Crocodilia Hayes, 2000
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publication ID |
https://doi.org/ 10.26879/1223 |
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persistent identifier |
https://treatment.plazi.org/id/EF7887D7-6533-D176-CAAD-FD41FC83FA68 |
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treatment provided by |
Felipe |
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scientific name |
Crocodilia Hayes, 2000 |
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Crocodilia Hayes, 2000 , table 1
dwarf alligatorid Bourque, 2013, p. 461
Referred specimens. Right premaxilla ( UF 422816; Figure 2 View FIGURE 2 ); complete parietal ( UF 333984; Figure 3 View FIGURE 3 ), fragment of a dorsal cranial bone (position uncertain; UF 425424; Figure 3 View FIGURE 3 ), right articular ( UF 422817; Figure 3 View FIGURE 3 ), fragment of dentary ( UF 425402; Figure 3 View FIGURE 3 ), 12 isolated teeth (for catalog numbers, see Appendix 1; select teeth in Figure 3 View FIGURE 3 ), neural arch of a dorsal vertebra ( UF 424653; Figure 3 View FIGURE 3 ), caudal vertebra ( UF 425435; Figure 3 View FIGURE 3 ), two unguals ( UF 424655, UF 425405; Figure 3 View FIGURE 3 ), and 83 partial to complete osteoderms (for catalog numbers, see Appendix 1; select osteoderms in Figure 3 View FIGURE 3 ).
Locality and horizon. Brooksville 2 is a series of at least five fissure-fill deposits of laminated clay and sand, formed within the older Suwannee Limestone, 35.5–33.3 Ma ( Hayes, 2000). The site is near the town of Brooksville, in Hernando County, Florida ( Figure 1). The age of the deposit was considered to be 26–25 Ma by Tedford et al. (2004) based on mammalian biochronology. Later analysis by Czaplewski and Morgan (2012) and Morgan et al. (2019) suggested a slightly older age range of 28–26 Ma for Brooksville 2. The premaxilla is from Quarry 1E, although some specimens are from Quarries 1A, 1B, 1D, and some of uncertain provenience within the site (further details in Appendix 1). Much of the material at this quarry is thought to have arrived via subaqueous transport through karst solution pipes ( Hayes, 2000). There were no fissures or sinkholes with younger fossils in this part of the quarry, and the unusual orange color of the Alligator tooth enamel ( Figure 3E–J View FIGURE 3 ) is also observed on Oligocene mammals from the same fissure-fills (e.g., Czaplewski and Morgan, 2012).
Description. The premaxilla recovered from Brooksville 2 (UF 422816) bears the characteristic premaxillary 'notch' alongside the naris that defines the genus Alligator ( Figure 2 View FIGURE 2 ; Brochu, 1999; Brochu, 2011). Moreover, it has a forward-facing external naris, consistent with A. prenasalis (Brochu, 1999) . This is counter to the more dorsal-facing naris of A. olseni and the extant Alligator mississippiensis ( Daudin, 1802) (Brochu, 1999) . Because the anterior end of the premaxilla is missing, and no part of the nasal is preserved, it is unclear whether or not the naris would have been fully bisected, as in other Alligator (Brochu, 1999) . However, as the premaxilla curves back anteriorly along the nasal suture, we can say the nasal almost certainly penetrated well into the naris. UF 422816 bears three preserved alveoli, although more were likely present in the anterior broken portion. Based on the presence of the suture with the maxillary, these would be the third through fifth positions. Of these three preserved alveoli, the fourth is the largest, followed by the third, then the fifth (see measurements in Table 1). Sutural surfaces are preserved with the right maxilla (posteriorly), left premaxilla (ventrally), and right nasal (medially). Part of an occlusal pit is preserved at the sutural contact with the right maxilla, for reception of the fourth dentary tooth. This character is consistent across all Alligator species (Brochu, 1999; Brochu, 2011), and is distinct from Crocodylidae as well as Oligocene Thecachampsa antiquus Leidy, 1852 (synonymized with Gavialosuchus ; Myrick, 2001; Brochu, 2011). The dorsal premaxillary process extends posteriorly only slightly between the nasal and maxillary bones, indicating a rather short snout. This process is also short in the fairly brevirostrine Alligator species, A. mcgrewi ( Schmidt, 1941) , and makes a similar angle from the acute posterior end between the nasal and maxillary sutures. This angle of the dorsal premaxillary process is wider in other Alligator species, including extant A. mississippiensis . The dorsal ornamentation is highly developed and rugose for such a small bone. The degree of pitting is typical of extant Alligator that are well beyond sexual maturity, yet the size is similar to an immature individual.
The parietal recovered from Brooksville 2 (UF 333984) is isolated, but complete, including sutures with the frontal, postorbital, squamosal, and supraoccipital ( Figure 3 View FIGURE 3 ). The frontoparietal suture is convex and remains on the skull table. The dermal part of the parietal overhangs the supratemporal fenestra weakly. There is a shallow fossa at the anteromedial corner of the supratemporal fenestra, and the medial parietal wall is
4th Premaxillary Alveolus Length 4.28
Width 3.92
5th Premaxillary Alveolus Length 2.78
Width 2.63
Premaxillary-Maxillary Suture Length 19.74
Premaxillary-Premaxillary Suture Length 10.91
Premaxillary-Nasal Suture Length 12.05
imperforate. The parietal and squamosal meet along the posterior wall of the supratemporal fenestra. The skull table is planar at maturity and does not slope ventrally. There is no supraoccipital exposure on the dorsal surface of the parietal ( Figure 2 View FIGURE 2 ), which is consistent with A. mcgrewi , A. olseni and A. mississippiensis but not with A. prenasalis (Brochu, 1999) . The supratemporal fenestra is longer than wide, with a thick posterior bar. There is a recess that connects with the pneumatic system (sensu Brochu, 2011).
The 12 preserved teeth from Brooksville 2 exhibit morphology that is consistent with Alligator ( Figure 3 View FIGURE 3 ). These include the globidontan morphology of posterior dentition ( Figure 3E View FIGURE 3 ), as well as spade-shaped morphology from the middle of the jaw ( Figure 3 View FIGURE 3 F-G). Several specimens include full roots, indicating they were likely not shed teeth. These teeth are also consistent in size with the premaxilla (UF 422816) and are inconsistent with that of contemporary Thecachampsa , which are longer and recurved in the middle of the jaw and more triangular in the rear (Myrick 2001).
A caudal vertebra was recovered at Brooksville 2 ( Figure 3 View FIGURE 3 U-V). Although only partial, it appears to represent roughly the mid-section of the tail. This vertebra is of small size (14.78 mm centrum length) and exhibits a fully closed neurocentral suture.
A total of 83 partial to complete osteoderms were recovered from Brooksville 2 ( Figure 3 View FIGURE 3 ). These have the characteristic patterns of a square or anteroposteriorly rectangular shape, median keel, anterior imbricating shelf, and dorsal pitting found in Alligator . The more complete osteoderms can be recognized as belonging to the dorsal shield, rather than the nuchal shield, due to the development of the highly rectangular shape. Several osteoderms are complete enough to exhibit fully-developed edges and lateral sutures ( Figure 3 View FIGURE 3 ), which are consistent with individuals well beyond yearling age (see Discussion). The presence of a keel is inconsistent with Thecachampsa , which also has mediolaterally rectangular osteoderms, rather than anteroposteriorly rectangular ones (Myrick, 2001).
CROCODYLIA Gmelin, 1789,
sensu Benton and Clark, 1988
sensu Norell et al., 1994
Referred specimens. Material from Live Oak ( Figure 4 View FIGURE 4 ) includes: three isolated teeth (UF 424639– 41), two caudal vertebrae (UF 424637–8), and four osteoderms (UF 424633–36). A partial osteoderm (UF 16729; Figure 5 View FIGURE 5 ) from the I-75 site is referred as well.
Localities and horizons. The Live Oak fossil site (a.k.a. SB-1A; Figure 1) represents an unstratified sequence of conglomerate deposited in a single fissure in the Suwanee Limestone ( Frailey, 1978). Mammalian biochronology suggests this site is slightly younger than Brooksville 2, at about 25–24 Ma ( Figure 1; Tedford et al., 2004). Fossils from the I-75 site ( Figure 1) were recovered from a small karst solution fill, exposed during road construction. The geologic age is around 30 Ma, either late Whitneyan or early Arikareean ( Patton, 1969; Hayes, 2000; Morgan et al., 2019). Other than the fossils of shark teeth and other marine fishes from the limestone bedrock, all the age-diagnostic fossils from these two localities provide a consistent date with no evidence of contamination of younger material.
Description. The additional three teeth preserved from Live Oak likewise display morphology entirely consistent with Alligator ( Figure 4 View FIGURE 4 ). More specifically, these teeth display the typical spade-shaped morphology from the middle of the jaw. One specimen also includes a full root, suggesting it was likely not a shed tooth (UF 424639; Figure 4B View FIGURE 4 ). Again, these teeth are consistent in size with the premaxilla from Brooksville 2 (UF 422816) and are inconsistent with that of contemporary Thecachampsa (Myrick, 2001) .
Two caudal vertebrae were recovered at Live Oak ( Figure 4 View FIGURE 4 ). Similar to Brooksville 2, these seem to represent the mid-section of the tail. These vertebrae are of even smaller size (10.34–12.00 mm centrum length) and also exhibit fully closed neurocentral sutures.
Four osteoderms have been recovered at Live Oak ( Figure 4 View FIGURE 4 ) and a partial osteoderm has been recovered from the I-75 fossil site ( Figure 5 View FIGURE 5 ). Much like the remains at Brooksville 2, these are all of small size, are anteroposteriorly rectangular, and possess a median keel, an anterior imbricating shelf, and dorsal pitting like that found in Alligator . The more complete osteoderms can be recognized as belonging to the dorsal shield. Again, these appear to represent individuals that were at least beyond yearling age (see Discussion). Not only are they much smaller, but they are inconsistent with the contemporary Thecachampsa (Myrick, 2001) .
| UF |
Florida Museum of Natural History- Zoology, Paleontology and Paleobotany |
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