Systematic palaeontology

Temnospondyli Zittel, 1888

Dvinosauria Yates & Warren, 2000

Timonya anneae gen. et sp. nov.

(Fig. 1, Supplementary Fig. 1, Supplementary Movie 1)

Figure 1: The dvinosaur temnospondyl Timonya anneae gen. et sp. nov. from the Cisuralian of northeastern Brazil. (a–c) holotype UFPI PV001. (a) dorsal view of skull. (b) CT rendering of posterior portion of palate in ventral view. (c) CT rendering of right jaw, occlusal view. (d–h) articulated skeleton of a juvenile individual in dorsal view, UFPI PV004. (d) general view of the skeleton. (e) details of the right pes. (f) pectoral girdle. (g) pelvic girdle and left limb. (h) counter-slab of UFPI PV004 showing skull roof in ventral view and details of anterior thoracic vertebrae and right forelimb. af, adductor fossa; bo, basioccipital; cb, ceratobranchial; exo, exoccipital; f femur; fib, fibula; h, humerus; i, intercentrum; icl, interclavicle; il, ilium; na, neural arches; paf parasymphysial foramen; pc, pleurocentrum; pgp, postglenoid process of the jaw; psp, parasphenoid; pt, pterygoid; rcl, right clavicle; tib, tibia. Scale bar, 10 mm (a–d) and 5 mm (e–h). Full size image

Etymology. Timonya refers to Timon Municipality; anneae is in recognition of temnospondyl specialist Anne Warren.

Holotype. UFPI PV001, skull and partial postcranium.

Paratypes. UFPI PV004, cranium and nearly complete articulated postcranium of a probable juvenile individual; PV010 and PV281, two partial crania and pectoral girdles of probable juvenile individuals; PV351, a partial cranium of a probable juvenile.

Referred specimens. UFPI PV006, PV008, PV009, PV272, PV274–PV280, PV282, PV283, PV289, PV291, PV345–PV347, PV349, PV352; various crania and postcranial elements.

Horizon and locality. Lower Pedra de Fogo Formation (Parnaíba Basin), Cisuralian. The holotype, PV004, PV008 and PV010 were found within the Timon Municipality, Maranhão State; all other specimens were collected within the Nazária Municipality, Piauí State, Brazil.

Diagnosis. A new member of Dvinosauria distinguished from all other dvinosaurs by the following autapomorphies: absence of prenarial snout formed by the premaxilla; combined width of both parietals less than interorbital width; maximum width of parietal subequal to that of supratemporal; occipital condyles at approximately the same level as posterior margin of skull table; presence of well-developed postglenoid area on the mandible that is much longer than glenoid fossa when seen from above. It also differs from other non-tupilakosaurid dvinosaurs by the following unique combination of characters: nares close to skull midline; well-developed rectangular to triangular tabulars; palatal and quadrate rami of pterygoid strongly differentiated from each other at the level of pterygoid corpus; foramen for internal carotid artery on the ventral surface of the parasphenoid plate is elongated and groove like; maxilla does not extend posteriorly to anterior border of the subtemporal vacuity; absence of fangs in the mandibular symphysis mesial to the marginal tooth row; presence of a parasymphyseal foramen on both sides of mandibular symphysis to accommodate the vomerine fangs.

Trimerorhachidae Cope, 1882

Procuhy nazariensis gen. et sp. nov.

(Fig. 2a–c)

Figure 2: Tetrapods from the Cisuralian of northeastern Brazil. (a–c) The trimerorhachid Procuhy nazariensis n. g. n. sp. (UFPI PV011), skull roof in ventral view and left hemimandibular ramus partially preserved in lingual view. a.c., anterior coronoid; ang, angular; ar, articular; d, dentary; f, frontal; fr, frontal; g.arc, arcadian groove; h, hamate process; it, intertemporal; j, jugal; l, lacrimal; m.c., middle coronoid; m, maxilla; n, nasal; p, parietal; pa, parietal; part, prearticular; p.c., posterior coronoid; pf, postfrontal; po, postorbital; pp, postparietal; prf, prefrontal; p.ra, retroarticular process; s, splenial; sq, squamosal; st, supratemporal; t, tabular; t, tooth. (d,e) partial skull table of a rhinesuchid (UFPI PV007) in ventral view, (f), right hemimandibular ramus of a rhinesuchid (UFPI PV003). f, frontal; fr, frontal; it, intertemporal; j, jugal; l, lacrimal; m, maxilla; n, nasal; p, parietal; pa, parietal; pf, postfrontal; po, postorbital; pp, postparietal; prf, prefrontal; sq, squamosal; st, supratemporal; t, tabular. (g) Right hemimandibular ramus of Captorhinus aguti, natural mould (UFPI PV014), anterior to the right. (h) Left hemimandibular ramus of Captorhinus aguti, in occlusal view, from Oklahoma, USA (FMNH PR 2107). Scale bar, 50 mm (a–e) 200 mm (f) and 10 mm (g,h). Full size image

Etymology. Procuhy from prôt (frog) and cuhy (fire) in the local Timbira language (Macro-Jê group), referring to the Pedra de Fogo Formation (‘Rock of Fire’ in Portuguese, after the presence of flint); nazariensis refers to Nazaria Municipality, where the holotype was discovered.

Holotype. UFPI PV011, partial skull and left mandibular ramus.

Horizon and locality. Lower Pedra de Fogo Formation (Parnaíba Basin), Cisuralian. Nazária Municipality, Piauí State, Brazil.

Diagnosis. A member of Dvinosauria distinguished from all other dvinosaurs (Fig. 3) by the following autapomorphies: length of posterior skull table greater than 90% of its width; presence of well-developed arcadian process on mandible that is longer than retroarticular process. It also differs from other trimerorhachids by the following unique combination of characters: combined width of both parietals larger than interorbital width; maximum length of the dorsal ornamented surface of tabular less than or equal to maximum length of postparietal; coronoids without denticle fields.

Figure 3: Location of the new faunal province and phylogenetic relationships of the temnospondyl taxa described herein. (a) reconstruction of Pangaea during the Cisuralian (278 Myr ago) showing the location of the Parnaíba Basin, and provenance and age of previous rhinesuchid and dvinosaurid temnospondyls: 1, southern USA (Cisuralian); 2, Greenland (Triassic); 3, Russian Platform (Triassic); 4, Paraná Basin (Lopingian); 5, Karoo Basin (Lopingian rhinesuchids and Triassic dvinosaurids); 6, Malawi (Lopingian); 7, Madagascar (Lopingian); 8, India (Lopingian). (b) Cladogram displaying the interrelationships of Rhinesuchidae with Dvinosauria and the position of Timonya and Procuhy within this group; symmetric resampling and decay index values are provided right and left of each node, respectively (symmetric resampling was calculated from 10.000 replicates [p=33] and decay index from 691 trees). Map illustrated by The PLATES Project, Institute for Geophysics, University of Texas at Austin. Full size image

Temnospondyli Zittel, 1888

Stereospondyli Zittel, 1888

Rhinesuchidae Watson, 1919

gen. et sp. indet.

(Fig. 2d–f)

Referred material. UFPI PV007, partial skull table; UFPI PV003 a nearly complete right hemimandibular ramus; UFPI PV360 the posterior half of a right hemimandibular ramus.

Horizon and locality. Lower Pedra de Fogo Formation (Parnaíba Basin), Cisuralian. UFPI PV007 was found at Monsenhor Gil Municipality, Piauí State, Brazil; UFPI PV003 and PV360 were collected at the Pedra de Fogo type-section in Pastos Bons, Maranhão State, Brazil.

Comments. The skull material UFPI PV007 is considered to belong to a rhinesuchid stereospondyl based on the following combination of derived character states: the presence of a long and stepped jugal-prefrontal contact anterior to the orbit, anteroposteriorly elongated prefrontal located between nares and orbits, an L-shaped postorbital; orbits located posterior to mid-point of skull table; lacrimal excluded from orbit by prefrontal-jugal contact; interorbital distance less than 25% of skull width at midorbital level; jugal extends anterior to anterior orbital margin. The mandibles UFPI PV003 and PV360 are considered to belong to Rhinesuchidae based on the following synapomorphies: relatively short postglenoid area, all three coronoids covered by a field of small denticles; enlarged chordatympanic foramen located on prearticular–articular suture; prearticular with hamate process on the anterior border of glenoid fossa above the level of surangular and articular.

Reptilia Laurenti, 1768

Captorhinidae Case, 1911

Captorhinus aguti Cope, 1882

(Fig. 2g)

Referred material. UFPI PV014, natural mould of a partial right hemimandibular ramus.

Horizon and locality. Lower Pedra de Fogo Formation (Parnaíba Basin), Cisuralian. Nazária Municipality, Piauí State, Brazil.

Comments. UFPI PV014 is referred to the North American Captorhinus aguti based on the autapomorphic presence of multiple rows of conical teeth that are aligned obliquely in relation to the long axis of the mandibular ramus10. UFPI PV014 can be differentiated from the small, multiple tooth-rowed captorhinid Captorhinikos valensis11, also from North America, by the following features: (a) presence of large teeth at the beginning of some tooth rows, in contrast to the distal increase of tooth size present in the tooth rows of Captorhinikos; (b) absence of mesial convergence of the tooth rows (tooth rows are radially oriented and distally branching in Captorhinikos); (c) at least one of the tooth rows is aligned along the main axis of the mandibular ramus in Captorhinikos, a condition not seen in UFPI PV014.

Cladistic analysis

To elucidate the relationships of the new temnospondyls, a phylogenetic analysis was conducted, resulting in a single most parsimonious cladogram with a length of 289 steps (consistency index=0.635 and retention index=0.513; Fig. 3). The outgroups, Eryops and Dendrerpeton, fall at the base of the tree as successive sister taxa of the ingroup. The ingroup encompasses two subclades, one formed by Rhinesuchidae+Dvinosauria and the second by Archegosaurus+Sclerocephalus, the latter representing the basal radiation of stereospondylomorphs. The position of Rhinesuchidae as more closely related to Dvinosauria than to stereospondylomorphs is probably a result of the limited taxon sampling of the data set. Several more inclusive analyses have repeatedly demonstrated that rhinesuchids are stereospondyl temnospondyls12,13,14. Support for the most parsimonious cladogram is relatively weak, with most nodes decaying in 1–3 steps and few nodes receiving >50% symmetric resampling support.

The results of our analysis (Fig. 3) indicate that the clade Dvinosauria consists of two sister-groups, the Trimerorhachidae (consisting of Neldasaurus, Procuhy and Trimerorhachis) and the clade including Timonya, Acroplous, Isodectes, Dvinosaurus, and Tupilakosauridae. Therefore, both of the new taxa from Brazil are dvinosaurs, but they fall within distinct subclades. Characters that support their placement in Dvinosauria12 include: reduction of the otic notch; parietals more than two and a half times as long as wide; reduced anterior extension of the prefrontal, which is located around the anteromedial border of the orbit; loss of the posterolateral flange on the palatine ramus of the pterygoid; and increased number of presacral vertebrae (>30). The position of Procuhy within Trimerorhachidae (Neldasaurus+(Trimerhorachis+Procuhy)) is supported by: presence of an intertemporal on the skull table; presence of an elongated postorbital; postparietal bones that do not taper abruptly laterally; prearticular that does not extend anterior to the level of the suture of the middle and posterior coronoids; presence of a hamate process on the anterior margin of the glenoid fossa of the mandible; and, presence of a parasymphysial foramen on both sides of the mandibular symphysis. Timonya is reconstructed as an early-diverging dvinosaur based on the presence of postparietals that taper abruptly laterally; reduced tabulars; presence of a dorsal process of the palatine exposed on the skull roof; absence of contact between the palatine ramus of the pterygoid and the vomer; presence of a vaulted palate formed by the downturned quadrate ramus of the pterygoid; and glenoid fossa of the mandible below the level of the dorsal surface of the dentary. Although we did not recover Timonya as a member of Tupilakosauridae (Slaugenhopia+Thabanchuia+Tupilakosaurus), it is interesting to note that the Brazilian dvinosaur shares several derived character states with that clade, which we interpret as homoplasies. These are: presence of a quadrangular or rounded postorbital; anterior border of the squamosal lying approximately at the mid-length of the parietal; broad basicranial suture between the pterygoid and the parasphenoid; and posterior edge of the pterygoid incised close to the suture with the parasphenoid.

Sedimentology and palaeoenvironment

Most vertebrate specimens were recovered from Pedra de Fogo outcrops near the margins of the Parnaíba Basin, in the adjacent municipalities of Nazária, Monsenhor Gil, and the capital city of Teresina, in the state of Piauí, and equivalent exposures in the municipality of Timon, in the neighbouring state of Maranhão (Fig. 4). However, previously described vertebrate fossils from the PFF, as well as some new specimens, were discovered in outcrops 220 km southwest of Teresina (Pastos Bons, Maranhão State), in strata that accumulated closer to the depocenter of the basin5,15,16,17. The presence of shared taxa in both fossil-bearing intervals suggests they represent equivalent time spans. The rocks exposed at the Timon quarry are massive, tabular strata of red siltstone interbedded with fine-grained sandstone and mudstone intervals. The fossil-bearing strata in this quarry are an ∼3 m thick succession of fissile dark reddish-brown mudstone overlying a finely laminated light-purple calcareous fine-grained sandstone with greenish grey mottles (3–6 m on Fig. 4). The wavy-laminated sandstone contains distinctive large oblate calcareous nodules and elongated chert breccia-filled tubes that resemble large rhizoliths. This sandstone grades upwards into very finely laminated dark reddish-brown mudstones with some surfaces covered in bird-foot septarian shrinkage cracks and others with oscillation ripples. The top of this mudrock unit contains lenses of fish scales and a few semi-articulated bony fishes. The sequence continues with very finely laminated dark red siltstone containing horizons of small oblate calcareous nodules that have been preferentially silicified. Fish scales occur scattered throughout this unit, and more complete remains occur around the 6 m level, where articulated temnospondyl skeletons have been recovered.

Figure 4: Study area in northeastern Brazil. Location of the collecting sites (represented by white dots) in the Parnaíba Basin, and sedimentological log of the Pedra de Fogo Formation, exposed in a quarry at Timon, type locality of the new dvinosaur temnospondyl Timonya anneae. Sst, sandstone. Full size image

The fossil-bearing interval (3–6 m on Fig. 4) is interpreted as fluvio-lacustrine in origin, deposited in a range of terrestrial and aquatic sub-environments on the margins and nearshore of large continental lakes, on seasonally wet floodplains and channels, and within small ponds (cf. facies association AF2 (ref. 18)). At the 6 m mark this interval is truncated by the basal erosion surface of a large fluvial channel sandstone structured with trough cross-bedding at the base, and ripple cross-lamination in the interdigitating sandstone stringers at the top. From this level upwards the succession becomes more floodplain-dominated, with vertical rhizocretions reflecting incipient palaeosol development in a sequence of weak red-coloured massive siltstone beds (at 12 m on Fig. 4).