Article a New Small Short-Snouted Dyrosaurid
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Journal of Vertebrate Paleontology 30(1):139–162, January 2010 © 2010 by the Society of Vertebrate Paleontology ARTICLE A NEW SMALL SHORT-SNOUTED DYROSAURID (CROCODYLOMORPHA, MESOEUCROCODYLIA) FROM THE PALEOCENE OF NORTHEASTERN COLOMBIA ALEXANDER K. HASTINGS,*,1 JONATHAN I. BLOCH,1 EDWIN A. CADENA,1 and CARLOS A. JARAMILLO2 1Florida Museum of Natural History, University of Florida, Gainesville, Florida 32611, U.S.A., akh@ufl.edu, jbloch@flmnh.ufl.edu, ecadena@ufl.edu; 2Smithsonian Tropical Research Institute, Box 0843-03092 and no. 8232, Balboa-Ancon, Panama, [email protected] ABSTRACT—The fossil record of dyrosaurid crocodyliforms spans the Late Cretaceous to Middle Eocene of Africa, Asia, Europe, North America, and South America. Prior to this study, specimens from South America have been limited to a few fossils with only two taxa diagnosed. We describe a nearly complete skull and unassociated mandible of a new dyrosaurid, Cerrejonisuchus improcerus gen. et sp. nov., from the Paleocene Cerrejon´ Formation of northeastern Colombia. The skull of C. improcerus has relatively elongate supratemporal fenestrae and well-developed occipital tuberosities, both diagnostic characteristics of Dyrosauridae. The rostrum of adult C. improcerus comprises 54–59% of the length of the skull, making it the shortest snout of any known dyrosaurid. A cladistic analysis using 82 cranial and mandibular characters for all species of Dyrosauridae known from crania yielded two most-parsimonious cladograms with C. improcerus as the sister taxon to a clade including Arambourgisuchus, Dyrosaurus, Hyposaurus, Congosaurus, Rhabdognathus, Atlantosuchus,andGuarin- isuchus.OnlyChenanisuchus, Sokotosuchus,andPhosphatosaurus, all known only from Africa, are more primitive within Dyrosauridae. Chenanisuchus from the Paleocene of Morocco, the only other known short-snouted dyrosaurid, is not closely related to C. improcerus and a short-snouted condition appears to have evolved independently at least twice within Dyrosauri- dae. Our analysis supports an African origin of Dyrosauridae with dispersals to the New World by the Late Cretaceous or earliest Paleocene. The presence of C. improcerus, together with undescribed taxa from the Cerrejon´ Formation, suggests a radiation of dyrosaurid crocodyliforms, possibly following the K-P boundary, in tropical South America. INTRODUCTION Dyrosauridae gen. et sp. indeterminate. Marshall and de Muizon Dyrosauridae is an extinct family of mesoeucrocodylians (1988) produced a faunal list from Tiupampa, Bolivia, that typically found in transitional marine sediments from the included a crocodyliform referred to the dyrosaurid Soko- Late Cretaceous through Late Eocene (Brochu et al., 2002). tosuchus aff. ianwilsoni and thought to be Late Cretaceous in age. Fossils from this site were later referred to Dy- Downloaded At: 19:17 29 January 2010 The family was named by Giuseppe De Stefano in 1903 for the type genus Dyrosaurus, named by A. Pomel for the rosauridae gen. et sp. indet. and considered Paleocene in age locality of the holotype, Djebel Dyr, near Tebessa,´ Alge- (Buffetaut, 1991). A mandibular symphysis of Sulcusuchus er- ria (Pomel, 1894). Dyrosaurid crocodyliforms are well known raini from Patagonia was attributed to Dyrosauridae (Gasparini from the Late Cretaceous to Eocene of northern Africa and and Spalletti, 1990; Gasparini, 1996), but was later referred southwestern Asia (e.g., Swinton, 1930, 1950; Arambourg, to Plesiosauroidea (Gasparini and de la Fuente, 2000) outside 1952; Halstead, 1973, 1975; Halstead and Middleton, 1976; of Crocodylomorpha (Gasparini, 2007). Additional dyrosaurid Buffetaut 1976a, 1976b, 1977, 1978, 1979, 1980; Storrs 1986; Buf- specimens from the Paleocene part of the Maria Farinha For- fetaut et al., 1990; Langston, 1995) as well as the Late Cre- mation have been found from the same unit that H. derbianus taceous to Paleocene of eastern North America (e.g., Troxell, was discovered, including some isolated teeth and vertebrae 1925; Parris, 1986; Denton et al., 1997), and possibly the Late (Carvalho and Azevedo, 1997; Gallo et al., 2001). Barbosa Cretaceous of Europe (Buffetaut and Lauverjat, 1978). How- et al. (2008) also recently described a new genus and species, ever, the fossil record of dyrosaurids in South America is more Guarinisuchus munizi, based on a complete skull and partial limited. lower jaw from the Maria Farinha Formation. Most of these sites Fossils of dyrosaurid crocodyliforms have previously been are south of the ancient tropical zone (Scotese, 2001; Fig. 1). Thus recovered from only four localities in South America. Hy- very little is known of the diversity of Dyrosauridae within South posaurus derbianus is known from somewhat fragmentary fos- America, and little is known of crocodyliforms as a whole for the sils from the Maria Farinha Formation in Pernambuco, Brazil ancient neotropics prior to the Eocene. (Cope, 1885, 1886). The Maria Farinha Formation was orig- Here we describe dyrosaurid fossils from the Cerrejon´ coal inally thought to be Late Cretaceous (Cope, 1885, 1886; mine in northeastern Colombia (Bloch et al., 2005; Hastings Buffetaut, 1976a, 1980), but has been more recently placed and Bloch, 2007, 2008). The fossil-bearing locality outcrops in in the Paleocene (Albertaoˆ et al., 1993). Argollo et al. the La Puente Pit and is situated in the underclay of Coal (1987) described a Late Cretaceous or Paleocene crocodyli- Seam 90 in the Cerrejon´ Formation. The age of the Cer- form assemblage from Huarachani in Bolivia that included rejon´ Formation has been estimated to be middle–late Pale- two teeth, two osteoderms, and a vertebra attributed to ocene based on carbon isotopes, pollen, spores, and dinoflag- ellate cysts (Fig. 2; Jaramillo et al., 2007). The surrounding matrix is comprised of bituminous coal and gray, fine-grained clay. The paleoenvironment of the section from which the fos- *Corresponding author. sils were recovered is transitional, with likely brackish water 139 140 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 30, NO. 1, 2010 FIGURE 1. World map of locations of known crocodyliform fossil material during the Paleocene. Circles represent locations ascertained as Pale- ocene in age, squares represent locations that have been contested as possibly Late Cretaceous in age, and the star represents the new locality in northeastern Colombia. Map of the Paleocene by Scotese, 2001. in a riverine-to-lagoonal setting. The environmental conditions SYSTEMATIC PALEONTOLOGY implied by the geology of the site, as well as associated fau- CROCODYLOMORPHA Walker, 1970 nas, including large freshwater turtles, a giant boid snake, CROCODYLIFORMES Hay, 1930 and dipnoan and elopomorph fishes (Bloch et al., 2008; Head MESOEUCROCODYLIA Whetstone and Whybrow, 1983 et al., 2009), are consistent with a transitional marine-freshwater Downloaded At: 19:17 29 January 2010 DYROSAURIDAE de Stefano, 1903 environment. The environment of the dyrosaurids in Colombia CERREJONISUCHUS, gen. nov. is likely more inland than the estuarine environment of the dy- rosaurid locality within the Umm Himar Formation of Saudi Ara- Etymology—Named for the Cerrejon´ Formation from which bia (Langston, 1995), but nearer to the coast than the fluvial set- the fossils were recovered within the Cerrejon´ coal mine on the ting of the northern Sudan dyrosaurid locality (Buffetaut et al., Guajira Peninsula of northeastern Colombia and -suchus, Greek 1990). for crocodile. We describe a new dyrosaurid based on three skulls, a lower Type and Only Known Species—Cerrejonisuchus improcerus jaw, and associated postcrania. Another 10 individual crocodyli- Range—Middle–late Paleocene, Colombia forms, represented by at least somewhat complete cranial or Diagnosis—As for type and only known species. mandibular material of at least two additional taxa of very dif- ferent morphotypes, have also been recovered from the Cerrejon´ CERREJONISUCHUS IMPROCERUS, sp. nov. Formation (e.g., Hastings and Bloch, 2008) and will be described elsewhere. Etymology—improcerus, Latin for diminutive, an allusion to Institutional Abbreviations—AMNH, American Museum not only its relatively short snout, but also its relatively small of Natural History; IGM, Museo Geologico,´ at the Insti- body size. tuto Nacional de Investigaciones en Geociencias, Minerıa´ y Holotype—UF/IGM 29, a nearly complete skull including the Quimica, Bogota,´ Colombia; UF, Florida Museum of Nat- entire snout, 11 teeth, a complete dorsal skull table (postorbital, ural History, University of Florida; YPM, Yale Peabody squamosal, parietal, and frontal) and a partial occipital region in- Museum. cluding exoccipitals, basioccipital, and partial basisphenoid. Terminology and Anatomical Abbreviations—Teeth and alve- Type Locality and Horizon—All known specimens are from oli will be referred to by numbers, with 1 being the most anterior. the Cerrejon´ Formation, underclay of Coal Seam 90 at the Premaxillary teeth and alveoli will have the initial ‘pm,’ maxillary La Puente Pit within the Cerrejon´ Coal Mine in Northeastern teeth and alveoli will use ‘m,’ and dentary teeth and alveoli will Colombia. Middle to Late Paleocene in age. Latitude 11.08.45.50 use ‘d.’ For example, the first tooth or alveolus of the premax- N, longitude 72.32.55.56 W. illa will be referred to as ‘pm1’ and the second tooth or alveolus Referred Specimens—UF/IGM 30, lower jaw including den- of the maxilla will be referred to as ‘m2.’ This nomenclature is taries and splenials and a total of 11 partial teeth. Latitude