Calligenethlon watsoni (Steen, 1934)

Adams, Gabrielle R., Otoo, Benjamin K. A., Bohus, Caleb P. W., Micucci, Logan M. & Maddin, Hillary C., 2025, Anatomy and revised diagnosis of the embolomere Calligenethlon watsoni from Joggins, Nova Scotia, based on micro-computed tomography, Zoological Journal of the Linnean Society (Statistics in Society) 203 (2), pp. 109-109 : 109-

Review of specimens referred to Calligenethlon watsoni

Specimen number:

RM 2.1122, type specimen (Supporting Information, Fig. S1 ) .

Original publication: Steen (1934).

Consists of: RM 2.1122 includes an articulated skull table, which is incomplete anteriorly, and a maxilla bearing teeth. Disarticulated postcrania include a scapulocoracoid, a possible clavicle, an interclavicle, a radius, rib fragments, and a broken femur. All bones are scatered and in various levels of completeness. RM 2.1122 represents a minimum of two individuals, based on the presence of four clavicles.

Comments: RM 2.1122 was found in an upright tree stump. Te skull is distinguished by elongate, parallel-sided lateral margins and slender tabular horns that protrude posteriorly far beyond the posterior margin of the skull ( Steen 1934). Te maxilla shows an undifferentiated dentition, like Archeria ( Holmes 1989) , but the morphology is conical or peg-like, unlike the chisel-shaped teeth in Archeria ( Holmes 1989) or the recurved apices in Proterogyrinus ( Panchen 1970, Holmes 1984). Te vertebral centra known from RM 2.1122 are deeply amphicoelous, distinguishing it from Dendrerpeton and other temnospondyls ( Steen 1934). Both single- and double-headed ribs are present ( Steen 1934). Tere is no evidence of the forelimbs but the scapulocoracoid is preserved, as well as four clavicles ( Carroll 1967). Te pelvis present in the same block as RM 2.1122 was considered by Steen (1934) to be of unknown affinity, but Carroll (1967) associated it with Calligenethlon . It is gracile and bears an extremely slender posterior process and a posteriorlyleaning dorsal process.

Specimen number:

RM 2.1193a (Supporting Information, Fig. S2 ), type specimen of Atopotera moneres Steen, 1934 , but was later referred to Calligenethlon watsoni ( Carroll, 1967) .

Original publication: Steen (1934).

Consists of: Impressions of the interior surfaces of two skull tables. The first preserves a fragmentary parietal, elongate frontal, and the postfrontal, prefrontal, and lacrimal, which surround the right orbital. The second impression preserves the right parietal, fragments of the postparietal, tabular, supratemporal, an elongate frontal and prefrontal of a skull table, as well as a squamosal, quadratojugal, and a narrow maxilla.

Comments: Tese skulls were found in upright lycopsid tree trunks at Joggins. RM 2.1193 was originally named ‘ Atopotera moneres ’ by Steen (1934) but was referred to Calligenethlon by Carroll (1967). Both skulls are clearly embolomeres and are not significantly different from the type of Calligenethlon ( Carroll 1967) . Tis referral added further knowledge of the anatomy of the cheek margin and anterior skull of Calligenethlon . In all instances, the cheek region was disarticulated from the skull table, possibly indicating a loose atachment in life ( Carroll 1967).

Specimen number:

RM 12115 (Supporting Information, Fig. S3 ) .

Original publication: Carroll (1967).

Consists of: Pterygoid, interclavicle, radius, and scapula.

Comments: Carroll (1967) tentatively included RM 12115 in the referral of ‘ Atopotera moneres ’ to Calligenethlon , suggesting that it may have been associated with the other ‘ Atopotera ’ material because of the similarity of the matrices. With this referral, part of the palate of Calligenethlon became known. Carroll (1967) describes the pterygoid as having a smooth medial margin and a denticulated ventral surface. Tis morphology has been noted in other Calligenethlon specimens, such as NHMUK R 4553 ( Carroll 1967). Te interclavicle was questionably associated with the rest of the ‘ Atopotera ’ material but is consistent with other interclavicles referred to Calligenethlon . Te interclavicle preserves a long posterior stem and an ovoid anterior plate, similar to the morphology seen in Gephyrostegus bohemicus Jaekel, 1902 ( Carroll, 1967). Te anteriormost margin bears many thin projections, like the teeth of a comb ( Carroll 1967). Tis morphology is also seen in Archeria ( Romer 1957) .

Specimen number:

NM 10050 (Supporting Information, Fig. S4 ) .

Original publication: Carroll (1967).

Consists of: Vertebrae, femur, and tibia.

Comments: NMC 10050 shows dorsally complete and incomplete intercentra, but always fully embolomerous pleurocentra ( Carroll 1967). Te femur of NCM 10050 preserves a long shaf and is more gracile than that of Archeria ( Romer 1957) . Similarly, the tibia is smaller and more lightly built than that of Archeria ( Romer 1957) and other embolomeres.

Specimen number:

NMC 10096 (Supporting Information, Fig. S5 ) .

Original publication: Carroll (1967).

Consists of: A basioccipital.

Comments: NMC 10096 may be associated with NMC 10050 ( Carroll 1967). Tis is the only braincase material known for Calligenethlon , apart from the braincase material present in the specimen described above. Te basioccipital is bullet-shaped, with a wide posterior width that tapers to a blunt point anteriorly. Te bone is incompletely preserved along most margins but there appears to be the base of a wing-like process on the lef lateral margin of the basioccipital, as is seen in Archeria ( Clack and Holmes 1988) and Pholiderpeton ( Clack 1987a) .

Specimen number:

NMC 10119 (Supporting Information, Fig. S6 ) .

Original publication: Carroll (1967).

Consists of: Clavicle and interclavicle.

Comments: Te interclavicle is known from the type specimen, RM 12115, and NMC 10119. Tese specimens show a broad, flat anterior plate with radiating grooves on the ventral surface. Te bone is diamond-shaped and NMC 10119 particularly shows thin, comb-like structures along the anterior margin. Similar structures are described for Archeria , but Calligenethlon displays them more extensively ( Carroll 1967). One clavicle is preserved in NMC 10119, but it is incomplete posteriorly. It shows a broad proximal head with radiating pits and grooves ( Carroll 1967). Other clavicles are known from NHMUK R 442, showing a narrow stem and distal head ( Carroll 1967).

Specimen number:

UMZC T.49 (Supporting Information, Fig. S7 ).

Original publication: Carroll (1967) as DMSW B.224.

Consists of: Right humerus.

Comments: Te humerus of Calligenethlon is also known from NHMUK R 4553 but is much more complete in UMZC T.49. Te overall morphology of the bone is similar to that in Archeria ( Romer 1957) in that it is lightly built and more elongated than those described for Pholiderpeton ( Clack 1987a) or Proterogyrinus ( Holmes 1984) . It preserves an entepicondylar foramen like Archeria ( Romer 1957) , Proterogyrinus ( Holmes 1984) , and other embolomeres. Te entepicondylar region is flat and extends further posteriorly than Pholiderpeton ( Clack 1987a) , but not as far as Proterogyrinus ( Holmes 1984) .

Specimen number:

NHMUK PV R 442 (Supporting Information, Fig. S8 ).

Original publication: Carroll (1967).

Consists of: Ulna, radius, and clavicle.

Comments: Carroll (1967) notes again the similarity in the clavicles and ulna to the morphology of Archeria ( Romer 1957) based on this specimen. NHMUK PV R 442 also reveals that Calligenethlon possesses a well-developed olecranon process of the ulna, similar to that seen in Pholiderpeton ( Clack 1987a) and Archeria ( Holmes 1989) , and quite different from that of Proterogyrinus ( Holmes 1984) . Te shaf of the ulna in NHMUK PV R 442 is broken distally, but it preserves an elongate, parallel-sided shape, similar to that of Archeria ( Romer 1957) .

Specimen number:

NHMUK R 4553 (Supporting Information, Fig. S9 ), type of Dendryazousa , now Calligenethlon watsoni ( Carroll 1967) .

Original publication: Steen (1934).

Consists of: Part and counterpart of the type skull, NHMUK R 4553. Includes the skull table and various disarticulated postcranial bones.

Comments: Tis specimen was named the type specimen of Dendryazousa by Steen (1934) but was later referred to Calligenethlon by Carroll (1967). Te pleurocentra are complete rings and intercentra are incomplete dorsally, like the condition seen in CMN 10050. Te ventral surface of the clavicles is wide and shaped similarly to those in RM 2.1122 and other Calligenethlon specimens. Te ilium is preserved in articulation with the ischium and pubis. It displays the beginnings of a slender posterior process, but it is very incomplete. Te morphology of the ischium is consistent with that of the type specimen in that its dorsal margin is slightly concave as it extends posteriorly ( Carroll 1967). Tis character is reminiscent of the ischium morphology described for Archeria ( Romer 1957) .

Specimen number:

NSM 988GF70.1 (Supporting Information, Fig. S10 ).

Original publication: Godfrey et al. (1991).

Consists of: A section of articulated trunk vertebrae, neural arches, and ribs.

Comments: Te vertebral section preserved in NSM 998GF70.1 shows progressive ossification of the dorsal suture in the intercentra moving posteriorly down the vertebral column, from a ventral crescent to a fully fused, disc-shaped intercentrum ( Godfrey et al. 1991). Both dorsally complete and dorsally incomplete intercentra are preserved in specimen NCM 10050, but NSM 998GF70.1 is the first conclusive evidence of both morphologies within one individual. Te neural spines are broad and similar in morphology to those of Proterogyrinus ( Godfrey et al. 1991) . Tis material also provides the first evidence of a larger embolomere at Joggins, which, if indeed are assignable to Calligenethlon , indicates Calligenethlon could obtain larger body sizes than previously thought.

Specimen number:

RM 20.4984 (Supporting Information, Fig. S11 ).

Original publication: Godfrey et al. (1991).

Consists of: A series of articulated posterior presacral vertebrae, along with haemal arches and neural spines. Also preserved are an ilium, femur, and tarsal bones.

Comments: Te morphology of the ilium in RM 20.4984 is markedly similar to that of the ilium in the Calligenethlon type specimen ( Godfrey et al. 1991). However, the length of the posterior process in RM 20.4984 is 220% that of the type specimen, which, like NSM 988GF70.1, suggests Calligenethlon could obtain much larger body sizes than was previously thought.

Specimen number:

NSM 994GF1.1 ( Fig. 1 ) .

Original publication: Holmes and Carroll (2010).

Consists of: Articulated anterior half of an embolomere skeleton.

Comments: NSM 994GF1.1 is one of very few tetrapod specimens found outside a stump at Joggins. In spite of exceptionally good preservation, the few diagnostic characters known for Calligenethlon were not preserved, making an unequivocal identification impossible ( Holmes and Carroll 2010). Because only one embolomere is currently known from Joggins, it was considered most plausible that NSM 944GF1.1 has some relation to Calligenethlon ( Holmes and Carroll 2010) .

Figures

Figure 1. Specimen photos of NSM 994GF1.1. A, dorsal view; B, ventral view.Scale bar equals 1 cm.

Figure 2. Full skeleton of NSM 994GF1.1 revealed by CT segmentation, dorsal view. Individual bones are labelled in subsequent figures.Scale bar equals 1 cm.

Figure 3. Full skeleton of NSM 994GF1.1 revealed by CT segmentation, ventral view. Individual bones are labelled in subsequent figures. Scale bar equals 1 cm.

Figure 4. NSM 994GF1.1 skull.A, dorsal view; B, ventral view; C, ventral view of skull roof. Scale bars equal 1 cm.

Figure 5. Lateral views of NSM 994GF1.1 skull. A, lef lateral; B, right lateral. Scale bar equals 1 cm.

Figure 6. Lef cheek region of NSM 994GF1.1. Lef cheek in (A) external and (B) internal views.Interior view (C) with quadrate removed and (D) with squamosal removed.Squamosal in (E) exterior and (F) interior views.Scale bars equal 1 cm.

Figure 7. Palate and partial endocranium of NSM 994GF1.1 skull.A, dorsal view; B, ventral view.Scale bars equal 1 cm.

Figure 8. Endocranial components of NSM 994GF1.1 inside the skull. A, dorsal view; B, ventral view; C, lef lateral; D, right lateral; E, anterior. Scale bars equal 1 cm.

Figure 9. Occiput of NSM 994GF1.1. A, endocranium in occipital view; B, occiput with with partial lef cheek; C, occiput with cheek bones. Scale bars equal 1 cm.

Figure 10. Lower jaw of NSM 994GF1.1.A, lateral view; B, medial view; C, dorsal view; D, ventral view. Scale bars equal 1 cm.

Figure 11. Lower jaw bones of NSM 994GF1.1. Surangular in (A) medial and (B) lateral views; pre-articular in (C) lateral/external and (D) medial/internal view; articular in (E) lateral, (F) medial, (G) posterior, and (H) anterior views.Scale bar equals 1 cm.