Tail breakage (caudal autotomy) in captorhinids

It is rare to find a fossil lepidosauromorph with a long complete tail.
Maybe there’s a reason for that.

LeBlanc et al. 2018 report in their abstract:
“Many lizards can drop a portion of their tail in response to an attack by a predator, a behaviour known as caudal autotomy. The capacity for intravertebral autotomy among modern reptiles suggests that it evolved in the lepidosaur branch of reptilian evolution, because no such vertebral features are known in turtles or crocodilians. Here we present the first detailed evidence of the oldest known case of caudal autotomy, found only among members of the Early Permian captorhinids, a group of ancient reptiles that diversified extensively and gained a near global distribution before the end-Permian mass extinction event of the Palaeozoic. Histological and SEM evidence show that these early reptiles were the first amniotes that could autotomize their tails, likely as an anti-predatory behaviour. As in modern iguanid lizards, smaller captorhinids were able to drop their tails as juveniles, presumably as a mechanism to evade a predator, whereas larger individuals may have gradually lost this ability. Caudal autotomy in captorhinid reptiles highlights the antiquity of this anti-predator behaviour in a small member of a terrestrial community composed predominantly of larger amphibian and synapsid predators.”

Figure 1. Eocaptorhinus apparently was able to drop its tail to confuse and evade a predator. Is this why the tail tip is missing in this specimen from 1979? The tail is certainly narrow!

Other candidates for caudal autotomy
In the large reptile tree (LRT, 1172 taxa) captorhinids are near the base of the Lepidosauromorpha branch of the Reptilia. Phylogenetic bracketing suggests one may find more examples of caudal autotomy and fracture planes between them. These include:

1. Eunotosaurus
2. Orobates
3. Limnoscelis
4. Bolosaurids like Bolosaurus
5. Diadectids like Diadectes
6. Procolophonids like Procolophon
7. Macroleterids like Macroleter
8. Owenettids like Owenetta
9. Basal lepidosauriformes like Jesairosaurus and Saurosternon
10. Basal sphenodontids like Gephyrosaurus and Brachyrhinodon
11. Derived sphenodontids like Trilophosaurus, Mesosuchus, and the rhynchosaurs.
12. Basal tritosaurs like Huehuecuetzpalli and Tijubina

Missing tail tips from several of the above taxa
(e.g. Owenetta, Barasaurus, Gephyrosaurus, Brachyrhinodon) may also be due to collection bias as the tail could be missing from the lost edge of the matrix. Icarosaurus has a shorter tail than sister taxa like Kuehneosaurus. Perhaps originally its tail was longer than preserved.

Wild 1975 described
“proof of the autotomy of the tail” in the derived tritosaur, Tanystropheus, but subsequent authors dismiss this.

The origin of caudal autotomy
may be traced to the origin of the caudal vertebra, which primitively, as in Bruktererpeton, is composed of an anterior intercentrum portion, a posterior pleurocentrum portion and a dorsal neural spine portion, together with an accompanying chevron. And yes, Bruktererpeton is missing the posterior portion of its tail.

Turtles are also lepidosauromorphs
but most living examples all have such short tails that predators would not attack them there. Snapping turtles have long tails, but they are mean SOBs that would rather fight back than run away. Extinct turtles with long tails, like Meiolania (Fig. 2) had armored tails.

Figure 2 Meiolania is another club-tailed, short-toed turtle like Proganochelys.

References
LeBlanc et al. 2018. Caudal autotomy as anti-predatory behaviour in Palaeozoic reptiles. Nature.com/scientificreports. https://www.nature.com/articles/s41598-018-21526-3.pdf
Wild R 1975. Der Giraffenhals-Saurier. Die Naturwissenschaften 62(4):149–153.

The Captorhinidae: herbivory and rates of evolutionary change

Dr. Neil Brocklehurst brings new insight to herbivory and evolution as he
compares rates of evolution as reptiles venture into a previously unexploited diet: plants. I did not comment on PeerJ where it is currently published without peer review because I thought it would be better here and Dr. Broklehurst reads this blog.

From the Brocklehurst abstract:
“Here I examine the impact of diet evolution on rates of morphological change in one of the earliest tetrapod clades to evolve high-fibre herbivory: Captorhinidae. Using a method of calculating heterogeneity in rates of discrete character change across a phylogeny, it is shown that a significant increase in rates of evolution coincides with the transition to herbivory in captorhinids.”

FIgure 1. Subset of the LRT focusing on the Captorhinidae. all herbivores.

Brocklehurst notes
“By the end of the Cisuralian (Early Permian), five tetrapod lineages had independently evolved a herbivorous diet (referencing Sues and Riesz 1998).”

1. Captorhinidae
2. Diadectidae
3. Pareiasauridae
4. Caseidae
5. Edaphosauridae

Matching the Brocklehurst cladograms
In the LRT the basal herbivore is also Thuringothyris, and it nests close to the base of the new Lepidosauromorpha (Fig. 1) at the base of the Captorhinidae. One wonders if the original dichotomy of reptiles actually separated slightly larger herbivores from slightly smaller insectivores in the Viséan (Early Carboniferous)?  At present evidence only supports a later adoption of herbivory in the Late Carboniferous among several lepidosauromorph taxa. So there had to have been an earlier undiscovered origin. In any case the first four clades in the Sues and Riesz list (above green) are all related to each other in the clade Lepidosauromorpha. They all had a single ancestor (see below). Later lepidosauromorphs, like turtles, lizards, snakes and pterosaurs reacquired insectivory, piscivory and carnivory independently.

Figure 3. Urumqia liudaowanensis (Zhang et al. 1984) ~20 cm snout-vent length, Lower Permian.

Late survivors of an earlier radiation
Urumqia (Fig. 3) nests as the basalmost lepidosauromorph, but fossils have only been found in Late Permian strata. Thus, Urumqia was a living fossil in the late Permian. Notably the gastralia were much wider than the posterior dorsal ribs. This created a large gut, ideal for herbivory (see below), but it also provided a larger volume for greater egg production.  Bruktererpeton was a sister and a basal lepidosauromorph with fossils found in Late Carboniferous strata with no obvious herbivorous traits. However, it too, nested with Thuringothyris (Fig. 1), so could have been an herbivore.

Figure 2. Captorhinidae according to Brocklehurst on PeerJ 2017. Most of the taxa also appear on the LRT, which is great case of congruence!

The taxon list
(Fig. 2) of Brocklehurst 2017 was restricted to his list of Captorhinidae. The LRT (Fig. 1) also nests most of his taxa within a single clade. However, Thuringothyris nests outside the Captorhinidae in the LRT but at its base. Saurorictus nests as the basal captorhinid in the LRT, despite its late appearance in the fossil record. It shares many traits with Millerettidae, a more derived taxon leading to all later lepidosauromorphs. Opisthodontosaurus appears in both cladograms, but its sister, Cephalerpeton appears only in the LRT. I have not yet seen data on Rhiodenticulatus and the derived captorhinid taxa are not present in the LRT. Limnoscelis and Orobates also nest as sisters to Saurorictus in the LRT. Limnoscelis is traditionally considered a carnivore, but since it is phylogenetically bracketed by herbivores, that hypothesis should be reexamined.

Sues and Reisz 1998 note:
“Dental features indicative of herbivorous habits include the presence of crushing and grinding dentitions, or marginal teeth with leaf-shaped, cuspidate crowns suitable for puncturing and shredding. Cranial features include short tooth rows and elevation or depression of the jaw joint for increased mechanical advantage during biting, large adductor chambers and deep lower jaws for accommodating large adductor jaw muscles, and jaw joints that permit fore-and-aft motion of the mandible.”

“The discovery of gut contents composed of conifer and pteridosperm ovules in specimens of the Late Permian diapsid reptile Protorosaurus (Munk and Sues 1992), long thought to be carnivorous based on its dentition, demonstrates that the consumption of plant material is not necessarily reflected by dental specialization.”

“The rib-cages of Palaeozoic herbivores are typically significantly wider and more capacious than those of their closest faunivorous relatives.”

Brocklehurst discusses rate variation:
“Discrete morphological character scores may be taken from the matrices used in cladistic analyses, and ancestral states are deduced using likelihood. This allows the number of character changes along each branch to be counted, and rates of character change are calculated by dividing the number of changes along a branch by the branch length. The absolute value calculated for the rate of each branch, however, can be misleading due to the presence of missing data (Lloyd et al. 2012). As such it is more useful to identify branches and clades where the rates of character change are significantly higher or lower than others, rather than comparing the raw numbers.”

Brocklehurst concludes:
“the evidence supporting an adaptive radiation of captorhinids coinciding with the origin of herbivory in this clade is compelling. It is only along herbivorous branches that significant increases in rates of morphological evolution are identified in the majority of the 100 time-calibrated trees.”

Brocklehurst has a good hypothesis with broader implications:
Among mammals, with the exception of tenrecs that turned into odontocete whales, the carnivores are more conservative than the herbivores, which developed horns, trunks and antlers, along with a variety of tooth morphologies. The clade Carnivora is quite conservative.

Among dinosaurs, with the exception of birds, the theropods are more conservative that the herbivores, which developed horns, long necks, great size, frills and duckbills.

Among basal reptiles, the lepidosauromorph herbivores developed into a wider variety of shapes and sizes while the archosauromorph insectivores were more conservative and stayed small until the advent of the lateral temporal fenestra that appeared in basal synapsids and diapsids.

References
Brocklehurst N 2017. Rates of morphological evolution in Captorhinidae: an adaptive radiation of Permian herbivores PeerJ Preprints (not peer-reviewed) PDF
Munk W and Sues H-D 1992. Gut contents of Parasaurus (Pareiasauria) and Protorosaurus (Archosauromorpha) from the Kupferschiefer (Upper Permian) of Hessen, Germany, Paläont. Z. 67, 169–176.
Sues H-D and Reisz RR 1998. Origins and early evolution of herbivory in tetrapods. Trends in Ecology and Evolution 13:141-145.

According to Wikipedia, PeerJ is 
“an open access peer-reviewed scientific mega journal covering research in the biological and medical sciences. PeerJ uses a business model that differs both from traditional publishers – in that no subscription fees are charged to its readers – and from the major open-access publishers in that the publication fees are levied not per article but per publishing researcher and at a much lower level. PeerJ charges authors a one-time membership fee that allows them – with some additional requirements, such as commenting upon, or reviewing, at least one paper per year – to publish in the journal for the rest of their life.^[12] Submitted research is judged solely on scientific and methodological soundness (like at PLoS ONE), with peer reviews published alongside the papers.”

SVP 20 – a Euryodus (microsaur) -like captorhinid, Opisthodontosaurus

We looked at this taxon, Opisthodontosaurus, earlier here.
Reisz et al. 2015 describe a captorhinid basal reptile similar to a microsaur.

Figure 1. Opisthodontosaurus (above) with missing bones in color. Black lines represent the referred specimen, OMNH 77470 scaled to fit the holotype, OMNH
77469, here in ghosted lines. Colors represent missing bones.

From the abstract
“The Lower Permian fossiliferous infills of the Dolese Brothers Limestone Quarry, near Richards Spur, Oklahoma, have preserved the most diverse assemblage of terrestrial vertebrates, including small-bodied reptiles, lepospondyl microsaurs, and dissorophoid temnospondyls. One taxon that was previously only known from isolated jaw elements at the locality was the microsaur Euryodus primus. Although it is known from more complete material elsewhere, other remains of E. primus have remained elusive at the Dolese Brothers Quarry.

Figure 1. Euryodus primus, a microsaur nesting between Scincosaurus and Micraroter. Note the odd posterior canine teeth, much more exaggerated than in Opisthodontosaurus.

The recent discovery of partial articulated skulls and skeletons of a small reptile at Dolese permits the recognition that the dentigerous elements that were previously assigned to Euryodus primus from this locality belong instead to a new captorhinid eureptile. The new captorhinid represents a major departure from other members of this clade in the unique anatomy of its jaws and dentition, which are characterized by their bulbous maxillary and dentary teeth. Three enlarged teeth are present on the maxilla, one in the anterior and two in the posterior region, whereas the premaxillary dentition is homodont and small. In addition, the largest dentary tooth is present along the posterior half of the bone. The dentary is characterized by the presence of a large well-developed coronoid process and deep lateral excavation in the posterior one-quarter of the bone. A phylogenetic analysis of captorhinid eureptiles yields two most parsimonious trees, with one in which the new captorhinid is recovered as the sister taxon to Concordia, this clade in turn being the sister to all other captorhinids, and a second in which the new captorhinid is the sister to all other derived captorhinids, to the exclusion of Concordia and Thuringothyris“

The sisters to captorhinids
also include Saurorictus (actually a basal captorhinid), Romeria primus, Reiszorhinus and Cephalerpeton in the large reptile tree, none of which have enlarged posterior teeth. Cephalerpeton had a complete set of enlarged maxillary teeth with an oddly raised posterior dentary, below the orbit. All of these taxa have a much taller squamosal and a much smaller suptratemporal. The postorbital and postfrontal are triangular. None of these taxa have a dentary with a deep lateral excavation, but otherwise are all quite similar to microsaurs.

Unique among microsaurs
Euryodus is rather unique among microsaurs with its enlarged posterior teeth. So the headline of Reisz, Leblanc and Scott is a little misleading. The large reptile tree nests Euryodus in a separate clade (Microsauria) from Opisthodontosaurus (with Cephalerpeton).

References
Reisz R, Leblanc A and Scott D 2015. A new early Permian captorhinid reptile (Amniota: Eureptilia) from Richards Spur, Oklahoma, shows remarkable dental and mandibular convergence with microsaurs.

Opisthodontosaurus – not quite a captorhinid and definitely not a microsaur

Figure 1. Opisthodontosaurus (above) with missing bones in color. Black lines represent the referred specimen, OMNH 77470 scaled to fit the holotype, OMNH
77469, here in ghosted lines. Colors represent missing bones. Note the concave maxilla ventral margin and the lower postorbital region compared to Cephalerpeton, its sister in the large reptile tree. These two and other taxa are sisters to captorhinids, but have narrower skulls.

A recent paper by Reisz et al. 2015 brings us a new basal reptile, Opisthodontosaurus carrolli (Fig. 1, Reisz et al. 2015; Artinskian, Early Permian ~289 mya), with teeth so robust it brought to mind a similar microsaur with thick posterior canines, Euryodus (Fig. 2).

Figure 2. Euryodus primus, a microsaur nesting between Scincosaurus and Micraroter. Note the odd posterior canine teeth.

Reisz et al. nested Opisthodontosaurus with Concordia (which it closely matches) and not far from Reiszhorhinus and Romeria primus. The large reptile tree duplicated these nestings, but recovered an excluded big-tooth taxon, Cephalerpeton (Fig. 1), closest to Opisthodontosaurus. I do not have data on another listed sister, Rhiodenticulatus, but will add it as soon as I am able to.

Reisz et al mentioned a depressed lateral dentary posterior to the tooth row. Since no large surangular was preserved and sister taxa have such a bone, it appears likely that  that depression received the missing surangular.

Like its sisters, Opisthodontosaurus is a basal lepidosaurmorph that nests with others that have a relatively narrower skull than outgroup taxa  including captorhinids and Thuringothyris. Tooth size varied a great deal in this clade.

Narrow-skulled sisters
to the captorhinids + cephalerpetontids, the larger Orobates and the smaller Milleretta, ultimately gave rise to the rest of the lepidosauromorphs, including limnoscelids, caseasaurs, diadectomorphs, pareiasaurs, turtles, lanthanosuchids, owenettids, kuehneosaurs and lepidosauriforms including pterosaurs.

Distinct from the microsaur Euryodus, Opisthodontosaurus had a taller squamosal, a greatly reduced supratemporal, a triangular postfrontal and postorbital along with a smaller basipterygoid with a more gracile cultriform process.

Thanks to Dr. Reisz for sending his paper this morning. This is a good discovery, well written and just missing one pertinent taxon.

References
Reisz RR et al. 2015. A new captorhinid reptile from the Lower Permian of Oklahoma showing remarkable dental and mandibular convergence with microsaurian tetrapods. The Science of Nature, October 2015, 102:50.

The biggest captorhinind – Moradisaurus

Known from a multi-tooth row jaw fragment, a few bits and pieces and a complete hind limb, Moradisaurus grandis (O’Keefe et al. 2005, Late Permian) is the largest known captorhinid. And it’s a little different, as well (Fig. 1).

Figure 1. Moradisaurus reconstructed from pieces illustrated in O’Keefe et al 2005). Digits p2.1 and p3.1 are colorized and transposed in the alternate reconstruction. Note the simpler PILs. And this pattern follows Captorhinus and Labidosaurus.

Moradisaurus has several distinct traits
I’m most curious about that distal fibula connection with that fused astragalus/intermedium with no connection at all to the calcaneum, which appears to have developed a tuber of sorts. Generally the distal fibula is broader than the proximal fibula, but not here. Also, note the fusion of the calcaneum with distal tarsal 5. The toes are shorter, befitting its greater size and mass, approaching the size of contemporary pareiasaurs and diadectids.

Otherwise, I’ve switched p2.1 with p3.1 for better PILs and to fall in line with the phylogenetic sisters to Moradisaurus, Labidosaurus and Captorhinus. O’Keefe et al. noted the reconstruction of the metatarsals was done with confidence, less so with the scattered digits. I think they only made one mistake, based on the PILs.

Phylogenetic nesting confirms a derived captorhinid node.

References
O’Keefe FR, Sidor Ca , Larsson HCE, Maga A and Ide O 2005. The vertebrate fauna of the Upper Permian of Niger—III, morphology and ontogeny of the hindlimb of Moradisaurus grandis (Reptilia, Captorhinidae), Journal of Vertebrate Paleontology, 25:2, 309-319.

The Captorhinidae

Updated October 08, 2915 with a revision to the inclusion set of the Captorhinidae.

Figure 1. Labidosaurus, a derived member of a basal reptile clade, the Captorhinidae

It is widely known that captorhinids were basal reptiles that appeared during the Early Permian and disappeared during the Late Permian, evolving from single tooth-row forms to those with multiple tooth-rows. All may be considered herbivores perhaps derived from insectivores. The problem is, which taxa are indeed captorhinids, and which are not?

The Reisz et al. 2011 List
Reisz et al. (2011) published the most recent phylogeny of the captorhinids. They found Thuringothyris nested at the base followed by Concordia, Rhiodenticulatus, Romeria, Protocaptorhinus, Saurorictus, Captorhinus, Captorhinikos, Labidosaurus, Labidosaurikos, Moradisaurus, Rothaniscus and Gansurhinus. This closely matched the phylogeny of Sumida et al. (2010).

Greater Numbers of Taxa Provide Greater Resolution
Here, in the large reptile study, the phylogeny closely matches that of Reisz et al (2011) and Sumida et al. (2010) with the following exceptions. Here, Cephalerpeton, Reiszorhinus, Concordia and Romeria primus nested just outside of the Captorhinidae at the base of all other lepidosauromorphs. Saurorictus and Romeria texana nested at the base of the Captorhinidae.

Independent Phylogenies
When independent phylogenies match, that’s a good test of validity. The exceptions merely alert others to expand the taxon list to test the exceptions on their own time using their own character lists.

Late Surviving Taxa
The presence of Concordia in the Latest Pennsylvanian indicates an earlier branching of basal captorhinids. The discovered fossils probably represent some of the broadest numerical extent of each taxon.

 

References
Muller J and Reisz RR 2006. The phylogeny of early eureptiles: Comparing parsimony and Bayesian approaches in the investigation of a basal fossil clade.” Systematic Biology, 55(3):503-511. doi:10.1080/10635150600755396
Reisz RR, Liu J, Li JL and Müller J 2011. A new captorhinid reptile, Gansurhinus qingtoushanensis, gen. et sp. nov., from the Permian of China. Naturwissenschaften 98 (5): 435–441. doi:10.1007/s00114-011-0793-0. PMID 21484260.
Sumida SS, Dodick J, Metcalf A and Albright G. 2010. Reiszorhinus olsoni, a new single-tooth-rowed captorhinid reptile of the Lower Permian of Texas. Journal of Vertebrate Paleontology 30 (3): 704–714. doi:10.1080/02724631003758078
wiki/Captorhinidae

What is Saurorictus?

Figure 1. Saurorictus australis reconstructed. The parietal, outlined in gray, is largely unknown. Click for more info.

Saurorictus australis
Captorhinids were basal lepidosauromorph reptiles that appeared in the Early Permian and evolved multiple tooth rows by the Late Permian.  Saurorictus (Modesto and Smith 2001) SAM PK-8666 was originally considered a late-surviving single-tooth row captorhinid that had “very slender marginal teeth” and reportedly lacked a supratemporal.

Figure 2. Saurorictus, Macroleter and Lanthanosuchus demonstrating the evolution of one to another and another of these three sister taxa. The derived sister taxon is Nyctiphruretus. An ancestor includes a sister to Orobates. The size increase is important.

A Larger Tree Nests Saurorictus Elsewhere
Here the large reptile tree nested Saurorictus with Lanthanosuchus and Macroleter, far from the captorhinids.  Like another sister, Nyctiphruretus, Saurorictus lacked an indented squamosal and lacked a lateral temporal fenestra. To move Saurorictus to the captorhinids requires an additional 17 steps. Saurorictus also nests between Stephanospondylus (which leads to turtles) and Nyctiphruretus (which leads to owenettids and lepidosauriformes). So this is a key taxon. And a tiny one!

Figure 3. The supratemporal in Saurorictus (ST, in pink) was originally considered a part of the parietal which is reasonable given their paradigm that Saurorictus was a captorhinid.

Missing a Supratemporal? Maybe Not.
The worst preservation in SAM PK-8666 occurs on the skull roof. The parietal is barely present and the pineal opening is nowhere to be found. Just dorsal to the squamosal is a plate-like bone that Modesto and Smith (2001) considered a parietal lacking a supratemporal between it and the squamosal. The skull of Saurorictus does indeed resemble that of captorhinids in general. The supratemporal in captorhinids is a tiny splint of bone and such a bone is indeed missing. I added the Saurorictus data (lacking a supratemporal) to the large reptile tree and was surprised to see it nested with Lanthosuchus and Macroleter, taxa with a large, plate-like supratemporal. Now the lack of a supratemporal seemed to be a very odd autapomorphy. Reexamining the published image (Modesto and Smith 2001) of Saurorictus I realized that the corner of bone originally labeled as a parietal was a large and mislabeled plate-like supratemporal, matching sister taxa.

Figure 4. Saurorictus nests with Macroleter and Lanthanosuchus.

Different and Similar
At first it would appear odd that round-skulled Saurorictus should nest with the cantilevered skulls of Macroleter and Lanthanosuchus, but round-skulled Nyctiphruretus also nests nearby. Diadectes and Procolophon also nest nearby, but Orobates is a more basal sister that shares certain plesiomorphic traits with Saurorictus. Here, apparently, we’re seeing a small, simple, pleisomorphic taxon that gives rise to the various odder, more derived sisters.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Modesto SP and Smith RMH 2001. A new Late Permian captorhinid reptile: a first record from the South African Karoo. Journal of Vertebrate Paleontology 21(3): 405–409.

wiki/Saurorictus