Dorsal Scutes Research Articles

A remarkable clupeomorph fish (Pisces, Teleostei) from a new Upper Cretaceous marine locality in Lebanon

A new clupeomorph fish,Sorbinichthys elusivo n. g., n. sp. is described from a new Upper Cretaceous (Middle ? Cenomanian) marine locality at Nammoura (Lebanon). The characteristic features of the new genus, such as dorsally expanded posttemporal, subrhomboid spiny dorsal scutes, a very wide and deep gap between second and third hypurals, second ray of dorsal and pectoral fins greatly elongated and filamentous, and anterior procurrent caudal fin rays deeply extended between vertebral spines are unusual for clupeomorphs and warrant the establishment of the new family Sorbinichthyidae. The new fish displays several clupeomorph and clupeiform characters, but its placement within the clupeiforms is problematic. The new family is referred to the Clupeomorpha incertae ordinis.

Influence of Externally Attached Transmitters on the Swimming Performance of Juvenile White Sturgeon

We measured the critical swimming speed of juvenile white sturgeons Acipenser transmontanus equipped with externally attached dummy ultrasonic transmitters and of untagged control fish in the laboratory. White sturgeons ranging from 31.9 to 37.0 cm fork length were subjected to one of three treatments: Control (handled but not tagged), tag attached below the dorsal fin, and tag attached with the anterior insertion point between the fourth and fifth dorsal scutes. Although transmitters were of recommended weight, we found that the swimming performance of tagged white sturgeons was significantly less than that of untagged control fish. Swimming performance of tagged fish was not differentially affected by tag location. Our results suggest that data from ultrasonic telemetry studies of externally tagged juvenile white sturgeons should be interpreted with caution due to the reduced swimming performance caused by external transmitters.

Illustrating Sturgeon Species: the art of science in highlighting morphological features

Illustrating Sturgeon Species: the art of science in highlighting morphological features

Neurologic examination of sea turtles

Objective To determine whether neurologic examination techniques established for use on dogs and cats could be adapted for use on sea turtles. Design Prospective controlled observational study. Animals 4 healthy Green Turtles (Chelonia mydas), 1 healthy Kemp's ridley sea turtle (Lepidochelys kempi), and 6 Green Turtles suspected to have neurologic abnormalities. Procedure Neurologic examinations were performed while sea turtles were in and out of the water and in ventral and dorsal recumbency. Mentation, general activity, head and body posture, movement and coordination, thoracic and pelvic limb movement, strength and muscle tone, and tail movement were observed. Thoracic and pelvic limb flexor reflexes and nociception, righting response, cranial nerve reflexes, clasp and cloacal reflexes, and neck, dorsal scute, cloacal, and tail nociception were tested. Results Results of neurologic evaluations were consistent for healthy sea turtles. Sea turtles suspected to have neurologic abnormalities had abnormal results. Clinical Implications Many of the neurologic examination techniques used to evaluate dogs and cats can be adapted and used to evaluate sea turtles. A standardized neurologic examination should result in an accurate assessment of neurologic function in impaired sea turtles and should help in evaluating effects of rehabilitation efforts and suitability for return to their natural environment. (J Am Vet Med Assoc 1997;211:1043–1047)

A revision ofSphenosuchus acutusHaughton, a crocodylomorph reptile from the Elliot Formation (late Triassic or early Jurassic) of South Africa

A detailed description is given of the osteology of the holotype ofSphenosuchus. The skull, particularly the braincase, is excellently preserved and shows a wealth of anatomical detail.Sphenosuchuswas one of the largest of the early crocodylomorphs, with a skull length of 192 mm and an estimated total length of 1.4 m. The primary head of the quadrate meets the prootic and squamosal but not the opisthotic (or laterosphenoid); quadrate and pterygoid are not fused to the braincase and the basipterygoid articulation is free. The braincase and some other skull bones are pneumatized. The otic capsule is crocodilian but the subcapsular buttress (ossified subcapsular process) does not enclose the vagus nerve or the internal carotid artery. The scapula blade is triangular; the coracoid has a long posteroventral extension which is thought to have articulated firmly with a large interclavicle. Clavicles were absent. Metatarsal I is reduced; metatarsals II and IV are symmetrical about III, which is longest. A paired series of dorsal scutes was present.Sphenosuchusis considered to have been cursorial and carnivorous. Comparison is made between the pneumatic spaces in theSphenosuchusskull and those of modern crocodiles and birds, and homologies are discussed. Representatives of the main cavities found in the crocodilian skull are present in the skull ofSphenosuchus, in some cases in a less clearly defined state. On the other hand, certain pneumatic spaces in theSphenosuchusskull are not found in the modern crocodile but resemble cavities in the bird skull. The courses of the internal carotid and stapedial arteries are reconstructed; the latter is considered to have passed through the postquadrate foramen, temporal canal and anterior temporal foramen as it does in modern forms. The problem of the position of the stapedial artery in the crocodile is discussed. It is believed that enclosure of the artery took place as a result of the forward migration of the quadrate head, leading to the formation of a temporal canal. Detailed comparisons are made between the otic capsule ofSphenosuchusand those of modern crocodiles and birds, which it closely resembles. Changes in otic capsule structure in archosaurs to give the crocodilian or bird condition, starting from a primitive form likeEuparkeria, are outlined. The skull is believed to have been kinetic, and the quadrate streptostylic, in the juvenileSphenosuchus. The parts of the proximal end of the crocodilian quadrate are differentiated; in particular, the `true' head is distinguished from the anterodorsal process. Although very reduced in the modern crocodile, the `true' head is in the same morphological position as inSphenosuchus; contact with the laterosphenoid has been brought about, not by further forward movement of the head, but by geniculation of the upper portion of the bone. The anterodorsal process is considered to have arisen as a result of the dorsal migration of an anterolateral projection somewhat similar to that of the thecodontianStagonolepis. This change was also responsible for the elongation of the quadratojugal in crocodylomorphs. The validity of the order Crocodylomorpha is discussed. It is concluded that the most important steps in crocodylomorph evolution, particularly in the skull, had taken place in sphenosuchians, hence they should be included in the same taxon as protosuchians and more advanced crocodilians, rather than with thecodontians.

Comparative Age-Determination Techniques for White Sturgeon in California

Abstract We compared growth patterns of clavicles, cleithra, opercles, medial nuchals, dorsal scutes, and pectoral fin ray sections from white sturgeon Acipenser transmontanus in California. The legibility and interpretability of growth patterns, ease of collection and processing, and relative precision of age estimates were evaluated for each structure with data collected on skeletal structures and morphometric measurements of 147 individuals ranging in size from 31 to 224 cm total length. Various methods were used to elucidate growth zones (thin-sectioning, oil and water clearing, staining, and X-ray radiography) to determine the most useful ageing technique for each structure. All calcified structures contained concentric growth zones that increased in number with the size of the fish and were interpreted as annual events. There was a direct linear relationship between size of the structures and size of the fish. Pectoral fin sections were the most practical ageing structure in terms of ease of collect...

A New Rhynchobdellid

IT seems hard to believe that a leech, common and abundant and possessing a chitinous dorsal scute, should have hitherto escaped notice. But Jackson, in his edition of the “Forms of Animal Life,” does not refer to such a structure, nor does Lang, and I do not find notice of it in more recent literature. In the hope that I am not adding a needless synonym, I give a short description of the animal, of which a detailed account is in preparation.