New insights into the morphology of the Carboniferous tetrapodCrassigyrinus scoticusfrom computed tomography

Abstract

The Carboniferous tetrapod Crassigyrinus scoticus is an enigmatic animal in terms of its morphology and its phylogenetic position. Crassigyrinus had extremely reduced forelimbs, and was aquatic, perhaps secondarily. Recent phylogenetic analyses tentatively place Crassigyrinus close to the whatcheeriids. Many Carboniferous tetrapods exhibit several characteristics associated with terrestrial locomotion, and much research has focused on how this novel locomotor mode evolved. However, to estimate the selective pressures and constraints during this important time in vertebrate evolution, it is also important to study early tetrapods like Crassigyrinus that either remained aquatic or secondarily became aquatic. We used computed tomographic scanning to search for more data about the skeletal morphology of Crassigyrinus and discovered several elements previously hidden by the matrix. These elements include more ribs, another neural arch, potential evidence of an ossified pubis and maybe of pleurocentra. We also discovered several additional metatarsals with interesting asymmetrical morphology that may have functional implications. Finally, we reclassify what was previously thought to be a left sacral rib as a left fibula and show previously unknown aspects of the morphology of the radius. These discoveries are examined in functional and phylogenetic contexts.

Bony lesions in early tetrapods and the evolution of mineralized tissue repair

“…4C,D). While we could not compare the femoral and tibial lesions with normal long bones (only one Crassigyrinus femur and one Crassigyrinus tibia have been found), there are six metatarsals attributed to Crassigyrinus (Herbst and Hutchinson 2018). Only one metatarsal has this growth, which supports its identification as a pathology.…”

Microcomputed tomography of the holotype of the early tetrapodIchthyerpeton bradleyae(Huxley in Wright and Huxley, 1866) from the Pennsylvanian of Ireland

“…Huxley's original description of Ichthyerpeton bradleyae mentions an “animal whose scaly integument and laterally compressed, fin-like, tail might easily lead one to take it for a fish, were not its true position among higher Vertebrata settled at once by the digitated hind limb” (Huxley in Huxley and Wright, 1867, p. 367). Here, this placement is further supported for I. bradleyae , which was a stout-limbed tetrapod with an elongated body similar to that seen in Crassigyrinus (Panchen and Smithson, 1990; Herbst and Hutchinson, 2019), colosteids (Hook, 1983; Godfrey, 1989), and tupilakosaurid temnospondyls (Warren, 1999); however, its relationship to other tetrapods is hard to establish. Characters of I. bradleyae are compared with those of other early tetrapods in Table 1.…”

“…Rhachitomous vertebrae, composed of a single intercentrum anteriorly and paired or fused pleurocentra posteriorly, are considered to be the plesiomorphic condition for tetrapods (Romer, 1947) and are found in Acanthostega (Jarvik, 1952; Coates, 1996), Crassigyrinus (Herbst and Hutchinson, 2019), colosteids (Hook, 1983; Godfrey, 1989), early temnospondyls (Milner and Sequeira, 1994; Holmes et al, 1998), and the cervical region of Acherontiscus (Carroll, 1969; Clack et al, 2019) but are not known in I. bradleyae. Due to the incomplete nature of TCD.T87, it is unclear whether I. bradleyae had rhachitomous vertebrae in the cervical region.…”

Befoltozták a Römer-rést – megoldás egy hatvanéves őslénytani rejtélyre • Filling up the Romer’s Gap—Solving a Sixty-year-old Palaeontological Enigma

“…A maradványokat legutóbb komputertomográfos vizsgálatoknak vetették alá (Herbst-Hutchinson, 2018), és megállapították, hogy a kicsiny, mindössze 5 cm-es hosszúságú bizarr kis élőlény, a Crassigyrinus, nagy valószínűséggel már másodlagosan volt vízi életmódú élőlény. Meghökkentő eredmény, aminek elgondolkodtató üzenete számunkra ismét az, hogy a tudományban (különösen a leíró tudományokban, mint amilyen az őslénytan is) dőreség nagyívű elméleteket leírni korlátozott feldolgozottságú faunák alapján.…”