Citation:

Adams, T. L., Polcyn M. J., Mateus O., Winkler D. A., & Jacobs L. L. (2011).  First occurrence of the long-snouted crocodyliform Terminonaris (Pholidosauridae) from the Woodbine Formation (Cenomanian) of Texas. Journal of Vertebrate Paleontology. 31, 712-716., Jan: So Methodist Univ, Univ Nova Lisboa

Abstract:

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INTRODUCTION

Here we report the occurrence of Terminonaris represented by three specimens recovered from the early Middle Cenomanian (96 Ma) Woodbine Formation of Lewisville Lake, Denton County, Texas. Crocodyliform fossils are relatively common throughout the Woodbine Formation of north-central, Texas, typically represented by isolated teeth, vertebrae, and osteoderms (Lee 1997a, 1997b; Jacobs and Winkler, 1998; Tykoski and Fiorillo, 2010). As yet, the only named species of crocodyliform from the Cenomanian of Texas is Woodbinesuchus byersmauricei Lee, 1997a, found in the lowermost Woodbine Formation (Lee 1997a; Jacobs and Winkler, 1998).

The first specimens of the longirostrine crocodyliform Terminonaris Osborn, 1904 (=Teleorhinus) were collected from the Late Cretaceous (Early Turonian) of south-eastern Montana in 1903 (Mook, 1934; Wu et al., 2001). Osborn (1904) described one of the two original skeletons recovered as Teleorhinus browni (AMNH 5851) and Mook (1934) the second as Teleorhinus robusta (AMNH 5859). Due to the preoccupation of the name Teleorhinus, Wu et al. (2001) replaced the genus name with Terminonaris, which had originally been provided by Osborn (1904). Wu et al. (2001) also placed Teleorhinus mesabiensis (SMM P68.56.1), described by Erickson (1969), into the synonymy of Terminonaris robusta Mook, 1934. Terminonaris robusta differs from the type species T. browni in having overall broader rostral and cranial widths and the presences of a small external mandibular fenestra (Wu et al., 2001; Shimada and Parris, 2007). In addition to the two Montana specimens, Terminonaris is known from an upper jaw fragment from the Late Cenomanian of Bavaria, Germany (Terminonaris cf. T. browni; Buffetaut and Wellnhofer, 1980; Wu et al., 2001), an anterior portion of rostrum from the Early Turonian of Minnesota (T. robusta; Erickson, 1969), a nearly complete skeleton from Saskatchewan (T. robusta; Wu et al., 2001) and partial nasals and maxillae from the Middle Turonian of Kansas (Terminonaris cf. T. browni; Shimada and Parris, 2007;).

     Institutional Abbreviations–AMNH, The American Museum of Natural History, New York; FHSM, Fort Hays State University, Sternberg Museum of Natural History, Hays, Kansas;

SMNH, Royal Saskatchewan Museum (formerly the Saskatchewan Museum of Natural History), Regina; SMM, Vertebrate Paleontology Section of the Science Museum, Minnesota, Saint Paul; SMU, Southern Methodist University Shuler Museum of Paleontology, Dallas, Texas.

AGE AND GEOLOGIC SETTING

The Upper Cretaceous Woodbine Formation of north-central Texas unconformably overlies the Grayson Marl, the uppermost formation of the Washita Group, and is unconformably overlain by the Eagle Ford Group (Fig.1; Dodge, 1969; Lee, 1997a, 1997b; Jacobs and Winkler, 1998). In outcrop, it extends from the Red River and thins to the south (Dodge, 1969; Jacobs and Winkler, 1998). Dodge (1969) designated four lithologic units within the formation near Dallas and Fort Worth, in ascending order: the Rush Creek, Dexter, Lewisville, and Arlington members. The Texas Terminonaris fossils were collected along the northern shore of Lewisville Lake at low lake level in the Arlington Member in the uppermost part Woodbine Formation (SMU Loc. 142 and 495; Fig. 2). The ammonite Conlinoceras tarrantense, a zonal marker for the base of the middle Cenomanian, were found within the Lewisville Member and in the Tarrant Formation (lowermost Eagle Ford Group), indicating an age no younger than early Middle Cenomanian (approximately 96 Ma; Kennedy and Cobban.1990; Emerson et al., 1994; Lee, 1997a; Jacobs and Winkler, 1998; Gradstein et al, 2004).

The matrix encasing specimen SMU 76590 is very fine- to fine-grained sandstone with ferruginous cement and iron concretions. SMU 71698 occurred in fine-grained glauconitic, trough cross-bedded sandstone, while SMU 71699 comes from ripple cross-bedded sandstone with planar laminations. The upper Woodbine sediments represent a lowstand sequence within an early transgressive system tract of the Greenhorn Cycle of Kauffman and Caldwell (1993). The uppermost Woodbine represents a terrigenous coastal depositional system with fluvio-deltaic influences (Powell, 1968; Dodge, 1969; Lee, 1997a, 1997b; Jacobs and Winkler, 1998).  

SYSTEMATIC PALEONTOLOGY

CROCODYLIFORMES Hay, 1930

MESOEUCROCODYLIA Whetstone and Whybrow, 1983

NEOSUCHIA Benton and Clark, 1988

PHOLIDOSAURIDAE Zittel and Eastman, 1902

TERMINONARIS Osborn, 1904 sensu Wu, Russell, and Cumbaa, 2001

TERMINONARIS ROBUSTA Mook, 1934

(Figs. 3–5)

     Referred Material– SMU 76590: nearly complete rostrum consisting of partial premaxillae, maxillae, nasals, dentaries, and partial splenials; fragment of left posterior mandible; posterior dorsal vertebra. SMU 71698: fragment of left maxilla. SMU 71699: partial osteoderm.

     Locality and Horizon– Arlington Member, uppermost Woodbine Formation, Upper Cretaceous (early Middle Cenomanian). SMU 76590 is from the Lakewood Village Locality (SMU Loc. no. 495), Lewisville Lake, Denton County, Texas. SMU 71698 and 71699 are from the Easy Street Locality (SMU Loc. no. 142), Lewisville Lake, Denton County, Texas.

DESCRIPTION

     General Description–The rostrum (SMU 76590), broken anterior to the orbits at the 22^nd maxillary alveoli, is well-preserved and strongly resembles that of the type specimen (AMNH 5850) and SMNH P2411.1 of T. robusta (Mook, 1934; Wu et al., 2001). Two transverse fractures separate the rostrum into thirds. The anterior one-third has maxillae and dentaries articulated in tight occlusion, while the remaining two-thirds are separated into upper and lower elements. The maximum length along the midline is 620 mm. It is 135 mm wide at the posterior end and gradually narrows anteriorly to its minimum width of 55 mm were it broadens again to 74 mm. The dorsal and ventral surfaces are ornamented with elongated pits and ridges, similar to SMNH P2411.1 described by Wu et al. (2001). 

     Cranial–The premaxillae are incomplete and do not include the anterior terminus. The preserved portion is elongate and narrows posteriorly to extend between the maxillae to the level of the ninth maxillary alveoli. The dorsal aspect of the anterior palate is exposed, and shows that the ventral premaxillae are separated by the anterior process of the maxillae just anterior to the first maxillary tooth.

The maxillae are separated dorsomedially by the premaxillae anteriorly and by the nasals posteriorly. The posterior termination of the maxillae is not preserved. There are 22 alveoli preserved in the right maxilla and 19 on the left. The maxillary alveoli are subequal in size with an average alveolar diameter of 14 mm. The interaveolar spacing ranges from 9 to 16 mm anteriorly and reduces to less than 5 mm at the posterior end. The alveolar edges are prominent, giving the rostrum an undulating appearance. As seen in T. robusta AMNH 5850, SMNH P2411.1, and SMM P68.56.1 (Mook, 1934; Erickson, 1969; Wu et al., 2001), a distinct longitudinal groove extends along the entire length of the lateral surface, dorsal to the dental margin. Wu et al. (2001) observed a similar groove, although weakly-developed, in Terminonaris browni (AMNH 5851). The majority of the ventral palate of the maxillae is not visible, due to either occlusion with the mandible or a lack of preservation. SMU 71698 is a fragment of left posterior maxilla. There are nine alveoli preserved with an average diameter of 10 mm (Fig. 5A and B).

The nasals are long and slender. At the 20^th maxillary alveoli, the nasals are 25 mm wide. They gradually narrow anteriorly to the level of the eighth alveoli, forming a wedge between the premaxillae. On their ventral surface, the nasals are smooth and concave and create a longitudinal ridge running along the midline, similar to T. robusta FHSM VP-4387 (Shimada and Parris, 2007). Only the most anterior portion of the left lacrimal can be discerned lateral to the posterior margin of the nasal. Although the frontals are not preserved, their position can be discerned at the posterior margin of the nasals, indicating that they extended anteriorly to the same level as the lacrimal.  

The dentaries have a longitudinal groove ventral to the dental margin, running along the lateral extent of the rostrum. The presence of a ventral groove was described in the type (AMNH 5850), and in SMNH P2411.1 and SMM P68.56.1 of T. robusta, but is absent in T. browni (AMNH 5851; Mook, 1934; Erickson, 1969; Wu et al., 2001). There are 23 alveoli preserved on the left dentary and 22 on the right. The anterior portion of the splenials extends between the dentaries to the level of the 14^th alveoli, and comprises 50% of the symphysis in ventral view. The rami diverge at the 21^st alveoli. The fragment of left posterior mandible (SMU 76590) consists of posterior dentary, splenial and anterior angular (Fig. 5C).

The 2^nd maxillary tooth is present in SMU 76590 and the remaining alveoli are occupied by either broken or replacement teeth. The teeth are homodont, conical, and recurved, projecting slightly anterior and labial. A carina is present along both the concave lingual and convex labial surfaces. The enamel is generally smooth, although there are fine striations on the surface of several broken teeth.

     Postcranial Skeleton–An isolated dorsal vertebra (SMU 76590) was recovered from the Lakewood Village Locality (Fig. 5D and E; SMU Loc. no. 495). It is amphicoelous and preserves the base of the neural arch. A partial dorsal osteoderm (SMU 71699) was found at the Easy Street Locality (Fig. 5F; SMU Loc. no. 142). It is 104 mm wide and is characterized by irregular pits, with no indication of a keel. The anterolateral portion of the osteoderm is not preserved, so the presence of a spur cannot be determined. Broad dorsal osteoderms with shallow, irregular pits and anterolateral spur are found in the mesosuchian families Goniopholididae, Pholidosauridae, and Teleosauridae, and most likely represents a plesiomorphic character.

DISCUSSION

     Phylogeny–Diagnostic characters for the genus Terminonaris include: (1) the anterior terminus of the premaxillae transversely broad and strongly reflected ventrally; (2) the posterolateral process of squamosal bearing a pronounced ventral process enclosing the dorsal half of lateral end of paroccipital process; (3) the lateral termination of the paroccipital process is greatly broadened dorsoventrally; (4) the exoccipital has a small but clear tuberosity dorsolateral to foramen magnum on its occipital surface (sensu Wu et al., 2001), which are not preserved in SMU 76590. However, the nasal contact with the premaxilla at the level of the ninth maxillary alveoli and the longitudinal groove running along the lateral expanse of the maxillae and dentaries justify identification as Terminonaris robusta.

The exclusion of the nasal from the external nares, by the premaxillae contact is synapomorphic of Pholidosauridae according to Sereno and Larsson (2009: character 8) and the posterodorsal premaxillary process extension beyond third maxillary alveolus and the absence of sculpturing along alveolar margin on lateral surface of maxilla, present in SMU 76590, claimed to be synapomorphic of the clade with Dyrosaurus, Terminonaris, Pholidosaurus, and Sarcosuchus (Sereno and Larsson, 2009) allow a confident classification of SMU 76590 as a Pholidosauridae.  The snout, however, is much longer than wide which is seen as a plesiomorphic condition.

A small number of recent phylogenetic analyses have included Terminonaris (Fig. 6; Sereno et al., 2001, 2003; Jouve et al., 2006; Pol et al., 2009; Sereno and Larsson, 2009) and all are consistent is reconstructing Terminonaris as more derived than Dyrosaurus. Dyrosaurids are reconstructed in a relatively basal position in most of these analyses sharing a basal dichotomy with Thalattosuchians in analyses in which that taxon is included. The exceptions are the analyses of Sereno et al, 2001, 2003 and Pol et al 2009 in which Pholidosaurus is the most basal form. Sereno and Larsson (2009) place Terminonaris within neosuchians in the clade Pholidosauridae, including Goniopholis, Dyrosaurus, Terminonaris, Pholidosaurus, and Sarcosuchus.  The placement of Pholidosaurus, Goniopholis and Dyrosaurus in the same family-ranked clade would give priority to the name Goniopholidae Cope 1875, while Pholidosauridae Zittel & Eastman 1902 and Dyrosauridae de Steffano 1903 become junior synonyms. Jouve et al. (2008) places Terminonaris as a sister group of Chananisuchus and other Dyrosauridae, while the phylogenetical analysis conducted by Hill et al. (2006) placed Terminonaris in a polytomy with the 'dyrosaurids', Suchosaurus,  Elosuchus and  Eutretauranosuchus. However, Jouve (2009) confirms the position of Terminonaris close to Pholidosaurus, and Sarcosuchus, but unrelated to Goniopholis. We retain the taxonomy Pholidosauridae because 1) Terminonaris and Pholidosaurus are consistently related in most phylogenetical analyses, and 2) Pholidosauridae takes priority over Dyrosauridae in the eventuality of synonymization.

     Occurrences–The Lewisville Lake specimens are not only significant for being the first record of Terminonaris in Texas; they are also the earliest and the southernmost occurrence of this crocodyliform globally. Up until now, known occurrences in North American were restricted to the Early and Middle Turonian deposits of the Western interior Sea.  The earliest known occurrence is from the Late Cenomanian of Europe (Buffetaut and Wellnhofer, 1980; Wu et al., 2001; Shimada and Parris, 2007). Shimada and Parris (2007) proposed that dispersal from Europe into North America took place by latest Cenomanian or earliest Turonian, following the paleocoastline of western Africa to South America, and the Baltic islands and continents to the east coast of North America, as proposed for the Late Cretaceous dolichosaurid, Coniasaurus (Caldwell and Cooper, 1999).

Irrespective of the differences in phylogenetic topology and nomenclature, the paleogeographic distribution of the constituent taxa (Fig. 6; Table 1) in the context of plate tectonics, provide some constraints on the timing and routes of dispersal of Terminonaris. Terminonaris is found in marginal marine and offshore deposits, and because of that, its distribution is known to include warm-temperate waters along the margins of seaways (Wu et al. 2001; Shimada and Parris, 2007). They have been described as being either marine (Hua and Buffetaut, 1997) or as a “sea-going ‘terrestrial’ vertebrate” as noted by Wu et al. (2001:507). Hua and Buffetaut (1997) proposed a life habit for Terminonaris as being similar to that of Crocodylus porosus, the extant salt-water crocodile.

The marine crocodyliforms Thalattosuchia have a global distribution and along with their early occurrence renders them uninformative. The earliest dyrosaurids are known from the Maastrichtian of North America and northwest Africa and younger forms are known from the Paleocene of North and South America and Africa, and the Eocene of northwest Africa. Their relatively late occurrences in the Maastrichtian, compared with their consistent basal position in the phylogenetic analyses, suggest a long ghost lineage of unknown origin and are therefore also uninformative. The phylogenetic relationship of Pholidosaurus is ambiguous and is known only from Europe and is based on relatively poorly preserved material. 

The consistently closely related Sarcosuchus has an Aptian (Early Cretaceous) African and South American distribution and although only included in the analysis of Jouve et al., 2006, the closely related Elosuchus is known only from the Late Aptian of Africa. Sarcosuchus and Elosuchus are only known from fluvial freshwater deposits (Buffetaut and Taquet, 1977; Sereno et al., 2001; Lapparent de Broin, 2002). The opening of the South Atlantic is placed at 132.4 ± 1.4 and 132.9 ± 2.8 Ma (Hawkesworth et al., 1992), prior to which overland movement between Africa and South America was possible (Fig. 7A), evidenced by the distribution of Sarcosuchus, amongst other Lower Cretaceous taxa.

By the first occurrence of Terminonaris in the Cenomanian (96 Ma) of North America, Europe, Africa and South America are widely separated (Fig. 7B), rendering an open ocean, cross-South Atlantic dispersal unlikely. Thus the geographic and temporal distribution of Sarcosuchus predicts a Gondwanan origin of the closely related Terminonaris in the later part of the Lower Cretaceous. Whether the migration into North America occurred prior to the Cenomanian is unknown; nonetheless, an early migration during periods of low sea level, as occurs in the Aptian is most likely. These are times when portions of the Apulian Plate are above sea level and although composed largely of shallow marine carbonate platform (Polcyn et al., 1999), these emergent landmasses may have facilitated movement between Gondwana and Europe. Land bridges between South and North America are unknown and the dinosaur faunas are disparate; nevertheless, the continental plates are in close proximity and overwater dispersal is not unlikely. The alternative would indicate an origin of Terminonaris in Laurasia or North America and communication via Beringia. However, given the phylogenetic hypotheses we are employing here, that is doubtful.