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A New Blunt-Snouted Dyrosaurid, Anthracosuchus Balrogus Gen. Et Sp

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A New Blunt-Snouted Dyrosaurid, Anthracosuchus Balrogus Gen. Et Sp Historical Biology, 2014 http://dx.doi.org/10.1080/08912963.2014.918968 A new blunt-snouted dyrosaurid, Anthracosuchus balrogus gen. et sp. nov. (Crocodylomorpha, Mesoeucrocodylia), from the Palaeocene of Colombia Alexander K. Hastingsa,b*, Jonathan I. Blocha and Carlos A. Jaramilloc aFlorida Museum of Natural History, University of Florida, Gainesville, FL, USA; bGeiseltalmuseum, Zentralmagazin Naturwissenschaftlicher Sammlungen, Martin Luther Universita¨t Halle-Wittenberg, Halle (Saale), Germany; cSmithsonian Tropical Research Institute, Balboa-Ancon, Panama (Received 23 March 2014; accepted 24 April 2014) A new exceptionally brevirostrine dyrosaurid is described from the middle Palaeocene (58–60 million years ago) Cerrejo´n Formation, northeastern Colombia, based on four partial skulls and associated postcrania. This taxon is unique among dyrosaurids not only in skull shape, but also in having orbital tuberosities, and osteoderms that are dorsoventrally thick and unpitted, a trait otherwise unknown in Crocodylomorpha. Results from a cladistic analysis of Dyrosauridae suggest that the new taxon, together with Cretaceous–Palaeocene Chenanisuchus lateroculi from Africa and Cerrejonisuchus improcerus also from the Cerrejo´n Formation, are the most basal members of the family. Results from a biogeographic analysis indicate at least three independent dispersals of dyrosaurids from Africa to the New World occurred in the Late Cretaceous or early Palaeocene. Widely set orbits in the new taxon indicate a deviation from surface-based predation, characteristic of other dyrosaurids, to sub-surface predation, as in modern Gavialis. Tooth impressions found on turtle shells recovered from the same locality match well with teeth of the new taxon indicating possible predation. http://www.zoobank.org/urn:lsid:zoobank.org:pub:AB2B24A5-27CC-4D3F-B580-F11F17851CE6 Keywords: Dyrosauridae; Crocodylomorpha; Palaeocene; Colombia; Cerrejo´n; biogeography Introduction dyrosaurids that expand our understanding of the ecological Crocodylomorpha has long been considered a ‘living fossil’ diversity of the group, with a previously published dwarf group (McGregor 2005). This largely stems from the fact that species (Cerrejonisuchus improcerus;Hastingsetal.2010) they have displayed conservative morphology in maintain- residing in freshwater habitats in adulthood, and a large- ing at least some members within the same body plan as bodied longirostrine taxon (Acherontisuchus guajiraensis; extant crocodylians since shortly after the group arose (Ross Hastings et al. 2011) also in freshwater sediments deposited 1989). However, numerous instances of incredibly varied in a large river system that drained into what is now the morphology have evolved time and again within the Caribbean Sea. crocodylomorph lineage. Forms have varied from slender Dyrosauridae originated and diversified during the late terrestrial ancestors (e.g. Sphenosuchus; Walker 1990), to Cretaceous, somehow survived the K–P extinction event heavily armoured forms (Armadillosuchus; Marinho and that wiped out other large-bodied marine reptiles (Benson Carvalho 2009) to fully marine with paddled feet and short et al. 2010) and ultimately became more diverse in the early Downloaded by [University of Florida] at 08:16 26 May 2014 powerful jaws skulls (Dakosaurus; Gasparini et al. 2006). Cenozoic (Jouve, Bardet, et al. 2008). The ability of Most dyrosaurids are thought to have been relatively limited dyrosaurids to inhabit both marine and fresh water may in ecological diversity, characterised as large near-shore have contributed to their preferential survival (Jouve, marine longirostrine piscivores with some variation Bardet, et al. 2008). Isotopic values for carbon and oxygen associated with juveniles possibly inhabiting freshwater may provide empirical evidence for a freshwater habitat, environments (Jouve, Bardet, et al. 2008). Freshwater supporting this hypothesis (Wheatley 2010). Described deposits (Jaramillo et al. 2007; Figure 1) of the middle here is a new genus and species of Dyrosauridae with a very Palaeocene-aged (58–60 million years ago) Cerrejo´n different skull shape relative to other dyrosaurids, likely Formation in northeastern Colombia have yielded not only reflecting a unique ecology associated with the invasion of plant fossils documenting the earliest evidence of a the freshwater ecosystem in tropical South America. neotropical rainforest (Wing et al. 2009), but also vertebrate The first skull of this new dyrosaurid (referred fossils including side-necked turtles (Cadena et al. 2010; specimen UF/IGM 69) was discovered in 2005, but the Cadena, Bloch, et al. 2012; Cadena, Ksepka, et al. 2012), a skull was missing its anterior end. Preservation of the giant boid snake (Head et al. 2009a, 2009b) and a diversity of posterior external nares indicated that the individual likely *Corresponding author. Email: [email protected] q 2014 Taylor & Francis 2 A. K. Hastings et al. has been assigned a unique number using the abbreviation UF/IGM. Casts of these specimens are also deposited at the collections of the Florida Museum of Natural History (UF). Institutional abbreviations IGM, Colombian Geological Survey, Bogota´, Colombia; NJSM, New Jersey State Museum, Trenton, NJ, USA; UF, University of Florida, Florida Museum of Natural History, Vertebrate Palaeontology Collection, Gainesville, FL, USA; USGS SAP, US Geological Survey – Saudi Arabian collection. Terminology and anatomical abbreviations Teeth and alveoli will be referred to by number with 1 being the most anterior. Premaxillary teeth and alveoli will have the initial ‘pm’, maxillary teeth and alveoli will use ‘m’, and dentary teeth and alveoli will use ‘d’. For example, the first tooth or alveolus of the premaxilla will be referred to as ‘pm1’ and the second tooth or alveolus of the maxilla will be referred to as ‘m2’. These follow the abbreviations of Hastings et al. (2010). Systematic palaeontology Crocodylomorpha Walker, 1970 Crocodyliformes Hay, 1930 Mesoeucrocodylia Whetstone and Whybrow, 1983 Dyrosauridae de Stefano, 1903 Anthracosuchus balrogus gen. et sp. nov. Etymology. Anthraco-, meaning coal, referring to the coal mine in which the type locality is located; -suchus, Downloaded by [University of Florida] at 08:16 26 May 2014 meaning crocodile. The specific term, balrogus, is named from a literary beast discovered within a deep mine, Figure 1. (Colour online) Locality map and stratigraphic originally written by Tolkien (1954). column for locality where all known Anthracosuchus balrogus Diagnosis. Possesses the following apomorphies: (1) a gen. et sp. nov. fossils are found. (A) Northern South America snout that is 44–53% of overall skull length; (2) rugose with star indicating Cerrejo´n fossil locality in northeastern Colombia. (B) Stratigraphic column of Cerrejo´n Formation (from orbital tuberosities anterior to medial margin of orbits; (3) Jaramillo et al. 2007). Fossil locality of Anthracosuchus is osteoderms that are dorsoventrally thick, unpitted and not underclay below Coal Seam 90, indicated with arrow above. imbricated; (4) premaxillae that are wider than long and had a short snout. A second skull with the anterior snout (5) external nares that are wider than long. preserved was discovered in early 2007, and indeed this Further differs from all other dyrosaurids in the skull exhibited a very short snout while maintaining other following unique combination of characters: (1) posterior diagnostic characters of Dyrosauridae. Two more skulls parietal margin straight; (2) interfenestral bar wide, were discovered later in 2007 bringing the minimum contributes to .10% of the skull table width, as measured number of individuals discovered thus far to 4. at anteroposterior midpoint of supratemporal fenestrae; (3) All specimens of the new taxon are deposited at the 8–10 maxillary teeth, of which 5–7 are antorbital; (4) Museo Geolo´gico Jose´ RoyoyGo´mez, Colombian strong constriction at the premaxilla–maxilla suture; (5) Geological Survey, Bogota´, Colombia. Each specimen nasal–prefrontal and nasal–lacrimal sutures subequal in Historical Biology 3 length; (6) orbits laterally placed and (7) teeth that are Comparative description robust, round and weakly striated. General. The rostrum is very stout and short in all Holotype. UF/IGM 67, nearly complete skull from specimens of Anthracosuchus, representing between 44% premaxilla to occipital condyle (missing medial portion of and 53% of the total skull length (Table 1). The rostrum of pterygoids and ventral braincase), nine ribs, seven Anthracosuchus is much shorter than that of any other vertebrae and unidentifiable bone. known dyrosaurid (Table 1). Cerrejonisuchus and Paratype. UF/IGM 68, skull from partial premaxilla to Chenanisuchus have much more longirostrine skulls occipital condyle (missing pterygoids and ventral brain- (Jouve, Bouya, et al. 2005; Hastings et al. 2010). The case), right articular, five osteoderms, five vertebrae, eight anterior rostrum of Anthracosuchus is much wider than ribs, distal pubis, distal ischium, haemal arch, three that of the other short-snouted dyrosaurids, even in the isolated teeth, proximal phalanx, sacral rib and unidentifi- case of UF/IGM 68 that has a snout only 2.5% shorter than able bone. Cerrejonisuchus (Hastings et al. 2010). The premaxilla Referred specimens. UF/IGM 69, skull from peri- and external nares of Anthracosuchus are both wider than orbital snout to posterior parietal (missing all but a long (Figures 2 and
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