Although our knowledge of the fossil record of early theropod dinosaurs has greatly improved over the last two decades, very little is known about European taxa because they are largely incomplete. Here we present an exceptionally well-preserved theropod skeleton from the Late Triassic of Europe, pertaining to a new genus and species. The specimen includes a nearly complete skull, two articulated forelimbs and stomach contents. Notatesseraeraptor frickensis gen. et sp. nov. is an early-diverging neotheropod with affinities to Dilophosaurus and Averostra and displays an interesting mixture of character states typically seen either in coelophysids or in dilophosaurids. Based on our phylogenetic analysis, N. frickensis gen. et sp. nov. is considered one of the currently oldest and most basal members of the lineage, leading to Averostra. A monophyletic ‘traditional Coelophysoidea’ including Dilophosaurus is not supported.
Since 1961 the Gruhalde clay pit in Frick (Aargau, Switzerland) has been well known for its abundant, articulated Plateosaurus material, which is derived from the middle part of the Gruhalde Member of the Klettgau Formation. Within this lithological unit a new dinosaur layer with articulated skeletal material was discovered in 2006. The new layer is located above the classic Plateosaurus bone beds. It forms the uppermost part of the Triassic in Frick (latest Norian1) and is overlain by marine sediments of the Early Jurassic1. Recent excavations in the new layer yielded the excellent preserved theropod N. frickensis gen. et sp. nov., some large isolated teeth that could be either theropod in origin or provide evidence for pseudo-suchians in Frick, and several specimens of a sauropodomorph. The recovered skeletal parts of N. frickensis gen. et sp. nov. belong to an immature individual of length 2.6–3.0 m.
The presence of the fairly complete skeleton of the new theropod N. frickensis gen. et sp. nov. in the upper Norian1 beds of Frick increases the scarce knowledge of Late Triassic European neotheropods considerably. The three previously known species are all fragmentary, and include Liliensternus liliensterni (von Huene2) and Procompsognathus triassicus Fraas, 1913 from the Middle and Late Norian of Germany, and Lophostropheus airelensis (Cuny & Galton, 1993) from the Rhetian to Hettangian Beds of France3. With the exception of the skull of the new Swiss theropod and a few incomplete cranial elements of Liliensternus, no European Late Triassic neotheropod skulls are known. And, even from the Lower Jurassic, there is only the recently reported Dracoraptor hanigani (Martill et al.4) from Wales with a preserved partial cranium.
Worldwide, however, the fossil record of Late Triassic and Early Jurassic dinosaurs has greatly improved in the past 20–25 years, and the origin and early radiation of Dinosauria has been widely studied, for example5,6,7,8,9,10,11. Nonetheless, there are different hypotheses about early theropod relationships. Most of the taxa that have been assigned to the Coelophysoidea (for example, Coelophysis, ‘Syntarsus’, Dilophosaurus, Liliensternus and Zupaysaurus12,13,14,15) represent the earliest major radiation of Neotheropoda. Within this group, the Coelophysidae (for example, Coelophysis and Syntarsus) is the best-supported clade. More recent studies, however, suggest that at least some members of the ‘traditional Coelophsoidea’ (for example, Dilophosaurus; this term was previously used in ref. 16) are more closely related to the tetanurans and that the Dilophosauridae may represent a second clade of early non-averostran neotheropods, for example17,18,19. Nevertheless, the monophyly of both traditional Coelophysoidea and Dilophosauridae is still controversial. Concerning this debate, N. frickensis gen. et sp. nov. is a taxon that is key to understanding the relationships of early theropods because it shares many features with both clades. In addition, due to its good preservation it will promote the phylogenetic assignment of less complete theropods more accurately in the future. In this paper we describe the new genus and species, Notatesseraeraptor frickensis gen. et sp. nov. and discuss its phylogenetic position.
For the clade Coelophysoidea, we follow the definition of ref. 20 (Coelophysoidea sensu stricto of Ezcurra & Brusatte16). Hence, it is understood as a monophyletic clade by definition but with changing taxonomic content, depending on individual phylogenetic analyses. Following the present study, the clade Dilophosauridae (phylogenetically defined in ref. 21) may include Dilophosaurus wetherilli, Cryolophosaurus ellioti, the fragmentary Dracovenator regenti and N. frickensis gen. et sp. nov. (see Supplementary information for further implications and a suggested diagnosis for Dilophosauridae).
Dinosauria Owen, 1842
Saurischia Seeley, 1887
Theropoda Marsh, 1881
Neotheropoda Bakker, 1986
N. frickensis gen. et sp. nov.
Nota, feature (Latin); tesserae, individually shaped tiles used to create a mosaic (Latin), in reference to the intermixture of features typically known from either dilophosaurid or coelophysoid neotheropods; raptor, predator (Latin) and frickensis, derived from the village of Frick.
Sauriermuseum Frick (SMF) 06-1 and 09-2: cranium (SMF 09-2) and partial postcranial skeleton (SMF 06-1) of a likely juvenile to subadult individual (stages of ontogenetic development sensu14) consisting of two articulated forelimbs; shoulder and pelvic girdle; 13 dorsal, four sacral and four proximal caudal vertebrae; cervical, dorsal and sacral ribs; chevrons; and gastralia. From the preserved contents of the stomach, a well-preserved maxilla of the rhynchocephalian Clevosaurus could be identified (Fig. 1l)22,23.
Horizon and locality
New upper dinosaur layer, 1 m beneath the Triassic–Jurassic boundary, uppermost Gruhalde Member, Klettgau Formation, latest Norian1; clay pit Gruhalde of the Tonwerke Keller AG, Frick, Canton Aargau, Switzerland. Coordinates 2° 642’ 960”/1° 261’ 963” (www.strati.ch).
Notatesseraeraptor frickensis gen. et sp. nov. differs from all other theropods in the following unique combination of morphological character states: four exceptionally long but slender premaxillary tooth crowns that are as long as the anterior maxillary teeth but mesio-distally less wide (ratio 3/1 versus 2.4/1); premaxillary tooth crowns labio-lingually flattened, mesially somewhat broader than distally and with fine serrations along their mesial and distal carinae (5 per 1 mm); two recesses in the maxillary antorbital fossa (homologous with the promaxillary foramen and maxillary fossa); supratemporal fossa restricted to the posterior half of the parietal (autapomorphy); shallow basisphenoid recess; exit of vagus nerve through a posterior foramen lateral to the foramina for hypoglossal nerve; three distinct processes of the articular (medial, dorsolateral and dorsal process); markedly low-rectangular neural spines (ratio 2/1) of the posterior dorsal vertebrae; posteriorly increasing height of dorsal neural spines; flattened ventral surfaces and expanded articular faces of sacral centra; deep fossa on lateral surfaces of second sacral vertebra; anterior caudals with longitudinal fossae on centra and neural arches; prominent antero-proximally located tubercular processes on the first four chevrons; pronounced expansion (boots) on the distal ends of the pubis and ischium, ischial expansion (boot) larger than pubic expansion.
Description and comparison
The cranial bones are disarticulated but still closely associated. With the exception of a few elements, each paired bone (facial, palatal, braincase and lower jaw) was recovered from at least one side (Fig. 1a–f). Thus over 90% of the skull elements are known, which makes SMF 09-2 the most complete theropod skull from the Late Triassic and Early Jurassic of Europe. The reconstructed cranium is proportionally long (about 225 mm from tip of premaxilla to end of quadrate condyle) and low, as is commonly found in traditional coelophysoid-grade neotheropods12,13,24,25,26,27. Based on a three-dimensional reconstruction of the skull, the preorbital region comprises about two-thirds of the total skull length, which is about 2.5 times the skull’s greatest depth in the middle of the orbit when the jaws are occluded. With Dilophosaurus wetherilli25, the Coelophysoidea12,13,14,24 and Tawa hallae10, it shares a ventral flange on the maxillary process of the premaxilla and a discontinuous upper tooth row (subnarial gap and diastema28) at the premaxilla–maxilla transition. Laterally, the premaxilla is perforated by six neurovascular foramina. One particular foramen that is located at the base of the nasal process is slit-shaped and also found in D. wetherilli25, Dracovenator regenti28 and Dracoraptor hanigani4. Most striking, however, is the above-mentioned morphology of the premaxillary teeth. In contrast to coelophysids where the mesial premaxillary teeth show only minor curvature, have a nearly circular cross-section and only a few to no serrations12,29, the premaxillary tooth crowns of N. frickensis gen. et sp. nov. are all strongly recurved, laterally compressed and bear fine serrations (14 per 3 mm) along their mesial and distal carinae. Furthermore, as in Eoraptor (Figs. 10 and 11 in ref. 30), the proportions of the premaxillary tooth crowns are similar to those of the anterior maxillary crowns. In the coelophysid ‘Syntarsus’ kayentakatae (MNA V2623), where the maxillary dentition looks similar to that of SMF 09-2, the premaxillary teeth are, on the other hand, conspicuously smaller and much more slender. Such a difference in size is also present in Coelophysis bauri29 (CM P-50530). As in Dracoraptor4 and Dilophosaurus25, the premaxillary crowns are procumbent. The maxilla forms the main border of the large internal antorbital fenestra that constitutes more than 30% of the estimated skull length. A pronounced horizontal ridge is oriented along the ventral rim of the antorbital fossa and, as in Eoraptor30,31, Zupaysaurus26,32, Monolophosaurus33 and abelisaurids34, the dorsal and ventral margins of the horizontal process are parallel. The antorbital fossa has two relatively large, oval recesses located where the ascending process meets the facial region of the maxilla, here referred to as homologous with the promaxillary foramen35 and maxillary fossa18. While a promaxillary foramen also occurs in S. kayentakatae13,14, a maxillary fossa or even a fenestra is absent in coelophysids, Dilophosaurus and ceratosaurians but both recesses are present in Zupaysaurus. As in Zupaysaurus, the maxillary fossa of N. frickensis gen. et sp. nov. approaches in size and shape the maxillary fenestra of basal tetanuran theropods (for example, Dubreuillosaurus26), in which the fenestra does not pierce the medial lamina of the maxilla. In SMF 09-2 both the nasal and lacrimal show no signs of pronounced cranial crests, typically developed in some potential dilophosaurid taxa for example17,25,28,36. Instead, these bones bear a low marginal ridge projecting dorsolaterally slightly above the maxilla. The preserved left maxilla bears at least 15 alveoli, which is clearly fewer than in most adult Coelophysis specimens29 with tooth rows bearing usually 22–24 alveoli. Anterior to the internal antorbital fenestra, N. frickensis gen. et sp. nov. has five alveoli in the preserved left maxilla; the juvenile C. bauri specimen NMMNH P-42200, on the other hand, already has six and adults have seven or even more alveoli (for example, CM31374). Laterally, the antorbital fossa of the L-shaped lacrimal is split by an anteriorly extended sinuous lamina. In SMF 09-2, the supratemporal fossa is well developed on the anterior and posterior processes of the postorbital, whereas it is restricted to the posterior half on the parietal. This restriction is most probably an autapomorphic feature of N. frickensis gen. et sp. nov. because, in closely related taxa, the supratemporal fossa is well developed throughout the parietal and even extends onto the frontal (for example, CM31374, QG194)13,17,26. Alongside the midline of the unfused parietals there is a longitudinal shallow trough, resembling the condition found in S. kayentakatae13. In N. frickensis gen. et sp. nov. and Zupaysaurus rougieri, the lateral surface of the jugal is quite flat and bears no horizontally running ridge, as is typically seen in Herrerasaurus ischigualastensis37 and the Coelophysidae18,27. Furthermore, the anterior process of the bone is rather long and possibly reached the internal antorbital fenestra in the articulated skulls of both taxa. There is no lacrimal process as seen, for example, in Allosaurus, but both N. frickensis gen. et sp. nov. and Z. rougieri (PULR 076) possess at least a dorsal bulge in the same anatomical position. The posterior and dorsal processes of the jugal form a near right angle in lateral view, and the lower temporal bar consists of the jugal and quadratojugal equally. In SMF 09-2, the quadratojugal and quadrate are not fused, which could also be related to its ontogenetic age22,23,38. Similar to D. wetherilli25, the lateral quadrate ala of N. frickensis gen. et sp. nov. is large, dorsally expanded and fan-shaped. The pterygoid ala on the other hand is double-lobed and looks like the inverted ear of an elephant, resembling strongly the condition seen, for example, in Coelophysis rhodesiensis39. The articulated left hemi-mandible of N. frickensis gen. et sp. nov. (Fig. 1d–f) is largely comparable to the long, but remarkably slender, mandibles of the coelophysids. However, compared to C. bauri (AMNH 7240), the teeth in the lower dentition are more widely spaced in the new taxon (two versus three alveoli per 10 mm)18. We estimate a total of 19–23 alveoli for each mandibular ramus38. The lateral surangular shelf is well developed and merges caudally into the anterior rim of the lateral portion of the glenoid fossa. The retroarticular process of N. frickensis gen. et sp. nov. (SMF 09-2; Fig. 1e,f) is long and narrow, as in Eoraptor30, the coelophysids and Dracovenator28. With the coelophysoids it also shares a dorsally orientated attachment area for the musculus depressor mandibulae18. Furthermore, N. frickensis gen. et sp. nov. possesses three distinct processes arising from the dorsal and medial rims of the articular, which otherwise are found only in the dilophosaurids and, in reduced numbers, also in averostrans (Fig. 1f). Therefore, the articular shows a mixture of character states that can be seen in C. rhodesiensis24 and D. regenti28.
Overall, the preserved postcranial elements of N. frickensis gen. et sp. nov. (SMF 06-1, observations based mainly on refs. 22,23; Fig. 1g–k) share most of their morphological similarities with S. kayentakatae22,23. In SMF 06-1, the length of the vertebrae increases posteriorly in both the dorsal (31 mm in D2 to 42 mm in D10) and caudal (28 mm in C1 to 33 mm in C4) series, but is constant in the sacral region. In regard to the length of the dorsal vertebrae, Dilophosaurus25 shows the same relative relation as observed in the Swiss specimen. In Herrerasaurus40, Coelophysis12,13 and Liliensternus2 on the contrary, the centrum length of the dorsal series is rather constant. Most of the preserved vertebrae of N. frickensis gen. et sp. nov. bear fossae (longitudinal, cranial and caudal fossa on the centra of anterior dorsals, fossa on centra of sacrals and longitudinal fossae on centra and neural arches of anterior caudals). The transverse processes of the anterior dorsal vertebrae in SMF 06-1 do not have the strongly backswept anterior margin seen in coelophysids and Ceratosaurus41, but are subrectangular and mainly laterally directed in dorsal view. Furthermore, the height of the dorsal neural spines increases posteriorly as seen in Eoraptor30, Herrerasaurus40 and tetanuran theropods (for example, Piatnitzkysaurus floresi42, Sinraptor dongi43 and Allosaurus fragilis44). Compared to most other early-diverging theropods where the ventral surfaces of the sacral centra are rounded or keeled45, they are flattened in SMF 06-1 and C. rhodesiensis24. The scapula is similar to the corresponding element in coelophysids, Dilophosaurus46 and Eodromaeus9 in possessing a nearly straight posterior margin and a distinctly expanded distal end. As in most basal theropods, N. frickensis gen. et sp. nov. has plesiomorphically long forelimbs. The radius (97 mm) is about three-quarters of the length of the humerus (≥128 mm) and the manus (second finger, ~127 mm) is of a length similar to the two former skeletal elements (Fig. 1f,h). The manus is composed of four digits, whereas the fourth is reduced to a very slim metacarpal, which is only half as wide as metacarpals I–III and has a single small phalanx. From proximal (I) to distal (IV), the corresponding phalanges of the digits become shorter and the first phalanx of the first digit is the longest non-ungual phalanx of the manus (Fig. 1g,h). Shape and proportions of the ilium are similar to those found in Coelophysis12,24 and other early neotheropods such as Dilophosaurus14,25. However, the outline of the bone differs slightly as the dorsal iliac margin is somewhat convex in lateral view, rather than straight (for example, Coelophysis12,24) or strongly rounded (for example, S. dongi43). On the caudo-lateral surface of the ilium, there is a distinct rim for the musculus iliofibularis that continues over the whole ventral margin of the posterior blade. The pubis has a slightly downward-curved shaft and is, like the shorter, rod-shaped ischium, long and slender. As in the Coelophysidae, the ischium has a straight shaft but, compared to the former clade in SMF 06-1, the bone is distally clearly more strongly expanded since the ischiadic boot is much larger than the pubic one. The pubis is about 1.7 times longer than the ischium and thus shows proportions similar to the pelvic elements of Dracoraptor4. In the Frick theropod material, Dilophosaurus25 and Liliensternus14, the distal expansion of the ischium is much larger than the corresponding structure of the pubis. In the Coelophysidae these structures are of equal size. As in Dilophosaurus14,25, there is a distinct antero-proximally located tubercular process on each of the four preserved cranially forked chevrons (C1–C4).
Our comprehensive phylogenetic analyses, with emphasis on early neotheropods, revealed that N. frickensis gen. et sp. nov. is an early averostran-line theropod outside the clade Coelophysoidea (Fig. 2). In concord with refs. 10,17,18,21,28,47,48, and regardless of taxa choice, a dichotomy is found at the base of Neotheropoda which is formed by the two monophyletic clades Coelophysoidea and averostran-line neotheropods. The best-supported clade in each of our conducted analyses is the clade that comprises N. frickensis gen. et sp. nov., Dilophosaurus, Cryolophosaurus, (Dracovenator if included) and Averostra. Eoraptor, Eodromaeus, Herrerasaurus and Tawa are always found to be outside Neotheropoda. One of the trees best reflecting the relationships is shown in Fig. 2.
Phylogenetic discussion and conclusion
Hypotheses on early neotheropod relationships still attract little general agreement. The assignment of several taxa to the Coelophysoidea is uncertain, and the monophyly of the clade Dilophosauridae is controversial10,16,49.
A reduced analysis, with the inclusion of only taxa with at least 40% of the available character states (‘40%-rule analysis’) and which also contained no Averostra, produced a single most parsimonious tree (MPT) where N. frickensis gen. nov. is found as a member of Dilophosauridae (see Supplementary Fig. 1 and Supplemetary information for a suggested diagnosis of the clade). A ‘dilophosaur clade’ has also been recovered by other authors, for example17,19,28, but as it was mostly supported by cranial crest characters it was thought that the grouping may be artificial33. In the 40%-rule analysis of this study, the monophyly of the Dilophosauridae is supported by three unambiguous synapomorphies and nine additional ones under DELTRAN and ACCTRAN optimization, where none is related to cranial crest character states (Supplementary Table 2a). In D. regenti, all of the seven synapomorphies pertaining to the articular and the premaxilla are also discernible. The addition of every further coelophysoid or dilophosaurid taxon to the 40%-dataset has no influence on the genaral tree topology, but changes at most the position of single neighbouring sister taxa. With the inclusion of any averostran theropod other than Piatnitzkysauru, the hypothesis of a monophyletic Diophosauridae is no longer supported. Instead it is suggested that there are several basal neotheropods, more closely related to Averostra than to Coelophysis. As shown by the phylogenetic tree in Fig. 2, which in the main results from the 40%-rule analysis supplemented by four averostrans, all members of the previously monophyletic Dilophosauridae (inclusive of N. frickensis gen. et sp. nov.) are recovered as successive basal sister taxa of Averostra. The bootstrap and Bremer support values show that the relationships within the averostran-line neotheropods are very well supported. In contrast, the Coelophysoidea as well as the affiliation of Zupaysaurus to the non-coelophysoid neotheropods are not supported after only one or two additional steps. In the same analysis, the deletion of N. frickensis gen. et sp. nov. leads to an increase from a single MPT to 12. The strict consensus tree therefore consists of poor resolution with a large polytomy at the base of Neotheropoda. Interestingly, the integration of Sinraptor as a fifth averostran theropod leads to the formation of a clade of D. wetherilli and C. ellioti. Thus, the dilophosaurids might yet form a monophyletic clade.
As shown by the description and the results of the phylogenetic analysis, N. frickensis gen. et sp. nov. is an important new taxon with an interesting combination of plesiomorphic and apomorphic features of early theropods. Our study strongly supports a dichotomy at the base of Neotheropoda, formed by the Coelophysoidea (sensu ref. 20) on the one hand and the averostran-line theropods, including potential dilophosaurid taxa and Averostra, on the other. The question that remains is whether the potential dilophosaurids are successive sister taxa to Averostra or form a monophyletic Dilophosauridae. Regardless of whether the Swiss taxon is indeed possibly the oldest dilophosaurid and the first member of this clade known from Europe, it is certainly one of the oldest averostran-line neotheropods and bolsters the origin of this clade in the Triassic. Thus at least two major neotheropod lineages have already diverged in the Late Triassic that both survived the Triassic–Jurassic extinction event.
In order to assess the phylogenetic position of N. frickensis gen. et sp. nov., we established a matrix based mainly on those of refs. 17,18,45 and scored 23 taxa for 285 character states (Supplementary information; two (character list) and three (character matrix)). Based on this dataset, several phylogenetic analyses with different numbers and combinations of taxa were run in PAUP (version 4.0b10). The goal of this multiple analyses was to estimate the possible effects of both missing data and phylogenetically unstable taxa on phylogenetic outcome. For the initial analysis we reduced the number of taxa to 11 (Eoraptor, Herrerasaurus, Tawa and 8 Triassic and Jurassic neotheropods) with at least 40% of the available characters scored, both cranial and total (cranial + postcranial) (Supplementary Table 1). This 40%-rule analysis was the starting point for every further analysis where we added additional coelophysoid and dilophosaurid taxa as well as averostrans, and where we always used all 285 features. Subsequently, all tree topologies and synapomorphies of the resulting clades were compared (for example, Supplementary Table 2). The single MPT resulting from the 40%-rule analysis is shown in Supplementary Fig. 1.
Dracoraptor hanigani Martill et al., 2016, which is fairly complete, is not included in the analyses since character scoring was nearly finished when the paper was published. The same is true for the more fragmentary coelophysoid specimens Camposaurus Hunt et al., 1998, Lepidus Nesbitt & Ezcurra, 2015, Lucianovenator Martínez & Appaldetti, 2017 and Powellvenator Ezcurra, 2017. Moreover, these taxa are represented mainly by a few elements of the hind legs that are not preserved in the Swiss theropod material.
This published work and the nomenclatural acts contained therein have been registered in ZooBank, the proposed online registration system for the International Code of Zoological Nomenclature (http://zoobank.org/). The Life Sciences Identifier for this publication is urn:lsid:zoobank.org:act:CD16B061-D440-447E-AD1C-9C11508DF897.
Further information on research design is available in the Nature Research Reporting Summary linked to this article.
All the data supporting the findings of this study are available within the paper and its Supplementary information.
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We thank M. Ezcurra, R. Irmis, A. Marsh, S. Nesbitt, A. Pauline-Carabajal, O. Rauhut, L. Rinehart and D. Scott for sharing unpublished photographs of early neotheropod specimens; individuals who permitted the use of their dinosaur silhouettes from PhyloPic; B. Pabst for excellent preparation of the specimen; B. Scheffold for the illustration of the preserved parts of N. frickensis gen. et sp. nov.; and all members of PIMUZ for their support. We also thank the Swiss National Fund (SNF) for supporting this study (project No. 31003A_163346).
The authors declare no competing interests.
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