394 taxa, subset Fig. 6), where all three Gracilisuchus specimens nest at or close to the base of the Archosauria (crocs + dinos only). However, that’s not how Lecuouna et al. see it (Figs. 3–5), based on Nesbitt 2011.

Figure 1. The ancestry of Scleromochlus going back to Lewisuchus, Saltoposuchus, Terrestrisuchus, SMNS 12591 and Gracilisuchus.

Figure 1. The ancestry of Scleromochlus going back to Lewisuchus, Saltoposuchus, Terrestrisuchus, SMNS 12591 and Gracilisuchus.

Key to the present discussion
is figuring out what is and is not an archosaur.

Definition
‘Archosauria’ is defined as crocs + birds, their last common ancestor and all descendants. The archosaur taxon list in Lecuona et al. (Fig. 3) is much broader than in the LRT (Fig. 6), where the clade Archosauria is restricted to just crocs + dinos. The last common ancestor of all known archosaurs in the LRT is one of the specimens Lecuona et al. assigned to Gracilisuchus, PVL 4597 (Fig. 2.

Inappropriate taxon inclusion
Lecuona et al. mistakenly recover pterosaurs with archosaurs. That’s because Lecuona et al. do not include the tested, but ignored pterosaur sisters in the clade Fenestrasauria. Pterosaurs are lepidosaurs, as their elongate wing fingers (digit 4) tell us. All archosaurs have a relatively small finger 4 and Scleromochlus (Fig. 1), a putative pterosauromorph (according to Benton 1999, Lecuona et al. 2017, and many others), has tiny hands! So Scleromochlus is not the taxon you want to nest with pterosaurs (contra Benton 1999). Inappropriate taxon inclusion and omission makes current archosaur cladograms not only fictional, but verging on ridiculous. No one, it seems, is checking their results.

Figure 2. The origin of dinosaurs to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.

Figure 2. The origin of dinosaurs to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Trialestes, Herrerasaurus, Tawa and Eoraptor.

The Lecuona et al. 2017 cladograms
(Figs, 3–5) suffer from taxon exclusion and inappropriate taxon inclusion.

Figure 3. This is Figure 19 from Lecuona et al. 2017. All taxa are archosaurs in the Lecuona et al. cladogram. Red taxa are not archosaurs in the LRT.

Figure 3. From Lecuona et al. 2017. Red taxa are not archosaurs in the LRT (subset figure 6).

The Lecuona et al cladogram of archosaurs
(Fig. 3) includes several taxa and clades that are not archosaurs in the LRT. Note how Lecuona et al. split pterosaurs from ornithosuchids at the base of the Archosauria. These two clades share very few traits, as everyone knows.

Figure 4. Figure 17 from Lecuona et al. 2017 with colors added to taxa that are not eu-archosauriforms in the LRT.

Figure 4. Figure 17 from Lecuona et al. 2017 listing archosauriformes from Nesbitt 2011. Colors added archosaurs (green(, pararchosauriforms (yellow), and non-archosauriformes (red).

It only gets worse for Lecuona et al.
(Fig. 4) when they add phytosaurs, nesting as the last common ancestors of pterosaurs, dinosaurs and ornithosuchids. In the LRT these four clades are not closely related to one another. One wonders how Nesbitt 2011 and Lecuona et al. 2017 were able to get their work published with such results.

Figure 5. Figure 18 from Lecuona et al. 2017 with colors and reconstructions added. Here the giant, derived CM 73373 specimen nests basal to Hesperosuchus and taxa leading to Crocodiliformes. The LRT (subset Fig. 6) does not recover this topology.

Figure 5. Figure 18 from Lecuona et al. 2017 with colors and reconstructions added. Here the giant, derived CM 73373 specimen nests basal to Hesperosuchus and taxa leading to Crocodiliformes. The LRT (subset Fig. 6) does not recover this topology and finds that bipedal locomotion developed convergently in these two taxa.

Above is the Lecuona et al. cladogram
(Fig. 5) that encouraged study of the CM 73372 specimen we looked at yesterday. In the Lecuona et al. cladogram CM 73372 and tiny Hesperosuchus are sisters. In the LRT (Fig. 6) the two are not related to one another despite their many convergent traits, including a bipedal stance and short fingers.

In the LRT
(Fig. 6) two specimens of Gracilisuchus nests with similarly sized and shaped, Saltopus and Scleromochlus. That clade was derived from similar Lewisuchus and these are sisters to the Junggarsuchus clade, which also includes bipedal Pseudhesperosuchus. Hesperosuchus nests in the middle of the Crocodylomorpha (Fig. 6), not at the base. We looked at taxon exclusion in the Crocodylomorpha recently here.

FIgure 1. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

FIgure 6. Subset of the LRT focusing on the Crocodylomorpha, dorsal scutes, elongate proximal carpals, bipedality and clades.

You’ll know a good cladogram
when enough candidate taxa are included that all sister taxa actually resemble one another, producing a gradual accumulation of derived traits. This is how evolution works, so this process should be accurately reflected in cladograms. If they don’t: add more taxa until they do.

References
Benton MJ and Clark JM 1988. Archosaur phylogeny and the relationships of the Crocodilia in MJ Benton (ed.), The Phylogeny and Classification of the Tetrapods 1: 295-338. Oxford, The Systematics Association.
Brinkman D 1981. The origin of the crocodiloid tarsi and the interrelationships of thecodontian archosaurs. Breviora 464: 1–23.
Butler RJ, Sullivan C, Ezcurra MD, Liu J, Lecuona A and Sookias RB (2014. New clade of enigmatic early archosaurs yields insights into early pseudosuchian phylogeny and
the biogeography of the archosaur radiation. BMC Evolutionary Biology 14:1-16.
Juul L 1994. The phylogeny of basal archosaurs. Palaeontographica africana 1994: 1-38.
Lecuona A and Desojo, JB 2011. Hind limb osteology of Gracilisuchus stipanicicorum (Archosauria: Pseudosuchia). Earth and Environmental Science Transactions of the Royal Society of Edinburgh 102 (2): 105–128.
Lecuona A, Desojo JB and Pol D 2017. New information on the postcranial skeleton of
Gracilisuchus stipanicicorum (Archosauria: Suchia) and reappraisal of its phylogenetic position. Zoological Journal of the Linnean Society, 2017, XX, 1–40.
Parrish JM 1993. Phylogeny of the Crocodylotarsi, with reference to archosaurian and crurotarsan monophyly. Journal of Vertebrate Paleontology 13(3):287-308.
Romer AS 1972. The Chañares (Argentina) Triassic reptile fauna. An early ornithosuchid pseudosuchian, Gracilisuchus stipanicicorum, gen. et sp. nov. Breviora 389:1-24.

wiki/Gracilisuchus

CM 73372 reconstructed

So far as I know,
Carnegie Museum specimen CM 73372 (Fig. 1) does not yet have a name, nor has it been reconstructed. Weinbaum 2013 included this skull-less image in a Postosuchus study, which makes sense at first sight, given the size, proportions and age (Late Triassic) of both specimens. The large reptile tree (LRT, 1394 taxa) nests CM73372 close to Postosuchus, but closer to Teratosaurus and Smok. Since Teratosaurus is known from skull-only data at present, there is loss of resolution at that node.

Figure 1. CM73372 in situ and reconstructed using DGS methodology. At first glance it seems to be a biped with short fingers, like Postosuchus. In situ image from Weinbaum 2013.

Figure 1. CM73372 in situ and reconstructed using DGS methodology. At first glance it seems to be a biped with short fingers, like Postosuchus. In situ image from Weinbaum 2013.

This is an interesting taxon because
Lucuona et al. 2017 and others nest it basal to Crocodylomorpha. Weinbaum considered it a member of the Archosauria and the Paracrocodylomorpha, a clade the large reptile tree (LRT, 1394 taxa) does not recover.

According to Wikipedia
Loricata was an early name for an order that includes crocodilesalligators, and gharials, although the order is now referred to as Crocodylia. Nesbitt 2011 defined it as the most inclusive clade containing Crocodylus niloticus (the Nile crocodile), but not the extinct Poposaurus gracilisOrnithosuchus longidens, or Aetosaurus ferox. In the LRT, that clade is a junior synonym for Crocodylomorpha, since Poposaurus is a member of the proximal outgroup, the Poposauria. In traditional paleontology Loricata includes Rauisuchia and Crocodylomorpha. If so, then it also includes Poposauria and Dinosauria, but that was not the original intention of this definition.

Paracrocodylomorpha is another clade invalidated by the LRT because it includes Poposauria and Loricata. In the LRT Rauisuchia is the basal clade, followed roughly by Poposauria and Archosauria (crocs + dinos only).

You might recall,
the Nesbitt 2011 cladogram finds phytosaurs arising from a sister to the distinctly different Euparkeria. Taxon exclusion is the problem here. Nesbitt 2011 also finds Ornithosuchia (Ornithosuchus and kin) and Pterosauria forming the first dichotomy arising from a basal sister to Phytosauria. Again taxon exclusion is the problem here, yet widely accepted in the paleo community for reasons unknown (except, possibly ease of use and fear of change). We talked about other odd and topsy-turvy sister taxa recovered by Nesbitt 2011 earlier here, here and here, three blog posts in a nine-part series.

This addition of CM73372 to the LRT sets us up
for tomorrow’s discussion on basal archosaurs.

References
Lecuona A, Desojo JB and Pol D 2017. New information on the postcranial skeleton of Gracilisuchus stipanicicorum (Archosauria: Suchia) and reappraisal of its phylogenetic position. Zoological Journal of the Linnean Society, 2017, XX, 1–40.
Weinbaum J 2013. Postcranial skeleton of Postosuchus kirkpatricki (Archosauria:
Paracrocodylomorpha), from the Upper Triassic of the United States. Geological Society London Special Publications · August 2013.

wiki/Paracrocodylomorpha
wiki/Loricata

Preondactylus skeleton model on a tree

Rummaging through my file cabinets,
I ran across some Polaroid photos of a wire and putty model of Preondactylus (Figs. 1, 2) I made decades ago and mounted to a backyard branch. Note the sprawling femora, a lepidosaur trait.

Figure 1. Years ago, back in the days of Polaroid cameras, I built this to scale model of Preondactylus, mounted it on a tree branch and took its picture.

Figure 1. Years ago, back in the days of Polaroid cameras, I built this to scale model of Preondactylus, mounted it on a tree branch and took its picture.

Preondactylus bufarinii (Wild 1984, Dalla Vecchia 1998; Norian, Late Triassic, ~205 mya) was considered by Unwin (2003) to be the most basal pterosaur. It is not. Derived from a sister to the Italian specimen of AustriadactylusPreondactylus phylogenetically preceded Dimorphodon. Distinct from Austriadactylus, the skull of Preondactylus was lower and narrower with a larger antorbital fenestra completely posterior to the naris. The cervicals were shorter, the caudals more robust. The scapula and coracoid were more robust and straighter. The sternum was much larger. The humerus was anteriorly concave. The ulna and radius were shorter. The pelvis and pes were relatively longer. Pedal digit IV was shorter and V was longer. The metatarsals were longer than the pedal digits and IV was shorter than III.

Figure 2. At the time I thought I would use this photo of Preondactylus for a basis for an illustration with all the problems of perspective worked out.

Figure 2. At the time I thought I would use this photo of Preondactylus for a basis for an illustration with all the problems of perspective worked out. This is literally a ventral view.

Contra traditional pterosaur paleontologists,
who readily admit they have no idea which taxa are proximal outgroups to Pterosauria, basal pterosaurs, like Late Triassic Preondactylus and their fenestrasaur ancestors, were bipedal. Even so they continued to use their long, sharp-clawed free fingers to cling to trees like this (Figs. 1, 2).

Note the digitigrade pedes in this basal pterosaur,
distinct from the flat-footed beachcombers that made most of the tracks. By the way, we have tracks of digitigrade anurognathid pterosaurs (Peters 2011) derived from digitigrade dimorphodontids, like Preondactylus.

Earlier
here, here and here we looked at other ways pterosaurs could stand on and hold on to tree branches. Two of the many ways we know pterosaurs are lepidosaurs are the elongate manual digit 1 and the elongate pedal digit 5, neither of which appear in archosaurs, both of which appear in tritosaur lepidosaurs.

References
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos, 7: 11-41.
Peters  D 2000b. A redescription of four prolacertiform genera and implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106: 293-336
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist.
Historical Biology 15: 277-301.
Peters D 2007. The origin and radiation of the Pterosauria. Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27.
Peters D 2011. A catalog of pterosaur pedes for trackmaker identification.
Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605
Wild R 1984. A new pterosaur (Reptilia, Pterosauria) from the Upper Triassic (Norian) of Friuli, Italy, Gortiana — Atti Museo Friuliano di Storia Naturale 5:45-62.

wiki/Preondactylus

The microsaur, Llistrofus, enters the LRT

Llistrofus (Carroll and Gaskill 1978; Gee et al. 2019, Fig. 1) nests with Tuditanus in the large reptile tree (LRT, 1391 taxa), just like it does in the Huttenlocker et al. 2013 analysis (Fig. 2) employed by Gee et all.

Figure 1. Llistrofus is very much like Tuditanus, but with such reduced squamosals that a lateral temporal fenestra appears.

Figure 1. Llistrofus is very much like Tuditanus, but with such reduced squamosals that a lateral temporal fenestra appears. Images from Gee et al. 2019.

The problem comes from taxon exclusion
(as usual). In the rest of the Huttenlocker et al. 2009 cladogram (Fig. 2), which Gee et al. 2019 cited as their source for nesting Llistrofus. In the Huttenlocker cladogram there is so much taxon exclusion that the Lepospondyli splits into two clades (maybe three if you count the Eryops incursion).

Figure 2. Cladogram of basal tetrapods from Huttenlocker et al. 2009 with colors added.

Figure 2. Cladogram of basal tetrapods from Huttenlocker et al. 2009 with colors added.

Another problem comes from taxon INCLUSION,
because the unrelated reptile, Limnoscelis, is included.

References
Bolt JR and Rieppel O 2015. The holotype skull of Llistrofus pricei Carroll and Gaskill, 1978 (Microsauria: Hapsidopareiontidae). Journal of Paleontology 83(3):471–483.
Carroll RL and Baird D 1968. The Carboniferous amphibian Tuditanus (Eosauravus) and the distinction between microsaurs and reptiles. American Museum novitates 2337: 1-50.
Carroll RL and Gaskill P 1978. The order Microsauria. Memoirs of the American Philosophical Society 126:1–211.
Gee BM, Bevitt JJ, Garbe U and Reisz 2019. New material of the ‘microsaur’ Llistrofus from the cave deposits of Richards Spur, Oklahoma and the paleoecology of the Hapsidopareiidae. PeerJ 7:e6327 DOI 10.7717/peerj.6327

wiki/Tuditanus
wiki/Llistrofus