Spectrovenator

Spectrovenator ("ghost hunter", named because the holotype was unexpectedly found under the holotype of Tapuiasaurus) is a genus of basal abelisaurid theropod that lived during the early Cretaceous period in what is now Brazil. It is known by a single species, S. ragei, recovered from the Quiricó Formation.[1]

Spectrovenator Temporal range: Barremian-Aptian, 125 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Family:	†Abelisauridae
Genus:	†Spectrovenator Zaher et al., 2020
Species:	†S. ragei
Binomial name
†Spectrovenator ragei Zaher et al., 2020

Description

Life reconstruction of Spectrovenator

Spectrovenator is known from a single specimen, MZSP-PV 833, stored in the Museu de Zoologia da Universidade de São Paulo, and was discovered in the Embira Branca Range, close to the Coração de Jesus Municipality, located in northern Minas Gerais. The specimen consists of a nearly complete skull, partial series of cervicodorsal vertebrae with ribs, complete sacrum, partial series of caudal vertebrae, and fully preserved hindlimb and hip bones.[1]

The well-preserved skull of Spectrovenator possesses several features which show it is a transitional taxon between more primitive Jurassic abelisaurids and the younger Late Cretaceous abelisaurids. It shares several cranial features with Rugops, another basal abelisaurid, indicating a similar position on the evolutionary tree. More derived taxa possessed adaptations allowing for a broader chamber for the muscles of the lower jaw, but Spectrovenator lacked these instead possessing plesiomorphic, or ancestral, traits in the temporal region of the skull, such as a broad parietal surface between the supratemporal fossae, and a narrow and elongated squamosal process of the postorbital. This indicates that Spectrovenator likely had a weaker bite force than more derived abelisaurids, which the authors note lends credence to the theory that bite force increased through evolution in abelisaurids. The authors conclude that based on the amount of basal traits exhibited by Spectrovenator, only the post-Cenomanian abelisaurids had the necessary adaptations for abelisaurids' characteristic feeding strategy.[1]

Spectrovenator preserves unique features in its skull, also known as autapomorphies, which help differentiate it from skulls of other abelisaurids. These are: the posterior ramus of the maxilla (the largest bone in the skull) is ornamented with vertically oriented grooves except for the smooth region in front of the maxilla-jugal suture; the lacrimal (the bone in front of the eye) lateral surface is rugose except for a smooth ventral region; a ventrally bowed posterior process of the jugal; a nuchal crest with a thin and smooth dorsal margin; a straight ventral margin of dentaries (part of the lower jaw) with a deep sulcus on the lateral surface; the dorsal margin of the surangular is slightly convex; and a longitudinal ridge along the posteroventral end of the mandibular ramus.[1]

Important features that Spectrovenator preserves are a transversely concave nasal and a row of large foramina (openings in the skull) on the skull roof. These have been hypothesized to represent the presence of blood vessels and nerves, probably related to the passage of the lateral nasal and supraorbital vessels and the trigeminal nerve.[1]

Classification

The affinities of Spectrovenator were analyzed in a phylogenetic analysis, based on an existing dataset. Several characters were found to support a position in Abelisauridae for Spectrovenator. The basal position of Spectrovenator within Abelisauridae is congruent with the age and morphology of this taxon. A simplified version of the analysis is shown below.[1]

Abelisauridae	Eoabelisaurus       Spectrovenator       Rugops       Arcovenator     Rajasaurus     Majungasaurus     Indosaurus     Abelisaurus   Brachyrostra     Skorpiovenator       Ekrixinatosaurus     Ilokelesia       Carnotaurini   Dahalokely     Carnotaurus     Aucasaurus     Rahiolisaurus

References

1. Zaher, H.; Pol, D.; Navarro, B.A.; Delcourt, R.; Carvalho, A.B. (October 2020). "An Early Cretaceous theropod dinosaur from Brazil sheds light on the cranial evolution of the Abelisauridae" (PDF). Comptes Rendus Palevol. 19 (6): 101–115. doi:10.5852/cr-palevol2020v19a6.