identifier	taxonID	type	CVterm	format	language	title	description	additionalInformationURL	UsageTerms	rights	Owner	contributor	creator	bibliographicCitation
CF7D87E5FFD6FFC25AC19FA65EC1FE8E.text	CF7D87E5FFD6FFC25AC19FA65EC1FE8E.taxon	http://purl.org/dc/dcmitype/Text	http://rs.tdwg.org/ontology/voc/SPMInfoItems#GeneralDescription	text/html	en	Necrosuchus SIMPSON 1937	<div><p>NECROSUCHUS SIMPSON, 1937</p><p>Emended diagnosis: A caimanine with the following combination of characters: differs from all other caimanines (except  Purussaurus brasiliensis Barbosa-Rodrigues, 1892 and some specimens of  Paleosuchus) in having the 13th dentary alveolus as the largest immediately caudal to fourth; differs from  Purussaurus in having a slender mandibular ramus and in not having the first four alveoli as the largest of the mandibular ramus; differs from  Paleosuchus in having an atlantal rib without a thin lamina in the anterior end, and the posterior mandibular alveoli and teeth not lateromedially compressed.</p><p>Type specimen:  Necrosuchus ionensis Simpson, 1937 .</p><p>Diagnosis: Same as for the genus, because it is the only species.</p><p>Holotype and only known specimen: AMNH 3219, right dentary with associated cranial fragments and partial postcranial skeleton.</p><p>Occurrence: Salamanca Formation, Palaeocene of Argentina.</p><p>Description and comparisons</p><p>After being described originally (Simpson, 1937), the holotype and only known specimen of  N. ionensis was subjected to a detailed redescription by Brochu (2011), making a detailed assessment on the anatomy of this species unnecessary. However, given our reanalysis of the holotype and of what has been published since about  N. ionensis, it is considered that its status as a valid species requires revision.</p><p>Two characteristics indicate that  N. ionensis is a caimanine alligatoroid: the presence of a slender process ventral to the basioccipital tubera (Brochu, 2011: Character 176, state 2; Fig. 1), which among  Crocodylia is found only in caimanines, and is present in all Caimaninae taxa except  Culebrasuchus (Hastings et al., 2013); and the splenial being excluded from the mandibular symphysis, with the anterior tip of the splenial passing dorsal to the Meckelian groove (Brochu, 2011: Character 54, state 2; Fig. 2A). This last feature is present in all caimanines except  Globidentosuchus brachyrostris Scheyer, Aguilera, Delfino, Fortier, Carlini, Sánchez, Carrillo-Briceño, Quiroz &amp; Sánchez-Villagra, 2013,  Gnatusuchus and  E. itaboraiensis . The scapulocoracoid synchondrosis of the holotype seems to be closing (see Brochu, 2011; Fig. 3A, B), and given that the holotype was not an osteologically mature individual upon death (Brochu, 2011), this possible early closure of the synchondrosis would be another feature to indicate that  N. ionensis belongs to Caimaninae (see Brochu, 1995, 1997b: Character 24; equivalent to Brochu, 2011: Character 25). In fact, the species has been recovered consistently in the Caimaninae clade by phylogenetic analyses that have included it (Brochu, 2011; Fortier et al., 2014; Hastings et al., 2016).</p><p>However, the differential diagnosis proposed by Brochu (2011) for  N. ionensis requires revision. Two of the characters used (the presence of a slender process ventral to the basioccipital tubera, and the dentary symphysis extending back to a level immediately behind the fourth dentary alveolus) are respectively shared with caimanines and the taxa of the crown-group caimanines according to Brochu (2011). Two other characteristics are, according to Brochu (2011), shared with other taxa: the first four dentary alveoli being widely spaced from one another is a feature typically present in caimanine taxa, and the presence of ≥ 18 dentary alveoli is shared with taxa such as  E. cavernensis,  Caiman and  Melanosuchus Gray, 1862 (see Brochu, 2011). Upon commenting on the last character, Brochu (2011) also notes that the dentary of  N. ionensis is slender. A slender dentary can also be seen in several caimanines, such as  Paleosuchus (GM Cidade personal observation),  E. cavernensis,  Centenariosuchus and  Tsoabichi (see Simpson, 1933; Brochu, 2010; Hastings et al., 2013). Additionally, the possibility that the width of the dentary might be subject to ontogenetic or individual variations makes this character not useful for taxonomy.</p><p>The last character included in the diagnosis of Brochu (2011) is the splenial bearing a slender anterior process that extends almost to the dentary symphysis. As previously mentioned, the splenial of  N. ionensis does not participate in the symphysis, and the anterior tip of the splenial passes dorsal to the Meckelian groove, which is a common character among caimanines (Brochu, 2011; Hastings et al., 2013; Cidade et al., 2017; Fig. 2A), but how close the splenial gets to the symphysis is variable in at least two extant caimanines:  C. crocodilus and  C. latirostris . Some specimens of  C. crocodilus exhibit splenials whose anterior tip is close to the symphysis (AMNH R 43291, AMNH R 137179, FMNH 69817, FMNH 69821, FMNH 69824, FMNH 69825, FMNH 69831 and FMNH 69842; Fig. 2B), whereas in others the anterior tip is more distant (FMNH 69819, FMNH 69832, FMNH 69854, FMNH 69855, FMNH 69865, FMNH 73700 and MN 1031; Fig. 2D). The same difference is observed for  C. latirostris, in which some specimens exhibit the anterior tip of the splenial close to the symphysis (MN 1255, MN 2078, MN 69, MN 1257 and MN 2395; Fig. 2C), whereas in others the anterior tip is more distant (MN 1041, MACN 30566 and MCT 156-RR). The specimens that exhibit the splenial anterior tip more distant from the symphysis are juveniles or subadults, which raises the possibility of an ontogenetic variation in this character. However, detailed studies about the relationship between the anterior tip of the splenial and the mandibular symphysis in extant caimanines are lacking. Nevertheless, the presence of the anterior tip of the splenial close to the symphysis in  C. crocodilus and  C. latirostris and the variation seen in those species make this character not recommendable to be used in taxonomy, at least for the time being, until detailed ontogenetic studies eventually reveal otherwise.</p><p>However, there is one character that differs in  N. ionensis from most other caimanines: the 13th dentary alveolus as the largest immediately caudal to the fourth dentary alveolus (Fig. 4B), which had already been noted by Simpson (1937) and which fits  N. ionensis into state 0 (the 13th or the 14th dentary alveolus as the largest immediately caudal to the fourth) of Character 51 of Brochu (2011). In most caimanines, the largest dentary alveolus immediately caudal to the fourth is either the 11th or the 12th (state 2 of the same character):  C. crocodilus,  C. latirostris,  C. yacare,  Centenariosuchus,  Melanosuchus and  Paleosuchus (even though there is individual variation in this last genus, as detailed below; see Fig. 4). Other caimanines have the 13th or the 14th alveolus as the largest, together with a series of large alveoli behind them (state 1):  C. brevirostris and  G. brachyrostris .</p><p>In other taxa of Caimaninae, a series of large posterior alveoli starts with a large 12th alveolus ( C. wannlangstoni and  Kuttanacaiman). In  N. ionensis, the 14th alveolus is only slightly smaller than the 13th, but the alveoli posterior to it are progressively slightly smaller instead. In  No. stromeri, the largest alveoli are the 15th and 16th. In  Mourasuchus, the first to the fifth alveoli are the largest of the tooth row, after which the alveoli become progressively smaller (see Langston, 1965). At least two  Purussaurus specimens [ Pu. brasiliensis specimens DGM 527-R (see Price, 1967) and UFAC-4559 (GM Cidade personal observation)] exhibit the 13th alveolus as the largest; most alveoli are not preserved in the holotype of  Purussaurus neivensis (Mook, 1941), while in the holotype of  Purussaurus mirandai Aguilera, Riff &amp; Bocquentin-Villanueva, 2006 the alveoli posterior to the fourth become progressively smaller (Aguilera et al., 2006). However,  N. ionensis is markedly distinct from  Purussaurus by overall mandibular morphology. In the latter, the mandibles are remarkably massive in accordance with the large size of  Purussaurus (see Langston, 1965; Aguilera et al., 2006; Aureliano et al., 2015) and because the first four alveoli are the largest of the dentary in  Purussaurus (see Barbosa-Rodrigues, 1892; Price, 1967; Aguilera et al., 2006; Salas-Gismondi et al., 2015), whereas in  Necrosuchus (see Simpson, 1937: fig. 3) and most caimanines (the other exception being  Mourasuchus, as noted above), one or more alveoli behind the tenth alveolous either approaches or overcomes the size of the first and fourth alveoli, which are usually the largest between the first four.</p><p>In some specimens of both species of  Paleosuchus, the 13th alveolus is either larger or of the same size as the 12th and the 11th ( Pa. palpebrosus: AMNH R 137170, AMNH R 137174, AMNH R 145071, AMNH R 93812, FMNH 69874, MCT 291-RR;  Pa. trigonatus: MN 65, MN 2491, AMNH R 129259, AMNH R 129260, AMNH R 66391 and USNM 234047; Fig. 4A), thus varying from the standard in the genus (Fig. 4C), which is state 2 of Character 51 of Brochu (2011). This alone raises the possibility that  Necrosuchus can be considered a  Paleosuchus specimen, but  Necrosuchus differs from the latter in other characters: the atlantal rib of  Necrosuchus lacks the thin laminae in the anterior end that is present in  Paleosuchus (see Brochu, 2011, in the scoring of Character 7); the dorsal margin of the iliac blade of  Necrosuchus is rounded, with a modest dorsal indentation (Brochu, 2011: Character 34, state 1; Fig. 5A), similar to  Caiman (e.g.  C. crocodilus; Fig. 5B) but different from  Paleosuchus, in which the dorsal margin of the iliac blade is narrow, with a dorsal indentation (Brochu, 2011: Character 34, state 3; Fig. 5C); and, most notably, the posterior alveoli and teeth of  Paleosuchus are lateromedially compressed, whereas those of  Necrosuchus are circular (Brochu, 2011: Character 79; Fig. 4).</p><p>The alveolar pattern of the dentary of the fossil caimanine  T. greenriverensis has some similarities with that of  Necrosuchus . The alveolar counting of  T. greenriverensis is not known, because the only significantly complete dentaries (those of the holotype, TMM 42509-1; see Brochu, 2010) have some anterior alveoli missing or fragmented. However, the posterior alveoli of the dentary exhibit two large alveoli followed by progressively slightly smaller ones, a morphology also observed in  Necrosuchus . Nevertheless, comparisons between the two taxa based on the specimens currently known are problematic, because  Necrosuchus preserves only four alveoli posterior to the two largest posterior alveoli (Fig. 4B), whereas the holotype of  Tsoabichi preserves from six to seven (see Brochu, 2010: fig. 1). Additionally, the placement of  Necrosuchus in or close to the Jacarea clade, together with the placement of  Tsoabichi as a member of the sister clade of  Paleosuchus in the phylogenetic analysis of this paper, argues against a proximity between these two taxa.</p><p>Additionally,  N. ionensis differs from  Eocaiman in having the dentary at the level of the first and fourth teeth at the same level as at the 11th and 12th teeth, whereas in  Eocaiman the dentary at the first level is lower than at the second (Pinheiro et al., 2013: Character 124). It also differs from  E. itaboraiensis, because in that species the splenial participates in the mandibular symphysis (Pinheiro et al., 2013).  Necrosuchus also differs from  Gnatusuchus owing to the presence of an extensive mandibular symphysis and a ‘shovel-like’ process in the anterior portion of the mandible in  Gnatusuchus, aside from the participation of the splenial in the mandibular symphysis in  Gnatusuchus (see Salas-Gismondi et al., 2015). From  Culebrasuchus,  Necrosuchus differs in having the dentary slightly curved between the fourth and tenth alveoli, whereas the same portion of the dentary in  Culebrasuchus is linear (see Brochu, 2011: Character 50; Hastings et al., 2013); additionally, the external mandibular fenestra in  Necrosuchus is small, whereas in  Culebrasuchus it is large (see Brochu, 2011: Character 63; Hastings et al., 2013). Furthermore, the exoccipital sends slender process ventrally to the basioccipital tubera in  Necrosuchus . In  Culebrasuchus, the processes are absent and the exoccipitals are located exclusively dorsal to the basioccipital tubera (see Brochu, 2011: Character 176; Hastings et al., 2013). Comparisons between  Necrosuchus and  Pr. peligrensis are limited because the only bone present in both species is the quadrate, which exhibits no systematically relevant differences between them.</p></div>	https://treatment.plazi.org/id/CF7D87E5FFD6FFC25AC19FA65EC1FE8E	Public Domain	No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.		Plazi	Cidade, Giovanne M;Fortier, Daniel;Hsiou, Annie S	Cidade, Giovanne M, Fortier, Daniel, Hsiou, Annie S (2020): Taxonomic and phylogenetic review of Necrosuchus ionensis (Alligatoroidea: Caimaninae) and the early evolution and radiation of caimanines. Zoological Journal of the Linnean Society 189 (2): 657-669, DOI: 10.1093/zoolinnean/zlz051, URL: https://academic.oup.com/zoolinnean/article/189/2/657/5546088
