| Dynamosuchus | |
|---|---|
 | |
| Fossil material and skeletal reconstruction | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Archosauria |
| Clade: | Pseudosuchia |
| Family: | †Ornithosuchidae |
| Genus: | †Dynamosuchus Mülleret al., 2020 |
| Species | |
Dynamosuchus is anextinctgenus ofpseudosuchianarchosaurs from the familyOrnithosuchidae. It is known from a single species,Dynamosuchus collisensis, which is based on a partial skeleton from theSanta Maria Formation ofBrazil.Dynamosuchus is considered a close relative ofVenaticosuchus, which is known from theIschigualasto Formation ofArgentina. Ornithosuchids are one of many groups which lived in the Santa Maria and Ischigualasto Formations, which formed at approximately the same time (theCarnian stage of theLate Triassic) and were ecologically similar. As a largescavenging reptile,Dynamosuchus helps to illuminate thetrophic structure of the Santa Maria Formation. It also supports the hypothesis that ornithosuchids had diversified throughoutSouth America by the start of the Carnian, and were not originally endemic to theIschigualasto-Villa Unión Basin.[1]
Dynamosuchus is known from a single partial skeleton, CAPPA/UFSM 0248, stored at the Centro de Apoio à Pesquisa Paleontológica da Quarta Colônia (CAPPA) of theFederal University of Santa Maria (UFSM). This specimen consists of parts of the skull, several cervical and dorsal vertebrae, and a large portion of the limbs. It was discovered at the Janner site near the town ofAgudo inRio Grande do Sul,Brazil. The Janner site preserves late Triassic sediments of theSanta Maria Formation. Based on the abundance ofExaerotodon (a large herbivorouscynodont) andHyperodapedon (arhynchosaur), it was probably equivalent in age and environment to theCarnian-ageIschigualasto Formation ofArgentina. Other animals known from the Janner site include basalsauropodomorphs (Pampadromaeus andBagualosaurus) and large carnivorous cynodonts (Trucidocynodon).[1]
The generic nameDynamosuchus isGreek for "powerful crocodile", in reference to itspseudosuchian heritage and strong bite force, as proposed for other ornithosuchids. The specific namecollisensis is based oncollis, theLatin term for hill, which references the fact that the Janner site is located at the base of a hill. The holotype skeleton was discovered in March 2019[2] and described in 2020 byRodrigo T. Müller (CAPPA/UFSM),M. Belén Von Baczko (Museo de la Plata),Julia B. Desojo (Museo de la Plata), andSterling J. Nesbitt (Virginia Tech).[1]
Like other ornithosuchids, the snout ofDynamosuchus had a hookedpremaxilla with three teeth, followed by a gap (adiastema) and a deepmaxilla with six to eight teeth. The maxilla was similar to that ofOrnithosuchus due to possessing pitting on its outer surface (absent inVenaticosuchus andRiojasuchus) and a not particularly deepantorbital fossa (unlikeRiojasuchus). Preserved skull bones generally reconstruct a skull with smallorbits andtemporal fenestration likeRiojasuchus, but thesquamosal is not as thick as in that taxon. Thequadratojugal bone was roughly textured and L-shaped, not as acute in angle asRiojasuchus. A hole known as a quadrate foramen separates the quadratojugal from thequadrate, and an additional smaller hole on the quadrate opens up into the quadrate foramen. The additional hole is anautapomorphy (unique characteristic) ofDynamosuchus absent in other ornithosuchids.[1]
Theparabasisphenoid bone at the bottom of the braincase has a semilunar depression like that ofVenaticosuchus, but the gap between its basipterygoid processes and basitubera is less acute than in that taxon.Dynamosuchus's basipterygoid processes are also more closely spaced and pointed further rearwards compared toVenaticosuchus. Thesurangular is similar to that ofRiojasuchus, with a pronounced blade-like crest on its outer surface and a large hole (a surangular foramen) at the rear of the jaw. The jaw as a whole deepens towards the chin and has a long mandibular fenestra.[1]
Thecervical (neck) vertebrae have a variety of features shared with various pseudosuchians, such as pits below thepostzygapophyses (rear connecting plates), expanded neural spines, and a strong keel on the underside.Dorsal vertebrae near the shoulder have a pair of centrodiapophyseal laminae, buttress-like crests connecting the diapophyses (rib facets) to the centrum (spool-shaped lower portion of each vertebra). These crests are shared withOrnithosuchus but absent inRiojasuchus and unknown inVenaticosuchus. In most other respects, the dorsal vertebrae ofDynamosuchus are more similar toRiojasuchus thanOrnithosuchus. For example,Dynamosuchus lacks prezygodiapophyseal and postzygodiapophyseal laminae. These crests, present inOrnithosuchus, connect the diapophyses to the zygapophyses (vertebral connecting plates).[1]
Dynamosuchus'sosteoderms are set in two rows along the back, are somewhat square-shaped, and are densely textured by radiating ridges and grooves. Osteoderms at the front of the body often have a sideways-oriented peak-like projection. The forelimb bones are thick and generally strongly built. Theradius expands towards the wrist more so thanOrnithosuchus, while thehumeral head is not as developed as that ofRiojasuchus. The hip has an overall shape like that ofOrnithosuchus, with a smooth and straight upper portion of theilium, a longpubis, and threesacral vertebrae. Like other ornithosuchids, the hindlimb bones are large and have prominent and/or unusual muscle scars. These include an anterior trochanter at the top of thefemur, and a knob-like scar for the iliofibularis muscle on the shaft of thefibula. The iliofibularis attachment is located about 1/3rd down the shaft of the fibula inDynamosuchus, while it is about halfway down inRiojasuchus.[1]
The relations ofDynamosuchus were investigated using aphylogenetic analysis adapted fromEzcurraet al. (2017).[3] The analysis foundDynamosuchus as asister taxon toVenaticosuchus based on a semilunar depression on theparabasisphenoid and an L-shapedquadratojugal. TheDynamosuchus +Venaticosuchus clade is itself sister toRiojasuchus based on a strongly downturnedpremaxilla and expanded outerradius.Ornithosuchus is found to be the most basal ornithosuchid, and ornithosuchids are related toerpetosuchids andaetosaurs, replicating the results of Ezcurraet al. (2017).[1]
The followingcladogram is based on the results of the phylogenetic analysis:[1]
.jpg)
